Ventilation and Gastric Insufflation During Three Levels of Inspiratory Pressure During Mask Ventilation

Plain-language summary

Pulmonary aspiration of gastric contents is one of the leading causes of general anesthesia-related mortality. Gastric insufflation during positive pressure mask ventilation increases the gastric volume, and consequently the risk of regurgitation. Thus, positive pressure mask ventilation should be avoided during rapid sequence induction of anesthesia when full-stomach is suspected (e.g. inadequate fasting hours, gastrointestinal obstruction, delayed gastric emptying, and lower esophageal disease) Although avoidance of positive pressure mask ventilation during induction would potentially minimize the risk of aspiration, this would lead to rapid hypoxia . Hence, finding a proper regimen for mask ventilation would avoid hypoxia which might be serious in high-risk patients. Pressure-controlled face mask ventilation previously proved to be the least regimen to cause gastric insufflation in comparison to manual, and volume-controlled mask ventilation during induction of anesthesia. Later, a pressure of 15 cmH2O during face mask ventilation had been reported optimum to achieve the balance between adequate ventilation and reduced gastric insufflation in non-paralyzed patients. This finding was not yet replicated in paralyzed patients who represent the majority of population who receive mask ventilation during induction of anesthesia. We hypothesize that in paralyzed patient, the optimum pressure during face mask ventilation might be lower than the pressure which was previously reported in non-paralyzed patients. However, no studies to the best of our knowledge had confirmed this hypothesis. Gastric insufflation was previously evaluated using auscultation with stethoscope, microphone placed in the epigastric area, or esophageal manometry. Recently, gastric antrum ultrasound was used successfully to gastric insufflation in real time by measuring the cross sectional area of gastric antrum before and after face mask ventilation. This newly developed method is more sensitive than the auscultatory method and less invasive than esophageal manometry method.

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