Oxygen delivery-consumption relationship in adult respiratory distress syndrome patients: The effects of sepsis

The oxygen consumption-delivery relationship (VO2/O₂) was studied in 15 sedated paralyzed patients with the adult respiratory distress syndrome (ARDS) due to multiple trauma and in whom sepsis was absent. Different levels (0 to 15 cm H2O) of positive end-expiratory pressure (PEEP) were applied. Oxygen delivery was calculated from cardiac index (thermodilution technique) and arterial oxygen content measurements. Oxygen consumption was calculated using Fick's equation. Regression lines were obtained for each patient. Oxygen supply dependency was defined as a significant (P < .05) relationship between changes in O2 and O₂ with PEEP. Results were compared with those obtained in 18 ARDS patients in whom ARDS was due to sepsis. In nonseptic ARDS patients no significant relationship between changes in VO2 and O₂ with PEEP was found within the experimental range of O₂ on zero end-expiratory pressure (ZEEP) (347 to 845 mL/min/m²). None of these patients had multiple organ system failure (MOSF), and 73% survived. In ARDS patients in whom sepsis was present, supply dependency was present only when O₂ on ZEEP ranged between 330 and 640 mL/min/m². All these patients developed MOSF and died. When O₂ on ZEEP ranged between 686 and 951 mL/min/m² in septic ARDS patients, the supply dependency phenomenon was absent and only three patients developed MOSF and died (70% survivors). In almost all patients PEEP reduced O₂ and therefore worsened OZ balance by either increasing OZ extraction ratio and approaching the critical threshold for supply dependency or dismissing O₂ from the range of non-supply dependency.