Oxygen Consumption, Hypoperfusion and Organ Injury After Cardio-pulmonary Bypass

Difference in oxygen consumption (VO2I via indirect calorimetry) in ml min-1 m-2 between patients with and without early hyperlactatemia (>2mmol/L)

Hypoperfusion parameters will be evaluated as a predictors of postoperative oxygen consumption (VO2I, ml min-1 m-2 via indirect calorimetry).

Blood gas parameters taken preoperatively and at spaced time-points up to 24 hrs after start of surgery:

• Central venous oxygen saturation (ScvO2, %, central venous blood gas), 2) Arterial lactate (mmol/L, arterial blood gas), 3) Base excess (BE, mmol/L, arterial blood gas), 4) Venous-to-arterial CO2 difference (ΔPCO2, mmHg, arterial and central venous blood gas) and its ratio with arterial -central venous oxygen content.

Clinical variables measured hourly or otherwise specified:

• Heart rate (beats/min), 6) Mean arterial pressure (MAP, mmHg), 7) Central venous pressure (CVP, mmHg), 8) Vasopressor or inotrope requirement (Y/N, low-intermediate-high), 9) Urine output (mL/24 hours), and 10) net fluid balance (mL/24 hours).

Additional explorative data analyses for hypothesis generating purposes can be performed.

Oxygen delivery (DO2I, ml min-1 m-2) and oxygen consumption (VO2I ml min-1 m-2) will be measured during cardiopulmonary bypass by continuous blood parameter monitoring or calculated by blood oxygen content and pump flow. Both mean levels and repeated measures will be analysed as predictors for postoperative oxygen consumption. Additional explorative data analyses for hypothesis generating purposes can be performed.

Organ injury markers will be evaluated as predictors for postoperative oxygen consumption. Absolute levels, changes from preoperative values, and above normal predicted value (yes/no) will be used in the analysis.

Blood sampling preoperatively and the day after surgery.

• Renal: Creatinine (mmol L-1), Estimated glomerular filtration rate; eGFR (ml min-1 1.73 m-2):
• Cardiac: Troponin T; TnT, creatinine kinase-MB; CK-MB, probrain natriuretic peptide; Nt-proBNP (ng L-1)
• Hepatic: Aspartate aminotransferase; ASAT, alanine aminotransferase; ALAT(mikrokat L-1)
• Brain: Neurofilament light chain; NFL, Glial fibrillary acidic protein, GFAP (ng L-1)
• Gut: Medium chain fatty acids; MCFA, Short chain fatty acids; SCFA, conjugated and non-conjugated bile acids (ng ml-1) Additional explorative data analyses for hypothesis generating purposes can be performed.