Answer
The preferred method of weaning is the SBT. This is an attempt to gauge how the patient might do if he or she is immediately removed from the ventilator. This method is also referred to as the "sink-or-swim" trial. The key is to withdraw ventilatory support while oxygenation is continued.
The simplest form of SBT is the T-piece trial. The patient is disconnected from the ventilator, and the endotracheal or tracheostomy tube is hooked to a flow-by oxygen system, usually from the wall oxygen outlet. The transition from the ventilator tubing to the new tubing attached to the wall oxygen outlet requires extra work and patient monitoring by the respiratory therapist.
The same assessment can be made by using the continuous positive-airway pressure (CPAP) mode while the patient is still connected to the ventilator. This is a relatively common method of assessing the patient's ability to do the work of breathing by himself or herself. Variations on this theme include adding a small amount of pressure and using a CPAP of 5 cm water or a CPAP of 0 but with a pressure-support ventilation (PSV) of 5-6 cm water to offset the resistance from the artificial airway. To the authors' knowledge, no controlled studies have shown any superiority in assessing the outcomes of weaning between these approaches.
In some studies, approximately 80% of patients receiving mechanical ventilation do not require prolong weaning. This observation explains why SBT is both useful and practical. This approach has had the most success with weaning in randomized controlled trials. Therefore, it is a preferred approach to removing patients from mechanical ventilation.
The SBT should last 30-90 minutes. At the end of the SBT, the patient should be evaluated for possible extubation, as his or her blood pressure, respiratory rate, heart rate, and gas exchange are also considered. A SBT should be performed only once a day. Several SBTs a day offer no additional benefit compared with one.
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An example of the Drinker and Shaw negative-pressure ventilator (iron lung).
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The pressure, volume, and flow to time waveforms for assist-control ventilation.
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The pressure, volume, and flow to time waveforms for controlled ventilation.
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The components of mechanical ventilation inflation pressures. Paw is airway pressure, PIP is peak airway pressure, Pplat is plateau pressure.
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The effects of decreased respiratory system compliance (A) and increased airway resistance (B) on the pressure-time waveform.
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Determination of the lower inflection point to estimate the best (optimal) positive end-expiratory pressure (PEEP) from the pressure-volume hysteresis curve.
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The effect of positive end-expiratory pressure (PEEP) on the pressure-time inflation curve.
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The pressure, volume, and flow to time waveforms for synchronized intermittent mandatory ventilation (SIMV).
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The pressure, volume, and flow to time waveforms for synchronized intermittent mandatory ventilation (SIMV) with pressure-support ventilation.
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The flow to time waveform demonstrating auto–positive end-expiratory pressure (auto-PEEP).
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The pressure, volume, and flow to time waveforms for pressure-regulated volume-controlled ventilation.
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The pressure, volume, and flow to time waveforms for proportional-assist ventilation.
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The pressure, volume, and flow to time waveforms for airway pressure–release ventilation.
