A 32-year-old male farmer is brought to the emergency department 30 minutes after accidental exposure to an organophosphate insecticide spray. He presents with profuse salivation, bronchospasm with audible wheezing, pinpoint pupils, muscle fasciculations, and a heart rate of 48 bpm. His blood pressure is 95/62 mmHg and SpO₂ is 88% on room air. Which of the following is the most appropriate immediate management?