SAN FRANCISCO--The American College of Chest Physicians (ACCP) has given physicians a sneak peek at its tentative guideline on weaning patients from mechanical ventilation. The final version of the guideline is scheduled for publication sometime in early 2001.

The sneak preview was presented at the most recent annual meeting of the ACCP. Neil R. MacIntyre, MD, a Professor in the Division of Pulmonary Medicine at Duke University Medical Center, in Durham, North Carolina, and other team leaders from the Evidence–Based Weaning Project summarized their most important recommendations.[1]

The quality of the evidence that backs the guideline varies from randomized, controlled trials to observational studies. In fact, the guideline authors discovered, many proposed weaning practices are not supported by research data but rather are based on clinical practice.

The guideline is a collaborative effort of the ACCP, the Society of Critical Care Medicine, and the American Association for Respiratory Care and was created, in part, using a comprehensive evidence-based medicine review conducted at McMaster University, in Hamilton, Ontario.

Funding was provided by the US Agency for Healthcare Research and Quality.

SPONTANEOUS BREATHING TRIALS

Spontaneous Breathing Trials The guideline focuses on patients receiving mechanical ventilation for respiratory failure. The authors recommend formal assessment for weaning readiness if all of the following are present:

• There is some reversal of the acute disease process that prompted intubation.

• Oxygenation is adequate, as indicated by a sufficient partial pressure of arterial oxygen (PaO2) on a low fraction of inspired oxygen (FiO2) and a PaO2/FiO2 ratio above 150 mm Hg with minimal positive end–expiratory pressure.

• The patient demonstrates hemodynamic stability, defined as a lack of hypotension or a need for only low–dose pressors.

• The patient can initiate an inspiratory effort.

For patients who meet these criteria, a brief spontaneous breathing trial is considered safe and is indicated at least once daily.[2] Practitioners may conduct these trials with a T–piece after taking the patient off the ventilator. The trials also may be performed while the patient is on the ventilator, with or without minimal pressure support or continuous positive airway pressure.

“I am not sure how much difference there is in those approaches for most patients,” commented Dean R. Hess, PhD, an Assistant Professor of Anesthesia at Harvard Medical School, in Boston.

To assess patient tolerance of a spontaneous breathing trial, it is necessary to monitor hemodynamics, gas exchange, and the patient’s comfort. “It appears that patients who tolerate 30 to 120 minutes of spontaneous breathing are probably ready for ventilator discontinuation,” said Scott K. Epstein, MD, who is an Associate Director of the Medical Intensive Care Unit at New England Medical Center, in Boston.[3]

Those patients who do not tolerate spontaneous breathing trials require a return to partial or full ventilatory support to allow adequate rest before the next trial. Several other interventions can also help maximize the chance of weaning success (see “Tips on Weaning From a Ventilator”).

In young, otherwise healthy patients with minimal comorbidity, it is acceptable to end spontaneous breathing trials after only 30 minutes if there is no evidence of tachycardia, tachypnea, diaphoresis, or hypoxemia. These patients clearly no longer need mechanical ventilation, the guidelines suggest. Clinical judgment is necessary to determine the appropriate duration of spontaneous breathing trials in older, more severely ill patients, who commonly show evidence of weaning failure after one hour.

Thirty–minute trials also may be too short to assess the discontinuation potential for patients who have required more prolonged mechanical ventilation, reported Dr. Epstein.

“We should consider removal of the artificial airway in a patient who has been successfully liberated [from the ventilator],” Dr. Epstein said. An important early step is to predict the likelihood of extubation failure by evaluating upper airway patency. Oxygenation and neurologic status must also be assessed.

“If there is no reason to suspect an upper airway problem, extubate [the] patient,” instructed E. Wesley Ely, MD, MPH, an Assistant Professor of Allergy, Pulmonary, and Critical Care Medicine at the Vanderbilt University School of Medicine, in Nashville. “This is an important window of opportunity … to save the patient from the development of a subsequent complication, such as ventilator–associated pneumonia.”

THE USE OF PROTOCOLS

Data suggest that weaning is more likely to succeed if it is guided by a standard protocol. In clinical trials, weaning protocols reduced the complication rate, weaning time, need for reintubation, and total per–patient intensive care unit (ICU) costs. However, “effective implementation [of weaning protocols] requires adequate staffing,” Dr. Ely stressed. “This is not a one–man or one–woman show.”

Patient sedation protocols also aid weaning efforts, especially when those protocols reduce the use of continuous sedative drips, which are associated with a threefold–higher reintubation rate than is bolus sedative administration or no sedation, Dr. Ely reported. Sedation protocols may further enhance weaning outcomes if they incorporate spontaneous awakening trials–delivery of sedative is stopped to let the patient briefly regain consciousness. This particular technique has been shown to reduce the duration of mechanical ventilation by two days, he added.

Provided they are stable enough for transfer, mechanically ventilated patients who fail weaning in the ICU should be sent to a post–ICU weaning unit or facility. “Post–ICU weaning should be slow–paced and employ gradually lengthening self–breathing trials,” said David J. Scheinhorn, MD, the Director of Research at the Barlow Respiratory Hospital, in Los Angeles.

Self–breathing trials typically continue until weaning is complete or it becomes obvious that the patient is ventilator dependent. “Patients probably should not be declared unweanable until two to three months of weaning attempts have failed,” Dr. Scheinhorn advised. That time frame includes the weaning efforts in both the ICU and post–ICU weaning unit or facility.

--Timothy Begany

References
1. MacIntyre NR, Epstein SK, Hess DR, et al. The Evidence–Based Weaning Project: a clinical practice guideline for weaning from mechanical ventilation. Paper presented at: CHEST 2000. October 26, 2000; San Francisco.

2. Ely EW, Baker AM, Dunagan DP, et al. Effect on the duration of mechanical ventilation of identifying patients capable of breathing spontaneously. N Engl J Med. 1996;335:1864– 1869.

3. Esteban A, Alia I, Tobin MJ, et al. Effect of spontaneous breathing trial duration on outcome of attempts to discontinue mechanical ventilation. Spanish Lung Failure Collaborative Group. Am J Respir Crit Care Med. 1999;159:512-518.

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