Page 717 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

536 PART 4: Pulmonary Disorders

LIBERATION STRATEGIES
Gradual reduction of mechanical support, termed weaning, is frequently
unnecessary and can prolong the duration of mechanical ventilation. Many intensivists have reasoned that by gradually reducing ventilatory
• Once a patient has been liberated from the ventilator, extuba- support, the respiratory muscles exercise at subfatiguing loads, leading
to gradual improvement of function. Some studies have suggested that
tion should follow if mechanisms of airway maintenance (cough, respiratory exercises (repetitions of low-load resistive breathing) can
gag, swallow) are sufficient to protect the airway from secretions. lead to successful extubation in patients who have previously failed.
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Whether to extubate is a decision which follows successful libera- However, no studies have established that respiratory muscle training,
tion from the ventilator. through the use of graded withdrawal of ventilatory support, hastens the
• In patients who fail their first trial of spontaneous breathing, atten- recovery to unassisted breathing.
tion should turn to defining and treating the pathophysiologic Two large studies assessed the role of weaning strategies once clini-
processes underlying failure. cians judge that weaning can proceed. Brochard and colleagues studied
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• One weaning regimen, the gradual reduction of intermittent man- 456 medical-surgical patients being considered for weaning, of whom
datory breaths, prolongs patients’ time on mechanical ventilation. 347 (76%) were successfully extubated on the first day. One hundred
• Liberation from mechanical ventilation is achieved most expedi- and nine patients who failed an initial spontaneous breathing trial (SBT)
tiously if patients are given a trial of spontaneous breathing (T-Piece were randomized to be weaned by one of three strategies: (1) T-piece
or pressure support ≤7 cm H O) each day. Patients remain on ventila- trials of increasing length until 2 hours could be tolerated; (2) synchro-
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tors unnecessarily when clinicians do not put this simple plan in place. nized intermittent mandatory ventilation (SIMV) with attempted reduc-
tions of 2 to 4 breaths/min twice a day, until 4 breaths/min could be
• Patients who have had most correctable factors addressed and tolerated; (3) pressure support ventilation (PSV) with attempted reduc-
remain marginal with regard to ventilatory capacity should in most tions of 2 to 4 cm H O twice a day until 8 cm H O could be tolerated.
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circumstances undergo a trial of extubation rather than remain Patients randomized to the three strategies were similar with regard to
intubated for protracted periods of time. Noninvasive positive disease severity and duration of ventilation before weaning. There was
pressure ventilation may be useful in these patients to transition no difference in the duration of weaning between the T-piece and SIMV
them to fully spontaneous breathing following extubation. groups, but PSV led to significantly shorter weaning compared to the
combined T-piece and SIMV cohorts.
Esteban and colleagues performed a similar study of 546 medical-
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Positive pressure ventilation can be lifesaving, but is also associated surgical patients, 416 (76%) of whom were successfully extubated on
with many complications (Table 60-1). Most studies have demonstrated their first day. The 130 patients who failed were randomized to undergo
that earlier withdrawal of mechanical ventilatory support, when fea- weaning by (1) once-a-day T-piece trial, (2) two or more T-piece or
sible, is associated with better outcomes. We will outline principles and CPAP trials each day as tolerated, (3) PSV with attempts at reduction of
approaches to the withdrawal of mechanical ventilation in a way to 2 to 4 cm H O at least twice a day, and (4) SIMV with attempts at reduc-
achieve this milestone at the earliest possible time and in a safe fashion. ing 2 to 4 breaths/min at least twice a day. Patients assigned to the four
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groups were similar with regard to demographic characteristics, acuity
TABLE 60-1 Complications Associated With Endotracheal Intubation of illness, and a number of cardiopulmonary variables. The weaning suc-
and Mechanical Ventilation cess rate was significantly better with once-daily T-piece trials than for
Complications Related to the Endotracheal Tube PSV and SIMV. Twice-daily T-piece trials were not significantly better.
Several important conclusions can be drawn from these relatively
Endotracheal tube malfunction—mucus plug, cuff leak large studies. First, and most important, the majority of patients can be
Endotracheal tube malposition successfully extubated on the first day that physicians recognize readi-
Self-extubation ness after a brief (30-120 minute) trial of breathing through a T-piece:
Nasal or oral necrosis weaning is not necessary for most patients. Second, both studies suggest
Pneumonia that in patients who have failed an initial T-piece trial, SIMV weaning
prolongs the duration of mechanical ventilation.
Laryngeal edema That most patients can be extubated on the first day suggests that cli-
Tracheal erosion nicians are slow to recognize that patients no longer require ventilatory
Sinusitis support. In a landmark study, a daily screen and SBT were used to iden-
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Complications Related to the Ventilator tify patients who had recovered from respiratory failure. Simply notify-
ing physicians that patients had passed an SBT reduced the duration of
Ventilator-induced lung injury (VILI) ventilation by 1.5 days; lessened complications; and lowered costs. This
Ventilator-induced diaphragm dysfunction (VIDD) was followed by another trial showing that a therapist-directed protocol
Alveolar hypoventilation/hyperventilation to conduct SBTs, without daily supervision by a weaning physician, was
feasible and safe.
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Atelectasis
Hypotension EXPEDITING LIBERATION
Pneumothorax
Since mechanical ventilation has numerous risks, including infection and
Diffuse alveolar damage barotrauma (see Table 60-1), it is appropriate to work aggressively to
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Effects on Other Organ Systems repair the “broken” patient; prevent new problems; and determine each
Gastrointestinal hypomotility day whether the patient still requires the ventilator. Many ICUs employ a
“ventilator bundle,” including head-of-bed elevation; daily sedative inter-
Pneumoperitoneum
ruption; breathing readiness assessment; and prophylaxes against throm-
Stress gastropathy and gastrointestinal hemorrhage boembolism and gastrointestinal hemorrhage to ensure attention to these
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Arrhythmias important measures. We highlight methods used to expedite readying
Salt and water retention the patient for liberation and to identify patients who are appropriate
candidates for liberation. We also describe an approach to patients who
Malnutrition
do not rapidly succeed at being liberated from mechanical ventilation.

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