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Acid base abnormalities

Specialties > Emergency medicine and intensive care

Background knowledge 🧠

Definition

  • Acid-base abnormalities refer to imbalances in the body’s pH, primarily involving alterations in the levels of hydrogen ions (H+) in the blood.
  • These abnormalities can manifest as acidosis (pH 7.45).
  • Maintaining a normal pH (7.35-7.45) is crucial for various cellular processes.

Epidemiology

  • Acid-base abnormalities are common in critically ill patients.
  • Metabolic acidosis is often seen in conditions such as sepsis and renal failure.
  • Respiratory alkalosis is frequently observed in patients with hyperventilation.
  • The prevalence varies depending on the underlying condition.

Aetiology and Pathophysiology

  • Acidosis: Caused by an accumulation of acids or loss of bicarbonate.
  • Alkalosis: Caused by an accumulation of bicarbonate or loss of acids.
  • Respiratory causes: Disorders that alter CO2 levels, e.g., COPD, hyperventilation.
  • Metabolic causes: Conditions that affect bicarbonate levels, e.g., renal failure, diabetic ketoacidosis.
  • Mixed disorders can occur, complicating diagnosis.

Types

  • Metabolic acidosis: Increased acid production or decreased excretion (e.g., lactic acidosis).
  • Metabolic alkalosis: Excessive bicarbonate or loss of acid (e.g., vomiting, diuretics).
  • Respiratory acidosis: Hypoventilation leading to CO2 retention (e.g., COPD).
  • Respiratory alkalosis: Hyperventilation leading to CO2 loss (e.g., anxiety, sepsis).

Clinical Features 🌡️

Symptoms

  • Acidosis: Confusion, lethargy, dyspnoea.
  • Alkalosis: Muscle twitching, tetany, dizziness.
  • Non-specific symptoms: Nausea, vomiting, palpitations.
  • Symptoms often relate to underlying cause (e.g., chest pain in respiratory alkalosis due to anxiety).

Signs

  • Kussmaul respiration: Deep, labored breathing seen in metabolic acidosis.
  • Hypotension: Common in severe acidosis.
  • Arrhythmias: Often associated with electrolyte disturbances.
  • Altered mental status: Seen in both severe acidosis and alkalosis.

Investigations 🧪

Tests

  • ABG (Arterial Blood Gas): Primary test to assess pH, PaCO2, HCO3-.
  • Electrolytes: Assess for imbalances (e.g., K+, Cl-).
  • Anion gap: Helps differentiate between causes of metabolic acidosis.
  • Lactate levels: Elevated in lactic acidosis.
  • Imaging: May be required to identify underlying causes (e.g., chest X-ray for respiratory causes).

Management 🥼

Management

  • Treat underlying cause (e.g., insulin for DKA, fluids for dehydration).
  • Oxygen therapy for respiratory acidosis if hypoxia is present.
  • Bicarbonate therapy in certain cases of metabolic acidosis.
  • Electrolyte correction as needed (e.g., K+, Mg2+).
  • Monitor ABGs to assess response to treatment.

Complications

  • Cardiac arrest: Severe acidosis can lead to fatal arrhythmias.
  • Seizures: Seen in severe alkalosis due to hypocalcaemia.
  • Respiratory failure: May result from severe respiratory acidosis.
  • Organ failure: Multiple organ dysfunction can occur if severe acid-base imbalance persists.

Prognosis

  • Prognosis depends on the underlying cause and severity of the imbalance.
  • Prompt identification and treatment improve outcomes.
  • Chronic imbalances (e.g., chronic respiratory acidosis) may have a variable prognosis depending on comorbidities.

Key Points

  • Acid-base balance is crucial for maintaining cellular function.
  • ABG is the cornerstone investigation in diagnosis.
  • Management focuses on treating the underlying cause.
  • Regular monitoring is essential for guiding treatment.

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Emergency medicine and intensive care