Arterial Blood Gases and Acid-Base Regulation

Disorders of acid-base status are common in the critically ill and prompt recognition is central to clinical decision making. The bicarbonate/carbon dioxide buffer system plays a pivotal role in maintaining acid-base homeostasis, and measurements of pH, PCO (2) , and HCO (3) (-) are routinely used in the estimation of metabolic and respiratory disturbance severity. Hypoventilation and hyperventilation cause primary respiratory acidosis and primary respiratory alkalosis, respectively. Metabolic acidosis and metabolic alkalosis have numerous origins, that include alterations in acid or base intake, body fluid losses, abnormalities of intermediary metabolism, and renal, hepatic, and gastrointestinal dysfunction. The concept of the anion gap is used to categorize metabolic acidoses, and urine chloride excretion helps define metabolic alkaloses. Both the lungs and kidneys employ compensatory mechanisms to minimize changes in pH caused by various physiologic and disease disturbances. Treatment of acid-base disorders should focus primarily on correcting the underlying cause and the hemodynamic and electrolyte derangements that ensue. Specific therapies under certain conditions include renal replacement therapy, mechanical ventilation, respiratory stimulants or depressants, and inhibition of specific enzymes in intermediary metabolism disorders.

Automated summary

Disorders of acid-base status are common in critically ill patients and their prompt recognition is crucial. The bicarbonate/carbon dioxide buffer system is vital for maintaining acid-base homeostasis and measurements of pH, PCO(2), and HCO(3)(-) are routinely used to assess the severity of metabolic and respiratory disturbances. Hypoventilation and hyperventilation lead to primary respiratory acidosis and alkalosis, respectively. Metabolic acidosis and alkalosis can have various causes, including changes in acid or base intake, fluid losses, abnormalities in metabolism, and dysfunction in the kidneys, liver, or gastrointestinal system. The concept of anion gap is used to categorize metabolic acidosis, while urine chloride excretion helps define metabolic alkalosis. The lungs and kidneys employ compensatory mechanisms to minimize pH changes caused by physiological and disease disturbances. Treatment of acid-base disorders should focus on correcting the underlying cause and addressing the associated hemodynamic and electrolyte imbalances. In certain conditions, specific therapies such as renal replacement therapy, mechanical ventilation, respiratory stimulants or depressants, and inhibition of specific enzymes may be considered.