Comparison of noninvasive cardiac output measurements using the Nexfin monitoring device and the esophageal Doppler

Abstract

Study Objective

To evaluate the validity of cardiac output (CO) measurements obtained using the Nexfin device in comparison to those obtained with the esophageal Doppler in steady-state conditions and after phenylephrine administration.

Design

Prospective observational study.

Setting

Operating room of a North American academic medical center.

Patients

25 ASA physical status 1, 2, and 3 patients referred for abdominal or orthopedic surgeries.

Interventions

After endotracheal intubation, patients who presented with a 20% or greater decrease in mean arterial pressure (MAP) received an intravenous (IV) bolus of 100 μg of phenylephrine. If MAP was still 20% lower than the patient's baseline level at least 10 minutes after the first vasopressor treatment, a second bolus of 100 μg of phenylephrine was given.

Measurements

CO was measured simultaneously by esophageal Doppler (CO_ED) and Nexfin (CO_NXF) at baseline and when blood pressure peaked after an IV 100 μg phenylephrine bolus. Comparisons were then made between the two devices to evaluate the ability of the Nexfin device to track changes in CO.

Main Results

66 pairs of data were obtained. Mean CO_ED and CO_NXF were 4.7 ± 1.8 L/min and 5.6 ± 2.0 L/min, respectively. There was a significant relationship between CO_ED and CO_NXF (r² = 0.82; P < 0.001). The agreement between CO_ED and CO_NXF was 0.88 ± 0.86 L/min (Bland Altman). The mean percent error (Critchley and Critchley) of CO_NXF versus CO_ED was 37%. Trending analysis found a 94% concordance between changes in CO_ED and CO_NXF after phenylephrine administration.

Conclusions

Intraoperative CO measurement using the Nexfin device has a strong correlation with CO measured by esophageal Doppler.

Introduction

In recent years there has been increasing interest in perioperative hemodynamic management through the incorporation of cardiac output (CO) measurements [1], [2], [3], [4]. Several technologies are now available for minimally invasive or noninvasive CO monitoring in the perioperative setting [5], [6]. However, most of these are either operator-dependent (esophageal Doppler) or require the use of intra-arterial catheters (pulse contour analysis). A new CO monitoring system based on the volume-clamp method (Nexfin; BMEYE B.V, Amsterdam, The Netherlands) was recently proposed for noninvasive and continuous CO monitoring. This method uses the area under the systolic part of the blood pressure waveform as input into an algorithm incorporating patient-specific aortic vascular characteristics to calculate beat-to-beat stroke volume (SV) and CO [7], [8]. This device is noninvasive, relatively simple, and nonoperator-dependent [7], and it has been tested in healthy volunteers during orthostasis and for optimization of cardiac resynchronization therapy [9], [10]. It has also been compared with thermodilution CO measurements in 25 awake patients after coronary artery bypass surgery [11]. All of these previous studies suggest that Nexfin CO readings have the potential to be used for intraoperative hemodynamic optimization. Currently we lack data focusing on the accuracy and trending abilities of this device during general anesthesia. Moreover, pulse contour analysis methods may be impacted by the administration of vasopressors [12], [13], [14] such as phenylephrine [15].

The esophageal Doppler is a minimally invasive hemodynamic monitoring device that measures beat-to-beat blood flow in the descending aorta. Cardiac output is then determined by multiplying the cross-sectional area of the aorta by blood flow velocity integrated over time [16], [17]. Hemodynamic optimization using Doppler-derived CO measurements leads to a decrease in perioperative morbidity and in postoperative intensive care unit (ICU) length of stay [18], [19]. This device was an acceptable surrogate for an invasive CO trending monitor in studies that evaluated the accuracy of new CO monitors [20], [21] and in studies focusing on fluid responsiveness [22], [23].

The goals of our study were to compare the CO measuring capabilities of the Nexfin device with those of the esophageal Doppler during general anesthesia and after phenylephrine administration.