O2 uptake in bled dogs after resuscitation with hypertonic saline or hydroxyethylstarch

Hemodynamic and metabolic variables were measured for the whole body and isolated hindlimb of anesthetized dogs during resuscitation from hemorrhagic shock, using a small volume of hypertonic saline or a larger volume of hydroxyethylstarch. Twelve dogs were bled and maintained at a mean arterial pressure (MAP) of 40 mmHg for 30 min. Six dogs were then infused with 7.5% NaCl in 5 ml/kg hydroxyethylstarch (HTS group), and six received 6% hydroxyethylstarch alone (HES group) in an amount to approximate the maximum MAP achieved with hypertonic saline. Hypertonic saline replacement was approximately 16% of shed blood volume compared with 66% for hydroxyethylstarch. With hypertonic saline, cardiac output returned to base line, but O2 delivery did not. Hydroxyethylstarch increased cardiac output above base line, and O2 delivery was near base line. O2 uptake with hydroxyethylstarch peaked at 40% above control at 10 min of resuscitation. Excess O2 uptake in recovery was higher than O2 deficit in hemorrhage with the HES group but not with the HTS group. In the isolated hindlimb, vascular resistance decreased rapidly on hypertonic saline infusion but reached similar levels at 10 min of resuscitation with both fluids. With progressive lowering of blood flow to the pump-perfused hindlimb, ability of limb muscle to extract O2 was the same for the HTS and HES groups. With hemodilution by volume replacement with acellular fluid after hemorrhage, a seemingly adequate cardiac output and arterial pressure may be underresuscitation if O2 delivery does not meet the increased O2 demand.