Data indicate that subglottic edema is among the most common complications experienced by children who require mechanical ventilation. Observational studies suggest that post-extubation upper airway obstruction (UAO) is the cause of one-third to one-half of re-intubation cases in children. However, risk factors and prevention strategies for post-extubation UAO have not been well defined.
“Post-extubation UAO can result from subglottic or superglottic obstruction, for which the risk factors and impact on outcomes are substantially different,” explains Robinder G. Khemani, MD, MsCI. “However, few studies have differentiated these two types of UAO, making prevention efforts difficult.”
Shedding New Light
For a study of children receiving mechanical ventilation—published in the American Journal of Respiratory and Critical Care Medicine—Dr. Khemani and colleagues had two goals. First, they wanted to determine whether a diagnostic technique they created—which uses esophageal manometry and respiratory inductance plethysmography (RIP) bands calibrated to measure airflow—was superior to clinicians in assessing patients who went on to receive treatment of UAO or be re-intubated and could differentiate subglottic from supraglottic UAO. The second goal was to use the allocation of subglottic versus supraglottic UAO created with this technique to identify risk factors for subglottic edema after extubation, stratified by cuffed versus uncuffed endotracheal tubes (ETTs).
The researchers found that 12% of participants had supraglottic UAO and 12% had subglottic UAO. “Considering that these rates are relatively high for both types of UAO, helping differentiate them is important,” says Dr. Khemani. “The prevention, treatment strategies, and risk factors are different for each type. Subglottic UAO is a bigger problem than supraglottic. Patients with post-extubation subglottic UAO are much more likely to be re-intubated. About 40% of cases of re-intubation were related to subglottic UAO in our cohort.”
Dr. Khemani stresses the importance of the finding that risk factors for UAO were based upon whether patients were intubated with cuffed or uncuffed ETTs. “For patients with a cuffed ETT, measuring a leak pressure before extubation was predictive of those who would have post-extubation subglottic UAO,” he says. “Those who did not have a leak at a pressure of less than 25 cm H2O with the cuff deflated were much more likely to have post-extubation UAO when compared with patients who had a leak with the cuff deflated. With an un-cuffed ETT, leak pressures weren’t predictive of who would or would not develop post-extubation UAO. The rates of subglottic post-extubation were similar between cuffed and uncuffed ETT.
Cuffed Vs Uncuffed
Dr. Khemani explains that the decision of whether or not to administer pre-extubation corticosteroids to mechanically-ventilated children is commonly based upon the findings of leak pressures prior to extubation. “Our results suggest that clinicians should not be basing this decision upon the presence or absence of a leak for an uncuffed ETT,” he says. “The presence of a leak with an uncuffed ETT does not assure against post-extubation UAO, and the absence of a leak does not predict post-extubation UAO. The probability of post-extubation UAO in patients with cuffed ETTs and a leak of less than 25 cm H2O with the cuff deflated is 2%. However, if these patients do not have a leak at this same pressure with the cuff deflated, the probability of requiring treatment for UAO is about 20%. This patient population needs to be studied further to establish whether or not they should receive steroids.”
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