The audible leak test is a reliable method for verifying appropriate tracheal tube sizes in infants and children, according to a recent study.
“Checking for audible leak is a common practice to rule out a tight-fitting tracheal tube in infants and children,” said Madhankumar Sathyamoorthy, MD, study author and assistant professor of pediatric anesthesiology at the University of Mississippi Medical Center, in Jackson. “But, interestingly, there are not many studies that investigate the accuracy or the reliability of the test.”
Many factors can affect the results of the audible leak test, according to the researchers. They conducted this study to determine the accuracy of this test by directly observing the presence of a leak around the endotracheal tube. Secondary outcome measures included examining the relationship between the presence of an audible leak and direct visualization for cuffed and uncuffed tubes.
“We observed that the otolaryngologists look for visual leak by looking for air bubbles around the tube when sizing the airway in cases of subglottic stenosis, and hypothesized that looking for air bubbles may be more sensitive to look for a leak around the tube,” said Dr. Sathyamoorthy, who presented his research at the 2016 annual meeting of the Society for Airway Management.
The study focused on 60 children between 1 month and 8 years of age who were scheduled for otolaryngological procedures. The average age was 4 years; patients were almost evenly split between boys and girls. Patients received mask induction with sevoflurane, and 1 to 3 mg/kg of propofol or 1 to 2 mcg/kg of fentanyl were given intravenously for tracheal intubation. Muscle relaxants were not used.
Audible Versus Visual Tests
In each case, an anesthesiologist performed the audible leak test while the patient was supine and the head was in a neutral position. With 6 L per minute of fresh gas flow and the pop-off valve in the anesthesia breathing circuit closed, the inspiratory pressure was slowly increased until an audible leak was heard at the mouth or over the larynx with a stethoscope. In the same position, an otolaryngologist, who was blind to the leak pressure, performed the visual leak test by inserting a rigid bronchoscope and looking for bubbles at the glottis around the tube. The anesthesiologist used either a cuffed or uncuffed tube, based on the patient’s age.
“We had some interesting observations. In some patients with thick secretions, initially higher opening pressures were needed to clear the secretions around the tube before an audible leak can be heard at a lower pressure,” Dr. Sathyamoorthy said. “While in other cases of dry mouth, saline had to be added to the mouth to visualize air bubbles.”
In addition, the percentage of tidal volume leak was measured as 100 times the ratio of the difference between the inspired and expired tidal volumes and inspired tidal volume. The research team found that audible leak pressure was 6.17 cm H2O greater than the visual leak pressure. The correlation coefficient between the two tests was positive.
“The good agreement and correlation between the two tests show that the audible leak test is reliable,” Dr. Sathyamoorthy said. “The higher pressures may give a safety margin of error since the actual leak may be at a lower pressure.”
Matteo Parotto, MD, PhD, assistant professor in the Department of Anesthesia at the University of Toronto, who moderated the poster presentations during the conference, wondered whether tube size, cuff size and cuff comfort could make a difference.
“In several cases, there was no leak, even when age-appropriate sized tubes were used,” Dr. Sathyamoorthy said. “We also found that listening with a stethoscope over the larynx led to many false-positive audible leak test results when there was no leak visualized.”
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