Functional haemodynamic monitoring.

Abstract

Functional haemodynamic monitoring is the assessment of the dynamic interactions of haemodynamic variables in response to a defined perturbation. Fluid responsiveness can be predicted during positive pressure breathing by variations in venous return or left ventricular output using numerous surrogate markers, such as arterial pulse pressure variation (PPV), left ventricular stroke volume variation (SVV), aortic velocity variation, inferior and superior vena cavae diameter changes and pulse oximeter pleth signal variability. Similarly, dynamic changes in cardiac output to a passive leg raising manoeuvre can be used in any patient and measured invasively or noninvasively. However, volume responsiveness, though important, reflects only part of the overall spectrum of functional physiological variables that can be measured to define physiologic state and monitor response to therapy. The ratio of PPV to SVV defines central arterial elastance and can be used to identify those hypotensive patients who will not increase their blood pressure in response to a fluid challenge despite increasing cardiac output. Dynamic tissue O2 saturation (StO2) responses to complete stop flow conditions, as can be created by measuring hand StO2 and occluding flow with a blood pressure cuff, assesses cardiovascular sufficiency and micro-circulatory blood flow distribution. They can be used to identify those ventilator-dependent individuals who will fail a spontaneous breathing trial or trauma patients in need of life-saving interventions. Functional haemodynamic monitoring approaches are increasing in numbers, conditions in which they are useful and resuscitation protocol applications. This is a rapidly evolving field whose pluripotential is just now being realized.