Written by Ketan Patel
Spoon Feed
Tidal volume (TV) delivered is hard to control during cardiac arrest, and evidence has shown that over-ventilation can be detrimental in physiological parameters integral to cardiac arrest survival. Small bags were thus integrated into a single EMS system to help combat over-ventilation. Paradoxically, large bags had a greater likelihood of return of spontaneous circulation (ROSC) in out of hospital cardiac arrests (OHCA).
Perhaps not a bunch of hot air?
International guidelines recommend TV delivery at 500 to 600 mL during CPR, but these recommendations are based on poorly matched data in healthy or animal models. We recently covered a study in which patients with better ventilation had improved ROSC. This study hoped to show that adhering closer to international TV recommendations would be a factor associated with better outcomes and ROSC in OHCA.
In 2017, smaller bags were implemented in the EMS system in Seattle to be utilized in OHCA. A retrospective, observational cohort analysis was subsequently performed on prospectively acquired OHCA data to quantify the effect of these changes on survival in OHCA.
Achievement of ROSC upon hospital arrival was significantly lower in the small bag group versus large bag group, 33% vs 40%: unadjusted odds ratio OR 0.74 (95%CI 0.61–0. 90, p<0.003). Adjustment for age, sex, witnessed arrest, delivery of bystander CPR and initial rhythm yielded no change in the OR. Further secondary analysis also failed to yield a change in the results and risk.
Despite inherent limitations, the authors were incredibly thoughtful about the analysis of resuscitation parameters when evaluating patient data. True ventilation volumes were not measured, however, which does give room for further exploration on the subject matter.
How will this change my practice?
For the time being, I will advise EMS to focus on good quality compressions and minimizing both over- and under-ventilation in cardiac arrest. Perhaps future studies and technology will allow us to better isolate the true volumes delivered to our patients and their subsequent effects in cardiac arrests.
Source
Association of small adult ventilation bags with return of spontaneous circulation in out of hospital cardiac arrest. Resuscitation. 2023 Dec:193:109991. doi: 10.1016/j.resuscitation.2023.109991. Epub 2023 Oct 5.
