Factors influencing oxygen store during denitrogenation in the healthy patient

Study Objective: To define the various factors that influence the rate of effective preoxygenation. Design: Prospective, randomized study. Setting: Procedure room in a teaching hospital. Subjects: 14 ASA physical status I volunteers who performed 4 sessions of breathing in random order. Of these volunteers, 7 performed two extra sessions using vital capacity breathing, which were also completed in random order. Interventions: Using the circle system, volunteers breathed with a mouthpiece and nose-clip until expired nitrogen reached 5%, using either a fresh gas flow of 5 L/min or 10 L/min or a system flushed with O₂. Measurements: End-expired levels of O₂, nitrogen, and CO₂ were recorded. Main Results: Minute ventilation, functional residual capacity, and age were significant factors for rate of denitrogenation. However, height and weight were not significant factors in predicting time to denitrogenation. At low flow rates, flushing with O₂ significantly decreased the time of denitrogenation. There appeared to be little clinical benefit of flushing with O₂ when a 10 L/min O₂ flow was used. Conclusions: A high gas flow rate appears critical to achieving rapid preoxygenation.