[Value of continuous venous blood oxygen measurement during external circulatory assistance]

A case is reported of a 40 year-old man, on the waiting-list for heart transplantation, who developed terminal heart failure. Using an Opticath catheter and a radial artery catheter, SV(-)O2 was monitored continuously, and cardiac output, pulmonary arterial and wedged pressures, and right atrial pressure were repeatedly measured. Despite appropriate treatment (adrenaline, dobutamine, glyceryl trinitrate), the patient remained in anuria and cardiogenic shock. External circulatory support (ECS) (BVS 5000 Abiomed) was therefore used as a bridge to cardiac transplantation. The resultant increase in systemic blood flow led to an early and fast rise in SV(-)O2, from 40% to 73%, with a decrease in the oxygen extraction ratio (ERO2) from 50 to 30%. Serum lactate concentrations returned to normal within the first six hours of ECS (less than 120 mg.l-1). During the first 24 h of ECS, SV(-)O2 decreased and ERO2 rose significantly on two occasions: during an episode of shivering, and another of restlessness during nursing. An attempt at weaning the patient from the ventilator at the 39th h also led to a sudden decrease in SV(-)O2, with a rise in ERO2. The Opticath catheter was finally removed after 150 h of ECS because of a decrease in reflected light intensity.