5.2 Weaning, Airway & Ventilator Complications

Assessing Weaning Readiness

Weaning begins only when the reason for intubation is resolving. Readiness criteria are: the underlying process improving, hemodynamic stability on minimal or no vasopressors, adequate oxygenation (PaO2/FiO2 above roughly 150-200 with PEEP 5-8 cmH2O and FiO2 at or below 0.4-0.5), an intact respiratory drive, an awake and cooperative patient (an appropriate RASS), afebrile status, and an adequate cough to clear secretions.

The Rapid Shallow Breathing Index

The rapid shallow breathing index (RSBI) quantifies weaning readiness as respiratory rate divided by tidal volume in liters (f/VT). An RSBI below 105 predicts weaning success; above 105 predicts failure. Example: a patient breathing 30 times a minute with a 250 mL (0.25 L) tidal volume has an RSBI of 30 / 0.25 = 120, a rapid, shallow pattern that predicts failure. A patient breathing 20 with a 0.5 L volume has an RSBI of 40 — favorable.

The Spontaneous Breathing Trial

The spontaneous breathing trial (SBT) places the patient on minimal support — low pressure support (5-8 cmH2O), CPAP, or a T-piece — for 30 to 120 minutes to see whether they can breathe on their own. SBT failure is signaled by a respiratory rate above 35, SpO2 below 90%, a heart rate over 140 or a change greater than 20%, systolic BP above 180 or below 90, or new agitation, anxiety, diaphoresis, and accessory-muscle use. A failed trial means returning to rest settings, finding the reversible cause, and retrying the next day.

Extubation and the Cuff-Leak Test

Before extubating a patient at risk of laryngeal edema (prolonged or traumatic intubation), perform a cuff-leak test: deflate the cuff and listen for air moving around the tube. Absence of a cuff leak suggests airway edema and warns of post-extubation stridor. At extubation, suction the airway and mouth, deflate the cuff, and remove the tube on inspiration. Watch closely for stridor from laryngeal edema, treated with racemic epinephrine and steroids, and keep reintubation equipment at the bedside.

Sedation During Weaning

Weaning is impossible through deep sedation. Modern practice favors an analgesia-first (analgosedation) approach, titrating to a light target such as a Richmond Agitation-Sedation Scale (RASS) of 0 to -1 and pairing a daily spontaneous awakening trial (SAT) with the SBT. A capnography waveform that suddenly falls to near zero, or a patient who is over-sedated and apneic, must be recognized quickly — the first is often tube displacement or a loss of circulation, the second a reason the SBT will fail.

Airway Management

An endotracheal tube (ETT) placement is confirmed by waveform capnography (EtCO2) — the gold standard — plus bilateral breath sounds and a chest x-ray showing the tip 2-4 cm above the carina. Keep cuff pressure at 20-30 cmH2O to seal against aspiration without causing tracheal mucosal ischemia; too little pressure risks aspiration and micro-leak, too much risks tracheal necrosis and later stenosis. A tracheostomy is considered after roughly 10-14 days of intubation or for anticipated prolonged ventilation; it lowers airway resistance and dead space, improves comfort and oral care, and often speeds weaning. Its danger is dislodgement: within the first 7 days the tract is immature, so a dislodged tube must NOT be blindly reinserted — oxygenate with a bag-mask over the mouth or stoma and call for expert help, because a false passage is fatal. Other tracheostomy emergencies are obstruction by a mucus plug (attempt suction, then remove the inner cannula) and bleeding, where late brisk bleeding raises concern for a tracheo-innominate fistula.

Ventilator Complications

Ventilator-Associated Pneumonia (VAP)

VAP is pneumonia developing more than 48 hours after intubation. The evidence-based ventilator bundle reduces it: elevate the head of bed 30-45 degrees, perform a daily sedation interruption (sedation vacation) coupled with a spontaneous awakening and breathing trial, give oral care with chlorhexidine and subglottic suctioning, and provide DVT prophylaxis and stress-ulcer (peptic ulcer disease, PUD) prophylaxis. When suctioning, limit each pass to about 10-15 seconds and hyperoxygenate first to avoid desaturation.

Barotrauma and Volutrauma

High pressures cause barotrauma and high volumes cause volutrauma; repeated alveolar opening and closing causes atelectrauma. These injuries manifest as pneumothorax, pneumomediastinum, or subcutaneous emphysema. A tension pneumothorax presents with sudden desaturation, rising peak pressure, absent breath sounds and tracheal deviation away from the affected side, and hypotension — a true emergency requiring needle decompression followed by a chest tube.

Auto-PEEP

Auto-PEEP (intrinsic PEEP, dynamic hyperinflation, breath stacking) is incomplete exhalation that traps gas, most common in obstructive disease (asthma, COPD) and at high respiratory rates. The trapped volume raises intrathoracic pressure, drops preload, and causes hypotension; it also makes triggering harder. Manage it by lowering the rate and tidal volume, prolonging expiratory time (I:E), giving bronchodilators, allowing permissive hypercapnia, and, if a patient becomes acutely hypotensive, transiently disconnecting the circuit to let the lungs fully deflate.

Oxygen Toxicity

Prolonged FiO2 above 0.6 for more than 24-48 hours generates free radicals that injure the alveoli and cause absorption atelectasis. This is why FiO2 is weaned to the lowest level maintaining an SpO2 of about 92-96% (88-92% in chronic CO2 retainers).

DOPE for sudden deterioration on the ventilator: Displacement of the tube, Obstruction (secretions/kink), Pneumothorax, Equipment failure. Disconnect and hand-ventilate while working through it.