OXYGEN-CONSUMPTION IS INDEPENDENT OF INCREASES IN OXYGEN DELIVERY BY DOBUTAMINE IN SEPTIC PATIENTS WHO HAVE NORMAL OR INCREASED PLASMA LACTATE

We asked whether the relationship between oxygen delivery and oxygen consumption is different between patients who have sepsis and normal (n = 6) or increased (n = 8) concentrations of plasma lactate. We determined oxygen consumption using analysis of respiratory gases while increasing oxygen delivery using a dobutamine infusion. The relationship between oxygen delivery and consumption was y = 124 + 0.043 * x in the normal lactate group and y = 131 - 0.003 * x in the high lactate group (95% CI for differences in slopes, -0.003 to 0.096; p less-than-or-equal-to 0.05 for slope, normal versus high lactate). In the normal lactate group, direct oxygen consumption increased by only 8 +/- 6 ml/min/m2 after dobutamine infusion (from 144 +/- 26 to 153 +/- 22 ml/min/m2, p less-than-or-equal-to 0.02) despite an average increase of 220 +/- 80 ml/min/m2 in oxygen delivery (from 446 +/- 91 to 666 +/- 90 ml/min/m2, p less-than-or-equal-to 0.01) The oxygen extraction ratio fell from 0.27 +/- 0.03 to 0.21 +/- 0.02 after dobutamine (p less-than-or-equal-to 0.017). In the high lactate group, direct oxygen consumption decreased by 1 +/- 6 ml/min/m2 after dobutamine (from 131 +/- 33 to 130 +/- 35 ml/min/m2, p > 0.60) despite an average increase of 168 +/- 138 ml/min/m2 in oxygen delivery (from 467 +/- 194 to 635 +/- 300 ml/min/m2, p less-than-or-equal-to 0.01). The oxygen extraction ratio fell from 0.30 +/- 0.14 to 0.26 +/- 0.12 after dobutamine (p less-than-or-equal-to 0.01). We conclude first that direct oxygen consumption remains relatively constant despite large increases in oxygen delivery in patients who have sepsis, and second that increased concentration of plasma lactate does not predict dependence of oxygen consumption on oxygen delivery.