Not too long ago, safety in airway management hinged on two pillars of safety: the first was the ability to mask ventilate, and the second was cricoid pressure (CP).
Explore This IssueACEP Now: Vol 33 – No 11 – November 2014
The ability to mask ventilate was perceived to be a required first step in elective airway management before giving muscle relaxants. Multiple anesthesia studies have now shown that muscle relaxation correlates with improvement in mask ventilation, not collapse of the airway as many of us were taught. Warters et al. demonstrated that rocuronium improved mask ventilation in 67 percent of patients, resulted in unchanged ventilation in 33 percent, and made ventilation more difficult in no instance.1
In addition to making mask ventilation easier, muscle relaxation has a second safety benefit—it permits insertion of a supraglottic airway (laryngeal mask airway [LMA] type device, or King LT-D). In the past, difficulty of mask ventilation led to awakening the patient and avoiding rapid sequence intubation; now some anesthesiologists advocate that the response should be the opposite—give muscle relaxants—and improve mask ventilation, insert an LMA, or intubate. Within the anesthesia community, many are questioning whether demonstrating mask ventilation prior to intubation should be abandoned.2,3
In the past, difficulty of mask ventilation led to awakening the patient and avoiding rapid sequence intubation; now some anesthesiologists advocate that the response should be the opposite—give muscle relaxants—and improve mask ventilation, insert an LMA, or intubate.
According to Kheterpal et al., who studied more than 53,000 anesthesia cases, the frequency of impossible ventilation is approximately 1 in 2,800, and only one in four of those with impossible ventilation were difficult to intubate.4 The LMA works in 95 percent of instances of difficult or impossible mask ventilation.5
Combining optimal mask ventilation (with muscle relaxants) with an LMA and intubation (direct/video laryngoscopy with passive apneic oxygenation) makes use of muscle relaxants very low risk in the hands of skilled operators.
The second pillar of safety, CP, seems to be fading fast into medical lore. Many studies show CP impedes laryngoscopy, worsens ventilation, and does not prevent regurgitation. The latest advanced cardiovascular life support (ACLS) guidelines no longer recommend its use in cardiac arrest; in other scenarios, ACLS states CP should be released if it impedes intubation or ventilation. A final nail in the coffin, I would argue, is that CP and the LMA are noncompatible. CP prevents LMA placement in the upper esophagus, and if applied after LMA insertion, it will push the LMA out of position.
New Rules: LMA
The LMA has rewritten the rules of airway management. An estimated 2 billion people around the world have had airway management with the LMA. It is now used in about 50 percent of elective general anesthesia cases in the United States and more than 90 percent in the United Kingdom. It is universally recognized as an essential backup device in airway management in any setting.