Several years ago there was a movie that probably everyone has heard of if not seen. The name of it was “The Karate Kid” with Ralph Machio and Pat Morita. In the move Pat Morita was teaching his young pupil the value of proper breathing techniques. He made a statement that hits home with ventilators. He said, “No Breath, no live!” Simple but true. Ventilators are the only machine in the medical world that can literally keep a person breathing after their brain functions have ceased.
Oddly enough ventilators are not as complicated as they seem. They are very basic mechanical devices with some sophisticated monitoring electronics to complete them. The major components of a ventilator include a BDU (Breath Delivery Unit), a GUI (Graphic User Interface), Compressor, Battery Backup Power Supply, and of course the stand it’s all mounted on. The ventilators we have in my hospital are the Puritan Bennett model 840’s. We have been using them for several years and so far, (knock on wood) they have been very reliable. I can count the number of legitimate repairs in the past 4 years for the 6 ventilators we have on one hand.
Starting at the top of the ventilator is the GUI. These are normally touch screen interfaces that allow the user to program the settings needed per patient. The most common failure as you can imagine is the display panel. How many times have we all seen a technician pounding on a touch screen because it’s not responding fast enough to suit them. Touch screens don’t like that. Unless they’re pounding on it with a hammer the defective part will have to be troubleshot.
Fortunately the 840 ventilator comes with a GUI self diagnostic that runs constantly in the background. Unfortunately because the most detailed error log is accessed through the touchscreen you will have to look at other ways to decipher the error codes. The 840 comes with 2 types of displays, a 9.4 inch and a 10.4 inch. On the back of the 10.4 inch GUI monitor is a row of LEDs that will flash error codes. Looking them up in the service manual will give you a starting point of whether the screen is bad or the circuitry on the GUI PC Board is the culprit, and of course ALWAYS CHECK CONNECTIONS FIRST!!!
That statement is for the newer biomeds in the field. Don’t always assume that the most complicated part of the machine has taken it down. Hospital equipment gets moved and handled tremendously and the majority of the time something as simple as a wire getting vibrated loose from a circuit board or somewhere else is causing the problem. GUI problems usually fall into one of four categories: No display, touch screen not responding, touch screen needs calibration, and finally it’s giving an error code. No display, verify that the machine is getting power by looking at the power on indicator first. Look for loose cables next. If the machine is getting power and there is no display you will need to look at the GUI PC board first and the main PC Board.
These boards have LEDs on them that flash error codes for detected problems. If you’re getting no display and no error codes then the screen back-light may have bit the dust. The best way to know for sure is to grab another Ventilator and swap GUI monitors. If the new monitor comes on you will be replacing parts in the defective one. If it exhibits the same problem you may have a GUI PC board dead.
Next is the BDU and is where the ventilator connects to the patient. The BDU has 2 sections, the first one is the inspirtory section that blows air into the patients lungs. The other section is responsible for monitoring expirations. The inspiratory section consists of an oxygen monitor, flow sensors, solenoids, and filters. There are several solenoids in the BDU the most important one is called the PSOL (Proportional Solenoid). The PSOL’s job is to proportion the mixture of air and oxygen as called for. It gets it’s information from the air flow sensor and oxygen flow sensor.
The oxygen and air flow sensors measure the percentage of air and oxygen flowing through the patient circuit. The oxygen sensor measures the amount of oxygen entering the machine from the supply. There are 3 filters that need to be replaced after every10,000 hours. An oxygen inlet filter, underneath it is a bronze filter that reduces the oxygen impact into the system, and finally there is an air inlet filter. When replacing the bronze filter be careful which direction it’s installed. There is a rough side and a smooth side. The rough side goes down.
Below the BDU is the Battery Backup Power which is capable of running the machine for about 30 minutes. It will not run the compressor though, the machine MUST be hooked up to a hospital air or oxygen supply. If you lose both, the patients chances of survival go to ZERO! The battery backup has indicator lights which tells when it is charging and ready to use. There is nothing more than a circuit board and the batteries inside. It either works or it doesn’t. Finally below that is the compressor. The compressor can deliver air to the patient in the event that the hoses get disconnected, split, or if the hospital loses its gas supply for whatever reason. The compressor is an emergency only device and automatically cycles on when the machine loses its hospital gas supply. The compressor only delivers air and not oxygen, therefore if a patient is attached to the machine and needs more than the standard 21% oxygen available in normal air an oxygen tank may need to be attached until the main supply from the wall can be restored. The compressor should be serviced every 15,000 hours of use. We have had our machines about 4 years and none of them have more than 500 hours on the compressor which is great considering the rebuild of one is a 2 hour chore.
This information is in no way meant to certify someone to work on ventilators. Special schooling and certification is required by most hospital biomed departments. I personally wouldn’t touch one without a certification or some training. If a patient died because of a faulty ventilator and you were the last one that worked on it guess who the board of inquiry is going to look at first? With certification you can state that you made every knowledgable attempt to restore the unit to normal functionality and the inquiry then moves to look for manufacturer defects. Without the certification you become jobless, moneyless (patient family lawsuits), and eventually homeless. Even if you have worked on them for years without formal training and certification and know more than the engineers that built it… when you’re standing in a courtroom the only thing that matters is that 8.5 inch by 11 inch piece of paper that says, “Certified”.
Saturday, July 4, 2009
Thermometers
Electronic thermometers are the most used piece of equipment in a hospital. They get the most abuse from being carried in pockets and henceforth banged against door jambs or laid on a table only to be knocked to the floor a few minutes later. All in all they are fairly sturdy little instruments. There are many different brands available such as Welch Allyn, Tyco, Philips, and others. The one thing they all have in common is a removable probe that fits in the patient’s mouth or rectum. I was once told by a doctor that the way you can tell the difference in probes is by the taste. Moving right along then!
Seriously though 99% of all thermometer complaints we get in our shop is probe related. These probes are very delicate especially at the tip. Inside the tip of a thermometer probe is an electronic component called a thermistor. A thermistor is a variable resistor. It’s resistance is varied in proportion to the amount of heat placed on it. As it heats up and the resistance changes it causes the monitoring circuitry attached to it to display the temperature on a digital readout. This thermistor is very tiny and doesn’t take shock very well. Bouncing it off the floor or swinging it against a wall will severely shorten its lifespan.
Another type of thermometer is called a tympanic thermometer. Tympanic thermometers use infrared technology to measure heat. Tympanic thermometers, or ear thermometers, use a different type of sensor. They typically use what is called a thermopile sensor. This sensor is made of several thermocouples that are placed in series. Each thermocouple is made of 2 different types of metal. A voltage is produced when there is a difference in temperature across the junction of the two metals. Since the eardrum gives off heat in the form of Infrared Radiation this heat is picked up by the thermocouple and the resulting temperature is measured against ambient air, (room temperature), and displayed on an LCD screen. Because the reaction of the metal is very quick a temperature reading can be made in less than a second. This makes the tympanic thermometer the choice of most pediatric departments where small children seldom sit still long enough to have a probe in their mouth or anywhere else for that matter.
Seriously though 99% of all thermometer complaints we get in our shop is probe related. These probes are very delicate especially at the tip. Inside the tip of a thermometer probe is an electronic component called a thermistor. A thermistor is a variable resistor. It’s resistance is varied in proportion to the amount of heat placed on it. As it heats up and the resistance changes it causes the monitoring circuitry attached to it to display the temperature on a digital readout. This thermistor is very tiny and doesn’t take shock very well. Bouncing it off the floor or swinging it against a wall will severely shorten its lifespan.
Another type of thermometer is called a tympanic thermometer. Tympanic thermometers use infrared technology to measure heat. Tympanic thermometers, or ear thermometers, use a different type of sensor. They typically use what is called a thermopile sensor. This sensor is made of several thermocouples that are placed in series. Each thermocouple is made of 2 different types of metal. A voltage is produced when there is a difference in temperature across the junction of the two metals. Since the eardrum gives off heat in the form of Infrared Radiation this heat is picked up by the thermocouple and the resulting temperature is measured against ambient air, (room temperature), and displayed on an LCD screen. Because the reaction of the metal is very quick a temperature reading can be made in less than a second. This makes the tympanic thermometer the choice of most pediatric departments where small children seldom sit still long enough to have a probe in their mouth or anywhere else for that matter.
Surgical Lasers
Most people know of the Matrix movie trilogy. In the first one there is a scene near the end when Neo is fighting Mr. Smith. While he is fighting the agent in the matrix, in real life robot machines, (Squiddy’s), are carving the ship he is on to pieces with lasers. Lasers have been used for many years and provide a myriad of services to us. Lasers can be used to scan barcodes on food in grocery stores, or provide police officers with evidence to throw you under the jail for speeding. Lasers can also be used for delicate surgery. There are several different types of surgical lasers such as YAG lasers, CO2 lasers, and Holmium lasers being the most common ones. Each one is vastly different in what produces the laser light.
YAG lasers are used for cataract surgery and minor eye surgeries. YAG stands for yttrium aluminium garnet which is the material used to dope the lens of the laser. (Yttrium is a rare earth metal with an atomic weight 39) YAG lasers have a shorter wavelength than the more powerful CO2 laser. This means that the YAG laser light is more easily absorbed by water filled human tissue. This makes the laser perfect for applications such as cataract removal. A cataract is a clouding of the area behind the lens of the eye. The Yag laser power level can be adjusted to remove the cataract without damage to the lens. This is possible because the lens is clear and passes the laser light easily to the cloudy cataract behind it. Most YAG lasers use a stepper motor configuration to increase or decrease the power level of the laser. Beam alignment is done through a series of mirrors that are adjusted for angle, tilt, and centering. Because the laser is used in extreme close proximity to the eye a guiding laser beam is usually not necessary. What is a guiding laser beam? Read on.
CO2 lasers are perhaps the most powerful of lasers used in surgery. An 80 watt CO2 laser can literally burn a hole through a 1/4″ thick piece of steel in seconds. These require extreme caution when working around them. This type of laser generally has 2 separate lasers that work as one. The first laser is a Helium Neon or HeNe laser. It is typically very low power such as milliwatts and is generated through a ruby crystal which gives it the bright red light that you can see. The real power is provided by the CO2 laser. Since CO2, (Carbon Dioxide) is a colorless gas it produces no visible beam of light. Carbon Dioxide is not the only gas present in the laser tube there is also Nitrogen, Helium, Hydrogen, and Xenon in varying percentages.
The Helium Neon laser light is adjusted to coincide with the CO2 laser beam. They emerge from the lens in perfect unison when the machine is properly calibrated. The HeNe light is red and visible and gives the surgeon something to see. When he steps on the power switch the CO2 laser is activated and the beam travels along the same path as the HeNe laser and cuts or burns whatever is required. When you see a laser cutting something remember it’s not the red light that is doing the cutting it’s the invisble CO2 that is hitting the same spot. Calibration is a little more difficult because not only does angle, tilt and center have to be calibrated but so does the Near/Far adjustment. The near/far adjustment is to bring the CO2 laser into precise conjunction with the HeNe laser. The near adjustment is usually done first followed by the far adjustment. Next comes the angle, tilt and center alignments. Adjusting most CO2 lasers can be a little time consuming and normally takes about 2 or 3 hours to complete. After adjusting the laser beam the power levels are normally verified and adjusted as well. Unlike the YAG laser which uses stepper motors the majority of CO2 lasers use digital circuits to adjust power.
Last but not least is the Holmium laser. Holmium lasers use the same YAG material for the lens but these lasers are used for a different type of surgery. They are normally used for the removal of kidney and gall bladder stones. These also use a guiding laser but in this case the guiding laser is produced by an emarald crystal which gives it a green colored light. Adjustment is the same as the other two with mirrors and alignment procedures outlined in their service manuals. One other difference worth noting is that Holmium lasers transfer the cutting power through a fiber optic cable into the patients body where precision manipulation by the surgeon can guide the fiber optic tip directly to the needed area. Because of this fiber optic delivery method of the laser power, (usually about 2o watts more or less), an addition of a piece called a blast shield is necessary. The blast shield stops the laser beam from burning through the sheathing of the fiberoptic cable at the point of attachment to the laser.
YAG lasers are used for cataract surgery and minor eye surgeries. YAG stands for yttrium aluminium garnet which is the material used to dope the lens of the laser. (Yttrium is a rare earth metal with an atomic weight 39) YAG lasers have a shorter wavelength than the more powerful CO2 laser. This means that the YAG laser light is more easily absorbed by water filled human tissue. This makes the laser perfect for applications such as cataract removal. A cataract is a clouding of the area behind the lens of the eye. The Yag laser power level can be adjusted to remove the cataract without damage to the lens. This is possible because the lens is clear and passes the laser light easily to the cloudy cataract behind it. Most YAG lasers use a stepper motor configuration to increase or decrease the power level of the laser. Beam alignment is done through a series of mirrors that are adjusted for angle, tilt, and centering. Because the laser is used in extreme close proximity to the eye a guiding laser beam is usually not necessary. What is a guiding laser beam? Read on.
CO2 lasers are perhaps the most powerful of lasers used in surgery. An 80 watt CO2 laser can literally burn a hole through a 1/4″ thick piece of steel in seconds. These require extreme caution when working around them. This type of laser generally has 2 separate lasers that work as one. The first laser is a Helium Neon or HeNe laser. It is typically very low power such as milliwatts and is generated through a ruby crystal which gives it the bright red light that you can see. The real power is provided by the CO2 laser. Since CO2, (Carbon Dioxide) is a colorless gas it produces no visible beam of light. Carbon Dioxide is not the only gas present in the laser tube there is also Nitrogen, Helium, Hydrogen, and Xenon in varying percentages.
The Helium Neon laser light is adjusted to coincide with the CO2 laser beam. They emerge from the lens in perfect unison when the machine is properly calibrated. The HeNe light is red and visible and gives the surgeon something to see. When he steps on the power switch the CO2 laser is activated and the beam travels along the same path as the HeNe laser and cuts or burns whatever is required. When you see a laser cutting something remember it’s not the red light that is doing the cutting it’s the invisble CO2 that is hitting the same spot. Calibration is a little more difficult because not only does angle, tilt and center have to be calibrated but so does the Near/Far adjustment. The near/far adjustment is to bring the CO2 laser into precise conjunction with the HeNe laser. The near adjustment is usually done first followed by the far adjustment. Next comes the angle, tilt and center alignments. Adjusting most CO2 lasers can be a little time consuming and normally takes about 2 or 3 hours to complete. After adjusting the laser beam the power levels are normally verified and adjusted as well. Unlike the YAG laser which uses stepper motors the majority of CO2 lasers use digital circuits to adjust power.
Last but not least is the Holmium laser. Holmium lasers use the same YAG material for the lens but these lasers are used for a different type of surgery. They are normally used for the removal of kidney and gall bladder stones. These also use a guiding laser but in this case the guiding laser is produced by an emarald crystal which gives it a green colored light. Adjustment is the same as the other two with mirrors and alignment procedures outlined in their service manuals. One other difference worth noting is that Holmium lasers transfer the cutting power through a fiber optic cable into the patients body where precision manipulation by the surgeon can guide the fiber optic tip directly to the needed area. Because of this fiber optic delivery method of the laser power, (usually about 2o watts more or less), an addition of a piece called a blast shield is necessary. The blast shield stops the laser beam from burning through the sheathing of the fiberoptic cable at the point of attachment to the laser.
Pulse Oximeters
Pulse oximeters are an interesting device. They measure the percentage of blood or hemoglobin that is saturated with oxygen in a patient’s body. An LED light source gets shined through a thin part of the body such as a fingertip or infants foot and picked up by a phototransistor on the other side. Because hemoglobin has a different color depending on the amount of oxygen it’s saturated with the pulse oximeter computer chip analyzes the difference in the wavelength of the light and computes the percentage of oxygen in the blood.
The pulse oximeter also detects heart rate or pulse and produces an audible beep with every pulse. Because the pulse oximeter is very dependent on pulsatile flow there are situations where it may not work well. Most of the time the problems we get in our shop involve the sensor attached to it. There have been rare cases when the sensor was fine and the complaint was that it would give erratic readings or suspiciously low saturation levels of a patient. With a little investigation it turned out that the patient had been brought in for hypothermia where they had been shoveling snow for an extended period of time.
Because the probe is attached to a finger most of the time, the patient had very little blood flow into their digits. Remember the pulse oximeter works on the basis of pulsatile flow. No flow, no SAT reading. After the patient warmed up a little while the pulse oximeter was tried again and worked fine. Certain heart conditions and medications that restrict vascular flow will also cause erroneous readings with the machine. Because the pulse oximeter shines a light through the patient I have seen instances where bright fluorescent lights in an emergency room cause false readings or in a few cases no readings. Simply covering the probe with a blanket or other object to restrict ambient light cured the problem.
Anesthesiologists depend heavily on pulse oximeters during surgical procedures. Because a patient has a mixture of several different gases being pumped into their lungs through the ventilator the oxygen amount in the blood becomes critical. An insufficient amount of oxygen for a prolonged surgical procedure will cause brain damage or paralysis to a patient. The anesthesiologist is constantly monitoring the patient’s oxygen saturation levels and adjusting the air, oxygen, nitrous and anesthetic gas accordingly to maintain a specific percentage of oxygen in the patient’s blood. There is no calibration for the machine but a PM generally using a simulator to simulate the pulse and oxygen percentages and compare them against the readout on the pulse oximeter screen. Standard deviation for most machines is 1% +/- of the displayed readings between the simulator and the pulse oximeter.
If a simulator is not available then it becomes necessary to test 3 or 4 pulse oximeters as a group with your own finger in a controlled situation and monitor the variance in machines. To do this correctly use the same probe for all 4 machines, and do them all in the same location by the same person with only one specific chosen finger, like the index finger of either hand. I like to use the index finger of my left hand because it’s closest to the heart and has the strongest pulse flow. If all machines measure within 1% of each other then it’s a suitable indication that the saturation measurements are accurate. The pulse rate will be more difficult to measure accurately with this method because subtle changes in temperature, body movement, external stimuli, (phone ringing, people talking) all will change the heart rate a little. I generally go with a 5% deviation in pulse rate when I use this method. For example a resting pulse rate of 70 beats per minute shouldn’t change more than 3.5 beats per minute +/- for the short duration of testing for these machines. If they fall within this range they pass.
The pulse oximeter also detects heart rate or pulse and produces an audible beep with every pulse. Because the pulse oximeter is very dependent on pulsatile flow there are situations where it may not work well. Most of the time the problems we get in our shop involve the sensor attached to it. There have been rare cases when the sensor was fine and the complaint was that it would give erratic readings or suspiciously low saturation levels of a patient. With a little investigation it turned out that the patient had been brought in for hypothermia where they had been shoveling snow for an extended period of time.
Because the probe is attached to a finger most of the time, the patient had very little blood flow into their digits. Remember the pulse oximeter works on the basis of pulsatile flow. No flow, no SAT reading. After the patient warmed up a little while the pulse oximeter was tried again and worked fine. Certain heart conditions and medications that restrict vascular flow will also cause erroneous readings with the machine. Because the pulse oximeter shines a light through the patient I have seen instances where bright fluorescent lights in an emergency room cause false readings or in a few cases no readings. Simply covering the probe with a blanket or other object to restrict ambient light cured the problem.
Anesthesiologists depend heavily on pulse oximeters during surgical procedures. Because a patient has a mixture of several different gases being pumped into their lungs through the ventilator the oxygen amount in the blood becomes critical. An insufficient amount of oxygen for a prolonged surgical procedure will cause brain damage or paralysis to a patient. The anesthesiologist is constantly monitoring the patient’s oxygen saturation levels and adjusting the air, oxygen, nitrous and anesthetic gas accordingly to maintain a specific percentage of oxygen in the patient’s blood. There is no calibration for the machine but a PM generally using a simulator to simulate the pulse and oxygen percentages and compare them against the readout on the pulse oximeter screen. Standard deviation for most machines is 1% +/- of the displayed readings between the simulator and the pulse oximeter.
If a simulator is not available then it becomes necessary to test 3 or 4 pulse oximeters as a group with your own finger in a controlled situation and monitor the variance in machines. To do this correctly use the same probe for all 4 machines, and do them all in the same location by the same person with only one specific chosen finger, like the index finger of either hand. I like to use the index finger of my left hand because it’s closest to the heart and has the strongest pulse flow. If all machines measure within 1% of each other then it’s a suitable indication that the saturation measurements are accurate. The pulse rate will be more difficult to measure accurately with this method because subtle changes in temperature, body movement, external stimuli, (phone ringing, people talking) all will change the heart rate a little. I generally go with a 5% deviation in pulse rate when I use this method. For example a resting pulse rate of 70 beats per minute shouldn’t change more than 3.5 beats per minute +/- for the short duration of testing for these machines. If they fall within this range they pass.
MRI Machines
An MRI or Magnetic Resonance Imaging machine uses magnetism to look inside the human body. How an MRI works is a fascinating concept. An extremely powerful magnetic field of 1.5 to 3.0 Tesla surrounds the patient. A Tesla is a unit of measurement of the magnets strength. To give an idea of the strength of an MRI magnet, the Earth’s core is pulling on objects with an intensity of about 0.5 Tesla. OK so the MRI is 3 times stronger right? Not quite, there are a lot of Physics calculations to consider but in reality the MRI is about 10,000 to 20,000 times stronger and this is based mostly on the proximity and mass of the object to the magnetic field.This magnetic field is created by taking several thousand turns of wire around a large open core and running current through it. These magnet wires are turned into superconductors by bathing them in liquid helium. The liquid helium drops the temperature of the wire to -450 Fahrenheit and effectively removes all resistance from the wire. This is the primary magnet and is responsible for aligning the hydrogen atoms in the human body.
MRI’s also use three other types of magnets called gradient magnets that have approximately 1/1000th of the strength of the primary magnet. The purpose of the gradient magnet is to focus on a specific part of the body. Each gradient magnet is responsible for focusing one plane of the 3-D image created by the primary magnet also sometimes just referred to as the coil. Those planes are coronal, sagittal, and axial.
The coronal plane separates the front of the body from the back. Imagine laying the human body on a table and cutting through it so the front half could be lifted away and the back would still be on the table. The Sagittal Plane would cut the body in half separating the left side from the right side. The Axial Plane separates the top half of the body from the lower half. For a better understanding see the image above.
The images produced all show up as a gray scale image of cross-sectional slices of the body. The varying shades of gray indicate the thickness, type and consistency of the tissue. After these slices are put in order a 3-dimensional image can be displayed. The MRI uses different types of coils to surround the body part that is intended to be scanned. These coils further fine tune the image by picking up magnetic induction being produced by the primary magnet and gradient magnets.
Some areas of the MRI in my hospital that have been problematic are the SSM, (System Support Module), the RF Gradient Amplifier, the Cold Head and various mechanical issues. We have an older model 1.5 Tesla magnet that requires periodic refilling of the liquid helium. I monitor the boil off rate as does the company that refills it. The boil off rate is the rate at which the liquid helium warms up enough to turn into gas and escape into the atmosphere. The normal refill rate of my magnet is around once every three months and has been for years. We recently noticed that the refills were becoming more frequent and checked the pressure of the magnet to find it had risen. Normally this indicates that the cold head is getting weak and sure enough it was. The cold head is the part of the magnet that keeps the liquid helium chilled at -450 Fahrenheit. The normal lifespan of a cold head is about 3 or 4 years. Ours was 9 years old! We replaced it and the boil off rate dropped.
Occasionally we get complaints that the image is hard to focus or one plane is out of whack. Normally a quick calibration of the gradient takes care of it. One particular instance the images had no resolution at all. The RF Gradient Amplifier circuit had become defective. This circuit is what boosts or amplifies the Micro or Pico voltages that are being picked up by the body coil, head coil, knee coil, or any one of a dozen different coils that are placed around the patient to help improve the signal. The gradient magnets themselves are pretty sturdy and usually respond well to the calibration procedure and start acting right again.
IV Pumps
IV Pumps are machines that deliver liquid medications through a needle into a patients veins. These are usually rugged little machines capable of withstanding a lot of abuse. Preventive Maintenance normally consists of measuring flow rate, delivery accuracy, proximal and/or distal occlusion pressure. To the biomedical technician we are generally concerned with setting up whatever analyzer we use and monitoring the numbers we get. We program the pump for 10 ml and our analyzer says we got 9.96 ml. All other tests have passed and we’re good to go. For those who would like to know a little more about what some of the terms used with IV pumps mean read on.
Occlusion pressure occurs when the IV delivery tubing gets twisted, clogged or otherwise kinked preventing flow. There are two places where the delivery tube can get messed up. The first is upstream between the IV solution bag and the pump itself. This is called the proximal area of the pump. The most common reason for proximal occlusions is a tubing clamp that was overlooked during setup. The next one is called the distal area and is between the pump and patient. This area is more critical than the first for several reasons.
Because this end is physically attached to the patients vein it is necessary that the IV needle is securely attached to the patient. The human cardiovascular system operates at a specific pressure. The heart is pumping blood through our bodies under fairly substantial pressure. We are also pumping fluid in from the IV pump. The IV pump must be able to recognize when the pressure in the vein is dangerously critical. Every IV pump has a specified area of pressure that will activate an alarm and shut the pump mechanism off instantly.
One thing most IV pumps cannot do well is detect infiltration of fluid. Infiltration is a medical term describing when fluid leaks into surrounding tissue of the body. There are numerous physiological conditions with a patient that can make them more susceptible to infiltration. Basically what is happening is that the fluid is being pumped into the body at a specific baseline pressure and the infiltration occurs at a small pressure. As an example assume we have a garden hose spraying water. If we insert a small sponge into the hose it will quickly absorb the water before becoming saturated and letting it escape.
The human body tissue is acting as a sponge during infiltration and slowing the infused solution down as it enters the vein. There is a pressure differential going on but if the IV pump is set at a low infusion rate of say 10 ml/hr the body tissue may be able to absorb this at a fast enough rate that the IV pump does not recognize the resultant back pressure. No alarm may occur because the occlusion alarm pressure setting has not been reached. This applies directly to the sensitivity of the pump pressure transducer.
Another term used with IV pumps is VTBI which stands for Volume To Be Infused. This is simply how much you want to pump through the machine. Rate is another term which is fairly self explanatory: How fast do you want it to pump? Titrate is a term used when a cassette is loaded with an additional syringe of different medication. For example a bag of Sodium is the primary delivery agent and on top of the cassette a syringe full of glucophage or other drug is added. Titrate literally means to add one solution to another in specific increments while monitoring the outcome and looking for a specific reaction. In this case the reaction expected would be lowering the blood sugar level to the patient to a level determined by the physician, once the proper mixture rate has been determined through the titrate function. Most IV pumps also have a back-prime function which allows the user to prime the cassette and remove all air bubbles before attaching it to the patients catheter.
Common ailments in the biomedical shop usually take the form of mechanically broken parts. Cassette doors get snapped off, AC plugs get yanked out of the wall instead of being gently removed which separates wires in the end of the plug, and of course every biomeds favorite complaint “I accidentally dropped it”. I have seen this on defective stickers attached to every type of equipment not just IV pumps. Sometimes I have read it and wonder “OK, they dropped it…but down which elevator shaft or from what 4th floor window did they drop it?” Battery power not working is another complaint. More often than not it’s because the pump was not plugged in long enough to recharge the batteries.
I like those kind of fixes, plug it in to the power strip on my desk and return it the next morning after a 30 to 45 minute check on battery power only. Find an empty closet and plug it in to recharge from the test I just gave it. Pump mechanisms do occasionally fail and have to be replaced. Depending on the manufacturer this can be a simple thirty minute job or a half day affair. I don’t think there is a biomedical technician anywhere that hasn’t wished that just once the engineers that design this stuff would have to work on them.
Occlusion pressure occurs when the IV delivery tubing gets twisted, clogged or otherwise kinked preventing flow. There are two places where the delivery tube can get messed up. The first is upstream between the IV solution bag and the pump itself. This is called the proximal area of the pump. The most common reason for proximal occlusions is a tubing clamp that was overlooked during setup. The next one is called the distal area and is between the pump and patient. This area is more critical than the first for several reasons.
Because this end is physically attached to the patients vein it is necessary that the IV needle is securely attached to the patient. The human cardiovascular system operates at a specific pressure. The heart is pumping blood through our bodies under fairly substantial pressure. We are also pumping fluid in from the IV pump. The IV pump must be able to recognize when the pressure in the vein is dangerously critical. Every IV pump has a specified area of pressure that will activate an alarm and shut the pump mechanism off instantly.
One thing most IV pumps cannot do well is detect infiltration of fluid. Infiltration is a medical term describing when fluid leaks into surrounding tissue of the body. There are numerous physiological conditions with a patient that can make them more susceptible to infiltration. Basically what is happening is that the fluid is being pumped into the body at a specific baseline pressure and the infiltration occurs at a small pressure. As an example assume we have a garden hose spraying water. If we insert a small sponge into the hose it will quickly absorb the water before becoming saturated and letting it escape.
The human body tissue is acting as a sponge during infiltration and slowing the infused solution down as it enters the vein. There is a pressure differential going on but if the IV pump is set at a low infusion rate of say 10 ml/hr the body tissue may be able to absorb this at a fast enough rate that the IV pump does not recognize the resultant back pressure. No alarm may occur because the occlusion alarm pressure setting has not been reached. This applies directly to the sensitivity of the pump pressure transducer.
Another term used with IV pumps is VTBI which stands for Volume To Be Infused. This is simply how much you want to pump through the machine. Rate is another term which is fairly self explanatory: How fast do you want it to pump? Titrate is a term used when a cassette is loaded with an additional syringe of different medication. For example a bag of Sodium is the primary delivery agent and on top of the cassette a syringe full of glucophage or other drug is added. Titrate literally means to add one solution to another in specific increments while monitoring the outcome and looking for a specific reaction. In this case the reaction expected would be lowering the blood sugar level to the patient to a level determined by the physician, once the proper mixture rate has been determined through the titrate function. Most IV pumps also have a back-prime function which allows the user to prime the cassette and remove all air bubbles before attaching it to the patients catheter.
Common ailments in the biomedical shop usually take the form of mechanically broken parts. Cassette doors get snapped off, AC plugs get yanked out of the wall instead of being gently removed which separates wires in the end of the plug, and of course every biomeds favorite complaint “I accidentally dropped it”. I have seen this on defective stickers attached to every type of equipment not just IV pumps. Sometimes I have read it and wonder “OK, they dropped it…but down which elevator shaft or from what 4th floor window did they drop it?” Battery power not working is another complaint. More often than not it’s because the pump was not plugged in long enough to recharge the batteries.
I like those kind of fixes, plug it in to the power strip on my desk and return it the next morning after a 30 to 45 minute check on battery power only. Find an empty closet and plug it in to recharge from the test I just gave it. Pump mechanisms do occasionally fail and have to be replaced. Depending on the manufacturer this can be a simple thirty minute job or a half day affair. I don’t think there is a biomedical technician anywhere that hasn’t wished that just once the engineers that design this stuff would have to work on them.
Film Processors
The days of fumbling around in the dark looking for a handle on an X-Ray film storage cabinet is becoming a thing of the past. Film processors are moving more towards digital processing every day. There have been remarkable strides in the development of image quality in machines like CR’s and DR’s. There are still a few smelly wet processors around but not many and they are usually used for special applications. First we need a little lesson in radiography in order to understand what happens in the processor.
Radiographic images are produced by exposing a light sensitive piece of film or image screen to an X-Ray beam. Different parts of the body have different densities. Bone is denser than surrounding muscle and tissue so X-Ray’s do not penetrate the bone as well. X-Rays are normally a reverse or negative image of the body part in question. Because bone is denser fewer X-Rays can get through to the film and causes it to appear white or unexposed. Muscle tissue varies in density and gray scale images of it can be seen around the bone because it absorbs some of the X-Rays but passes the rest. To learn more about X-Ray technology click here to read my other blog about general X-Ray equipment.
Film that is used in wet processors has a coating of a light sensitive emulsion affixed to one or sometimes both sides of the film. When the exposed film is run through the wet processor it first enters a tank full of developer chemicals. This causes the emulsion on the section of film that was exposed to radiation to adhere more to the film and other sections that got less radiation lets loose and get recycled in the silver mercury recovery unit underneath the processor. Next the film travels through a series of rollers and gets dumped into a fixer chemical tank. This tank of chemicals fixes the image permanently on the film. Next the film is rolled through to a water bath that rinses all chemicals and residual emulsion away. Next the film is run through a dryer that removes all the water from the film and finally it falls into a catch tray at the opposite end of the processor.
The most important thing to remember about processors is that you must NEVER allow any fixer not even a single drop to get into the developer tank. Extreme caution must be used when removing the racks that the rollers are attached to. The reason is that the processor gets a Quality Control film run on it daily for mammography and weekly for general X-Ray. The density of the QC film is then read with a machine called a sensitometer. The numbers generated by the sensitometer are the readings for varying densities placed on the film in the dark room by a densitometer.
If the numbers are out of range the films run after that will be of questionable diagnostic value. Areas of the film may not be readable enough to spot things like cancers or malignant areas of tissue. Mixing the chemicals even minutely like one drop can throw the numbers way out of proportion. Getting it back into range requires dumping the chemical in the infected tank and refilling it. Starter solution is normally added and this is where it gets hairy. The starter solution must be added proportionally to the degree that the numbers were out of range. In the few times I have seen this chemical contamination happen it required a phone call to the third party vendor we use for service on the machine to come in and get it back in range.
Temperature also plays a major factor in film quality of wet processors. The temperature must be kept constant in the developer tank with a variance of usually less than one degree. The temperature in the fixer and water tank is unimportant. The processor must constantly dump a small amount of chemicals while it is turned on and fresh chemicals are running through it to replenish the supply at a replenish rate set in the processor. If a large number of films are being run through and the replenish rate is too low, after several films are run it can be noticed that they are getting lighter, which means the quality is getting worse. A new QC film will usually verify that the numbers have drifted out of acceptable range and the chemicals must be replenished faster. Fortunately there is a button on most processors that you hold down for a minute or 2 and the replenishing motor will run constantly pumping in a few ounces of fresh chemicals. This normally fixes the problem.
CR’s are a digital form of processor that uses an intensifying screen inside a film cassette that the exposure is made on. The term CR means Computed Radiography and is just that. A cassette is tagged at the work station with the patient demographic data then inserted into the X-Ray machine. The X-Ray is taken and the cassette is inserted into the CR processor. The processor reads the tag and knows which X-Ray machine was used and attaches the patient information to the digital image it will produce. The cassette is opened up inside the machine and the intensifying screen is removed. The image is scanned with a laser and the digital image is produced as a jpeg image on the CR monitor for the X-Ray technicians and doctors to read.
After the image is uploaded to the monitoring computer the intensifying screen is exposed to light erasing the current image. The screen is then reinserted into the cassette and the cassette is ejected back to the technicians to use again. CR cassettes are expensive but will pay for themselves very quickly because they are reusable. Each cassette is capable of several thousand exposures before becoming useless. Each CR manufacturer uses basically the same technology to read and erase the intensifying screens. The major difference is how the cassette is physically handled by the machine. AGFA machines open the cassette, develop the image and then spin a large assembly inside that holds the cassette. The screen is then reinserted and ejected out to the user. Kodak and Fuji CR’s open the cassette, read It, and reinsert it without moving the cassette around. Each have their pros and cons.
DR’s or Digital Radiography units use the same image production process but with one thing removed. The cassette is taken out of the equation. The image is transferred digitally from the X-Ray machine right to the image processing software of the DR. The advantage is no moving parts, no machinery to take up space like the CR, and images can be seen almost instantly. The disadvantage is that only newer X-Ray machines may be capable of making full use of the technology. Older X-Ray machines may not be upgradeable to digital imaging. Some X-Ray machines also have software compatibility issues with the newer digital software. As an example most X-Ray machines use MS DOS as the primary operating system for communication. I’m talking about pre-Windows 95 operating systems.
The advantage of using a CR or DR is in image quality control. In wet processors the chemicals control the quality of the image. With CR’s and DR’s the doctor controls the image. He can use the software to increase density, contrast, sharpness, or several other parameters to get the best quality image he can. CR’s and DR’s are much better for radiographic diagnostics because of that feature. The Doctor can enhance any area of the image to reveal things that would otherwise have been lost on wet processed film.
Radiographic images are produced by exposing a light sensitive piece of film or image screen to an X-Ray beam. Different parts of the body have different densities. Bone is denser than surrounding muscle and tissue so X-Ray’s do not penetrate the bone as well. X-Rays are normally a reverse or negative image of the body part in question. Because bone is denser fewer X-Rays can get through to the film and causes it to appear white or unexposed. Muscle tissue varies in density and gray scale images of it can be seen around the bone because it absorbs some of the X-Rays but passes the rest. To learn more about X-Ray technology click here to read my other blog about general X-Ray equipment.
Film that is used in wet processors has a coating of a light sensitive emulsion affixed to one or sometimes both sides of the film. When the exposed film is run through the wet processor it first enters a tank full of developer chemicals. This causes the emulsion on the section of film that was exposed to radiation to adhere more to the film and other sections that got less radiation lets loose and get recycled in the silver mercury recovery unit underneath the processor. Next the film travels through a series of rollers and gets dumped into a fixer chemical tank. This tank of chemicals fixes the image permanently on the film. Next the film is rolled through to a water bath that rinses all chemicals and residual emulsion away. Next the film is run through a dryer that removes all the water from the film and finally it falls into a catch tray at the opposite end of the processor.
The most important thing to remember about processors is that you must NEVER allow any fixer not even a single drop to get into the developer tank. Extreme caution must be used when removing the racks that the rollers are attached to. The reason is that the processor gets a Quality Control film run on it daily for mammography and weekly for general X-Ray. The density of the QC film is then read with a machine called a sensitometer. The numbers generated by the sensitometer are the readings for varying densities placed on the film in the dark room by a densitometer.
If the numbers are out of range the films run after that will be of questionable diagnostic value. Areas of the film may not be readable enough to spot things like cancers or malignant areas of tissue. Mixing the chemicals even minutely like one drop can throw the numbers way out of proportion. Getting it back into range requires dumping the chemical in the infected tank and refilling it. Starter solution is normally added and this is where it gets hairy. The starter solution must be added proportionally to the degree that the numbers were out of range. In the few times I have seen this chemical contamination happen it required a phone call to the third party vendor we use for service on the machine to come in and get it back in range.
Temperature also plays a major factor in film quality of wet processors. The temperature must be kept constant in the developer tank with a variance of usually less than one degree. The temperature in the fixer and water tank is unimportant. The processor must constantly dump a small amount of chemicals while it is turned on and fresh chemicals are running through it to replenish the supply at a replenish rate set in the processor. If a large number of films are being run through and the replenish rate is too low, after several films are run it can be noticed that they are getting lighter, which means the quality is getting worse. A new QC film will usually verify that the numbers have drifted out of acceptable range and the chemicals must be replenished faster. Fortunately there is a button on most processors that you hold down for a minute or 2 and the replenishing motor will run constantly pumping in a few ounces of fresh chemicals. This normally fixes the problem.
CR’s are a digital form of processor that uses an intensifying screen inside a film cassette that the exposure is made on. The term CR means Computed Radiography and is just that. A cassette is tagged at the work station with the patient demographic data then inserted into the X-Ray machine. The X-Ray is taken and the cassette is inserted into the CR processor. The processor reads the tag and knows which X-Ray machine was used and attaches the patient information to the digital image it will produce. The cassette is opened up inside the machine and the intensifying screen is removed. The image is scanned with a laser and the digital image is produced as a jpeg image on the CR monitor for the X-Ray technicians and doctors to read.
After the image is uploaded to the monitoring computer the intensifying screen is exposed to light erasing the current image. The screen is then reinserted into the cassette and the cassette is ejected back to the technicians to use again. CR cassettes are expensive but will pay for themselves very quickly because they are reusable. Each cassette is capable of several thousand exposures before becoming useless. Each CR manufacturer uses basically the same technology to read and erase the intensifying screens. The major difference is how the cassette is physically handled by the machine. AGFA machines open the cassette, develop the image and then spin a large assembly inside that holds the cassette. The screen is then reinserted and ejected out to the user. Kodak and Fuji CR’s open the cassette, read It, and reinsert it without moving the cassette around. Each have their pros and cons.
DR’s or Digital Radiography units use the same image production process but with one thing removed. The cassette is taken out of the equation. The image is transferred digitally from the X-Ray machine right to the image processing software of the DR. The advantage is no moving parts, no machinery to take up space like the CR, and images can be seen almost instantly. The disadvantage is that only newer X-Ray machines may be capable of making full use of the technology. Older X-Ray machines may not be upgradeable to digital imaging. Some X-Ray machines also have software compatibility issues with the newer digital software. As an example most X-Ray machines use MS DOS as the primary operating system for communication. I’m talking about pre-Windows 95 operating systems.
The advantage of using a CR or DR is in image quality control. In wet processors the chemicals control the quality of the image. With CR’s and DR’s the doctor controls the image. He can use the software to increase density, contrast, sharpness, or several other parameters to get the best quality image he can. CR’s and DR’s are much better for radiographic diagnostics because of that feature. The Doctor can enhance any area of the image to reveal things that would otherwise have been lost on wet processed film.
General X-Ray Equipment
After learning a little about X-Ray equipment and X-Ray generation I always wondered if Superman’s X-Ray vision caused cancer if you were exposed to it too long. X-Ray’s were first generated in December 1895 in the middle of the night, by Professor Wilhelm Conrad Roentgen. He had been working on the machine for several years and in the middle of that December night asked his wife to put her hand on a photographic plate. He pushed a button and then took the plate to a dark room and developed it. The result was an image of the bones in her hand and the ring she wore on her finger. X-Ray technology took the world by storm after that.
X-Rays are generated by using extremely high voltages and low current. Voltages range up to 150 kilovolt Peak-to-Peak or 150kVp. Current is normally in the milliamp range. An X-Ray tube is made up of two filaments on the Cathode end and a spinning disc called an Anode on the other end. The filaments are on the negative side of the high voltage cable and the anode is on the positive side. At the X-Ray console the user selects the kVp, (voltage) and mA or mAs (milliamps or milliamps per second). The filament current is turned on and the filament glows brightly just like the filament in a light bulb.
When the exposure switch is pressed the high voltage causes the photons in the filament to flow across an open space and strike the face of the spinning anode. The anode is not flat but has an angle on the face of it. The photons are changed to electrons when they hit the anode and are deflected out of a small window in the tube and pass through a collimator through the patient and into the film that is developed later. When the electrons hit the face of the target anode is when they change and become X-Rays. This effect is called brehmsstrahlung effect or braking radiation because the electrons are slowed tremendously when they strike the anode.
The collimator is a device that is positioned in front of the tube. Its purpose is to limit the amount of radiation being generated by the tube. The collimator is lined with lead just as the tube is to prevent X-Rays from going everywhere. Inside the collimator are movable lead fingers that open and close to limit the size of the field. For example if a 9” x 9” film cassette is inserted into the bucky the sizing sensors in the bucky tell the collimator to adjust the fingers and only allow a 9”x9” area of X-Rays to come through. Manual override can further limit the size to pinpoint an area of the body. The bucky is nothing more than a tray that holds the film cassettes and slides in and out of the machine.
Because over exposure to radiation can cause burns, radiation poisoning and other serious problems, most X-Ray machines come with a feature called AEC. AEC stands for Automatic Exposure Control. AEC is programmed into various types of exposures. For example an exposure on a small body part like a hand doesn’t have to be as lengthy as an exposure on a thicker part of the body like a chest would. AEC combines the kVp selected by the user with the mA or mAs and determines what the maximum time of the exposure should be for the selected body part and study type. If the selections are outside the range of the pre-programmed AEC limits the X-Ray machine will not expose but will send up an alert message to the user telling them to make a different selection.
X-Rays can also be used to do fluoroscopy. Fluoroscopy is continuous X-Ray exposure but usually at a low kVp and mAs which limits the amount of exposure to X-Rays. Fluoroscopy allows a doctor to watch what is happening inside the body as it happens. It’s like watching a movie of what’s going on inside the patient. For example a Barium Swallow test is done with fluoroscopy. A patient is given some barium to swallow and while they are swallowing it the image is being displayed fluoroscopically on a monitor and the doctor is watching the swallowing process to determine abnormalities in the patient’s digestive tract. The barium works its way through the digestive system and when it reaches the area of concern the doctor can tell if blockages are present or if some other obstruction is casing the patient discomfort.
Some of the primary concerns with X-Ray quality are Density, Contrast, and Sharpness to name a few. Density is defined as the amount of blackening on an image. Density is directly related to the amount of kVp selected. As kVp increases Density increases because more x-rays are getting through the patient. Contrast is defined as the amount of difference in two adjoining areas. For example the amount of contrast between the colors black and white is very high. You can clearly see the edge where one begins and the other stops. Apply the same theory to two colors of gray and the edge becomes less clear which is considered low contrast. Contrast is also controlled by kVp and mA. Sharpness is simply how clear is the image and is there any distortion apparent.
X-Rays are generated by using extremely high voltages and low current. Voltages range up to 150 kilovolt Peak-to-Peak or 150kVp. Current is normally in the milliamp range. An X-Ray tube is made up of two filaments on the Cathode end and a spinning disc called an Anode on the other end. The filaments are on the negative side of the high voltage cable and the anode is on the positive side. At the X-Ray console the user selects the kVp, (voltage) and mA or mAs (milliamps or milliamps per second). The filament current is turned on and the filament glows brightly just like the filament in a light bulb.
When the exposure switch is pressed the high voltage causes the photons in the filament to flow across an open space and strike the face of the spinning anode. The anode is not flat but has an angle on the face of it. The photons are changed to electrons when they hit the anode and are deflected out of a small window in the tube and pass through a collimator through the patient and into the film that is developed later. When the electrons hit the face of the target anode is when they change and become X-Rays. This effect is called brehmsstrahlung effect or braking radiation because the electrons are slowed tremendously when they strike the anode.
The collimator is a device that is positioned in front of the tube. Its purpose is to limit the amount of radiation being generated by the tube. The collimator is lined with lead just as the tube is to prevent X-Rays from going everywhere. Inside the collimator are movable lead fingers that open and close to limit the size of the field. For example if a 9” x 9” film cassette is inserted into the bucky the sizing sensors in the bucky tell the collimator to adjust the fingers and only allow a 9”x9” area of X-Rays to come through. Manual override can further limit the size to pinpoint an area of the body. The bucky is nothing more than a tray that holds the film cassettes and slides in and out of the machine.
Because over exposure to radiation can cause burns, radiation poisoning and other serious problems, most X-Ray machines come with a feature called AEC. AEC stands for Automatic Exposure Control. AEC is programmed into various types of exposures. For example an exposure on a small body part like a hand doesn’t have to be as lengthy as an exposure on a thicker part of the body like a chest would. AEC combines the kVp selected by the user with the mA or mAs and determines what the maximum time of the exposure should be for the selected body part and study type. If the selections are outside the range of the pre-programmed AEC limits the X-Ray machine will not expose but will send up an alert message to the user telling them to make a different selection.
X-Rays can also be used to do fluoroscopy. Fluoroscopy is continuous X-Ray exposure but usually at a low kVp and mAs which limits the amount of exposure to X-Rays. Fluoroscopy allows a doctor to watch what is happening inside the body as it happens. It’s like watching a movie of what’s going on inside the patient. For example a Barium Swallow test is done with fluoroscopy. A patient is given some barium to swallow and while they are swallowing it the image is being displayed fluoroscopically on a monitor and the doctor is watching the swallowing process to determine abnormalities in the patient’s digestive tract. The barium works its way through the digestive system and when it reaches the area of concern the doctor can tell if blockages are present or if some other obstruction is casing the patient discomfort.
Some of the primary concerns with X-Ray quality are Density, Contrast, and Sharpness to name a few. Density is defined as the amount of blackening on an image. Density is directly related to the amount of kVp selected. As kVp increases Density increases because more x-rays are getting through the patient. Contrast is defined as the amount of difference in two adjoining areas. For example the amount of contrast between the colors black and white is very high. You can clearly see the edge where one begins and the other stops. Apply the same theory to two colors of gray and the edge becomes less clear which is considered low contrast. Contrast is also controlled by kVp and mA. Sharpness is simply how clear is the image and is there any distortion apparent.
Monday, May 18, 2009
How Defibrillators Work
A defibrillator is a machine used to deliver a shock to the human heart. Many people falsely think that the defibrillator is used to start a person’s heart when it has stopped beating. In reality it is used to reestablish a correct rhythm to the heart. When a person suffers from a myocardial infarction, (heart attack), it can be triggered by many different things. One of the most common things that can happen during a heart attack is that the normal rhythm of the heart is altered.
The heart is made up of 4 chambers, left and right atrium on the top, and left and right ventricles on the bottom. The area of the heart that is responsible for maintaining the normal rhythm of the heart is located in the right atrium and is called the sinoatrial node. It’s a small area of neurons that fires an electrical pulse causing the heart muscle to contract and squeeze blood through the four chambers. Occasionally during a heart attack the sinoatrial node may either misfire or get weak. When this happens it can cause the lower chambers to “flutter” because they are not receiving the correct signal and don’t know when to contract. This is called ventricular fibrillation and is where the defibrillator would be used to reestablish the correct rhythm to the heart.
The defibrillator essentially delivers enough of a shock to get all of the chambers to settle down and allow the sinoatrial node to begin its job again. So how does the defibrillator itself work? The defibrillator uses batteries and a series of transistors and inverters to switch the voltages rapidly enough to simulate an AC sine wave. The voltage is then fed through a high voltage transformer that steps the 12 volts up to a higher voltage. This is rectified and stored in a capacitor until the shock button is pressed on the defibrillator paddles. The shock is then delivered from one paddle through the patient and back to the other paddle completing a circuit.
Defibrillators also have a sync feature which allows them to monitor the heart and deliver the shock at the right point of the QRS wave. During the QRS complex the heart goes through a polarization period known as the P-Wave. Then the sinoatrial node fires causing the QRS spike and subsequent heart muscle contraction and then depolarizes during the T-Wave. If the defibrillator delivers the shock at the wrong time it can damage the muscles and cause death. The Shock has to be delivered after the QRS spike during the depolarization of the T-Wave.
The heart is made up of 4 chambers, left and right atrium on the top, and left and right ventricles on the bottom. The area of the heart that is responsible for maintaining the normal rhythm of the heart is located in the right atrium and is called the sinoatrial node. It’s a small area of neurons that fires an electrical pulse causing the heart muscle to contract and squeeze blood through the four chambers. Occasionally during a heart attack the sinoatrial node may either misfire or get weak. When this happens it can cause the lower chambers to “flutter” because they are not receiving the correct signal and don’t know when to contract. This is called ventricular fibrillation and is where the defibrillator would be used to reestablish the correct rhythm to the heart.
The defibrillator essentially delivers enough of a shock to get all of the chambers to settle down and allow the sinoatrial node to begin its job again. So how does the defibrillator itself work? The defibrillator uses batteries and a series of transistors and inverters to switch the voltages rapidly enough to simulate an AC sine wave. The voltage is then fed through a high voltage transformer that steps the 12 volts up to a higher voltage. This is rectified and stored in a capacitor until the shock button is pressed on the defibrillator paddles. The shock is then delivered from one paddle through the patient and back to the other paddle completing a circuit.
Defibrillators also have a sync feature which allows them to monitor the heart and deliver the shock at the right point of the QRS wave. During the QRS complex the heart goes through a polarization period known as the P-Wave. Then the sinoatrial node fires causing the QRS spike and subsequent heart muscle contraction and then depolarizes during the T-Wave. If the defibrillator delivers the shock at the wrong time it can damage the muscles and cause death. The Shock has to be delivered after the QRS spike during the depolarization of the T-Wave.
Hospital Equipment Preventive Maintenance
Part of the job of the Biomedical or Clinical Engineering Department is preventive maintenance on equipment. There is a debate among some biomedical technicians that the PM’s we do are unnecessary and have no value to the equipment. It is true that many time I have completed a PM on a piece of equipment only to get a call from the nursing staff that it’s broken a few hours later. One might say that the PM was done incorrectly then. When the defective equipment is examined it is usually determined that something completely outside the realm of the PM failed in the machine.
How can you test for quality though? An IV pump may deliver the exact amount at the specified flow rate and occlusion pressures during testing and pass the PM. Remember that the pump mechanism is a mechanical device subject to wear and therefore failure, if you have ever had an engine problem on your car strand you somewhere then you can understand. You drive to the grocery store, and then drive to the dry cleaners, and then pick up the kids for soccer practice, and then stop at the pharmacy and when you come back out your car won’t start because something in the engine failed. Yet you made all of those stops and starts in your car not to mention driving it for maybe years without trouble. If you happen to live in a state as I do where they still require annual vehicle inspection it makes you wonder why the inspection didn’t catch the failing engine component. The answer is because it was not part of the inspection.
Even if we disassembled the IV pump and looked at the mechanism it is still impossible to know if it will fail soon. So the question is: Why do we bother with PM’s? We just tested it and put a sticker on the side saying it is OK to use and the nurse is standing there saying it’s broken. This kind of makes us look silly don’t you think? I believe that some PM’s are not useful at all. Thermometers, hand held pulse oximeters, laboratory centrifuges, and several other things either work or they don’t. I can’t begin to imagine how much rubber I have worn off my shoes looking for these things too. Some biomedical departments have started adopting a policy of no PM’s on anything less than life critical equipment.
Life critical equipment is things like ventilators, anesthesia machines, defibrillators, and electrosurgical units to name a few. This type of equipment should get regular checkups because it is directly used to sustain life or alter the human anatomy. But how many people do you know died because the thermometer used on them gave the wrong temperature reading? Anyone that works as a biomedical technician knows that the job can be very stressful at times. Broken equipment seems to come in waves. It’s difficult at times to juggle repairs with requests for information from different departments without having to worry about where Nurse Nancy hid her thermometer so you can do a PM on it. Which is basically nothing more than sticking the probe in your mouth to see if you get a temperature close to normal body temperature, unless you’re lucky enough to have a calibration key for it, which by the way does not calibrate it. The calibration key simply verifies that the default temperature set at the factory and programmed into a microchip is still the same.
I know there will be a few people reading this saying without PM’s I am not a necessary employee and could be let go. We were hired for our knowledge of electronics, troubleshooting skills and customer service abilities. When something breaks that is when we shine the brightest. PM’s normally go completely under the radar of most hospital staff. Let something break though and we become the most needed people in the hospital. Nurses and doctors can’t do their job with broken equipment.
How can you test for quality though? An IV pump may deliver the exact amount at the specified flow rate and occlusion pressures during testing and pass the PM. Remember that the pump mechanism is a mechanical device subject to wear and therefore failure, if you have ever had an engine problem on your car strand you somewhere then you can understand. You drive to the grocery store, and then drive to the dry cleaners, and then pick up the kids for soccer practice, and then stop at the pharmacy and when you come back out your car won’t start because something in the engine failed. Yet you made all of those stops and starts in your car not to mention driving it for maybe years without trouble. If you happen to live in a state as I do where they still require annual vehicle inspection it makes you wonder why the inspection didn’t catch the failing engine component. The answer is because it was not part of the inspection.
Even if we disassembled the IV pump and looked at the mechanism it is still impossible to know if it will fail soon. So the question is: Why do we bother with PM’s? We just tested it and put a sticker on the side saying it is OK to use and the nurse is standing there saying it’s broken. This kind of makes us look silly don’t you think? I believe that some PM’s are not useful at all. Thermometers, hand held pulse oximeters, laboratory centrifuges, and several other things either work or they don’t. I can’t begin to imagine how much rubber I have worn off my shoes looking for these things too. Some biomedical departments have started adopting a policy of no PM’s on anything less than life critical equipment.
Life critical equipment is things like ventilators, anesthesia machines, defibrillators, and electrosurgical units to name a few. This type of equipment should get regular checkups because it is directly used to sustain life or alter the human anatomy. But how many people do you know died because the thermometer used on them gave the wrong temperature reading? Anyone that works as a biomedical technician knows that the job can be very stressful at times. Broken equipment seems to come in waves. It’s difficult at times to juggle repairs with requests for information from different departments without having to worry about where Nurse Nancy hid her thermometer so you can do a PM on it. Which is basically nothing more than sticking the probe in your mouth to see if you get a temperature close to normal body temperature, unless you’re lucky enough to have a calibration key for it, which by the way does not calibrate it. The calibration key simply verifies that the default temperature set at the factory and programmed into a microchip is still the same.
I know there will be a few people reading this saying without PM’s I am not a necessary employee and could be let go. We were hired for our knowledge of electronics, troubleshooting skills and customer service abilities. When something breaks that is when we shine the brightest. PM’s normally go completely under the radar of most hospital staff. Let something break though and we become the most needed people in the hospital. Nurses and doctors can’t do their job with broken equipment.
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