Altered breathing with postoperative pain relief

Many patients experience some degree of breathing difficulty after major surgery and breathing difficulties may be the basis for serious, but uncommon complications of anaesthesia and surgery. The use of sedatives and morphine-like drugs for the relief of pain, although very necessary, contributes to decreased breathing effort, pauses and obstruction. Patients with obstructive sleep apnoea (OSA) syndrome, associated with a history of snoring, observed pauses in breathing during sleep and daytime sleepiness, may be at especially high risk with anaesthesia. This syndrome is associated with obesity, and may be a partial cause for, many types of heart and lung disease. Specialized high-dependency postoperative care is advocated for these patients. We are interested in patients who do not have a definite diagnosis of OSA or severe symptoms, but who do have a high body mass index (BMI) and some abnormal airway features that imply increased risk of obstruction. Such patients may make up to 20% of patients presenting for elective surgery at the RMH. An initial respiratory monitoring study in progress, suggests that patients with these risk factors have increased breathing difficulties and reduced blood oxygen in the period after surgery. In the proposed study, patients who are considered to be at risk of breathing problems on the basis of questionnaires and examination prior to surgery, will be randomized to either standard opioid (morphine) pain relief for the first day after surgery or to a group where other pain relieving dugs (ketamine, parecoxib and tramadol) are used in an attempt to reduce opioid use while maintaining adequate pain relief. In both groups dugs will be used according to protocols approved by the Acute Pain Service at the Royal Melbourne Hospital.