The effects of neuromuscular paralysis on systemic and splanchnic oxygen utilization in mechanically ventilated patients.

OBJECTIVE

To evaluate the effect of neuromuscular paralysis on systemic and splanchnic oxygen utilization in patients in respiratory failure during controlled mechanical ventilation.

SETTING

A university-affiliated teaching hospital.

INTERVENTION

Mechanically ventilated patients, who were undergoing hemodynamics monitoring and who had a gastric intramucosal pH (pHi) of less than 7.35, were studied. Prior to paralysis, the patients were sedated with lorazepam and morphine to standard end points, and the cardiac output and oxygenation were optimized. The patients were then paralyzed with doxacurium and the ventilator rate adjusted to keep the PaCO2 at baseline value. The hemodynamic and oxygenation profile and pHi were determined prior to paralysis and repeated 2 to 2.5 h later.

RESULTS

Eight patients were studied; their mean age was 63 +/- 8 years and acute physiology and chronic health evaluation II score was 22 +/- 4. The mean fraction of inspired oxygen, positive end-expiratory pressure, and venous admixture ratio prior to the study was 0.7 +/- 0.14, 11.8 +/- 2.4 cm H2O, and 26 +/- 9%, respectively. Prior to paralysis, the mean set assist controlled ventilation rate was 15 +/- 2 breaths/min and the patient rate was 23 +/- 5 breaths/min. With neuromuscular paralysis, the cardiac index fell from 4.6 +/- 2.2 to 4.3 +/- 2.4 L/min/m2 (p=0.1), the oxygen delivery fell from 537 +/- 129 to 471 +/- 95 mL/min/m2 (p=0.03), and the oxygen consumption and extraction ratio fell from 200 +/ 77 to 149 +/- 35 mL/min/m2 (p=0.03) and 36 +/- 5 to 31 +/- 10, respectively (p=0.2). The pHi increased from 7.21 +/- 0.16 to 7.29 +/- 0.1 (p=0.02).

CONCLUSION

In critically ill patients in respiratory failure, neuromuscular paralysis decreased whole body oxygen consumption and increased pHi. Presumably, by eliminating the work of breathing, there is a redistribution of blood flow from the respiratory muscles to the splanchnic and other nonvital vascular beds.