Round Table Discussion

Acidosis and alkalosis are terms used to describe opposite types of disturbance of acid-base balance of the body fluids. From the chemical point of view acidosis may be defined as the condition in the blood characterized by a reduction of the BHCO3/HHCO3 ratio, and alkalosis as an increase. When BHCO3 is primarily affected, the disturbance is referred to as metabolic in origin; when HHCO3 concentration is the first to be altered, the resulting change is considered to be of respiratory origin. Primary changes of either BHCO3 or HHCO3 usually stimulate compensatory changes in the other which tend to restore the original normal ratio. When compensation for acidosis is incomplete, an increased H+ ion concentration (decreased pH) of the blood results, and such a change is referred to as acidemia. The opposite condition is called alkalemia. From the clinical point of view a much broader concept of acidosis and alkalosis exists and includes in addition all related changes in metabolism (carbohydrate, fat, protein, water, mineral, enzyme) which may give rise to definite symptoms and signs of illness. Such metabolic changes may be either primary or secondary, and, as either, may be very important in determining prognosis as to life or death. In practice one is prompted to consider the possibility of acidosis or alkalosis by noting suspicious signs or symptoms and then diagnoses with certainty the presence and extent of change by chemical determinations of serum CO2 content and pH. The most important signs and symptoms of acidosis are: hyperpnea, which is considered not primary, stupor, dehydration, ketosis and strongly acid urine. Any or all may be absent. The most important signs and symptoms of alkalosis are: depressed respiration, considered compensatory, or hyperventilation, considered primary, tetany, and forceful vomiting, thought to be the result of pyloric or high intestinal obstruction, and strongly alkaline urine. Again any or all such symptoms may be absent. Furthermore, ketosis may be associated with alkalosis; secretion of alkaline urine may give rise to acidosis, and alkalosis may be accompanied by formation of acid urine. Also, it is not unusual to see in the same subject conditions favoring the development of both acidosis and alkalosis, but with the presence of neither. For absolute diagnosis of acidosis or alkalosis two of the three variables, BHCO3, HHCO3 and pH have to be determined. Since pH and BHCO3 usually move in the same direction, it has been widespread clinical practice to determine only BHCO3 by determining serum CO2 content by the Van Slyke manometric method. In this connection it should be remembered that when so determined about 20/21 of the CO2 comes from BHCO3, the remainder coming from HHCO3 In the past it was customary not to separate BHCO3 and HHCO3, but to record them together as the total CO2 content.