LAUSR

OBJECTIVE To compare time to desaturation after induction of anesthesia following administration of oxygen via face mask or flow-by for 3 minutes. STUDY DESIGN Randomized crossover study. ANIMALS A group of six healthy adult dogs weighing 15.0 ± 3.4 kg. METHODS 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 < 0.05). RESULTS FIO2, Fe'O2 and PaO2 (mean ± standard deviation) were significantly higher after mask preoxygenation [89.7 ± 5.5%, 83.0 ± 7.6% and 394 ± 112 mmHg (52.4 ± 14.9 kPa)] compared with flow-by [30.0 ± 5.4%, 22.7 ± 3.8% and 133 ± 22 mmHg (17.7 ± 2.9 kPa)], respectively. Time to desaturation was significantly longer after mask treatment compared with flow-by (187 ± 67 versus 66 ± 17 seconds). CONCLUSIONS AND CLINICAL RELEVANCE Mask preoxygenation provided longer time to desaturation compared with the flow-by technique tested.