A Prospective Randomized Controlled Pilot Study Nitrous Oxide for the Treatment of Complex Regional Pain Syndrome
Phase: PHASE3
Conditions: Complex Regional Pain Syndrome
Sponsor: The Cleveland Clinic

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Nitrous Oxide for the Treatment of Complex Regional Pain Syndrome: A Prospective 
Randomized Controlled Pilot Study  
 
Version 1.0 Dated:  December 20, 2018 
Version 2.0 Dated:  March 5, 2019 
Version 3.0 Dated: March 23, 2019 
Version 4.0 Dated: March 28, 2019 
Version 5.0 Dated: July 8, 2019 
Version 6.0 Dated: October 22, 2019 
Version 7.0 Dated: December 6, 2019 
 
 
 
 
 
Investigators:  
Dr. Jason Hale, M.D. PGY-2 
Anesthesiology Institute 
Cleveland Clinic Foundation 
 
Dr. Alparslan Turan, M.D. 
Department of Outcomes Research 
Anesthesiology Institute 
Cleveland Clinic Foundation 
 
Dr. Jijun Xu, M.D. Ph.D. 
Department of Pain Management 
Anesthesiology Institute 
Cleveland Clinic Foundation 
 
Natalya Makarova, M.S.  
Department of Quantitative Health Science 
Department of Outcomes Research, Anesthesiology Institute 
Cleveland Clinic Foundation 
 
 
 
 

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Version 2.0 - February 26, 2019 Amendment 1 
Page 7 – changed from the control group will receive 100% oxide to control group will receive 50% oxide 
 
Version 3.0 – March 23, 2019 Amendment 1 
Page 7 – Active Control: The control group that receives 50% oxygen will also receive 2mg midazolam by 
intravenous injection.  The study group that receives nitrous oxide will receive 2ml normal saline by 
intravenous injection as a placebo. 
 
Version 4.0 – April 28, 2019 Amendment 1 
Pages 7 – Initial Recruitment: the recruitment process was edited to incorporate use of the recruitment 
letter. 
Page 9 – schema was edited to reflect this change as well. 
 
Version 5.0 – July 8, 2019 Amendment 1 
Page 7 – Treatment Phase: Active Control.  After discussion with our research team, we decided to give 
all patients (control and study group) a 2mg dose of intravenous midazolam, to infuse over 5 minutes, at 
the start of each breathing treatment session.  We believe this will greatly reduce participants’ ability to 
determine which arm of the study they are in. 
 
Version 6.0 – October 18, 2019 Amendment 1 
Page 9 – Allocation will be stratified by use of spinal cord stimulator.  
 
Version 7.0 – October 18, 2019 Amendment 1 
Page 6 – We will include Patients ages 18-70 
Page 8 – added approximately  
 
 
 
 

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Background and Significance 
 
Medical Background and Pharmacologic Basis 
Complex Regional Pain Syndrome (CRPS), formerly known as reflex sympathetic dystrophy, is a 
debilitating neuropathic chronic pain condition that most commonly develops as a sequela of traumatic 
injury to an extremity.  The condition is characterized by severe pain (including hypersensitivity and 
allodynia), swelling, decreased range of motion, as well as skin and bone changes.  The incidence is 
approximately 6 per 100,000 person-years, and the condition can have a profound impact on quality of 
life.1  The annual healthcare cost is high, and was reported to be €5700 per year in the Netherlands in 
1998.2  There is little addition data regarding current healthcare costs, but many patients with CRPS do 
not work, worsening the disease’s socioeconomic impact.3  
The approach to treatment is often multimodal, including various classes of pain medications, physical 
therapy, nerve blocks, peripheral and central neural stimulation, and intrathecal drug therapy.4  Patients 
who are refractory to many treatment modalities may be candidates for subanesthetic ketamine 
infusions, typically administered for several sessions over days.5  At our institution, patients who 
undergo ketamine infusions receive sub-anesthetic infusions for four hours each day over a period of 
five days.  Ketamine is a well-known N-methyl-D-aspartate (NMDA) receptor antagonist, and this 
pharmacologic mechanism is believed to underpin its efficacy in this setting.  NMDA agonism is believed 
to contribute to hypersensitivity within the central nervous system and play a fundamental role in the 
pathophysiology of CRPS.6,7  Furthermore, ketamine is known to provide an analgesic effect long after 
the drug has been eliminated.8  Ketamine appears to be effective in the treatment of CRPS, but only one 
double-blind placebo-controlled study examining ketamine therapy for this condition has been 
published.9  Ketamine infusion may provide more than 30% pain reduction in 58% of CRPS patients 
during the 1-3 month follow up period according to a recent meta-analysis.55 
Unfortunately, ketamine infusions are costly, require intravenous access, and necessitate continued 
patient monitoring.  Ketamine has a well-known side effect profile.  For patients undergoing outpatient 
ketamine infusions for CRPS, these side effects specifically include feelings of inebriation, nausea, 
psychotomimetic effects, headaches, hypertension, and elevated liver enzymes as the most common 
problems.10  Other potential side effects include agitation, confusion, arrythmias, vomiting, anaphylaxis, 
and even respiratory depression at high doses.  Though perhaps beneficial for certain patients, ketamine 
is not an ideal medication for easy outpatient administration. 

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In addition to ketamine, there are only a handful of other commonly used NMDA receptor antagonists 
used in clinical practice, one of which is nitrous oxide.  Nitrous oxide gas is a low potency inhalation 
anesthetic used frequently for both general anesthesia as well as sedation for less invasive office-based 
medical procedures.  Though commonly used in operating rooms around the world, its role as an 
analgesic agent in chronic pain had scarcely been studied.  The side effect profile is minimal to 
negligible, patient monitoring requirements are far less, ventilation and oxygenation are not affected, 
and it is rapidly eliminated via the lungs, making nitrous oxide a much easier drug to administer in the 
outpatient setting. 
Recent literature regarding nitrous oxide primarily focuses on its use peri-operatively as an analgesic 
agent with the potential to reduce opioid use and the development of chronic pain in surgical 
patients.11,12,13  Nitrous oxide has also been shown to inhibit opioid-induced hyperalgesia in humans in 
the setting of acute surgical pain.14  With respect to chronic pain, animal studies have demonstrated the 
efficacy of nitrous oxide in alleviating pain hypersensitivity in rats with neuropathic pain.  The efficacy 
was not only dose dependent but persistent as well (at least 3 weeks with 50% nitrous oxide).15    
Another neuropathic pain rat model study showed that a single nitrous oxide exposure caused a 
reduction in pain hypersensitivity of the injured extremity, abolished pain hypersensitivity of the 
contralateral extremity, and prevented thermal allodynia completely.  These effects were persistent for 
more than 1 month.16   We have successfully administered nitrous oxide to chronic pain patients in an 
outpatient setting.17   
CRPS can be a truly debilitating disease with the potential to significantly compromise quality of life.  
Treatment of refractory CRPS patients can be both costly and unsuccessful, and better treatment 
modalities are needed for this complex disease.  Based on the abovementioned preclinical reports and 
the essential role of the NMDA receptor in the pathophysiology of CRPS, we believe that nitrous oxide 
will provide clinically meaningful pain reduction and functional improvement in patients suffering from 
CRPS. 
 
Clinical Research of CRPS and Selecting Outcomes 
Subjective Data - Patient Reported Outcomes: 
Until recently, there was no proposed standardized set of outcome measures for clinical studies of 
CRPS.  CRPS studies have previously employed a diverse range of questionnaire outcome measures, 
making aggregation and comparison of data difficult.  In 2017, McCabe et. al. published a proposed core 
measurement set to help researchers standardize their approach to CRPS clinical research 
outcomes.18  This core measurement set, “Core Outcome Measurement set for complex regional PAin 
syndrome Clinical sTudies” (COMPACT), provides recommendations for studying CRPS based on eight 
domains: patient characteristics (demographics), pain, disease severity, participation of physical 
function, emotional and psychological function, catastrophizing, self-efficacy, and patient's global 
impression of change. 
The measurement set proposed in COMPACT is a compilation of pre-existing items frequently used for 
Patient-Reported Outcomes Measurement (PROM).  More specifically, COMPACT recommends the 

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PROMIS-29 Profile (version 2) survey.  PROMIS-29 v2 comes from the Patient-Reported Outcomes 
Measurement Information System (PROMIS), which is a National Institute of Health funded system. 
 
PROMIS-29 v2 includes a 0 through 10 pain scale, which will be used for our primary outcome.  Because 
PROMIS-29 v2 also encompasses three of the eight domains listed above (pain, participation and 
physical function, emotional and psychological function), we selected PROMIS-29 v2 scores as one of our 
secondary outcomes.   
 
 
Objective Data 
We will collect daily opioid consumption data by having patients record and report their daily opioid use 
before and after treatment.  Oral and transdermal opioids will be converted to standardized morphine 
equivalents and adjusted for bioavailability. 
 
Objectives and Hypotheses 
Primary Aim: To evaluate the efficacy of intermittent nitrous oxide exposure in reducing pain in CRPS. 
Primary Hypothesis:  Nitrous oxide exposure in CRPS patients will decrease pain scores compared to 
patients who do not receive nitrous oxide over the follow-up time period (1 week and 1 month after the 
last inhalation treatment). 
 
Secondary Aim 1:  To more broadly evaluate the efficacy of intermittent nitrous oxide exposure as a 
treatment modality for CRPS. 
Primary Hypothesis 1:  Nitrous oxide exposure in CRPS patients will improve (increase) PROMIS-29 v2 
survey scores when compared with survey scores of patients who do not receive nitrous oxide over the 
follow-up time period (1 week and 1 month after the last inhalation treatment). 
 
Secondary Aim 2:  To evaluate patients’ overall perception of disease improvement. 
Secondary Hypothesis 2:  Nitrous oxide exposure in patients with CRPS will improve (reduce) patients’ 
Global Impression of Change scores (PGIC scale) when compared with patients who do not receive 
nitrous oxide over the follow-up time period (1 week and 1 month after the last inhalation treatment). 
 
Exploratory Aim 1:  To evaluate the effect of nitrous oxide exposure on opioid consumption in patients 
with CRPS. 

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Exploratory Hypothesis 1:  Nitrous oxide exposure in patients with CRPS will reduce average daily opioid 
use (converted in mg IV morphine equivalents) when compared with patients who do not receive 
nitrous oxide over the follow-up time period (1 week and 1 month after the last inhalation treatment). 
 
Exploratory Aim 2:  To evaluate the effects of nitrous oxide on neuropathic pain symptoms in patients 
with CRPS. 
Exploratory Hypothesis 2:  Nitrous oxide exposure in patients with CRPS will improve (decrease) scores 
for the 6 neuropathic pain items in the short-form McGill Pain Questionnaire 2 when compared with 
patients who do not receive nitrous oxide over the follow-up time period (1 week and 1 month after the 
last inhalation treatment). 
 
Methods 
This study is a prospective randomized controlled pilot trial. 
 
Study Population 
Patients ages 18-70 with a diagnosis of CRPS (type I and type II) who are seen at Cleveland Clinic’s Pain 
Management clinic will be considered for invitation to participate. 
Inclusion criteria: 
1. Patients must be diagnosed with CRPS based on the revised International Association for the 
Study of Pain criteria.   
2. Duration of disease must be at least 6 months. 
3. Written informed consent. 
Exclusion criteria: 
1. Patients who had no subjective benefit from ketamine infusions, as determined by interview 
during the recruitment process.  
2. Patients taking more than 60mg of morphine equivalents or more daily for an alternative 
chronic pain condition. 
3. Patients with both coronary artery disease (as determined by cardiac catheterization) and a 
functional status of less than 4 metabolic equivalents.  The limited functional status must be 
secondary to cardiopulmonary symptoms (angina, dyspnea on exertion).  Patients with coronary 
artery disease and a limited functional status (<4 METS) secondary to chronic pain can be 
included. 
4. Patients with congestive heart failure of any etiology that are NYHA Class III or IV 
5. Patients with moderate or severe pulmonary hypertension as determined by echocardiogram or 
right heart catheterization. 
6. Patients with intraocular surgery within the past 14 days 

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7. Patients with worker’s compensation claims and active litigation. 
8. Patients who have been diagnosed with COPD. 
9. Patients who use home oxygen therapy for any condition. 
10. Diagnosis of Alcohol Use Disorder as defined by the Diagnostic and Statistical Manual of Mental 
Disorders (DSM-5). 
11. Illicit drug use within the past three months (not including marijuana). 
12. Pregnant patients or patients with upcoming planned pregnancy. 
 
 
Initial Recruitment 
A list of patients who are seen at CCF Pain Management clinic with a diagnosis of CRPS (type I and type 
II) will be screened by manual chart review for eligibility.  Patients who appear to meet the 
inclusion/exclusion criteria will be mailed the recruitment letter. 
Patients who call back to express interest in participating will be provided with the informed consent 
document (by mail or E-mail, whichever the patient prefers).  Patients may either take time to consider 
the informed consent form and call back at another time, or they can schedule an appointment with CCF 
Pain Management clinic at main campus. 
When the patient comes for this scheduled clinic appointment, they will meet with the research 
coordinators afterwards and complete the informed consent process, provided that they still meet all 
inclusion/exclusion criteria.  Patients will then be scheduled for their three breathing sessions, and they 
will also be given their first 7-day opioid use log. 
 
Treatment Phase 
Patients will present for the first scheduled treatment and they will fill out the PROMIS-29 v2 survey and 
the SF-MPQ-2 (6 neuropathic pain items).  They will also turn in their opioid use log.  They will receive a 
phone call 1 week before the first session to remind them to start filling out the opioid use log. 
Vital signs will be obtained.  Patients with significantly abnormal vital signs or vital signs that are 
significantly deviated from baseline will be referred to appropriate medical care. 
Patients will then be randomized via a web-based randomization system Redcap with stratification by 
spinal cord stimulator status to either the nitrous oxide study group or the 50% oxygen control group.  
The nitrous oxide group will receive 50% nitrous oxide mixed with 50% oxygen, and the control group 
will receive 50% oxygen (oxygen plus air mixture). 
Active Control:  Because patients may be able to tell if they are receiving nitrous oxide, patient blinding 
may be compromised.  Therefore, we plan to utilize an active control.  The study group that receives 
nitrous oxide and the control group that receives 50% oxygen will BOTH receive 2 mg of intravenous 
midazolam, a short-acting mild sedative that will simulate the effects of nitrous oxide.  This baseline 

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sedation given to all patients will significantly reduce the likelihood that patients will be able to tell 
which arm of the study they are in. 
Intravenous access will be obtained by research staff or a registered nurse in a non-affected extremity.  
Patients will receive the midazolam injection immediately upon starting each breathing treatment 
session, and the 2mg dose will infuse over a duration of five minutes.  IVs will be removed at the 
conclusion of each breathing treatment. 
Both groups will undergo inhalation therapy for a duration of 2 hours via an FDA-approved mask 
breathing circuit.  Vital signs (blood pressure, respiratory rate, heart rate) will be monitored every 30 
minutes.  Pulse oximetry monitoring will be continuous.  Patients will be monitored for side effects 
including nausea, vomiting, desaturation, sedation, respiratory depression, and dizziness.  Patients and 
other involved providers will be blinded to the treatment type.  Research investigators administering the 
treatments will not be blinded. 
At the conclusion of inhalation therapy, the gas will be turned off and patients will breathe room air.  All 
patients will be monitored for an additional 30 minutes.  This recovery time is more than sufficient to 
ensure nitrous oxide is completely eliminated in those patients who receive it.  Patients will be 
monitored and asked about side effects. 
Patients will receive a total of three treatments (6 total exposure hours) over one week with 2 or 3 days 
between each session.  Possible treatment schedules: Monday-Wednesday-Friday, Wednesday-Friday-
Monday, or Friday-Monday-Wednesday.  After the conclusion of the third treatment, patients will be 
followed with phone calls as detailed in the Measurement section below. 
 
Measurements 
Demographic data will be collected and recorded: age, sex, duration of disease, extremity/extremities 
affected. 
Patients will have two follow-up phone call appointments at approximately   1 week and at approximately 
1 month after the final inhalation treatment session.  Patients will be instructed (and reminded) to record 
their daily opioid use during the week preceding each phone call appointment.  During each phone call 
appointment, patients will: 
1. Complete the PROMIS-29 v2 survey questionnaire (including the 0-10 pain scale) 
2. Complete the Patient’s global impression of change survey measured with PGIC, which is a seven 
point scale ranging from 1 – “very much improved” to 7 – “very much worse.” 
3. Complete the 6 neuropathic items of short form McGill pain questionnaire 2 (SF-MPQ-2); each 
item ranging from 0 (no pain) to 10 (worse pain). 
4. Report their daily opioid use over the past seven days; average daily opioid use in mg IV morphine 
equivalents will be calculated for statistical analysis. 

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The REDcap (Research Electronic Data Capture) database, which is a Cleveland Clinic internal database 
system, will be used to collect and store all the study information, including screening log, randomization, 
demographics, the outcomes, and the follow-up call logs. 
 
Blinding 
The initial set of pre-treatment data for each patient (PROMIS-29 v2, SF-MPQ-2, opioid use log) will be 
collected prior to randomization on Treatment Day 1.  Only research fellows/staff who are directly 
administering inhalation therapy will know which treatment the patient is receiving.  For the duration of 
the study, patients will be blinded and will not know which treatment they are receiving.  Alternate 
research fellows/staff who call patients for follow up data collection (PROMIS-29 v2, SF-MPQ-2, PGIC 
score, opioid use log) over the phone will be blinded to which treatment patients received.   
 
Randomization 
Patients who have met inclusion/exclusion criteria and are enrolled in the study will be randomized on 
Treatment Day 1 using the Redcap randomization module immediately before receiving the first 
inhalation therapy.  Allocation will be stratified by those who have a spinal cord stimulator implanted 
and those who do not. 
See schema below. 

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PGIC – Patient’s Global Impression of Change 
SF-MPQ-2 – short form McGill pain questionnaire 2 (the 6 neuropathic pain items) 
Opioid use log – patients will report their recorded daily opioid use over the previous seven days, which will be averaged 
 
Assessment of Resources 
Patients’ contact information will be stored securely in a log so that investigators will be able to contact 
participants with instructions and reminders to ensure consistent follow up and participation.  A screening 
log will be maintained in REDcap. All screened candidates will be documented for inclusion and also 
reasons for exclusions from the study. Research fellows and staff in the Department of Outcomes 

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Research (Anesthesiology Institute) will be primarily responsible for recruiting participants, obtaining 
informed consent, administering surveys, administering the inhalation treatments, providing patients 
with instructions, and ensuring consistent follow up. 
 
Additional Study Procedures 
1. Drug Handling Instructions 
a. Nitrous oxide for the study will be stored at room temperature in appropriately labeled 
E-cylinder tanks.  Empty tanks can be refilled and reused.  Remaining nitrous oxide at 
the conclusion of the study can be returned. 
b. Midazolam is a controlled medication and only non-blinded research staff administering 
this medication will have access to it. 
 
Data Analysis 
Standard descriptive statistics will be used to compare the randomized groups on baseline variables. Any 
imbalanced covariables will be adjusted for, in both primary and secondary analyses. Balance between 
groups will be assessed using absolute standardized difference (ASD), defined as the absolute difference 
in means, mean ranks, or proportions divided by the pooled standard deviation. Groups were defined as 
imbalanced on baseline variables if ASD > 1.96 × √
1
𝑛1 +
1
𝑛2, where n1 and n2 correspond to the number of 
patients in each treatment group. [Austin PC. Balance diagnostics for comparing the distribution of 
baseline covariates between treatment groups in propensity-score matched samples. Stat. Med. 
2009;28(25):3083-3107. doi:10.1002/sim.3697]. Our primary analysis will be intent-to-treat.   
Primary analysis 
First, the randomized groups will be compared on the pain scores profiles (NRS scores ranging from 0 to 
10) over follow-ups (1 week and  1 month) using multivariable linear mixed effects model (i.e. random 
slope and intercept model if a linear time trend of NRS appeared appropriate) with adjustment for 
baseline pain level as a covariate. The assumptions of normality for the outcome NRS pain score and no 
interaction between the treatment group and baseline pain score on the outcome will be assessed. If 
either assumption is not met, then the baseline covariate would need to be categorized, or another 
method (i.e. analyze the change from baseline or percent change from baseline) would be used, as 
appropriate. The model based Wald test would be used for formal assessment at 0.05 significance level. 
If the significant difference between two study groups in pain scores profiles is observed, then the two 
separate testing for each follow-up time point (1 week  and 1 month) will be performed using two separate 
multivariable linear regression models with same adjustment for baseline pain level and possibly for 
interaction between the treatment group and baseline score.  This testing will be done at the overall 0.05 
significance level and will be adjusted for multiple testing via Bonferroni correction (0.05/2 follow-up 
tests=0.025). The interaction between the treatment assignment and spinal cord stimulation implant 

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status on the primary outcome will be assessed (P-value < 0.10 will be considered as significant for 
interaction). 
 
Secondary analysis 
To compare the randomized groups on the PROMIS-29 v2 survey scores over 1 week and 1 month post 
treatment, the multivariable linear mixed effects model will be employed with adjustment for the baseline 
score. Transformations of the data will be made as needed to meet model assumptions. The model based 
Wald test would be used for formal assessment at 0.025 significance level (Bonferroni correction for two 
secondary outcomes: 0.05/2=0.025). If the significant difference between two study groups in PROMIS 
score profiles is observed, then the two separate testing for each follow-up time points (1 week and 1 
month) will be performed in the same manner as the primary analysis. The Bonferroni correction for 
multiple testing (0.025/2=0.0125) will be employed. 
In the same manner, first, the PGIC score profiles will be compared overall over follow-up time using 
multivariable linear mixed effects model; if significance is observed, PGIC scores will be compared 
separately at 1 week and 1 month follow-up with significance criteria of 0.0125. 
The interaction between the treatment assignment and spinal cord stimulation implant status on two 
secondary outcomes will be assessed (P-value < 0.10 will be considered as significant for interaction). 
 
Exploratory analysis 
For exploratory analysis we report by study groups the appropriate summaries of daily opioid use (median 
[interquartile range]) and 6 neuropathic pain items in the SF-MPQ-2 (mean and standard deviations). 
SAS 9.4 software (SAS Institute, Cary, NC) will be used for all analyses and graphics. 
 
Sample size consideration 
This study is a pilot trial, which aim to collect initial information on nitrous oxide effect on pain reduction 
and functional improvement in patients suffering from CRPS. Given an average annual number of the CRPS 
(type I and type II) patients at Cleveland Clinic’s Pain Management and limited amount of resources we 
plan for about 40 study patients total to limit this study within 2 years. 
The sample size is based on being able to detect the clinically important differences of 2 units or more in 
the mean numeric rating scale (NRS: between 0-10) of the nitrous oxide and placebo groups using analysis 
of covariance on the outcomes at 1 week follow-up. Using an SD estimate of 2 units for NRS (based on 
experience and literature) with standard type I and type II error rates (alpha = 0.025 due to Bonferroni 
correction for multiple testing, ß = 0.20),  a 21 patients per group are needed (total sample size of 42 
patients) 

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We also plan for one interim analyses at 50% of the planned enrollment, therefore, interim adjusted 
sample size is N=22 patients per group, or N=44 total.  We will use the gamma spending function with 
parameters -4 and -1 for alpha (efficacy) and beta (futility), respectively.  If the alternative hypothesis is 
true there will be a cumulative probability of 37% and 100% of crossing either an efficacy or futility 
boundary at the 1st and final analyses, respectively. Table 1 and Figure 1 below contains boundary 
Information. Planned first interim analyses will be performed upon accrual of 22 patients. Therefore, 
planned number of patients for the analysis is N=22 patients per group, or N=44 total. 
Also, assuming the drop-out rate of about 20% (due to withdraw and other unexpected events) we plan 
to enroll 27 patients in each group, total of 54 patients. If drop-out rate is less or more than expected the 
number of enrolled patients will change to reach N=44 patients needed for the analysis. In addition, we 
plan for 2 pilot patients (1 per group) in the beginning of the study. Therefore, we anticipate enrolling 28 
patients in each group, total of N=56 patients. 
 
Table 1.  Boundary Information for interim analysis (2 analyses = 2 stages:  50% interim and final): 
Boundary Information (Standardized Z Scale) 
Stage 
Information 
level 
Alternative 
Boundary Values 
Reference 
Lower 
Upper 
Proportion 
Lower 
Upper 
Alpha 
Beta 
Beta 
Alpha 
1 
0.5 
-2.349 
2.349 
-2.750 
-0.591 
0.591 
2.750 
2 
1.0 
-3.322 
3.322 
-1.946 
-1.946 
1.946 
1.946 
 

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Figure 1 Boundary Information 
 
Study Limitations 
Potential limitations: 
1. Patients may be able to discern whether they are receiving nitrous oxide or 50% oxygen plus 
midazolam.  This may impact survey results.   
2. As CRPS severity and treatment response is quite variable, our study results may not apply to all 
patients with CRPS. 
3. Despite using validated surveys/questionnaires, much of the data collected will be subjective. 
 
Ethical Considerations 
1. Informed Consent 
a. Patients who satisfy inclusion and exclusion criteria and agree to participate in the study 
will undergo the informed consent process immediately after their regular, non-
research-study pain management clinic appointment. 
b. The research study will be explained in detail to each patient, and, if patients are still 
willing to participate, they will sign the informed consent associated with this study. 

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c. Patients will be informed that their decision to participate in this study is entirely 
voluntary and will not influence their regular medical care in any way.  Choosing not to 
participate in the study will also not affect their care in any way. 
d. Investigators listed in this protocol will be involved in explaining the research study and, 
briefly, its scientific basis.  Investigators will also explain the schedule and follow up 
timeline, the potential benefits, the possibility of side effects, and the fact that patients 
will be randomized to either the study group or the control group when they present for 
treatment.  Patients will be informed that they will be blinded to the treatment they 
receive.  Further, patients will be informed that participants randomized to the control 
group are not expected have any benefit from the treatment sessions. 
e. The patient will be required to verbalize their understanding of the research study and 
its intended purpose. 
f. 
Patients will be informed of their right to opt out of study participation at any time. 
2. Risks and Side Effects 
a. The potential for side effects using a gas mixture of 50% nitrous oxide with 50% oxygen 
is extremely low.  This gas mixture has been shown not to predispose to desaturation, 
nausea, or vomiting.19 
b. A known side effect of nitrous oxide is peripheral neuropathy.  This effect is attributed 
to nitrous oxide causing irreversible inhibition of methionine synthase, an important 
enzyme in DNA synthesis that is vitamin B12 (cobalamin) dependent.  Prolonged 
exposure to anesthetic concentration of nitrous oxide may lead to bone marrow 
depression and/or peripheral neuropathy.20  Clinically, this effect has primarily been 
reported as case reports of peripheral neuropathy in the setting of individual patients 
who habitually and chronically abused nitrous oxide for its euphoric effect.  These 
patients had heavy use of nitrous oxide for extended periods of time.  Furthermore, the 
peripheral neuropathy that develops is reversible with discontinuation of nitrous 
oxide.21,22,23  Therefore, with only a brief duration of exposure as outlined in this 
protocol, it is exceedingly unlikely that patients participating in the study would develop 
this complication. 
c. Adverse events 
i. Serious adverse events from the administration of nitrous oxide, oxygen, or 
both is exceedingly unlikely.  Patients who develop concerning symptoms such 
as chest pain, respiratory distress, or severe headache will have their inhalation 
therapy stopped and they will be referred to the Emergency Department for 
immediate evaluation. 
ii. Serious adverse events from the administration of 2mg midazolam is 
exceedingly unlikely.  Patients will be continuously monitored via intermittent 
vital signs and continuous pulse oximetry. 
iii. Patients will not be compensated for care related to adverse events. 
3.  Benefits to Subjects 
a. Patients with CRPS who are randomized to receive nitrous oxide may experience a 
reduction in pain, a reduction in pre-existing disability, and/or a reduction in the amount 
of opioids they use on a daily basis. 

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b. Demonstrating benefit from nitrous oxide exposure will further the scientific and 
medical communities’ understanding of neuropathic pain management.  Demonstrated 
benefit may also lead to an additional treatment option for CRPS. 
4. Cost to Subjects 
a. Cost to participants includes the cost of travelling to appointments and treatment 
sessions. 
5. Compensation to Subjects 
a. None. 
6. Provisions for vulnerable subjects 
a. There will be no vulnerable subjects in this study. 
7. Subject Privacy and Data Confidentiality 
a. Privacy of Participants 
i. Subject participation in this study will not be disclosed to anyone other than 
their regular pain physician 
ii. Participants will be able to discuss their participation with a research 
investigator in a private setting (office or exam room) 
iii. Participants may be visible to other patients, research staff, and any additional 
clinical staff while they are undergoing inhalation treatment in the designated 
treatment area. 
b. Confidentiality of Data 
i. Upon entering into the study and completing the informed consent process, 
patients will be assigned an identifier number that does not contain any 
protected health information.  The identifiers will be linked with patient’s 
names in a separate spreadsheet that will be accessed only for the purpose of 
patient identification. 
ii. Only the research investigators who are enrolling patients (including informed 
consent), administering treatments, scheduling patients for 
appointments/treatment, collecting survey and other subjective data, or 
collecting blood samples will have access to this spreadsheet that links patient 
names with identifiers. 
iii. Both the patient name/identifier spreadsheet and the main data collection 
spreadsheet will be stored securely on Cleveland Clinic servers. 
iv. Data of any kind will not be allowed off campus.  Non-electronic data (i.e. any 
printed data) must be appropriately destroyed when no longer needed. 
v. All investigators will have access to the de-identified main data collection 
spreadsheet. 
c. Plans for Record Retention and disposal 
i. The completed de-identified data will be retained indefinitely on a Cleveland 
Clinic secure server in the event that re-analysis or additional analysis of the 
data is ever desired. 
ii. The patient name/identifier spreadsheet will be deleted upon completion of all 
study procedures and statistical analyses. 

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17 | P a g e  
 
 
Plans for Dissemination of Findings 
The data and relevant statistical analysis will be prepared as a manuscript for publication in a peer-
reviewed journal.  Prior to completion of the finished manuscript, this research study may be presented 
as an abstract at a relevant regional or national medical conference. 
 
References 
1.  
Bussa M, Guttilla D, Lucia M, Mascaro A, Rinaldi S. Complex regional pain syndrome type I : a 
comprehensive review. Acta Anaesthesiol Scand. 2015:685-697. doi:10.1111/aas.12489 
2.  
Goebel A. Complex regional pain syndrome in adults. Rheumatology. 2011;50:1739-1750. 
doi:10.1093/rheumatology/ker202 
3.  
Sandroni P, Benrud-larson LM, Mcclelland RL, Low PA. Complex regional pain syndrome type I : 
incidence and prevalence in Olmsted county, a population-based study. Pain. 2003;103(1-2):199-
207. doi:10.1016/S0 
4.  
Gierthmühlen J, Binder A, Baron R. Mechanism-based treatment in complex regional pain 
syndromes. Nat Publ Gr. 2014;10(9):518-528. doi:10.1038/nrneurol.2014.140 
5.  
Zhao J, Wang Y, Wang D. The Effect of Ketamine Infusion in the Treatment of Complex Regional 
Pain Syndrome : a Systemic Review and Meta-analysis. Curr Pain Headache Rep. 2018;22(2):12. 
6.  
Bennett GJ. Update on the Neurophysiology of Pain Transmission and Modulation : Focus on the. 
J Pain Symptom Manage. 2000;19(1):2-6. 
7.  
Petrenko AB, Yamakura T, Sakimura K, Baba H. Defining the role of NMDA receptors in 
anesthesia : Are we there yet ? Eur J Pharmacol. 2014;723:29-37. 
doi:10.1016/j.ejphar.2013.11.039 
8.  
Rabben T, Skjelbred PER, Øye I. Prolonged Analgesic Effect of Ketamine, an N -Methyl- D - 
Aspartate Receptor Inhibitor, in Patients with Chronic Pain. J Pharmacol Exp Ther. 
1999;289(2):1060-1066. 
9.  
Schwartzman RJ, Alexander GM, Grothusen JR, Paylor T, Reichenberger E, Perreault M. 
Outpatient intravenous ketamine for the treatment of complex regional pain syndrome : A 
double-blind placebo controlled study. Pain. 2009;147(1-3):107-115. 
doi:10.1016/j.pain.2009.08.015 
10.  
Azari P, Lindsay DR, Briones D, Clarke C, Buchheit T, Pyati S. Efficacy and Safety of Ketamine in 
Patients with Complex Regional Pain Syndrome A Systematic Review. CNS Drugs. 2012;26(3):215-
228. 
11.  
Richebe P. Nitrous Oxide Revisited: Evidence for Potent Antihyperalgesic Properties. 
Anesthesiology. 2005;(4):845-854. 
12.  
Chan MT V, Wan ACM, Gin T, Leslie K, Myles PS. Chronic postsurgical pain after nitrous oxide 

Version 7.0 December 6, 2019 
 
 
18 | P a g e  
 
anesthesia. Pain. 2011;152(11):2514-2520. doi:10.1016/j.pain.2011.07.015 
13.  
Roth J. Chronic Pain and the Opioid Epidemic: Are We Ignoring the Potential Benefits of Nitrous 
Oxide? Anesth Analg. 2018;126(4):1423-1424. doi:10.1213/ANE.0000000000002710 
14.  
Elgueta F, Fierro C, Bugedo D, Faba G, In R. Nitrous oxide (N2O) reduces postoperative opioid-
induced hyperalgesia after remifentanil – propofol anaesthesia in humans. Br J Anaesth. 
2011;107(September):959-965. doi:10.1093/bja/aer323 
15.  
Boujema M Ben, Laboureyras E, Pype J, et al. Nitrous oxide persistently alleviates pain 
hypersensitivity in neuropathic rats : A dose-dependent effect. Pain Res Manag. 2015;20(6):309-
315. 
16.  
Bessiere, B, Laboureyras, E, Chateauraynaud, J, Laulin, J.P., and Simonnet G. A Single Nitrous 
Oxide (N2O) Exposure Leads to Persistent Alleviation of Neuropathic Pain in Rats. J Pain. 
2010;11(1):13-23. doi:10.1016/j.jpain.2009.05.003 
17.  
Turan A, Sarwar S, Atim A, et al. Nitrous Oxide for the Treatment of Chronic Low Back Pain. 
Anesth Analg. 2015;121(5):1350-1359. doi:10.1213/ANE.0000000000000951 
18.  
Grieve S, Perez RSGM, Birklein F, et al. Recommendations for a first Core Outcome Measurement 
set for complex regional PAin syndrome Clinical sTudies (COMPACT). Pain. 2017;158(6). 
19.  
Peyton PJ, Ph D, Wu CY. Nitrous Oxide – related Postoperative Nausea and Vomiting Depends on 
Duration of Exposure. Anesthesiology. 2017;(5):1137-1145. 
20.  
Hadzic, Admir, Glab, Krzysztof, Sanborn, Kevin, Thys D. Severe Neurologic Deficit after Nitrous 
Oxide Anesthesia. Anesthesiology. 1995;83:863-866. 
21.  
Richardson PG. Peripheral neuropathy following nitrous oxide abuse. Emerg Med Australas. 
2010;22:88-90. doi:10.1111/j.1742-6723.2009.01262.x 
22.  
Cheng HM, Park JH, Hernstadt D. Subacute combined degeneration of the spinal cord following 
recreational nitrous oxide use. BMJ Case Rep. 2013:2012-2014. doi:10.1136/bcr-2012-008509 
23.  
Hsu, C, Chen, Y, Lung V, His, S, Lo, H, Shyu H. Myelopathy and polyneuropathy caused by nitrous 
oxide toxicity: a case report. Am J Emerg Med. 2012;30(6):3-6. doi:10.1016/j.ajem.2011.05.001