Respiratorymiddle twist
A 71-year-old woman with chronic obstructive pulmonary disease presents with two days of worsening breathlessness and purulent sputum. She is treated with 28% oxygen via a Venturi mask, nebulised salbutamol and ipratropium, oral prednisolone and antibiotics. One hour later she is drowsy but rousable, with a respiratory rate of 28/min and oxygen saturation of 89%. An arterial blood gas on this therapy shows pH 7.26 (7.35–7.45), PaCO2 74 mmHg (35–45), PaO2 60 mmHg (80–100) and bicarbonate 32 mmol/L (22–32). Which one of the following is the most appropriate next step in management?