Further applications of blood gas analysis to gastric acidity determination.

It has been shown that the transient increase in total body bicarbonate that accompanies any acceleration of gastric acid secretion (the 'alkaline tide') is derivable from the associated changes in base excess in arterial blood and is precisely equivalent to the amount of acid secreted when the latter is simultaneously recovered. For the alkaline tide to qualify as a 'tubeless' measure of acid secretion, its equivalence to the latter has to be demonstrated without simultaneous aspiration of gastric juice. We therefore studied the course of the alkaline tide following pentagastrin injection and its relationship to pentagastrin-stimulated acid secretion as measured by aspiration on a separate occasion. In 12 duodenal ulcer patients, the sequential changes in base excess in arterial blood in response to pentagastrin invariably described coherent curves. Peak values occurred most frequently 45 min after injection. In 12 similar patients, alkaline tide 45 min after pentagastrin, as per analysis of arterialized venous blood, correlated well (r = 0.86) with 'peak acid output' (PAO) as measured by aspiration at another time. In 14 patients post vagotomy and pyloroplasty for duodenal ulcer, the 45-min alkaline tide was determined as above and PAO was predicted from the previously established regression-line: The 3 patients with recurrent duodenal ulceration had the highest predicted values for PAO, clearly discriminating them from the others. Measurement of alkaline tide holds promise as a valuable substitute for conventional gastric analysis. For the sake of accuracy, readings should be based on individually constructed time-curves of base excess, in preference to the raw data. Arterialized venous blood appears to be satisfactory substitute for arterial blood for studies of this type.