Blood lactate variations during cardiac surgery

Fifty consecutive patients were monitored during cardiac surgery. Cardiac index (CI), O2 delivery (O2 del), O2 uptake (VO2) and blood lactates were collected: before surgery (1); at the end of surgery (II); at the first hour in the Intensive Care Unit (ICU) (III); at the sixth hour in ICU (IV). Time variations were significant for all the parameters studied. Progressive lactate increase up to time I occurred simultaneously with a progressive CI and O2 del decrease, even though the latter values were greater than the critical levels for patients under anesthesia or sedation. Positive correlations at time III, especially between CI and lactates and between O2 del and lactates, indicate than an O2 debt had already begun to develop, probably during CPB. At time IV, blood lactate decrease accompanied by CI, O2 del and VO2 increase, indicated metabolic and O2 debt improvement. Negative correlations at this time further explained this trend. Failure to normalize blood lactate was due to the continually low O2 del value compared to time I. As result of this findings it seems important to continue to rigorously support and monitor CPB patients in the ICU during the first critical postoperative hours.