Relationship between oxygen uptake and oxygen delivery in septic Patients

Abstract

To compare the effects of prostacyclin (PGI2) and dobutamine on the relationship between oxygen delivery (DO2) and oxygen uptake (VO2) in stable septic patients. Prospective study using a crossover design with alternate order of medications. Seventeen patients with documented sepsis and a stable hemodynamic status with normal blood lactate concentrations. Eleven patients were mechanically ventilated. Eight patients eventually died. DO2 and VO2 were calculated before and after a 20-min infusion of 5 ng/kg/min of PGI2 followed or preceded by 5 micrograms/kg/min of dobutamine. Both medications increased cardiac output significantly. At the dose used, PGI2 infusion reduced mean arterial pressure from 90.8 +/- 16.8 to 81.5 +/- 17.3 mm Hg (p < .01) and PaO2 from 97 +/- 25 torr to 82 +/- 22 torr (from 12.9 +/- 3.3 to 10.9 +/- 2.9 kPa) (p < .01) and increased venous admixture from 17.5 +/- 0.6% to 23.8 +/- 8.2% (p < .01). Dobutamine had no significant influence on these variables. PGI2 increased DO2 by 19% (from 470 +/- 105 to 557 +/- 117 mL/min/m2, p < .01) while dobutamine increased DO2 by 27% (from 463 +/- 103 to 589 +/- 156 mL/min/m2, p < .01). PGI2 increased VO2 by 5% (from 148 +/- 38 to 155 +/- 36 mL/min/m2) while dobutamine increased VO2 by 10% (from 146 +/- 36 to 161 +/- 41 mL/min/m2, p < .01). Accordingly, there was an identical decrease in oxygen extraction with PGI2 (from 32.4 +/- 8.2% to 28.6 +/- 7.1%, p < .01) and dobutamine (from 32.4 +/- 8.3% to 28.5 +/- 7.8%, p < .01). The responses to these medications were similar in survivors and nonsurvivors. PGI2 and dobutamine at the doses used have similar effects on oxygen extraction in critically ill, septic patients, but dobutamine increases DO2 more consistently and is better tolerated than prostacyclin.