Critical Care · Year 4 · from Critical Care
Case 2: Weaning Failure and Spontaneous Breathing Trial Assessment
Clinical Image
Source: Wikimedia Commons - Mechanical Ventilation - CC BY-SA 3.0
Case Presentation
A 62-year-old man with COPD and heart failure is on ICU day 5 following intubation for acute hypercapnic respiratory failure during a COPD exacerbation. His pneumonia has been treated and he is now on stable, low ventilator settings: pressure support 10 cmH2O, PEEP 5 cmH2O, FiO2 35%. He meets weaning readiness criteria: FiO2 40% or less, PEEP 8 cmH2O or less, hemodynamically stable (no vasopressors), alert and following commands, and cough reflex present. The team initiates a spontaneous breathing trial (SBT) using pressure support of 5 cmH2O and PEEP 5 cmH2O. After 15 minutes, he develops respiratory distress with respiratory rate increasing from 18 to 38 breaths/min, tidal volumes decreasing from 450 mL to 250 mL, and oxygen saturation falling from 95% to 88%. His rapid shallow breathing index (RSBI = RR/VT in liters) calculates to 38/0.25 = 152, well above the threshold of 105 indicating likely weaning failure. The SBT is terminated and he is returned to full support. Evaluation for causes of weaning failure reveals newly elevated BNP (2,400 pg/mL) and bilateral pleural effusions on bedside ultrasound. He is diuresed with IV furosemide, achieving 3 liters negative fluid balance over 48 hours. Repeat SBT on day 7 shows RR 22, VT 400 mL (RSBI = 55), and SpO2 94% maintained throughout 30 minutes. He is successfully extubated with prophylactic BiPAP given his COPD history.
Key Learning Points
- Weaning readiness criteria include: FiO2 40% or less, PEEP 8 cmH2O or less, hemodynamic stability, alertness, intact cough, and resolution of the condition requiring intubation
- The rapid shallow breathing index (RSBI = respiratory rate / tidal volume in liters) predicts weaning success: RSBI less than 105 suggests likely success; RSBI greater than 105 predicts failure
- SBT failure criteria include: RR greater than 35, SpO2 less than 90%, HR change greater than 20%, signs of distress (accessory muscle use, diaphoresis, agitation)
- Common causes of weaning failure include cardiac dysfunction (requiring diuresis), weakness (requiring rehabilitation), secretions (requiring pulmonary toilet), and anxiety (requiring reassurance or anxiolysis)