A 56-year-old woman presented to our hospital with acute severe asthma. As a consequence of severe refractory airflow limitation, moderate hypercapnia ensued for several days. Unexpectedly, the patient died as a result of brain stem herniation, in the absence of hypoxaemia, arterial hypotension or an intracranial mass lesion. We discuss the mechanisms that may have precipitated severe intracranial hypertension resulting in brain death, and the possible methods to detect and avoid such a devastating consequence.