The patient is a 72-year old diagnosed with grade IV COPD treated with HOT at 2l/min with nasal cannulae for the past 3 years. The patient used the O2 some 20h/day. Spirometry done after the administration of salbutamol showed: FVC 2500 (83%), FEV1 800 (32%) and FEV1/FVC 32. Chest radiography presented signs of chronic bronchopathy without any other findings of interest, and the stomach was visualized in its anatomically correct location. The patient reported continuous cough over the course of the last year, with little expectoration. The cough had increased, even interfering with sleep and making it impossible to speak normally. The existence of gastro-esophageal reflux had been ruled out by esophageal pH. The patient had come to the hospital's Emergency Department reporting suffocating cough and dyspnea and was therefore hospitalized with the diagnosis of COPD exacerbation. Arterial gasometry showed: pH 7.40, PO2 64mmHg with O2 at 2l/min through nasal cannulae, PCO2 44mmHg. The complementary studies done (chest radiograph, ECG, blood analysis) did not show relevant alterations or changes compared with previous studies. Given the intensity of the cough and its accentuation with oxygen therapy, we decided to administer O2 to the patient with AIRVO® equipment (Fisher & Paykel, Auckland, New Zealand). The air flow from the device is regulated at 35l/min and the O2 flow of the flow meter at 3l/min, in order to achieve an estimated FiO2 of 28%. The clinical response was spectacular, with the complete disappearance of the cough 5min after initiating the therapy. The patient continued with the treatment for one week and was later discharged with conventional HOT. One month afterwards, the patient was seen in the outpatient consultation. The cough had reappeared, but was much milder and tolerable.

We present a COPD patient with HOT and chronic cough related with the administration of O2 after having ruled out other causes of chronic cough at both the pulmonary and digestive levels. The administration of O2 at body temperature and 100% relative humidity made the cough disappear almost instantaneously, a situation which was maintained for a prolonged period. It is well known that the medical O2 that patients receive is a cold, dry gas. Its temperature is 15°C, and the absolute humidity is 0.3mg/l. The effect of adding a cold bubbler improves the absolute humidity of the gas, reaching values of 15mg/l, although this is far from the 44mg/l necessary to reach a relative humidity of 100%.3 The thermal humidity provided by AIRVO® imitates the natural balance of temperature and humidity produced in healthy lungs (37°C, 44mg/l), achieving a greater well-being of the patient and a greater tolerance to treatment while restoring the defense mechanisms of the respiratory apparatus, especially the mucociliary function.4,5 The patient returned to a conventional HOT system after being discharged from the hospital.6 The reappearance of the cough, although milder and tolerable, one month after discharge leads us to believe that the patient would still be under the beneficial effects of the thermal humidification on the mucosa, although sooner or later the cough would probably become more intense. Is this patient a candidate for receiving HOT through a system of thermal humidification, either continuous or discontinuous? We believe so. This opens new areas of research in the field of HOT, while identifying the need to individualize the prescription of oxygen therapy.