To the Editor:
The recent article of Amathieu et al. 1that prospectively validated a modified difficult airway management algorithm incorporating video devices in routine anesthesia practice was of great interest to us. The authors should be congratulated for their excellent works in such a large cohort of anesthetized, paralyzed patients. However, there are several aspects of this study that should be clarified and discussed. We believe that such information would be helpful for others who would like to try this modified difficult airway management algorithm.
First, because authors did not provide the method of anesthesia induction used in this study, it was not clear whether the spontaneous breathing ceased when assessing facemask ventilation (FMV) before giving muscle relaxant in all patients with fewer than three adverse predictors. Moreover, if the amount of anesthetic is inadequate, airway spasm, a common cause of difficult FMV, can occur in response to irritation of the epiglottis and glottis from oropharyngeal or nasopharyngeal airway and secretions. In addition, when assessing FMV, authors should clearly describe whether all components of an optimal-best attempt at FMV, such as good mask seal, correct jaw thrust, optimal head and neck position, and use of proper size oropharyngeal or nasopharyngeal airway2had been achieved.
Second, this modified difficult airway management algorithm required the use of succinylcholine in patients with three or more adverse predictors during anesthesia induction and in those with grade III and IV difficult FMV after anesthesia induction. Also, authors found that the use of succinylcholine never worsened FMV quality in anesthetized patients, but rather improved it in most cases. Despite these positive results, we would still argue that in the patients with a recognized or questionable difficult airway, routine use of succinylcholine may not be the best opinion. Moreover, the decision whether to administer a muscle relaxant before endotracheal intubation (ETI) in the anesthetized patient really depends on many factors, such as ability of FMV, concrete situations of patients, and validity of rescue airway plans.3It should again be emphasized that continuous maintenance of adequate oxygenation throughout airway procedure is an exclusive core problem that the anesthesiologist must contend with to achieve various measures, because severe adverse outcomes including death or brain injury are caused by failure of oxygenation rather than failure of ETI.4ETI is only one of the measures used to maintain adequate oxygenation but can be never regarded as a final goal. Thus, we persevere that for patients with a recognized or questionable difficult airway, adequate FMV must be ensured before administering a muscle relaxant.3Moreover, if a patient presents significant difficult ventilation under an optimal-best attempt at FMV after anesthesia induction before muscle relaxant is given, a laryngoscopy attempt should be immediately performed to determine the ease of ETI. For an experienced anesthesiologist, an optimal-best attempt at laryngoscopy can be completed within 30–60 s. If the chances of achieving successful ETI are high (i.e. , a fairly good laryngoscopic grade), yet it is difficult to accomplish ETI because of no muscle paralysis, administration of succinylcholine may be appropriate.2However, if a difficult laryngoscopy (i.e. , grade III or IV laryngeal view) is obtained and ETI using direct or video laryngoscopy with use of gum elastic bougie fails, the rescue airway algorithm should be moved to the step that manages a “cannot intubate-cannot ventilate” situation; for example, immediate use of the LMA or LMA CTrach™ for emergency ventilation to reduce or avoid severe airway-related adverse outcomes.5
Third, this algorithm aimed to solve the ETI problems in patients with difficult airways, but the authors failed to report intubation time in all patients and apnea time in patients with difficult airways. We noted that a 90% end-tidal oxygen concentration (FEO2) was achieved with preoxygenation before anesthesia induction in all patients, but hypoxemia (oxygen saturation measured by pulse oximetry [Spo2] <90%) and severe hypoxemia (Spo2<80%) episodes still occurred in 87 and 17 patients, respectively. Also, most of the severe hypoxemia episodes occurred during failed intubation with either direct or Airtraq laryngoscopes (Prodol Meditec S.A., Vizcaya, Spain). A computer model describing the rate of oxyhemoglobin desaturation during apnea reveals that, when a preapnea FEO2is 87%, apnea times required for Spo2to decrease to 80% is 8.7 min in a 70-kg adult patient and 3.1 min in a 127-kg obese patient, respectively.6This model has been found to agree reasonably well with actual data from patients whose weight and degree of normalcy and preoxygenation are reliably known.7–9Based on these data, we deduce that apnea time by ETI procedure in this study is at least 3 min in the morbidly obese patient with severe hypoxemia, and is longer than 8 min in the nonobese patient with severe hypoxemia. The transient episode of severe hypoxemia by prolonged ETI procedure does not cause adverse outcomes in health patients, but may become a problem in elderly patients with ischemic heart or brain diseases. Also, a prolonged ETI procedure can increase the risks of airway injury and pulmonary aspiration.3,10To ensure patient safety, therefore, we advise that the notion as to the reasonable time limits of ETI procedure with direct and Airtraq laryngoscopes should be added to this algorithm. This is especially important for patients with decreased apnea tolerance, such as morbidly obese patients, elderly patients, patients with lung diseases, and pregnant women.9
*Plastic Surgery Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People's Republic of China. email@example.com