Review of Apneic Oxygenation during endotracheal intubation.
I first came across the concept of apneic oxygenation as an observer on a TEAM (training in emergency airway management) course several years ago. An emergency medicine registrar mentioned it as they were asked to justify their approach to a rapid sequence induction (RSI). This was rapidly poo-pooed by an anaesthetic consultant as complete rubbish. This was before I had discovered social media. However, this comment sparked my interest during the development of my advanced airway skills and came upon Weingart’s (2011) paper on pre oxygenation. Of course, I then discovered emcrit.org and Richard Levitan, and off I flew into the world of FOAMED.
As part of my MSc and critical care practitioner training, I produced a BestBets review on the subject in 2013. Since then, a number of papers produced from the emergency medicine and critical care fields have expanded upon the initial anaesthesia based studies. So here is my update.
Three part question.
In patients requiring endotracheal intubation, does the administration of nasal oxygen during the apneic period following induction increase the time to de-saturation?
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Comment.
Apneic oxygenation has been used for decades in the assessment of brain stem death, maintaining oxygenation, but allowing carbon dioxide to rise, maximising the brain stem’s stimulus to breathe. Frumin et al (1959) showed that patients can remain oxygenated for greater than thirty minutes. However, this is usually achieved with insufflation of oxygen via a tracheal cannula.
Basic Physiology
The basic physiology behind apneic gas flow centres on the continuing consumption of oxygen during apnea, at resting and unstressed physiological states, this is around 250ml per minute. The gradient that this produces between the capillary and the alveolus ensures that alveolar oxygen continuously flows across the concentration gradient. As a result of this continuing gas flow from the alveolar space to the capillary, a negative pressure is generated in the alveolus. Where the airway is kept open, this negative alveolar pressure will continuously draw gas from the upper airway along this negative pressure gradient, apneic gas flow. Apneic oxygenation utilises this physiology to provide oxygenation during apnea.
Early versus later studies.
Early anaesthesia based studies conducted by Teller et al (1998), Taha et al (2006) and Lee et al (1988), although very small studies, clearly demonstrate that the time before desaturation during apnea can be significantly prolonged or negated altogether. More recently Patel has added to this evidence with an apnea time of up to 66 minutes. The debate from this point has been whether this technique is applicable to the non-anaesthetic environment, the critically ill and injured. Where patients will likely have ventilation-perfusion miss-match. Miguel-Montanes et al (2014), Sakles et al (2016) and Wimalasena et al (2015) observational, before and after studies suggested that apneic oxygenation reduced desaturation events across an array of critically ill patients. Despite the size of these cohorts, this is not high-level evidence and the limitations and biases of these kinds of observational studies have to be acknowledged.
What do the RCTs say?
Now we come to the randomised controlled trials (RCT). We now have two RCT’s in critically ill patients, showing no effect. Is this the definitive answer? No. Unfortunately, the significant confounders for these studies are not in the primary papers. Semler’s et al (2016) study was not a true apneic oxygenation study as only 50 patients were not ventilated through the apneic period. There is no subgroup analysis of the “non-ventilated” patients. The on-line supplement for this paper is essential reading to critique this paper. Semler’s investigation tells us that apneic oxygenation does not offer benefit if the patient is ventilated through apnea, and has not answered our question. Vourc’h et al (2015) study has also not answered the question. The “no apneic oxygenation” group received PEEP and this strategy may have accounted for the apneic oxygen benefit by better functional residual capacity recruitment and denitrogenation. More importantly, Vourc’h et al (2015) apneic oxygenation patients did not have their airways maintained open during apnea. Clearly apneic oxygenation delivered to a closed airway prevents any apneic oxygenation. These issues are not evident in the Vourc’h paper, but were high lighted by Scott Weingart of emcrit.org when he interviewed the investigators (https://itunes.apple.com/gb/podcast/emcrit-podcast-critical-care/id314020330?mt=2&i=345966308).
So, we have high-level evidence that apneic oxygenation works in the stable elective patient. Low level evidence (with good patient numbers) suggests we can get an absolute reduction of desaturation of around six percent in the critically ill and injured population. We have high level evidence that significantly muddies the waters.
What are the Harms?
What are the harms? High flow nasal oxygen systems are now becoming commonly employed in critical care and use flows of 40 litres or more. It seems unlikely that there is a significant down side to apneic oxygenation using 15 litres. The only harms I have found in my literature searches are of gastric rupture when nasal oxygen is used with nasal trumpets on a closed airway, there are only two or three reports of this that I have found. Is apneic oxygenation a distraction, from more important interventions. I invariably find that nasal oxygen has often already been used on a patient requiring intubation and is very quickly and easily applied during the preparation for RSI. The technique is low risk, cheap, and in all likelihood effective.
Does apneic oxygenation give the operator a false sense of security? Personally, preparation for RSI is about maximising first-pass success and building redundancy into the procedure. Apneic oxygenation is not a panacea of safe RSI. However, using small percentage gains adds redundancy to a dangerous procedure. Head up, PEEP pre-oxygenation, bougie, and gentle low volume apneic ventilation, end tide carbon-dioxide monitoring, check lists and apneic oxygenation.
Bottom Line.
Apnoeic oxygenation can extend the time to apneic desaturation and reduce desaturation episodes during endotracheal intubation.
Other posts on the web:
St Emlyns- JC: The last breath for apnoeic oxygenation?
LITFL- Apneic oxygenation
PHARM Podcast 132 Apnoeic Oxygenation in Emergency Intubations with Dr John Sakles
HEFTEMCAST- APNEIC OXYGENATION
EMergucate- FOAM Eye-Catchers 10: Apnoeic Oxygenation – new trial questions value of NODESAT
References:
Miguel-Montanes, R., Hajage, D., Messika, J., Bertrand, F., Gaudry, S., Rafat, C., Labbé, V., Dufour, N., Jean-Baptiste, S., Bedet, A., Dreyfuss, D., and Ricard, J.-D. (2014) ‘Use of High-Flow Nasal Cannula Oxygen Therapy to Prevent Desaturation During Tracheal Intubation of Intensive Care Patients with Mild-to-Moderate Hypoxemia’. Critical Care Medicine 1
Semler, M.W., Janz, D.R., Lentz, R.J., Matthews, D.T., Norman, B.C., Assad, T.R., Keriwala, R.D., Ferrell, B.A., Noto, M.J., McKown, A.C., Kocurek, E.G., Warren, M.A., Huerta, L.E., Rice, T.W., FELLOW Investigators and the Pragmatic Critical Care Research Group (2016) ‘Randomized Trial of Apneic Oxygenation During Endotracheal Intubation of the Critically Ill.’. American Journal of Respiratory and Critical Care Medicine 193 (3), 273–280
Vourc’h, M., Asfar, P., Volteau, C., Bachoumas, K., Clavieras, N., Egreteau, P.-Y., Asehnoune, K., Mercat, A., Reignier, J., Jaber, S., Prat, G., Roquilly, A., Brule, N., Villers, D., Bretonniere, C., and Guitton, C. (2015) ‘High-Flow Nasal Cannula Oxygen During Endotracheal Intubation in Hypoxemic Patients: a Randomized Controlled Clinical Trial’. Intensive Care Medicine 41 (9), 1538–1548
Weingart, S.D. and Levitan, R.M. (2012) ‘Preoxygenation and Prevention of Desaturation During Emergency Airway Management’. Annals of Emergency Medicine 59 (3), 165–75.e1
Gavin Denton
– Current role: Critical care practitioner, critical care, West Midlands. Roles include; assessment and management of the critically ill patient, insertion of invasive lines, advanced airway management (under supervision), transfer of the critically ill patient, resuscitation (from airway, to team leader to post resus care). Teaching and support of junior doctors of the above.
Graduated from the University of Birmingham with BN(hons). BSc from Birmingham City University. About to complete MSc in health sciences from the University of Warwick.
Working background: 15 years working within various aspects of critical care. 7 years in critical care, 6 years in critical care outreach, 2 years as a critical care practitioner. Adult life support instructor. Independent non-medical prescriber.
Future aims: faculty of critical care medicine affiliation. FEEL course, POCUS training.
Clinical interests: USS, airway management.