Noninvasive cardiac output: accuracy between the ultrasound cardiac output monitor and the esophageal Doppler monitor
KeywordsCardiac Index Pulmonic Valve Measure Blood Flow Cardiac Output Measurement Doppler Probe
The hypothesis is that measurement of the cardiac index (CI) is accurate between the ultrasound cardiac output monitor (USCOM) and the esophageal Doppler monitor (EDM). The EDM is a minimally invasive device that has demonstrated strong correlation with cardiac output measurements obtained by thermodilution. A disadvantage of the EDM is the need for probe placement in the esophagus, effectively limiting its use to mechanically ventilated patients. The USCOM, in contrast, can measure cardiac hemodynamics by use of a CW Doppler probe placed on the skin to measure blood flow across either the aortic or pulmonic valve.
A prospective study of adult ED patients who were intubated and managed concurrently with an EDM. Setting: urban tertiary care center with >90,000 annual visits. Exclusion criteria: ESRD, ascites, known valvular heart disease and pre-existing tracheotomy. IRB approval was obtained with waiver of informed consent. USCOM measurements of CI were obtained, blinded to EDM values measured concurrently. Repeated pairs were obtained every 30–60 minutes, in a similar manner. Statistical analysis: correlation and Bland–Altman plots using SPSS 9.0.
A total of 95 paired measures were obtained from 20 patients with an average age of 60.1 years, 60% male and 70% African American. The mean CI was 5.2 with a range of 1.4–6.6 l/min/m2. For the aggregate, r = 0.81 (P < 0.001) and bias was 0.14 with limits of agreement (LOA) of -1.48 to 1.76. Excess scatter was noted at CI > 4.0 CI. For CI < 4.0, correlation was 0.80 (P < 0.001) with bias and LOA of -0.15 and -1.01 to 0.71. At CI < 2.5, greater accuracy was noted with bias of 0.01 and LOA of 0.73 to 0.75.
CI measurement with the USCOM has a high degree of agreement with the EDM, most notably when CI is below 4.0. Of particular interest is the high degree of accuracy seen at low CI values (<2.5). These findings support the use of the USCOM for CI measurement in mechanically ventilated patients and a wider range of patients in which the EDM would be impractical or difficult to use.