3.4 Weaning & Liberation from Mechanical Ventilation

CRT/RRT Respiratory Therapist Exam Exam

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1 Introduction: NBRC TMC Exam Overview

NBRC TMC Exam Overview Credential Pathway: CRT to RRT Study Strategies for the TMC Exam Content Domains & Weight Distribution

2 Chapter 1: Patient Data Evaluation

1.1 Patient History & Physical Assessment 1.2 Diagnostic Procedures & ABG Interpretation 1.3 Hemodynamic Monitoring & Waveform Analysis 1.4 Laboratory Values & Diagnostic Data

3 Chapter 2: Airway Management & Oxygen Therapy

2.1 Airway Anatomy & Assessment 2.2 Airway Management Devices & Procedures 2.3 Oxygen Therapy Devices & Delivery 2.4 Humidification & Aerosol Therapy

4 Chapter 3: Mechanical Ventilation

3.1 Ventilation Fundamentals 3.2 Initial Ventilator Settings 3.3 Ventilator Monitoring & Waveform Analysis 3.4 Weaning & Liberation from Mechanical Ventilation

5 Chapter 4: Pharmacology & Equipment

4.1 Respiratory Pharmacology 4.2 Equipment & Troubleshooting 4.3 Specialty Procedures

6 Chapter 5: Infection Control, Ethics & Professional Practice

5.1 Infection Control & Prevention 5.2 Emergency Procedures & Resuscitation 5.3 Professional Practice & Ethics

3.4 Weaning & Liberation from Mechanical Ventilation

Key Takeaways Explain This Topic AI

Confirm weaning readiness first: underlying cause improving, FiO2 ≤0.40, PEEP ≤5–8 cmH2O, hemodynamically stable, alert with adequate cough

Rapid Shallow Breathing Index (RSBI) = frequency ÷ tidal volume in liters; <105 predicts weaning success, >105 predicts failure

Negative Inspiratory Force (NIF/MIP) more negative than −20 to −30 cmH2O indicates adequate inspiratory muscle strength

The Spontaneous Breathing Trial (SBT) is the gold standard, run 30–120 minutes via T-piece, low-level PSV 5–8, or CPAP 5

Stop the SBT for RR >35, SpO2 <90%, HR or BP change >20%, agitation, diaphoresis, or paradoxical breathing — then wait ~24 hours before retrying

Pair a daily spontaneous awakening trial (sedation off) with the SBT to shorten ventilator days

A failed cuff-leak test (no air escapes around a deflated cuff) predicts post-extubation stridor from laryngeal edema

Treat post-extubation stridor with racemic epinephrine; give IV corticosteroids beforehand in high-risk patients and keep reintubation gear at the bedside

Last updated: June 2026

Step 1 — Screen Readiness Before You Test

Weaning shortens ICU stay and reduces ventilator-associated complications, but only when the patient is actually ready. Confirm the screening criteria before measuring any parameter — testing an unready patient just wastes effort and risks decompensation.

Criterion Requirement
Underlying cause Resolving or resolved
Oxygenation FiO2 ≤0.40, PEEP ≤5–8 cmH2O, PaO2 ≥60 mmHg, P/F >150–200
Hemodynamics Stable BP, off pressors or low-dose only
Neurologic Alert, follows commands, intact cough and gag
Drive Initiating spontaneous breaths
Acid-base pH 7.25–7.50
Sedation Minimized or off; passed a spontaneous awakening trial (SAT)
Step 2 — Weaning Parameters

Parameter Pass threshold What it measures
RSBI (f/VT) <105 breaths/min/L Demand vs. capacity balance
NIF / MIP More negative than −20 to −30 cmH2O Inspiratory muscle strength
Vital capacity >10–15 mL/kg IBW Cough and deep-breath ability
Spontaneous VT >5 mL/kg IBW Adequate unsupported volume
Spontaneous RR <35/min Not in respiratory distress
Minute ventilation <10 L/min Manageable total demand
Step 3 — The RSBI, the Marquee Predictor

The Rapid Shallow Breathing Index (RSBI) is the single most-tested weaning number:

RSBI = respiratory rate (f) ÷ tidal volume in liters (VT) , measured during about one minute of unassisted breathing (T-piece or CPAP 0).

RSBI <105 → favorable, ~80% positive predictive value for successful extubation.

RSBI >105 → rapid, shallow breathing (high rate, low VT) → likely failure.

Worked example: a patient breathing 24/min with VT 0.35 L has RSBI = 24 ÷ 0.35 = 69 → favorable. A patient at 34/min with VT 0.18 L has RSBI = 34 ÷ 0.18 = 189 → fails the threshold.

Step 4 — The Spontaneous Breathing Trial (Gold Standard)

The SBT directly tests whether the patient can breathe with minimal or no support and is the best predictor of extubation success. Daily linking of an SAT to the SBT reduces ventilator days.

Element Detail
Duration 30–120 minutes
Methods T-piece, low-level PSV 5–8 cmH2O + PEEP 5, or CPAP 5
Monitoring Continuous SpO2, HR, BP, RR, and patient comfort

Stop the SBT (and return to full support) for any of: RR >35; SpO2 <90% or a >4% drop; HR change >20% from baseline; systolic BP >180 or <90 mmHg; agitation, anxiety, or diaphoresis; paradoxical (abdominal) breathing or accessory-muscle use; VT <4 mL/kg IBW. After a failed trial, identify the cause and typically wait about 24 hours before retrying — do not extubate a failing patient.

Step 5 — Extubation and the Post-Extubation Window

Pre-extubation checklist: passed the SBT; strong cough able to clear secretions; manageable secretion volume; a positive cuff-leak test (air audibly escapes around the deflated cuff, indicating no critical laryngeal edema); low aspiration risk; reintubation equipment at the bedside.

The cuff-leak test is purely an airway-edema screen — it says nothing about muscle strength or oxygenation. Absent leak suggests laryngeal edema and a stridor/reintubation risk; consider IV corticosteroids before extubation in high-risk patients (intubated >4 days, traumatic or repeated intubation, large tube).

After extubation, watch for inspiratory stridor from laryngeal edema, usually within the first 24–48 hours. First-line treatment is racemic epinephrine by nebulizer, whose mucosal vasoconstriction shrinks the edema; add corticosteroids and escalate to non-invasive ventilation or high-flow nasal cannula as rescue, with reintubation if obstruction progresses. Keep reintubation gear ready for 24–48 hours.

Why Trials Fail and How the Exam Frames It

Most weaning failures fall into three buckets, and recognizing the bucket usually points to the fix. The first is a respiratory pump problem — weak inspiratory muscles (low NIF), residual sedation, or critical-illness neuromyopathy after a long course of ventilation; here the answer is more time, nutrition, mobilization, and minimizing sedation rather than another immediate trial. The second is a load problem — bronchospasm, secretions, or auto-PEEP that makes each breath cost too much; the answer is to treat the obstruction and clear the airway before retesting.

The third, and the one examiners love to slip into a weaning vignette, is cardiac : switching a patient from positive-pressure ventilation back to negative-pressure spontaneous breathing increases venous return and left-ventricular afterload, and a patient with marginal cardiac reserve can flash into pulmonary edema partway through the SBT. The tip-off is a rising heart rate and blood pressure with new crackles rather than primary hypoxemia.

The exam also tests the order of operations relentlessly. The correct sequence is screen readiness, measure parameters, run the SBT, perform the cuff-leak test, then extubate and monitor — and the most-missed point is that passing weaning numbers does not equal readiness to extubate . A patient can have a beautiful RSBI of 60 and still fail extubation because of a poor cough, copious secretions, or laryngeal edema; airway protection is a separate question from ventilatory capacity.

Likewise, a single failed SBT is not a verdict — identify the cause, optimize it, and retry, typically the next day, rather than abandoning weaning or, worse, extubating into distress. Mastering this stepwise logic, the numeric thresholds, and the cardiac-versus-pump-versus-load distinction covers the great majority of liberation questions you will face.