acidemias

Acidemias are disorders characterized by a lower systemic pH (pH < 7.35) due to excess hydrogen ions or loss of bicarbonate. They arise from increased acid production, decreased acid excretion, or loss of bicarbonate. The two primary categories are metabolic acidosis, in which bicarbonate is reduced, and respiratory acidosis, in which carbon dioxide accumulates from hypoventilation. Mixed acidemia can occur when disturbances involve both systems. The body may compensate through ventilation changes or renal bicarbonate handling, but compensation does not fully correct the abnormal pH.

Metabolic acidosis has multiple causes and is often categorized by the anion gap. High-anion-gap acidosis includes lactic acidosis, ketoacidosis, renal failure, toxins, and certain drugs (the MUDPILES framework). Non–anion-gap (hyperchloremic) acidosis results from bicarbonate loss (eg, diarrhea) or reduced acid excretion. In metabolic acidosis, the respiratory system compensates by increasing ventilation, with expected PaCO2 approximately 1.5 × [HCO3−] + 8 ± 2.

Respiratory acidosis occurs when CO2 is retained due to hypoventilation or impaired gas exchange. Causes include airway obstruction, chest wall restriction, neuromuscular weakness, and central depression. PaCO2 rises and pH falls. Renal compensation, via increased bicarbonate reabsorption, develops over days. Distinguishing the primary disorder relies on arterial blood gas values and the clinical context.

Diagnosis integrates arterial blood gas with electrolytes and clinical assessment. Management targets the underlying cause and supportive measures such as airway or ventilation support and correction of electrolyte disturbances. Bicarbonate therapy is considered only in select severe cases and is approached with caution, as it can worsen outcomes depending on the situation.