Wickham, A; Highton, D; Martin, D; Pan London Perioperative Audit and Research Network (PLAN); (2016) Care of elderly patients: a prospective audit of the prevalence of hypotension and the use of BIS intraoperatively in 25 hospitals in London. Perioperative Medicine , 5 , Article 12. 10.1186/s13741-016-0036-1.