Pre-Ox, Ap-Ox, and NO DESAT - Water Cooler Rundown

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Pre-Ox, Ap-Ox, and NO DESAT

Water Cooler Discussion on “Preoxygenation and Prevention of Desaturation During Emergency Airway Management” by Weingart and Levitan

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In 2012 in the Annals of Emergency Medicine, Weingart and Levitan published a review of preoxygenation and peri-intubation oxygenation techniques in the emergency airway management of adult patients.  Topics reviewed included the evidentiary support for preoxygenation and denitrogenation, appropriate positioning and patient selection, the utility of positive pressure in select circumstances, apneic oxygenation, as well as a proposed risk stratification approach based on pulse oximetry levels and peri-intubation risk.

A great discussion was had with many excellent learning points, upon which some were elaborated in great detail in the article and some only briefly mentioned.  What follows is a brief summary of learning points from the article as well as from the discussion. 

For those faint of heart -- and who only want to appreciate the nuts and bolts -- refer to Bill Hinckley’s first point:

O2 DISSOCIATION CURVE 1.png

“There are very few absolutes in EM.  But two of them are: we should absolutely read this paper in its entirety more than once, and we should absolutely do ap ox for each and every RSI we do.”

‘nuff said. 

Preoxygenation extends the safe apnea period.  It should be done for every ED intubation

Every patient, every time.  As Bill Hinckley points out -- “even if our patient is an Olympic marathoner with a pre pulse ox of 150%.”   

Recognize that a non-rebreather is NOT a non-rebreather -- Jeff Hill

Standard reservoir facemasks @ 15Lpm only deliver 60-70% FiO2.  Thus, preoxygenation should be performed for AT LEAST 3 minutes prior to ED intubation -- ideally. 

If your patient has shunt physiology or fails to increase sats during preoxygenation -- add some positive pressure -- Jeff Hill

Apneic oxygenation alone is unlikely to benefit critically ill patients with high degrees of shunt physiology.  Thus, don’t be afraid of additional measures such as NIPPV (CPAP vs BiLevel) or PEEP valves with BVM

Preoxygenate in a “head-elevated” position

Whenever possible, either sit the patient up during preoxygenation or perform this step in a reverse Trendelenburg position for those (seemingly innumerable) patients in spinal immobilization.

How much time do I have?

The answer to this question is multifactorial.  The primary benefit of preoxygenation is to denitrogenate the lungs and create an oxygen reservoir in the alveoli, as opposed to increase the PaO2 in the bloodstream.  As classically described by Benumof et al (see curve below), time to desaturation ranges from ~3 - 8 minutes.  However, this does not take into account critical pathophysiology such as poor CO, sepsis, anemia, and volume depletion.  Studies in the ICU setting have proposed safe apnea times of only 23 seconds (Mort 2005).

Thus, Weingart and Levitan conclude that it is “impossible to predict the exact duration of safe apnea in a patient [...] critically ill patients [...] are at high risk of hypoxemia with prolonged tracheal intubation and may desaturate immediately.”

Also, as borne out in the discussion, data has suggested that succinylcholine may increase O2 consumption and shorten the safe apnea time. 

Beware of prolonged apnea times -- particularly in acidotic and TBI patients

Pretreat with Lidocaine when you can to diminish fasciculations and the reportedly increased O2 consumption/CO2 production.  Move quickly or provide ventilatory assistance in those patients who are at significant risk of hypercapnea, respiratory acidosis, and its downstream effects, particularly those patients who start off significantly acidotic or in patients with head injury. 

Finally…

Think twice before applying cricoid pressure

“Doing RSI with only one source of O2 isn’t acceptable anymore.” -- Bill Hinckley

“Make damn sure not to cut the tubing of the ETT cuff.” -- Bill Hinckley

References

  • Weingart, SD and Levitan, RM.  Preoxygenation and prevention of desaturation during emergency airway management. Ann Emerg Med 2012;59:165-175.
  • http://emcrit.org/preoxygenation/
  • Mort, T.C. Preoxygenation in critically ill patients requiring emergency tracheal intubation. Crit Care Med. 2005; 33:2672–2675
  • Benumof, J.L., Dagg, R., and Benumof, R. Critical hemoglobin desaturation will occur before return to an unparalyzed state following 1 mg/kg intravenous succinylcholine. Anesthesiology. 1997; 87: 979–982