You are caring for a 5-year-old male child who is brought to you because of respiratory distress. He is lethargic and moans to deep painful stimuli, capillary refill is delayed at 4 seconds and his skin is mottled. The heart rate is 38, blood pressure is 64/30 and the respiratory rate is 6 per minute. Oxygen saturations are 72% on room air. The most appropriate initial intervention is: