A 20 year - old man is brought to hospital having been found in a running car in shut garage. On arrival he is ataxic and listless with a GCS of 11. Haemodynamically stable with a RR of 30 bpm and SaO2 99%. Arterial blood gas showed: PaO2 40 kPa (300 mmHg), PaCO2 3.6 kPa (27 mmHg), carboxyhaemoglobin 22%, lactate 11 (99 mg/dl). Which of the following statements is/are correct?: