Mask ventilation in the period between induction and intubation has traditionally been used to confirm the ability to ventilate the patient while awaiting the onset of adequate neuromuscular blockade. However, recent studies that have utilized gastric ultrasound to investigate aspiration risk have uncovered some concerning findings: not only is gastric insufflation extremely common in patients who are mask-ventilated, but a large percentage of patients arrive to the operating suite with significant gastric volumes despite adequate fasting.1–4 Although these studies have identified a wide variety of risk factors for aspiration, a significant number of patients who aspirate perioperatively have no known risk factors.5–7 Given that perioperative aspiration results in intensive care unit (ICU) admission 30% of the time and is the primary cause of 50% to 63% of all airway-related deaths under anesthesia, perhaps now is the time to reexamine the practice of routine mask ventilation after induction, before endotracheal intubation.5–8
A review of an Australian anesthetic complication database found that 86% of confirmed perioperative aspiration events occurred during mask ventilation, if one excludes the aspiration events that occurred while a supraglottic airway (SGA) was in place.5 This is likely because gastric insufflation during mask ventilation is difficult to avoid in a significant proportion of patients: a 2014 randomized control trial (RCT) of healthy nonobese patients undergoing general anesthesia found that 53% of the patients had ultrasound-detected gastric insufflation during 2-handed mask ventilation, with an oral airway, at an inspiratory airway pressure of 20 cm H2O delivered by a ventilator. The ultrasound was even able to detect gastric insufflation in 35% of the patients who were ventilated at 15 cm H2O, and 19% of patients ventilated at 10 cm H2O. In contrast, the epigastric stethoscope that was utilized simultaneously was far less sensitive in detecting gastric insufflation at these lower inspiratory pressures, identifying gastric insufflation only 12% and 0% of the time, respectively. However, patients in this study were given a remifentanil bolus and infusion instead of a muscle relaxant, since previous studies had reported excellent intubating conditions with this regimen.1 In another RCT, patients were given a nondepolarizing neuromuscular blocker during induction and were mask-ventilated by hand for 3 minutes without any required airway maneuvers. The investigators of this study found that 71% of these patients had gastric insufflation detected on gastric ultrasound. The highest peak airway pressure during mask ventilation was 19 cm H2O on average for patients in this study.2 One explanation could be that a surprising number of these patients may have had unrecognized hiatal hernias: a 2018 study done on a representative sample of the Swedish population found that 43% of patients had a sliding hiatal hernia length of ≥2 cm on upper endoscopy. Hiatal hernias of this length are considered clinically significant and are associated with acid regurgitation and heartburn symptoms.9
These findings are especially concerning since a recent prospective study found that 28% of surgical patients who were compliant with the American Society of Anesthesiologists’ (ASA) fasting guidelines had >1.5 mL/kg seen on gastric ultrasound before induction.3 Another recent prospective study found similar results: 26% of patients presenting for elective surgery and 64% of patients presenting for urgent or emergent surgery had intermediate or full stomachs.4 Patients presenting with obesity, diabetes, esophageal reflux, kidney disease, preoperative opioid use, and urgent surgery were at the highest risk of having full stomachs before induction in these studies.3,4 These findings are consistent with previously established risk factors for aspiration, which also include acute intra-abdominal processes, depressed consciousness, and a history of bariatric surgery, according to reports by ASA and the Royal College of Anaesthetists.5–7 However, these common conditions are frequently overlooked by anesthesia providers: in 2 studies, 93% of patients who had a major perioperative aspiration event resulting in an ICU admission in the United Kingdom or a malpractice claim in the United States had one or more risk factors for aspiration.6,7 These patients could have been identified as high-risk preoperatively, yet anesthetic management was judged to be substandard in 59% of these aspiration-related malpractice claims.7 This is not surprising since only 48% of patients in the United Kingdom with severe aspiration were recognized as having any risk factors preoperatively.6 Even more concerning is the fact that 7% to 24% of patients who aspirated under anesthesia had no risk factors for aspiration on retrospective review.5–7 Furthermore, patients undergoing a variety of surgeries now participate in enhanced recovery protocols during which they are encouraged to drink clear fluids and/or liquid carbohydrates up to 2 hours before surgery. Patients then receive preoperative oral medications, often <2 hours before induction. Even the Enhanced Recovery After Surgery Society acknowledges that these practices may result in increased gastric volume at the time of induction for patients with diabetes, obesity, and abdominal pathology.10 In addition, patients presenting for urgent or emergent surgery have been found in multivariate analysis to be 27 times more likely to have a full stomach before induction, regardless of fasting time.4 However, the category of urgent surgery is particularly vague; one could argue that all inpatient surgeries and many outpatient surgeries are in fact urgent. The fact that surgical urgency is a spectrum and is simultaneously the most predictive risk factor for incomplete gastric emptying makes preoperative evaluation of aspiration risk challenging for anesthesiologists.4,7
One possible solution could be to use preoperative gastric ultrasonography on all patients with risk factors. However, this strategy is fairly resource-intensive since it would utilize both an anesthesiologist trained in ultrasonography and an ultrasound machine. In addition, as previously mentioned, not only do anesthesia providers frequently overlook risk factors for aspiration but a significant proportion of patients presenting with full stomachs may not have any known risk factors.5–7 Furthermore, patients with empty stomachs on gastric ultrasound may still aspirate on vomitus from the proximal small bowel. Another strategy could be to use cricoid pressure to minimize gastric inflation whenever mask ventilation is used. Cricoid pressure prevents gastric inflation by increasing the inspiratory airway pressure required to inflate the stomach. Although effective, one RCT found that 17% of patients who were mask-ventilated with cricoid pressure still had gastric insufflation detected on ultrasound.2 In particular, obese patients would be at higher risk even with cricoid pressure, since they are more likely to have hiatal hernias and may require higher inspiratory pressures during mask ventilation, due to their body habitus and the fact that they are often more difficult to mask-ventilate.11 A third solution could be to bypass ventilation altogether by routinely using succinylcholine immediately after induction. Given that this has been the standard of care for patients with full stomachs for many decades, this tried-and-true approach seems at first to be appealing. However, succinylcholine puts certain patients at risk for hyperkalemic cardiac arrest, malignant hyperthermia, and prolonged paralysis from pseudocholinesterase deficiency. In addition, around half of the patients who receive succinylcholine complain of myalgias for the next 2 days, which may adversely affect postoperative pain scores, opioid use, and patient satisfaction.
A simpler way to reduce the risk of aspiration during elective airway management is to routinely use a 0.9-mg/kg dose of rocuronium on induction to bypass mask ventilation. At this dose, onset time of rocuronium is not significantly different from 1.2-mg/kg rocuronium and succinylcholine.12 With adequate preoxygenation, anesthesia providers should have enough time to secure the airway without exposing the patient to unnecessary risk during mask ventilation. In fact, one RCT found that overweight patients who received 0.9-mg/kg rocuronium were able to maintain saturations above 92% without mask ventilation for 46 seconds longer than patients who received succinylcholine.13 This is likely because succinylcholine-induced fasciculations increase total-body oxygen consumption and, thus, decrease time to desaturation in apneic patients. Therefore, because higher doses of rocuronium can increase the amount of time that a patient can remain apneic before desaturating, and can provide rapid and complete paralysis as quickly as succinylcholine, anesthesia providers can now safely avoid mask ventilation on induction of general anesthesia without exposing patients to the risks of succinylcholine.
This technique can be considered in any adult with a reassuring airway examination whose surgery is expected to take >1 hour. Half of the patients who receive 0.9-mg/kg rocuronium can be reversed with neostigmine after 42 minutes, and half of the patients who receive 1.2 mg/kg can be reversed with neostigmine after 57 minutes. The 1.2-mg/kg dose of rocuronium may be slightly more consistent in its onset and may be used for patients at higher risk of aspiration or desaturation. At these doses, the duration of action of rocuronium does display significant interpatient variability. However, even at the upper range of rocuronium’s duration, patients who receive 0.9-mg/kg rocuronium are almost always able to be reversed with neostigmine after 75 minutes.12 If a patient is still unable to be reversed with neostigmine at the end of a case due to an unexpectedly prolonged neuromuscular blockade, 4-mg/kg sugammadex can be used to reverse patients with a posttetanic count of ≥1. Thus, anesthesia providers who would prefer to reverse the majority of their patients with neostigmine can use 0.9-mg/kg rocuronium for suitable procedures lasting >45 minutes. Providers who would prefer to reverse nearly all their patients with neostigmine can instead use 0.9-mg/kg rocuronium for cases expected to last >75 minutes. However, the anesthesiologist should always weigh the risks and benefits when using this technique, particularly in patients who may not tolerate brief episodes of hypercarbia and patients with anticipated difficult airways in which documentation of the ease of mask ventilation may be especially helpful for future anesthetics. This technique may also not be appropriate for patients undergoing neuromonitoring or short procedures.
By utilizing rapid and deep neuromuscular blockade to bypass mask ventilation, anesthesia providers can avoid an airway maneuver that is associated with 68% of perioperative aspiration events, while also minimizing the risk of other airway emergencies after induction.5 For example, patients may bronchospasm when they aspirate secretions during mask ventilation or laryngospasm during airway manipulation without paralytic. These airway crises are frequently managed with emergent intubation, which may be more difficult when muscle relaxation is either absent or inadequate.11,12 Inadequate muscle relaxation in the first minute after conventional nondepolarizing muscle-relaxant administration may also result in retching or active vomiting during oral airway placement, laryngoscopy, and other airway maneuvers. Rapid-acting neuromuscular blockade would eliminate the need to block airway reflexes and, thus, may act as an induction anesthetic sparing agent. This may be helpful for avoiding postinduction hypotension particularly in elderly and debilitated patients. Thus, by minimizing the time and the number of airway maneuvers between a patient’s loss of consciousness and the placement of a secure airway, anesthesia providers can reduce the risk of all airway emergencies after induction of anesthesia. As an added benefit, anesthesiologists could also save 1 to 2 minutes per case that would otherwise be spent waiting for lower doses of nondepolarizing muscle relaxants to take full effect.12 These minutes may be especially valuable when there are multiple cases to start at the same time.
It is understandable that many anesthesia providers may feel uncomfortable giving such high doses of rocuronium to their patients, especially if they perceive that most of the benefits only apply before endotracheal intubation. However, recent research has demonstrated that deeper neuromuscular blockade also provides a wide range of intraoperative and postoperative benefits. For example, a meta-analysis and RCT found that patients undergoing laparoscopic and spine surgeries who were maintained at a posttetanic count of ≤2 had significantly improved surgical operating conditions compared to patients maintained at a train-of-four of 1 to 2.14,15 This approach may be particularly helpful for obese patients, who often have suboptimal operating conditions with conventional paralytic dosing due to their excess soft tissue. Patients who were maintained at a posttetanic count of ≤2 even experienced less pain due to decreased intra-abdominal insufflation pressures in laparoscopic surgeries and decreased surgical retraction in spine surgeries.14,15 Furthermore, deeper muscle relaxation could allow patients to be maintained at a lighter plane of anesthesia while still providing optimal surgical conditions. A meta-analysis on bispectral index monitoring found that a 19% decrease in anesthetic depth significantly reduced postoperative nausea and vomiting, emergence times, and recovery room times, even in healthier ambulatory surgery patients.16 For more debilitated and elderly patients, deeper neuromuscular blockade and lighter anesthesia may be particularly helpful since these populations are more prone to postoperative sedation, delirium, and cognitive dysfunction from excessive anesthetic and opioid administration. A 2018 Cochrane meta-analysis found moderate evidence that avoiding deep planes of anesthesia in patients >60 years of age decreased the incidence of postoperative delirium by 29% and the incidence of severe postoperative cognitive dysfunction 12 weeks after the surgery by 29% as well.17
Anesthesia providers may also be concerned that patients who receive higher doses of rocuronium would be more likely to have fewer than 3 twitches on train-of-four stimulation at the end of the case and, therefore, require sugammadex administration. However, sugammadex administration has also been shown to have numerous postoperative benefits as well. For example, a recent meta-analysis found that patients who received sugammadex had an 18% higher train-of-four ratio at the time of extubation and a 95% lower risk of postoperative residual paralysis compared to patients who received neostigmine. Since stronger patients are less likely to obstruct or develop atelectasis in the postanesthesia care unit, it is not surprising that this meta-analysis also found that patients who received sugammadex had a 64% lower risk of postoperative respiratory adverse events.18 Sugammadex administration may be particularly beneficial to obese and elderly patients who are already more prone to postoperative respiratory depression and are more likely to be adversely affected by residual paralysis. Similarly, patients who received sugammadex instead of neostigmine experienced 77% fewer cardiac adverse events, which may be particularly beneficial to patients with a history of cardiac disease.18 Despite these substantial benefits, sugammadex administration is not without some risk. According to a large multicenter observational study, sugammadex has a higher incidence of anaphylaxis compared to neostigmine: 0.02% of patients who received sugammadex had an anaphylactic reaction with a confirmatory skin test, compared to 0% of the patients who received neostigmine. Even though all 6 patients with sugammadex-induced anaphylaxis recovered with no major problems, these findings emphasize how anesthesia providers must weigh the many benefits of sugammadex administration against its increased risk of anaphylaxis when deciding which reversal agent to use.19
Now many would argue that anesthesia providers need to confirm the ability to mask-ventilate before administration of muscle relaxant to preserve the ability to wake up the patient. However, many influential opinion and review articles have previously advocated for the administration of neuromuscular blocking agents immediately after induction as the safest tactic for routine practice. These articles argue that deeply anesthetized patients are unlikely to resume adequate spontaneous ventilation before they become severely hypoxic due to airway collapse from reduced pharyngeal muscle tone. They also provide ample evidence that muscle relaxation almost uniformly facilitates facemask ventilation. “Thus, once we have crossed [the] Rubicon (ie, have abolished spontaneous respiration), our goal must not be to ‘consider preserving a way back over the bridge’ (ie, wake up the patient), but to concentrate all our efforts on putting up camp quickly and safely on the other side of the river (ie, provide effective ventilation).”11 However, we would argue that the patient is not “safely on the other side of the river” until confirmation of endotracheal tube placement. If we use the logic of these articles, the true safest tactic for routine practice would be to administer a dose of muscle relaxant that would facilitate rapid intubation immediately after induction, like 0.9-mg/kg rocuronium. Not only would this allow us to “cross the Rubicon” to a secure airway as soon as possible, but this would rapidly optimize conditions for mask ventilation and possible SGA placement should our intubation efforts fail.11 And in a true impossible intubation and ventilation scenario, our “way back over the bridge” would still be intact since patients who were given up to 1.2-mg/kg rocuronium could be rapidly reversed with 16-mg/kg sugammadex, and attempts can be made to awaken the patient.
Even before the widespread availability of videolaryngoscopy, patients undergoing anesthesia in 1999 were nearly 5 times more likely to die from an aspiration event than an impossible intubation and ventilation scenario, according to the French national mortality database.8 Today, videolaryngoscopy has made airway management safer than ever: 99.3% of patients who were unable to be intubated with direct laryngoscopy could be successfully intubated with a videolaryngoscope, according to a 2009 prospective study.20 Meanwhile, the prevalence of aspiration risk factors like obesity, diabetes, kidney disease, opioid use, and bariatric surgery have only increased in recent decades. Without a significant change in routine practice, aspiration may continue to pull farther ahead as the most common cause of anesthesia-related death.6,8 Fortunately, sugammadex has now made the 0.9-mg/kg dose of rocuronium safe for routine use for most general anesthesia cases lasting >1 hour. Because of this, mask ventilation may now be viewed as completely optional for the majority of patients with reassuring airway exams. Since higher doses of rocuronium provide rapid and deep paralysis that could allow anesthesiologists to quickly transition to a secure airway during induction, avoid the harmful effects of deep anesthesia during maintenance, improve surgical operating conditions, and decrease postoperative pain, anesthesia providers should now consider lowering their threshold for avoiding mask ventilation.
Name: Kevin J. Min, MD.
Contribution: This author helped conceive, research, draft, and edit the manuscript.
Name: Anna L. Rabinowitz, MD.
Contribution: This author helped provide feedback and edit the manuscript.
Name: Cary J. Hess.
Contribution: This author helped research and edit the manuscript.
This manuscript was handled by: Richard C. Prielipp, MD.
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