Entonox as an analgesic agent during panretinal photocoagulation

A Comprehensive Meta-Analysis on the Role of Analgesics and Anti-Inflammatories in Pan-Retinal Photocoagulation

PURPOSE

Pan-retinal photocoagulation (PRP) is the mainstay of treatment for proliferative diabetic retinopathy (PDR), reducing the risk of severe vision loss. Pain poses a potential obstacle to effective laser delivery and patient compliance. Therefore, implementing pain relief strategies can enhance both treatment efficacy and patient comfort.

DESIGN

A systematic review and meta-analysis.

METHODS

We conducted a systematic review and meta-analysis according to PRISMA guidelines. The PubMed, Embase and Cochrane Central Register of Controlled Trials databases were searched for randomized controlled trials (RCTs) that enrolled patients undergoing PRP due to DR and compared analgesics or non-steroidal anti-inflammatory drugs (NSAID) to placebo. Pain was evaluated with the visual analogue scale. The version 2 of the Cochrane Collaboration's Risk of Bias in Randomized Controlled Trials tool and its version for crossover trials were used to assess the risk of bias. The Grading of Recommendations, Assessment, Development, and Evaluation tool was used to measure the certainty of evidence.

RESULTS

A total of 13 studies were included, comprising 1404 eyes from RCTs, nine of which were crossover. Patients who were administered analgesia reported a significantly lower pain sensitivity compared to those who received placebo (Standardized mean difference [SMD] -0.38; 95% confidence interval [CI] -0.58, -0.17; P < .01; I2 = 69%). Subgroup analysis of systemic administration of analgesics/NSAIDs (metamizole, Entonox, acetaminophen, ibuprofen, caffeine, mefenamic acid, intramuscular ketorolac tromethamine, and potassium diclofenac) also showed a statistically significant reduction in pain when compared to placebo (SMD -0.28; 95% CI -0.50, -0.07; P < .01; I2 = 43%). Exclusive eye drops administration (ketorolac tromethamine 0.5% and sodium diclofenac 0.1%) also showed a significant difference in pain sensitivity (SMD -0.46; 95% CI -0.88, -0.05; I2 = 83%), however with a more significant heterogeneity.

CONCLUSIONS

The results of this meta-analysis including over 1000 patients demonstrated that the use of analgesics significantly reduced pain sensitivity during PRP, and systemic analgesia is potentially better than topical administration when compared to placebo.

Comparative Analysis of Pain and Duration in Panretinal Photocoagulation: Navilas Laser versus Conventional Laser in Proliferative Diabetic Retinopathy

Objectives

To compare the pain perception and treatment duration in patients undergoing panretinal photocoagulation (PRP) for high-risk proliferative diabetic retinopathy (PDR) using Navilas laser versus conventional laser.

Methods

A study was conducted involving 40 patients with bilateral high-risk PDR. Each patient underwent PRP with conventional laser in one eye and Navilas laser in the other. Laser parameters, including spot size and pulse duration were standardized. Pain perception was evaluated using Verbal Rating Scale (VRS) and Visual Analogue Scale (VAS).

Results

The Navilas and conventional laser groups showed no significant differences in baseline visual acuity, lens status, intraocular pressure, cup-to-disc ratio, or cystoid macular edema. The duration of laser treatment was significantly shorter with Navilas laser group (517.3±48.78 seconds, p<0.001). Pain scores (VAS and VRS) were significantly lower in the Navilas laser group (p<0.001, p=0.002 respectively) than in conventional laser group. There was no correlation between VAS and VRS scores and laser time in both the Navilas and conventional laser groups (p>0.05).

Conclusion

Utilizing the Navilas laser for PRP in PDR patients offers advantages over conventional lasers, including reduced pain and expedited procedures. These findings contribute valuable insights for optimizing clinical decisions, potentially enhancing patient compliance and minimizing the risk of visual deterioration in diabetic retinopathy treatment.

Pain Management Strategies before Pan-Retinal Photocoagulation for Diabetic Retinopathy: A Systematic Review

Purpose

This systematic review aims to consolidate key findings regarding the efficacy of pain relief medications administered prior to pan-retinal photocoagulation (PRP) for diabetic retinopathy (DR).

Methods

A comprehensive search of major databases from 1993 to 2023 was conducted. Clinical trials comparing pain relief drugs before PRP in patients diagnosed with DR requiring PRP treatment were eligible for inclusion. The assessment of pain scores involved the use of various scales, such as the visual analog scale (VAS), numerical rating scale (NRS), verbal rating scale (VRS), and other ordinal pain scales. In addition, laser parameters were taken into consideration during the analysis.

Results

Twenty-two clinical trials from initial 150 studies were included in the review. Nine studies evaluated the pain relief effects of nonsteroidal anti-inflammatories NSAIDs (selective NSAID and nonselective NSAID), two studies compared the effects of opioids (conventional opioids and atypical opioids), and eleven studies investigated the effects of benzodiazepines, lidocaine, and other sedatives.

Conclusion

This review synthesizes findings from multiple studies reporting pain as an adverse outcome of PRP in patients with advanced DR. Based on the evidence from reviewed clinical trials, the administration of lidocaine 2% via transconjunctival, retrobulbar, or peribulbar block along with specific NSAIDs, such as topical ketorolac administrated 24 hours before treatment or oral diclofenac potassium (50 mg) prior to PRP, demonstrated beneficial effects among patients with DR.

Pre-Emptive Topical Ketorolac Tromethamine 0.5% for Panretinal Photocoagulation

Purpose: To evaluate the efficacy of topical ketorolac tromethamine 0.5% given pre-emptively a day before, for alleviating pain in patients undergoing panretinal photocoagulation (PRP) treatment. Methods: A controlled single-blinded study was conducted on 33 patients with diabetic retinopathy (DR; severe nonproliferative DR, proliferative DR, or advanced diabetic eye disease) who required PRP treatment in both eyes simultaneously. Each eye of the patients was randomly assigned for ketorolac tromethamine 0.5% eyedrop or placebo. Both eyedrop bottles were randomly labeled. Eyedrops were self-administered by the patients, 4 times a day before the procedure (at 6 am, 12 noon, 6 pm, and 12 midnight) and every 15 min for 1 h (4 times) before the laser. Each patient was subjected to PRP using a Visulas 532s Zeiss device set to spot size 200 μm, time 0.10 s, and ∼600 burns in each eye. The pain score was evaluated immediately after treatment in each eye independently with Scott's visual analog scale (VAS) and the McGill Pain Questionnaire (MPQ). Results: VAS pain score in ketorolac-treated eyes (median 3.0, interquatile range [IQR] ±2.5) was lower than in placebo-treated eyes (median 5.0, IQR ±3.0). Total Pain Rate Index score from MPQ was lower in ketorolac-treated eyes (median 3.0, IQR ±3.0) than in placebo-treated eyes (median 3.0, IQR ±2.5). Both pain score differences are statistically significant with P ˂ 0.05. Conclusion: Topical ketorolac tromethamine 0.5% given pre-emptively a day before is effective in alleviating pain in patients undergoing PRP treatment.

Comparison of navigated laser and conventional single-spot laser system for induced pain during panretinal photocoagulation

To compare the panretinal photocoagulation (PRP)-induced pain response between novel navigated laser (Navilas) and conventional single-spot laser. The eyes were randomly assigned to Navilas or conventional laser. Contralateral eyes underwent PRP with the other system with 30 min resting interval. Pulse duration was 100 ms in conventional laser and 30 ms or 100 ms in Navilas and power setting was enough to create gray-white light burn on both devices. Pain response was evaluated by verbal scale (VS) (0-4) and visual analog scale (VAS) (0-10) after each PRP application. The mean age of 70 patients (140 eyes) was 62.52 ± 9.49 years. Mean power and spot numbers for Navilas and conventional laser were 291.9 ± 85.3 mW vs 368.4 ± 72.0 mW, and 375.4 ± 108.4 vs 374.2 ± 105.0 (p < 0.001 and p = 0.53, respectively). Pain scores for Navilas and conventional laser were 1.19 ± 0.73 and 1.99 ± 0.84 for VS and 2.41 ± 1.65 and 4.74 ± 2.17 for VAS (p < 0.001 and p < 0.001). More comfortable PRP is achieved with Navilas system in comparison with conventional single-spot laser system. However, small number of patients treated with same pulse duration and different contact lenses used for two systems should be taken into consideration. Besides, we did not report comparative clinical efficiency of either laser system.

A 50-50% mixture of nitrous oxide-oxygen in transrectal ultrasound-guided prostate biopsy: A randomized and prospective clinical trial

Introduction

Transrectal ultrasound-guided biopsy (TUSPB) is the standard method of diagnosis for prostate cancer, and although it is well tolerated by some patients, it presents a discomfort rate of 65 to 90%, which may be associated with pain. For convenience, it is agreed that a method of analgesia and sedation is necessary. For this purpose, this study aimed to evaluate the impact of inhalation of a 50–50% N₂O-O₂ gas mixture on pain intensity in these patients.

Material and methods

Randomized, double-blinded clinical trial, conducted at Antônio Pedro University Hospital (Hospital Universitário Antônio Pedro), Niterói, RJ, Brazil, containing two groups of 42 patients: a control (C) group, which received 100% oxygen inhalation, and a nitrous oxide (NO) group, which received inhalation of the 50–50% N₂O-O₂ mixture, self-administered during TUSPB. The pain intensity and degree of satisfaction were evaluated through a visual analogue scale (VAS), as was the frequency of adverse events.

Results

Eighty-four patients were included in the study, with 42 in each group. The mean pain intensity was lower in the NO group than in the C group [2.52 (0–10) vs 5.95 (0–10), p < 0.001], and the degree of satisfaction was higher in the NO group than in the C group (8.14 vs. 4.69, p < 0.001). The adverse effects were somnolence, dizziness, nausea, vomiting, discomfort and euphoria without differences between the groups.

Conclusion

The 50–50% N₂O-O₂ mixture was effective in reducing pain intensity and increasing the degree of satisfaction in TUSPB, with tolerable side effects.

Analgesic Effect of Topical Sodium Diclofenac before Retinal Photocoagulation for Diabetic Retinopathy: A Randomized Double-masked Placebo-controlled Intraindividual Crossover Clinical Trial

PURPOSE

To evaluate the analgesic effect of topical sodium diclofenac 0.1% before retinal laser photocoagulation for diabetic retinopathy.

METHODS

Diabetic patients who were candidates for peripheral laser photocoagulation were included in a randomized, placebo-controlled, intraindividual, two-period, and crossover clinical trial. At the first session and based on randomization, one eye received topical sodium diclofenac 0.1% and the other eye received an artificial tear drop (as placebo) three times before laser treatment. At the second session, eyes were given the alternate drug. Patients scored their pain using visual analogue scale (max, 10 cm) at both sessions. Patients and the surgeon were blinded to the drops given. Difference of pain level was the main outcome measure.

RESULTS

A total of 200 eyes of 100 patients were enrolled. Both treatments were matched regarding the applied laser. Pain sensation based on visual analogue scale was 5.6 ± 3.0 in the treated group and 5.5 ± 3.0 in the control group. The calculated treatment effect was 0.15 (95% confidence interval, -0.27 to 0.58; p = 0.486). The estimated period effect was 0.24 (p = 0.530) and the carryover effect was not significant (p = 0.283).

CONCLUSIONS

Pretreatment with topical sodium diclofenac 0.1% does not have any analgesic effect during peripheral retinal laser photocoagulation in diabetic patients.

Manual acupuncture for relieving pain associated with panretinal photocoagulation

OBJECTIVE

The feasibility of manual acupuncture for reducing pain associated with panretinal photocoagulation (PRP) was investigated.

METHODS

This was a prospective, comparative nonrandomized study on patients with proliferative diabetic retinopathy who were receiving PRP treatment. The protocol of PRP included three sequential sessions of treatment at 2-week intervals. Both the acupuncture (acuPRP) and control groups had no acupuncture in the first session. In the second session, acupuncture was given to the acuPRP group only. The third session of PRP completed the laser treatment course. Acupuncture performed only at GB 37 (Guāngmíng) just before PRP, and the needle was removed after the treatment. An 11-point Likert-type verbal pain score test was given to all patients after each PRP treatment.

RESULTS

Of 34 patients with proliferative diabetic retinopathy, 18 patients were allocated to the acuPRP group and 16 patients were allocated to the control group. After the first PRP treatment, there was no statistical difference in mean pain scores between the acuPRP and control groups (6.8±1.2 versus 6.3±2.1, respectively, p=0.383). After the second PRP treatment, the mean pain score in the acuPRP group was significantly lower, compared with the control group (3.9±1.8 versus 7.4±1.9, respectively, p<0.0001). Within the group, the mean pain scores were significantly higher during the second PRP treatment, compared with the first PRP treatment, in the control group (p=0.0003). In contrast, the mean pain scores were significantly lower during the second PRP treatment, compared with the first PRP treatment in the acuPRP group (p<0.0001). No adverse reactions or complications were noted.

CONCLUSIONS

Acupuncture might help reduce pain during PRP treatment. However, further randomized studies are necessary to verify these preliminary results.

Analgesic effect of etoricoxib (Arcoxia®) 120 mg during retinal laser photocoagulation

Purpose

Panphotocoagulation reduces the risk of vision loss in proliferative diabetic retinopathy. However, not many patients tolerate this treatment well due to pain. Therefore, we evaluated the analgesic effect of etoricoxib during photocoagulation in patients with proliferative diabetic retinopathy.

Methods

A prospective, randomized, double-blind study was conducted on 44 consecutive patients eligible for panphotocoagulation due to proliferative diabetic retinopathy. During the first panphotocoagulation session, both groups were treated without medication. During the following session, the control group received a placebo pill while the other group received etoricoxib 120 mg. Both groups took the medicines 1 hour before the treatment. After each session, the patients quantified the level of pain on a subjective visual scale.

Results

A total of 52 patients were selected for the study and the data of 44 patients were analyzed. In the control group, the average level of pain in the first session was 7.68 (standard deviation 1.70), dropping to an average of 7.32 (standard deviation 1.39) after ingestion of placebo. Therefore, there was no statistical difference (p=0.1187). In contrast, the average level of pain without the drug in the group taking etoricoxib 120 mg was 7.95 (standard deviation 1.46) vs 5.18 (standard deviation 1.65) with the drug, a significant statistical difference (p<0.001).

Conclusions

Etoricoxib 120 mg reduces pain and can be used before panphotocoagulation. Data show that the medication is more effective against pain during photocoagulation than placebo.

Pain perception at laser treatment of peripheral retinal degenerations with green and infrared wavelengths

PURPOSE

To compare the pain perception at laser treatment of peripheral retinal degenerations with green (532-nm) and infrared (810-nm) wavelengths.

DESIGN

Prospective randomized clinical trial.

METHODS

Sequential patients with indications for photocoagulation of bilateral peripheral retinal degenerations were invited to participate in the study. Thirty patients (60 eyes) were enrolled in the study. Each patient had 1 eye treated with infrared laser (diode, 810-nm wavelength) and the other eye treated with green laser (frequency-doubled solid-state laser, diode-pumped, with 532-nm wavelength). The eyes were randomized to infrared or green wavelengths. The right eye was the first treated in all cases regardless of the wavelength arrangement. Immediately after photocoagulation of each eye, the patient was asked to grade pain perception according to an 11-point (ie, 0-10) numerical rating scale (NRS), with 0 meaning "No pain" and 10 meaning "Pain as bad as you can imagine." The primary outcome was the assessment of pain.

RESULTS

The mean grading of pain perception was 2.80 (SD 1.27; mode and median = 2) to green wavelengths and 5.07 (SD 1.36; mode = 4 and median = 5) to infrared wavelengths (P < .001).

CONCLUSIONS

The results showed a statistically and clinically significant difference of pain perception between the 2 groups, with advantage to the green laser group.

Reduction of fluence to decrease pain during panretinal photocoagulation in diabetic patients

BACKGROUND AND OBJECTIVE

To assess the effect of laser fluence reduction to reduce pain during panretinal photocoagulation.

PATIENTS AND METHODS

Twenty-five patients (50 eyes) with diabetic retinopathy who had indication for panretinal photocoagulation were included in this prospective, interventional, and comparative study. The right eyes were treated using low fluence parameters (LFP), whereas the left eyes were treated with standard fluence parameters (SFP). At the end of each session, the patient was asked to rate pain from 0 (no pain) to 10 (maximum pain) for each eye (NRS-11 scale). Fluence per burn and total fluence were determined for each eye. Statistical analysis was performed using the Mann-Whitney U test and the Pearson correlation coefficient.

RESULTS

Pain perception (P < .01) and fluence per burn (P < .01) were significantly less using LFP compared with SFP. Pain was proportional to fluence per burn (R(2) = 0.4), but not to number of burns (R(2) = -0.2).

CONCLUSION

The use of LFP seems to be a good option to diminish the pain during panretinal photocoagulation.

Analgesic effects of tramadol during panretinal photocoagulation

Purpose

To evaluate the effectiveness of tramadol for the reduction of pain in panretinal photocoagulation (PRP).

Methods

A double-masked randomized controlled study was performed. Fifty-eight eyes in 29 patients with proliferative diabetic retinopathy were enrolled. The eyes of the patients were randomized into two groups. Group A received an empty capsule. Group B received an oral intake of 100 mg tramadol. The capsule used in Group A had the same appearance as that used in Group B. Pain during PRP was assessed using a visual analog scale. Vital signs, including blood pressure and heart rate, were measured.

Results

The mean pain scores for groups A and B were 4.80±2.10 and 3.83±1.82 (p=0.09). There were no significant differences in the mean pain scores between the two groups. More patients in group A complained of greater pain than moderate intensity (visual analogue scale=4). Systemic blood pressure increased significantly in group A after laser treatment. However, there were no significant differences in the diastolic blood pressure changes between the two groups. We found no statistical correlation in the heart rate changes.

Conclusions

We failed to prove that tramadol is effective for pain relief because of the small sample size. However, tramadol was effective for the relief of more severe pain. It was also found to stabilize vital sign changes, such as systolic blood pressure during PRP.

Oral versus topical diclofenac for pain prevention during panretinal photocoagulation

PURPOSE

To investigate the effect of pretreatment oral and topical diclofenac on pain reduction during panretinal laser photocoagulation (PRP) for proliferative diabetic retinopathy (PDR).

DESIGN

Prospective, randomized, double-masked, placebo-controlled clinical trial.

PARTICIPANTS AND CONTROLS

A total of 90 patients with PDR requiring PRP for the first time were assigned randomly to 1 of 3 study groups: oral diclofenac (n = 30), topical diclofenac (n = 31), or placebo (n = 29).

METHODS

Study medications were administrated before the first PRP treatment, and pain levels experienced during and 15 minutes after PRP were recorded on a visual analog scale (VAS). Pain levels during a second PRP session, performed on a later date with no pretreatment medications, also were recorded on a VAS.

MAIN OUTCOME MEASURES

The primary outcome measures were the mean VAS pain scores during the first PRP treatment. Secondary outcome measures were the mean VAS pain scores 15 minutes after the first PRP and during the second PRP, and reported side effects after the first PRP.

RESULTS

Mean VAS pain scores during the first PRP were: oral diclofenac, 25.7+/-19.9; topical diclofenac, 33.8+/-27.9; and placebo, 41.3+/-31.0. The pain score difference between oral diclofenac and placebo was both clinically significant (>or=13) and statistically significant (P = 0.02), whereas differences between oral and topical diclofenac (P = 0.20) and topical diclofenac and placebo (P = 0.33) were not. Multivariate regression analysis for age, gender, and total laser energy demonstrated lower pain levels for both oral diclofenac (P = 0.015) and topical diclofenac (P<0.0001) versus placebo, but no difference between oral and topical diclofenac (P = 0.67). For the first PRP, all 3 groups had lower mean pain scores at 15 minutes after treatment compared with during treatment (P<or=0.0003). Mean pain scores were higher during the second compared with the first PRP for the oral diclofenac (P = 0.02) and placebo (P = 0.05) groups. No significant rate difference for any side effect was found between groups.

CONCLUSIONS

When given in a single dose, oral diclofenac is an effective pretreatment analgesic agent for reducing the pain experienced during PRP for PDR.

FINANCIAL DISCLOSURE(S)

The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Advances in understanding the actions of nitrous oxide

Nitrous oxide (N(2)O) has been used for well over 150 years in clinical dentistry for its analgesic and anxiolytic properties. This small and simple inorganic chemical molecule has indisputable effects of analgesia, anxiolysis, and anesthesia that are of great clinical interest. Recent studies have helped to clarify the analgesic mechanisms of N(2)O, but the mechanisms involved in its anxiolytic and anesthetic actions remain less clear. Findings to date indicate that the analgesic effect of N(2)O is opioid in nature, and, like morphine, may involve a myriad of neuromodulators in the spinal cord. The anxiolytic effect of N(2)O, on the other hand, resembles that of benzodiazepines and may be initiated at selected subunits of the gamma-aminobutyric acid type A (GABA(A)) receptor. Similarly, the anesthetic effect of N(2)O may involve actions at GABA(A) receptors and possibly at N-methyl-D-aspartate receptors as well. This article reviews the latest information on the proposed modes of action for these clinical effects of N(2)O.

Topical Ketorolac 0.5% for Ocular Pain Relief During Scatter Laser Photocoagulation with 532 nm Green Laser

PURPOSE

The aim of this study was to evaluate the analgesic effect of topical ketorolac tromethamine 0.5% during scatter laser photocoagulation procedure in proliferative diabetic retinopathy patients.

METHODS

60 eyes of 30 consecutive proliferative diabetic retinopathy patients were included to this prospective, randomized, double-masked, controlled study. One (1) h before laser treatment session, ketorolac tromethamine 0.5% was instilled to 1 eye and artificial tear drop to the fellow eye. Just after treatment, the patients were asked for the severity of pain in both eyes. Visual analog scale was used to assess the level of pain.

RESULTS

Mean pain level for placebo-instilled eyes was 4.88+/-2.56 and ketorolac instilled eyes were 4.45+/-2.25. There was no significant difference for pain levels between placebo and ketorolac-instilled eyes (P=0.29).

CONCLUSIONS

Topical ketorolac tromethamine usage is no more effective than artificial tears for pain relief during posterior segment laser procedures in proliferative diabetic retinopathy patients.

Involvement of brain protein kinase C in nitrous oxide-induced antinociception in mice

Exposure of mice to the anesthetic gas nitrous oxide (N(2)O) produces a marked antinociceptive effect. Protein kinase C is a key regulatory enzyme that may be targeted by general anesthetics. However, a relationship between N(2)O-induced antinociception and protein kinase C has yet to be established. The present study was conducted to identify whether protein kinase C might influence N(2)O-induced antinociception in mice. Regular exposure (11 min) to N(2)O produced concentration-dependent antinociception in mice, as determined using the abdominal constriction test. N(2)O-induced antinociception was attenuated by i.c.v. pretreatment with phorbol 12,13-dibutyrate, a protein kinase C activator. This phorbol 12,13-dibutyrate antagonism of N(2)O-induced antinociception was reversed by i.c.v. pretreatment with calphostin C, a protein kinase C inhibitor. Long-term exposure (41 min in total, including 30 min prior to, and 11 min of analgesic testing) to 70% N(2)O produced reduced analgesic effects, compared with regular exposure to 70% N(2)O, thus indicating acute tolerance to N(2)O-induced antinociception. However, mice pretreated with calphostin C, chelerythrine, which is another protein kinase C inhibitor, and phorbol 12,13-dibutyrate, did not develop acute tolerance. Regarding activation of protein kinase C, regular exposure to 70% N(2)O did not increase protein kinase C within the membrane fraction of brain tissue, as determined by immunoblot analysis, but long-term exposure to 70% N(2)O did. The i.c.v. pretreatment with calphostin C and phorbol 12,13-dibutyrate prevented the increase in protein kinase C observed with long-term exposure to 70% N(2)O. These results suggest that brain protein kinase C negatively regulates the antinociceptive effect of N(2)O, and that activation of brain protein kinase C is related to the development of acute tolerance to N(2)O-induced antinociception in mice.

Double masked randomised controlled trial to assess the effectiveness of paracetamol in reducing pain in panretinal photocoagulation

AIM

To assess the effectiveness of pre-emptive analgesia with paracetamol in reducing pain associated with panretinal photocoagulation (PRP) in a prospective, double masked, randomised controlled trial.

METHOD

60 patients undergoing PRP for the first time were enrolled and randomised to paracetamol or placebo, taken for 2 days starting 24 hours before the laser treatment. The laser treatment was performed following a standardised protocol. Pain during and after treatment was assessed using the McGill pain questionnaire (MPQ) and visual analogue scales (VAS).

RESULTS

The statistical analysis looked for differences between the two study groups immediately after the laser surgery and 24 hours later. There was no statistically significant difference in the primary outcome measure of perception of pain during and 24 hours after PRP, between the paracetamol and placebo group. However, none of the patients in the paracetamol group reported increased total pain at 24 hours, whereas six patients in the placebo group reported increased pain; this difference (21%) was significant to p = 0.01.

CONCLUSIONS

Pre-emptive analgesia with paracetamol did not significantly reduce pain associated with PRP. This study has described for the first time the type of pain associated with PRP, which is perceived mainly as a discomfort. The main attributes of the pain that patients described, were sharp, flashing, tiring, intense, piercing, intermittent, and brief.

[Premixed 50% nitrous oxide and oxygen: theoretical recalls and practical modalities]

The concept of premixed 50% nitrous oxide and oxygen dated back to 1961 in England, where it is commercialised under the name Entonox. In France, after a so marginal use, premixed 50% nitrous oxide and oxygen now knows such a revival since we first consider the pain provoked by the cure. To use correctly premixed 50% nitrous oxide and oxygen, we need to know the main properties of the nitrous oxide. The four commercial versions, now on the market, are presented (Kalinox, Medimix, Antasol, Oxynox. Except a few contraindications, these indications are large, as well at hospital as outside. In less than 10% of the cases, side effects are possible. Conditions of administration are given in details. The limits of the technic and the particular precautions of use are precised.

Interventions for relieving pain associated with panretinal photocoagulation: a prospective randomized trial

PURPOSE

To evaluate the efficacy of pain relief by oral diazepam, acetaminophen, mefenamic acid, intramuscular ketorolac tromethamine, and peribulbar anaesthesia in panretinal photocoagulation (PRP).

METHODS

A total of 220 patients with proliferative diabetic retinopathy requiring PRP treatment were enrolled in this study. Before laser treatment, the patients were allocated randomly to one of eight groups: group 1: diazepam (n=22), group 2: acetaminophen (n=21), group 3: mefenamic acid (n=21), group 4: diazepam and acetaminophen (n=22), group 5: diazepam and mefenamic acid (n=22), group 6: peribulbar anaesthesia with lidocaine (n=23), group 7: intramuscular injection of ketorolac tromethamine (n=22), group 8: placebo (n=67). Pain after the laser treatment was assessed by a verbal descriptive scale. Blood pressure and heart rate were measured before and after laser treatment.

RESULTS

Patients receiving peribulbar anaesthesia had a significantly lower pain score than the control group (P<0.0001). Additionally, the peribulbar anaesthesia-treated group had the significantly least PRP-associated rise in either systolic (P=0.043) or diastolic blood pressure rates (P=0.030). There were no significant differences in pain score using other anesthetic agents when compared with the control group. There were no significant changes in heart rate after PRP treatment.

CONCLUSION

Peribulbar anaesthesia is effective in reducing pain and blood pressure increase after PRP treatment. Oral diazepam, mefenamic acid, and acetaminophen (either alone or in combination with each other) are not effective in preventing PRP treatment-associated pain. Intramuscular injection of ketorolac tromethamine is also not effective in reducing PRP-associated pain.

Role of nitric-oxide synthase isoforms in nitrous oxide antinociception in mice

Exposure of mice to the anesthetic gas N2O evokes a prominent antinociceptive effect that is sensitive to antagonism by nonselective nitric-oxide synthase (NOS) inhibitors. The present study was conducted to identify whether a specific NOS isoform is implicated in N2O antinociception in mice. In the abdominal constriction test, exposure of mice to 25, 50, and 70% N2O resulted in a concentration-dependent antinociceptive effect that persisted for up to 6 min following removal of the mice from the N2O atmosphere into room air. This N2O antinociceptive effect was antagonized by pretreatment with S-methyl-l-thiocitrulline (SMTC) and higher doses of l-N5-(1-iminoethyl)-ornithine (l-NIO), which reportedly inhibit the neuronal and endothelial isoforms of NOS, respectively. Nevertheless, the N2O-induced antinociception was unaffected by pretreatment with low doses of either SMTC or l-NIO or by pretreatment with 2-amino-5,6-dihydro-6-methyl-4H-1,3-thiazine (AMT), which selectively inhibits inducible NOS. The s.c. pretreatment with SMTC and l-NIO reduced brain NOS activity in a dose-dependent manner, whereas AMT had no such effect. Moreover, in blood pressure experiments, SMTC increased SBP in dose-unrelated fashion, whereas l-NIO showed an appreciably weaker but dose-related increase in SBP. The i.c.v. pretreatment with SMTC also reduced N2O antinociception and brain NOS activity without increasing of SBP. These results suggest that it is the neuronal isoform of NOS that is involved in mediation of the antinociceptive effect of N2O in the mice.