Reference — Clinical Skills
Bedside Pulmonary Measurements & Weaning Thresholds
The bedside ventilatory numbers and the thresholds that flag weaning readiness, in one lookup table — vital capacity, MIP, MEP, rate, minute ventilation, and RSBI, with the caveat that no single value decides alone.
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.
Overview
These bedside ventilatory measurements quantify reserve and muscle strength and inform weaning readiness. No single value is definitive — interpret them together and with the clinical picture (resolving cause, hemodynamic stability, oxygenation, mental status, secretions).
Measurements & Thresholds
| Measurement | Normal | Weaning Threshold |
|---|---|---|
| Spontaneous tidal volume (VT) | 5–8 mL/kg | ≥ 5 mL/kg |
| Vital capacity (VC) | 65–75 mL/kg | ≥ 10–15 mL/kg |
| Respiratory rate (f) | 12–20 /min | < 35 /min |
| Minute ventilation (VE) | 5–10 L/min | < 10 L/min |
| MIP / NIF | −80 to −100 cmH₂O | More negative than −20 to −30 cmH₂O |
| MEP | > +100 cmH₂O | ≥ +40 cmH₂O |
| RSBI (f/VT) | < 105 breaths/min/L (comfortable spontaneous breath) | < 105 breaths/min/L |
| PaO₂/FiO₂ ratio | > 400 | > 150–200 (PEEP ≤ 5–8 cmH₂O; FiO₂ ≤ 0.4–0.5) |
Clinical Notes
- Thresholds are guides, not guarantees. Weaning success depends on the whole clinical picture, not any single number.
- Effort and coaching matter. VC and MIP results depend on patient effort; a mouthpiece leak will falsely lower both.
- RSBI is measured during spontaneous breathing and is the most widely used single predictor of successful extubation.
- A more negative MIP indicates stronger inspiratory muscles.Values less negative than −20 cmH₂O suggest insufficient reserve for sustained spontaneous ventilation.
Related Resources
Sources
- MacIntyre NR, Cook DJ, Ely EW, et al. Evidence-based guidelines for weaning and discontinuing ventilatory support. Chest. 2001;120(6 Suppl):375S-395S.
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021. Discontinuing ventilatory support.