Bench-to-bedside review: functional hemodynamics during surgery - should it be used for all high-risk cases?

Abstract

The administration of a fluid bolus is done frequently in the perioperative period to increase the cardiac output. Yet fluid loading fails to increase the cardiac output in more than 50% of critically ill and surgical patients. The assessment of fluid responsiveness (the slope of the left ventricular function curve) prior to fluid administration may thus not only help in detecting patients in need of fluids but may also prevent unnecessary and harmful fluid overload. Unfortunately, commonly used hemodynamic parameters, including the cardiac output itself, are poor predictors of fluid responsiveness, which is best assessed by functional hemodynamic parameters. These dynamic parameters reflect the response of cardiac output to a preload-modifying maneuver (for example, a mechanical breath or passive leg-raising), thus providing information about fluid responsiveness without the actual administration of fluids. All dynamic parameters, which include the respiratory variations in systolic blood pressure, pulse pressure, stroke volume and plethysmographic waveform, have been repeatedly shown to be superior to commonly used static preload parameters in predicting the response to fluid loading. Within their respective limitations, functional hemodynamic parameters should be used to guide fluid therapy as part of or independently of goal-directed therapy strategies in the perioperative period.

Figure 1

Static and dynamic parameters used to guide fluid management. (a) Receiver operating characteristic curves of static parameters: left ventricular end-diastolic area (EDAi), intra-thoracic blood volume index (ITBVI), mean arterial pressure (MAP) and central venous pressure (CVP). (b) Receiver operating characteristic curves for functional hemodynamic parameters: respiratory systolic variation test (RSVT), systolic pressure variation (SPV), pulse pressure variation (PPV), Delta down (dDown) and stroke volume variation (SVV). Note the obvious superiority of dynamic parameters over static parameters in predicting fluid responsiveness. Reproduced with permission from [15].

Figure 2

The arterial pressure waveform. (a) Responder and (b) nonresponder.

Figure 3

Principles for calculation of dynamic parameters based on the hemodynamic effects of a mechanical breath. (a) Systolic pressure variation. (b) Pulse pressure variation. PPmax, maximum pulse pressure; PPmin, minimum pulse pressure. (c) Stroke volume variation. SVmax, maximum stroke volume; SVmin, minimum stroke volume.