AJP - Heart and Circulatory Physiology, Vol 250, Issue 3 342-H350, Copyright © 1986 by American Physiological Society
Continuous blood densitometry: fluid shifts after graded hemorrhage in animals
H. Hinghofer-Szalkay
To evaluate rapid fluid shifts after graded hemorrhage in splenectomized
animals, four pigs and two dogs were bled 15-23 ml/kg body wt in steps of
2.2-6.0 ml/kg. Arterial blood density (BD), mean arterial pressure (MAP),
and central venous pressure (CVP) were recorded continuously, and arterial
plasma density (PD) and hematocrit (Hct) were determined from blood
samples. Erythrocyte density was computed from PD, BD, and Hct. Starting
with stable control conditions, MAP, CVP, and BD fell from the beginning of
hemorrhage. Each blood withdrawal was followed by an immediate and rapid
decrease in BD, even at the lowest (less than 3 ml/kg) initial blood
losses. The time course of BD change mirrored that of the volume
replacement, with time constants of 3.0-9.6 min and amplitudes depending on
the magnitude of the relative volume loss. The PD decrease was significant
(P less than 0.01) after 5.4 +/- 0.7 ml/kg hemorrhage. At 15 ml/kg blood
loss the mean PD and BD had dropped by 0.99 +/- 0.15 and 2.42 +/- 0.26 g/l,
respectively, and Hct had dropped by 2.40 +/- 0.47 units. Calculations
suggest that either the inward-shifted fluid has a higher density than
normal ultrafiltrate and/or there is a rise of the whole-body-to-large
vessel Hct (F cell ratio). The rapid fluid replacement ranged from 5.8 +/-
0.8 to 10.6 +/- 2.0% of the initial plasma volume, or one-fifth to
one-third of the lost volume with a 20% hemorrhage. Transvascular fluid
shifts can be monitored with continuous high-precision blood densitometry.
