Impact of Macintosh blade size on endotracheal intubation success in intensive care units: a retrospective multicenter observational MacSize-ICU study
Godet T, De Jong A, Garin C, et al. Intensive Care Med. 2022;48(9):1176-118.
Despite a move toward routine use of video laryngoscopy, and increased use of airway adjuncts such as the bougie, proficiency in direct laryngoscopy (DL) remains a fundamental to ED-based airway management.
In performing DL, few decisions must be made other than blade size. Although many physicians have strong opinions regarding use of a Macintosh number 3 vs number 4 blade, surprisingly few studies have compared the first-pass success rates between them.
One randomized trial on mannequins (n = 200) and another trial on edentulous patients (n = 35) have been reported. Both studies were limited but favored the use of the smaller blade.
In this study, the MacSize ICU study, the authors retrospectively analyzed data from 3 published prospective randomized studies and 1 observational study; patients were not randomized to blade size.
Adults from 48 French ICUs who received DL with a Macintosh blade for their first attempt (other techniques were excluded), regardless of the reason for intubation, were examined. Blade choice was at the discretion of the treating physician.
The primary outcome was first-attempt success according to blade size (number 3 vs number 4).
The data set contained 2,139 intubations, 29.4% with a number 3 blade and 70.6% with a number 4 blade.
Patients intubated with the number 4 blade were more likely to be male and taller, but did not have a higher body mass index.
First-attempt success rates statistically differed between the number 3 and number 4 blades (79.5 vs 73.3%, relative risk, 1.41; P = .0025); thus, the NNT to prevent 1 first-attempt failure was 14.6.
Glottic views were nearly identical between groups, on the basis of Cormack-Lehane scores; notably, percentage of glottic opening (POGO) scores were not reported.
Because the groups differed in patient-level characteristics, the authors calculated propensity scores and used them to assess the inverse probability of treatment weighting, a statistical technique used to remove the effects of confounders on a model. These weights were applied to the study population, thus creating a pseudopopulation in which confounders were equally distributed between the exposed and unexposed groups.
The results held across the multivariate regression model, and sensitivity checks favored the number 3 blade (OR 1.44).
Complication rates (both minor and severe) were similar between groups.
The statistical analyses were very well conducted, and data collection in the parent trials was rigorous. However, because this study was not a trial, the reason why a number 3 blade was used in some cases and a number 4 blade was used in others is unknown; perhaps some unmeasured patient-level characteristic might have been responsible for the findings rather than the blade size itself. Moreover, all intubations were performed in the ICU, and the average body mass index was approximately 25, thus limiting the generalizability of the results to some ED populations.
EDITOR’S COMMENTARY: Although many ED providers passionately believe that there is a “correct” Macintosh blade size to use when performing DL, these opinions are largely based on learning and personal experiences rather than real data. Shockingly, this is the first large study published to date comparing the number 3 and number 4 blades. Although the study was not randomized, the first-pass success was higher with the number 3 blade across over 2,000 ICU patients, without any differences in complication rates. The study provides hypothesis-generating data that set the stage for a prospective trial designed to answer the question of whether size matters (these authors suggest that it does).
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