Introduction.
The USCOM is an ultrasonic cardiac output monitor which has recently become available in clinical practice. In essence, the USCOM works by measuring the velocity of the aortic or pulmonary blood flow as it leaves the heart. Validated internal algorithms calculate the diameter of the aortic and pulmonary valve based upon the patient's height and weight. If we know how big the pipe is and how fast the blood is flowing through it, then we know how much blood flows per minute, which is, by definition, the cardiac output. Ultrasound is incredibly accurate at measuring blood flow velocities and the validated nomogram has also been shown to give accurate predicted values for the diameters of the outflow tract of the great arteries. In the hands of an experienced user, the USCOM provides readings of cardiac output which are in the order of 98% accurate. It is the most accurate method of measuring cardiac output in clinical practice and is far superior in this regard to all the other methods such as pulmonary artery catheterisation (Swan-Ganz) which is around 80-85% accurate or PiCCO, which is about 65-70% accurate. The USCOM is also totally non-invasive.
The USCOM is much more than simply a method for measuring cardiac output however. This brief booklet outlines some of the many features that the USCOM brings to clinical practice and particularly its role in the optimisation of hemodynamics. This booklet is not intended to be the definitive work on hemodynamics, but rather a quick look-up guide to what the numbers produced by the USCOM mean in simple language and what they mean for your patients. There are many complex clinical entities covered by the global term of hemodynamics which are beyond the scope of this booklet, but a sound understanding of hemodynamics and what the USCOM can tell you, coupled to your medical knowledge and a little interpolation, should help you diagnose and treat even the most complex cardiovascular and pulmonary problems. If this guide seems basic in parts I make no apology; hemodynamics is not rocket science, but simply good basic physiology.
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