A 42-year-old farmer from Punjab is brought to the emergency department 30 minutes after accidental exposure to an organophosphate pesticide (monocrotophos) during spraying. He presents with excessive salivation, lacrimation, muscle fasciculations, pinpoint pupils, and respiratory distress. His respiratory rate is 32/min and oxygen saturation is 88% on room air. What is the most appropriate immediate next step in management?