Does the Speed of Sternal Retraction Affect Postoperative Pain Outcomes

The overall objective of the current investigation is to determine whether increasing the time to sternal retraction to 15 minutes (from the standard ~30 sec), will result in reduced acute and chronic post-sternotomy pain and an improved quality of life. The hypothesis here is that increased time to sternal retraction will result in: reduced required force, less physical trauma, less inflammation, and less nerve damage. Specifically, the hypothesis is that slow steady sternal retraction (occurring over 15 minutes) will 1) reduce the incidence of CPSP by 40% 2) reduce the severity of acute postoperative pain by at least 20-30% and 3) significantly improve quality of life 6 months postoperatively.

The current investigation will be a prospective blinded, randomized, controlled trial. Following institutional ethics approval and signed consent, eligible patients scheduled for elective coronary artery bypass graft surgery will be randomly assigned (stratified by gender and surgeon to ensure equality between groups) either to the Standard group (in which sternal retraction occurs over ~30s) or the Slow group in which sternal retraction occurs over 15 minutes. Patients and research personnel performing the postoperative assessments will remain blinded to group assignment until conclusion of the investigation. All other intra-operative variables will be performed as per standard practice by the cardiac surgeons at Kingston General Hospital. The extent of sternal retraction will be to the surgeon's discretion to enable appropriate exposure of the heart to allow safe conduct of the operation but it will be recorded in all cases.

The primary outcome measure will be the incidence of chronic post-sternotomy chest pain 6 months following CABG with median sternotomy. However, we will also measure the incidence of CPSP at 3 and 12 months to determine the trajectory. Secondary outcomes will include: Pain intensity (numeric rating scale-NRS) of chest pain (which differs from preoperative) at rest and while coughing daily while in hospital until discharge and at 1 week postoperatively. Analgesic consumption (morphine equivalents) daily while in hospital until discharge, 1 week post-operatively and then at 3, 6, and 12 months postoperatively. Intra-operative data will include time from initiation to full retraction, latency from full retraction to sternal closure, width of sternal opening at full retraction. Pain quality, quality of life, and pain interference with daily function at 3, 6 and 12 months post-operatively. All assessments following discharge from the hospital will be via telephone calls from a research nurse blinded to randomization assignment. In-hospital assessments will also be done by a research nurse blinded to group assignment.

Inclusion criteria

• elective coronary artery bypass graft surgery
• understand written informed consent
• ASA I,II or III

Exclusion criteria

• revision cardiac surgery
• current alcohol/substance abuse
• pre-existing chronic pain requiring chronic analgesic use
• rest pain in proposed surgical area preoperatively
• chronic steroid use
• inability to perform postoperative assessments