Respiratory Muscle Weakness and Extubation Failure in Critically Ill Children*

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Extubation failure is prevalent in critically ill children, and upper airway obstruction is a major risk factor associated with extubation failure in pediatric patients (1, 2). Also ventilator-induced diaphragmatic weakness is a risk factor associated with difficult extubation in critically ill adult patients (3). In this issue of Critical Care Medicine, Khemani et al (4) studied the association between respiratory muscle strength and extubation failure in pediatric patients. They reported a secondary analysis of prospectively collected data on 409 mechanically ventilated children at the time of extubation, and they found that neuromuscular weakness (at the time of extubation) was associated with extubation failure, especially when postextubation respiratory effort was high.
The authors are to be applauded for addressing the relationship between respiratory muscle strength and extubation failure in an understudied age group of critically ill pediatric patients. Their study was eloquently conducted using esophageal manometry, spirometry, and plethysmography to estimate patients’ respiratory muscle strengths and efforts. Of interest, the article objectively demonstrates the interaction between respiratory effort and strength, especially postextubation in patients with upper airway obstruction.
Preextubation assessment of upper airway obstruction is a challenge. The air leak test around the endotracheal tube is used to assess preextubation subglottic edema/stenosis. However, the test has a poor sensitivity and therefore cannot be used as a screening tool to predict extubation failure or success. In a retrospective study, we have shown that an air leak test is predictable of postextubation stridor, but it is not predictable of extubation failure in critically ill pediatric patients (5). Similarly, in a prospective observational study, Wratney et al (6) have shown that an air leak test is not predictable of extubation failure in critically ill children. Therefore, delaying extubation because of an abnormal air leak test may prolong days of mechanical ventilation and exacerbate the risk of ventilator-induced respiratory muscle weakness. Khemani et al (4) in their current study have shown that in patients with postextubation upper airway obstruction, a preextubation low airway pressure (aPiMax), or respiratory muscle weakness is associated with a higher risk of extubation failure. Therefore, the preextubation measurement of aPiMax is helpful to predict extubation failure in patients at risk for postextubation upper airway obstruction. Future studies are needed to determine whether adding aPiMax measurement improves the performance and sensitivity of the air leak test in predicting extubation failure secondary to upper airway obstruction.
Since impairment of respiratory muscle strength is associated with extubation failure, strategies to reduce ventilator-induced respiratory muscle weaknesses are needed. For instance, the adoption of a standardized approach to liberate children from mechanical ventilation may reduce the length of mechanical ventilation. Spontaneous breathing trials (SBT) have been used successfully in children to evaluate patients for extubation readiness and liberation from mechanical ventilation (7). However, such approach has not gained popularity among pediatric critical care specialists. In a recent survey of 417 pediatric critical care specialists, we found that the majority of pediatric critical care physicians wean ventilator settings instead of performing SBT in preparation for extubation (8). Frequent assessment for extubation readiness may reduce the length of mechanical ventilation and avoid potential development of ventilator-induced respiratory muscle weakness.
The Rapid Shallow Breathing Index (RSBI) has been shown to be predictable of extubation failure in critically ill children. However for the same RSBI value, the probability of extubation failure varies with the duration of mechanical ventilation (7). Traditionally, the RSBI was studied in patients who were not extubated to noninvasive respiratory support. In their current study, Khemani et al (4) did not find statistically significant differences in RSBI between patients who did and those who did not fail extubation.
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