Clinical death and the measurement of stressed vascular volume

Objectives To measure stressed vascular volume in humans and to review the concepts of stressed and unstressed vascular volume. Design Observational study during surgical procedure. Setting Operating room at a university hospital. Patients Five patients undergoing hypothermic circulatory arrest for surgery on major vessels. Intervention We measured the volume that drained from the patient to the reservoir of the pump when the pump was turned off. Measurements and Main Results Stressed volume was 20.2 +/- 1.0 mL/kg, which is 30% of the predicted blood volume of these patients. Conclusion The amount of blood volume that determines vascular filling pressure is only about a quarter of the total predicted volume, which means that there is a large reserve of unstressed volume that can be recruited to maintain vascular filling pressure. (Crit Care Med 1998; 26:1061-1064)