To the Editor:
With great interest, we read the article by Sato et al.,1 which reports the influences of obstructive sleep apnea on mask ventilation during induction of general anesthesia by comparing patients with or without sleep-disordered breathing.In addition to the limitations described in the discussion, we note other issues that may have influenced their findings, and the determination of how much of the difference of mask ventilation was caused by obstructive sleep apnea. Specifically, factors influencing the onset time of rocuronium could affect mask ventilation, and these factors were not clearly described.
First, the exact peripheral intravenous sites of rocuronium administration were not described. The onset time of succinylcholine is closely related to drug transit time from the peripheral to the central circulation,2 and rocuronium has a similar onset time to succinylcholine.3 For vecuronium, administration into the pulmonary artery shortened the onset time by approximately 40 s compared with a dorsal vein of the hand.4 Different intravenous sites of rocuronium may produce different onset times. Therefore, the intravenous sites should be similar in the two groups in order to avoid potential bias.
Second, pressure-controlled ventilation was started 20 s after rocuronium injection,1 but it was not specified whether that was the time from injection start or finish. There is a 5 s difference between start and finish for a 50-kg patient (1 mg/kg) and 1 ml/s injection (5 ml), while the outcomes of mask ventilation were obtained in the 60 s in the study. Also, it was not specified whether all doses were diluted to equal volume and injected with equal speed.
Third, the manuscript did not report parameters relevant to cardiac output, which can affect rocuronium onset.5 Cardiac output may be lower in patients with obstructive sleep apnea.6 Heart rate and mean arterial blood pressure might be used to speculate on the indirect influence of cardiac output on mask ventilation.
We believe that addressing the above issues could further increase the value of this study.
The authors declare no competing interests.