Nitrous-oxide analgesia in myocardial infarction

Reduction of anterior shoulder dislocation in emergency department; is entonox(®) effective?

INTRODUCTION

An appropriate procedural sedation and analgesia (PSA) is crucial to reduce a dislocated shoulder successfully in emergency department. This study compares sedative effect of inhalational Entonox(®) (En) to intra-venous (IV) Midazolam plus Fentanyl (F+M).

METHODS

120 patients with recurrent anterior shoulder dislocation were randomly assigned into two groups. 60 patients (group F+M) received 0.1 mg/kg IV Midazolam plus 3µg/kg IV Fentanyl and 60 patients (group En) received Entonox(®) with self administration face mask on an on-demand basis. Traction/counter-traction method was used to reduce the dislocated shoulder joint in both groups.

RESULTS

48 out of 60 (80%) patients in group F+M and 6 out of 60 (10%) patients in group En had successful reduction (p < 0.0001). The mean pain score reduction was 6.3 ± 1.2 for group F+M and 3 ± 0.9 for group En (p < 0.0001). There was a statistically significant difference in mean patient satisfaction (assessed with Likert score) between two groups (4.45 ± 0.6 for group F+M and 2.3 ± 1 for group En; p < 0.0001). Duration of entire procedure (since the beginning of PSA up to the end of successful or unsuccessful reduction) was shorter in Group F+M, but successful reductions occurred earlier in group En. No major side effect such as airway compromise, retracted respiratory depression, or circulatory failure was occurred in any group.

CONCLUSION

Entonox(®) may not be an appropriate agent to help reducing a dislocated shoulder.

Effects of nitrous oxide on haemodynamic and electroencephalographic responses induced by tetanic electrical stimulation during propofol anaesthesia

We studied the effect of nitrous oxide on haemodynamic and electroencephalographic responses caused by noxious stimulation during propofol anaesthesia. Thirty-four patients (ASA I-II) were anaesthetised with propofol 3 mg x kg(-1) and were randomly allocated to receive either 60% nitrous oxide in oxygen or 40% oxygen in air. Anaesthesia was maintained using propofol infusion of 10 mg x kg(-1) x h(-1) for the first 10 min, 8 mg x kg(-1) x h(-1) for the next 10 min and 6 mg x kg(-1) x h(-1) thereafter. Thirty minutes after the induction of anaesthesia, tetanic electrical stimulation (80 mA, 100 Hz) was applied to the ulnar nerve. Tetanic stimulation significantly increased blood pressure and heart rate in both groups (p < 0.005 or less), but did not induce any arousal pattern on the electroencephalograph. Nitrous oxide significantly attenuated the tetanic stimulation-induced increase in blood pressure (p < 0.05 or less), but not the heart rate.

Acute myocardial infarction patients' chest pain as monitored and evaluated by ambulance personnel

A delicate duty for ambulance personnel is to care for patients who suffer from chest pain, caused by acute myocardial infarction (AMI-patient). In Sweden pain-relieving drugs may be administered, such as: oxygen, entonox, or morphine according to the skill of the ambulance personnel. The aim of this study was to find out if AMI-patients' expressions of pain were monitored and evaluated, in which way the AMI-patients received pain-relief, and to which degree they were relieved of pain. Examinations of the records of the ambulance personnel's observations during transport of AMI-patients revealed that nine tenths of those who complained about chest pain received pain-relieving drugs. The results of the treatments varied, however, from a good rate of response to morphine to less responses to oxygen and entonox. In order to treat AMI-patients who are in need of pain-relief during their transit to hospital the ambulance personnel must possess thorough knowledge of both pain theory and communication theory. Furthermore, they need tools for assessment of pain and for administering adequate pain-relieving drugs in clinical practice. In the future it may be necessary to differentiate between ambulance personnel in routine service and those in emergency service according to their levels of education.

Nitrous oxide sedation/analgesia in emergency medicine

Nitrous oxide:oxygen mixtures are safe and effective sedative/analgesic agents for use in emergency medicine. They are suitable for prehospital care because of their safety, rapid onset, and short duration of action. The self-administered form of a 50:50 mixture is the most acceptable system, but other methods of administration should be investigated, particularly in the ED setting. While there are unresolved questions concerning the use of nitrous oxide as an anesthetic and analgesic agent, it is difficult to extrapolate many of the findings to the low-dose, patient-controlled 50:50 mixture used in emergency medicine. Use of the gas mixture in a variety of clinical settings has been associated with no major adverse occurrences, and experience continues to support its safety. Future possibilities for study include the use of the gas mixture in combination with other agents or TENS. No one drug can be considered a panacea for all painful states. Nitrous oxide:oxygen mixtures certainly do not meet all the criteria for the ideal analgesic. Those clinicians who seek a safe and effective sedative/analgesic for mild to moderate pain will be satisfied that we can now offer more to our patients in the early management of their problems.

Pre-hospital analgesia with Entonox

Pre-hospital self-administered analgesia using a 50:50 mixture of nitrous oxide and oxygen (Entonox) was evaluated in 240 patients. Of these, 93.4 per cent experienced either complete or partial relief from traumatic, chest, abdominal or back pain. Drowsiness was the most common side effect noted. No complications occurred during delivery of the mixture. Attention is drawn to the effect of extreme temperatures on the Entonox mixture and recommendations are made with respect to its use below-freezing climates. Because of its ease of use and short duration of action, Entonox appears to be well suited for the treatment of pre-hospital pain by Emergency Medical Technicians.

Nitrous oxide at higher elevations

Because patients given 50% nitrous oxide and 50% oxygen failed to show any significant clinical response, a mixture of 70% nitrous oxide and 30% oxygen was administered to 124 patients at an altitude of 5,280 feet in the emergency department at Denver General Hospital. Seventy-five percent of the patients were 25 years of age or younger. Twenty-two (17.7%) had minimal or no response, while 71 (57.3%) had good to excellent response. More than 20% of the patients received concomitant analgesic medications. Six patients experienced side effects during administration. Of these patients, four had received narcotic medication prior to administration of nitrous oxide. The mixture of 70% nitrous oxide and 30% oxygen was safe and effective in treating juvenile and adult patients presenting with pain in the emergency department at a higher elevation.

Administration of nitrous oxide in normal subjects. Evaluation of systems of gas delivery for their clinical use and hemodynamic effects

Nitrous oxide (concentrations of 30 to 50%) was administered to 22 healthy volunteer subjects via nasal prongs, rebreathing mask, and an airlines mask to assess the efficiency of systems of delivery and the hemodynamic effects. The end-expired concentration of nitrous oxide, expressed as a percentage of the inspired concentration of nitrous oxide, was 19% for nasal prongs, 34% for the rebreathing mask, and 95% for the airlines mask (most accurate delivery). The pulse rate fell from a mean of 79+/-3 beats per minute to 67+/-2 with nasal prongs, to 64+/-2 with the rebreathing mask, and to 64+/-2 with the airlines mask. Both systolic and diastolic pressures fell from means of 122+/-4 and 74+/-2 mm Hg, respectively, to 98+/-3 mm Hg and 64+/-2 mm Hg, respectively, with the airlines apparatus. The fall in systolic blood pressure (slope, -0.79) exceeded that in the diastolic (slope, -0.35). In additional eight normal subjects, administration of 30% nitrous oxide via airlines mask produced identical changes in blood pressure and pulse rate, but there was no effect from 30 minutes of administration of 30% nitrous oxide on the end-systolic volume index, cardiac index, ejection fraction, normalized wall velocity determined echocardiographically, ejection time, or the ratio of preejection period to ejection time.

An analysis of 1,331 sedations using inhalation, intravenous, or other techniques

The safety and efficacy of various sedative techniques was studied. Inhalation sedation provided the mainstay of anxiety control, whereas intravenous and combination techniques were reserved for more difficult patients or procedures. Pooled data from all techniques yielded an 87% effectiveness rate and 93% patient acceptance rate. Sedation was less often effective in persons with poorer health status than in healthy persons. Complications encountered were few, rarely of serious potential, and easily managed. Nitrous oxide sedation was effective 88.5% of the time and usually at concentrations of 50% or less. The safety and efficacy of intravenous, oral, combination, and especially inhalation sedation given by individuals not formally trained in general anesthesia appears to be confirmed. No correlation of side effects to a specific technique of administration or to patients suffering significant medical disorders could be established. However, more data need to be obtained in this area before firm conclusions can be made.

A double-blind trial of patient-controlled nitrous-oxide/oxygen analgesia in myocardial infarction

The analgesic effect of self-administered nitrous oxide 50%/oxygen 50% ('Entonox" analgesic apparatus) was compared with air given by the same method in a double-blind trial in 81 patients with myocardial infarction. Self-administered nitrous oxide/oxygen, which was associated with a low frequency of side-effects, proved significantly more effective than air in the early relief of severe cardiac pain, but not in the relief of moderate or slight pain or when administration was continued after ten minutes.