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Mixed venous oxygen saturation predicts short- and long-term outcome after coronary artery bypass grafting surgery.

Editor—We read with interest the study by Holm and colleagues which assessed the shortand long-term effects of mixed venous saturations (SvO2 ) after coronary artery bypass grafting (CABG) surgery. We thought that it was appropriate to study such outcomes in this group of patients, given the results showed that an SvO2 ,60% is associated with both worse shortand long-term outcomes, and with increased perioperative morbidity. However, the technique of measuring SvO2 , from an epidural catheter placed by the surgeon 15 cm into the pulmonary artery via the right ventricular outflow tract, then bought out to the skin through epidural needle puncture of the right ventricular wall and abdominal wall, may have associated risks that could reduce uptake by other groups. We note in the study that there were no complications recorded due to this catheterization and congratulate the authors for this. With the declining use of pulmonary artery catheters (PACs), due to documented lack of clear evidence of benefit in cardiac or perioperative patients and the data on mortality associated with PAC use difficult to interpret, we feel an opportunity has been missed to compare values of SvO2 and central venous saturations (ScvO2 ) in postoperative CABG patients, and so determine the shortand long-term effects of varying levels of ScvO2 . As it remains to be documented if the information obtained by sampling from central venous catheters is interchangeable with that from PACs, 5 to know if there is an ScvO2 value which may affect shortand long-term outcomes after CABG surgery would be useful.