Persistent Laryngospasm

[doctormike]

...for contributing to this discussion ( my question's genesis is a point made in a "Rescue" thread over in the Advanced Diving section ).

Well, I'm a little out of my depth here as a snotologist, but I'll give it a shot... you will get better answers from the real docs here!

Now, what about the time frame? Any suggestions as to how long one might remain in spasm after loss of conciousness?

I doubt that there is any human data to answer that question, but remember it is not the loss of consciousness but the progression towards a hypoxic brain death that you seem to be tracking. Unconscious patients can and do have prolonged laryngospasm, but eventually progressive hypoxia and hypercapnia (elevated carbon dioxide) would override the airway protective reflex that is (when exaggerated) larygospasm.

Further; I've queried several doctors on the subject of cardiac sustainability after cessation of respiration, & have received a variety of estimates. Would anyone care to speak to that issue?

Temperature has a lot to do with this.... there are a number of case studies of young drowning victims in cold water for up to around 30 minutes who are successfully resuscitated. As they say in the ERs of the great white north, "you are not dead until you are warm and dead". In general, though, successful resuscitation is rare after more than 5 minutes or so of apnea.

Lastly, how imperative is the "chin-up" posture for the patient's head when ascending during a rescue of an unresponsive diver? I have read one opinion where the author opined that pulmonary air will escape regardless of the patient's head position because of Boyle's Law, though this seems to run contrary to conventional wisdom as I understand it.

That actually has more to do with clearing the obstruction to the airway caused by the tongue. When you are resuscitating someone (above water), you do a head tilt maneuver to move the base of the tongue away from the back of the throat, to make respiration easier (spontaneous or by resuscitation). So this is more of an issue once you hit the surface. As far as air escaping from the chest during ascent, it shouldn't matter either way, since the expanding gas will push its way out one way or the other, thanks to Boyle...

 

[TSandM]

As far as cardiac sustainability after apnea goes, it depends in part on what the ppO2 at the time of apnea is. Eventually, high CO2 levels and acidosis will induce arrhythmias, but hypoxia will do it, too, and which intervenes and how quickly depends on ppO2, exertion level, and temperature. But you aren't really interested in cardiac sustainability -- you're interested in neurologic survival. That's estimated at about 4 minutes on land, at normal body temperature, assuming that you are breathing ambient air. Ceasing respirations at depth, with the elevated ppO2 associated therewith, and with possibly a decreased core temperature, will lengthen that period significantly.

Keeping the chin up on ascent IS important, because if the head falls forward, the airway can be kinked and occluded. My husband had a cardiac arrest after a simple surgical procedure because of this -- he lost consciousness in a wheelchair, and the nurse pushing him from behind didn't realize that when his head fell forward, he could no longer breathe.

 

[doctormike]

As far as cardiac sustainability after apnea goes, it depends in part on what the ppO2 at the time of apnea is. Eventually, high CO2 levels and acidosis will induce arrhythmias, but hypoxia will do it, too, and which intervenes and how quickly depends on ppO2, exertion level, and temperature. But you aren't really interested in cardiac sustainability -- you're interested in neurologic survival. That's estimated at about 4 minutes on land, at normal body temperature, assuming that you are breathing ambient air. Ceasing respirations at depth, with the elevated ppO2 associated therewith, and with possibly a decreased core temperature, will lengthen that period significantly.

See, I KNEW a real doctor would be around here somewhere...

Keeping the chin up on ascent IS important, because if the head falls forward, the airway can be kinked and occluded. My husband had a cardiac arrest after a simple surgical procedure because of this -- he lost consciousness in a wheelchair, and the nurse pushing him from behind didn't realize that when his head fell forward, he could no longer breathe.

Wow, so sorry to hear that! That is terrifying...

However, just to be pedantic about it (and after all, that is why we are here) - underwater the physiology is a bit different. Because of the anatomy of the upper aerodigestive tract, the head going forward does not really "kink" the airway (like a soft tube that is folded), but rather pushes the tongue back into the hypopharynx. And if you are breathing air spontaneously (or receiving resuscitative ventilation), increased negative lower airway pressure (or positive oronasal pressure) will tend to draw the tongue further back and further occlude the airway. That is why the head-tilt and chin-lift maneuver is important in CPR, and why the scenario that TSandM describes is indeed potentially lethal. Tongue obstruction only gets worse as the patient tries to breathe in or as ventilation is attempted by mask or mouth-to-mouth.

However, in the context of the physics of gas dynamics on ascent with an unconscious patient, the situation is reversed. Airflow is going to be continuous and out of the lungs, which will counteract any passive obstruction caused by the tongue. So I think that you would get the same release of air on ascent no matter what the head position.

HOWEVER, the head-up guideline is obviously meant as a good training point for rescue divers, and once you hit the surface it IS important to keep the head back (as described above). I don't think that the people who write these protocols want to confuse the issue by going into this - much better to have a simple rule which will initially put you in the right position once you are no longer underwater! I only bring it up because it is interesting to discuss the physics...

 

[TSandM]

Ah -- very nice to learn something new from somebody who knows what he's talking about! Thank you, Mike.

 

[doctormike]

Ah -- very nice to learn something new from somebody who knows what he's talking about! Thank you, Mike.

A specialist is someone who knows more and more about less and less, until they know everything about nothing...

 

[DeepSeaDan]

...the people who write these protocols want to confuse the issue by going into this - much better to have a simple rule which will initially put you in the right position once you are no longer underwater! I only bring it up because it is interesting to discuss the physics...

Thanks for that Dr. Mike.

What concerns me as a trainer of rescue divers is the relative difficulty I've observed in many rescue students to perform the "chin-up" aspect of rescuing an unresponsive diver.

This problem is less of a concern for warm water rescues where the patient is wearing a conventional scuba kit, as patient manipulation & control is considerably simpler than performing the same skill in cold water &/or when the patient is "decked for tec."

I've addressed this issue in the past by advising my students to simply get the patient to surface in the safest, most expedient manner possible if & when they find they cannot, for whatever reason, bring the patient to surface in the chin-up posture. Still, I worry that there are those who would ignore this advice & battle on, with potentially serious consequences for all involved, because of an inate fear of causing lung expansion injury to the patient.

So...would it not be prudent to make the information provided by you available to the rescue student?

DSD

 

[doctormike]

Thanks for that Dr. Mike.



I've addressed this issue in the past by advising my students to simply get the patient to surface in the safest, most expedient manner possible if & when they find they cannot, for whatever reason, bring the patient to surface in the chin-up posture. Still, I worry that there are those who would ignore this advice & battle on, with potentially serious consequences for all involved, because of an inate fear of causing lung expansion injury to the patient.

So...would it not be prudent to make the information provided by you available to the rescue student?

DSD

Oh, no... now I'm going to be sued by PADI..!!!

Well, my experience with this sort of training (having been a CPR instructor a LONG time ago) is that the people who put together the materials go to a lot of trouble to minimize the possibility of misunderstanding, and maximize the effectiveness in the field. To that end, most training programs are constantly refining their protocols. If you are continually recertifying in something, this can be frustrating - "why was the precordial thump ok when I first trained, but not now?". But the protocols are built with the one time student in mind, and you want to maximize the chance that they will be remembered and will be effective when put to use.

Of course, feel free to discuss basic physics and physiology with your students as you see fit, but be careful of confusing them. Sometimes it is better for them to just have "chin up" hammered into their heads, then to rely on them accurately remembering the nuances in an emergency situation.

Realize that maybe 1-2% of your students will ever have to use these skills, and then maybe not until decades later. It might be better that they not have to stop and try to remember "let's see, did Dr. Mike say head tilt only on the surface or until the surface??"

Part of being a good rescuer is situational awareness, calm and the ability to think flexibly. Every situation is different, and of course, it would be foolish to waste a lot of time trying to get a tight hood off someone so that you could do an underwater head tilt. And to be perfectly honest, this discussion here is more of a thought experiment - I am sure that before changing a published teaching protocol, the training agency would need to be SURE that the underwater head tilt didn't help - even to a small degree - with the ventilation of air from the lungs. Probably some sort of cadaver or model experiment would make the most sense... And even if you did come up with a good "answer" (e.g. head tilt underwater drops the pressure gradient by .2 atmospheres, or whatever), you would then have to make the analysis as to whether it was worth the time it took to achieve that, instead of just going to the surface and relying on the expanding air to push past the tongue...

In any case, I'm glad that you like the discussion and found it useful...!

Mike