Weaning of ventilation in PICU
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Patients who have been ventilated for a number of days, especially if due to respiratory failure, often require a gradual reduction in their ventilatory support ( ie weaning from ventilation).
This process needs to be individualised for each patient but there are certain principles which are applicable to all:
- Successful weaning relies on the patient having an intact respiratory system ie an adequate central respiratory drive, sufficient respiratory muscle strength, and lungs that can support gas exchange. If these prerequisites are not met weaning is unlikely to be successful.
- Adequate nutrition is essential to maintain respiratory muscle strength and provide energy for breathing (with stiff lungs work of breathing can take up to 20% of total body energy). Over-nutrition is harmful though, as it can lead to an increase in CO2 production which exceeds the capacity for clearance.
- After a period of mechanical ventilation respiratory muscles atrophy and need a period of retraining to recover function. This retraining should never be to the point of exhaustion as this will delay muscle recovery. After each training period there should be a rest/recovery period. If patients are pushed to the point of respiratory exhaustion they then will require a prolonged recovery period which will delay weaning.
- Most patients are given increasing periods of time with reduced respirator support during the day and rested overnight with increased support.
- A formalised weaning protocol should be documented for each patient and will need constant updating.
- Weaning is often easier with a tracheostomy as it decreases airway resistance and allows for periods totally off the ventilator. This is less likely to be performed in children who require ventilation for less than 3-4 weeks but is often done in adults who are thought to need ventilation for longer than 1 week.
- Despite the rapid growth in different ventilator weaning modes none have proven to be superior to T piece weaning ( this involves giving the patient progressively longer periods off the ventilator over a number of days). Some of these new modes actually prolong weaning time by slowing respiratory muscle retraining.
- Patients with very borderline cardiac function may not be able to provide for the increased demands of spontaneous breathing. They may fail weaning due to inadequate blood supply to their respiratory muscles. To successfully wean these patients they require increased levels of cardiac support. A clue to this is that the venous saturation will drop before the arterial saturation as they start to fail weaning.
- It is inadvisable to wean ventilation and cardiac support simultaneously.
- Patients with poor left heart function may develop increased heart failure as positive pressure ventilation is weaned due to increased LV afterload.
- Avoid excessive amounts of free water which can result in increased lung water making the lungs less compliant. As the patient goes from positive pressure ventilation to spontaneous (negative pressure) ventilation intrathoracic blood volume will increase which may also increase lung water.
- Patients prone to atelectasis eg mordidly obese patients, may not tolerate weaning as a decrease in distending pressures may result in increased collapse causing hypoxia and increased work of breathing. They may require high levels of CPAP/PEEP during weaning.
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- Date last published: 01 November 2005
- Document type: Clinical Guideline
- Services responsible: Paediatric Intensive Care Unit
- Author(s): Dave Buckley
- Editor: John Beca
- Review frequency: 2 years
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