Acid-base abnormalities

Rationale

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.

Causal Conditions

(list not exhaustive)

1. Metabolic acidosis
   1. High anion gap
      1. Increased acid production
         1. Exogenous (e.g., methanol)
         2. Endogenous (e.g., ketoacidosis)
      2. Decreased renal acid excretion (e.g., 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, neuromuscular disease)
   2. Pulmonary causes of decreased alveolar ventilation (e.g., severe asthma exacerbation with impending respiratory failure)
   3. Kyphoscoliosis
   4. Hypoventilation (e.g., due to obesity)
4. Respiratory alkalosis
   1. Hypoxemia with tachypnea
   2. Metabolic (e.g., hepatic failure)
   3. Cardiopulmonary 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.

Enabling Objectives

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

1. through efficient and focused data gathering, diagnose the cause of acidemia or alkalemia expeditiously;
2. list and interpret critical clinical and laboratory findings that are key in the processes of exclusion, differentiation, and diagnosis, including those derived from
   1. an accurate arterial blood gas (ABG) analysis; and
   2. complementary investigations for acidemia or alkalemia aimed at identifying the primary abnormality and the adequacy of the associated secondary compensation; and
3. construct an effective initial management plan for acidemia or alkalemia, including
   1. describing general supportive measures;
   2. describing management for specific acid-base disorders; and
   3. determining whether the patient needs to be referred for consultation.