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

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.