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CARDIOVASCULAR ANESTHESIA

Monitoring End-Tidal Carbon Dioxide During Weaning from Cardiopulmonary Bypass in Patients Without Significant Lung Disease

Andrew Maslow, MD*, Gary Stearns, CCP, Arthur Bert, MD*, William Feng, MD, David Price, CCP, Carl Schwartz, MD*, Scott MacKinnon, MD*, Fred Rotenberg, MD*, Richard Hopkins, MD, George Cooper, MD, Arun Singh, MD, and Stephen H. Loring, MD

Departments of *Anesthesiology and Surgery, Rhode Island Hospital, Providence, Rhode Island, Department of Anesthesia and Critical Care, Beth Israel Deaconess Medical Center, Boston, Massachusetts

Address all correspondence and reprint requests to Andrew Maslow, MD, Department of Anesthesiology, Rhode Island Hospital, 593 Eddy Street, Davol 129, Providence, RI 02903. Address e-mail to amaslow{at}lifespan.org

End-tidal carbon dioxide tension (PETCO₂) changes with fluctuations in cardiac output (CO). We compared PETCO₂ to pulmonary artery blood flow (PAQt) during weaning from cardiopulmonary bypass (CPB) in normothermic patients without significant pulmonary disease. Fifteen consecutive adult cardiac surgical patients were prospectively studied during and shortly after weaning from CPB. Before separation from CPB, PETCO₂ and PAQt were measured, the latter by transesophageal Doppler echocardiography. At the time of measurements patients were normothermic, and ventilated at 6 breaths/min with tidal volumes of 10 mL/kg. After separation from CPB, thermodilution cardiac output (TDCO) was measured in addition to PAQt and PETCO₂. Regression and bias analyses were used to compare PETCO₂, PAQt, and TDCO. Seventy measurements were recorded; 31 before separation from CPB and 39 after separation from CPB. A good correlation was seen between PAQt and PETCO₂ (r = 0.88) and between TDCO and PAQt (r = 0.93; mean bias 0.03 L/min; SD 0.52 L/min). The regression analysis of PAQt on PETCO₂ showed greater variability at PETCO₂ levels > 34 mm Hg (n = 22; r = 0.14). Increases in PETCO₂ plateaued at this level, although PAQt continued to increase. When PETCO₂ was more than 30 mm Hg, all PAQt and TDCO values were >4.0 L/min (>2.0 L/min/m²). When PETCO₂ exceeded 34 mm Hg, all values of PAQt, and 28/29 values of TDCO were more than 5 L/min (>2.5 L/min/m²). One patient had TDCO of 4.69 L/min (2.39 L/min/m²). In normothermic patients without significant pulmonary disease, PETCO₂ is a useful index of PAQt during separation from CPB. Under the clinical settings in this study, a PETCO₂ greater than 30 mm Hg was invariably associated with a CO more than 4.0 L/min or a cardiac index >2.0 L/min/m².

Implications: In normothermic patients without pulmonary disease, acute changes in PETCO₂ during separation from cardiopulmonary bypass were reflective of changes in pulmonary artery blood flow. Specific PETCO₂ values were predictive of cardiac output values under the clinical conditions of the study.