 Induction of general anaesthesia will be done in a standardized fashion with fentanyl 2 μgKg, propofol 1-4 mgKg and vecuronium 0.1 mgKg if intubation is required. For anaesthetic maintenance, isoflurane 0.7-2 on 1:2 oxygen : nitrous oxide gas mixture, and fentanyl boluses 1 μgKg to keep a bispectral index BIS between 40 to 60, and a heart rate and mean arterial pressure between 70-130 from pre-induction baselines. Preemptive antiemetics e.g.: granisetron, ondansetron, metoclopramide, dexamethasone, etc. should not be given. No additional analgesics should be administered e.g.: ketorolac or other NSAIDs, dipyrone. 