MRCP2-4198

A 57-year-old man with severe asthma presents with two days of shortness of breath and tightness in his chest. He has a history of multiple exacerbations and was intubated four months ago for a severe exacerbation. He is currently taking montelukast, beclometasone and salbutamol.

Upon arrival, he is cyanosed and his oxygen saturation is at 92% in air. He is using accessory muscles and is unable to speak beyond groans. His respiratory rate is 22/min and there is a quiet wheeze heard bilaterally in his chest. Despite nebulisers, steroids and magnesium sulfate, he has not responded. He is scheduled for intubation and the initiation of aminophylline.

What is the essential recording to make when administering aminophylline?