Chart — Emergency Respiratory Care
Type I vs Type II Respiratory Failure
Respiratory failure splits into two types, and the blood gas tells them apart instantly. A low PaO₂ with a normal or low CO₂ is Type I (oxygenation failure); a high CO₂ with acidosis is Type II (ventilatory failure). The type points straight to the support that fits, and many sick patients have both.
Written by Apex Respiratory Editorial Team
Educational use only. This material supports respiratory therapy education and exam review. It is not medical advice and is not a substitute for clinical judgment, institutional protocols, or physician orders. Always follow facility policies and current provider orders, and verify calculations independently before clinical use.
The Comparison
| Feature | Type I (Hypoxemic) | Type II (Hypercapnic / Ventilatory) |
|---|---|---|
| Defining gas | PaO₂ under 60 mmHg (on room air) | PaCO₂ over 50 mmHg with pH under 7.35 (acute) |
| Core problem | Oxygenation failure (gas exchange) | Ventilation or “pump” failure (CO₂ clearance) |
| Main mechanism | V/Q mismatch and shunt | Alveolar hypoventilation |
| A-a gradient | Elevated | Often normal (pure hypoventilation), or elevated if lung disease coexists |
| Typical causes | Pneumonia, pulmonary edema, ARDS, atelectasis, pulmonary embolism | COPD, severe asthma, drug overdose, neuromuscular disease, chest-wall disorders, fatigue |
| ABG pattern | Low PaO₂; PaCO₂ low or normal | High PaCO₂ with respiratory acidosis; PaO₂ often low too |
| First-line support | Oxygen, HFNC; PEEP/recruitment for shunt | NIV (BiPAP) for patients with an intact drive and airway; reverse the cause |
| Escalation | Intubation for refractory hypoxemia | Intubation if NIV fails or the airway is unprotected |
How to Use This Chart
Sort the type from the gas first, then let the type point you to the support that fits. Type I is an oxygenation problem; Type II is a ventilation problem — and the difference dictates whether more oxygen or more ventilation is the answer. Real emergencies still follow current ACLS and unit protocols and physician orders; this chart orients the reasoning, not the order set.
- The blood gas sorts the type instantly: a low PaO₂ with a normal or low CO₂ is Type I; a high CO₂ with acidosis is Type II. Many sick patients have both.
- Type I shunt physiology resists supplemental oxygen and needs PEEP and recruitment; Type II responds to ventilation (NIV or intubation), not just more oxygen.
- In chronic CO₂ retainers, judge the acuity by the pH, not the absolute CO₂.
Related Resources
Sources
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021. Respiratory failure chapters.
- Rochwerg B, Brochard L, Elliott MW, et al. Official ERS/ATS clinical practice guidelines: noninvasive ventilation for acute respiratory failure. Eur Respir J. 2017;50(2):1602426.