EFFECTS OF DOBUTAMINE ON OXYGEN-CONSUMPTION IN SEPTIC PATIENTS - DIRECT VERSUS INDIRECT DETERMINATIONS

Dobutamine has been proposed as a means of disclosing a pathologic oxygen supply (DO2) dependency in critically ill patients. Like other catecholamines, however, dobutamine might increase cellular metabolism, so that oxygen consumption (VO2) would increase regardless of the presence or absence of a supply dependency. This study investigated the effects of graded doses of dobutamine on VO2 in stable, septic patients. Since it has been suggested that the use of reverse Fick equation to determine VO2 can induce a spurious VO2/DO2 dependency owing to a mathematical coupling of data, we determined VO2 both by respiratory gas analysis (VO(2)DIR) and from the reverse Fick equation (VO(2)INDIR). In 12 adult patients with signs of sepsis but an otherwise stable hemodynamic status (normal blood lactate levels, and no change in vasoactive drugs or fluid administration for at least 2 h), a dobutamine infusion was administered at a dose of up to 10 mu g/kg/min in increments of 2 mu g/kg/min every 10 min. Complete hemodynamic and gas measurements were obtained at baseline, at each dose of dobutamine, and 20 min after discontinuation of the infusion. All of the measured parameters were similar at baseline and after discontinuation of the dobutamine infusion. Dobutamine induced a dose-related increase in the cardiac index (from 3.84 +/- 0.97 to 6.19 +/- 1.56 L/min/m(2), p < 0.01) and DO2 (from 501 +/- 123 to 801 +/- 219 ml/min/m(2), p < 0.01). Both VO(2)DIR and VO(2)INDIR increased, from 161 +/- 37 to 183 +/- 40 ml/min/m(2) and from 140 +/- 29 to 168 +/- 42 ml/min/m(2), respectively (p < 0.01). Changes in VO2 became statistically significant at and above a dobutamine dose of 6 mu g/kg/min. The mean slope of the relationship (calculated by individual single regression) was 8.8% for VO(2)DIR and 10.5% for VO(2)INDIR. There was a strong correlation and good agreement between VO(2)DIR and VO(2)INDIR. In stable septic patients, the increase in DO2 resulting from dobutamine administration is associated with a moderate increase in VO2. No significant difference was found in the evolution of VO(2)DIR and VO(2)INDIR. Under the conditions of the present study, no methodologic problems were found in association with calculations of VO2 from the Fick equation.