Hemodynamic and metabolic effects of morphine in the critically ill

To assess the effects of i.v. injection of morphine, 0.5 mg/kg, hemodynamic studies were performed on 24 critically ill patients under controlled ventilation. An esophageal balloon was used to estimate intrapleural pressure and transmural cardiac filling pressures were calculated. After injection of morphine, there were significant decreases in heart rate (13%), cardiac index (18%), stroke index (17%) and arterial pressure (15%) and there was a nonsignificant increase in esophageal pressure (15%). Transmural cardiac filling pressures decreased significantly (21% for the pulmonary wedge pressure); intravascular filling pressures were unchanged. Oxygen consumption decreased significantly, by 21%, in 10 patients with initially elevated oxygen consumption and by 9% in 14 patients with initially normal oxygen consumption. The oxygen extraction ratio was unchanged, suggesting that the decrease in oxygen consumption was caused by decreased oxygen demand rather than by inadequate oxygen delivery. These results indicate that the hemodynamic effects of morphine (0.5 mg/kg) administered to critically ill patients were associated with a significant decrease in oxygen consumption, which probably reflected sedation and analgesia.