DOI: 10.1097/SA.0b013e3181caea24
,
Issn Print: 0039-6206
Publication Date: 2010/02/01
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Excerpt
Anne-Grethe Lorentzen, Christian Lindskov, Erik Sloth, and Carl-Johan Jakobsen
(J Cardiothorac Vasc Anesth, 22:853-857, 2008)
Department of Anesthesia and Intensive Care, Aarhus University Hospital-Skejby, Aarhus, Denmark.
Most patients undergoing cardiac surgery have a central venous catheter that could be used to determine central venous oxygen saturation (ScvO2). This method offers an inexpensive alternative to measurement of mixed venous oxygen saturation (SvO2) by means of pulmonary artery (PA) catheterization. Twenty patients scheduled for elective cardiac surgery participated in a prospective study to determine whether ScvO2 and SvO2 measurements are interchangeable.
Patients eligible for the study had a preoperative left ejection fraction higher than 40% and inotropic support of dopamine or dobutamine less than 6 μg/kg per minute. All received oral diazepam (5-10 mg) 1 hour before surgery and a standardized anesthesia protocol. The cardiopulmonary bypass technique was normothermic using intermittent crystalloid cardioplegia. To assess ScvO2, blood samples were drawn from the distal port of the central venous catheter and immediately analyzed. The fiberoptic PA catheter module was calibrated with a blood sample drawn from the distal port of the catheter for immediate SvO2 analysis. At least 8 measurements were recorded for each patient, starting approximately 30 minutes after the patient arrived in the intensive care unit until tracheal extubation.
Patients were 16 men and 4 women, ranging in age from 55 to 79 years. Most were undergoing coronary artery bypass grafting (CABG), aortic valve replacement, or both; there was 1 case of mitral valve replacement. A total of 236 measurement pairs of ScvO2 and SvO2 were collected. Values of ScvO2 were generally higher than those of SvO2. The overall bias between these measurements was 1.9%. Whereas the bias was 0.6% in CABG patients, it rose to 6.4% in procedures involving aortic valve replacement. Bias was 10.7 when peripheral saturation was less than 92%, but only 0.8 when peripheral oxygen saturation was >99%.
This lack of agreement between ScvO2 and SvO2 measurements can be crucial, especially in patients undergoing aortic valve surgery. Although not completely accurate in terms of absolute venous saturations, the less invasive ScvO2 may be useful, however, in patients undergoing CABG. Analysis of ScvO2 may help to diagnose the primary cause of low oxygen saturation.
