Ventilators

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”.