The Levels of Nitrous Oxide Analgesia

Parbrook, G.D.

doi:10.1093/bja/39.12.974

Cited by 45 publications

(18 citation statements)

References 39 publications

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“…Nitrous oxide is a weak volatile anaesthetic with a minimum alveolar concentration (MAC) of 104%, achievable only in hyperbaric environments [17]. Nitrous oxide is capable of producing mild sedation and analgesia, and has been shown to be safe and effective for use in a variety of practice environments including colonoscopy, transoesophageal echocardiography, transrectal prostate biopsy, emergency department procedures and labour pain management [10][11][12][13][14]18].…”

Section: Discussionmentioning

confidence: 99%

The effect of nitrous oxide on intra‐ocular pressure in healthy adults*

Lalwani¹,

Fox²,

et al. 2012

Anaesthesia

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SummaryMany anaesthetic agents affect intra-ocular pressure, yet little is known about nitrous oxide and intra-ocular pressure. This study assessed the effect of nitrous oxide on intra-ocular pressure in 20 healthy adult volunteers. The intra-ocular pressure was measured at baseline, while breathing a 70:30 mix of nitrous oxide and oxygen for 12 min, and then while breathing room air for 15 min. A linear mixed effects model was used to assess change in intra-ocular pressure over time. There was no significant difference in intra-ocular pressure between baseline and during or after nitrous oxide inhalation. Several differences in intra-ocular pressure were noted between internal time-points: pressure increased by 2.4 mmHg between 3 and 6 min of breathing nitrous oxide (p = 0.01); it increased by 1.4 mmHg between 3 and 9 min of breathing nitrous oxide (p = 0.046); and it decreased by 2.2 mmHg between 6 min of breathing nitrous oxide and 15 min of breathing room air (p = 0.035). This study indicates that nitrous oxide inhalation does not significantly change intra-ocular pressure from baseline values in a population of healthy adults. Accepted: 25 October 2011There have been few studies to assess the effect of nitrous oxide (N 2 O) on intra-ocular pressure (IOP) [1]. This is an important question, as many anaesthetic agents produce clinically significant changes in IOP. Volatile agents like halothane, isoflurane and sevoflurane have been shown to decrease IOP, as has the intravenous anaesthetic agent propofol [2][3][4]. Other drugs, such as suxamethonium, can produce an increase in IOP [5]. Several human and animal studies have peripherally investigated the effect of N 2 O on IOP, but all have used N 2 O in combination with anaesthetic agents that are known to affect IOP [6][7][8]. One report indicates that N 2 O seems to have no effect on IOP, but supporting data or references are not given [9]. To our knowledge, there are no other studies that have explored the effect of isolated N 2 O administration on IOP in humans.Reliable IOP measurements are essential for the effective management of glaucoma, yet accurate values are

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Section: Discussionmentioning

confidence: 99%

The effect of nitrous oxide on intra‐ocular pressure in healthy adults*

Lalwani¹,

Fox²,

et al. 2012

Anaesthesia

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“…The cardiorespiratory depressant actions attributed to nitrous oxide (Sonnerstein et al, 1948;Parbrook, 1967) may be partly counteracted by the high oxygen concentration in the Entonox to provide effects on the diastolic blood pressure and heart rate that causes variation in the Oxygen and Entonox treatment groups. Naturally, since oxygen is always required to be used when nitrous oxide is being given, this can only be speculation.…”

Section: Resultsmentioning

confidence: 99%

Minor procedures in the accident and emergency department: can Entonox help?

Payne

Edbrooke²,

Davies³

1991

Emergency Medicine Journal

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SUMMARYThe efficacy of Entonox as a supplement to local anaesthesia for minor surgical procedures was studied. Eighty-five patients undergoing surgery for the incision and drainage of a subcutaneous abscess using a local anaesthetic were involved in a trial to ascertain the level of pain associated with such procedures and to investigate the possibility of using on-demand Entonox to supplement the local anaesthesia provided. Patients received either the standard local anaesthesia, or, alternatively, the local anaesthesia was supplemented with oxygen or Entonox via on-demand apparatus.Patients indicated on three linear visual analogue scales their pain, anxiety and total discomfort, and also on a cartoon pain rating scale, at different stages during the operation.Results showed that there was no statistically significant reduction in pain provided by the Entonox, despite general patient approval. Both oxygen and Entonox showed some anxiolytic properties. Pure oxygen was also seen to produce a rise in heart rate, while both gases (pure oxygen and Entonox) caused an increase in diastolic blood pressure. It was also seen that the patient's short term memory of the pain experienced was unaffected by pure oxygen or Entonox.

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“…An Ao, of 31% is not mandatory for these patients during balanced anaesthesia provided they have continuous pulse oximeter monitoring. The higher percentage of nitrous oxide will provide more analgesia [12] and thus reduce the requirements for analgesics. But the anaesthetist must be alert to rapid alterations in the patients' condition.…”

Section: Discussionmentioning

confidence: 99%

Calculation of inspired oxygen fraction during anaesthesia based on awake oxygen saturation

Mandal

Chaudhary

1994

Anaesthesia

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SummaryOne hundred ASA grade I or 2 patients were studied to assess the use of awake oxygen saturation to determine the necessary inspired oxygen fraction during anaesthesia. The inspired oxygen fraction was adjusted gradually to the lowest possible value to maintain the pre-operative oxygen saturation at a constant level. Normocapneic ventilation was maintained and analgesia was provided with 0.5 mg.kg-' of pethidine given intravenously. In addition to routine monitoring and measurement (electrocardiograph, oxygen saturation, expired carbon dioxide concentration and noninvasive blood pressure), arterial samples for blood gas analysis and venous samples for lactate and pyruvate levels were taken when awake and 30 min after achieving a steady state with a minimum inspired oxygen fraction. The mean inspired oxygen fraction required in these patients was 20.91 (SD 1.92%) ranging from 18-25%. The arterial pH were 7.34 ( S D 4.04) (awake) and 7.35 (SD 3.15) (after 30 rnin), the partial pressure of oxygen 13.17 ( S D 1.97) (awake) and 13.83 (SD 1.6 kPa) (after 30 min) and the partial pressure of carbon dioxide and base excess were normal. Serum lactate levels were 1.04 (SD 0.25) (awake) and 1.15 (SD 0.48) (after 30 min) mmol.l-', whilst pyruvate levels were 0.1 (SD 0.02) (awake) and 0.12 (SD 0.21) (after 30 min) mmol.1-I. Patients' recovery and postoperative course were uneventful. Key wordsOxygen; blood level. Measurement techniques; pulse oximetry.It is common practice to provide at least 3 170 oxygen with nitrous oxide during anaesthesia. This concept has been well accepted by anaesthetists in past decades when proper monitoring facilities were not available [l-31. At that time anaesthetists had to depend on calculated alveolar oxygen tension (PAo,) and intermittent sampling of arterial blood to assess oxygenation. Such guesswork has been eliminated by the availability of in-line inspired oxygen (Ro,) monitors (0, analyser) and continuous noninvasive arterial oxygen saturation monitors (pulse oximeter). However, even after the recognition of these monitors as minimum standard monitoring devices, anaesthetists are still providing 31 ' YO oxygen during anaesthesia.It is known that cardiac output [4,5] does not decrease during thiopentone and nitrous oxide anaesthesia with spontaneous ventilation, and that oxygen consumption falls to approximately 15% below basal level during controlled ventilation [6]. In spite of these findings, no study has used the pre-operative arterial oxygen saturation (Spo2) value as a guide for adjustment of the intraoperative Ro2 below 31%.The main objective of this study was to determine whether the conventional 3 1 ?LO inspired oxygen fraction is necessary to maintain a constant (pre-operative) Spo, during balanced anaesthesia using nitrous oxide. MethodsOne hundred adult patients of ASA grade 1 or 2 who had no cardiac or respiratory disease or diabetes mellitus were recruited into the study. Patients were of either sex and they acted as their own control. Ethics committee approval and inf...

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The Levels of Nitrous Oxide Analgesia

Cited by 45 publications

References 39 publications

The effect of nitrous oxide on intra‐ocular pressure in healthy adults*

The effect of nitrous oxide on intra‐ocular pressure in healthy adults*

Minor procedures in the accident and emergency department: can Entonox help?

Calculation of inspired oxygen fraction during anaesthesia based on awake oxygen saturation

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