A 5-year-old boy is brought to the Emergency Department by ambulance following a fall from a climbing frame at school. He has sustained an isolated, closed, deformed fracture of his left distal radius and ulna. He is distressed and in significant pain, despite having received oral paracetamol 30 minutes ago. The child's mother is present and mentions he has a history of pulmonary hypertension for which he is followed up regularly at the regional paediatric cardiology centre.

On examination, there is obvious deformity of the left wrist with swelling but no neurovascular compromise. The skin is intact. The rest of the examination is unremarkable except for a loud P2 component of the second heart sound on auscultation.

Which of the following is the most appropriate analgesic strategy for this child while preparing for fracture reduction?