Defibrillators can be used in flight without causing disasters provided a few factors are considered. In my five or so years as a flight physician I only had to do it once.
Factors:
Equipment usability/efficacy
Safety of Patient
Safety of Crew
Equipment:
Two basic types of defibrillator - Manual operated and automatic (and versions which have both modes)
Automatic ones (the types that are found now in airliners, shopping centres etc can have problems sensing the rhythm because of vibration of aircraft etc. They may then either fire inappropriately or not fire when needed. This is because the rhythm which is the prime shockable rhythm is one which looks like a coarse wavy line on the ECG, just what vibration can induce in the leads if the contacts are not really good.
Poor contact and vibration may also cause the sensor error trapping routines of the microprocessor to not allow it to fire.
The manual ones don't have that problem. Press the buttons and it fires regardless. Problem is that your ECG from which you diagnose whether a shock is appropriate may be unusable because of same vibrations as discussed above.
But at least if you have all the other signs of cardiac arrest then it can be given on spec, as probably would be appropriate anyway.
Patient Safety:
If you don't have good contact with skin and moreso if you have to use multiple shocks patients can get burns from pads/paddles.
Getting a good contact is a bit more of a problem in the confines of a helicopter so it's a consideration.
Crew/Aircraft Safety:
It is absolutely true that if anyone else is in contact with the patient or pads/paddles etc then they will get a shock as well if there's a path through them to earth. I have seen a nurse get a bolt that threw him six feet up against the wall in our ICU when he contacted the paddles via conducting gel that he had on his hands (we used to use gel from a squeeze tube but now we have sticky gel pads so that problem isn't so bad) But if it happened in an aircraft there probably isn't a path to earth so I suspect it may not happen. However the answer is to judiciously insulate the patient from the aircraft and crew. Most times we had them off the floor on a plastic stretcher with plastic/foam padding, with cotton sheets and blankets etc which is enough to insulate them. If there is no other pathway the current can take it goes from one paddle to the other a distance of less than a foot in a fairly direct line with some rapid attenuation outwards.
Our SOPs were to treat the defib just as you would in the ICU/ward. Insulate and separate the patient, call "all clear" and press the buttons.
Dr. John Martin
Specialist Anaesthetist
Flight Physician (Retired)
Cairns Base Hospital/Qld Rescue Helicopter Service