Chronic Pain and the Opioid Epidemic

Nitrous oxide for the treatment of complex regional pain syndrome: a randomized blinded trial

INTRODUCTION

Complex Regional Pain Syndrome (CRPS) is a debilitating neuropathic condition often refractory to conventional treatments. N-methyl-D-aspartate (NMDA) receptor antagonists have a well-established role in the development and modulation of chronic neuropathic pain. Nitrous oxide is widely used and generally safe anesthetic gas with NMDA receptor antagonist activity. We therefore tested the hypothesis that brief periods of nitrous oxide exposure reduce pain in patients with CRPS.

METHODS

Patients with a diagnosis of CRPS were randomized to either 2 hours of nitrous oxide exposure on three alternating days (Nitrous Oxide) versus a placebo air/oxygen mixture (Air-Oxygen). Our primary outcome was patient-reported pain scores at 1 week and 1 month. Secondary and exploratory outcomes were physical and mental health (PRMOIS-29 v2 survey), specific neuropathic pain symptoms (McGill short-form questionnaire), and opioid consumption.

RESULTS

44 patients participated in the study; 20 were randomized to Nitrous Oxide and 24 were assigned to Air-Oxygen. Pain scores did not differ significantly, with the estimated difference in means (Nitrous Oxide-Air-Oxygen) of -0.57 (95% CI: -1.42 to 0.28) points, p=0.19. There were also no differences detected in secondary outcomes, with the estimated difference in mean Z-scores for physical health (Nitrous Oxide-Air-Oxygen) of 0.13 (95% CI: -0.16 to 0.43), mental health 0.087 (95% CI: -0.31 to 0.48), and Patient Global Impression of Change score -0.7 (95% CI: -1.85 to 0.46).

CONCLUSIONS

Compared with air/oxygen, 2 hours of nitrous oxide/oxygen exposure for three sessions did not provide meaningful therapeutic potential for patients with chronic CRPS. Our results do not support using nitrous oxide for the treatment of CRPS.

Evaluation of antihyperalgesic and analgesic effects of 35% nitrous oxide when combined with remifentanil: A randomised phase 1 trial in volunteers

BACKGROUND

Remifentanil is an effective drug in peri-operative pain therapy, but it can also induce and aggravate hyperalgesia. Supplemental administration of N2O may help to reduce remifentanil-induced hyperalgesia.

OBJECTIVE

To evaluate the effect of 35 and 50% N2O on hyperalgesia and pain after remifentanil infusion.

DESIGN

Single site, phase 1, double-blind, placebo-controlled, randomised crossover study.

SETTING

University Hospital, Germany from January 2012 to April 2012.

PARTICIPANTS

Twenty-one healthy male volunteers.

INTERVENTIONS

Transcutaneous electrical stimulation induced spontaneous acute pain and stable areas of hyperalgesia. Each volunteer underwent the following four sessions in a randomised order: 50 to 50% N2-O2 and intravenous (i.v.) 0.9% saline infusion (placebo); 50 to 50% N2-O2 and i.v. remifentanil infusion at 0.1 μg kg-1 min-1 (remifentanil); 35 to 15 to 50% N2O-N2-O2 and i.v. remifentanil infusion at 0.1 μg kg-1 min-1 (tested drug) and 50 to 50% N2O-O2 and i.v. remifentanil infusion at 0.1 μg kg-1 min-1 (gas active control). Gas mixtures were inhaled for 60 min; i.v. drugs were administered for 30 min.

MAIN OUTCOME MEASURES

Areas of pin-prick hyperalgesia, areas of touch-evoked allodynia and pain intensity on a visual analogue scale were assessed repeatedly for 160 min.

RESULTS

Data from 20 volunteers were analysed. There were significant treatment and treatment-by-time effects regarding areas of hyperalgesia (P < 0.001). After the treatment period, the area of hyperalgesia was significantly reduced (P < 0.001) in the tested drug and in the gas active control (30.6 ± 9.25 and 24.4 ± 7.3 cm2, respectively) compared with remifentanil (51.0 ± 17.0 cm2). There was also a significant difference between the gas active control and the tested drug sessions (P < 0.001). For the area of allodynia and pain rating, results were consistent with the results for hyperalgesia.

CONCLUSIONS

Administration of 35% N2O significantly reduced hyperalgesia, allodynia and pain intensity induced after remifentanil. It might therefore be suitable in peri-operative pain relief characterised by hyperalgesia and allodynia, such as postoperative pain, and may help to reduce opioid demand.

TRIAL REGISTRATION

EudraCT-No.: 2011-000966-37.

A meta-analysis of randomized controlled trials: combination of ketamine and propofol versus ketamine alone for procedural sedation and analgesia in children

Although ketamine has been used for procedural sedation and analgesia, some researchers have assessed ketamine-propofol as a better alternative because of its reduced adverse events. The goal of this review was to compare adverse events between ketamine-propofol and ketamine for procedural sedation and analgesia in children. We searched the literature from their inception to May 2018 without the restriction of language. We included all randomized controlled trials comparing ketamine-propofol with ketamine for procedural sedation and analgesia in children. The meta-analysis was conducted using the Stata software. A total of six studies involving 693 individuals were included. Pooling of data showed that subjects with ketamine-propofol had similar incidence of respiratory adverse events compared to those with ketamine (RR 1.16, 95% CI 0.68-1.98). However, ketamine-propofol was effective in reducing cardiovascular adverse events compared to ketamine (RR 0.11, 95% CI 0.04-0.31). Ketamine-propofol was also effective in reducing psychomimetic adverse events compared to ketamine (RR 0.39, 95% CI 0.16-0.93). In regard to nausea and vomiting, ketamine-propofol was significantly effective (RR 0.43, 95% CI 0.25-0.74). In addition, we could not demonstrate differences in efficacious sedation between ketamine-propofol and ketamine. Although our study was not able to demonstrate differences in efficacious sedation between ketamine-propofol and ketamine, we confirmed that ketamine-propofol sedation had a lower frequency of adverse events compared to ketamine sedation in children.