1

Introduction

High flow oxygen therapy (HFOT) has become a popular method of delivering high volumes of oxygen for respiratory support via nasal cannula. Continuous positive airway pressure (CPAP) has traditionally been the respiratory support of choice. Its ability to maintain patent alveoli and upper airways leads to improved respiratory function . However, CPAP also has been shown to result in a number of complications. These include, but are not limited to, nasal stuffiness, dry mouth, nasal mucosal trauma, nasal deformity, and overall discomfort . As a result of these unfavorable consequences of CPAP, HFOT is often considered as an alternative.

HFOT allows for the delivery of humidified oxygen at flows that can reach 60 liters/minute (L/min) without many of the complications associated with CPAP. Previous studies have shown HFOT allows for easier application and reduced nasal trauma when compared to CPAP . Additionally, HFOT is better tolerated than a conventional face-mask and results in better oxygenation in patients with acute respiratory failure .

The nasopharynx serves as a drainage pathway of the middle ear via the Eustachian tube. Therefore, high nasopharyngeal pressures have been linked to simultaneous high middle ear pressures . This phenomenon has been described in physiologic processes including nose blowing and during valsalva. It has been shown that positive pressures are produced in the nasopharynx in patients using HFOT in both pediatric and adult populations . However, to our knowledge, middle ear pressures have not been studied with respect to HFOT .

Evaluating the effects of HFOT on middle ear pressures is important, as it will allow for a better understanding of optimal oxygen volumes and inform whether or not HFOT can be safely used as an oxygen delivery device in patients undergoing otologic procedures. We hypothesize that HFOT will increase middle ear pressures proportionally to oxygen volumes due to increased nasopharyngeal pressures.

2

Materials and methods

Institutional review board permission was granted for our study. The study was performed prospectively at a tertiary medical center. Ten patients were recruited into our study after obtaining informed consent. All patients recruited were in an ICU setting, as high flow nasal cannula therapy can only be administered in a critical care unit at our facility. In the study group, data collected included patient demographics, indication for high flow nasal cannula therapy, fractional inspired oxygen (FiO ₂ ), liters of oxygen delivered, pertinent medical history, subjective hearing loss, and previous otologic history. Patients with cerumen impaction, perforated tympanic membranes, previous ear surgery, or history of Eustachian tube dysfunction were excluded from our study. All patients underwent an otoscopic exam prior to tympanometry to ensure patency of the external auditory canal and visualization of an intact tympanic membrane. A disposable tympanometer probe sized to fit the external canal to provide a complete seal was placed in the left and right external auditory canals and tympanometry carried out with GSI Tympstar Tympanometer. The mean with standard deviation was generated for data points of interest. Pearson coefficients and p-values were obtained for percent FiO2 and liters of oxygen delivery and observed patient middle ear pressures. A p-value < 0.05 was considered to be statistically significant. Metric data are presented as means ± standard deviation.

2

Materials and methods

Institutional review board permission was granted for our study. The study was performed prospectively at a tertiary medical center. Ten patients were recruited into our study after obtaining informed consent. All patients recruited were in an ICU setting, as high flow nasal cannula therapy can only be administered in a critical care unit at our facility. In the study group, data collected included patient demographics, indication for high flow nasal cannula therapy, fractional inspired oxygen (FiO ₂ ), liters of oxygen delivered, pertinent medical history, subjective hearing loss, and previous otologic history. Patients with cerumen impaction, perforated tympanic membranes, previous ear surgery, or history of Eustachian tube dysfunction were excluded from our study. All patients underwent an otoscopic exam prior to tympanometry to ensure patency of the external auditory canal and visualization of an intact tympanic membrane. A disposable tympanometer probe sized to fit the external canal to provide a complete seal was placed in the left and right external auditory canals and tympanometry carried out with GSI Tympstar Tympanometer. The mean with standard deviation was generated for data points of interest. Pearson coefficients and p-values were obtained for percent FiO2 and liters of oxygen delivery and observed patient middle ear pressures. A p-value < 0.05 was considered to be statistically significant. Metric data are presented as means ± standard deviation.