The level of accuracy and precision of each device needs to be understood as the data cannot be superimposed from one system to another. The advantages of these arterial pressure-based cardiac output monitoring systems over PAC-derived measurements is primarily kinase inhibitor Brefeldin A their less invasive nature.The major weakness of all these devices is the drift in values whenever there is a major change in vascular compliance, as, for example, in vascular leak syndrome with increased vessel wall edema leading to decreased arterial compliance. Aortic valve regurgitation may further decrease the accuracy of these techniques. Over-or under-damped arterial pressure waveforms will also decrease the precision of these monitors.Echocardiography and echo-DopplerEchocardiography allows measurement of cardiac output using standard two-dimensional imaging or, more commonly, Doppler-based methods.

The main interest in echocardiography in general is that it can be used not only for measurement of cardiac output but also for the additional assessment of cardiac function. Echocardiography is particularly useful as a diagnostic tool because it allows the visualization of cardiac chambers, valves and pericardium. Small ventricles (‘kissing ventricles’) may incite fluid administration whereas a poorly contractile myocardium may suggest that a dobutamine infusion is a better choice. Right ventricular dilatation may orient towards the diagnosis of massive pulmonary embolism or myocardial infarction whereas the presence of pericardial fluid may suggest a diagnosis of pericardial tamponade.

Severe valvulopathy can also be recognized promptly. However, echocardiography instruments and expertise may not be readily available everywhere; in some institutions, this is still the domain of the cardiologists and they need to be called to do the procedure.If an ultrasound beam is directed along the aorta using a probe, part of the ultrasound signal will be reflected back by the moving red blood cells at a different frequency. The resultant Doppler shift in the frequency can be used to calculate the flow velocity and volume and hence cardiac output. Echo-Doppler evaluation can provide reasonable estimates of cardiac output, but again is operator-dependent and continuous measurement of cardiac output using this technique is not possible. Echo-Doppler evaluation may be applied either transthoracically or transesophageally.

However, transthoracic techniques do not always yield good images and transesophageal techniques are more invasive such that some sedation, and often endotracheal intubation, is required in order to obtain reliable measurements. Moreover, the esophageal probe is uncomfortable in non-intubated patients, although may be better tolerated if inserted nasally, and should Entinostat be used cautiously in patients with esophageal lesions.