Effect of temperature during cardiopulmonary bypass on gastric mucosal perfusion

The purpose of our study was to prospectively study the splanchnic response to hypothermic and tepid cardiopulmonary bypass (CPB) using alpha-stat management of arterial blood gas tensions. Twenty-four patients for elective CABG surgery were allocated randomly to tepid (35-36°C) or hypothermic (30°C) bypass groups. Measurements were made at four times: (1) baseline, (2) stable during CPB (inflow temperature=nasopharyngeal temperature) 30°C for hypothermic patients, bypass +20 min for tepid patients, (3) 10 min before the end of bypass, (4) after bypass, skin closure. Both groups demonstrated a significant reduction in gastric intramucosal pH (pH(im)) from time 1 to time 4 and there was no difference in the incidence of a low pH(im) between the tepid and cold groups (4/12 vs 3/12; ns) at time 4. pH(im) was significantly lower in the tepid group at time 3 (P = 0.03) but this discrepancy may have been because of an artefactually high pH(im) in the cold group. There was a significantly higher incidence of postoperative non-cardiac complications in patients who had a low pH(im) at time 4 (P = 0.0008) Therefore, we conclude that although the temperature during CPB had a transient effect on pH(im) it is unlikely to be a major determinant in the pathogenesis of gut mucosal hypoperfusion after bypass.