Adequacy of tissue oxygenation in cardiac surgery: regional measurements

The aim of the study was to measure visceral and peripheral perfusion and oxygenation during and immediately after cardiac surgery.

Central hemodynamics, blood gases, core temperature, visceral and peripheral tissue perfusion, and oxygenation were studied in eight patients undergoing coronary artery bypass grafting and in the early postoperative period in another group of ten coronary artery bypass grafting patients.

The variables were measured after induction of anesthesia, after sternotomy, during cardiopulmonary bypass, after rewarming and after closing the wounds. Postoperatively, the measurements were carried out hourly up to 8 hrs after the arrival of patients in the ICU.

The patients were operated on under moderate hemodilution and systemic hypothermia. The inspired oxygen concentration was maintained at 30 volumes percent during the postoperative study.

Visceral perfusion was indirectly assessed by determining the gastric intramucosal pH. Peripheral tissue perfusion was assessed in the upper extremity by continuous recording of subcutaneous tissue PO2, laser-Doppler skin erythrocyte flux, transcutaneous PO2, and fingertip temperature. Transcutaneous PO2 index (transcutaneous PO2/PaO2) was calculated.

Gastric intramucosal pH, PaO2, and transcutaneous PO2 reached maximum values during cardiopulmonary bypass at the deepest level of hypothermia, and gastric intramucosal pH reached its minimum at the end of the operation. During the first 3 hrs after admission of patients to the ICU, gastric intramucosal pH decreased progressively, reached its minimum value at 5 hrs, and increased slowly thereafter. Subcutaneous tissue PO2, laser-Doppler skin erythrocyte flux, and fingertip temperature decreased markedly during cardiopulmonary bypass, increased during rewarming, and decreased again at the end of surgery. The peripheral vascular bed was vasoconstricted on ICU admission, as indicated by the low values of subcutaneous tissue PO2, transcutaneous PO2, transcutaneous PO2 index, laser-Doppler skin erythrocyte flux, and fingertip temperature. These variables began to increase over the next 2 to 4 hrs and reached their maximum value by the end of the 8-hr postoperative study period, indicating complete vasodilation of the peripheral vascular bed.

These data suggest that the visceral perfusion of patients is well maintained during cardiopulmonary bypass, while, at the same time, these patients develop hypoperfusion and hypoxia of peripheral tissues. After closing the wounds, gastric intramucosal pH, transcutaneous PO2 index (transcutaneous PO2/PaO2), and other peripheral tissue perfusion variables were at the lowest values, indicating impending residual hypothermia and tissue hypoperfusion after rewarming. During the first few hours in the ICU, both the visceral and peripheral oxygenation and perfusion variables reflected hypoperfusion of tissues coinciding in time with the period most vulnerable for hemodynamic disasters and cardiac arrhythmias.