Background: Test ventilating prior to administration of neuromuscular blockade (NMB) in order to avoid a cannot intubate-cannot ventilate situation is a classic anesthesia teaching. The primary aim of our study was to show that facemask ventilation (FMV) after NMB was not inferior to FMV prior to NMB with respect to exhaled gas volumes before and after their administration.
Methods: This study was approved by the University of Washington Human Subjects Division (Seattle, Washington, USA). Written informed consent was obtained from all patients. Measurements of tidal volume (Vte) as well as other respiratory parameters during FMV were made for 60 s after induction of anesthesia and again after NMB. Difficult, impossible, inadequate, and dead-space only mask ventilation was graded using published definitions. Difficult intubation was defined as >2 attempts at intubation. The primary outcome was non-inferiority in Vte during both study periods defined as a mean difference of <50 mL. Multivariate analysis was performed to assess for interaction between operator experience, patient risk factors for difficult mask ventilation, exhaled volumes, and use of airway adjuncts.
Results: Two-hundred and ten patients were studied. Overall, FMV improved after NMBD. The mean (SD) Vte in mL/breath increased from 399 (169) to 428 (166) (mean dif. 30 mL, p = 0.001) and the minute ventilation in L/min from 5.6 (2.5) to 6.3 (2.5) (mean dif. 0.6, p < 0.001). No patient who was difficult to ventilate after induction became impossible after NMB.
Discussion: In patients at risk for or judged to be a difficult FMV by clinical grading scales, tidal volumes improved after administration of NMBDs. None of these patients exhibited a decline in ventilation or became impossible to ventilate after NMBDs. Several limitations are noted, including the use of hand-delivered breaths and inability to account for time-related changes in ventilation conditions independent of NMBDs.
Conclusion: We conclude that FMV is no worse after NMB than before and is likely to improve airway conditions.
Trial registration: ClinicalTrials.gov Identifier: NCT02237443 . Registered August 28, 2014.