Oxygen Consumption Is Independent of Changes in Oxygen Delivery in Severe Adult Respiratory Distress Syndrome

TLDR

The study examined whether oxygen consumption depends on oxygen delivery in 17 severe ARDS patients, including 10 with elevated plasma lactate. Oxygen consumption was measured via respiratory gas analysis while oxygen delivery was increased by blood transfusion. Oxygen consumption did not change after transfusion, remaining constant despite a 24 % increase in oxygen delivery and even in patients with elevated lactate, indicating that measured consumption is independent of delivery and that any apparent dependence in calculated values is likely methodological.

Abstract

We asked whether oxygen consumption is dependent on oxygen delivery in 17 patients who had severe adult respiratory distress syndrome (ARDS), 10 of whom had increased concentrations of plasma lactate. We determined oxygen consumption using analysis of respiratory gases while increasing oxygen delivery using blood transfusion. Oxygen consumption did not change after transfusion (from 227 ± 83 to 225 ± 82 ml/min, p < 0.38). Oxygen delivery increased from 1,043 ± 468 to 1251 ± 486 ml/min (24%, p ⩽ 0.001). Even in the 10 patiente who had increased concentration of plasma lactate and metabolic acidosis, oxygen consumption remained constant after increasing oxygen delivery (pretransfusion, 224 ± 101 ml/min; post-transfusion, 225 ± 99 ml/min; p ⩽ 0.83). These data have more than 99% power of detecting a change in oxygen consumption of 20 ml/min after transfusion. Therefore, we conclude that directly measured oxygen consumption remains constant and independent of increases in oxygen delivery in our patiente with severe ARDS. Because simultaneously determined oxygen consumption calculated from variables shared with the calculation of oxygen delivery yielded a dependent relationship, we speculate that finding dependence of calculated oxygen consumption on oxygen delivery may be the result of methodologic error.