Measurement of cardiac output by nurses using a non-invasive cardiac output monitor

Amanda Corley, Dan Mullany, Adrian Barnett, John F Fraser

Critical Care Research Group, Prince Charles Hospital,Brisbane, QLD

Introduction and aims

USCOM (ultrasonic cardiac output monitor) is a non-invasive monitor which utilises continuous wave Doppler to determine cardiac output (CO). Our study compared CO measurements obtained with USCOM with those obtained using the pulmonary artery catheter (PAC), and also assessed the learning curve for use of USCOM by non-echocardiographically trained intensive care nurses.

Methods

Twenty-four patients, aged 24–65 years, who were spontaneously breathing and required PAC as part of evaluation for heart failure, were studied. Demographic and clinical data were recorded. In a blinded fashion, we compared CO obtained by USCOM with CO based on simultaneous thermodilution measurements obtained by PAC and estimated from a modified Fick equation. As each patient had multiple recordings, a generalised estimating equation was used to assess correlation between the methods. The Bland–Altman method was used to assess agreement.

Results

CO measured by PAC ranged from 2.6 to 7.1 L/min for thermodilution and from 3.1 to 8.7 L/min by Fick. USCOMderived CO was highly correlated with CO obtained by both thermodilution and the Fick method. The mean difference was − 0.35 L/min (95% CI, −0.74 to 0.04 L/min), with limits of agreement from − 1.9 to 1.2. Despite the technically difficult study population, time to optimal image acquisition decreased from 25 minutes to 5 minutes between the commencement and conclusion of the study(approximately 1 year).

Conclusions

USCOM is reliable and accurate for measuring CO. The learning curve for successful use of USCOM by an intensive care nurse is satisfactorily short, which suggests USCOM could be used by appropriately trained nursing staff to determine CO non-invasively. Further investigation of its use is required in ventilated patients.