Critical Hematocrit in Intestinal Tissue Oxygenation during Severe Normovolemic Hemodilution

Abstract

A critical point in oxygen supply for microvascular oxygenation during normovolemic hemodilution has not been identified. The relation between organ microvascular oxygen partial pressure (μPo2) and organ oxygen consumption (JOURNAL/anet/04.02/00000542-200101000-00026/ENTITY_OV0312/v/2017-07-22T060359Z/r/image-pngo2) during a decreasing oxygen delivery (Do2) is not well understood. The present study was designed to determine the systemic hematocrit and organ Do2 values below which organ μPo2 and JOURNAL/anet/04.02/00000542-200101000-00026/ENTITY_OV0312/v/2017-07-22T060359Z/r/image-pngo2 cannot be preserved by regulatory mechanisms during normovolemic hemodilution.

Eighteen male Wistar rats were randomized between an experimental group (n = 12), in which normovolemic hemodilution was performed with pasteurized protein solution (PPS), and a control group (n = 6). Systemic hemodynamic and intestinal oxygenation parameters were monitored. Intestinal μPo2 was measured using the oxygen-dependent quenching of palladium-porphyrin phosphorescence.

Baseline values in hemodilution and control group were similar. Hemodilution decreased hematocrit to 6.2 ± 0.8% (mean ± SD). Constant central venous pressure measurements suggested maintenance of isovolemia. Despite an increasing mesenteric blood flow, intestinal Do2 decreased immediately. Initially, μPo2 was preserved, whereas mesenteric venous Po2 (Pmvo2) decreased; below a hematocrit of 15%, μPo2 decreased significantly below Pmvo2. Critical Do2 was 1.5 ± 0.5 ml·kg−1·min−1 for JOURNAL/anet/04.02/00000542-200101000-00026/ENTITY_OV0312/v/2017-07-22T060359Z/r/image-pngo2, and 1.6 ± 0.5 ml·kg−1·min−1 for μPo2. Critical hematocrit values for JOURNAL/anet/04.02/00000542-200101000-00026/ENTITY_OV0312/v/2017-07-22T060359Z/r/image-pngo2 and μPo2 were 15.8 ± 4.6% and 16.0 ± 3.5%, respectively.

Intestinal μPo2 and JOURNAL/anet/04.02/00000542-200101000-00026/ENTITY_OV0312/v/2017-07-22T060359Z/r/image-pngo2 were limited by a critical decrease in Do2 and hematocrit at the same time. Beyond these critical points not only shunting of oxygen from the microcirculation could be demonstrated, but also a significant correlation between intestinal μPo2 and JOURNAL/anet/04.02/00000542-200101000-00026/ENTITY_OV0312/v/2017-07-22T060359Z/r/image-pngo2.