Central and regional hemodynamics during acute hypovolemia and volume substitution in volunteers

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Abstract
To study the central and regional hemodynamics and oxygen consumption during acute hypovolemia and volume replacement with crystalloid and colloid solutions. Prospective, randomized, laboratory investigation. Clinical physiology department at a university hospital. Eighteen healthy male volunteers, between 21 and 35 yrs of age (mean 26). Catheters were inserted in the cubital vein, brachial artery, pulmonary artery, thoracic aorta, right hepatic vein, and left renal vein for measurements of systemic arterial and pulmonary arterial pressures, total and central blood volumes, extravascular lung water, and the splanchnic (liver) and renal blood flow rates. The exchange of respiratory gases was measured, using the Douglas bag technique. Withdrawal of 900 mL of blood decreased cardiac output and the splanchnic and renal blood flow rates by between -16% and -20%. The oxygen uptake decreased by 13% in the whole body, while it remained unchanged in the liver and kidney. The systemic and pulmonary vascular resistances increased, while the extravascular lung water decreased. Autotransfusion of fluid from tissue to blood was indicated by hemodilution, which was most apparent in subjects showing only a minor change in peripheral resistance. Withdrawal of 900 mL of blood induces similar reductions in cardiac output as in the splanchnic and renal blood flow rates. A fluid shift from the extravascular to the intravascular fluid compartment might restore up to 50% of the blood loss. Optimal volume substitution with Ringer's solution can be effectuated by infusing between 100% and 200% of the amount of blood lost. (Crit Care Med 1997; 25:635-640)