Ceasing routine use of nitrous oxide-a follow up

Effects of Inhaled Nitrous Oxide on the Induction Dose and Time Requirements of Propofol: A Prospective, Randomized, Double-blind Study

Context:

Propofol is a commonly used induction agent during general anesthesia. As a sole agent, it does not provide any strong analgesic effect. The nitrous oxide (N₂O) used along with propofol for induction of anesthesia augments the induction characteristics and reduces the dose of propofol.

Aims:

To study the effects of inhaled N₂O on the induction dose and time of propofol during general anesthesia and also its hemodynamic response and adverse effects.

Settings and Design:

The present research is a prospective, randomized, double-blind comparative study.

Subjects and Methods:

The study population consisted of eighty patients aged 18–60 years from either sex, American Society of Anesthesiologists physical status 1 and 2 which were scheduled for various elective surgical procedures under general anesthesia. The patients were randomly allocated into two groups comprising forty patients in each group. All patients were premedicated with glycopyrrolate 0.2 mg, ondansetron 4 mg, and fentanyl 1 μg/kg intravenously. Group FN received breathing mixture of gases (67% N₂O @ 4 L/min and 33% O₂ @ 2 L/min), and propofol and Group FO received 100% O₂ @ 6 L/min and propofol. The different hemodynamic parameters (heart rate, mean arterial pressure, systolic blood pressure, diastolic blood pressure, and SpO₂) were measured.

Statistical Analysis:

All observations were analyzed using Chi-square test, Student's t-test, and analysis of variance.

Results:

The mean induction time and dose were significantly less in Group FN as compared to Group FO (P < 0.05). The mean induction time was 172 ± 32 s in Group FN as compared to 242 ± 43 s in Group FO (P < 001), whereas the mean induction dose was 56.10 ± 13.92 mg in Group FN as compared to 81.67 ± 17.64 mg in Group FO (P < 0.05). The hemodynamic parameters remained stable with no complications.

Conclusion:

The coadministration of N₂O during induction of anesthesia with propofol not only reduced the induction dose of propofol but also reduced induction time significantly. Furthermore, it provided stable hemodynamics without any complications.

The choice of anaesthetic--sevoflurane or propofol--and outcome from cancer surgery: a retrospective analysis

BACKGROUND

Commonly used inhalational hypnotics, such as sevoflurane, are pro-inflammatory, whereas the intravenously administered hypnotic agent propofol is anti-inflammatory and anti-oxidative. A few clinical studies have indicated similar effects in patients. We examined the possible association between patient survival after radical cancer surgery and the use of sevoflurane or propofol anaesthesia.

PATIENTS AND METHODS

Demographic, anaesthetic, and surgical data from 2,838 patients registered for surgery for breast, colon, or rectal cancers were included in a database. This was record-linked to regional clinical quality registers. Cumulative 1- and 5-year overall survival rates were assessed using the Kaplan-Meier method, and estimates were compared between patients given propofol (n = 903) or sevoflurane (n = 1,935). In a second step, Cox proportional hazard models were calculated to assess the risk of death adjusted for potential effect modifiers and confounders.

RESULTS

Differences in overall 1- and 5-year survival rates for all three sites combined were 4.7% (p = 0.004) and 5.6% (p < 0.001), respectively, in favour of propofol. The 1-year survival for patients operated for colon cancer was almost 10% higher after propofol anaesthesia. However, after adjustment for several confounders, the observed differences were not statistically significant.

CONCLUSION

Propofol anaesthesia might be better in surgery for some cancer types, but the retrospective design of this study, with uneven distributions of several confounders, distorted the picture. These uncertainties emphasize the need for a randomized controlled trial.

Oxygen concentrators performance with nitrous oxide at 50:50 volume

BACKGROUND AND OBJECTIVES

Few investigations have addressed the safety of oxygen from concentrators for use in anesthesia in association with nitrous oxide. This study evaluated the percent of oxygen from a concentrator in association with nitrous oxide in a semi-closed rebreathing circuit.

METHODS

Adult patients undergoing low risk surgery were randomly allocated into two groups, receiving a fresh gas flow of oxygen from concentrators (O293) or of oxygen from concentrators and nitrous oxide (O293N2O). The fraction of inspired oxygen and the percentage of oxygen from fresh gas flow were measured every 10 min. The ratio of FiO2/oxygen concentration delivered was compared at various time intervals and between the groups.

RESULTS

Thirty patients were studied in each group. There was no difference in oxygen from concentrators over time for both groups, but there was a significant improvement in the FiO2 (p<0.001) for O293 group while a significant decline (p<0.001) for O293N2O. The FiO2/oxygen ratio varied in both groups, reaching a plateau in the O293 group. Pulse oximetry did not fall below 98.5% in either group.

CONCLUSION

The FiO2 in the mixture of O293 and nitrous oxide fell during the observation period although oxygen saturation was higher than 98.5% throughout the study. Concentrators can be considered a stable source of oxygen for use during short anesthetic procedures, either pure or in association with nitrous oxide at 50:50 volume.

[Impact of the decrease of nitrous oxide use on the consumption of halogenated agents]

OBJECTIVE

Nitrous oxide (N2O) toxicity and its impact on pollution lead to restrict its use. A decrease of N2O consumption should increase the hypnotic inhaled consumption. This monocentric study estimated consumptions and costs of halogenated agents (HA) and N2O over 5 years when the N2O consumption was reduced.

STUDY DESIGN

Retrospective from a computerized database.

PATIENTS

Between 2006 and 2010, 34,097 procedures were studied after two meetings exposing the risks of the N2O.

METHODS

At the end of anesthesia, consumptions of hypnotic agents (millilitres transmitted by the injectors and the blender) were archived in the database. The annual consumption of agents was obtained by adding the individual consumptions, then divided by the annual number of cases. The costs were given by the hospital pharmacy from invoices.

RESULTS

N2O consumption per anesthesia constantly decreased during the study, from 75.1L by act to 22.7L. The sum of the annual consumptions of N2O and air did not change suggesting that total fresh gas flow remained stable. Between 2006 and 2010, the sevoflurane consumption by act increased by 25%, from 16.5 to 20.6mL, and desflurane consumption by 37%, from 46.1 to 63.1mL by patient. The costs of the administration of hypnotic agents remained stable.

CONCLUSION

N2O consumption decrease had an impact on the consumption of HA. The cost reduction of the N2O was counterbalanced by the increase of halogenated vapor cost. The profit of the ecological impact of the reduction in N2O use could be quantified.

The carrier gas in anaesthesia: nitrous oxide/oxygen, medical air/oxygen and pure oxygen

PURPOSE OF REVIEW

The gas passing the module for the delivery of inhalation anaesthetics and carrying vapourized anaesthetics into the breathing system is called the carrier gas. Oxygen is the absolutely indispensable component of the carrier gas. Additive gaseous components can be medical air (nitrogen), nitrous oxide, cyclopropane, or xenon, the latter three being anaesthetic gases themselves. Cyclopropane is not used any more and xenon is not approved as a medical gas yet, leaving medical air and nitrous oxide as the only currently available adjuncts to oxygen.

RECENT FINDINGS

As review articles on nitrous oxide recommend unequivocally not using this gas routinely, and many anaesthetists already consistently omit any use of this gas, the alternative carrier gases are either a mixture of medical air and oxygen or pure oxygen. A nitrogen/oxygen mixture is absolutely inert with respect to metabolism or environment; there are no contraindications or shortcomings at all. The use of pure oxygen will result in high oxygen concentrations, improving the patients' safety by increasing the pulmonary oxygen reservoir and rendering impossible the development of hypoxic gas mixtures within the breathing system. Whether the incidence of postoperative wound infections or postoperative nausea and vomiting is reduced by perioperative hyperoxia is still under scientific discussion. In general, the use of high oxygen concentrations over a period of 6-8 h is not harmful for the patient, assuming the performance of recruitment manoeuvres, consistent use of positive end-expiratory pressure, and thorough observance of the contraindications that can result from the increased vulnerability of tissues to hyperoxia.

SUMMARY

Nitrous oxide should not be used routinely as a component of the carrier gas any more. A mixture of medical air and oxygen must be acknowledged to be the gold standard. Pure oxygen may be used as a carrier gas if medical air or properly performing flow controls for medical air are not available.

Effects of nitrous oxide on intraoperative bowel distension

PURPOSE OF REVIEW

To evaluate evidence and present an objective view on the effect of nitrous oxide on bowel function.

RECENT FINDINGS

We determined in a metaanalysis that the chance of having intraoperative bowel distension was increased about two fold in patients receiving nitrous oxide as the anaesthetic carrier gas compared with those receiving nitrogen or oxygen. In a separate logistic regression analysis, we found that the duration of nitrous oxide exposure was a key factor in explaining this difference, as well as the variability of previously published data. In contrast to bowel distension, surgical operating conditions were not hindered by the use of nitrous oxide; however, the number of patients analysed for operating conditions was much less than that for bowel distension data.

SUMMARY

Nitrous oxide causes clinically and statistically recognizable bowel distension. This distension, however, does not always exacerbate the surgical conditions, nor does it appear to delay bowel movement or hospital discharge. Although no major problems were noted in bowel functions other than distension, we recommend avoiding nitrous oxide administration during prolonged bowel operations.

[Premixed 50% nitrous oxide and oxygen: theoretical recalls and practical modalities]

The concept of premixed 50% nitrous oxide and oxygen dated back to 1961 in England, where it is commercialised under the name Entonox. In France, after a so marginal use, premixed 50% nitrous oxide and oxygen now knows such a revival since we first consider the pain provoked by the cure. To use correctly premixed 50% nitrous oxide and oxygen, we need to know the main properties of the nitrous oxide. The four commercial versions, now on the market, are presented (Kalinox, Medimix, Antasol, Oxynox. Except a few contraindications, these indications are large, as well at hospital as outside. In less than 10% of the cases, side effects are possible. Conditions of administration are given in details. The limits of the technic and the particular precautions of use are precised.