Nasal dryness discomfort in individuals receiving dry oxygen via nasal cannula.

The majority of hospitals and home respiratory care companies do not use humidification when delivering oxygen at 4 L/ min or 5 L/min via nasal cannula, based on the recommendations of 2 guidelines.1,2 The American Association for Respiratory Care clinical practice guidelines for oxygen therapy1 indicate that oxygen supplied to adults via nasal cannula at flows 4 L/min does not require humidification. The American Thoracic Society statement on the diagnosis and care of patients with chronic obstructive pulmonary disease2 mentions a lack of evidence on the need for humidification when oxygen is delivered via nasal cannula at flows 5 L/min. These guidelines are based on a letter3 that determined the expected excessive water loss from the airway during inhalation of dry oxygen, and also on clinical studies by Estey4 and Campbell et al.5 Neither study found significant differences in severity of subjective symptoms between dry oxygen inhalation and humidified oxygen inhalation in groups of randomly selected patients. Since those studies were not crossover trials, the subjects were unable to compare nasal comfort between dry and humidified oxygen. We therefore wondered whether subjects might notice any difference and thus prefer humidified or dry oxygen. We performed a single-blind crossover trial with 20 healthy volunteers (mean SD age 24 1 y), recruited from students at Hokkaido University, and 18 patients with pulmonary disease (mean SD age 68 3 y) recruited from out-patients at Hokkaido UniversityHospital,whohadnoexperiencewith oxygen inhalation. Subjects inhaled dry and humidified oxygen via nasal cannula for 1 min at flows of 1, 2, 3, 4, and 5 L/min, in random order. After 1 min at a given flow, the subject graded his or her feeling of nasal dryness by marking a 10-cm visual analog scale, which was marked in quarters from 0 to 4 (0 none, 0.5 very slight, 1 slight, 2 moderate, 3 severe, 4 very severe). There was a 1-min rest period between each 1-min trial. This procedure was repeated until the subject had inhaled all 5 oxygen flows both with and without humidification (ten 1-min trials). Each subject underwent 2 sets of this procedure, for a total of twenty 1-min trials. The score sheet had 20 horizontal visual analogue scales: one for each trial. Data from the second set of trials were used for analysis. Two-way factorial analysis of variance for repeated measures was applied, followed by a Scheffé post hoc test. For all tests, differences were considered statistically significant when p 0.05. The study protocol was approved by the university ethics committee of the Hokkaido University School of Medicine, and all subjects provided written informed consent to participate in the study. The subjects were uninformed about the purpose of this study, to minimize the risk of bias. Throughout the experiments the subjects were blinded to whether the oxygen source had humidification (the device was concealed by a curtain), and listened to music via headphones to promote relaxation and mask sound from the bubble-type humidifier (TO-90-5L, Teijin, Tokyo, Japan). Temperature and humidity in the room were approximately 22–25°C and 43–45%, respectively. Figures 1 and 2 summarize the subjective nasal dryness ratings. In the young healthy subjects, discomfort was significantly higher with dry oxygen than with humidified oxygen at all flow rates, and the discomfort difference between dry and humidified oxygen was larger at flows 3 L/ min. In contrast, the patient group felt significant differences between the dry and humidified oxygen only at flows 3 L/min. All the subjects reported a sensation of gas flow hitting the nasal mucosa during