Respiratory Acidosis Lecture Notes

Overview

• Definition: Respiratory acidosis occurs due to failure of ventilation and accumulation of carbon dioxide.
• Key Disturbance: Elevated arterial partial pressure of carbon dioxide (PCO2) leading to decreased blood pH.
• Compensation: Kidneys excrete more acid and reabsorb more bicarbonate to normalize pH.

Objectives

• Identify causes of respiratory acidosis.
• Review clinical presentation and physical exam findings.
• Explain management strategies.
• Enhance care coordination among interprofessional teams.

Etiology

• Control of Ventilation: Regulated by respiratory centers in the pons and medulla.
• Chemoreceptors: Respond to changes in PCO2, PO2, and pH levels.
• Types:
  • Acute Respiratory Acidosis: Sudden PCO2 elevation due to ventilation failure; causes include CNS depressants, muscle disorders.
  • Chronic Respiratory Acidosis: Often due to COPD or muscular fatigue; gradual renal compensation.
  • Mixed Acute-on-Chronic: Acute insult in chronic patients causing ventilation/perfusion mismatch.

Epidemiology

• Varies based on etiology; common in end-stage COPD and surgical patients.

Pathophysiology

• CO2 retention leads to increased hydrogen ions and bicarbonate.
• Buffer System:
  • Equilibrium Reaction: CO2 + H2O -> H2CO3 -> HCO3- + H+
  • Buffers pH changes by interacting with H+ and OH- ions.

Clinical Presentation

• Symptoms vary by severity and progression: dyspnea, anxiety, wheezing, sleep disturbances, altered mental status.
• Severe cases: cerebral vasodilation, increased intracranial pressure, risk of herniation.
• Chronic cases: memory loss, impaired coordination, polycythemia, pulmonary hypertension.

Evaluation

• Arterial Blood Gas (ABG) Test: Elevated PCO2 (>45 mmHg), elevated HCO3- (>30 mmHg), decreased pH (<7.35).
• Classification: Acute vs chronic based on HCO3- increase relative to PCO2.
• Additional tests for underlying causes; possible drug screen if unexplained.

Treatment/Management

• Correct underlying cause and hypercapnia gradually.
• Pharmacologic Therapy: Bronchodilators (beta-agonists, anticholinergics), naloxone for opioid overdose.

Differential Diagnosis

• Includes botulism, bronchitis, diaphragm disorders, asthma, opioid use, COPD, obesity.

Key Management Points

• Monitor severe cases in ICU; may require mechanical ventilation.
• Avoid CNS stimulants; efficacy not proven.
• Team Coordination: Important for effective management and improved outcomes.

Enhancing Healthcare Outcomes

• Emphasize interprofessional collaboration for diagnosis and management.
• Gradual correction of hypercapnia to avoid seizures.

References

• Cited studies and reviews provide insights on pathophysiology and management practices.