Acid-base physiology and interpreting blood gas results

Abstract Each day there is a production of acid by the body's metabolic processes. To maintain balance, these acids need to be excreted or metabolised. Normally, the body can respond very effectively to changes in acid production. Multiple homeostatic mechanisms interact to ensure a stable concentration of hydrogen ions [H + ] exists so that enzymes can function efficiently. Pathological derangement of pH will slow reactions or even permanently denature proteins. The most useful investigation into acid-base balance in the acute setting is a blood gas. A blood gas can help with diagnosis, assessing physiological state, reviewing response to treatment, and prognosis in resuscitation. Having a structured approach to reviewing blood gases can be invaluable in paediatric practice and having a knowledge of how acid-base turnover, buffering, compensation, respiratory and renal excretion co-exist will help you understand what is going on particularly in situations where there is a critically ill child. This review aims to revise acid-base physiology and provide a structure to interpreting a blood gas, with particular emphasis on metabolic conditions.