Acid-base abnormalities

Abnormally high or low hydrogen ion concentration—acidemia and alkalemia, respectively—is encountered relatively frequently, particularly in hospital-based practice. Acidemia may be caused by an underlying life-threatening condition. Several acid-base abnormalities can coexist in a single patient.

• Metabolic acidosis

  • High anion gap

    • Increased acid production

      • Exogenous (e.g., methanol)

      • Endogenous (e.g., ketoacidosis)

    • Decreased renal acid excretion (e.g., kidney injury)

  • Normal anion gap

    • Gastrointestinal bicarbonate loss (e.g., diarrhea)

    • Renal bicarbonate loss (e.g., renal tubular acidosis, interstitial nephritis)

• Metabolic alkalosis

  • Expanded effective arterial blood volume (e.g., mineralocorticoid excess)

  • Contracted effective arterial blood volume

    • Gastrointestinal loss (e.g., vomiting)

    • Renal loss (e.g., diuretics)

  • Exogenous ingestion

• Respiratory acidosis

  • Neuromuscular causes (e.g., medications, illicit drugs, neuromuscular disease)

  • Pulmonary causes of decreased alveolar ventilation (e.g., severe asthma exacerbation with impending respiratory failure)

  • Kyphoscoliosis

  • Hypoventilation (e.g., due to obesity)

• Respiratory alkalosis

  • Hypoxemia with tachypnea

  • Metabolic (e.g., hepatic failure)

  • Cardiopulmonary disorders (e.g., pneumonia, embolism)

  • Central nervous system disorders (e.g., subarachnoid hemorrhage)

  • Drugs (e.g., salicylate)

  • Miscellaneous (e.g., fever, pain, pregnancy)

Given a patient with an acid-base abnormality, the candidate will diagnose the cause, severity, and complications and will initiate an appropriate management plan, particularly when dealing with a high anion gap metabolic acidosis.

• through efficient and focused data gathering, diagnose the cause of acidemia or alkalemia expeditiously;

• list and interpret critical clinical and laboratory findings that are key in the processes of exclusion, differentiation, and diagnosis, including those derived from

  • an accurate arterial blood gas (ABG) analysis; and

  • complementary investigations for acidemia or alkalemia aimed at identifying the primary abnormality and the adequacy of the associated secondary compensation; and

• construct an effective initial management plan for acidemia or alkalemia, including

  • describing general supportive measures;

  • describing management for specific acid-base disorders; and

  • determining whether the patient needs to be referred for consultation.