Evidence favoring a cardiac mechanism in irreversible hemorrhagic shock

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

Shock was induced in 55 dogs by removing blood until the arterial pressure had fallen to 30 mm Hg. The pressure was kept at this level for as long as 10 hr by constantly adding additional blood to the reservoir. The hematocrit was kept constant to prevent large variations in the viscosity. Mean pressures of the right and left atrium, the pulmonary artery, and the systemic arterial system were recorded as well as oxygen consumption and A-V oxygen difference. Total peripheral resistance and cardiac output were calculated. That period of time during which the animal passed from a reversible stage of shock to an irreversible stage of shock was studied. It was found that no significant change occurred in oxygen consumption, cardiac output, or peripheral resistance during this transition phase. However, changes did occur in the operating parameters of the heart. The left atrial pressure began rising with the transition from reversible to irreversible shock and continued rising until death of the animal. It is suggested that irreversible hemorrhagic shock is due to acute cardiac failure.

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