Surgery and anaesthesia
After entering the operating room, electrocardiography, oxyhemoglobin saturation, the mean arterial pressure and central temperature were monitored. Anaesthesia was induced with sufentanil, midazolam, etomidate and rocuronium and subsequently maintained with sufentanil, propofol and rocuronium according to the clinical needs in all patients. The depth of anaesthesia was monitored by a bispectral index and it was maintained between 45 and 55 intraoperatively. All patients underwent biological valve replacement with CPB via a median sternotomy. Patient‐controlled intravenous analgesia with sufentanil and flurbiprofen axetil was used to perform postoperative analgesia and 50 mg flurbiprofen axetil was injected i.v. at 6 h intervals as a supplementary analgesic. We selected the surgeries of the same group of surgeons in our study. All patients were sent to the ICU after the surgery.