Digitalis, electrolytes and the surgical patient.

Abstract Recognition of the complex interrelations between electrolytes and digitalis action is of vital importance in the management of surgical patients with heart disease. Experimental data bearing on this subject have been examined and the literature reviewed. The following pertinent facts emerge: 1. 1. With due recognition that change in a single ion never occurs without other alterations in the total water-electrolyte structure, it is nevertheless clear that in the digitalized patient a decrease in body potassium from whatever cause may precipitate digitalis intoxication. By contrast, administration of potassium will abolish all digitalis-induced arrhythmias even in patients with a presumably normal total of body potassium content. The interaction between digitalis and potassium thus occurs at a cellular level. The cardiac sensitivity to this drug has little relation to the serum potassium concentration. 2. 2. However, toxic doses of digitalis interfere with the disposition of potassium within the body. Administration of potassium to patients with advanced heart failure exhibiting digitalis intoxication may cause serious hyperkalemia. The explanation of this fact appears to be twofold: release of potassium by the liver and interference with its uptake by skeletal muscle when under the influence of digitalis. Thus, the treatment of digitalis intoxication with potassium, while essential, carries special hazards in this group. 3. 3. Calcium and digitalis have similar actions on the contractility and excitability of the isolated heart. In the intact animal a synergism between calcium and digitalis on cardiac excitability is not demonstrable. Acute reduction in the concentration of ionized calcium results in a hypodynamic myocardium leading rapidly to shock and death. This deleterious action can be prevented either by digitalis administration or by the infusion of calcium salts. 4. 4. Magnesium exerts an antiarrhythmic effect on the myocardium and can abolish, transiently, digitalis-induced ectopic rhythms. When the body is chronically depleted of magnesium by dietary deficiency of this ion, the heart becomes sensitized to the toxic action of digitalis. The clinical use of digitalis drugs in the preoperative, intraoperative and postoperative periods is outlined. Simplicity of medication and the avoidance of rapid parenteral digitalization are desirable objectives in surgery. Injudicious rigorous diuresis immediately prior to operation can precipitate serious complications in the digitalized cardiac patient and lead to digitalis toxicity. The diagnosis and management of cardiac arrhythmias in surgical patients is discussed. Rapid heart action with hypotension in the operative or postoperative period is a particularly difficult problem, and necessitates the differentiation of blood volume deficiency, cardiac arrhythmia, underdigitalization or digitalis toxicity as the etiologic factor. The special problems imposed by posttraumatic metabolism in the cardiac patient are reviewed. The biochemical settings for these problems are: post-traumatic hyponatremia with hyperkalemia, oliguria followed by diuresis, acute acid-base changes, and alterations in ionized calcium. Finally, it is to be emphasized that the majority of available data dealing with the interrelations between digitalis and body electrolytes concerns only the effects on cardiac excitability. As yet there is a paucity of information concerning the influence of electrolyte alterations on digitalis-induced changes in cardiac contractility. Clearly, much additional investigation is needed on this subject which also bears importantly on the welfare of the surgical patient.