What is Weaning from Mechanical Ventilation?
It is crucial to get the timing just right as to when to discontinue mechanical ventilation and extubate. If too early, this might result in reintubation and reinstitution of ventilatory support - this has been shown to be associated with adverse outcomes. On the other hand, if extubation is delayed, problems can arise due to prolonged mechanical ventilation. Determining readiness is the most important aspect of weaning. The underlying disease process that necessitated mechanical ventilation should be under control. The patient should be awake and able to respond, deep breathe and cough on command. Secretions should not be too much or too thick. The gas exchange should be satisfactory - generally, a PO2 of about twice the FiO2 is considered adequate. Once these criteria are met, it is appropriate to give the patient a trial of spontaneous breathing. This may be; (i) a trial on Pressure Support mode of 8 to 10 cm of H2O, or (ii) on a ‘T' piece. After about two hours of spontaneous breathing on one of these modes, if the patient remains OK the patient may be liberated from mechanical ventilation, i.e. extubated.
Signs of unsuccessful weaning
• Respiratory rate goes up,
• Tidal volumes too shallow,
• Hypoxia/hypercarbia,
• Tachycardia,
• Hypertension or hypotension,
• Reduced responsiveness,
• Sweating, and
• Use of accessory muscle of breathing.
If any one of these signs develop, the spontaneous breathing trial should be aborted, the patient returned back to sufficient mechanical ventilatory support and rested. The trial may be repeated the next morning. Several spontaneous breathing trials in a day is not recommended.