Time to consider supraglottic airway device oropharyngeal leak pressure measurement more objectivelyOropharyngeal leak pressure (OLP) is considered a measure of successful placement, adequate performance and is a useful comparator between supraglottic airway devices (SADs). OLP measurement is based on the premise that the SAD is sited properly in the hypopharynx after blind placements, but the evidence suggests otherwise. Several limitations and controversies surround OLP. This editorial addresses the uses and pitfalls of OLP, the rationale for and methods of ascertaining OLP, the pros and cons of OLP measurement and newer modalities to improve its accuracy.

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BackgroundHyperventilation may be used to hasten recovery from general anesthesia with potent inhaled anesthetics. However, its effect may be less pronounced with the newer, less soluble agents, and it may result in rehypnotization if subsequent hypoventilation occurs because more residual anesthetic will be available in the body for redistribution to the central nervous system. We used GasMan® simulations to examine these issues.MethodsOne MAC of isoflurane, sevoflurane, or desflurane was administered to a fictitious 70 kg patient for 8 h with normoventilation (alveolar minute ventilation [VA] 5 L.min-1), resulting in full saturation of the vessel rich group (VRG) and >95% saturation of the muscle group. After 8 h, agent administration was stopped, and fresh gas flow was increased to 10 L.min-1 to avoid rebreathing. At that same time, we continued with one simulation where normoventilation was maintained, while in a second simulation hyperventilation was instituted (10 L.min-1). We determined the time needed for the partial pressure in the VRG (FVRG; representing the central nervous system) to reach 0.3 MAC (MACawake). After reaching MACawake in the VRG, several degrees of hypoventilation were instituted (VA of 2.5, 1.5, 1, and 0.5 L.min-1) to determine whether FVRG would increase above 0.3 MAC(= rehypnotization).ResultsTime to reach 0.3 MAC in the VRG with normoventilation was 14 min 42 s with isoflurane, 9 min 12 s with sevoflurane, and 6 min 12 s with desflurane. Hyperventilation reduced these recovery times by 30, 18, and 13% for isoflurane, sevoflurane, and desflurane, respectively. Rehypnotization was observed with VA of 0.5 L.min-1 with desflurane, 0.5 and 1 L.min-1 with sevoflurane, and 0.5, 1, 1.5, and 2.5 L.min-1 with isoflurane. Only with isoflurane did initial hyperventilation slightly increase the risk of rehypnotization.ConclusionsThese GasMan® simulations confirm that the use of hyperventilation to hasten recovery is marginally beneficial with the newer, less soluble agents. In addition, subsequent hypoventilation results in rehypnotization only with more soluble agents, unless hypoventilation is severe. Also, initial hyperventilation does not increase the risk of rehypnotization with less soluble agents when subsequent hypoventilation occurs. Well-controlled clinical studies are required to validate these simulations.