Prognostic value of low cardiac output early after cardiac surgery

Introduction

The benefit of routine measurement of cardiac output after cardiac surgery is still discussed. Some studies found no benefit of routine right heart catheterisation [1] while others found a reduce length of stay [2]. Clinical prediction of cardiac output is poor after cardiac surgery [3]. Clinicians also do not really know what value of cardiac output is necessary after cardiac surgery. The aim of the present study was to verify whether the commonly accepted lower value of cardiac index of 2.2 l/min/m² [4] at arrival in the ICU was a good predictor of complications after cardiac surgery.

Methods

Seventy-three consecutive patients with a value of cardiac index lower than or equal to 2.2 were included in a prospective observational study. Right heart catheterisation was decided in the operating room if the patient had a complex surgery or a left ventricular dysfunction. Routine hemodynamic measurements were performed at arrival in the ICU, 2, 6 and 18 hours later and included arterial and mixed venous blood gases. Postoperative complications were defined as death, renal insufficiency, and need for prolonged mechanical ventilation.

Results

Fifty-one patients had no complication (Group 1), and 22 patients (Group 2) present a postoperative complication (including four deaths). No difference was found between the two groups for preoperative or intraoperative data (age, ejection fraction, EuroSCORE, length of bypass or aortic clamp) or for the blood lactate level, pH or base excess. At the arrival in the ICU and 18 hours later, hemodynamic parameters were similar between the two groups. Complicated patients had lower cardiac output and SVO₂ values 2 and 6 hours after the arrival in ICU. In the logistic regression analysis, a reduced cardiac index at 2 and 6 hours after admission in the ICU had the strongest independent predictive value for postoperative complication.

Discussion

A low cardiac output 2 or 6 hours after arrival in the ICU is associated with a high level of postoperative complication. Using right heart catheterisation allows early prediction and treatment of low cardiac output in order to prevent postoperative complication [2].