The Use of the Ratio between the Veno-arterial Carbon Dioxide Difference and the Arterial-venous Oxygen Difference to Guide Resuscitation in Cardiac Surgery Patients with Hyperlactatemia and Normal Central Venous Oxygen Saturation

BACKGROUND: After cardiac surgery, central venous oxygen saturation (ScvO(2)) and serum lactate concentration are often used to guide resuscitation; however, neither are completely reliable indicators of global tissue hypoxia. This observational study aimed to establish whether the ratio between the veno-arterial carbon dioxide and the arterial-venous oxygen differences (P(v−a)CO(2)/C(a−v)O(2)) could predict whether patients would respond to resuscitation by increasing oxygen delivery (DO(2)). METHODS: We selected 72 patients from a cohort of 290 who had undergone cardiac surgery in our institution between January 2012 and August 2014. The selected patients were managed postoperatively on the Intensive Care Unit, had a normal ScvO(2), elevated serum lactate concentration, and responded to resuscitation by increasing DO(2) by >10%. As a consequence, 48 patients responded with an increase in oxygen consumption (VO(2)) while VO(2) was static or fell in 24. RESULTS: At baseline and before resuscitative intervention in postoperative cardiac surgery patients, a P(v−a)CO(2)/C(a−v)O(2) ratio ≥1.6 mmHg/ml predicted a positive VO(2) response to an increase in DO(2) of >10% with a sensitivity of 68.8% and a specificity of 87.5%. CONCLUSIONS: P(v−a)CO(2)/C(a−v)O(2) ratio appears to be a reliable marker of global anaerobic metabolism and predicts response to DO(2) challenge. Thus, patients likely to benefit from resuscitation can be identified promptly, the P(v−a)CO(2)/C(a−v)O(2) ratio may, therefore, be a useful resuscitation target.