Desaturation times between dogs preoxygenated via face mask or flow-by technique before induction of anesthesia

To compare time to desaturation after induction of anesthesia following administration of oxygen via face mask or flow-by for 3 minutes. Randomized crossover study. A group of six healthy adult dogs weighing 15.0 ± 3.4 kg. Dogs were anesthetized twice separated by 14 days. Intramuscular administration of dexmedetomidine (4 μg kg−1), acepromazine (0.01 mg kg−1) and butorphanol (0.2 mg kg−1) provided sedation for percutaneous insertion of a catheter into the tracheal lumen. The tip was advanced to the thoracic inlet and position confirmed using fluoroscopy. Using a sample aspiration rate 200 mL minute−1, inspired (FIO2) and end-tidal oxygen (Fe′O2) were measured. Oxygen (100 mL kg−1 minute−1) was delivered into a circle delivery system and administered to the dog for 3 minutes via face mask or flow-by from the circle Y-piece 2.5 cm from the nares. Then, propofol was administered to induce anesthesia and apnea. A pulse oximeter (lingual probe) measured hemoglobin saturation (SpO2). At SpO2 90% (desaturation point), an endotracheal tube was inserted to allow administration of oxygen and artificial ventilation. Arterial blood and data were collected at baseline (before oxygen administration), 5 seconds after induction of anesthesia, and every 30 seconds until the desaturation point was reached. Data were analyzed using an unpaired and paired t test with (p