The hemodynamic effect of rapid fluid infusion in critically ill patients

Abstract

The response to a rapidly administered volume infusion (250 ml of 5% albumin over 30 minutes) was studied in 28 critically ill patients. Cardiovascular responses were assessed by means of invasive hemodynamic parameters (i.e., cardiac index [CI], central venous pressure [CVP], pulmonary artery pressure [PAP], and pulmonary capillary wedge [PCWP] pressure as well as radionuclide [RN] angiography). This allowed for the simultaneous measurement of right (RVEF) and left (LVEF) ejection fractions, and right (RVEDV) and left end-diastolic (LVEDV) and end-systolic (LVESV) volumes. Twenty patients responded (R) to volume infusion by demonstrating an increase in stroke volume. This response was secondary to an increase in LVEDV in 11 (R-1) and an increase in the LVEF in nine (R-2). Neither response was predictable before treatment. The responders also demonstrated a significant decrease in heart rate (P less than 0.05). The increased ejection fraction in some responders (R-2) was associated with a decrease in systemic vascular resistance index (SVRI) (P less than 0.05) and LVESV (P less than 0.05) suggesting a reduced afterload secondary to peripheral vasodilation concomitant on volume change. The PCWP appeared to be related more to right ventricular (RV) loading factors (i.e., CVP, RVEDV, and pulmonary vascular resistance [PVRI] [R2 = 0.85, P less than 0.005]) then to the LVEDV (P = NS). Left ventricular (LV) loading with volume infusion appeared to be dependent on both RV performance and the PVRI in some patients, since responders who increased the LVEDV (R-1) were characterized by a simultaneous increase in RV stroke work and decrease in PVRI. The response to fluid infusion in critically ill patients is complex with both increases in LVEF and LV preload contributing to its beneficial effect. Clinical assessment of LV filling pressures (PCWP) does not accurately predict the response to volume infusion and does not allow a reliable assessment of the LV preload. This is most likely due to the broad range of LV compliance characteristics noted in critically ill patients. RV function also appears to be important in the clinical response to volume challenge.