“Guidelines are not ‘one size fits all,’ ” stressed Dr. Ely. “They should be personalized by each institution.” The new guidelines are intended to enhance, not replace, clinical judgment, he said.

Dr. Ely explained that if, in a particular situation, there was an important reason to deviate from a protocol, “then clinical judgment and ‘gestalt’ should be used to allow appropriate decision making. Otherwise, evidence supports that the majority of patients can be managed safely and effectively by protocols.” He also noted that the use of protocols “results in numerous improvements in clinical outcomes.”

Each recommendation in the new weaning guidelines was based on one of three grades of evidence: (A) randomized and non-randomized controlled trials with consistent, statistically significant results; (B) observational studies or controlled trials with less consistent findings; or (C) expert opinion when more scientific evidence was lacking.

BEGINNING THE PROCESS

The process of withdrawing ventilatory support begins with recognition of adequate recovery from respiratory failure, the guidelines state. Therefore, a formal assessment of the possibility of discontinuing mechanical ventilation is usually warranted if there is evidence that:

• The underlying cause of respiratory failure has been at least partially reversed.

• Oxygenation is adequate.

• The patient is hemodynamically stable and can initiate an inspiratory effort.

The guideline authors acknowledge, however, that there is only grade B evidence to support these specific criteria.[2]

However, there is grade A evidence to support an assessment of weaning readiness through use of a brief period of spontaneous breathing (ie, one without substantial ventilatory support). Such a spontaneous breathing trial can establish the patient’s ability to be liberated from a ventilator.[3] Tolerance of a spontaneous breathing trial can be judged by the respiratory pattern, adequacy of gas exchange, hemodynamic stability, and the patient’s level of comfort.

Permanent withdrawal of ventilatory support should be considered for patients who can tolerate a spontaneous breathing trial lasting 30 to 120 minutes. Such patients are successfully removed from the ventilator at least 77% of the time, multiple studies have shown. Furthermore, there are no data to show that a spontaneous breathing trial adversely affects a patient’s outcome if it is terminated promptly once evidence of weaning failure develops.

Assessments of airway patency and the ability to protect the airway determine if extubation is also appropriate (grade C evidence). Airway patency can be evaluated with the cuff leak test while the patient is still being mechanically ventilated. This test involves measuring the volume of air that escapes around an endotracheal tube when the cuff is deflated. The quality of cough with suctioning, the amount of airway secretions, and suctioning frequency help to gauge the ability to protect the airway.

WHEN WEANING FALLS

If the patient cannot tolerate a spontaneous breathing trial, the causes of failure should be identified, if possible. After the reversible causes of failure are corrected, a repeat spontaneous breathing trial should be performed every 24 hours (grade A evidence). However, the repeat trial should be undertaken only if:

• The acute disease phase is resolved.

• The physician believes successful withdrawal of ventilatory support is possible.

• The patient exhibits adequate cough reflexes, mentation, oxygenation, and hemoglobin levels; metabolic and cardiovascular stability; and no fever or significant respiratory acidosis.

Between spontaneous breathing trials, patients should be given a stable, non-fatiguing, comfortable form of ventilatory support because it is far less time-consuming than is a gradual reduction in support (grade B evidence). More important, a stable level of ventilatory support optimizes patient comfort and minimizes sedation needs by reducing the risk of ventilatory muscle overload. It has also been associated with more rapid weaning.[4]

Unless there is clear evidence of irreversible disease (eg, a high spinal cord injury or advanced amyotrophic lateral sclerosis), a patient who requires prolonged mechanical ventilation should not be deemed permanently ventilator-dependent until at least three months of weaning trials have failed to produce evidence that the patient can breathe spontaneously (grade B evidence). In a few patients, it may take up to six months to make that determination, the guideline authors point out.

When it becomes clear that prolonged mechanical ventilation is required, tracheostomy should be considered (grade B evidence). However, in most cases, tracheostomy should not be performed until after an initial period of stabilization on the ventilator. In many cases, the procedure offers patients better comfort and mobility, the ability to speak and eat, and a more secure airway. Tracheostomy is not without risk, however, and it may increase costs.

Early tracheostomy—performed two to 10 days after the start of ventilation—is most likely to benefit patients who:

• Need high levels of sedation to tolerate translaryngeal tubes.

• Have marginal respiratory mechanics (a tracheostomy tube with lower resistance may reduce the risk of ventilatory muscle overload).

• May benefit psychologically from the ability to speak, eat, or move about.

• Require physical therapy (the enhanced mobility permitted by tracheostomy may facilitate the therapy).

ANCILLARY STRATEGIES

Depressed respiratory drive and pain are the main reasons for ventilator dependence in postsurgical patients. For these patients, the guidelines advise anesthesia/sedation, pain management, and ventilator strategies aimed at early extubation (grade A evidence).

Five randomized, controlled studies have shown that a lower anesthetic/sedation regimen permits earlier extubation after cardiac surgery. In fact, the guideline authors report, pooled results showed that the lower anesthetic/sedation regimen reduces the duration of mechanical ventilation by a mean of seven hours. Aggressive strategies to reduce ventilatory support have also been linked with earlier weaning in postsurgical patients.

However, strategies to optimize sedation, analgesia, and reductions in ventilatory support need not be time-consuming; in fact, they can be protocol driven. One such protocol, implemented by nurses, reduced the duration of mechanical ventilation by 50% in a large, randomized, controlled trial; it decreased the median ICU stay and hospital stay by two and three days, respectively.[5]

This is far from the only randomized controlled trial to show that protocols driven mainly by nonphysician health care workers can improve clinical outcomes among mechanically ventilated patients. The guidelines therefore advise ICUs to develop and implement weaning protocols for use by these workers (grade A evidence).

—Timothy Begany

References
1. Ely EW, Baker AM, Dunagan AP, et al. Effect on the duration of mechanical ventilation of identifying patients capable of breathing spontaneously. N Engl J Med. 1996;335:1864-1869.
2. MacIntyre NR, Cook DJ, Ely EW Jr, 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(suppl 6):375S-395S.
3. Ely EW, O’Meade M, Haponik E, et al. Mechanical ventilator weaning protocols driven by non-physician health care professionals. Chest. 2001; 120(suppl 6):454S-463S.
4. Esteban A, Frutos F, Tobin MJ, et al. A comparison of four methods of weaning patients from mechanical ventilation. N Engl J Med. 1995;332: 345-350.
5. Brook AD, Ahrens TS, Schaiff R, et al. Effect of a nursing-implemented sedation protocol on the duration of mechanical ventilation. Crit Care Med. 1999;27:2609-2615.

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