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(Circulation. 2001;104:I-159.)
© 2001 American Heart Association, Inc.

Surgery for Congenital Heart Disease

Impact of Inspired Gas Mixtures on Preoperative Infants With Hypoplastic Left Heart Syndrome During Controlled Ventilation

Sarah Tabbutt, MD, PhD; Chandra Ramamoorthy, MB, BS; Lisa M. Montenegro, MD; Suzanne M. Durning, BS, RRT; C. Dean Kurth, MD; James M. Steven, MD; Rodolfo I. Godinez, MD, PhD; Thomas L. Spray, MD; Gil Wernovsky, MD; Susan C. Nicolson, MD

Department of Pediatrics, Division of Cardiology (S.T., G.W.), Department of Anesthesia and Critical Care Medicine (S.T., L.M.M., C.D.K., J.MS, R.I.G., S.C.N.), Department of Surgery, Division of Cardiothoracic Surgery (T.L.S.), and Department of Respiratory Care (S.M.D., R.I.G.), The Children’s Hospital of Philadelphia and the University of Pennsylvania School of Medicine, Philadelphia, and the Department of Anesthesia (C.R.), Children’s Hospital Medical Center and the University of Washington School of Medicine, Seattle.

Correspondence to Sarah Tabbutt, MD, PhD, The Cardiac Center, The Children’s Hospital of Philadelphia, 34th St and Civic Center Boulevard, Philadelphia, PA 19104. E-mail tabbutt{at}email.chop.edu

Background— Management strategies for preoperative infants with hypoplastic left heart syndrome (HLHS) include increased inspired nitrogen (hypoxia) and increased inspired carbon dioxide (hypercarbia). There are no studies directly comparing these 2 therapies in humans. This study compares the impact of hypoxia versus hypercarbia on oxygen delivery, under conditions of fixed minute ventilation.

Methods and Results— Ten anesthetized and paralyzed preoperative infants with HLHS were evaluated in a prospective, randomized, crossover trial comparing hypoxia (17% FIO₂) with hypercarbia (2.7% FICO₂). Each patient was treated in a random order (10 minutes per condition) with a recovery period (15 to 20 minutes) in room air. Arterial (SaO₂) and superior vena caval (SvO₂) co-oximetry and cerebral oxygen saturation (ScO₂) measurements were made at the end of each condition and recovery period. ScO₂ was measured by near infrared spectroscopy. Hypoxia significantly decreased both SaO₂ (-5.2±1.1%, P=0.0014) and SvO₂ (-5.6±1.7%, P=0.009) compared with baseline, but arteriovenous oxygen saturation (AVO₂) difference (SaO₂-SvO₂) and ScO₂ remained unchanged. Hypercarbia decreased SaO₂ (-2.6±0.6%, P=0.002) compared with baseline but increased both ScO₂ (9.6±1.8%, P=0.0001) and SvO₂ (6±2.2%, P=0.022) and narrowed the AVO₂ difference (-8.5±2.3%, P=0.005). Both hypoxia and hypercarbia decreased the balance between pulmonary and systemic blood flow (Qp:Qs) compared with baseline.

Conclusions— In preoperative infants with HLHS, under conditions of anesthesia and paralysis, although Qp:Qs falls in both conditions, oxygen delivery is unchanged during hypoxia and increased during hypercarbia. These data cannot differentiate cerebral from systemic oxygen delivery.

Key Words: heart defects, congenital • hypoxia • cardiac output • blood flow • physiology