Weaning / Discontinuation  Spontaneous Breathing Trials




The best way to determine suitability for discontinuation of mechanical ventilation is to perform a spontaneous breathing trial. There are three ways to do this: putting the patient  on a minimum pressure support and PEEP (for example 5-7cmH2O PS/5cmH2O PEEP performing mechanics and extubating), using CPAP alone, or using a T-piece.

A T-piece (or trach-collar) trial involves the  patient breathing through a T-piece (essentially the endotracheal tube (ett) plus a flow of oxygen-air and no ventilatory assistance) for a set period of time. The work of breathing is higher than through a normal airway (although this simulates laryngeal edema/airway narrowing). If tolerated, the chances of successful extubation are high. If not reattachment to a ventilator is simple.
 An alternative variant to this is the use of a CPAP circuit, which overcomes some of the work of breathing through the ett and prevents airway collapse.
 Many physicians extubate the patient directly from PS and PEEP (the PS overcomes the tube resistance). The conventional wisdom is that 7cmH2O of pressure support is required to overcome the resistance through a size 7.5mm (internal diameter) endotracheal tube, and 3cmH2O through a tracheostomy. If a smaller tube is in place, pressure support of 10cmH2O is required.

If the patient tolerates a spontaneous breathing trial with any of these modes, then one should proceed to extubation.

General measures:

  • Ensure the patient is suitable for weaning CLICK HERE
  • Conduct wean to extubation (spontaneous breathing) trials early in the morning, when the patient is fully rested and there is a full compliment of staff available.
  • During these trials the patient should be awake and co-operative, apyrexial and on minimal pressor support (vasopressors are not a contraindication to extubation, although they are a sign that the patient may still require pulmonary support).
  • Place the patient in the upright or semi-upright position and explain what you are attempting to do.
  • Check for a cuff leak by deflating the cuff and occluding the ett. The absence of a cuff leak is not a contraindication to extubation, as the tube may be snug with the trachea, but should alert the physician to the possibility of laryngeal edema.
  • Suction out the tube, airway and oropharynx.

How do I know if the patient is intolerant of a spontaneous breathing trial?

Source: MacIntyre NR, Cook DJ, Ely EW, Jr., Epstein SK, Fink JB, Heffner JE et al. Evidence-based guidelines for weaning and discontinuing ventilatory support: a collective task force facilitated by the American College of Chest Physicians; the American Association for Respiratory Care; and the American College of Critical Care Medicine. Chest 2001; 120(6 Suppl):375S-395S




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