[Noninvasive determination of cardiac output in ventilated patients . Clinical evaluation of a simplified quick method]

Abstract

Objective: This study was performed to evaluate a new simplified rebreathing method to determine cardiac output (CO) in mechanically ventilated patients.

Methods: Using a rebreathing system (AMIS 2001, Innovision, Dänemark), effective pulmonary blood flow (PBF) and oxygen consumption (V(radical)O2) were determined non-invasively in 40 patients. After estimation of arterial (CaO2) and capillary oxygen (CcO2) content from the results of an arterial blood gas analysis, intrapulmonary shunt was calculated as Q(s)/Q(t) = [CcO2CaO2] * PBF/V(radical)O(2). Cardiac output was determined by the rebreathing method as CO(rb) = PBF/(1- Q(s)/Q(t)). The cardiac output measured by thermodilution (CO(thd)) was used to determine reference values, which were calculated as mean value of CO(thd) and CO(rb). Intrapulmonary shunt calculated from arterial and mixed-venous blood gas analyses served as reference for the non-invasive determination. In addition, reproducibility of the new method was determined in 15 patients.

Results: CO(thd) varied from 3.7-9.5 l/min (6.1 +/- 1.6 l/min; mean +/-SD). Bias and precision of CO(rb) determination accounted for 0.18 l/min (2.9%) and +/- 0.61 l/min (10%), respectively. Precision of intrapulmonary shunt measurement accounted for +/-2.1%. Reproducibility of the CO measurements accounted for 0.24 l/min or 3.9%.

Conclusion: The rebreathing system evaluated in the present study allows the noninvasive determination of cardiac output with rather high accuracy and good reproducibility. However, technical improvement and further investigation in patients with extremely high cardiac output and shunt values will be needed before its routine clinical use.