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Does Maximal Exhalation Improve the Efficacy of Preoxygenation Tidal Volume and Deep Breathing Techniques?
Usharani Nimmagadda, M.D., Ninos J. Joseph, B.S., M. Ramez Salem, M.D., Istvan Miko, M.D.
Department of Anesthesiology, Advocate Illinois Masonic Medical Center, Chicago, Illinois, United States.
INTRODUCTION: Preoxygenation techniques, ranging from 3 to 5 min of tidal volume breathing (TVB) to 30 s to 2 min of deep breathing, have been advocated.1,2,3 Recently, it has been suggested that the efficacy of preoxygenation is enhanced by maximal exhalation preceding TVB.4 It was theorized that by exhaling maximally, lung nitrogen content and the subsequent dilution of incoming oxygen are minimized.4 This study was designed to determine the influence of maximal exhalation preceding the two techniques of preoxygenation, TVB and deep breathing in the same subjects.

METHODS: With IRB approval, 15 consenting healthy adult volunteers (8 males/7 females; mean age 31.9 ± 4.5 yrs; mean weight 70.6 ± 18.8 kg) without history of lung or cardiac disease were studied in the supine position using a semi-closed circle absorber system. After obtaining baseline measurements breathing room air, simulated preoxygenation was performed using a tight-fitting mask using four different regimens in random order: 1) TVB for 5 min without prior maximal exhalation; 2) TVB for 5 min after maximal exhalation; 3) 2-min of deep breathing (8 breaths/min) without prior maximal exhalation; and 4) 2-min of deep breathing after maximal exhalation. Mass spectrometric measurements of inspired and end-tidal O2, N2 and CO2 were obtained at 30 sec intervals. An ANOVA for repeated measures was employed to identify significant (P < .05) differences between 30 sec intervals.

RESULTS: (Figures 1 & 2) During the intial 2.5 min of TVB, ETO2 increased steeply and plateaued between 92% and 94%, thereafter. Maximal exhalation prior to TVB resulted in a slight increase in ETO2 at 0.5 and 1 min. Beyond 1 min, maximal exhalation did not have any impact on ETO2. During deep breathing, with or without prior maximal exhalation, the ETO2 had steeply increased at 0.5 min and continued to increase at each interval. The ETO2 peaked over 90% between 1.5 and 2 min. Further analysis (Life Tables, SPSS, Chicago, IL), using an ETO2 ≥ 90% as an endpoint, revealed no improvement in achieving maximal preoxygenation when maximal exhalation preceded preoxygenation using either TVB or deep breathing techniques. In addition, prior maximal exhalation had no effect on inspired O2 or N2 and end-tidal N2 or CO2.

DISCUSSION: The current findings suggest that prior maximal exhalation offers limited value during the first min of preoxygeantion with TVB, but no benefit with deep breathing. A minimum of 3 min of TVB or 1.5 min of deep breathing is still needed to reach the target ETO2 > 90%.

REFERENCES: 1. Anesthesiology 1985;62:827-9; 2. Anesthesiology 1999;91:612-5; 3. Anesth Analg 2001;92:1337-41; 4. Anesth Analg 2003;97:1533-5

Anesthesiology 2004; 101: A1558
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