Special Feature: Evaluation for Extubation
Special Feature
Evaluation for Extubation
By Dean R. Hess, PhD, RRT, Respiratory Care, Massachusetts General Hospital, Department of Anesthesiology, Harvard Medical School, Boston, is Associate Editor for Critical Care Alert.
Dr. Hess reports no financial relationship to this field of study.
Extubation is defined as removal of the endotracheal tube.1,2 The decision to extubate is usually based on three considerations: 1) need for invasive respiratory support; 2) patency of the upper airway; and 3) ability to clear secretions from the lower respiratory tract. The clinical decision to extubate is not trivial. Mortality is higher in patients who require re-intubation within 24-72 hours after extubation. However, prolonged intubation is also not benign and can increase the risk of nosocomial pneumonia, upper airway injury from the tube, and ventilator-induced lung injury.1,2 This essay will take a critical look at the evaluation for extubation.
Ventilator Liberation
A daily spontaneous breathing trial (SBT), perhaps coupled with a spontaneous awakening trial, is now standard practice to identify whether a patient can be liberated from mechanical ventilation.3 However, the increasing use of non-invasive ventilation (NIV) has changed the actions we might take if a patient passes or fails an SBT. Some patients who fail an SBT might be extubated directly to NIV. Other patients who pass an SBT, but are at risk for extubation failure, might also be extubated directly to NIV. Note that in both of these scenarios, patients are extubated directly to NIV. This is in contrast to the use of NIV to rescue a failed extubation, which is not supported by randomized controlled trials.
Burns et al performed a meta-analysis of five randomized controlled trials of NIV to facilitate weaning from mechanical ventilation4 in other words, earlier extubation directly to NIV. They found that extubation to NIV was associated with lower mortality, less ventilator-associated pneumonia, shorter course of mechanical ventilation, shorter ICU stay, and shorter hospital stay. Because more than 80% of the patients in these studies had COPD, it is unknown whether the benefit is limited primarily to patients with COPD. Epstein recommends the following criteria when considering the use of NIV for early extubation:5 1) the patient must be able to breathe spontaneously for at least a short period; 2) the patient should be able to adequately clear secretions; 3) the patient should be able to tolerate the interface and to breathe spontaneously for at least 5-10 minutes to allow for necessary mask and ventilator adjustments; 4) NIV is strongly discouraged if the patient would be technically difficult to re-intubate.
Three randomized controlled trials support that NIV is effective when used immediately after extubation in patients at high risk for extubation failure.6-8 Risk factors for extubation failure in these studies were age greater than 65 years, cardiac failure as the cause of intubation or chronic heart failure, APACHE-II score greater than 12 on the day of extubation, more than one consecutive failed SBT, PaCO2 > 45 mm Hg, more than one comorbidity (excluding chronic heart failure), weak cough, and stridor at extubation not requiring immediate reintubation. With the possible exception of COPD exacerbation, NIV should not be used routinely after extubation or in established post-extubation respiratory failure.
Airway Protection
No clinician will debate the prudence of keeping the endotracheal tube in place if upper airway obstruction were to occur in the absence of the tube. Likewise, no rational clinician recommends extubation for a patient at risk for aspiration of upper airway secretions or gastric contents. The challenge is to identify patients at risk.
Poor mental status is commonly given as a reason why patients who pass an SBT are not extubated, the reason being concerns of airway protection. In neurosurgical patients, Namen et al reported that the odds of successful extubation increased by 39% with each Glascow Coma Score (GCS) increment.9 A GCS ≥ 8 at extubation was associated with success in 75% of cases vs a success rate of 33% for a GCS < 8.10
These results are at odds with those of Coplin et al, who explored the implications of extubation delay in brain-injured patients.11 They found that timely extubation in this patient population was safe. Although patients with worse neurologic condition had more delay, some patients with good neurologic condition were kept intubated after meeting extubation readiness criteria and some patients in coma were successfully extubated. Patients were successfully extubated despite absent cough, gag, or increased suctioning needs. Extubation delay was associated with morbidity and mortality. The authors concluded that this study does not support delaying extubation when impaired neurologic status is the only concern prolonging intubation. My personal observation has been that poor mental status is commonly used as justification not to extubate when members of the team are opposed to extubation for whatever the reason may be.
Some intubated patients with poor mental status also have difficulty handling upper airway secretions and are clinically observed to drool their oral secretions. In such patients, concern about aspiration of oral secretions after extubation is reasonable. Although this has not been investigated to my knowledge, it might be reasonable to delay extubation in patients with difficulty handling upper airway secretions.
Upper Airway Edema
Airway obstruction due to laryngeal edema following extubation occurs in 3%-30% of patients, of whom < 5% require re-intubation.12 A cuff-leak test is often used to screen for upper airway obstruction before extubation. To perform this test, the cuff of the endotracheal tube is deflated and the air leak around the tube through the upper airway during positive pressure ventilation is assessed. Absence of a leak, or a small leak, suggests upper airway obstruction. The result of the test can be expressed qualitatively, presence or absence of leak, or quantitatively, in which the difference between inhaled and exhaled tidal volume is measured.
Ochoa et al conducted a systematic review and meta-analysis to assess the diagnostic accuracy of the cuff leak test.12 The analysis included 11 studies and 2303 patients. The overall positive likelihood ratio for upper airway edema (no leak) was 5.9 and the overall negative likelihood ratio (leak) was 0.48. Only three studies were included for the outcome of re-intubation. The overall positive likelihood ratio for re-intubation (no leak) was 4.04 and the overall negative likelihood ratio (leak) was 0.46. If we take a pre-test probability for upper airway edema of 15%, the post-test probability is increased to 51%. With a negative likelihood ratio (presence of leak) of 0.48, the post-test probability fell to 8%. For a reported incidence of re-intubation secondary to upper airway obstruction of 5%, the absence of leak increases the probability for re-intubation to 17%, and the presence of leak decreases the probability for re-intubation to 2%.
The results of this meta-analysis suggest that the presence of a positive cuff-leak test (absence of leak) is suggestive of a higher risk of upper airway obstruction and re-intubation.12 On the other hand, the presence of a detectable leak has a low predictive value and does not rule out the occurrence of upper airway obstruction or the need for re-intubation. A reasonable recommendation might be to reserve the leak test for patients with high pre-test probability such as those with difficult intubation or other clinical reasons to suspect upper airway edema. In such patients who have a positive leak test (no leak), it would be reasonable to delay extubation and administer a short course of methylprednisolone before extubation.13
Cough and Secretions
One of the functions of the endotracheal tube is to provide a conduit for suctioning and bronchoscopy. A legitimate consideration before extubation is whether the patient can adequately clear airway secretions.
Khamiees et al evaluated potential predictors of extubation outcome in patients who have successfully completed an SBT.14 Cough strength was measured with a semi-objective scale of 0 to 5; the magnitude of endotracheal secretions was measured as none, mild, moderate, or abundant; and patients were asked to cough onto a white card held 1-2 cm from the endotracheal tube. If secretions were propelled onto the card, it was termed a positive white card test result. They found that there was synergism between poor cough strength and abundant endotracheal secretions in predicting extubation failure.
In a follow-up study, Smina et al evaluated cough peak flow and extubation outcomes.15 After patients passed an SBT and extubation was being considered, they were asked to cough into a peak flow meter connected to the endotracheal tube. The volume of endotracheal secretions suctioned 2-6 hours prior to extubation was measured. Interestingly, the magnitude of endotracheal secretions was not associated with the outcomes assessed. But patients with a cough peak flow < 60 L/min were five times more likely to be unsuccessfully extubated and were 19 times as likely to die during the hospital stay.
Salam et al evaluated neurologic status, cough, secretions, and extubation outcomes.16 Patients who were unable to complete four simple tasks (open eyes, follow with eyes, grasp hand, stick out tongue) were more than four times as likely to fail as those who completed these commands. There was synergistic interaction between these risk factors; failure rate was 100% for patients with all three risk factors (poor neurologic status, cough, and secretions) compared to 3% for those with no risk factors. Patients who failed a trial of extubation were nearly four times as likely to have any two risk factors compared to those who were successful. Those with a cough peak flow ≤ 60 L/min were nearly five times as likely to fail extubation. Patients with secretions of more than 2.5 mL/hr were three times as likely to fail.
Su et al induced a cough in inbutated patients by instilling 2 mL of saline at the end of inspiration and measuring cough peak flow using a hand-held respiratory mechanics monitor.17 In a multivariate analysis, they found that involuntary cough peak flow and APACHE II were the primary predictors of extubation success in critically ill patients who passed an SBT.
These studies are commonly discussed in the context of assessing extubation readiness. To my knowledge, however, these results have never been replicated and measurement of cough peak flow and quantitative measures of secretion volume are not used commonly in everyday practice. But these studies do support that cough strength and secretion volume are important considerations in the decision to extubate. I think it is important to evaluate both cough and secretions. For example, a patient with copious secretions and who also has a strong cough may adequately clear the airway after extubation. Similarly, a patient with a weak cough but minimal airway secretions may do well after extubation. The patient with a weak or absent cough and copious secretions is at greatest risk for extubation failure.
The cough-assist device (mechanical in-exsufflator) is used to assist cough and airway clearance in patients with neuromuscular disease.18 However, it has not been commonly used in the ICU. A case might be made for its use post extubation, given that many mechanically ventilated patients have generalized weakness. It is possible that post-extubation use of NIV and the cough-assist device might prevent extubation failure in patients with a weak cough. This deserves appropriate study in a randomized controlled trial.
Summary
Clinicians should separate the need for mechanical ventilation from the need for an endotracheal tube. Before extubation, the ability to clear secretions and protect the airway should be assessed. The use of NIV and the cough-assist device may allow extubation of some patients who otherwise might require prolonged intubation or tracheostomy.
References
- Epstein SK. Extubation. Respir Care 2002;47:483-495.
- Epstein SK. Decision to extubate. Intensive Care Med 2002;28:535-546.
- MacIntyre NR, 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 (6 Suppl):375S-395S.
- Burns KE, et al. A meta-analysis of noninvasive weaning to facilitate liberation from mechanical ventilation. Can J Anaesth 2006;53:305-315.
- Epstein SK. Noninvasive ventilation to shorten the duration of mechanical ventilation. Respir Care 2009;54:198-211.
- Nava S, et al. Noninvasive ventilation to prevent respiratory failure after extubation in high-risk patients. Crit Care Med 2005;33:2465-2470.
- Ferrer M, et al. Early noninvasive ventilation averts extubation failure in patients at risk: A randomized trial. Am J Respir Crit Care Med 2006;173:164-170.
- Ferrer M, et al. Non-invasive ventilation after extubation in hypercapnic patients with chronic respiratory disorders: Randomised controlled trial. Lancet 2009;374:1082-1088.
- Robertson TE, et al. Multicenter implementation of a consensus-developed, evidence-based, spontaneous breathing trial protocol. Crit Care Med 2008;36:2753-2762.
- Namen AM, et al. Predictors of successful extubation in neurosurgical patients. Am J Respir Crit Care Med 2001;163 (3 Pt 1):658-664.
- Coplin WM, et al. Implications of extubation delay in brain-injured patients meeting standard weaning criteria. Am J Respir Crit Care Med 2000;161:1530-1536.
- Ochoa ME, et al. Cuff-leak test for the diagnosis of upper airway obstruction in adults: A systematic review and meta-analysis. Intensive Care Med 2009;35:1171-1179.
- Fan T, et al. Prophylactic administration of parenteral steroids for preventing airway complications after extubation in adults: Meta-analysis of randomised placebo controlled trials. BMJ 2008;337:a1841.
- Khamiees M, et al. Predictors of extubation outcome in patients who have successfully completed a spontaneous breathing trial. Chest 2001;120:1262-1270.
- Smina M, et al. Cough peak flows and extubation outcomes. Chest 2003;124:262-268.
- Salam A, et al. Neurologic status, cough, secretions and extubation outcomes. Intensive Care Med 2004;30:1334-1339.
- Su WL, et al. Involuntary cough strength and extubation outcomes for patients in an ICU. Chest 2010;137:777-782.
- Bach JR, et al. Extubation of patients with neuromuscular weakness: A new management paradigm. Chest 2010;137:1033-1039.
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