Arterial pressure based cardiac output in the septic patient

Introduction

In the treatment of severe sepsis and septic shock inotropes, vasopressors and vasodilatation drugs are needed to improve cardiac performance and microcirculation. The cardiac output is used to measure the cardiac performance. Pulmonary artery catheter (PAC)-based cardiac output measuring is often used but major complications can occur. A cornerstone and also a quality indicator of intensive care medicine is the prevention of complications within the intensive care. Alternative methods to measure cardiac output are developed to minimize complications. Until now, every new introduced method has been shown to have limitations. One of the latest alternatives is arterial pressure-based cardiac output (APCO) measuring.

Objective

To assess the usefulness of APCO in critically ill patients with severe sepsis and septic shock.

Methods

Patients with severe sepsis or septic shock who needed a PAC to guide therapy were connected to the APCO FlowTrac^™ (Edwards Lifesciences, Irvine, CA, USA). Data collected from the APCO were evaluated and compared with the intermitted cardiac output measurement using the PAC. Results of both observational methods are compared using the Blend-Altman method.

Patients

In this study the results of the first 10 patients are analysed. The mean age is 72 years (36–86 years).

The mean APACHE II score is 23 (18–31). The severe sepsis originated from the abdomen in five patients. The other five cases originated from the lungs.

Results

A total of 208 cardiac output measurements have been obtained in critically ill patients of different origin. Comparing the different cardiac output measurements in the individual patient, we found a comparable trend in both methods. The presence of a tricuspid and or mitral valve regurgitation should be known when using the PAC-based cardiac output, especially when comparisons are made. There is an interesting difference in subgroup analysis when valvular abnormalities are considered. Significant differences were found between patients with and without valvular abnormalities (Mann-Whitney U test; P < 0.001). A moderate correlation was seen for the group of patients with valvular abnormalities between the magnitude of the cardiac output and the size of the difference between monitoring methods (Pearson's r = 0.53; P < 0.001), whereby bigger differences were found for higher cardiac output volumes. Correcting for this output-size effect, the difference between monitoring methods remained significantly higher (mean diff.: 1.53; 95% limits of agreement: -1.57 to 4.63) for patients with valvular abnormalities (Mann-Whitney U test; P < 0.001).

Conclusion

To us, the exact algorithm used by the APCO to calculate the cardiac output is unknown. Nevertheless we find comparable cardiac output measurements in patients with severe sepsis and septic shock. Because of this we think there is a place in clinical use of the APCO in the treatment of critically ill patients with severe sepsis and septic shock. More research is needed to fully understand the APCO and its implications.