Matt Semler, MD and colleagues performed an RCT on Apneic Oxygenation in Medical ICU patients. I got a chance to sit down and interview him on the trial.
Bottom Line Review
Additional Written Comments from Matt Semler
as provided by Matt Anderson (@ccinquisivist)
From: Anderson, Matthew J
I'm a CCM fellow at the University of Wisconsin, interested in airway mgmt in the ICU.
Just saw your article published in ATS. I had a question about the airway mgmt protocol (or if there was one?). Did the airway team leader/intubator maintain a patent airway (ie were they instructed to do this just prior to the intubation attempt when getting sedation/analgesia and/or NMB)? I am unable to find/get to the supplement which this information may be listed but I didn't see any mention in the main manuscript, which I think is a extremely important discussion point. Previous, studies in the OR w/ or w/o maintenance of airway patency resulted in ‘no difference in the non-airway patency (ie jaw thrust/head tilt chin lift) group vs ‘stat significant difference in the airway patency group' during apneic oxygenation. If airway patency was maintained in your study this would be one of the first ‘negative' results I have seen with apneic oxygenation. If airway patency was not required, this may explain the ‘no difference' that was found in your study, which in my opinion, makes the use of apOX still an important part of endotracheal intubation. Until a randomized control trial to evaluate apOx with airway patency versus no apOx with airway patency confirms that previous. Further trials may need 30 degree ramp/optimal positioning, as well?
Thanks for taking the time to answer my questions and publish/perform important ICU airway research.
Critical Care Medicine Fellow, PGY5
From: Semler, Matthew
Thanks for your interest in the trial. You ask two really important questions — actually two of the same points Rich Levitan emphasized when he visited during the conduct of the trial.
(1) When discussing the effect of airway patency on outcomes of apneic oxygenation, the time-period in question is between administration of RSI medications (with anything prior to induction technically a part of pre-oxygenation) and the onset of laryngoscopy (when patency of the airway is directly established by the laryngoscope better by external maneuvers). Objectively assessing whether the airway is patent during this period is challenging. For the 30% or so in the trial who were on BIPAP between induction and laryngoscopy, the airway was known to be patent through monitoring of the returned tidal volumes. In cases where NIV was not present, the operator was charged with maintaining patency of the airway between induction and laryngoscopy. In 60% of cases this required an oral airway and a head-tilt-chin-lift maneuver. In around 40 patients, the operator felt the airway was patent without such a maneuver. Whether these maneuvers were effective in maintaining patency or whether patency was truly present in those patients who were not felt to require a maneuver is difficult to know. We did analyze the subgroup of those who were on BIPAP and we were certain the airway was patent and there was not a significant effect of apneic oxygenation on lowest oxygen saturation in this group — though obviously this is a not a large population.
An important thing to consider when thinking about the period between induction and laryngoscopy is that high flows of oxygen are being delivered in BOTH arms. The AO group was getting 15LNC on top of a non-rebreather or BIPAP or bag-valve-mask but its not like in the usual care group their preoxygenation device (BIPAP, NRB, etc) was REMOVED at induction. So, even if airway patency were maintained PERFECTLY in both groups, usual care and AO both had high flows of oxygen available during this period and it was not until laryngoscopy started that the difference in available oxygen became more extreme (usual care group had NO oxygen and AO had 15L/min NC).
All that said, a big potential difference between our study and prior studies was patient population. I don't know of any randomized trial of AO previously in any population except those with healthy lungs undergoing elective intubation. The one trial I do think is really relevant is the PREOXYFLOW trial (attached) which functionally compared apneic oxygenation with 60L/min NC to no oxygen during laryngoscopy. They included a similar population of sick ICU patients with a lot of pulmonary dysfunction and saw pretty similar results to ours. I think the idea that oxygenation generally doesn't work as well when you have profoundly damaged lungs make me more inclined to want to see a study of AO in acute intubations for trauma or stroke or some setting where lung function is preserved to see if the results would be different there.
(2) I could not agree more that patient positioning is a potentially important subject for emergent airway management research. Historically, the recommendation has been for “sniffing” position based on intubations in the operating room but I agree with you that there are some interesting preliminary studies of ramping between 25-35 degrees (with regard to both grade of view and duration of apnea without desaturation). To help untangle this question, we are currently performing a randomized trial of ramped versus sniffing position for ICU intubations (clinicaltrials.gov # NCT02497729).
Thanks for the great questions. There are not a lot of ICU folks interested in airway management research so if you all are working on projects that might be relevant to what we are trying to do or where there might be room for collaboration, please don't hesitate to contact me.