Respiratorymiddle twist
A 29-year-old man with asthma is treated for an acute exacerbation with repeated nebulised salbutamol, ipratropium and corticosteroids. Initially he was agitated and breathing rapidly; two hours later he is quieter, with a respiratory rate of 34 per minute, pulse rate of 128 per minute and peak expiratory flow rate of 24% of predicted. His oxygen saturation is 92% on high-flow oxygen. A repeat arterial blood gas shows PaCO2 43 mmHg (35–45), whereas it was 29 mmHg (35–45) on arrival. Which one of the following is the most appropriate next step?