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      Management of trauma pain in the emergency setting: low-dose methoxyflurane or nitrous oxide? A systematic review and indirect treatment comparison

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          Abstract

          Background

          Low-dose methoxyflurane and nitrous oxide (N 2O; 50:50 with oxygen) are both self-administered, self-titrated, rapid-acting, nonnarcotic, and noninvasive inhalational agents with similar onset times of pain relief. The aim of this review was to compare the clinical efficacy, safety, and tolerability of these analgesics in emergency care.

          Materials and methods

          A systematic literature search and review according to Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines were performed using Embase, Medline, the Cochrane Library, several clinical trial registers, and emergency-medicine conference material.

          Results

          Although both compounds have been used for many years in emergency care, the search found only a few controlled studies and no head-to-head trials performed in this setting. Two double-blind, randomized studies comparing their respective study medication (low-dose methoxyflurane or N 2O) to placebo were identified that could be compared in an indirect approach by using placebo as a bridging comparator. Both agents provided rapid pain relief to trauma patients, with no significant differences between them; both treatments were generally well tolerated.

          Conclusion

          Both low-dose methoxyflurane and N 2O are suitable options for the pain treatment of trauma patients in the emergency setting. Due to the ease of administration and portability, inhaled low-dose methoxyflurane, however, may not only offer advantages in emergency situations in remote or difficult-to-reach locations and mass-casualty situations but also be of significant value in urban and rural environments.

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          Most cited references 30

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          The results of direct and indirect treatment comparisons in meta-analysis of randomized controlled trials.

          When little or no data directly comparing two treatments are available, investigators often rely on indirect comparisons from studies testing the treatments against a control or placebo. One approach to indirect comparison is to pool findings from the active treatment arms of the original controlled trials. This approach offers no advantage over a comparison of observational study data and is prone to bias. We present an alternative model that evaluates the differences between treatment and placebo in two sets of clinical trials, and preserves the randomization of the originally assigned patient groups. We apply the method to data on sulphamethoxazole-trimethoprim or dapsone/pyrimethamine as prophylaxis against Pneumocystis carinii in HIV infected patients. The indirect comparison showed substantial increased benefit from the former (odds ratio 0.37, 95% CI 0.21 to 0.65), while direct comparisons from randomized trials suggests a much smaller difference (risk ratio 0.64, 95% CI 0.45 to 0.90; p-value for difference of effect = 0.11). Direct comparisons of treatments should be sought. When direct comparisons are unavailable, indirect comparison meta-analysis should evaluate the magnitude of treatment effects across studies, recognizing the limited strength of inference.
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            Validation of a verbally administered numerical rating scale of acute pain for use in the emergency department.

            Verbally administered numerical rating scales (NRSs) from 0 to 10 are often used to measure pain, but they have not been validated in the emergency department (ED) setting. The authors wished to assess the comparability of the NRS and visual analog scale (VAS) as measures of acute pain, and to identify the minimum clinically significant difference in pain that could be detected on the NRS. This was a prospective cohort study of a convenience sample of adults presenting with acute pain to an urban ED. Patients verbally rated pain intensity as an integer from 0 to 10 (0 = no pain, 10 = worst possible pain), and marked a 10-cm horizontal VAS bounded by these descriptors. VAS and NRS data were obtained at presentation, 30 minutes later, and 60 minutes later. At 30 and 60 minutes, patients were asked whether their pain was "much less," "a little less," "about the same," "a little more," or "much more." Differences between consecutive pairs of measurements on the VAS and NRS obtained at 30-minute intervals were calculated for each of the five categories of pain descriptor. The association between VAS and NRS scores was expressed as a correlation coefficient. The VAS scores were regressed on the NRS scores in order to assess the equivalence of the measures. The mean changes associated with descriptors "a little less" or "a little more" were combined to define the minimum clinically significant difference in pain measured on the VAS and NRS. Of 108 patients entered, 103 provided data at 30 minutes and 86 at 60 minutes. NRS scores were strongly correlated to VAS scores at all time periods (r = 0.94, 95% CI = 0.93 to 0.95). The slope of the regression line was 1.01 (95% CI = 0.97 to 1.06) and the y-intercept was -0.34 (95% CI = -0.67 to -0.01). The minimum clinically significant difference in pain was 1.3 (95% CI = 1.0 to 1.5) on the NRS and 1.4 (95% CI = 1.1 to 1.7) on the VAS. The findings suggest that the verbally administered NRS can be substituted for the VAS in acute pain measurement.
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              STOP!: a randomised, double-blind, placebo-controlled study of the efficacy and safety of methoxyflurane for the treatment of acute pain

              Objective To evaluate the short-term efficacy and safety of methoxyflurane for the treatment of acute pain in patients presenting to an emergency department (ED) with minor trauma. Methods STOP! was a randomised, double-blind, multicentre, placebo-controlled study conducted at six sites in the UK. A total of 300 patients, 90 of whom were adolescent patients (age 12–17 years), were randomised 150:150 to receive either methoxyflurane via a Penthrox inhaler or placebo. The primary end point of the study was the change in pain intensity as measured using the visual analogue scale (VAS) from baseline to 5, 10, 15 and 20 min after the start of study drug inhalation. Patients were supplied with one inhaler containing 3 mL methoxyflurane or 5 mL placebo after enrolment and initial assessments. Age group (adolescent/adult) and baseline VAS score were controlled for in the statistical analyses. Results A total of 149 patients received methoxyflurane, and 149 patients received placebo. Demographic and baseline characteristics were comparable between the groups. Methoxyflurane reduced pain severity significantly more than placebo (p<0.0001) at all time points tested, with the greatest estimated treatment effect of −18.5 mm (adjusted change from baseline) seen at 15 min after the start of treatment. Methoxyflurane was well tolerated, with the majority of adverse reactions being mild, transient and in line with anticipated pharmacological action. Conclusion The results of this study suggest that methoxyflurane administered via the Penthrox inhaler is an efficacious, safe, and rapidly acting analgesic. Trial registration number: NCT01420159.
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                Author and article information

                Journal
                J Pain Res
                J Pain Res
                Journal of Pain Research
                Journal of Pain Research
                Dove Medical Press
                1178-7090
                2018
                20 December 2017
                : 11
                : 11-21
                Affiliations
                [1 ]University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK
                [2 ]Parexel International Ltd, Chandigarh, India
                [3 ]Mundipharma International Ltd, Cambridge, UK
                [4 ]Mundipharma GmbH, Limburg, Germany
                Author notes
                Correspondence: Alice Eberhardt, Mundipharma GmbH, Mundipharmastrasse 2, 65549 Limburg, Germany, Tel +49 6431 7010, Email alice.eberhardt@ 123456mundipharma.de
                Article
                jpr-11-011
                10.2147/JPR.S150600
                5741984
                © 2018 Porter et al. This work is published and licensed by Dove Medical Press Limited

                The full terms of this license are available at https://www.dovepress.com/terms.php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License ( http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed.

                Categories
                Review

                Anesthesiology & Pain management

                pain treatment, emergency, trauma, methoxyflurane, nitrous oxide

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