VALUE OF THE VENOUS-ARTERIAL PCO2 GRADIENT TO REFLECT THE OXYGEN-SUPPLY TO DEMAND IN HUMANS - EFFECTS OF DOBUTAMINE

Objective: To test the value of venous arterial Pco(2) gradient (Delta Pco(2)) measurements to reflect the adequacy of cardiac index (CI) to oxygen demand in patients submitted to rapid changes of CI and oxygen demand. Design: Prospective, comparative study. Setting: Medical inte nsive care unit of a university hospital. Patients: Ten patients with congestive heart failure exhibiting low baseline CI (less than or equa l to 2.5 L/min/m(2)) but no evidence of global tissue hypoxia, as atte sted by the absence of clinical signs of shock and by normal blood lac tate concentrations. Interventions: Infusion of incremental doses of d obutamine: 0 (D-0) 5 (D-5) 10(D-10), and 15(D-15) mu g/kg/min. Measure ments and Main Results: The CI increased by a linear fashion from D-0 (1.6 +/- 0.1 L/min/m(2)) to D-15 (2.4 +/- 0.2 L/min/m(2)) (p< .05). Th e mixed venous oxygen saturation (S (v) over bar o(2)) increased from D, (49 +/- 2%) to D-10 (61 +/- 2%) (p <.05) and remained unchanged fro m D-10 to D-15 (60 +/- 2%). The oxygen extraction ratio (O-2 ER) and t he Delta Pco(2), decreased from D-0 (48 +/- 2% and 9 +/- 1 torr [1.2 /- 0.3 kPa], respectively) to D-10 (36 +/- 2% and 5 +/- 1 torr [0.7 +/ - 0.1 kPa], respectively) (p <.05 for both comparisons) and remained u nchanged from D-10 to D-15 (36 +/- 2% and 6 +/- 1 torr [0.8 +/- 0.1 kP a], respectively). The biphasic courses of S (v) over bar o(2), O-2 ER , and Delta Pco(2) were related to the course of oxygen consumption th at remained constant from D, (113 +/- 9 mL/min/m(2)) to D-10 (112 +/- 8 mL/min/m(2)) and significantly increased from D-10 to D-15 (127 +/- 10 mL/min/m(2))(p<.05). Conclusions: Delta Pco(2) can be reliably used at the bedside for informing on the adequacy of CI with respect to a given metabolic condition, and particularly for detecting changes in o xygen demand (e.g., the changes accompanying drug induced changes in C I). In this regard, Delta Pco(2), together with O-2 ER and S (v) over bar o(2), can help to assess the adequacy of CI to global oxygen deman d.