Relationship between intra- and postoperative oxygen transport and prolonged intensive care after cardiac surgery: a prospective study

Background: Prolonged intensive care is a rare but serious complication of cardiac surgery. It is required in less than 10% of operated patients but they use more than 30% of all the intensive care resources needed for cardiac surgery. The aim of our study was to describe the clinical course of the patients who need prolonged intensive care following cardiac surgery and to assess whether the intra- and postoperative oxygen transport variables are different in these patients as compared to patients with an uncomplicated course.
Methods: The study patients were divided into two groups according to the length of stay in the intensive care unit (ICU) after the operation: Group I, n=241, ICU-stay 5 days and Group II, n=20, ICU-stay≥5 days. Hemodynamic and oxygen transport data were prospectively obtained intra- and postoperatively and postoperative organ dysfunctions were recorded.
Results: The patients in the prolonged intensive care group tended to be older, have lower ejection fraction and longer cardiopulmonary bypass time. Postoperatively, this group had significantly increased oxygen extraction rate ( P =0.035, repeated measures for ANOVA). In the logistic regression analysis, in creased oxygen extraction (31% in Group I vs. 36% in Group II, P < 0.005) at 6 hours after arrival at the intensive care unit had the strongest independent association with the need for prolonged intensive care.
Conclusions: There was no significant relationship between the factors conventionally assumed to be risk factors for prolonged intensive care. Instead, an increase in whole body oygen extraction, reflecting a mismatch between the whole body oxygen demand and supply, was associated with the need for prolonged intensive care. Oxygen extraction increased to compensate for the reduced oxygen delivery, which in turn was caused by a lower arterial oxygen content.