Spontaneous Breathing during General Anesthesia Prevents the Ventral Redistribution of Ventilation as Detected by Electrical Impedance Tomography

Spontaneous Breathing during General Anesthesia Prevents the Ventral Redistribution of Ventilation as Detected by Electrical Impedance Tomography A Randomized Trial Oliver C. Radke, M.D., Ph.D., D.E.A.A.,* Thomas Schneider,† Axel R. Heller, M.D., Ph.D.,‡ Thea Koch, M.D., Ph.D.§ ABSTRACT What We Already Know about This Topic • Controlled mechanical ventilation under general anesthesia increases ventilation in the ventral parts of the lung • We do not know whether pressure support ventilation prevents the redistribution of ventilation Background: Positive-pressure ventilation causes a ventral redistribution of ventilation. Spontaneous breathing during general anesthesia with a laryngeal mask airway could pre- vent this redistribution of ventilation. We hypothesize that, compared with pressure-controlled ventilation, spontaneous breathing and pressure support ventilation reduce the extent of the redistribution of ventilation as detected by electrical impedance tomography. Methods: The study was a randomized, three-armed, obser- vational, clinical trial without blinding. With approval from the local ethics committee, we enrolled 30 nonobese patients without severe cardiac or pulmonary comorbidities who were scheduled for elective orthopedic surgery. All of the proce- dures were performed under general anesthesia with a laryn- geal mask airway and a standardized anesthetic regimen. The center of ventilation (primary outcome) was calculated be- fore the induction of anesthesia (AWAKE), after the place- ment of the laryngeal mask airway (BEGIN), before the end What This Article Tells Us That Is New • Using a noninvasive and radiation-free imaging technique of lung function, electric impedance tomography, under general anesthesia in nonparalyzed adults, this study demonstrates no difference of regional ventilation distribution between the modes of pressure-controlled ventilation and pressure sup- port ventilation, whereas spontaneous breathing prevented the redistribution of anesthesia (END), and after arrival in the postanesthesia care unit (PACU). Results: The center of ventilation during anesthesia (BEGIN) was higher than baseline (AWAKE) in both the pressure-controlled and pressure support ventilation groups (pressure control: 55.0 vs. 48.3, pressure support: 54.7 vs. 48.8, respectively; multivariate analysis of covariance, P ⬍ 0.01), whereas the values in the spontaneous breathing group remained at baseline levels (47.9 vs. 48.5). In the post- anesthesia care unit, the center of ventilation had returned to the baseline values in all groups. No adverse events were recorded. Conclusions: Both pressure-controlled ventilation and pres- sure support ventilation induce a redistribution of ventila- tion toward the ventral region, as detected by electrical im- pedance tomography. Spontaneous breathing prevents this redistribution. * Assistant Clinical Professor, San Francisco General Hospital, Department of Anesthesia & Perioperative Care, University of Cali- fornia San Francisco, San Francisco, California, and Senior Attending Anesthesiologist, Klinik und Poliklinik fu¨r Anasthesiologie und In- tensivtherapie, Fetscherstr, Dresden, Germany. † Ph.D. Student, ‡ Professor of Anesthesia, § Chair, Klinik und Poliklinik fu¨r Ana¨s- thesiologie und Intensivtherapie, Fetscherstr. Received from Klinik und Poliklinik fu¨r Ana¨sthesiologie und Intensivtherapie, Fetscherstr, Dresden, Germany. Submitted for publication March 22, 2011. Accepted for publication February 6, 2012. Support was provided solely from institutional and/or depart- mental sources. Dra¨ger Medical (Lu¨beck, Germany) provided the electrical impedance tomography prototype free of charge for use in this study. Presented as a poster at the annual meeting of the American Thoracic Society, May 15, 2011, Denver, Colorado, and at the meeting of the European Association of Cardiothoracic Anaes- thesiologists, June 3, 2011, Vienna, Austria. Address correspondence to Dr. Radke: San Francisco General Hospital, Department of Anesthesia & Perioperative Care, University of California San Francisco, 1001 Potrero Avenue, San Francisco, California 94110. oradke@pcat.de. Information on purchasing re- prints may be found at www.anesthesiology.org or on the masthead page at the beginning of this issue. A NESTHESIOLOGY ’s articles are made freely accessible to all readers, for personal use only, 6 months from the cover date of the issue. I NTUBATION and mechanical ventilation cause a redis- tribution of ventilation: 1,2 compared with spontaneous breathing (SB) in the awake state in supine position, positive- 䉬 This article is accompanied by an Editorial View. Please see: Canet J, Gallart L: The dark side of the lung: Unveiling regional lung ventilation with electrical impedance tomog- raphy. A NESTHESIOLOGY 2012; 116:XXX–XXX. Copyright © 2012, the American Society of Anesthesiologists, Inc. Lippincott Williams & Wilkins. Anesthesiology 2012; 116:1–1 Anesthesiology, V 116 • No 6 June 2012