A 58-year-old man with COPD presents to the emergency department with acute dyspnea. ABG shows: pH 7.28, PaCO₂ 65 mmHg, HCO₃⁻ 28 mEq/L, PaO₂ 55 mmHg. What is the most appropriate immediate next step in management?

## Acid-Base Interpretation **Key Point:** This patient has acute respiratory acidosis with metabolic compensation (HCO₃⁻ is elevated but pH is still low, indicating the respiratory component dominates). ### ABG Analysis - pH 7.28 → acidemia - PaCO₂ 65 mmHg → hypercapnia (primary problem) - HCO₃⁻ 28 mEq/L → appropriate metabolic compensation for acute respiratory acidosis - PaO₂ 55 mmHg → severe hypoxemia **High-Yield:** In acute respiratory acidosis, the primary goal is to improve ventilation, not to correct pH chemically. The kidneys cannot respond acutely enough to compensate for acute CO₂ retention. ### Management Hierarchy ```mermaid flowchart TD A[Acute Respiratory Acidosis]:::outcome --> B{Severe hypoxemia + altered mental status?}:::decision B -->|Yes, unstable| C[Immediate intubation]:::urgent B -->|No, compensated| D[Non-invasive ventilation]:::action D --> E[Supplemental O₂ + CPAP/BiPAP]:::action E --> F[Treat underlying cause]:::action F --> G[Antibiotics if infection, bronchodilators if COPD]:::action ``` **Clinical Pearl:** NIV (CPAP or BiPAP) is the first-line intervention in acute respiratory acidosis with hypercapnia, provided the patient is conscious, cooperative, and hemodynamically stable. This patient meets criteria: pH > 7.25, no altered mental status mentioned, and COPD exacerbation is the likely trigger. **Mnemonic: SAVE** — Supplemental O₂, Airway support (NIV first), Ventilation improvement, Etiology treatment. ### Why NOT Sodium Bicarbonate? Sodium bicarbonate is contraindicated in respiratory acidosis because it increases CO₂ production and worsens hypercapnia. It is only indicated in metabolic acidosis. [cite:Harrison 21e Ch 48]