Reference — Mechanical Ventilation
Normal Ventilator Parameters & Weaning Criteria
Target ranges for the parameters you monitor on every ventilated patient, and the screening thresholds protocols use to judge whether a patient is ready to be liberated from the ventilator.
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
The first table lists the mechanics you track to keep ventilation safe and lung-protective; the second lists the numbers used to screen for weaning readiness. Calculate the bedside ones directly with the RSBI calculator and the compliance calculator.
Monitored Ventilator Parameters
| Parameter | Target | Notes |
|---|---|---|
| Plateau pressure (Pplat) | ≤ 30 cmH₂O | Lung-protective ceiling; reflects alveolar pressure |
| Driving pressure (Pplat − PEEP) | < 15 cmH₂O | Lower values associated with better ARDS outcomes |
| Static compliance | ~40 – 80 mL/cmH₂O | Typical ventilated adult; healthy lungs 50 – 100+ |
| Airway resistance | 0.6 – 2.4 cmH₂O/L/s | Unintubated normal; intubated commonly ~5 – 10 (tube adds resistance) |
| Auto-PEEP | Target 0 | Air trapping / incomplete exhalation |
| VD/VT (dead-space fraction) | 0.3 – 0.4 | Normal; rises in ARDS and pulmonary embolism |
Weaning Readiness Criteria
| Criterion | Threshold | Notes |
|---|---|---|
| RSBI (f/VT) | < 105 breaths/min/L | Rapid shallow breathing index |
| NIF / MIP | More negative than −20 to −30 cmH₂O | Inspiratory muscle strength |
| Vital capacity | ≥ 10 – 15 mL/kg | Ventilatory reserve |
| Spontaneous VT | ≥ 5 mL/kg | Spontaneous tidal volume |
| Minute ventilation (V̇E) | < 10 L/min | With acceptable gas exchange |
| Respiratory rate | ≤ 35 breaths/min | Spontaneous rate |
| Oxygenation | FiO₂ ≤ 0.4 – 0.5, PEEP ≤ 5 – 8 | Adequate oxygenation at low support |
| Hemodynamics / pH | Stable, pH > 7.25 | Overall physiologic readiness |
Clinical Notes
Thresholds are screening values, not absolute gates. They raise or lower suspicion of readiness; no single number should pass or fail a patient on its own. The decision rests on the whole clinical picture — mental status, secretions, hemodynamics, and the trajectory of the illness — and on the patient’s institutional weaning protocol, which takes precedence over any individual cutoff listed here.
Related Resources
Sources
- Kacmarek RM, Stoller JK, Heuer AJ. Egan's Fundamentals of Respiratory Care. 12th ed. Elsevier; 2021.
- Ouellette DR, Patel S, Girard TD, et al. Liberation from mechanical ventilation in critically ill adults: an official ATS/ACCP clinical practice guideline. Chest. 2017;151(1):166-180.
- Yang KL, Tobin MJ. A prospective study of indexes predicting the outcome of trials of weaning from mechanical ventilation. N Engl J Med. 1991;324(21):1445-1450.