Ventilation before Paralysis

To the Editor: I read with great interest the article by Ikeda et al.1 and the accompanying editorial.2 Surprisingly, the editorial did not refer to the recently published findings of a prospectively assessed algorithm for difficult airway management involving 12,225 facemask ventilations (FMV).3 Patients with indications for awake fiberoptic intubation were excluded. In contrary to traditional teaching, the algorithm required that patients with greater than or equal to three risk factors for difficult airway management receive succinylcholine right after induction of anesthesia without previous assessment of quality of FMV. In patients with less than three risk factors, quality of FMV was assessed before administration of a muscle relaxant. Patients with grade I or II difficulty of FMV received a nondepolarizing muscle relaxant; patients with grade III or IV difficulty of FMV received succinylcholine. Most relevant in this context, in no case of difficult FMV was any attempt undertaken to awaken the patient. In 56 of the 90 patients (62%) with FMV difficulty grade III, quality of FMV improved by one grade after the administration of succinylcholine. In none of the 12,003 patients with FMV difficulty grade I and II did the quality of FMV worsen after administration of the nondepolarizing muscle relaxant. This confirms previous findings showing that in patients with unimpaired4 or with a mix of unimpaired and moderately difficult FMV,5 quality of FMV either remained unchanged or improved after the administration of a muscle relaxant, but never worsened. All 12,225 patients who were routinely paralyzed, irrespective of the quality of FMV, could ultimately be orotracheally intubated using various airway devices. In another study, of 37 patients with impossible FMV, all but one were successfully intubated.6 The 97% intubation success rate after impossible FMV is likely to have been due to the early administration of the muscle relaxant in all but one of the 37 patients.7 It is questionable that endotracheal intubation could have been that successfully performed in the absence of muscle relaxation, or that these patients could have safely been awoken. The editorialists mistakenly interpret the findings by Ikeda et al.1 as showing a superior effect of succinylcholine over nondepolarizing muscle relaxants on the quality of FMV. However, as the investigators studied patients with successful FMV before administration of any muscle relaxant, the data can only be interpreted as showing that administration of muscle relaxants does not worsen preexisting effective FMV. As this had been a nonrandomized study, baseline values for nasal and oral ventilatory volumes had differed between patients receiving rocuronium or succinylcholine, and less than optimal statistical testing had been applied (use of paired Student t test for comparison of data from three successive observation points), the data do not necessarily support the conclusion of different effects of succinylcholine and nondepolarizing muscle relaxants on the quality of FMV. Second, in this study, the endoscopy at the isthmus of the fauces showed that the narrowed oral airway space abruptly and significantly dilated during oscillatory movements of the soft palate and the tongue base (pharyngeal fasciculation) after succinylcholine administration. Thus, the FMV improvement after succinylcholine administration is contributed to reopening of the pharyngeal airway by the pharyngeal muscle contraction. However, other than the soft tissue airway at the pharynx, the laryngeal aperture is another important site that may significantly affect gas flow of the upper airway.2,5 It has been shown that the vocal cord closure is a primary source of difficult or impossible FMV during anesthesia induction with sufentanil.7,8 After anesthesia induction, it is also possible for the epiglottis to overlie and obstruct the laryngeal aperture or to seal against the posterior pharyngeal wall, especially when the patients are placed in a neutral head and mandible position without any airway intervention.5 Because the authors did not observe changes of both position of the epiglottis in the pharynx and configuration of the laryngeal aperture during succinylcholine-induced upper airway muscle fasciculation, contribution of these factors to the FMV improvement by succinylcholine cannot be excluded.