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Durham, NC
Dr. MacIntyre is Professor, Duke University Medical Center.
Correspondence to: Neil MacIntyre, MD, FCCP, Duke University Medical Center, Durham, NC 27710; e-mail: neil.macintyre{at}duke.edu
When the underlying respiratory failure begins to stabilize and reverse in patients requiring mechanical ventilation, consideration for ventilator discontinuation should begin. A multisociety-sponsored evidence-based task force (EBTF)1 has recommended that a patient be considered for withdrawal assessments when the following occur: (1) the lung injury is stable/resolving; (2) the gas exchange is adequate, with low positive end-expiratory pressure/fraction of inspired oxygen requirements (eg, positive end-expiratory pressure < 5 to 8 cm H2O; fraction of inspired oxygen, < 0.4 to 0.5); (3) hemodynamics are stable without a need for pressors; and (4) there is the capability to initiate spontaneous breaths. This information is usually readily available at the bedside, and the EBTF recommended that these issues be assessed daily.1 A variation of this concept could be taken to the postsurgical arena, where respiratory recovery is often rapid and this assessment could be done on a more frequent basis.
In patients meeting these initial criteria, the subsequent assessments for the potential to remove mechanical ventilatory support involve a two-step process. The first step is to assess the continued need for positive pressure respiratory support (minute ventilation and positive end-expiratory pressure). The second step is to assess the continued need for an artificial airway
For the first step, the EBTF has recommended the use of a spontaneous breathing trial (SBT) as the best way to assess the need for continued positive pressure respiratory support.1 The SBT involves a patient assessment during spontaneous breathing with little or no ventilator assistance (eg, t-piece trial or using up to 5 cm H2O continuous positive airway pressure or 5 to 7 cm H2O of pressure support from the ventilator). This EBTF further recommended that no single parameter be used to judge SBT success or failure. Rather, an integrated assessment of the respiratory pattern (especially the development of tachypnea), hemodynamic status (especially tachycardias, bradycardias, or BP swings), gas exchange (especially oxygen saturation by pulse oximetry decreases), and patient comfort (especially the development of anxiety or diaphoresis) should be done. The SBT must last at least 30 min but no longer than 120 min. If it is not clear that the patient is an SBT success at the 120-min mark, then the patient should be considered an SBT failure.
A patient who successfully completes an SBT has a high likelihood of tolerating ventilator discontinuation permanently, and thus the removal of positive pressure ventilatory support in such patients is appropriate.1 In these patients, the next step is to assess the ongoing need for the artificial airway, and this involves different measurements than those used to determine ventilatory support removal. First, artificial airway removal must be done only in patients with the ability to protect the airway. Thus patients must demonstrate good coughing strength and minimal need for suctioning (eg, no more than every 2 h). Second, alertness and the ability to follow commands can greatly improve the success rate of artificial airway removal. Thus, sedation needs and level of consciousness need to be assessed. Third, in borderline cases, the decision to remove the artificial airway may need to take into account the difficulty anticipated in replacing the airway if needed. Finally, some have recommended that the cuff leak assessment (detecting airflow around a deflated artificial airway balloon cuff) to predict the risk of postextubation airway obstruction be done. This recommendation, however, is supported by only conflicting and controversial data.1
Because ventilator discontinuation and artificial airway removal are not exact sciences, a certain reintubation rate is to be expected for even the most skilled of clinicians. Large surveys suggest that 10 to 15% reintubation rates are typical for most well-run ICUs.2 Rates significantly above or below this range should prompt reassessment of potentially either overaggressive (high reintubation rates) or underaggressive (low reintubation rates) practices.
The article in this issue of CHEST (see page 1864) by Frutos-Vivar et al3 adds to our understanding of this ventilator withdrawal/extubation process. These investigators evaluated predictors for extubation failure in 121 patients (of a total of 900 extubated patients) from 37 hospitals. The study patients had all passed an SBT and were judged appropriate by their physician for the removal of the artificial airways. In this population, extubation failure was primarily due to cardiorespiratory dysfunction (as opposed to airway protection issues) and was correlated with a higher spontaneous frequency/tidal volume ratio, positive fluid balance, and a pneumonia diagnosis. The strengths of this study are the large sample size and the careful analysis. Their 13% reintubation rate is similar to many other reports in the literature as noted above. Moreover, the relationship of a spontaneous rapid-shallow ventilatory pattern and fluid overload to a continued need for ventilator assistance confirms the results of many other studies.
What this study does not supply, however, is insight into the physician judgment factors that drove the second step: the decision to remove the artificial airway in patients passing the SBT. Specifically, we do not know why some of these patients were allowed to be extubated while others were not. This is a crucial question that no doubt involved various (but undefined) assessments of the patient’s ability to protect the airway (and perhaps other factors). The fact that very few of the extubation failures reported in this study were related to airway protection issues (ie, retained secretions accounted for only 11% of the extubation failures) suggests that these judgment factors were sensitive (ie, they detected most of the patients who would have had airway protection issues). This is difficult to quantify, however, as this study did not record the number or the characteristics of these nonextubated patients. Moreover, because they were not extubated, we do not know the specificity of these judgment factors (ie, the proportion of those truly needing prolonged intubations vs those who could have protected the airway but were not allowed to do so). Understanding these physician judgment factors should be the focus of future studies by this group and others.
Ventilator withdrawal and artificial airway removal are important issues, as unnecessarily prolonged respiratory support and/or artificial airway use increases the risk of ventilator-associated pneumonia, exposes the lung to potentially injurious airway pressures, increases the need for sedation, and drives up costs. The reverse, however, is also true: premature ventilator withdrawal and artificial airway removal can precipitate ventilatory muscle fatigue, worsen gas exchange, expose the lungs to aspiration risks, and even result in the loss of a functioning airway. We have made particular progress in understanding factors related to the continued need for positive pressure ventilation and these new data from Frutos-Vivar and colleagues3 add to this understanding, especially in demonstrating how extubation failure can often be a result of an imperfect assessment of the need for continued ventilatory support. We also need, however, a better understanding of the factors related to the continued need of an artificial airway after a patient has been determined to no longer need positive pressure respiratory support. Much like earlier studies using specific protocols to determine the assessment tools appropriate for removing mechanical ventilatory support, carefully designed prospective studies using explicit rules for guiding artificial airway removal are clearly needed to improve the decision process for managing the artificial airway.
Footnotes
Dr. MacIntyre is a consultant to Viasys Health Care.
References
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