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.
Monday, May 18, 2009
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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