Medical Council of Canada

Medical expert

Acid-Base Abnormalities Hydrogen - 45


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

Causal Conditions

(list not exhaustive)
  1. Metabolic acidosis
    1. High anion gap
      1. Increased acid production
        1. Exogenous (e.g., methanol)
        2. Endogenous acids (e.g., ketoacidosis)
      2. Decreased renal acid excretion (kidney injury)
    2. Normal anion gap
      1. Gastrointestinal bicarbonate loss (e.g., diarrhea)
      2. Renal bicarbonate loss (e.g., renal tubular acidosis, interstitial nephritis)
  2. Metabolic alkalosis
    1. Expanded effective arterial blood volume (e.g., mineralocorticoid excess)
    2. Contracted effective arterial blood volume
      1. Gastrointestinal loss (e.g., vomiting)
      2. Renal loss (e.g., diuretics)
    3. Exogenous ingestion
  3. Respiratory acidosis
    1. Neuromuscular causes (e.g., medications, illicit drugs)
    2. Pulmonary causes of decreased alveolar ventilation (e.g., chronic obstructive pulmonary disease)
    3. Kyphoscoliosis
    4. Hypoventilation (e.g., due to obesity)
  4. Respiratory alkalosis
    1. Hypoxemia
    2. Metabolic (e.g., hepatic failure)
    3. Cardio-pulmonary disorders (e.g., pneumonia, embolism)
    4. Central nervous system disorders (e.g., subarachnoid hemorrhage)
    5. Drugs (e.g., salicylate)
    6. Miscellaneous (e.g., fever, pain, pregnancy)

Key Objectives

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.


Given a patient with an acid-base abnormality, the candidate will

  1. through efficient, focused, data gathering, diagnose cause of acidemia/alkalemia expeditiously
  2. list and interpret critical clinical and laboratory findings which were key in the processes of exclusion, differentiation, and diagnosis:
    1. appropriate investigations for acidemia/alkalemia in order to identify the primary abnormality and the adequacy of the associated secondary compensation;
  3. construct an effective initial plan of management for acidemia/alkalemia
    1. describe general supportive measures;
    2. describe management for specific acid-base disorders;
    3. determine if the patient needs to be referred for consultation.
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