Oxygen transport in hemorrhagic shock as a function of the hematocrit ratio

¹ Department of Physiology and Biophysics, University Medical Center, Jackson, Mississippi

The oxygen consumption, arterial and venous oxygen concentration, and the arterial blood pH were measured, and the cardiac output, peripheral resistance and maximum oxygen transport capacity determined in 75 dogs with different hematocrit ratios in which the blood pressure had been maintained at 30 mm Hg for 15 minutes. The O₂ consumption increased as the hematocrit ratio increased until the hematocrit ratio reached 42. However, an increase in the hematocrit ratio above 42 caused a decrease in O₂ consumption. This optimal hematocrit ratio occurs because of the dual role of the hematocrit ratio in determining O₂ content of blood and blood viscosity. A curve obtained by multiplying cardiac output times arterial O₂ showed that when the hematocrit ratio is 42 the O₂ transport is maximal. The oxygen consumed by the animal was determined by the oxygen available. Arterial blood pH was highest in those dogs with the greatest oxygen consumption, but the pH was below limits compatible with life in the anemic animals. Total peripheral resistance increased greatly as the hematocrit ratio increased. Analysis of the data showed that the rate of maximum resistance to hemorrhagic shock coincides with the hematocrit ratio range of maximum O₂ transport. Also, the rate of development of an oxygen debt determines how long the animals can remain hypotensive without developing irreversible shock and indicates that, regardless of the hematocrit ratio, a fixed oxygen deficit must occur before irreversible shock develops.

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