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WEANING

• Weaning from invasive mechanical ventilation is the process of gradually decreasing ventilatory support until such time as the patient can breathe without mechanical assistance.

• Weaning is deemed successful when the patient has been independent of the ventilator for 48 consecutive hours.

• The aim of weaning from mechanical ventilation is to maximize respiratory function without fatiguing the respiratory muscles. If the muscles are fatigued it may take 48 hrs to recover.

• Prior to extubation use of spontaneous breathing trials may be of benefit.

• All patients receiving ventilatory support should be assessed on a daily basis for their suitability for weaning.

When to Initiate Weaning ?

• Reversal of primary problem causing need for ventilation

• Patient is awake and responsive, ability to cough

   

• FiO₂ <40%

• PaO₂ > 60mmHg / SaO₂ >90% unless underlying chronic lung condition

• RR<35bpm

• Acceptable levels of PEEP/CPAP (5 cmH₂O)

• Vital Capacity >10 -15 ml/kg, Spontaneous tidal volume : >5 ml/kg

• Minute ventilation :10 – 15 L/min

• Acceptable acid/base balance^* (pH>7.25)

• Hb>7 gm/dl and hemodynamically stable

• Adequate pain control

^*:based on clinical diagnosis

How to wean

1. Reduction in level of ventilator support.

    

• PSV & SIMV are the most commonly used ventilatory modes when weaning is being attempted, although ACV may also be useful.

• The degree of ventilatory support should be gradually weaned so that patient contributes increasingly to the work of breathing.

2. Introduction of Ventilator Independence

    

• A T-piece trial ideally for 30 minutes upto a maximum of 2 hours. If successful the patient can be extubated immediately. If failed repeat trial on a daily basis.

• Alternatively a gradual weaning trial with T-piece initially for around 5 minutes under close observation. As the patients condition improves the duration and frequency of trial is increased. It may take few hours to weeks for independence is achieved.

   

2. Management of artificial airway

    

• Weaning may be facilitated by the use of a tracheostomy tube. This allows reducing the dead space, discontinuing sedation, but impairs swallowing and adequate coughing.

Spontaneous Breathing Trial

• The spontaneous breathing trial is an traditional approach to weaning patients from mechanical ventilation.

• It usually involves disconnecting from ventilator and connecting to T-Piece . Other variants of SBT are low level PSV, CPAP to overcome resistance to breathing through an endotracheal tube.

• Trials comprising CPAP (5cmH₂o), PSV (7cmH₂O) and T-piece methods to ascertain readiness for extubation do not demonstrate any greater superiority of one method to another.

• Patients successfully completing an SBT may proceed to extubation. Those who fail SBT's may require a slower form of weaning involving SBT of a gradually increasing duration. Consider tracheostomy as well.

Patients failing SBT

• Patient's failing their initial SBT are weaned gradually with either

1. T-Piece trial

2. SIMV or

3. PSV

1. T-Piece Trial

• T-piece trial involve periods of supported ventilation being gradually broken by SBT. The duration and frequency are increased gradually until the patient can manage 2h without problems.

   

2. SIMV

• In SIMV the patient is weaned off gradually by decresing the manadatory breath rate by 2-4 bpm on a twice daily basis. The end point is RR of 4-5 bpm. The patient meeting the preset criteria are then extubated.

   

3. PSV

• In PSV the PS is gradually reduced by 2-4 cmH₂O twice a day and more often if tolerated. The end point is PSV at around 5 -8 cmH₂O for a duration of 2 -24 h.

• Once the patients satisfy all prerequisites they are extubated.

Some trials have shown that SIMV was found to be least effective method of weaning. In modern ventilators SIMV has PS function as well where the spontaneous breaths are supported and act as a PSV.

Tracheostomy

• It is generally accepted that tracheostomy benefits the patients requiring long term ventilatory support.

• This helps to give better oral care, improved mobility of the patient, improved patient comfort, reduce dead space and need for sedation.

• It also reduces length of hospital stay and rates of pneumonia.

Updated on 21/9/2015

Reference

• Intensive care society national guidelines – When and how to wean. 2007

• Weaning from mechanical ventilation. Jeremy . Continuing Education in Anasthesia, Critical Care & Pain. Volume5 Number 4. 2005

• Practical pulmonary and critical care medicine. Zab Mosenifar.