Weaning from mech vent: Mgmt

Before an attempt is made to wean from mechanical ventilation and extubate a patient in the ICU the paitent must meet basic criteria:

• Must be adequately mentating, able to protect airway and initiate respiration.
• Must be hemodynamically stable – may include minimal circulatory support
• Usually able to maintain PaCO₂ < 60 with a pH > 7.25
• Able to obtain PaO₂ > 60 mmHg and maintain SaO₂ > 90% on minimal PEEP (5-10 cmH₂O) and moderate FiO₂ (40-50%)

If the patient meets these criteria then they should be considered eligible for a screening assessment for liberation from mechanical ventilation. Often these are assessed daily based on a protocol deployed by an ICU. The Awake and Breathing Controlled Trial (ABC) used this approach and immediately implemented a spontaneous breathing trial if the patient met these criteria.

While multiple predictors of successful weaning have been reported, the Rapid Shallow Breathing Index (RSBI) is one simple and often applied method. This examines the ratio of the RR / Vt (in L). Patients who are likely to fail often have high respiratory rates or low tidal volumes, thus would have high RSBI values. A Vlaue less than 105 is considered to be a predictor of success.

If a patient passes both of these assessments a period of Spontaneous Breathing Trial can be entered into. The patient is placed on a minimal amount of support – i.e. 5-10 cmH₂O of CPAP, low level Pressure Support Ventilation to assist in the overcoming of resistance of tube or even T-Piece only for 30mins to 2 hrs. If the patient does not tire, and appears to be doing well at the conclusion of the test then they proceed to extubation.

Re-intubation rates are around 25% in the described literature. Patients who fail extubation are at an increased risk of mortality.