Cricoid Pressure, Gender, and Black Cats
We have several critical points to make regarding the article by Zeidan et al.1 First, neck circumference was not measured. Increased neck circumference may require higher pressure for effective cricoid pressure (CP) such that neck circumference could be a predictive factor independent of, or additive to, patient gender. Second, the anatomical model described is only realistic for videolaryngoscopy (VLS). Direct laryngoscopy aims to obtain a line of sight by alignment of oropharyngolaryngeal axis with a lifting/levering maneuver that unavoidably changes the anatomical relationship between the larynx and esophagus. CP has been evaluated (and applied for years) on such an anatomical basis. VLS is accomplished with less need for axis alignment and less force for laryngeal visualization.2 As a consequence, the different laryngoesophageal relationships for VLS and standard laryngoscopy preclude tout-court extension of Zeidan’s results to CP during classic laryngoscopy. The third point of contention is the assumption that a failed gastric tube passage is proof of effective CP. Failed passage could have been, partly or completely, due to variant esophageal alignment that occurs in up to 50% of patients,3 esophageal sphincter (UES) tone, esophageal peristalsis, or other causes despite optimal UES visualization (Figure). In Zeidan’s study,1 13 patients out of 73 were excluded for missed esophageal visualization. Fourth, the cricoid cartilage in a woman is smaller than in a man. This could be enough to conclude that same force applied for CP in a woman as in a man results in a higher “closing” pressure spread across a smaller application area. But reducing CP force based solely on physical calculations and results from a study potentially biased by these methodological limitations could be somewhat dangerous.
The final concern is the real effectiveness of CP. We know that correctly applied CP works on anatomic–physiological mechanisms, which intrinsically cause difficult ventilation, laryngoscopy, and intubation regardless of the force applied such that interference with airway management is unavoidable. So the real question is not how much force we should apply, but if it is worth the effort to apply any force.4 Despite certainty of its side effects and uncertainty of its benefits, CP is still suggested or recommended in recent airway guidelines. We should not forget that the grade of evidence sustaining CP is the same as changing route when a black cat crosses our way. In difficult airway situations, sometimes there are no other routes left.