The optimum hematocrit

Area of Science:

• Physiology
• Biomedical Engineering
• Hematology

Background:

• Hematocrit (Hct) influences both oxygen-carrying capacity and blood viscosity.
• An optimal Hct for tissue oxygenation is theoretically derived from its dual role.
• Physiological Hct ranges vary between sexes (women: 35-40%, men: 39-50%).

Purpose of the Study:

• To investigate the concept of an optimal hematocrit for oxygen transport.
• To compare theoretical optimal Hct values with clinical observations in various medical conditions.
• To explore reasons for the discrepancy between optimal Hct in health and disease.

Main Methods:

• Viscometric studies of red blood cell (RBC) suspensions at varying shear rates.
• Perfusion experiments using artificial microvascular networks.
• Analysis of clinical data from large studies on anemia correction and transfusion strategies.

Main Results:

• Viscometric studies indicated an optimal Hct of 50-60% for RBC suspensions.
• Artificial microvascular perfusion showed an optimal Hct of 60-70% under high pressure.
• Optimal Hct shifted lower with reduced shear rates or pressures.
• In athletes, supra-normal Hct can enhance exercise performance.
• Clinical studies demonstrate improved outcomes with restrictive transfusion strategies (Hct 20-24%) in various disorders.

Conclusions:

• Theoretical optimal Hct for oxygen transport in healthy individuals may exceed physiological ranges.
• Clinical evidence suggests lower Hct levels are beneficial in disease states.
• Discrepancies may stem from factors like reduced perfusion pressure, endothelial dysfunction, and leukocyte adhesion in illness.