Chart — Respiratory
Respiratory Failure Comparison Chart
Type I (hypoxemic) vs Type II (hypercapnic) respiratory failure compared side by side — oxygenation, CO₂, ABG patterns, causes, and treatment priorities for rapid clinical differentiation.
Educational use only. Diagnosis and management of respiratory failure require provider evaluation, ABG analysis, and clinical context. This chart supports learning and NCLEX preparation. This material supports nursing education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional policy, or medical direction. Always follow facility protocols and current provider orders.
Type I vs Type II Comparison
| Parameter | Type I — Hypoxemic | Type II — Hypercapnic |
|---|---|---|
| Primary failure | Oxygenation | Ventilation (CO₂ removal) |
| Definition | PaO₂ <60 mmHg on room air | PaCO₂ >45 mmHg + pH <7.35 (acute) |
| PaO₂ | Low (<60 mmHg) | Low (secondary to hypoventilation) |
| PaCO₂ | Normal or low (hyperventilating to compensate) | HIGH (>45 mmHg) — defines Type II |
| pH | Normal or elevated (respiratory alkalosis from compensatory hyperventilation) | Low (<7.35 acute); near-normal if compensated/chronic |
| HCO₃ | Normal | Elevated if chronic (metabolic compensation for CO₂ retention) |
| Response to O₂ | Partial — FiO₂ increase improves SpO₂ unless true shunt (ARDS) | Improves hypoxemia but does NOT correct CO₂ problem |
| Mechanism | V/Q mismatch, intrapulmonary shunt, diffusion impairment | Decreased minute ventilation (RR × Vt); inadequate CO₂ removal |
| Treatment priority | Optimize oxygenation: PEEP, HFNC, treat cause | Support ventilation: BiPAP, mechanical ventilation, reverse cause |
Common Causes
| ARDS | Bilateral diffuse alveolar damage; refractory hypoxemia |
| Pneumonia | Consolidation blocks O₂ exchange in affected segments |
| Pulmonary edema | Cardiogenic or non-cardiogenic; fluid in alveoli |
| Pulmonary embolism | Dead space lesion; V/Q mismatch |
| Pneumothorax | Lung collapse eliminates ventilation-perfusion |
| Pulmonary fibrosis | Diffusion impairment; interstitial thickening |
| COPD exacerbation | Most common — acute-on-chronic CO₂ retention |
| Opioid/sedative overdose | Suppressed central respiratory drive |
| Neuromuscular disease | Guillain-Barré, myasthenia gravis, ALS, high spinal cord injury |
| Severe asthma (late) | Respiratory muscle fatigue; shifting from Type I to Type II |
| Chest wall deformity | Kyphoscoliosis, flail chest |
| Obesity hypoventilation | Elevated diaphragm; blunted respiratory drive |
ABG Pattern Quick Reference
| Type | pH | PaCO₂ | PaO₂ | HCO₃ |
|---|---|---|---|---|
| Type I (acute) | Normal or ↑ | Normal or ↓ | ↓ (<60) | Normal |
| Type II (acute) | ↓ (<7.35) | ↑ (>45) | ↓ | Normal or slightly ↑ |
| Type II (chronic, compensated) | Near-normal (7.35–7.45) | ↑ (chronically elevated) | ↓ or normal with O₂ | ↑ (metabolic compensation) |
NCLEX Pearls
- ›Type I = PaO₂ <60 on room air. Type II = PaCO₂ >45 + acidosis. These are the defining criteria.
- ›ARDS is the most severe Type I failure — bilateral infiltrates, refractory hypoxemia, non-cardiogenic.
- ›COPD exacerbation is the most common Type II failure — acute-on-chronic CO₂ retention.
- ›Adding O₂ to Type II failure does NOT fix it — the patient needs ventilatory support (BiPAP or intubation).
- ›Rising PaCO₂ in a distressed asthma patient = impending respiratory failure (they were initially hypocapnic).
- ›Chronic COPD patients have compensated Type II: high HCO₃, high PaCO₂, near-normal pH. Acute exacerbation = pH falls.
Related Resources
Standards & sources
Fact-checked Jun 21, 2026This page is written to align with ATS / ERS Respiratory Failure Guidelines. It is an educational summary, not a citation of any single document — always verify specific doses, values, and protocols against current guidelines and your facility policy. How we source content →