Reliability of clinical monitoring to assess blood volume in critically ill patients

TLDR

Blood volume was quantified by indicator dilution in over 1,500 critically ill patients and compared with MAP, CVP, wedge pressure, hematocrit, and cardiac output. Despite significant changes during resuscitation and fluid loading, these monitored variables showed poor correlation with actual blood volume, indicating they inadequately reflect volume status in critical illness.

Abstract

Blood volumes measured by indicator dilution method in over 1500 instances of critically ill patients of various etiologies and at various times throughout their critical illness were compared with the values of concomitantly measured mean arterial pressure (MAP), CVP, pulmonary arterial wedge pressure (WP), Hct, and cardiac output. During resuscitation from hypovolemic shock, the patients' blood volumes and the monitored variables were significantly altered. However, there were poor correlations between the extent of blood volume changes and these variables during resuscitation as well as throughout the critical illness, irrespective of the etiologic type or stage of shock. With administration of a fluid load, blood volume and values of the commonly monitored variables improved appropriately, but the correlation coefficients, in general, were not good. The data suggest that the commonly monitored variables, in and of themselves, do not reflect adequately the blood volume status in critically ill patients.