To B (VM) or Not to B (VM) THAT is the question!

Source: Casey et. al. Bag-Mask Ventilation during Tracheal Intubation of Critically Ill Adults. NEJM. February 18, 2019DOI: 10.1056/NEJMoa1812405

Whether ‘tis noble in the mind to suffer the slings and arrows of aspiration or by bagging end them?

This is a great methodological (and probably landmark) trial by the impressive authors at Vanderbuilt et al. They have been publishing amazing literature recently. What a great read. The question they ask here is does BVM prevent hypoxia or is the old dogma concerned about aspiration correct? Like all research I think the answer to the question here is it depends but this certainly adds to the current literature. It also raises more questions like any good research should. It’s an interesting paper but I’m not sure its definitely says no more BVM. 

Bottom Line:

This was a randomized intention to treat, unblinded pragmatic trial of BVM vs no BVM in patients in the ICU with low risk of aspiration. While they did NOT meet the primary outcome of a 5% difference between the lowest oxygen saturation for BVM vs no ventilation, they did find an interesting 10% less patients who had oxygen saturation’s less than 80% in the BVM vs the No BVM Group. While this is a secondary (hypothesis generating) outcome it is quite striking.

This is definitely a dogma breaking study. There are definitely limitations however, I think one possible conclusion is: In patients where you are sure aspiration is not a high risk then BVM may a safe way to prevent hypoxia by giving the patient assisted ventilations from the time of induction until laryngoscopy. If you wait until saturation’s drop to 90% you will have a lower overall oxygenation and that could be associated with harm

The Details:

This was a randomized unblinded pragmatic trial of BVM for Endotracheal Intubation. Intervention was BVM from induction until the initiation of laryngoscopy vs No BVM allowed unless they had a “failed” intubation with sat <90%. However only 5 people in the No BVM group got BVM. 

The BVM group received training on best practices for BVM whereas the no BVM did not. Did this bias the results?

  1. Patient population:
  • These are ICU patients and NOT ED patients. So this cohort would naturally be more likely to have empty stomachs being in the ICU and less likely to aspirate
  • 49 pts were excluded (as listed in exclusion criteria) for being “high risk of aspiration”. That is a problem for broadly applying this study to the ED population. 
  • 50% of the patients were known to be fasting for the prior 6 hours in both groups.  (See table S3 in the supplement)
  • The trial was not blinded so was there some part of the unblinding that contributed to the difference?
  • Non-invasive pressure ventilation was not allowed between induction and laryngocospy but was allowed before. BIPAP was utilized in 16% vs 23% of BVM vs no BVM. 
  1. Primary Outcome:
  • The primary outcome was the lowest oxygen sat. So the differnce was 96 vs 93. Their study was powered to find a 5% difference and they did NOT achieve this so you can’t say the primary outcome was met. 
  • They say a post hoc  analysis adjusting for variables was 5.2 but that doesn’t appear to be prespecified and certainly wasn’t stated in the primary outcome
  1. Secondary outcome
  • The lowest sat <80 stat is interesting and almost double. However, I wonder why this no BVM group got so low. They said that a BVM was not permitted except after a failed attempt O2 <90%. So why did the non BVM group get so low? In the supplement it states only 5 patients of the no BVM trial got BVM. 
  1. Group differences
  • The BVM group had a higher (3%) first pass success rate and lower use of bougie. Was the no-ventilation group more difficult airway? It’s hard to say from the supplment table S3 (difficult airway). No overall assessment of difficulty was asked but we don’t have a great tool for that anyway. 
  • Supplemental oxygen: Why did the no-BVM have lower proportion of patients given supplemental oxygen (77 vs 100)? What does this mean? In the supplement table S3 they do say 7 patients had no preoxygenation vs 3 in the BVM group. 

The most interesting part I found was in the supplement in a table that looks something like this (I recreated their numbers):


(I made the above bar chart from their supplement pages)

Quite the striking difference. Overall will this change my practice? Maybe, I’ll probably consider bagging earlier and see if that helps.

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