acidosis

Acidosis is a pathophysiological condition characterized by a fall in blood pH below 7.35, usually due to an excess of hydrogen ions or a deficit of bicarbonate. The body maintains acid–base balance through buffering systems and organ-based compensation, but when these mechanisms are overwhelmed, acidosis can result from metabolic or respiratory origins.

Metabolic acidosis refers to a primary decrease in bicarbonate with accompanying acidemia. It is commonly classified by the anion gap: high anion gap metabolic acidosis occurs with lactic acidosis, ketoacidosis, renal failure, or toxin ingestion; normal anion gap (hyperchloremic) metabolic acidosis occurs with bicarbonate loss from diarrhea or renal tubular disorders, or from certain medications. Other contributing factors include renal failure and endocrine disturbances. Symptoms may include rapid breathing, fatigue, and confusion, depending on severity and chronicity.

Respiratory acidosis arises from impaired removal of carbon dioxide, leading to increased CO2 and hydrogen ions. It is seen in lung diseases such as COPD, hypoventilation from sedation or neuromuscular disorders, and airway obstruction. The body compensates for metabolic acidosis by increasing ventilation to blow off CO2, while the kidneys compensate for respiratory acidosis by retaining bicarbonate and increasing acid excretion over days.

Diagnosis relies on arterial blood gas measurements: a pH below 7.35 indicates acidemia, with low bicarbonate supporting metabolic acidosis and elevated PCO2 supporting respiratory acidosis. Assessing the anion gap and other labs helps identify the underlying cause.

Treatment targets the underlying disorder and may include volume resuscitation and support for perfusion, ventilatory management for respiratory failure, and cautious bicarbonate administration in severe metabolic acidosis. Ongoing monitoring of electrolytes and acid–base status guides care.