Page 561 - Clinical Application of Mechanical Ventilation

Weaning from Mechanical Ventilation 527

WEANING PROCEDURE

The spontaneous breathing trial (SBT) is the major diagnostic test to deter-
spontaneous breathing trial
(SBT): An evaluation of a mine if patients can be successfully extubated and weaned from mechanical ven-
patient’s readiness for weaning tilation. Low level pressure support (PS), continuous positive airway pressure
from mechanical ventilation and
extubation. Spontaneous breath- (CPAP), or automatic tube compensation (ATC) may be used along with SBT
ing may be augmented with to augment a patient’s spontaneous breathing efforts (Keenan, 2002). Based on
low-level (#8 cm H 2 O) of pres-
sure support, CPAP, or automatic the results of the sixth International Consensus Conference on Intensive Care
tube compensation (ATC). SBT Medicine, synchronized intermittent mandatory ventilation (SIMV) should
may last up to 30 minutes.
be avoided as a stand-alone weaning modality (Boles et al., 2007). However,
SIMV remains an effective tool in providing partial ventilatory support during
synchronized intermittent continuous mechanical ventilation.
mandatory ventilation (SIMV):
A mode of ventilation that permits
spontaneous breaths between Spontaneous Breathing Trial
ventilator breaths. The ventilator
breaths are synchronized (manda-
tory breaths that may come Once a decision is made to proceed with weaning, the patient may be discontinued
slightly sooner or later) to coincide
with the patient’s inspiratory from full ventilatory support and placed on a spontaneous breathing mode via the ven-
efforts.
tilator or T-tube (Brigg’s adaptor) for up to 30 minutes. Oxygen and low level pressure
support may be used to supplement oxygenation and augment spontaneous breathing.
The criteria for passing an SBT include normal respiratory pattern (i.e., absence
of rapid shallow breathing), adequate gas exchange, and hemodynamic stability.
The results of six studies show that only 13% of patients who successfully passed the
SBT and were extubated required reintubation (Boles et al., 2007).
There is no difference in terms of successful SBT among patients undergoing
stand-alone SBT, SBT with low level of pressure support, and SBT with CPAP
or automatic tube compensation (Boles et al., 2007). Since patients who fail the
SBT do so within the first 20 to 30 minutes of SBT, there is no need to use an ex-
tended SBT (e.g.,120-min trial) (Yang et al., 1991; Perren et al., 2002). Table 16-4
describes the procedure for the spontaneous breathing trial and other partial ven-
tilatory support procedures. Note that SIMV is used to provide partial ventilatory
support and it is not recommended as a stand-alone weaning modality.

Failure of SBT

Patients who fail the SBT often do so within the first 20 to 30 minutes of the trial.
They also exhibit the following clinical signs and symptoms: agitation and anxiety,
diminished mental status, diaphoresis, cyanosis, and evidence of increased work of
breathing (Boles et al., 2007). Clinical data that correlate with failure of SBT are
summarized in Table 16-5.

Pressure Support Ventilation

Pressure support ventilation (PSV) or similar adjuncts (e.g., proportional pressure
support, volume-assured pressure support) may be applied during weaning. PSV

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