Reduction of postburn hyperalgesia after local injection of ketorolac in healthy volunteers

Methodology and applicability of the human contact burn injury model: A systematic review

The contact burn injury model is an experimental contact thermode-based physiological pain model primarily applied in research of drug efficacy in humans. The employment of the contact burn injury model across studies has been inconsistent regarding essential methodological variables, challenging the validity of the model. This systematic review analyzes methodologies, outcomes, and research applications of the contact burn injury model. Based on these results, we propose an improved contact burn injury testing paradigm. A literature search was conducted (15-JUL-2020) using PubMed, EMBASE, Web of Science, and Google Scholar. Sixty-four studies were included. The contact burn injury model induced consistent levels of primary and secondary hyperalgesia. However, the analyses revealed variations in the methodology of the contact burn injury heating paradigm and the post-burn application of test stimuli. The contact burn injury model had limited testing sensitivity in demonstrating analgesic efficacy. There was a weak correlation between experimental and clinical pain intensity variables. The data analysis was limited by the methodological heterogenicity of the different studies and a high risk of bias across the studies. In conclusion, although the contact burn injury model provides robust hyperalgesia, it has limited efficacy in testing analgesic drug response. Recommendations for future use of the model are being provided, but further research is needed to improve the sensitivity of the contact burn injury method. The protocol for this review has been published in PROSPERO (ID: CRD42019133734).

High-dose naloxone: Effects by late administration on pain and hyperalgesia following a human heat injury model. A randomized, double-blind, placebo-controlled, crossover trial with an enriched enrollment design

Severe chronic postsurgical pain has a prevalence of 4–10% in the surgical population. The underlying nociceptive mechanisms have not been well characterized. Following the late resolution phase of an inflammatory injury, high-dose μ-opioid-receptor inverse agonists reinstate hypersensitivity to nociceptive stimuli. This unmasking of latent pain sensitization has been a consistent finding in rodents while only observed in a limited number of human volunteers. Latent sensitization could be a potential triggering venue in chronic postsurgical pain. The objective of the present trial was in detail to examine the association between injury-induced secondary hyperalgesia and naloxone-induced unmasking of latent sensitization. Healthy volunteers (n = 80) received a cutaneous heat injury (47°C, 420 s, 12.5 cm²). Baseline secondary hyperalgesia areas were assessed 1 h post-injury. Utilizing an enriched enrollment design, subjects with a magnitude of secondary hyperalgesia areas in the upper quartile (‘high-sensitizers’ [n = 20]) and the lower quartile (‘low-sensitizers’ [n = 20]) were selected for further study. In four consecutive experimental sessions (Sessions 1 to 4), the subjects at two sessions (Sessions 1 and 3) received a cutaneous heat injury followed 168 h later (Sessions 2 and 4) by a three-step target-controlled intravenous infusion of naloxone (3.25 mg/kg), or normal saline. Assessments of secondary hyperalgesia areas were made immediately before and stepwise during the infusions. Simple univariate statistics revealed no significant differences in secondary hyperalgesia areas between naloxone and placebo treatments (P = 0.215), or between ‘high-sensitizers’ and ‘low-sensitizers’ (P = 0.757). In a mixed-effects model, secondary hyperalgesia areas were significantly larger following naloxone as compared to placebo for ‘high-sensitizers’ (P < 0.001), but not ‘low-sensitizers’ (P = 0.651). Although we could not unequivocally demonstrate naloxone-induced reinstatement of heat injury-induced hyperalgesia, further studies in clinical postsurgical pain models are warranted.

A literature review on the pharmacological sensitivity of human evoked hyperalgesia pain models

AIMS

Human evoked pain models can be used to determine the efficacy of new and existing analgesics and to aid in the identification of new targets. Aspects of neuropathic pain can be simulated by inducing hyperalgesia resulting from provoked sensitization. The present literature review aimed to provide insight into the sensitivity of different hyperalgesia and allodynia models of pharmacological treatment.

METHODS

A literature search was performed to identify randomized, double-blind, placebo-controlled studies that included human hyperalgesia pain models and investigated the pharmacodynamic effects of different classes of drugs.

RESULTS

Three hyperalgesia models [ultraviolet B (UVB) irradiation, capsaicin and thermode burn] have been used extensively. Assessment of hyperalgesia/allodynia and pharmacological effect are measured using challenge tests, which generally comprise thermal (heat/cold) or mechanical stimulation (pin-prick, stroking or impact). The UVB model was sensitive to the antihyperalgesic effects of nonsteroidal anti-inflammatory drugs (NSAIDs) and opioids. The capsaicin model was partially sensitive to opioids. The burn model did not detect any antihyperalgesic effects when NSAIDs or local anaesthetics were administered but responded to the effects of N-methyl D-aspartate (NMDA) receptor antagonists by moderately reducing mechanical hyperalgesia.

CONCLUSIONS

Based on pharmacological sensitivity, the UVB model adequately reflects inflammatory pain and was sensitive to NSAIDs and opioids. Findings from the capsaicin and burn models raised questions about the translatability of these models to the treatment of neuropathic pain. There is a need for a reproducible and predictive model of neuropathic pain, either in healthy subjects or in patients.

Analgesia and sedation for children undergoing burn wound care

Standard care of burn wounds consists of cleaning and debridement (removing devitalized tissue), followed by daily dressing changes. Children with burns undergo multiple, painful and anxiety-provoking procedures during wound care and rehabilitation. The goal of procedural sedation is safe and efficacious management of pain and emotional distress, requiring a careful and systematic approach. Achieving the best results needs understanding of the mechanisms of pain and the physiologic changes in burn patients, frequent evaluation and assessment of pain and anxiety, and administration of suitable pharmacological and nonpharmacological therapies. Pharmacological therapies provide the backbone of analgesia and sedation for procedural pain management. Opioids provide excellent pain control, but they must be administered judiciously due to their side effects. Sedative drugs, such as benzodiazepines and propofol, provide excellent sedation, but they must not be used as a substitute for analgesic drugs. Ketamine is increasingly used for analgesia and sedation in children as a single agent or an adjuvant. Nonpharmacological therapies such as virtual reality, relaxation, cartoon viewing, music, massage and hypnosis are necessary components of procedural sedation and analgesia for children. These can be combined with pharmacological techniques and are used to limit the use of drugs (and hence side effects), as well as to improve patient participation and satisfaction. In this article, we review the pathophysiologic changes associated with major thermal injury in children, the options available for sedation and analgesia for wound care procedures in these children and our institutional guidelines for procedural sedation.

Ketorolac analgesia for inguinal hernia repair is not improved by peripheral administration

PURPOSE

It has been suggested that ketorolac, a non-steroidal anti-inflammatory drug (NSAID) available for parenteral use, may result in prolonged (24 hr) postoperative analgesia through a peripheral mechanism when added to local anesthetic infiltration. Our objective was to assess this effect by controlling for systemic absorption of the drug.

METHODS

This randomized, double-blind trial studied 40 men undergoing elective inguinal hernia repair under spinal anesthesia. All patients received 19 mL of lidocaine 1% infiltrated in the operative field before incision. Patients were randomized into two groups of 20. The surgical site group received ketorolac 30 mg added to the lidocaine infiltration. In the control group, ketorolac 30 mg was injected subcutaneously in the contralateral abdominal wall. Numeric rating scores (0-10) of pain at rest and with movement were recorded at the time of discharge from the recovery room and at 24 hr postoperatively. Time to first analgesia, postoperative iv morphine use, total time in the recovery room, and total oral analgesic use in the first 24 hr were also compared.

RESULTS

There were no significant differences between groups with respect to any of the measured variables. In both groups, pain scores were low at rest (1.9 +/- 1.4 vs 2.2 +/- 1.8, surgical site and systemic groups, respectively) and moderate with movement (5.3 +/- 2.2, 5.0 +/- 1.8) after anesthetic recovery. Pain scores were similar at 24 hr (1.1 +/- 1.3, 1.9 +/- 1.6 at rest; 5.7 +/- 2.0, 6.2 +/- 2.2 with movement).

CONCLUSION

Adding ketorolac to lidocaine infiltration for hernia repair does not improve or prolong postoperative analgesia compared to systemic administration.

The effect of topical non-steroidal anti-inflammatory cream on the incidence and severity of cutaneous burns following external DC cardioversion

INTRODUCTION

Cutaneous burns are a common cause of morbidity following direct current (DC) cardioversion. We designed a study to determine whether the application of non-steroidal anti-inflammatory cream prior to cardioversion reduces their incidence and severity.

MATERIALS AND METHODS

Two hours before elective DC cardioversion, we randomised 55 patients to receive ibuprofen 5% cream or placebo cream over sternal and apical pad sites, with patients acting as their own controls. Two hours after cardioversion an independent blinded observer measured skin temperature, erythema index, and minimum sensory and pain detection thresholds at sternal and apical pad sites. Visual analogue pain score (VAS) for each site was recorded at 2 h and 24 h post-cardioversion.

RESULTS

There was a statistically significant difference between pain measured by VAS, skin temperature and pain detection threshold measured at pad sites with pre-applied ibuprofen 5% cream and those with pre-applied aqueous cream, after elective DC cardioversion.

CONCLUSION

Prophylactic application of topical ibuprofen 5% cream 2h prior to elective DC cardioversion reduces pain and inflammation. Consideration should be given to use of prophylactic application of topical ibuprofen as routine treatment for elective DC cardioversion.

Pain management in burn injury

Traumatic bum injuries and the associated treatments are a tremendous pain management challenge. The degree of tissue damage in severe burns can initiate physiologic changes in nociceptive pathways that place the patient at risk for undertreatment. The use of analgesic guidelines that address both background and procedural pain and associated anxiety can provide a rational and consistent approach to treatment. The key to successful treatment is the continuous and accurate assessment of the patient's pain and the response to therapy. Medications, especially opioids, should be regularly evaluated and adjusted to achieve maximum effect and minimal side effect.Nursing's role is perhaps the most important in the essential focused surveillance of bum pain and it's successful treatment.

Intradermal sufentanil does not improve lidocaine-induced local anesthesia

PURPOSE

Peripheral opioid receptors may result in antinociceptive effects when occupied by opioids. This study examined intradermally injected sufentanil (S), a highly lipid soluble opioid, administered with and without lidocaine (L), in a thermal pain model.

METHODS

Nine volunteers were instructed on the method of magnitude estimation of pain before undergoing baseline testing with seven seconds thermal stimuli between 44 and 52 degrees C, delivered by a contact thermal stimulator at five cutaneous forearm sites. Then, four sites randomly received injections of equal volumes (0.1 mL) of either normal saline (NS), lidocaine 0.5% (L), sufentanil 0.75 microg (S), lidocaine 0.5% plus sufentanil 0.75 microg (L+S), and one site was not injected and served as reference (REF). Testing was repeated at six, 30, 60, 90, 120, and 150 min following injection. The pain elicited by each stimulus was normalized to the subject's response to the 50 degrees C stimulus at the REF site.

RESULTS

Baseline testing showed small (P = ns) differences in pain scores. At six minutes, the lidocaine sites (L, L+S) had pain scores that were mean 83% (range 78-88%) lower than the other sites (P < 0.05), but there was no difference between the L and L+S sites or between the S and NS or REF sites. At 30 and 60 min these pain scores were mean 38% (29-44%) and 20% (8-30%) less than at the REF, NS, and S sites (P = ns). At 90 min and later times, the pain scores had returned to baseline.

CONCLUSIONS

These results suggest that intradermal sufentanil alone has no analgesic effect. Further, in combination with lidocaine, sufentanil does neither potentiate nor prolong the analgesic effect of lidocaine.

Treatment of pain in acutely burned children

The child with burns suffers severe pain at the time of the burn and during subsequent treatment and rehabilitation. Pain has adverse physiological and emotional effects, and research suggests that pain management is an important factor in better outcomes. There is increasing understanding of the private experience of pain, and how children benefit from honest preparation for procedures. Developmentally appropriate and culturally sensitive pain assessment, pain relief, and reevaluation have improved, becoming essential in treatment. Pharmacological treatment is primary, strengthened by new concepts from neurobiology, clinical science, and the introduction of more effective drugs with fewer adverse side effects and less toxicity. Empirical evaluation of various hypnotic, cognitive, behavioral, and sensory treatment methods is advancing. Multidisciplinary assessment helps to integrate psychological and pharmacological pain-relieving interventions to reduce emotional and mental stress, and family stress as well. Optimal care encourages burn teams to integrate pain guidelines into protocols and critical pathways for improved care.

A method for overcoming the ceiling effect of bounded pain scales

OBJECTIVE

The Verbal Numerical Scale (VNS) for rating pain is bounded between 0 (= no pain) and 10 (= worst pain imaginable). We hypothesized that the limitations inherent to this boundary when rating extremely painful stimuli may be identified by integrating the VNS with an unbounded score such as magnitude estimation of relative change.

METHODS

Volunteers received stimuli of increasing current via cutaneous electrodes until they rated >5 on the VNS scale. This stimulus, termed S, was arbitrarily assigned a magnitude estimate of 100%. Then, stimuli of varying currents were delivered; two were 10 mA and 20 mA higher than S (S(+10) and S(+20)), two were 1/2 of the current for the S stimulus (S(1/2)), and one was at the original current (Srepeat). The pain elicited by each stimulus was scored in proportion to the S stimulus. The extrapolated VNS score (VNSext) was determined by multiplying this magnitude estimate (%) by the VNS score for S.

MAIN RESULTS

Seventy percent of the stimuli with higher intensity than S generated a VNSext score above 10. The mean magnitude estimations for S(+10) and S(+20) were 186% and 242%: they generated mean (median) VNSext values of 12.4 and 16.2, respectively (p = 0.019 for the difference between them by Wilcoxon signed rank test).

CONCLUSIONS

The combined use of VNS and magnitude estimation confirmed that the ceiling of the bounded pain scale may significantly limit a patient's ability to describe a new pain stimulus. VNSext may provide a means of overcoming this limitation.

Effect of topical local anesthetic application to skin harvest sites for pain management in burn patients undergoing skin-grafting procedures

OBJECTIVE

To determine if topical administration of local anesthesia, applied to fresh skin-harvest sites, reduces pain and analgesic requirements after surgery.

SUMMARY BACKGROUND DATA

Nonopioid treatments for pain after therapeutic procedures on patients with burns have become popular because of the side effects associated with narcotics. The topical administration of local anesthesia originally offered little advantage because of poor epidermal penetration.

METHODS

This study compares 2% lidocaine with 0.5% bupivacaine or saline, topically applied after skin harvest, to determine what effect this may have on pain and narcotic use. Sixty patients with partial- or full-thickness burns to approximately 10% to 15% of their body were randomly divided into three groups: group 1 received normal saline, group 2 had 0.5% bupivacaine, and group 3 had 2% lidocaine sprayed onto areas immediately after skin harvest. Blood samples were subsequently obtained to measure concentrations of the local anesthetic. Hemodynamic variables after surgery, wake-up times, emetic symptoms, pain, and narcotic use were compared.

RESULTS

Higher heart rates were noted in the placebo group than in those receiving lidocaine or bupivacaine. No differences were noted in recovery from anesthesia or emetic symptoms. Pain scores were lower and 24-hour narcotic use was less in patients who received lidocaine. Plasma lidocaine levels were greater than bupivacaine at all time points measured.

CONCLUSIONS

Topical lidocaine applied to skin-harvest sites produced an analgesic effect that reduced narcotic requirements compared with patients who received bupivacaine or placebo. Local anesthetic solutions aerosolized onto skin-harvest sites did not affect healing or produce toxic blood concentrations.

The dose-response relationship of ketorolac as a component of intravenous regional anesthesia with lidocaine

Ketorolac (K) is a useful addition to lidocaine for i.v. regional anesthesia (IVRA). However, the minimal dose of K that is effective for this purpose has not been established. We added 0, 5, 10, 15, 20, 30, and 60 mg of K to 0.5% lidocaine IVRA for either carpal tunnel release or tenolysis. Pain was assessed in the postanesthesia care unit by using a visual analog scale. The duration of analgesia (time to first request for pain relief) and the use of Tylenol No. 3 tablets (T3) were measured. A linear dose-response relationship was observed between the dose of K and the duration of analgesia (r = 0.988) up to 20 mg of K. Similarly, the number of T3 tablets used was inversely related to the dose of K (r = 0.960) over the same range. There were no significant differences among the groups who received 20, 30, or 60 mg of K. We conclude that 20 mg of K is the optimal dose for inclusion with 0.5% lidocaine for IVRA under the conditions of our study.

IMPLICATIONS

The antiinflammatory drug ketorolac is a useful addition to lidocaine for i.v. regional anesthesia. This study showed that 20 mg of ketorolac is equally effective as 60 mg in this context. However, smaller doses provided less effective pain relief, and a linear dose-response relationship was demonstrated.

The effect of intradermal administration of lidocaine and morphine on the response to thermal stimulation

Opioids appear to exert a peripheral effect by gaining access to peripheral opioid receptors. It has been proposed that inflammatory processes and highly osmotic substances could alter the perineural barrier, thereby allowing easy access to opioid receptors. Although local anesthetics do not have osmotic activity, they are highly active on neural tissue and appear to work synergistically with opioids when administered for major conduction blockade. We therefore evaluated, in a double-blind fashion, the combination of lidocaine plus morphine in an attempt to provide a scientific basis for the use of a combination of morphine plus local anesthetics in the periphery. Seven thermal stimuli in 2 degrees C increments (range 40-52 degrees C) were delivered in a random sequence by a computer-controlled thermistor to one of three pretreated sites on 10 volunteers' forearms: reference site (no injection), lidocaine site (0.1-mL intradermal injection of lidocaine 0.5%), or lidocaine plus morphine site (0.1 mL of 0.5 mg of morphine plus lidocaine 1%). Pain responses to the thermal stimuli were rated by the volunteers using the method of magnitude estimation. Pain scores indicated that the combination of lidocaine plus morphine was not more effective than lidocaine alone in attenuating the heat-induced pain. Twenty and 120 min after injection, scores at the lidocaine plus morphine site were 37% and 20% greater than those at the lidocaine site. The addition of morphine to lidocaine did not result in an improvement in the analgesic efficacy and actually had an antianalgesic effect.

Comparison of tenoxicam by intramuscular injection or wound infiltration for analgesia after inguinal herniorrhaphy

We compared wound infiltration with small-dose tenoxicam (7.5 mg) to intramuscular (IM) administration of the same dose to treat pain after herniorrhaphy. In a randomized, double-blind study, 50 patients received either preoperative wound infiltration with tenoxicam, 7.5 mg in 40 mL of 0.9% saline (WI group; n = 25) or IM tenoxicam 7.5 mg (IM group; n = 25). In each group a saline placebo of equal volume was given by the alternate route, i.e., those who received wound infiltration with tenoxicam received 0.75 mL of 0.9% saline IM; those who received IM tenoxicam received 40 mL of 0.9% saline for wound infiltration. Postoperative pain was assessed with a verbal pain scale and a visual analog scale (VAS) at rest and during movement and cough, 1, 2, 4, 6, and 24 h postoperatively. Wound tenderness was assessed with an electronic algometer preoperatively, and 2, 4, and 6 h postoperatively. The need for supplementary analgesics (acetaminophen and morphine) was registered. No differences were observed between groups in VAS pain scores, verbal rating pain scores, pain pressure thresholds, or in need for supplementary analgesics. We conclude that tenoxicam 7.5 mg has no local analgesic effect on postoperative pain after herniorrhaphy.