Relationship between oxygen consumption and oxygen delivery during anesthesia in high-risk surgical patients.

OBJECTIVE

To identify critical oxygen delivery (DO2) and oxygen extraction ratio in high-risk surgical patients studied preoperatively and intraoperatively.

DESIGN

Prospective study. Consecutive series of intraoperatively monitored patients.

SETTING

The surgical ICU in a tertiary care center.

PATIENTS

High-risk surgical patients undergoing major noncardiac surgery.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Twenty high-risk patients were studied during the preoperative and intraoperative periods. All patients were monitored with triple-lumen thermodilution catheters. Hemodynamic profiles consisted of determinations of intravascular pressures, cardiac output, and arterial and venous pulmonary gases. Oxygen transport variables were calculated by standard formulas. Multiple determinations were carried out during the perioperative period in each patient. The critical levels of DO2, determined by a polynomial regression method, were 375 and 390 mL/min/m2 in the preoperative and intraoperative periods, respectively. Oxygen extraction reached at the critical level of DO2 was significantly (p < .01) lower during the intraoperative period (31 +/- 4.5% vs. 18 +/- 2.3%). Critical mixed venous oxygen tension was significantly (p < .01) higher in the intraoperative period (36 +/- 5 vs. 46 +/- 4 torr [4.8 +/- 0.7 vs. 6.1 +/- 0.5 kPa]).

CONCLUSIONS

Our data show that the intraoperative period might be associated with a reduction in tissue ability to extract oxygen. If this reduction in oxygen extraction is proportionately higher than the reduction in metabolic oxygen demand produced by anesthetic agents and hypothermia, then the critical value for DO2 may be similar to, or higher than, that value in the preoperative period. Thus, the intraoperative period represents, for this patient population, a high-risk condition for the development of a tissue oxygenation debt in the presence of a limitation in DO2. Cautious dosing of inhaled agents, maintenance of normothermia, and early optimization of the oxygen delivery/oxygen consumption relationship seem to constitute reasonable measures in the intraoperative handling of these patients in order to reduce perioperative morbidity and mortality.