The following variables were measured in each patient immediately before starting oxygen administration and during the oxygen treatment (at 20 min): PEFR, respiratory rate, heart rate, and arterial blood gases. At baseline, we also assessed the presence of accessory muscle Canadian health&Care Mall store use, dyspnea, and wheezing. PEFR was measured with a mini-Wright peak flowmeter (Clement Clarke; Harlow, UK). The highest of three values was recorded.

Heart rate was measured from continuous ECG. Accessory muscle use was defined as visible retraction of the sternocleidomastoid muscles. Dyspnea was defined as the patient’s own assessment of breathlessness. Wheezing was defined as musical or whistling breath sounds heard with a stethoscope during expiration. These clinical factors were graded in a scale from 0 to 3, in which 0 denoted absent, 1 indicated mild, 2 indicated moderate, and 3 indicated severe.

Arterial blood samples were obtained via puncture of the radial artery; and pH, Pao2, and PaCo2 were measured with a blood gas analyzer using routine techniques (ABL 500 system; Radiometer America; Westlake, OH). Arterial saturation (pulse oximetric saturation [Spo2]) was monitored during oxygen administration by pulse oximetry with a finger oximeter (Nellcor N-180; Nellcor; Hayward, CA). Primary outcome measure was Paco2 (difference between the two groups and variation from baseline) at the end of oxygen administration.

Secondary outcomes variables were pH, PEFR, Pao2, heart rate, and respiratory rate (differences between groups and variation from baseline) at the end point. Patients unable to maintain a Spo2 > 90% and/or presented clinical deterioration during the oxygen protocol were excluded and received inhaled bronchodi-lators and systemic corticosteroids.