Different dosages of dobutamine in septic shock patients: determining oxygen consumption with a metabolic monitor integrated in a ventilator

Objective: Oxygen consumption (VO2) obtained from respiratory gases by indirect calorimetry (VO2,IC) with a metabolic monitor integrated in a ventilator were to be compared to VO2 obtained by the Fick principle (VO2,Fick) in septic patients following an increase in oxygen delivery (DO2) induced by positive inotropic support. Design: Prospective clinical study. Setting: University Hospital, Surgical Intensive Care Unit (ICU). Patients: Thirty patients suffering from sepsis. Interventions: DO2 was increased by dobutamine infusion, starting with an initial dosage of 5 mug.kg.min, increased to a maximum of 10 mug.kg.min. Measurements and main results: Dobutamine infusion induced a dosage-related increase in DO2 (from 577 +/- 192 to 752 +/- 202 ml.min.m(2), p < 0.01), which was associated with a statistically significant increase in VO2, IC (from 173 +/- 30 to 188 +/- 28 ml.min.m(2), 140 +/- 25 to 156 +/- 24 ml.min.m(2), p < 0.01). The comparison between VO2,IC and VO2,Fick revealed differences (bias and precision - 33 +/- 32 ml min m(2)). Conclusions: With a metabolic monitor integrated in a ventilator it was possible to carry out continuous monitoring of calorimetric data under clinical conditions. In contrast to previous studies using indirect calorimetry, this study showed a moderate correlation between VO2 and DO2 in septic patients using either method. The clinical relevance of this finding requires further investigation. Different factors (e.g. injectant temperature, pulmonary VO2) produced substantial differences between VO2,IC and VO2,Fick as previously shown.