Gastric-arterial PCO2 gradient does not reflect systemic and splanchnic hemodynamics or oxygen transport after cardiac surgery

Gastric mucosal-arterial PCO2 gradient (Pg-aCO2) is used to assess splanchn ic perfusion and oxygenation. We evaluated whether Pg-aCO2 reflects whole b ody (Q) and splanchnic (Qsp) blood flow, oxygen delivery (DO2) and consumpt ion (VO2) after coronary artery by pass graft (CABG) operation. Thirty pati ents received dobutamine or dopexamine to increase cardiac index, 15 patien ts enalapril or sodium nitroprusside to lower blood pressure, and 30 patien ts were controls. We measured Q, Qsp (hepatic vein catheter and indocyanine green), and gastric mucosal PCO2 (nasogastric tonometer) before and after interventions. Multiple linear regression model showed that none of the cha nges in Q, Qsp, and splanchnic or systemic DO2 and VO2 significantly explai ned changes in Pg-aCO2 (Delta Pg-aCO2). All independent variables together explained only 7% of Delta Pg-aCO2. Increased splanchnic blood flow (0.65 /- .19 vs. 0.94 +/- .31 L/min/m(2), P < 0.001) and increased splanchnic DO2 (101 +/- 28 vs. 143 +/- 42 mL/min/m(2), P < 0.001) during catecholamine in fusions were associated with increased Pg-aCO2 (8 +/- 8 vs. 11 +/- 7 mmHg, P = 0.003). Pg-aCO2 does not reflect whole body or splanchnic blood flow, D O2 or VO2 after CABG operations. The physiology of Pg-aCO2 is complex and t herefore it is difficult for clinicians to interpret changes in gastric muc osal-arterial PCO2 gradient in individual patients after cardiac surgery.