Authors: Kanishka Indraratna.
Severe vasodilatation during cardiac surgery has been known for many years. It is characterized by a low systemic vascular resistance, a high cardiac index, and a low blood pressure, which can be resistant to even high doses of vasoconstrictors. This condition is associated with a high mortality. After cardiac surgery, there can be cardiac dysfunction as well. However with a low systemic vascular resistance, the cardiac function curve would be shifted upwards and to the left, giving the impression of good contractility. The ejection fraction, which is the commonly used measurement of cardiac contractility, cannot therefore be relied upon for a correct assessment under these circumstances. This can affect fluid and inotrope management. Therefore a measurement which does not depend on the afterload, but measures pure myocardial contractility is required. Ventricular elastance is such a measure. A measurement of arterial elastance which reflects the flow characteristics and pulsatility of flow may be more appropriate than systemic vascular resistance to measure arterial tone. Ventricular-arterial coupling has to be maintained for optimum myocardial performance. The severe vasodilatation, the possible myocardial impairment and also its treatment with high doses of vasoconstrictors can affect the relationship between the ventricular and arterial systems. Therefore measurement of ventricular arterial coupling is also important.
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