When is the patient ready to start ventilator weaning?

• Resolution of pathology resulting in the need for mechanical ventilation

• Able to assess mental status (ie can the patient follow commands)

• Hemodynamics and respiratory physiology is optimized (ie ABG normalized or returned to patients baseline, and normalization or stabilization of cardiac function)

• Minimal ventilator settings (FiO2 21%, PEEP 5)

• NOTE: Even if there is no immediate plan to extubate, sedation holiday and spontaneous breathing trials should still be performed [unless there are specific contraindications]

Spontaneous breathing trial

• Spontaneous mode of ventilation (such as pressure support or CPAP) with 5-8 cm H2O support during inspiration (basically overcoming the force required to breath through the small diameter of the ETT)

Failing SBT

• Hemodynamic instability (hypotension or hypertension, tachycardia or bradycardia)

• Agitation

• Respiratory instability (hypoxia, inadequate tidal volume, tachypnea or decreased respiratory rate)

Extubation parameters- how do we know if the patient is ready to be liberated from the ventilator?

• Able to generate adequate minute ventilation

• Rapid shallow breathing index (RSBI)- RR/ TV. High respiratory rate (rapid) and low tidal volume (shallow) are more suggestive that a patient isn't appropriate for extubation. Value <105 suggests the patient will successfully extubate. This is also known as the Tobin index.[1]

• Negative inspiratory force (NIF)- the patient's ability to generate negative pressure with inhalation.

• Cuff leak- ability to move air around the endotracheal tube. Not mandatory to evaluate for cuff leak prior to extubate EXCEPT for patients is at high risk for airway edema (traumatic intubation, intubated >6 days, large ETT, female, reintubation after unplanned extubation).

Reasons for failed ventilator weaning

• Prolonged hospitalization and associated weakness

• Hypophosphatemia

• Primary process requiring mechanical ventilation is unresolved

Passed SBT...but failed ventilator liberation?

• Excess secretions/ inability to cough

• Cardiac instability related to physiological changes with loss of positive pressure (specifically decrease in intra-thoracic pressure leading to decreased cardiac output)

1.  Tobin Index. Yang KL, Tobin MJ. A Prospective Study of Indexes Predicting the Outcome of Trials of Weaning from Mechanical Ventilation. N Engl J Med. 1991 May 23;324(21):1445-50.