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The Effect of Bupivacaine on Pain Relief After Lumbar Decompression Surgery

Aim: there are many reports about the efficacy of analgesics in reducing postoperative pain after lumbar decompressive surgery. This study aimed to investigate the effect of subdermal and intramuscular injection of bupivacaine on the severity of postoperative pain after lumbar decompression surgery. Material and Methods: in this randomized double-blind trial, 50 patients who candidate for lumbar decompressive surgery elective for this them. Bupivacaine (0.25%) in the intervention group and normal saline (40 ml) in the control group were injected subcutaneously and intramuscularly. Factors of age, size of surgical cutting, number of operating spaces, duration of operation, the rate of need to analgesia, and the severity of pain at times of 3,12 and 24 hours after surgery were assessed. Results: the severity of pain in Bupivacaine group, in hours 3, 12 and 24 after postoperative surgery was less than control group (P value<0.05). Also, there was no significant difference between the two groups in terms of mean pain intensity using repeated measure design (P value<0.05). But within Bupivacaine group, pain severity significantly decreased during the 24 hours after surgery. (p<0.05) Conclusion: Although bupivacaine (0.25%) results in reducing pain after surgery, more studies are recommended to investigate the effect of bupivacaine in combination with other drugs in cases of lumbar decompressive surgery. Also, it reduces pain during the 24 hours after surgery is very important.

sympathetic system, uncontrolled postoperative pains may lead to complications and even death. Sympathetic activity increases myocardial oxygen consumption and causes cardiac ischemia and infarction [7]. Sympathetic activity may also decrease gastro-intestinal motility and depth of inspiration leading to paralytic ileus and respiratory complications [7]. Administration of non-steroidal anti-inflammatory drugs (NSAIDs) and opioids is a common method in postoperative pain control [8]. Using opioids alone in not effective in reducing these types of pains, so different drugs including corticosteroids and local anesthetics are also noted [9]. Although analgesics are usually used to control moderate to severe post discectomy pains, but their side effects reduce their applying range [4].
Local anesthetics affect cell wall proteins and inhibit secretion and activity of prostaglandins and nociceptors stimulating lysosome enzymes [10]. On the other way, local anesthetics, by inhibiting the Na pumps, block the transit of neural messages along the nerve [11].
Local anesthetics for reducing pain Decreases the high costs of anti-inflammatory drugs, opioids and infusion pumps. Local infiltration of bupivacaine is a known method of postoperative pain reduction in many other surgical specialties effective in some [12,13], noneffective in others [14,15]. Combination of long acting anesthetic agent and corticosteroid can reduce postoperative discomfort [16]. As there are limited numbers of such studies in our country, we decided to perform the study to see whether it could lead to better pain control or not. There is no conflict with ethical considerations. Also, the re-  Table 1.   The effect of bupivacaine on pain reduction in regard to patients' characteristics were not significant but in women and in ages below 42 and also in patients with one level surgery and operations lasting more than 80 minutes, bupivacaine mildly reduced the pain during 24 hours after operation.

Discussion
In this study, we compared the effects of bupivacaine and saline (as placebo) injection in time intervals and found no significant differences in the two study groups, with regard to mean age, gender distribution, pain relief and analgesic drug requirement. Cook  (2015) also showed no significant difference in pain relief in "bupivacaine" and "saline" groups [18]. Donadi et al (2017) concluded that the local injection of magnesium sulfate and bupivacaine provided better pain control and analgesic effect was more significant [5]. Steel et al (1998) concluded that bupivacaine can reduce patients' pain score by more than 50% in the recovery room [19].
A reliable study to show the individual effects of bupivacaine on nociceptors is not available yet. Although in the present study normal saline 0.9% is supposed to be none effective on nociceptors but it may reduce the pain by decreasing the concentration of inflammatory mediators. Saline may also compress the nerve end- ings, thereby blocking the conduction of nerve pulses and producing analgesia [20]. In study on cats (2007) normal saline was none effective on thermal, electrical and pressures no inceptor's [21].
In some studies, bupivacaine alone or in a combination with other drugs has been reported to be effective in reducing postoperative pain and the length of postoperative hospital stay [5]. Some recent studies have shown effectiveness of pregabalin in reducing pain and postoperative anxiety [22][23][24].

Conclusion
With regard to previous studies and our present study, although bupivacaine alone had the effectiveness dose at less pain post-surgery, performing wider studies on the effect of bupivacaine combined with other drugs is suggested in lumbar spine surgery.