Hyperalgesia and increased sevoflurane minimum alveolar concentration induced by opioids in the rat: a randomised experimental study

Determination of acute tolerance and hyperalgesia to remifentanil constant rate infusion in dogs undergoing sevoflurane anaesthesia

OBJECTIVE

To determine if acute opioid tolerance (AOT) or opioid-induced hyperalgesia (OIH) could develop and limit the remifentanil-induced reduction in the sevoflurane minimum alveolar concentration (MAC). The response to mechanical nociceptive threshold (MNT) was evaluated and related to OIH.

STUDY DESIGN

A crossover, randomized, experimental animal study.

ANIMALS

A total of nine Beagle dogs.

METHODS

The dogs were anaesthetized with sevoflurane in 50% oxygen. Baseline sevoflurane MAC was measured (MACb1). Remifentanil (0.3 μg kg^-1 minute^-1) or 0.9% saline constant rate infusion (CRI) was administered intravenously (IV). Sevoflurane MAC was determined 20 minutes after CRI was initiated (MACpostdrug1), 30 minutes after MACpostdrug1 determination (MACpostdrug2) and after 1 week (MACb2). The MNT was determined at baseline (before anaesthesia), 3 and 7 days after anaesthesia. An increase of MACpostdrug2 ≥0.25% compared to MACpostdrug1 was considered evidence of AOT. A decrease in MNT at 3 and 7 days or an increase in MACb2 or both with respect to MACb1 were considered evidence of OIH.

RESULTS

Remifentanil CRI reduced sevoflurane MACpostdrug1 by 43.7% with respect to MACb1. MACpostdrug2 was no different from MACpostdrug1 with the saline (p = 0.62) or remifentanil (p = 0.78) treatments. No significant differences were observed in the saline (p = 0.99) or remifentanil (p = 0.99) treatments between MACb1 and MACb2, or for MNT values between baseline, 3 and 7 days.

CONCLUSION AND CLINICAL RELEVANCE

In dogs, under the study conditions, remifentanil efficacy in reducing sevoflurane MAC did not diminish in the short term, suggesting remifentanil did not induce AOT. Hyperalgesia was not detected 3 or 7 days after the administration of remifentanil. Contrary to data from humans and rodents, development of AOT or OIH in dogs is not supported by the findings of this study.

Endogenous Opiates and Behavior: 2016

This paper is the thirty-ninth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2016 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia, stress and social status, tolerance and dependence, learning and memory, eating and drinking, drug abuse and alcohol, sexual activity and hormones, pregnancy, development and endocrinology, mental illness and mood, seizures and neurologic disorders, electrical-related activity and neurophysiology, general activity and locomotion, gastrointestinal, renal and hepatic functions, cardiovascular responses, respiration and thermoregulation, and immunological responses.

The Effect of Chronic Opioid Use on End-Tidal Concentration of Sevoflurane Necessary to Maintain a Bispectral Index Below 50: A Prospective, Single-Blind Study

BACKGROUND

Opioid analgesics decrease the minimum alveolar concentration of inhalation agents during the acute phase response. However, the effect of chronic opioid exposure on minimum alveolar concentration of inhalation agents remains unknown. This study aimed to determine the concentration of sevoflurane necessary to maintain a bispectral index (BIS) <50 (SEVOBIS50) in patients with chronic opioid use compared with those naïve to opioid use.

METHODS

We included chronic opioid users who received a stable dose of oral morphine of at least 60 mg/d according to the morphine equivalent daily dose for at least 4 weeks and opioid-naïve patients. General anesthesia that included thiopental, vecuronium, and sevoflurane in oxygen was administered to all patients. Anesthesia was maintained using predetermined end-tidal sevoflurane concentrations. Fifteen minutes after achieving the determined end-tidal sevoflurane concentration through closed circuit anesthesia, BIS was measured for 1 minute in both groups. SEVOBIS50 was determined using Dixon's up-down method and probit analysis.

RESULTS

Nineteen and 18 patients from the chronic opioid and control groups, respectively, were included in the final analysis. SEVOBIS50values for the chronic opioid and control patients were 0.84 (95% confidence interval, 0.58-1.11) and 1.18 (95% confidence interval, 0.96-1.40), respectively (P = .0346).

CONCLUSIONS

Our results suggest that the end-tidal concentration of sevoflurane necessary to maintain a BIS <50 is lower for chronic opioid users than for opioid-naïve patients.

Metamizole (dipyrone) effects on sevoflurane requirements and postoperative hyperalgesia in rats

Unlike non-steroidal anti-inflammatory drugs (NSAIDs), metamizole has poor anti-inflammatory effects; and is suitable for models where analgesia, but not anti-inflammatory effects, is desirable. Like opioids, these drugs produce perioperative analgesia while reducing anaesthetic requirements, but it remains unclear whether they may develop tolerance or hyperalgesia, and thus decrease in analgesic efficacy. The aim was to determine whether tolerance or hyperalgesia to metamizole occurred in rats, and whether the sevoflurane minimum alveolar concentration (MAC) was affected. In a randomized, prospective, controlled study, male Wistar rats ( n = 8 per group) were administered metamizole (300 mg/kg, day 4). Previously, the following treatments were provided: daily metamizole for four days (0-3), morphine (10 mg/kg; positive control, day 0 only) or saline (negative control). The main outcome measures were mechanical (MNT) and warm thermal (WNT) nociceptive quantitative sensory thresholds. The baseline sevoflurane MAC and the reduction produced by the treatments were also determined. The mean (SD) baseline MAC [2.4(0.2)%vol] was decreased by morphine and metamizole by 45(11)% and 33(7)% ( P = 0.000, both), respectively. Baseline MNT [35.4(4.5) g] and WNT [13.2(2.4) s] were decreased by morphine and metamizole: MNT reduction of 22(6)% ( P = 0.000) and 22(7)% ( P = 0.001), respectively and WNT reduction of 34(14)% ( P = 0.000) and 24(13)% ( P = 0.001). The baseline MAC on day 4 was neither modified by treatments nor the MAC reduction produced by metamizole (days 0 and 4; P > 0.05). In conclusion, repeated metamizole administration may produce hyperalgesia, although it may not modify its anaesthetic sparing effect. The clinical relevance of this effect in painful research models requiring prolonged analgesic therapy warrants further investigation.

The Effects of the Toll-Like Receptor 4 Antagonist, Ibudilast, on Sevoflurane's Minimum Alveolar Concentration and the Delayed Remifentanil-Induced Increase in the Minimum Alveolar Concentration in Rats

BACKGROUND

Ultralow doses of naloxone, an opioid and toll-like receptor 4 antagonist, blocked remifentanil-induced hyperalgesia and the associated increase in the minimum alveolar concentration (MAC), but not tolerance. The aim was to determine the effects of the toll-like receptor 4 antagonist, ibudilast, on the MAC in the rat and how it might prevent the effects of remifentanil.

METHODS

Male Wistar rats were randomly allocated to 5 treatment groups (n = 7 per group): 10 mg/kg ibudilast intraperitoneally, 240 µg/kg/h remifentanil IV, ibudilast plus remifentanil, remifentanil plus naloxone IV, or saline. The sevoflurane MAC was determined 3 times in every rat and every day (days 0, 2, and 4): baseline (MAC-A) and 2 further determinations were made after treatments, 1.5 hours apart (MAC-B and MAC-C).

RESULTS

A reduction in baseline MAC was produced on day 0 by ibudilast, remifentanil, remifentanil plus ibudilast, remifentanil plus naloxone (P < 0.01), but not saline. Similar effects were found on days 2 and 4. A tolerance to remifentanil was found on days 0, 2, and 4, which neither ibudilast nor naloxone prevented. The MAC increase produced by remifentanil on day 4 (P = 0.001) was prevented by either ibudilast or naloxone.

CONCLUSIONS

Ibudilast, besides reducing the MAC, prevented the delayed increase in baseline MAC produced by remifentanil but not the increase in MAC caused by tolerance to remifentanil.

Tramadol-induced hyperalgesia and its prevention by ketamine in rats: A randomised experimental study

BACKGROUND

Opioid analgesia not only reduces inhalational anaesthetic requirements but may also induce delayed hyperalgesia, with potential effects on the minimum alveolar concentration (MAC) of inhalational anaesthetics.

OBJECTIVES

The objective of this study was to evaluate the development of tramadol-induced hyperalgesia and the associated changes in MAC, and whether ketamine prevents both processes.

DESIGN

A randomised, experimental study.

SETTING

Experimental Surgery Unit, La Paz University Hospital, Madrid, Spain.

ANIMALS

Thirty-nine adult male Wistar rats.

INTERVENTIONS

Mechanical nociceptive thresholds (MNT) were determined up to 21 days after the intraperitoneal administration of a single dose of tramadol (50 mg kg) with or without ketamine (10 mg kg), or 0.9% saline. The MNT and the MAC of sevoflurane were also assessed in a second experiment before, early (30 min) and 7 days after drug administration with the same treatments.

MAIN OUTCOME MEASURES

The MAC and MNT were evaluated. The analysis of variance (ANOVA) test was employed to determine differences between treatments and times on MAC and MNT.

RESULTS

Tramadol, alone or combined with ketamine, produced an early increase in MNT. However, tramadol given alone decreased MNT from day 1 up to 3 weeks, which was associated with an increase in the MAC of sevoflurane (P < 0.05; day 7). Ketamine administration prevented both the reduction in MNT and the increase in MAC (P > 0.05).

CONCLUSION

Tramadol-induced hyperalgesia in the rat lasted for several weeks and was associated with an increase in the MAC of sevoflurane. Prior administration of ketamine blocked both phenomena.