Australian and New Zealand Journal of Obstetrics and Gynaecology 2009; 49: 142– 144 DOI: 10.1111/j.1479-828X.2009.00948.x 142 © 2009 The Authors Journal compilation © 2009 The Royal Australian and New Zealand College of Obstetricians and Gynaecologists Blackwell Publishing Asia Original Article Measurement of cardiac output in normal pregnancy by a non-invasive two-dimensional independent Doppler device Catharina C. M. KAGER, Gus A. DEKKER and Monique C. STAM Department of Obstetrics and Gynaecology, Lyell McEwin Hospital, University of Adelaide, Adelaide, South Australia, Australia Aims: To compose a normogram regarding cardiac output during pregnancy measured with ultrasonic cardiac output monitor (USCOM), a non-expensive simple continuous wave Doppler device and to investigate if this machine could be useful for haemodynamic monitoring during pregnancy. Methods: Cardiac output was measured in 172 pregnant women with a gestational age < 21 weeks (n = 59), 21–32 weeks (n = 48), and > 32 weeks’ gestation (n = 48). Interobserver differences were determined by measuring 24 patients and comparing results between three different observers. Results: A good signal could be obtained in 155 (90.2%) pregnant women. Haemodynamic profiles were in line with data published in the literature. In 9.8 % of cases it was difficult to get a good result. Interobserver variations between the research officer (CK) and two clinicians were good (r = 0.9359 and r = 0.9609). Conclusion: USCOM appears to be a reliable and fast method to measure cardiac output compared with existing highly complex ultrasounds machines used in cardiology. It is easy to learn, cheap and quite reproducible between different observers. Further research is required to define its place in the management of hypertensive complications during pregnancy. Key words: haemodynamics, pregnancies, ultrasound. Introduction Blood pressure measurement is essentially a very crude way to assess an individual’s haemodynamic profile, because it is made up by two major components: cardiac output and systemic vascular resistance (SVR). From a haemodynamic perspective it makes sense to treat a pregnant hypertensive patient with an appropriate, that is, haemodynamically tailored drug, for example nifedipine for those with primarily vasospasm and for instance labetalol if increased cardiac output is the main culprit. Some large USA centres have started to use this haemodynamically targeted approach in the treatment of pre-eclamptic patients. 1 The major haemodynamic changes that occur already in the very early stages of pregnancy have been described in detail, the primary change being a massive drop in SVR, followed by an increase in cardiac output and circulating blood volume. 2 There are different techniques to assess the haemodynamic status. The gold standard is the Swan–Ganz pulmonary artery catheter (PAC). This monitoring device is primarily used in an intensive care. PAC is an invasive technique and associated with some limitations and significant risks. PAC requires central venous access and is associated with a range of complications like haemorrhage, pulmonary infarction and cardiac dysrhythmias. 3 Another technique is the pulsed Doppler echocardiography technique. This is a non-invasive technique. Research shows that this technique is reliable when compared with PAC as gold standard. 4 A problem with this technique is that the outflow tract diameter has to be calculated and to do that the cross-sectional area of the vessel needs to be measured by a two-dimensional echocardiogram, a relatively complex procedure, requiring quite costly ultrasound equipment. A modification of the pulsed Doppler echocardiography technique described above is the ultrasonic cardiac output monitor (USCOM Pty Ltd, Sydney, NSW, Australia). This technique was introduced for clinical use in 2004. This is a non-invasive continuous-wave Doppler technique to measure cardiac output and subsequently calculate the haemodynamic profile. It is based on the assumption that the outflow tract diameter correlates linearly with height; so when a patient’s height is known, cardiac output and derived haemodynamics can be calculated. 5,6 This methodology could provide a Correspondence: Professor Gus A. Dekker, Department of Obstetrics and Gynaecology, Lyell McEwin Hospital, University of Adelaide, Haydown Road, Elizabeth Vale, 5112 SA, Australia. Email: gustaaf.dekker@adelaide.edu.au This research was not supported by USCOM Pty Ltd, Sydney, NSW, Australia, and was performed totally independent from USCOM. Received 18 January 2008; accepted 14 September 2008.