Effectiveness of local anesthesia with lidocaine in chronic opium abusers.

CONTEXT: It had been demonstrated that chronic opium abusers have lower pain thresholds compared with than non-abusers. AIMS: This study aimed to compare the required dose of lidocaine, a common local anesthetic drug, with regard to the onset of anesthesia in opium abusers with that in non-abusers undergoing similar suturing of minor hand lacerations.
MATERIALS AND METHODS: In this study, 109 opium abusers and 91 non-abusers underwent similar suturing for hand lacerations known as digital block. We explained the patients that their case records would remain confidential and admitting to any history of opioid abuse could assist in alleviating any pain associated with the procedure.
RESULTS: There was no statistically significant difference between the two groups with regard to age, gender, and cause of injury (P > 0.05). We found a significantly longer duration of onset of analgesia in nonopioid abusers (5.42 ± 1.93 min) than that in abusers (10.30 ± 1.79 min) (P < 0.001). In addition, the lidocaine dose administered to abusers (6.67 ± 1.21 ml) was higher (4.07 ± 1.26) as well as statistically significant (P < 0.001) than that in non-abusers.
CONCLUSION: The findings from this study suggest a longer duration of onset of anesthesia and requirement of a higher lidocaine dose in opium abusers compared with nonopioid abuser. Moreover, chronic opium abusers (4-5 years) experienced significantly higher time of onset of anesthesia compared with nonchronic abusers. This outcome may be useful in selecting a more suitable local anesthetic protocol in such patients.

INTRODUCTION

Opioid analgesics represent a cornerstone therapy for ameliorating moderate to severe pain and chronic pain, including that in both malignant and nonmalignant patients.[12] Analgesic tolerance phenomenon is observed in prolonged opioid abusers with a progressive need for higher doses to achieve constant analgesic effects.[134] Although analgesic tolerance mechanisms are not fully understood, certain hypotheses have been proposed, including changes in the shape, function, and concentration of opioid receptors.[345] In both, previous studies and medical practice, the duration of anesthesia in opium abusers has been reportedly shorter than that in non-abusers.

Recent advances in knowledge of the mechanisms of pain have revealed that there is cross-interaction and cross-tolerance between local anesthetics and opioid compounds in chronic opioid users.[67] Previous studies have shown there is an increased need for supplemental analgesics to achieve effective sedation in opium abusers. In addition, shorter duration of spinal anesthesia with local anesthetics has been observed in chronic abusers compared with that in non-abusers.[8]

Lidocaine, a local anesthetic and antiarrhythmic drug, has been used for many years for relief of several painful conditions.[9] Previous studies investigated changes in spinal neuronal activity, their mediators, neuronal cellular channels, and receptors in the presence of exposure to repeat dosage of opioids.[10111213] Previous findings revealed that neuroplastic changes caused by opioid consumption include adaptive changes in promoting pain transmission and the subsequent diminished antinociception as a result of opioid tolerance.[134] The present clinical study was designed to compare the required lidocaine dose and analgesic time in opium abusers and non-abusers undergoing similar suturing for finger lacerations.

MATERIALS AND METHODS

Patients

In this descriptive, analytical, case-control study, we evaluated 200 patients (age range, 18-60 years; 109 opium abusers and 91 non-abusers) with finger lacerations referred to the emergency department for ambulatory surgery. Since no similar studies have been performed in this field, we conducted this cross-sectional study between March 2012 and March 2013 to evaluate all finger laceration patients who referred to Imam Reza Hospital, which is a referral trauma center in Mashhad City, east of Iran. The exclusion criteria included history of diabetes, past or present neuropathy, repetitive lacerations at the affected site, concurrent bone fracture, vascular or tendon damage, and mental disorders. We explained the patients that their case records would remain confidential and admitting to any history of opioid abuse could assist in alleviating any pain associated with the procedure.

The patients included in the case group were chronic opium users who had been self-administering either orally or by inhalation for at least 1 year. In addition to self-reporting, the control group subjects had no history of opium use for any reason within the preceding 2 years.

Suturing

Digital block anesthesia was performed by nurses in 200 subjects undergoing surgical repair of finger lacerations. The ideal procedure was described both theoretically and practically for the nurses who would be performing it.

Order of blocking

Digital block was performed on one side of the affected finger[14] by inserting a 25-gauge needle to the side of the extensor tendon. The needle, while kept close to the phalanx, was then advanced toward the volar skin at the most distal part of the web. The needle was kept in place until complete pain relief was achieved.

Prior to the procedure, local paresis was assessed by needle sensation at the distal end of the injured finger. Next, 2 mL of 1% lidocaine was slowly injected, every 30 s and the attainment of paresia retested. In case sensation was still evident, an extra dose of 0.5 mL of 1% lidocaine was injected until complete pain relief was obtained. Time to onset of complete analgesia and lidocaine dose administered were recorded for each subject. Instructions were given to administer a fixed analgesic dose by the initial injection and to leave a 5-min interval before further administration. Intensity of pain is usually evaluated using a visual analog scale (VAS), a 10-cm horizontal line ranged from no pain to severe pain, and numbered from 0 to 10 (0 = no pain, 5 = moderate pain, and 10 = worst pain). The patient marks the point that he/she feels represents his/her perception of his/her current state. In this study, VAS method was used to assess the severity of pain. It is a measurement instrument for subjective characteristics or attitudes that cannot be directly measured. When responding to a VAS item, respondents specify their level of agreement to a statement by indicating a position along a continuous line between two end points.[15]

This was a blind study, those performing the abovementioned procedures and recording them were unaware of whether subjects were addicts.

Statistical analysis

The data were analyzed using Statistical Package for Social Sciences (SPSS) for Windows version 11.05 (SPSS Inc, Chicago, IL, USA). All data were checked for normality by Kolmogorov — Smirnov test (KS test). In addition, descriptive statistics and comparison of means (one sample t-test and paired sample t-test) were used. P-values less than 0.05 were considered significant. Numerical data are expressed as either mean ± standard deviation (SD) or a proportion of the sample size. We used an independent sample t-test between the two groups (opium abusers and non-abusers) for evaluating the difference between variables considered, including gender, duration of anesthesia, and the required lidocaine dosage.

RESULTS

Both groups were matched regarding age, body weight, and duration of surgery, and there was no statistically significant difference between age group and the required dose of lidocaine. However, mean difference in onset of anesthesia among age groups was significant (P = 0.04). Patients aged 50-60 years of age had a higher duration of onset time of anesthesia than other groups.

In the opium abuser group (79 males and 30 females), there was no statistically significant difference in onset time of anesthesia between male (11.03 ± 1.45 min) and female patients (8.40 ± 1.07 min) (P < 0.05). In addition, the mean required lidocaine dose in male (7.10 ± 1.08) and female patients (5.53 ± 0.09) in the opium abuser group was significant (P < 0.001). Comparison of the two groups showed that lidocaine dose and time to onset of anesthesia were significant [Table 1]. Moreover, this table shows that opium abusers needed significantly higher lidocaine doses compared with that of non-abusers. Furthermore, the duration of time to onset of anesthesia in opium abusers was prolonged significantly compared with that in non-abusers (P < 0.001). Among different age groups of opium abusers, there was no statistically significant difference in onset of anesthesia and lidocaine dose. Evaluation of the effect of chronic opium use showed a statistically significant difference between opium abusers for 4-5 years compared with that in abusers for less than 5 years (P = 0.001). This subgroup of chronic opium abusers (4-5 years) experienced significantly higher time of onset of anesthesia compared with nonchronic abusers (P = 0.001).

Table 1

Distribution of onset of anesthesia and lidocaine dose in the two groups

DISCUSSION

Opioids include a group of substances such as opium, morphine, heroin, codeine, tramadol, and methadone.[1617181920] To the best of our knowledge, the current study is the first to compare the required lidocaine dose and the duration of onset of anesthesia in opium abusers and non-abusers referred for repair of finger lacerations. In the present study, we found a significantly longer delay of analgesia in nonopioid abusers than that in abusers. In addition, we found that an increased dose of lidocaine was required in abusers compared with that in non-abusers. Moreover, we observed that opium abusers with a more than 5-year history of opium abuse were significantly different compared with chronic abusers with less than 5-year history of opium use regarding both delay in time to onset of anesthesia and dose of lidocaine. In addition, male abusers experienced significantly prolonged onset of anesthesia and required much higher lidocaine doses compared with female abusers, but not significantly more than normal gender variation. Gupta et al.,[21] reported similar findings in a study about intrathecal fentanyl with 5% bupivacaine in chronic opium abusers. They reported much longer mean time to onset of adequate analgesia in opium abusers than that in non-abusers.

Nevertheless, although the primary cause of change in anesthetic mechanisms is still unclear, the following factors are debatable: Some type of cross-tolerance between local anesthetic agents and opioids based on voltage-gated sodium channels or classic opioid receptors in the central and peripheral nervous systems and structural similarities between opioid and local anesthetic receptors in the spinal cord.[222324] Dabbagh et al.,[25] showed a significantly shortened duration of neural block, both sensory and motor, with bupivacaine in opium abusers. They proposed that at the neuronal level, there were numbers of possible mechanisms including cross-tolerance between local anesthesia and opioid compounds. Therefore, such patients should be managed for a prolonged duration of anesthesia and analgesia.

Vosoughian et al.,[26] studied chronic opium abusers receiving intrathecal hyperbaric preservative — free 5% lidocaine in dextrose and documented a shortened duration of spinal block in opium abusers. Ossipov et al.,[1] demonstrated that repetitive exposure to opioids could trigger certain mechanisms that induced exaggerated pain sensation due to descending facilitation, upregulation of spinal dynorphin, and enhanced release of excitatory transmitters from primary afferents.

The condition termed opioid-induced hyperalgesiais characterized by the absence of nociceptive sensitization caused by chronic exposure to opioids. In chronic pain patients who experience worsening pain despite increasing doses of opioids, the clinical role of opioid-induced hyperalgesia is gaining more recognition. This phenomenon is characterized by a paradoxical response whereby a patient can become more sensitive to painful stimuli.[2728] In addition, it explains the loss of opioid efficacy in our patients as well as other similar studies.[12526]

It is believed that some opioids and its metabolites can activate N-methyl-D-aspartate receptor, which may result in increased neuronal excitation. Thus, when these receptors and associated neurons are stimulated, painful neuron impulse may be caused.[29]

Meanwhile, because the mechanism of action of lidocaine is via the Na channel block,[30] in chronic opium abuser, it may cause changes in the function of action of lidocaine and reduce the effects of lidocaine, but more research is needed to prove this.

CONCLUSION

The findings of this study suggest a longer time to onset of anesthesia and higher lidocaine dose required in opium abusers, particularly chronic abusers, compared with similar patients not abusing opium. Moreover, the difference in the required lidocaine dose observed in the current study is a variable that has not previously been studied and may be useful in the design of further clinical trials to evaluate different procedures to quantify the optimum dosage for this patient group.