Factors influencing oxygen store during denitrogenation in the healthy patient

Abstract

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 O 2. Measurements End-expired levels of O 2, nitrogen, and CO 2 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 O 2 significantly decreased the time of denitrogenation. There appeared to be little clinical benefit of flushing with O 2 when a 10 L/min O 2 flow was used. Conclusions A high gas flow rate appears critical to achieving rapid preoxygenation.