PRE-EMPTIVE ANALGISIA: A PROSPECTIVE STUDY OF POST OPERATIVE PAIN

Abstract

The inhibition of neural input by infiltration of local anaesthetic around the operation site prior to the trauma of an operation may reduce subsequent pain post-operatively. Prevention of the normal phenomenon of central and peripheral sensitisation in the nervous system stops the post operative hypersensitivity state that manifests as a decrease in the pain threshold at the site of injury. The underlying clinical principle is for therapeutic intervention to be made in advance of the pain rather than as a reaction to it ¹. We performed a prospective double blind randomised clinical trial to measure the effect of pre operative infiltration of local anaesthetic around arthroscopy wounds compared to post-operative infiltration on post operative pain relief.

Thirty six patients undergoing day case unilateral knee arthroscopy between October 2000 and March 2001 were studied. All patients gave written informed consent. They were randomised into 2 groups using block randomisation to ensure equal group sizes. The sealed envelope technique was used. The pre-operative group had 10ml 0.25% bupivicaine infiltrated around the arthroscopy portal site following induction of general anaesthesia (G.A.), the post-operative group received 10ml 0.25% bupivicaine after the procedure but before reversal of the G.A. The injection technique and G.A. used were standardised. Pain was assessed using a 10cm Visual Analogue Score (VAS) at pre-operative, 1, 2 and 24h post-operative. At each assessment the patients were blinded to the previous scores that they had submitted. Oral analgesic use in the post-operative 24 hours was also recorded.

There were 18 patients in each group. Demographic details did not differ between the 2 groups. One patient in the post-operative group was excluded, as intravenous sedation was required in recovery due to an extreme anxiety state. The mean Visual Acuity Pain Scores (VAS) were lower in the post-operative group (1.3) compared to the pre-operative group (1.58) at pre-operative assessment. However this difference was not statistically significant (p =0.5607). At 1h post op the mean VAS in the post op group was 1.58 and in the pre op group 2.59 (p =0.18). The mean VAS at 2h post op in the pre op group was 1.76 compared to 1.82 in the post op group (p =0.9932).

At 24h the pre op group had a lower mean VAS (2.25) than the post op group (2.4). This difference was however not statistically significant (p =0.7418).

Analysis of the postoperative analgesia requirement in both groups failed to reveal a statistically significant difference (p =0.3965). In day case knee arthroscopy under general anaesthesia there is no beneficial role in the use of pre-emptive local anaesthetic infiltration around the arthroscopy portal sites as compared to post-operative infiltration.