The importance of acid-base management for cardiac and cerebral preservation during open heart operations.
The basic physiologic characteristics of acid-base equilibria during hypothermia were briefly reviewed. By graphic analysis, four possible clinical strategies for managing the acid-base status of the patient undergoing H-CPB were documented. The effect of hemodilution on buffer capacity was charted in a manner applicable to common current operative procedures. During hypothermia for cardiac operations as presently conducted, the perfusionist is in control of the temperature of the body and the perfusion preservation of the body and brain; the surgeon must assume responsibility for preservation of the heart. The literature pertinent to the relationship of the acid-base state to the functions and structural preservation of the heart and brain during the conditions of cooling to and rewarming from deep hypothermia associated with cardiopulmonary bypass, aortic cross clamping, cardioplegia and total circulatory arrest have been reviewed. The evidence is overwhelming that myocardial anoxia caused by aortic occlusion or total circulatory arrest at any temperature to 15 degrees C. result in progressive acidosis which, of itself, is myotoxic. In contrast, alkalinity is ionotropic. Myocardial ischemia, in both adults and infants, should be prevented and treated by alkaline perfusion cooling and by frequent coronary perfusion of a cardiopreservative solution which is extremely cold (4 to 8 degrees C.), oxygenated, has a pH of 7.8, slightly hyperosmolar and which has a hematocrit of 20 per cent (imidazole, erythrocytes and plasma protein colloid), a cardioplegic ionic pattern and energy substrates. Reperfusion of the heart should begin at a 37 pH of 7.8. Evidence is strong that the use of CO2 added to any gas mixture is harmful. It increases myocardial acidosis; it does not increase cerebral blood flow during hypothermia. Protection of the unperfused brain of an infant should emphasize prevention of circulatory arrest prolonged to more than 40 minutes. Temporary reperfusion at that time limit should be used. Probably the best general management of the body for H-CPB is alpha-stat, which preserves biologic neutrality. The uncorrected analyzer reads pH 7.4 and Pco2 at any temperature. However, the need for preservation of the hypoxic heart is overwhelming and, thus, the best acid-base management for cardiac hypothermic operations is significant respiratory alkalosis. The most appropriate sites for the collection of blood samples for gas analysis and measuring temperatures were discussed; "body temperature" is the most unreliable parameter measured. The major characteristics of an "ideal" cardiopreservative solution were described.(ABSTRACT TRUNCATED AT 400 WORDS)
D000136:Acid-Base Equilibrium; D000328:Adult; D000471:Alkalosis / Q000209:etiology; D000818:Animals; D001831:Body Temperature; D001921:Brain / Q000502:physiology*; D001923:Brain Chemistry; D002245:Carbon Dioxide / Q000502:physiology; D006348:Cardiac Surgical Procedures; D002315:Cardiopulmonary Bypass / Q000009:adverse effects; D003327:Coronary Disease / Q000517:prevention & control; D004285:Dogs; D006321:Heart / Q000502:physiology*; D006324:Heart Arrest, Induced; D006438:Hemodilution; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007036:Hypothermia, Induced; D007223:Infant; D008954:Models, Biological; D009200:Myocardial Contraction / Q000187:drug effects; D013997:Time Factors
D002245:Carbon Dioxide