Hemodynamic parameters to guide fluid therapy

The clinical determination of the intravascular volume can be extremely difficult in critically ill and injured patients as well as those undergoing major surgery. This is problematic as fluid loading is considered the first step in the resuscitation of hemodynamically unstable patients. Yet, multiple studies have demonstrated that only about 50% of hemodynamically unstable patients in the ICU and operating room respond to a fluid challenge. Cardiac filling pressures including the central venous pressure and pulmonary artery occlusion pressure have traditionally been used to guide fluid management. However, studies performed over the last 30 years have demonstrated that cardiac filling pressures are unable to predict fluid responsiveness. Over the last decade a number of studies have been reported that have used heart–lung interactions during mechanical ventilation to assess fluid responsiveness. Specifically, the pulse pressure variation derived from analysis of the arterial waveform, the stroke volume variation derived from pulse contour analysis and the variation of the amplitude of the pulse oximeter plethysmographic waveform have been shown to be highly predictive of fluid responsiveness. While the left ventricular end-diastolic area as determined by transesophageal echocardiography is a more accurate measure of preload than either the central venous pressure or pulmonary artery occlusion pressure, it does not predict fluid responsiveness as well as the dynamic indices. This paper reviews the evolution and accuracy of methods for assessing fluid responsiveness in patients in the ICU and operating room.