Hanna Machin1, Tristan Merlin2, Jaime Viscasillas2. 1. Anaesthesia Service, Department of Veterinary Clinical Science, Royal Veterinary College, University of London, Hawkshead Lane, AL9 7TA, Hatfield, UK. Electronic address: hmachin@rvc.ac.uk. 2. Anaesthesia Service, Department of Veterinary Clinical Science, Royal Veterinary College, University of London, Hawkshead Lane, AL9 7TA, Hatfield, UK.