Originally published by 2 Minute Medicine® (view original article). Reused on AccessMedicine with permission.

1. In a small prospective cohort of children undergoing direct laryngoscopy and endoscopy, airway impedance did not correlate with gastroesophageal reflux scores based on inspection of the larynx.

2. Airway impedance was significantly lower in subjects who had evidence of aspiration or dysphagia on swallow study within 6 months of impedance measurement.

Evidence Rating Level: 2 (Good)

Study Rundown:

Along with symptoms like pain and discomfort, gastroesophageal reflux disease (GERD) can cause esophageal and laryngeal inflammation. Visual inspection for redness and edema on laryngoscopy, however, has been shown to correlate poorly with this inflammation. This study aimed to assess the potential of airway impedance as a diagnostic marker for GERD in children. Children already undergoing direct laryngoscopy and endoscopy were prospectively recruited. Among 73 subjects, airway impedance measured using a specialized catheter during endoscopy did not correlate with reflux scores based on the appearance of the airway. Airway impedance was significantly lower among patients with evidence of aspiration or oropharyngeal dysphagia on swallow study within 6 months of endoscopy. Eosinophilic involvement on esophageal biopsy was not correlated with airway impedance but was correlated with impedance within the esophagus itself. This study provides a proof of concept for the measurement of airway impedance in the setting of suspected GERD, and impedance did differ based on relevant factors such as aspiration and medication use. Although the authors expected limited concordance with existing biomarkers such as airway appearance, it is difficult to determine the diagnostic performance or even the potential of airway impedance without standards for direct comparison. The fact that airway impedance did not significantly correlate with esophageal inflammation based on biopsy and that 17% of impedance measures needed to be excluded due to artifact both constitute significant limitations, as they suggest limited accuracy and difficulty obtaining airway impedance, respectively.

In-Depth [prospective cohort]:

Scoring of the airways for the appearance of reflux (reflux finding scores) was performed based on video by three blinded otolaryngologists. Airway impedance was measured just below the vocal cords after airway suctioning. Airway impedance values were calculated as averages of the first, minimum, and maximum values within a five-second recording. Among 88 endoscopies, results from 15 were excluded due to artifact (at least one impedance value of 10,000 Ω). Esophageal impedance was measured using the same device at three esophageal heights, from which biopsies were also taken. Among 11 subjects on proton pump inhibitors (PPIs), the mean airway impedance was 706 Ω, compared to 1069 Ω for other patients (p=0.06). At a cutoff of 1192 Ω, airway impedance was 83% sensitive and 50% specific for diagnosing aspiration or oropharyngeal dysphagia. In a multivariable model adjusting for the presence of diagnosed esophagitis or aspiration, PPI use, and inhaled steroid use, PPI use and aspiration status were significantly associated with lower mean airway impedance.

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