title: Accuracy and precision of the ultrasound cardiac output monitor (USCOM 1A) in pregnancy: comparison with three-dimensional transthoracic echocardiography.
abstract: BACKGROUND
  Cardiac output (CO) monitoring is helpful in the assessment of critically ill pregnant women, but invasive monitors are often unsuitable for use. We aimed to measure agreement between the non-invasive ultrasound cardiac output monitor (USCOM) and three-dimensional transthoracic echocardiography (3D-TTE) in pregnant women.
  
  
  METHODS
  Healthy pregnant women from 25 weeks gestation onwards participated. In the left lateral position at rest, CO was measured with the USCOM and 3D-TTE. A single operator performed all USCOM measurements, with a different operator performing all echocardiography. Both were blinded to results from the other device. Each USCOM trace was analysed using two modes: flowtrace (FT) and touchpoint (TP). A second, blinded USCOM reading was taken to assess reproducibility.
  
  
  RESULTS
  USCOM readings were obtained in 92, and 3D-TTE images in 85 participants. The mean CO was 5.7, 7.7, and 6.2 litre min(-1) measured by 3D-TTE, USCOM FT, and USCOM TP, respectively. USCOM bias was +2.0 litre min(-1) (FT) and +0.4 litre min(-1) (TP). Limits of agreement were -0.2 to +4.2 litre min(-1) (FT) and -1.4 to +2.3 litre min(-1) (TP). The mean percentage difference was 32.6% (FT) and 31.4% (TP) for CO and 27.0% (FT) and 27.5% (TP) for stroke volume. Intraclass correlation between repeated USCOM readings was 0.9 (FT) and 0.86 (TP).
  
  
  CONCLUSIONS
  USCOM has acceptable agreement with 3D-TTE for the measurement of CO in pregnancy. The positive bias of the USCOM, particularly in the FT mode, may be due to the hyperdynamic cardiovascular state in pregnancy. We suggest using the TP mode in this patient population.
authors.affiliation: Tom Bryson Department of Anaesthesia, Liverpool Women's Hospital, Liverpool, UK helenmcnamara@doctors.org.uk.
authors.forename: H
authors.initials: H
authors.lastname: McNamara
authors.affiliation: Tom Bryson Department of Anaesthesia, Liverpool Women's Hospital, Liverpool, UK.
authors.forename: P
authors.initials: P
authors.lastname: Barclay
authors.affiliation: Department of Cardiology, Royal Liverpool University Hospital, Liverpool, UK.
authors.forename: V
authors.initials: V
authors.lastname: Sharma
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology; D002302:Cardiac Output / Q000502:physiology*; D016638:Critical Illness; D004452:Echocardiography / Q000379:methods*; D019560:Echocardiography, Three-Dimensional / Q000379:methods*; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008991:Monitoring, Physiologic / Q000295:instrumentation* / Q000379:methods*; D015588:Observer Variation; D011247:Pregnancy / Q000502:physiology*; D015203:Reproducibility of Results; D013815:Thermodilution / Q000379:methods
keywords: heart, cardiac output; measurement techniques, cardiac output; monitoring, echocardiography; monitoring, ultrasound; pregnancy