Is there a generally valid, minimum acceptable hemoglobin level?

Abstract

The different versions of autologous blood transfusion have rekindled interest in a generally valid 'minimum acceptable hemoglobin concentration' of patients around or below 10 g Hb/dl. The adequate Hb concentration capable of covering the oxygen demands of the body depends on several variables measurable at the bedside: oxygen consumption VO2, arterial oxygen tension paO2, body temperature, arterial and mixed venous pH, and cardiac output CO as the most important compensatory variable in anemia. Because of the strain imposed on the myocardium and the coronary circulation, anemia should not raise CO to more than twice the resting value, i.e. less than 10 l/min. Similarly, the mixed venous pO2, as an indicator of tissue oxygenation, should not fall below 35 mm Hg. With these two restrictions, we studied the relationships of the above-mentioned parameters in a computer-supported model. Under otherwise similar conditions, pvO2 falls with an increase in VO2, a decrease in paO2, a decrease in the temperature, an increase in pH, and a decrease in CO. A resting and slightly acidotic patient without other impediments of his cellular oxygen supply--e.g. the patient on chronic hemodialysis--tolerates a Hb level of 6-7 g/dl with a pvO2 barely exceeding 35 mm Hg and a CO approximately 50% above baseline. By contrast, the hypermetabolic and hypoxemic intensive care patient needs Hb levels in the low normal range, i.e. 12-13 g/dl, especially if he is also alkalotic. A generally valid 'minimum acceptable hemoglobin level' does not exist; the adequate Hb concentration is an individual characteristic needing careful attention.(ABSTRACT TRUNCATED AT 250 WORDS)