The calculation of the osmotic volumes of distribution of hypertonic sodium bicarbonate and other hypertonic solutions: a theoretical approach.

Correction of a base deficit with hypertonic sodium bicarbonate (NaHCO3) according to the formula 0.3 x body weight (kg) x BE may overestimate the real demands, especially during shock and cardiopulmonary resuscitation (CPR). Life threatening alkalosis and osmolal poisoning may be the consequence. As an explanation, the possibly impaired functional distribution space related to low cardiac output and volume centralization during CPR is proposed. By application of our own and outside literature, data equations are specified for an approximate precalculation of osmolality and pH changes due to infusion of hypertonic NaHCO3. Calculation of the osmotic volumes of distribution of NaHCO3 during cardiopulmonary resuscitation (CPR) from emergency literature data demonstrates a possible reduction of the functional distribution spaces of about 70 to 80% compared with normal values. This is in good agreement with the reported reduction of cardiac output to about 25% of normal during CPR. The calculated amount of sodium bicarbonate to be recommended during CPR, thus, should not exceed 50 mmol given in time intervals of at least 10 min, severe acidosis and sufficient ventilation presumed.