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Removing a patient
from a ventilator involves discontinuation of mechanical ventilation and
extubation.
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There are two parts to
weaning: weaning to partial ventilator support and weaning to
discontinuation. There is little evidence that partial modes are more
effective than T-piece trails. Of these modes, pressure support is the
best.
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The single most
traumatic event for the patient is conversion from positive pressure to
negative pressure ventilation.
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To extubated a
patient, they need to be awake, able to cough and protect their airway.
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If it is possible to
wean a patient to extubation, but the patient cannot protect his/her
airway, it is best to perform tracheotomy.
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Although the
ventilator only appears to support on organ system, the lungs, this is
not in fact the case.
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For a patient to self
ventilate, many body systems must be functioning: the cardiopulmonary
apparatus, the central nervous system, the nerves that supply the
diaphragm (including the neuromuscular junctions), the muscles
themselves. Moreover the patient must be willing to breath and maintain
their own functional residual capacity (not if there is diaphragmatic
splinting due to pain). There must be room in the abdomen for the
diaphragm and lungs to move into. There must be adequate hemoglobin to
deliver oxygen to the tissues.
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It may be difficult to
wean a patient if ongoing inflammatory processes persist in the lungs:
consolidation, fibrosis, auto-PEEP, diffusion defects.
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To overcome these
problems, a holistic approach must be adopted. Muscles must be trained
and nourished, and patient-ventilator interaction encouraged.
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There most effective
method of weaning to discontinuation is spontaneous breathing trials (SBT).
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One must determine suitability for SBTs
before commiting to them.
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If a patient fails an SBT, then it is
important to look for the reason and reverse it. SBTs should not be
performed more than once daily.
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A reintubation rate of
10% is acceptable. Patients deserve a trial of extubation, and many will
do well in spite of poor mechanics (you must use clinical judgment).
