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Background

Relative analgesia (RA), defined as the use of inhalation sedation with nitrous oxide and oxygen, is one of the most common pharmacological behavior management techniques used to provide sedation and analgesia for dental patients. This study aimed to assess RA licensed Brazilian dentists’ practices and opinions about nitrous oxide/oxygen sedation in the dental setting.

Methods

A cross sectional national survey was conducted with 281 dentists who were certified to perform RA, using an electronically mailed self-administered questionnaire containing closed questions about their practices and opinions regarding RA. Practice and opinion were individually analyzed by descriptive statistics. Non-parametric tests assessed the relationships between RA practice and independent variables. To test the interplay between practices and opinions, a k-means clusters analysis was used to divide the group for statistical comparisons.

Results

The response rate was 45.2%. Women made up 64.6% of the respondents, the mean age was 39.1 years (SD = 9.8), and the mean time since graduation in dentistry was 16 years (SD = 9.7). Seventy-seven percent of respondents reported the use of RA in clinical practice, most of them ‘sometimes’ (53.5%), and focusing more on adult patients. Patients with certain physical or mental deficiencies were indications associated with RA practice. ‘Equipment acquisition’ (p < 0.001) and ‘living in Southeast and South regions’ (p < 0.02) were also associated with RA practice. The scores for dentists’ opinions ranged from 15 to 41 points (mean 29.2, SD = 5.6), based on nine items scored from 1 to 5. Two clusters representing more favorable (n = 65) and less favorable (n = 55) opinions were established. Dentists who were women (p = 0.04), practiced RA in dental settings (p < 0.01) or practiced it frequently (p < 0.001), had more favorable opinions about RA.

Conclusion

Most of the RA licensed Brazilian dentists interviewed currently use RA. Current practice of RA and frequency of use determined the degree of favorable opinion about this inhalation sedation among this group of respondents.

Trials have been organized by a Medical Research Council committee to assess the effectiveness and safety for analgesia in labour of oxygen and nitrous oxide mixtures in different proportions. In a preliminary trial concentrations of 50% and 60% v/v nitrous oxide were compared, but, as the replies of 409 mothers revealed little difference between the two, the results of administering either 50% or 70% nitrous oxide to 778 mothers were then compared. The data relating to normal labour, obtained on 501 of the mothers in this main trial, showed that the relief of pain given was much the same. There was a suggestion, however, that the higher concentration of nitrous oxide might be useful in abnormal labour. The proportion of mothers with normal deliveries who lost consciousness, though very small, was significantly higher with 70% nitrous oxide than with the lower concentration. Ninety-two per cent. of mothers found the gas and oxygen machine helpful, and midwives reported complete or good co-operation by 77% of those using it. It is concluded that the 50% oxygen and 50% nitrous oxide mixture can safely be used by unsupervised midwives.

In rats, the jaw-opening reflex is elicited by activation of a nociceptive receptor by the electric stimulation of the tooth pulp. This study was undertaken to assess the effects of 30% nitrous oxide and 30% nitrous oxide with idazoxan, an alpha 2-adrenergic antagonist, on this reflex. Each rat received electric stimulation for the jaw-opening reflex at 3, 5, 7, 10, 15, and 20 min after both the start of inhalation and the withdrawal of 100% oxygen or 30% nitrous oxide in oxygen. Idazoxan, 400 micrograms/ kg, was administered intravenously at the start of the inhalation period. Amplitudes significantly decreased during inhalation of nitrous oxide, but they returned gradually to control levels after cessation of nitrous oxide inhalation. In the cases of 100% oxygen, 100% oxygen with idazoxan, and 30% nitrous oxide in oxygen with idazoxan, amplitudes did not change from controls during and after 30% nitrous oxide inhalation. The latency remained unchanged irrespective of the treatment. Since in rats the degree of inhibition by 30% nitrous oxide in oxygen is partially diminished by administration of idazoxan, we conclude that nitrous oxide affects an alpha 2-adrenergic receptor in the central nervous system.

Aims: To evaluate the efficacy and safety of nitrous oxide–oxygen for children with juvenile idiopathic arthritis (JIA) undergoing intra-articular corticosteroid injection.

Methods: A total of 55 consecutive patients with JIA undergoing intra-articular corticosteroid injection, using self administered nitrous oxide–oxygen for analgesia were studied. Patient, nurse, and parent pain scores were compared using a 0–10 cm visual analogue scale (VAS) immediately after the procedure.

Results: A total of 70 joints were injected in 55 patients (median age 13.54 years). The median pain score for patient, nurse, and parent was 1 (0–10 cm VAS). The mean rank patient score was 2.12, which was greater than the nurse score (1.97), which was greater than the parent score (1.91). These differences were significant. There were no serious adverse events in any patient.

Conclusions: Nitrous oxide–oxygen provides safe and effective analgesia for intra-articular injection in children. In some cases, nurses and parents underestimated pain related to the procedure compared to the child.

As a result of the durability problems associated with the first Abrams-Lucas mitral valve, a redesigned model has recently been introduced into limited clinical trials. The new valve was subjected to in-vitro pulsatile flow studies, and measurements were made of mean diastolic pressure gradient and volume of reflux on closure. Similar measurements were made on other mitral valve prostheses of comparable size. High-speed cinematography was used to analyse the motion of the occluder during the simulated cardiac cycle, and the flow patterns produced by the valve in the model ventricular cavity were observed and photographed. The pressure gradient of the Abrams-Lucas valve was significantly lower than that of the 29 mm Björk-Shiley valve and all other prostheses tested, but its reflux level was higher at 12 ml per stroke. The valve opened and closed smoothly and the flow visualisation study revealed that the valve produced a large vortex or swirl in the model ventricular cavity.

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This study was undertaken to assess the sensitivity of nitrous oxide (N2O) analgesia to antagonism by intrathecally (IT) and intracerebroventricularly (ICV) administered antagonists selective for kappa- and mu-opioid receptors. Male ICR mice were pretreated IT or ICV with the kappa antagonist nor-binaltorphimine (nor-BNI), 1 or 50 nmol, respectively, or distilled water (control), then exposed to N2O (50% or 75% in oxygen). Compared with IT control mice, IT nor-BNI-pretreated mice responded with significantly less analgesia. Compared with ICV control mice, ICV nor-BNI-pretreated mice also showed markedly reduced analgesic response. Other mice were pretreated IT or ICV with either the selective and irreversible mu antagonist beta-funaltrexamine (beta-FNA, 5.0 micrograms) or distilled water (control). When exposed to N2O 24 h later, beta-FNA-pretreated and control mice exhibited comparable analgesic responses. These preliminary results suggest that N2O analagesia in mice may involve spinal and supraspinal kappa-opioid receptors but not mu-opioid receptors.

Background and Objectives

The aim of this study was to assess mechanical valve function using 64-slice multidetector computed tomography (MDCT).

Subjects and Methods

In 20 patients (mean age, 50±12 years; male-to-female ratio, 10:10), 30 St. Jude bileaflet mechanical valves (15 aortic and 15 mitral valves) were evaluated using MDCT. We selected images vertical and parallel to the mechanical valve. The valve orifice area (OA) and valve length were determined by manual tracing and the opening and closing angles were measured using a protractor. The OA and length of the mechanical valves were compared with the manufacturer's values.

Results

The geometric orifice areas (GOAs) based on the manufacturer's values and the OAs determined by MDCT were 3.4±0.2 cm2 and 3.4±0.3 cm2 for the mitral valves and 2.1±0.3 cm2 and 2.1±0.4 cm2 for the aortic valves, respectively. The correlation coefficients between the OA measures were 0.433 for the mitral valves and 0.874 for the aortic valves (both p<0.001). The lengths based on the manufacturer's values and determined by MDCT were 29.3±1.99 mm and 29.6±1.65 mm for the mitral valves and 21.5±2.1 mm and 20.7±2.3 mm for the aortic valves, respectively. The correlation coefficients between the measures were 0.651 for the mitral valve and 0.846 for the aortic valve (both p<0.001). The opening and closing angles determined by MDCT were 10.9±0.6° and 131.1±3.2° for the mitral valves and 11.1±0.9° and 120.6±1.7° for the aortic valves, respectively.

Conclusion

MDCT is an accurate modality with which to assess the function and morphology of bileaflet mechanical valves.

Cardiac valves function in a mechanically complex environment, opening and closing close to a billion times during the average human lifetime, experiencing transvalvular pressures and pulsatile and oscillatory shear stresses, as well as bending and axial stress. Although valves were originally thought to be passive pieces of tissue, recent evidence points to an intimate interplay between the hemodynamic environment and biological response of the valve. Several decades of study have been devoted to understanding these varied mechanical stimuli and how they might induce valve pathology. Here, we review efforts taken in understanding the valvular response to its mechanical milieu and key insights gained from in vitro and ex vivo whole-tissue studies in the mechanobiology of aortic valve remodeling, inflammation, and calcification.

Background

For many long standing practices, the rationale for them is often lost as time passes. This is the situation with respect to the storage and handling of equimolar 50% nitrous oxide and 50% oxygen volume/volume (v/v) mixtures.

Methods

A review was undertaken of existing literature to examine the developmental history of nitrous oxide and oxygen mixtures for anesthesia and analgesia and to ascertain if sufficient bibliographic data was available to support the position that the contents of a cylinder of a 50%/50% volume/volume (v/v) mixture of nitrous oxide and oxygen is in a homogenous single gas phase in a filled cylinder under normal conditions of handling and storage and if justification could be found for the standard instructions given for handling before use.

Results

After ranking and removing duplicates, a total of fifteen articles were identified by the various search strategies and formed the basis of this literature review. Several studies were identified that confirmed that 50%/50% v/v mixture of nitrous oxide and oxygen is in a homogenous single gas phase in a filled cylinder under normal conditions of handling and storage. The effect of temperature on the change of phase of the nitrous oxide in this mixture was further examined by several authors. These studies demonstrated that although it is possible to cause condensation and phase separation by cooling the cylinder, by allowing the cylinder to rewarm to room temperature for at least 48 hours, preferably in a horizontal orientation, and inverting it three times before use, the cylinder consistently delivered the proper proportions of the component gases as a homogenous mixture.

Conclusions

The contents of a cylinder of a 50%/50% volume/volume (v/v) mixture of nitrous oxide and oxygen is in a homogenous single gas phase in a filled cylinder under normal conditions of handling and storage. The standard instructions given for handling before are justified based on previously conducted studies.

An echocardiographic study was carried out on 23 young diabetics, 19 of whom had retinopathy. Their diastolic function was analysed by comparing the timing and pattern of mitral valve opening with the pattern of left ventricular wall movement. Only six patients had all their values within the normal range. Fourteen patients had abnormalities similar to those seen in patients with cardiomyopathy; the close time relation between mitral valve movement and wall movement was lost and mitral valve opening delayed in eight patients. Three other patients had considerable outward wall movement before mitral valve opening, which is characteristic of ischaemic heart disease. Although these studies provide no definite evidence of a cause, the abnormalities found may reflect a subclinical diabetic cardiomyopathy due to small-vessel disease.

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Background

Although there are various methods for painless delivery such as using entonox gas, most of the people are unfamiliar or concerned about it yet.

Objectives

The purpose of this study was to assess maternal expectations and experience of labor analgesia with nitrous oxide.

Patients and Methods

In a clinical trial study, 98 pregnant women in active phase of delivery were studied randomly in two groups (intervention group = 49, control group = 49) after obtaining written consent. Efficacy, experience satisfaction, and also expectation of pregnant women about entonox gas in two groups were compared, likewise in intervention group before and after using entonox gas.

Results

Most of the pregnant women receiving entonox gas had less labor pain (91.8%), and were satisfied with it (98%). The severity of pain in the most of entonox user was moderate level (46.94%), while for the control group it was severe (55.10%) which was significant, 40.82% of the mother in entonox group had a severe pain and 10.20% had a very severe pain, whereas in the control group (55.10%) of the mother had a severe pain and 26.53% of the had very severe pain (P = 0.004). efficacy of labor pain was in moderate level in most cases. 49% of pregnant women receiving gas described their experience as a good and excellent. 80.9% indicated that they will request the mentioned painless method in the future. The amount of suffering from gas side effects was mild in most patients of intervention group (63%). Expectations of the majority of pregnant women in intervention group (before receiving gas) and control group for painless delivery were weak (65.3%, 40.9%). The percentage of positive expectations had increased after receiving entonox gas (P = 0.01). There was a difference between the expectations of intervention group receiving entonox gas and control group (P = 0.001). Positive expectations were more in intervention group than the control group. Most differences of expectations in intervention group before and after receiving the gas were about higher efficacy (P = 0.001), more satisfaction (P = 0.001), fewer complications (P = 0.001), information about gas as painless delivery method (P = 0.02), and also previous experience of intolerable labor pain (P = 0.04).

Conclusions

This study has shown that using entonox gas caused less labor pain, favorable expectations and experiences and also more maternal satisfaction.

The interaction with nitrous oxide analgesia of drugs that act at the benzodiazepine receptor was evaluated in the rat tail flick model. Nitrous oxide produced dose-related analgesia, which was potentiated by diazepam, a benzodiazepine agonist, antagonized by noreleagnine, a benzodiazepine inverse agonist. Pretreatment with the benzodiazepine antagonist Ro 15-1788 blocked the effects of both diazepam and noreleagnine on nitrous oxide analgesia. Subanesthetic doses of sodium pentobarbital and chloral hydrate produced nonsignificant trends to reduce the analgesic action of nitrous oxide. These data provide evidence for the presence of specific benzodiazepine receptors capable of modulating the analgesic effect of nitrous oxide.

Objectives:

The mitral valve is a complex structure that is altered by disease states. The classical image of the mitral valve is a bicuspid valve with two leaflets and two papillary muscles. The reason for the present study is to study the morphology and morphometry of the mitral valve.

Materials and Methods:

This study was carried out on 116 human cadaveric hearts. Hearts were opened along the left border through the atrioventricular valve. The diameter and circumference of the annulus was measured and the number of valve leaflets was observed.

Results:

The mean annular diameter was 2.22 cm. The mean circumference of mitral valve annulus was 9.12 cm. The standard description of the mitral valve is bicuspid. In the present study, we found the number of cusps to be variable, from monocuspid to hexacuspid and classified them accordingly.

Conclusions:

The mitral valve is not always a bicuspid valve. The number of cusps varies greatly. An increase in the number of the cusp and their improper approximation most likely causes various valvular disorders.

Background

Valve dysfunction is a common cardiovascular pathology. Despite significant clinical research, there is little formal study of how valve dysfunction affects overall circulatory dynamics. Validated models would offer the ability to better understand these dynamics and thus optimize diagnosis, as well as surgical and other interventions.

Methods

A cardiovascular and circulatory system (CVS) model has already been validated in silico, and in several animal model studies. It accounts for valve dynamics using Heaviside functions to simulate a physiologically accurate "open on pressure, close on flow" law. However, it does not consider real-time valve opening dynamics and therefore does not fully capture valve dysfunction, particularly where the dysfunction involves partial closure. This research describes an updated version of this previous closed-loop CVS model that includes the progressive opening of the mitral valve, and is defined over the full cardiac cycle.

Results

Simulations of the cardiovascular system with healthy mitral valve are performed, and, the global hemodynamic behaviour is studied compared with previously validated results. The error between resulting pressure-volume (PV) loops of already validated CVS model and the new CVS model that includes the progressive opening of the mitral valve is assessed and remains within typical measurement error and variability. Simulations of ischemic mitral insufficiency are also performed. Pressure-Volume loops, transmitral flow evolution and mitral valve aperture area evolution follow reported measurements in shape, amplitude and trends.

Conclusions

The resulting cardiovascular system model including mitral valve dynamics provides a foundation for clinical validation and the study of valvular dysfunction in vivo. The overall models and results could readily be generalised to other cardiac valves.

Introduction

Pain is the commonest reason that patients present to an emergency department (ED), but it is often not treated effectively. Patient controlled analgesia (PCA) is used in other hospital settings but there is little evidence to support its use in emergency patients. We describe two randomised trials aiming to compare PCA to nurse titrated analgesia (routine care) in adult patients who present to the ED requiring intravenous opioid analgesia for the treatment of moderate to severe pain and are subsequently admitted to hospital.

Methods and analysis

Two prospective multi-centre open-label randomised trials of PCA versus routine care in emergency department patients who require intravenous opioid analgesia followed by admission to hospital; one trial involving patients with traumatic musculoskeletal injuries and the second involving patients with non-traumatic abdominal pain. In each trial, 200 participants will be randomised to receive either routine care or PCA, and followed for the first 12 h of their hospital stay. The primary outcome measure is hourly pain score recorded by the participant using a visual analogue scale (VAS) over the 12 h study period, with the primary statistical analyses based on the area under the curve of these pain scores. Secondary outcomes include total opioid use, side effects, time spent asleep, patient satisfaction, length of hospital stay and incremental cost effectiveness ratio.

Ethics and dissemination

The study is approved by the South Central—Southampton A Research Ethics Committee (REC reference 11/SC/0151). Data collection will be completed by August 2013, with statistical analyses starting after all final data queries are resolved. Dissemination plans include presentations at local, national and international scientific meetings held by relevant Colleges and societies. Publications should be ready for submission during 2014. A lay summary of the results will be available to study participants on request, and disseminated via a publically accessible website.

Registration details

The study is registered with the European Clinical Trials Database (EudraCT Number: 2011-000194-31) and is on the ISCRTN register (ISRCTN25343280).

In a study of the effects of methoxyflurane on renal function, the urinary and blood urea concentrations, the urinary and plasma osmolalities, and the packed cell volume were studied in each of 50 mothers before and after delivery. Methoxyflurane 0·35% was used as an analgesic in 25 patients and the other 25 had 50% nitrous oxide and 50% oxygen (Entonox). There was no evidence of renal dysfunction in either group, nor were there any significant differences between the groups. In a further 200 mothers, of whom 100 had methoxyflurane and 100 had nitrous oxide analgesia, the urinary and blood urea concentrations were measured on the morning of discharge from hospital. There were no significant differences between the groups. These results suggest that methoxyflurane is not nephrotoxic when used as a self-administered analgesic.

The enhancement of production of asperenone (Fig. 1), an inhibitor of lipoxygenase and human platelet aggregation from Aspergillus niger CFTRI 1105, was achieved by UV and nitrous acid mutagenesis. Nitrous acid mutants exhibited increased inhibitor production when compared with UV irradiated mutants. I N 41 a first-generation nitrous acid mutant produced 5.1 fold increased asperenone over parent strain. Mutant II N 31 obtained by second-generation nitrous acid treatment produced 60.3 mg asperenone/g biomass, which was 131 fold increase when compared to first generated mutant I N 41 and 670 fold increase over the parent strain. This mutant was stable for several generations on production medium.

The outcome of labour of 185 low-risk pregnancies at an isolated general practitioner maternity unit was compared with that for 185 comparable low-risk pregnancies at a specialist maternity hospital. No difference was found in mode of delivery or in the proportion of women requiring no analgesia, although significantly more women in the general practice group received analgesia beyond nitrous oxide. There was a significantly higher level of intervention in labour in the maternity hospital group in the form of fetal monitoring and augmentation of labour. The duration of first stage of labour was longer and meconium staining less frequent in the general practice group. Fourteen (7.6%) of the general practice group were transferred in labour to the specialist unit.

The results suggest that where considerations for selection of low-risk pregnancy permit, the general practice maternity unit can provide a distinctive style of intrapartum care with minimum intervention.

Background

Pain relief during labour is a topic of major interest in the Netherlands. Epidural analgesia is considered to be the most effective method of pain relief and recommended as first choice. However its uptake by pregnant women is limited compared to other western countries, partly as a result of non-availability due to logistic problems. Remifentanil, a synthetic opioid, is very suitable for patient controlled analgesia. Recent studies show that epidural analgesia is superior to remifentanil patient controlled analgesia in terms of pain intensity score; however there was no difference in satisfaction with pain relief between both treatments.

Methods/design

The proposed study is a multicentre randomized controlled study that assesses the cost-effectiveness of remifentanil patient controlled analgesia compared to epidural analgesia. We hypothesize that remifentanil patient controlled analgesia is as effective in improving pain appreciation scores as epidural analgesia, with lower costs and easier achievement of 24 hours availability of pain relief for women in labour and efficient pain relief for those with a contraindication for epidural analgesia.

Eligible women will be informed about the study and randomized before active labour has started. Women will be randomly allocated to a strategy based on epidural analgesia or on remifentanil patient controlled analgesia when they request pain relief during labour. Primary outcome is the pain appreciation score, i.e. satisfaction with pain relief.

Secondary outcome parameters are costs, patient satisfaction, pain scores (pain-intensity), mode of delivery and maternal and neonatal side effects.

The economic analysis will be performed from a short-term healthcare perspective. For both strategies the cost of perinatal care for mother and child, starting at the onset of labour and ending ten days after delivery, will be registered and compared.

Discussion

This study, considering cost effectiveness of remifentanil as first choice analgesia versus epidural analgesia, could strongly improve the care for 180.000 women, giving birth in the Netherlands yearly by giving them access to pain relief during labour, 24 hours a day.

Trial registration number

Dutch Trial Register NTR2551, http://www.trialregister.nl

Background:

Epidural analgesia is claimed to result in prolonged labor. Previous studies have assessed epidural analgesia vs systemic opioids rather than to parturients receiving no analgesia. This study aimed to evaluate the effect of epidural analgesia on labor duration compared with parturients devoid of analgesia.

Methods:

One hundred sixty nulliparous women in spontaneous labor at full term with a singleton vertex presentation were assigned to the study. Parturients who request epidural analgesia were allocated in the epidural group, whereas those not enthusiastic to labor analgesia were allocated in the control group. Epidural analgesia was provided with 20 mL bolus 0.5% epidural lidocaine plus fentanyl and maintained at 10 mL for 1 h. Duration of the first and second stages of labor, number of parturients receiving oxytocin, maximal oxytocin dose required for each parturient, numbers of instrumental vaginal, vacuum-assisted, and cesarean deliveries and neonatal Apgar score were recorded.

Results:

There was no statistical difference in the duration of the active-first and the second stages of labor, instrumental delivery, vacuum-assisted or cesarean delivery rates, the number of newborns with 1-min and 5-min Apgar scores less than 7 between both groups and number of parturients receiving oxytocin, however, the maximal oxytocin dose was significantly higher in the epidural group.

Conclusion:

Epidural analgesia by lidocaine (0.5%) and fentanyl does not prolong labor compared with parturients without analgesia; however, significant oxytocin augmentation is required during the epidural analgesia to keep up the aforementioned average labor duration.

Echocardiographic findings in five patients with pulmonary embolism were studied. Tricuspid echocardiograms showed abnormalities in valve motion, that is a monophasic triangular wave during diastole in all the patients as well as an increased dimension of the right ventricle. An "a' dip of the pulmonary valve echocardiogram was also recognised in all five. Later tricuspid echocardiograms regained the normal M-shaped configuration. The monophasic triangular pattern of the tricuspid valve during diastole may be related to the shorter duration of tricuspid valve opening compared with that of the mitral valve. Tachycardia cannot explain this difference between tricuspid and mitral valve motion, which seems to be caused by a prolonged isovolumic relaxation time of the right ventricle resulting in a delayed opening of the tricuspid valve. These results were obtained by comparing these data with those of control subjects and patients with chronic right ventricular overloading resulting from atrial septal defect.

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This study investigated whether the jet diameter measured by a multigated pulsed Doppler system could be used to assess the severity of valve disease in children with pulmonary (n = 11) or aortic (n = 4) valve stenosis. The results obtained were compared with those obtained at cineangiography and at operation. Multigated pulsed Doppler examination of a stenosed valve showed a region of relatively high velocities in the velocity profile (jet flow). There was good agreement between the diameter of the disturbed region on the Doppler echocardiogram and the diameter of the jet on the lateral angiocardiogram. In severe valve stenosis the agreement between the valve diameters measured by multigated pulsed Doppler and at operation was also good. In less severe valve stenosis Doppler measurements systematically underestimated the valve diameter at operation. It is likely that the functional opening of a semilunar valve is a more relevant estimate of the degree of stenosis than the anatomical measurement of the orifice. The findings of this study indicate that multigated pulsed Doppler systems are useful in the noninvasive diagnosis of stenotic valve disease.

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Background

Procedural burn pain is the most intense acute pain and most likely type of burn injury pain to be undertreated due to the physician’s fear of the adverse effect of analgesia and lack of anesthetist present. At our institution, in most of the cases, local burn detersion and debridement were performed at the ward level without any analgesics. This article describes a study designed to test the analgesia effect of a fixed nitrous oxide/oxygen mixture on burn dressing pain.

Methods/design

The experiment was carried out in three centers. The patients were given a number from 1 to 240. A randomization list was produced by a statistician according to our preliminary study. Due to the severity of the pain suffered, ethically it was decided to help as many as possible, so patients given the letters A, B or C were treated using a canister with the appropriate letter containing preprepared nitrous oxide/oxygen mixture (NOOM). Those with D were given oxygen only, from an identical-looking canister labeled D. Neither patients, nor doctors, nor nurses, nor data collector knew what was in each canister, thus they were all blind. The nursing officer who implemented the intervention handed the doctors envelopes containing the patients’ name and allocation of A, B, C or D. Thus, patients receiving NOOM or oxygen were in the ratio 3:1. Parameters, including pain severity, blood pressure, heart rate, digital oxygen saturation and the Chinese version of the burn specific pain anxiety scale (C-BSPAS), were taken before, during and after dressing for each group. A video and audio record was taken individually for later communication coding and outcome analysis. Rescue analgesic was recorded.

Discussion

Based on the findings from our previous qualitative study that physician’s reluctance to order narcotic analgesia is due to its adverse effect and from our pilot experiment, this study aims to test the hypothesis that a fixed nitrous oxide/oxygen mixture will promote better burn dressing pain alleviation and outcomes. Analyses will focus on the effects of the experimental intervention on pain severity during dressing (primary outcomes); physiological parameters, C-BSPAS and acceptance of both health care professionals and patients (secondary outcomes). If this model of analgesia for burn pain management implemented by nurses proves successful, it could potentially be implemented widely in hospital and prehospital settings and improve patients’ satisfaction and quality of life.

Trial registration

(Clinical Trials Identifier: CHICTR-TRC11001690).

A pilot study of prehospital analgesia with 50% nitrous oxide and 50% oxygen was undertaken in patients experiencing severe pain from various sources. Under the supervision of an ambulance attendant N2O/O2 was administered through a face mask held by the patient and connected to a portable regulator/tank unit. Two types of units were evaluated -- Entonox (with premixed N2O and O2) and Nitronox (with separate cylinders of N2O and O2, the gases being mixed at the time of administration). Of the 72 patients 69 obtained worthwhile analgesia (marked or partial relief of pain) during treatment in the field or in the ambulance. There were no serious side effects, and those that did occur reflected N2O's expected action (e.g., giddiness). N2O/O2 is thus considered a safe and effective analgesic, suitable for use by ambulance personnel.

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Nitrous oxide analgesia is presented as the analgesic method of choice in medically compromised patients. The resemblance between the action of nitrous oxide and that of morphine is emphasized. The combination of the opiate-like action of nitrous oxide with the advantages of an inhalation technique makes it preferable and superior to parenteral opiate administration. It may thus be termed as an inhalation “opiate”.

Since its introduction into clinical use by Wells in 1844 (1), nitrous oxide (N20) has been applied as an anesthetic and analgesic agent in various medical situations, including dentistry (2). The development of equipment affording safe administration of accurate concentrations of either pre-mixed or adjustable N20 and oxygen enabled the application of “relative analgesia” as an important technique in the relief of pain. The pharmacological action and analgesic properties of N20 received renewed interest after Berkowitz et al (3) showed the resemblance between its mode of action and that of opiates. Recent human and animal studies indicated that N20 activates the endogenous opiate system(s) in a manner similar to that of morphine (4). The availability of an analgesic gas which, on the one hand, mimics opiate action whilst on the other hand its administration is continuously adjustable, as opposed to other modes of sedation, makes it into an ideal adjunct in dental procedures. Owing to its minimal side effects, the use of N20 is especially recommended in the management of anxious children and medically compromised patients.

This report presents three illustrative patients in whom nitrous oxide proved to be the drug of choice during dental procedures.