Does prewarming children improve outcomes in children with cerebral palsy having major lower limb surgery?

INTERVENTION: The intervention is for patients to lie in a bed and be prewarmed with a forced air warming blanket set at 40 degrees for one hour prior to induction of anaesthesia. CONDITION: Children with severe cerebral palsy undergoing elective bilateral femoral valgus derotational osteotomies PRIMARY OUTCOME: To determine whether prewarming can prevent hypothermia. Skin temperature and core temperature (tympanic) will be measured pre and post anaesthesia. During anaesthesia, temperature will be measured using an oesophageal temperature probe. SECONDARY OUTCOME: To determine whether effects the rate of wound infections. Wounds will be classified as infected if there was a purulent discharge or painful erythema that lasted for 5 days and was treated with antibiotics within 6 weeks of surgery. To determine whether prewarming effects the amount of surgical blood loss. To assess intraoperative and postoperative blood loss we will use (a) Weighing packs, (b) Measuring Drains and (c) Haemoglobin Balance method. To determine whether prewarming effects the duration of recovery from anaesthesia. INCLUSION CRITERIA: 1)Children with severe cerebral palsy undergoing elective bilateral femoral valgus derotational osteotomies 2) Children aged between 5 ‐20 years 3) Any weight