A mechanical ventilator is a device that assists a patient to breathe (ventilate) when they are having surgery or cannot breathe on their own due to a critical illness. The patient is connected to the ventilator with a hollow tube (artificial airway) that goes in their mouth and down into the primary airway or trachea. They remain on the ventilator until they improve adequate to breathe on their own. Weaning from mechanical ventilation can be defined as the procedure of abruptly or gradually withdrawing ventilatory aid. Now, let’s see when to wean a patient.

The three most important parameter need to be looked upon before weaning ventilators are

1. The primary cause for ventilation is corrected
2. Hemodynamically stable
3. Ease of oxygenating and ventilate

A complete resolution of the inciting cause of respiratory failure leading to the requirement of ventilation, is not mandatory but a partial resolution is needed prior to weaning. For hemodynamically stable, there should be no evidence of ongoing ischemia, fresh arrhythmias, or the need for vasopressors which indicate worsening hemodynamics. Normally 40% of the CO is required by the respiratory system to perform its function. In cases of respiratory failure when the work of breathing is increased the respiratory requirement would be, even more, thus make it more difficult to wean an unstable patient. Other general measures that need to be corrected like, correction of acid-base disorder, electrolyte imbalance, avoid volume overload, adequate mental status, avoiding malnutrition. Acidosis increases mechanical ventilator requirements to normalize pH. Especially in COPD, correcting acidosis rapidly on the ventilator will lead to bicarbonaturia through renal compensation which will then produce acute respiratory acidosis at the time of spontaneous breathing and lead to failure. Apart from these, adequate oxygenation and ventilation are also looked upon. The balance between respiratory muscle strength and load. Tidal Volume > 4ml/kg (PPV of 0.67 and  NPV of 0.85), vital capacity > 5 and < 10 ml/kg (needs patient cooperation and hence not easy). Maximum voluntary ventilation is also to be looked upon.

To know more about weaning and extubation, you can enroll in Mechanical Ventilation (A Case-based Approach) by Dr. Sanjith Saseedharan (HOD- Critical Care, S.L.Raheja Hospital) here, https://docmode.org/mechanical-ventilation-a-case-based-approach/