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Interesting Airway Case

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Not to hijack too much, but if you suspected an air embolism, would you consider helicopter flight to be contraindicated? What about subcutaneous emphysema?

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Not to hijack too much, but if you suspected an air embolism, would you consider helicopter flight to be contraindicated? What about subcutaneous emphysema?

I am not sure, I wouldn't think so, I know nitrogen can expand with flight (e.g. decompression sickness) or gas filled spaces (e.g. N2O in pneumothorax) but most helicopters fly very low anyway, 500-1,000ft and i do not think oxygen would be a problem

I know SFA about flight physiology, which is interesting considering all the aviation and medical crap I've done

Edited by Kiwiology

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Hi, in regards to your post about suspected air embolism. It would not be a contraindication for HEMS, as Kiwi stated our cruise altitude would be between 1000-1500 feet. There are certain cases that you have to be concerned with pressure changes and altitude taking into account Boyle, Charles and Dalton Law(s) etc. Those type of flights would be primarily FW, where you could pressurize the cabin to your desired altitude. For example I recall flying (by FW) a 4 month with pulmonary complications who was vented at 800 agl, and had desaturations upon assent. We formulated a plan with the FW pilots to keep the cabin pressure at 1000 feet agl, and made some minor vent changes i.e. increasing FiO2 and were able to successfully transport patient while maintaining his saturations. Another thing we did during that transport was to replace the air in the cuff of his ETT with saline to ensure constant pressure. I hope this answers your question. Here is also a link to a relatively short article about air embolism.

http://www.hboorcca....ir Embolism.pdf

Edited by flightmedic608

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I found a couple of references to air embolism complications vis a vis altitude changes during helicopter flight, but no definitive articles. Most of them refer to people suffering decompression sickness en route to a hyperbaric chamber.

According to this chart I'm looking at, an altitude of 1500 feet does show only a negligible drop in air pressure, only a difference of 38 mmHg, but with 95% the amount of oxygen present at ground level. The reason this was in my head was because at a transport job a long time ago we would once in a while take a stroke patient over a long distance by ground, as they said the changes in the air pressure could be detrimental. I think I learned something today.

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You can very roughly model the atmosphere as decreasing in pressure by about 4% per 313 meters or so (about 1,000 feet). Asys's numbers seem fairly accurate, or accurate enough to gain some quantitative understanding of the situation. With this information, we can build a model and plug in some numbers.

Let's just say we are looking at an isolated air embolism that occupies a volume of 10 ml at sea level, barometric pressure of 760 mmHg. Let's take the patient to 1,000 feet mean sea level (MSL) and look at the situation isolated and in a vacuum. Doing so requires ignoring factors such as temperature and metabolism and simply model the air embolism as being a collection of ideal gas in an isolated system. At 1,000 MSL, the barometric pressure will be about 722 mmHg. Using Boyle's law, we simply plug and chug:

Pressure 1 * Volume 1 = Pressure 2 * Volume 2

760mmHg * 10 ml = 722 mmHg * x

x= 10.53 ml

From this exercise, we can all agree that there is a small but non-negligible increase in the volume as we ascend. The concern for me is what happens when we have multiple air emboli in multiple areas of the body and the patient is taken to altitude?

Regarding the original scenario, it sounds as though the patient has a partial tracheal transection. Attempts to intubate or manipulate the airway could result in a complete transection and a disaster regardless of the tools we have on hand to manage the airway. It sounds as though the initial EMS crew did the right thing; allowed the patient to maintain his own airway and simply supported him with non-invasive techniques. I would not do anything different. Personally, I would not fly the patient. Depending on the aircraft, you are likely to have better patient access and control in the back of an ambulance and a Delta of three minutes regarding transport time does not compel me to favour rotor wing evacuation of the patient over ground transport. Additionally, I would have no desire to chemically alter this patient's ability to protect their airway.

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It is interesting to read what others may have done when presented with this case. As you can imagine, we have tremendous peer review and discussed this at length. When I give airway lectures to local FD/EMS systems we discuss this case as a teaching tool. I strongly believe there is no right or wrong way to treat this patient. Each clinican has to understand his or her ability, resources and tool(s) that they can utilize. This case presents many challenges for a provider to work through; patient care, logistics, safety.

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