1 Unit of Anaesthesia and Pain Therapy, Rizzoli Orthopaedic Institute IRCCS, via Pupilli 1, 40136 Bologna, Italy. Electronic address: andrea.tognu@ior.it.
2 Unit of Anaesthesia and Pain Therapy, Department of Obstetrics, Gynecology and Pediatrics, Sant'Orsola-Malpighi University Hospital, Bologna, Italy.