SummaryThe decrease in plasma potassium level induced by hyperventilation alkalosis is in accordance with the relationship between extracellular K concentration and pH, proposed by Scribner 10 years ago. The purpose of our study was to evaluate the clinical implication of this relationship in anaesthesia and reanimation : a decrease in plasma potassium level is desirable in hvperkalaemia but undesirable in hypokalemic and in digitalized patients.Five patients presenting conditions frequently encountered in réanimation were studied : severe renal failure, neurologic coma, acute repiratory failure. Hyperventilation lasted from 40 minutes to 39 hours. The pH increments ranged from 0.16 to 0.38 unit. The observed plasma potassium concentration changes were not of the same magnitude as those observed in the experimental animal : during the first hour, the plasma potassium level did not change or even increased despite frank alkalosis. Hypokalemia was noted in onlv two cases, where is was moderate and delayed.These results are confronted with the data of the literature : the effect of the respiratory acid-base disturbances on extracellular potassium concentration is smaller, slower and less predictable than that of the metabolic disturbances. The data collected during animal experimentation are more significant than those obtained in studies on normal man and especially on patients. Hypokalemia is very inconstant in anaesthetized and hyperventilated individuals, where respiratory alkalosis eventually induces initial and transient hvperkalaemia.The severity of the illness of the patients herein studied, as well as the inability to maintain constant their hyperventilation explain the discrepancies between our results and those of the literature. The different behaviour of extracellular potassium concentration under the influence of acid-base disturbances of respiratory and of metabolic origins is possibly explained by the slow diffusion of strong acids into the cellular compartment, opposed to the marked diffusihility of C02.It is concluded that hyperventilation does not constitute a safe procedure to treat impending hvperkalaemia. Other means which are safer and faster, are 10 be preferred, such as infusion of glucose-insulin, or alkalinisation with sodium lactate or bicarbonate.