Abstract
Introduction: Adequately managing post-operative pain following ankle and hindfoot surgery can be difficult. Conventional analgesics have significant side effects including nausea and gastric irritation. The results of a pilot study of continuous infusion v’s single bolus popliteal block encouraged us to perform the full PRCT.
Method: The trial was approved by the local Research and Ethics Committee and registered with the European Clinical Trials Database. Approval was obtained from the Medicines and Healthcare products Regulatory Authority (MHRA) for the use of normal saline infusion as a placebo. The recommendations of Good Clinical Practice in the conduct of clinical trials on medicinal products for human use were respected.
Inclusion criteria were all patients who were undergoing significant hind foot or ankle procedures. Exclusion criteria included coexisting peripheral neuropathy and any inability to fill in the questionnaire.
The pilot study provided a standard deviation of pain scores which allowed us to calculate the sample size required; 25 patients in each group would have 90% power to detect a difference in means VAS scores of 3 which we considered to be clinically significant. A total number of 56 (to allow for 10% loss to follow-up) were recruited. The patients and the assessors were blinded to the treatment allocated. Sealed envelopes contained random allocations and were opened by the anaesthetist. A bolus of 20ml 0.25% bupivacaine was injected and then the catheter was inserted and connected to a pump. Patients were randomly assigned to receive either an infusion of normal saline or bupivacaine over the next 72 hours.
The patients were asked to complete a visual analogue pain chart, three times daily, for 72 hours postoperatively. Data was also recorded regarding supplementary opiate analgesic requirements and any problems or complications.
Statistical analysis was performed using MedCalc for Windows, version 9.6.4 (MedCalc software, Mariakerke, Belgium). A Mann-Whitney U test was used for the non-parametric data sets.
Results: Both groups had very low median VAS pain scores on the day of operation and there was no difference between the two; study 1.167, control 1.000 (p=0.893). On the 3 post operative days studied there were significantly lower pain scores in the study group; day 1: 1.67 v’s 3.67 (p=0.003), day 2: 1.33 v’s 2.83 (p=< 0.001), day 3: 1.11 v’s 2.56 (p=< 0.001).
There was no difference in median milligrams of morphine usage on the day of operation; study = 10, placebo = 10 (p = 0.942). The morphine usage was lower in the study group on all post operative days and this was significant on days 2& 3; day 1: 10 v’s 15 (p=0.054), day 2: 10 v’s 20 (p=< 0.001), day 3: 7.5 v’s 10 (p=0.02). Median total morphine requirements over the 3 post operative days were 30mg for the study group compared to 52.5mg for the control group and this was significant (p=0.012).
The study group on average spent less nights as an inpatient with a median value of 1 compared to 2 for the control but this was not significant (p=0.430).
There were no major complications with the administration of the blocks or with the catheters.
Conclusion: The bolus of bupivacaine given to all patients prior to surgery meant that low pain scores were seen in both groups in the immediate post operative period with no significant difference between them. The continuous infusion of bupivacaine via a pain pump provided significantly better analgesia than normal saline with significantly less requirement for supplementary oral analgesic agents over the 72 hours after major ankle or hind foot surgery. This is a safe and effective method of managing post operative pain in these patients.
Correspondence should be addressed to: Mr Andrew H. N. Robinson, Editorial Secretary, Department of Trauma and Orthopaedics, BOX 37, Addenbrooke’s Hospital, Cambridge CB2 2QQ, England.
