BACKGROUNDAfter 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 ).

METHODSWe 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.

RESULTSAt 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%.

CONCLUSIONSP(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.