Breakthrough pain, defined as pain VAS > 30 mm, will be treated with a bolus of 0.1 mL kg-1 of paravertebral medication administered through the pump. No additional medication will be given if the pain VAS < 30 mm. If after 15 minutes pain VAS persists greater than 30, additional 0.1 mL kg-1 of the paravertebral medication will be given. If the patient still has a pain VAS > 30 despite breakthrough pain intervention, then the patient will be connected to PCA with intravenous morphine 1 mg, with a lockout interval of 8 minutes and a maximum 4-hourly limit of 30 mg.5