Energy Metabolism of Thoracic Surgical Patients in the Early Postoperative Period

Effect of Posture

¹ From the Department of Surgery, Intensive Care Unit at School of Anesthesiology and Intensive Care, University of Pisa, Italy
² From the Department of Surgery, Division of Thoracic Surgery, University of Pisa, Italy

Study objective: To determine the effect of elective thoracic surgery on energy metabolism and gas exchange and to evaluate whether the 30° sitting position would affect these variables.

Design: Prospective, unblinded, controlled study.

Setting: Surgical ICU in a university hospital.

Patients: Twenty-two adult patients undergoing elective pulmonary resection.

Interventions: Posture change from supine to 30° sitting position.

Measurements and results: Oxygen consumption (VO₂), carbon dioxide production (VCO₂), respiratory quotient (RQ), and energy expenditure (EE) were measured by means of computerized indirect calorimetry before and after surgery. Heart rate and respiratory frequency were measured continuously during gas exchange measurement. Blood gases were analyzed with an automated blood gas analyzer. Preoperatively, altering position did not affect energy metabolism, gas exchange, and cardiopulmonary variables. Postoperatively, the measured EE was 116% of the expected value. Mean EE and VO₂ values for each position were higher than the preoperative values for the corresponding postures (p<0.05 for each position), while VCO₂ increased only in the supine position (p<0.05). Mean percent increases in EE, VO₂, and VCO₂ were significantly lower in the 30° sitting position than in the supine position (EE:7.9±2.7% vs 14.4±2.3%; p<0.001; VO₂:9.0±3.0% vs 16.4±2.6%; p<0.001; VCO₂:3.2±2.1% vs 6.5±1.4%; p<0.05). Arterial oxygen tension and all the physiologic indexes of gas exchange for each position were worse than the preoperative values for the corresponding postures (p<0.05 for each position). Mean arterial pressure, heart rate, and respiratory frequency for each position were higher than the preoperative values for the corresponding postures (p<0.05 for each position). No changes in mean values of these variables occurred between the two positions postoperatively.

Conclusions: The early postoperative period of patients undergoing elective thoracic surgery is characterized by a condition of impaired gas exchange and by ahypermetabolic state. Hypermetabolism can be partly mitigated by assuming the 30° sitting position.

Key Words: energy expenditure • indirect calorimetry • intensive care unit • metabolism • monitoring • postsurgical period • posture • thoracic surgery

Submitted on April 21, 1995
Accepted on September 11, 2007