Nitrous Oxide for the Treatment of Chronic Low Back Pain

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.

Nitrous oxide intoxication: systematic literature review and proposal of new diagnostic possibilities

Background

Nitrous oxide (N2O), also called “laughing gas,” is the most commonly used inhalation anesthetic in dentistry. The N2O is no longer used, because of the long-term neurologic and cardiovascular sequelae. Due to its sedative and euphoric properties, N2O is often used for recreational use or in some erotic activities. Accidental deaths are mainly associated with the uses of N2O: death can occur from sudden cardiac arrhythmia or, most commonly, acute asphyxiation due to hypoxia. This paper aims to study the literature concerning deaths due to N2O intoxication and highlight pathological findings useful for diagnosis when the crime scene investigation does not reveal any evidence.

Materials and methods

The authors conducted the literature search by PubMed and Scopus databases, searching for articles from 1 January 1970 to 1 March 2020 using the key terms: “Nitrous oxide,” “Laughing gas,” “Hypoxic damage,” “Nitrous oxide anesthesia,” and “Nitrous oxide death.”

Results and discussion

A total of 244 articles were collected. Only 26 articles were included in the systematic review. Most of the deaths from intoxication are due to asphyxiation; the diagnosis is often difficult and immunohistochemistry could be helpful. Nitrous oxide increases the intracellular adhesion molecule expression, E- and P-Selectin (markers of the early inflammatory response), and HIF-1 α (indicative of oxidative stress during ischemia-reperfusion).

Conclusion

The macroscopic and microscopic signs of N2O intoxication are non-specific, but N2O has been proven to cause hypoxic damage to the brain. The suspicion of the presence of the gas in the environment should guide the pathologist. Tissue analyzes provide important information; immunohistochemical stains can confirm hypoxic damage through the use of markers such as HIF-1 α, E-Selectin, and P-Selectin.

A new mechanistic approach for the treatment of chronic neuropathic pain with nitrous oxide integrated from a systems biology narrative review

The limitations of the currently available treatments for chronic neuropathic pain highlight the need for safer and more effective alternatives. The authors carried out a focused review using a systems biology approach to integrate the complex mechanisms of nociception and neuropathic pain, and to decipher the effects of nitrous oxide (N2O) on those pathways, beyond the known effect of N2O on N-methyl-D-aspartate receptors. This review identified a number of potential mechanisms by which N2O could impact the processes involved in peripheral and central sensitization. In the ascending pathway, the effects of N2O include activating TWIK-related K+ channel 1 potassium channels on first-order neurons, blocking voltage-dependent calcium channels to attenuate neuronal excitability, attenuating postsynaptic glutamatergic receptor activation, and possibly blocking voltage-dependent sodium channels. In the descending pathway, N2O induces the release of endogenous opioid ligands and stimulates norepinephrine release. In addition, N2O may mediate epigenetic changes by inhibiting methionine synthase, a key enzyme involved in DNA and RNA methylation. This could explain why this short-acting analgesic has shown long-lasting anti-pain sensitization effects in animal models of chronic pain. These new hypotheses support the rationale for investigating N2O, either alone or in combination with other analgesics, for the management of chronic neuropathic pain.

Postoperative Rigid Cervical Collar Leads to Less Axial Neck Pain in the Early Stage After Open-Door Laminoplasty-A Single-Blinded Randomized Controlled Trial

BACKGROUND

Cervical collars are used after laminoplasty to protect the hinge opening, reduce risks of hinge fractures, and avoid spring-back phenomena. However, their use may lead to reduced range of motion and worse neck pain.

OBJECTIVE

To investigate the clinical, radiological, and functional outcomes of patients undergoing single-door laminoplasty with or without collar immobilization.

METHODS

This was a prospective, parallel, single-blinded randomized controlled trial. Patients underwent standardized single-door laminoplasty with mini-plates for cervical myelopathy and were randomly allocated into 2 groups based on the use of collar postoperatively. Clinical assessments included cervical range of motion, axial neck pain (VAS [visual analogue scale]), and objective scores (short-form 36-item, neck disability index, and modified Japanese Orthopaedic Association). All assessments were performed preoperatively and at postoperative 1, 2, 3, and 6 wk, and 3, 6, and 12 mo. Comparative analysis was performed via analysis of variance adjusted by baseline scores, sex, and age as covariates.

RESULTS

A total of 35 patients were recruited and randomized to collar use (n = 16) and without (n = 19). There were no dropouts or complications. There were no differences between groups at baseline. Subjects had comparable objective scores and range of motion at postoperative time-points. Patients without collar use had higher VAS at postoperative 1 wk (5.4 vs 3.5; P = .038) and 2 wk (3.5 vs 1.5; P = .028) but subsequently follow-up revealed no differences between the 2 groups.

CONCLUSION

The use of a rigid collar after laminoplasty leads to less axial neck pain in the first 2 wk after surgery. However, there is no additional benefit with regards to range of motion, quality of life, and complication risk.

Collar Fixation Is Not Mandatory After Cervical Laminoplasty: A Randomized Controlled Trial

STUDY DESIGN

Prospective randomized controlled study.

OBJECTIVES

To determine the effect of collar-aided fixation on outcomes after laminoplasty for cervical compressive myelopathy.

SUMMARY OF BACKGROUND DATA

Patients are often placed in a Philadelphia collar for weeks after cervical laminoplasty. However, the benefit of postoperative collar use remains controversial. We hypothesized that treatment outcomes in postoperative pain in patients without collars would not be inferior to the outcomes in patients using Philadelphia collars for 2 weeks.

METHODS

This trial analyzed 74 patients (52 males, 22 females, mean age 72.7 years) with cervical compressive myelopathy who had undergone double-door laminoplasty. Before surgery, we randomly assigned patients to the collar-fixation (CF) group (postoperative Philadelphia collar for 2 weeks) or the no-collar (NC) group. The primary outcome was the visual analog scale (VAS) for cervical pain up to 1 year after surgery. Secondary outcomes were Japanese Orthopedics Association score, Short Form 36 score (SF-36), cervical range of motion (ROM), lordotic angle, and complications.

RESULTS

VAS scores up to 1 year after operation were similar with or without collar fixation (P = 0.487, two-way ANOVA). JOA scores improved significantly in both groups (P = 0.002 in CF, P < 0.001 in NC). There was no statistically significant difference between groups with regard to the improvement of JOA scores (54.9% in CF, 47.0% in NC, P = 0.80). The improvement in SF-36 was similar in both groups. Loss of ROM and lordotic angle of the cervical spine did not differ between groups (P = 0.61 in CF, P = 0.82 in NC). The incidence of complications was similar in both groups.

CONCLUSION

The VAS scores of cervical pain with the postoperative treatment without collar fixation were not inferior to those when using Philadelphia collars for 2 weeks. Moreover, other outcomes such as JOA scores, SF-36, ROM, lordotic angle, and complications were similar in both groups.

LEVEL OF EVIDENCE

2.