Strategies of Weaning from Mechanical Ventilation

INTRODUCTION

1. Readiness Testing - determining if the patient can tolerate withdrawal of support
2. Weaning / Liberation - the method by which ventilatory support is actually removed

PHASE 1: READINESS ASSESSMENT

A. Clinical Criteria for Weaning Readiness

B. Mechanical Weaning Parameters (Weaning Indices)

C. Rapid Shallow Breathing Index (RSBI) - Yang-Tobin Index

• RSBI < 105: ~70% chance of successful extubation
• RSBI > 120: ~80% chance of weaning failure - retain ventilator support
• RSBI > 105 accurately predicts weaning failure; RSBI ≤ 105 is less accurate at predicting success

PHASE 2: WEANING STRATEGIES

OVERVIEW ALGORITHM (Harrison's, 22E)

Strategy 1: Spontaneous Breathing Trial (SBT)

• Positive pressure is set to a minimum (PSV 5-7 cmH₂O) to compensate for ETT resistance, or the patient is placed on a T-piece
• Trial duration: 30 to 120 minutes
• If CPAP is used, set at 5 cmH₂O

• No marked anxiety or dyspnea
• Respiratory rate < 35 breaths/min
• SaO₂ > 90%
• Systolic BP between 90-180 mmHg
• Heart rate change < 20% from baseline
• RSBI < 105

• Tachypnea (RR > 35), accessory muscle use, paradoxical breathing
• SpO₂ < 90%
• Tachycardia, hypertension, arrhythmias
• Diaphoresis, agitation, altered mentation

Strategy 2: T-Piece / Spontaneous Breathing Trial

• T-piece attaches directly to the ETT or tracheostomy tube
• Humidified oxygen-air mixture flows into the proximal limb; exits distally
• Gas flow must be sufficient to prevent inspired air from recirculating
• End-tidal CO₂ monitoring may be used for additional safety

• Tachypnea, tachycardia, arrhythmias
• Chest retractions, use of accessory muscles
• Hypertension or hypotension
• Diaphoresis, anxiety

• Start with 10-30 min trials; progressively increase by 5-10 min
• Increase only if patient is comfortable, SpO₂ acceptable, no hypercarbia

Strategy 3: Pressure Support Ventilation (PSV) Weaning

• Initial PSV typically set at 15-20 cmH₂O; PEEP at 5 cmH₂O
• Gradually decrease PSV by 2-3 cmH₂O at a time
• Monitor VT (target 4-6 mL/kg), RR (target < 30 breaths/min), ABG
• When PSV reaches 5-8 cmH₂O, patient is considered weaned - proceed to extubation

• Reduces work of breathing imposed by the ETT
• Patient-triggered - maintains respiratory muscle activity and prevents disuse atrophy
• More comfortable; less sedation needed
• Better patient-ventilator synchrony

Strategy 4: SIMV (Synchronized Intermittent Mandatory Ventilation) Weaning

• Mandatory rate is progressively decreased by 1-2 breaths/min
• Reduce only when ABG is acceptable: PaCO₂ < 45-50 mmHg, RR < 30 breaths/min
• Recheck ABG after minimum 15-30 min at each new setting
• When IMV rate reaches 2-4 breaths/min, discontinue if oxygenation remains acceptable
• If PSV is added to SIMV, reduce PSV to 5-8 cmH₂O before discontinuing

• SIMV has the poorest weaning outcomes of all three techniques
• Mandatory breaths may impose excessive work if not well-synchronized
• Gradual step-down takes longer, prolonging ICU stay
• Still used most frequently in surgical and neurosurgical patients due to familiarity and ability to provide backup breaths

Strategy 5: CPAP (Continuous Positive Airway Pressure) Weaning

• Applied at low levels (5 cmH₂O) to maintain FRC and prevent atelectasis when bypassing the larynx with an ETT
• Can serve as an SBT method, especially post-cardiac surgery patients
• Prevents the loss of physiological glottic PEEP

Strategy 6: Automated Weaning Strategies

a. Volume Support Ventilation (VSV)

• Delivers pressure-controlled breaths targeted to a set volume
• As patient effort increases and mechanics improve, PSV automatically decreases
• If effort diminishes or mechanics worsen, PSV automatically increases
• Risk: If set volume is excessive, a recovering patient may not take over the work of breathing; if set volume is inadequate, patient performs excessive work

b. Adaptive Support Ventilation (ASV)

• Uses a sophisticated algorithm to adjust the ventilatory pattern during machine-triggered breaths
• Small clinical studies show ASV can automatically wean ventilatory support safely
• Limitation: No large RCTs comparing ASV weaning to regular daily SBT strategies yet

c. PAV+ (Proportional Assist Ventilation Plus)

• Delivers support proportional to patient-generated flow and volume
• No set pressure, flow, or volume - the "gain" on patient effort is boosted
• Uses transient end-inspiratory occlusions to measure elastance and resistance, then calculates work of breathing
• Conceptually improves flow and cycle synchrony versus conventional PSV

1. Patient rapidly recovering from sedatives/anesthesia (alerts clinicians to return of adequate spontaneous effort)
2. Patients requiring prolonged MV who have failed multiple SBTs (serves as diagnostic alert to return of respiratory function)

POST-EXTUBATION MANAGEMENT

Extubation to NIV (Non-Invasive Ventilation)

• In COPD patients intubated for acute respiratory failure, extubation to NPPV/NIV is associated with a reduction in mortality
• Indicated for patients with hypercapnia after extubation

High-Flow Nasal Oxygen (HFNO)

• For non-hypercapnic patients at high risk of post-extubation respiratory failure
• Similar efficacy to NIV in preventing reintubation; generally better patient comfort
• High-risk criteria for post-extubation failure: Age > 65, CHF, COPD, APACHE-II > 12, BMI > 30, significant secretions, > 2 comorbidities, > 7 days on MV

Cuff Leak Test

• For patients at risk of laryngeal edema (angioedema, traumatic intubation)
• Absence of cuff leak should generally preclude extubation
• Treat with IV corticosteroids for 12-24 hours before extubation in such patients

CAUSES OF WEANING FAILURE

COMPARISON OF WEANING STRATEGIES

PROTOCOL-DRIVEN WEANING

• Reduced incidence of VAP
• Shorter duration of mechanical ventilation
• Reduced ICU length of stay
• Consistent daily assessment of weaning readiness

1. Daily screening using criteria checklist
2. If criteria met → perform SBT (T-piece or low PSV)
3. If SBT passed → evaluate for extubation
4. If SBT failed → identify and treat reversible causes; repeat daily
5. Daily sedation interruption ("spontaneous awakening trial" SAT) combined with SBT

SUMMARY

• Morgan & Mikhail's Clinical Anesthesiology, 7e, pp. 2539-2542
• Harrison's Principles of Internal Medicine 22E (2025), pp. 2351-2352
• Washington Manual of Medical Therapeutics, pp. 291-292
• Murray & Nadel's Textbook of Respiratory Medicine, pp. 3185-3186
• Schwartz's Principles of Surgery, 11e, pp. 2345-2346