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Preface: Nitrous oxide: time to say goodbye—again?
Best Practice & Research Clinical Anaesthesiology Vol. 15, No. 3, pp. vii±viii, 2001
doi:10.1053/bean.2001.0164, available online at http://www.idealibrary.com on
Preface: Nitrous oxide: time to say goodbye ± again? Nitrous oxide (N2O) has now been in use for more than 150 years, longer than any of the other modern anaesthetics. There thus exists considerable experience in using N2O including both the pros and cons. Recently, there has been a trend towards decreasing or even abandoning the use of N2O. This trend is mostly due to the transition from high-¯ow to low-¯ow or minimal-¯ow anaesthesia. When used under these reduced ¯ow conditions, N2O may be hazardous because it promotes the formation of a hypoxic gas mixture. However, there are other potential side eects of N2O that have, now and then, led to the request to completely abandon the use of N2O in anaesthetic practice. In some European countries such as Germany, there is at present a vigorous discussion about abandoning N2O. What are the arguments of those who advocate abandoning N2O in anaesthesia? One has to weigh the risks and bene®ts of a drug in order to reach a de®nite conclusion. The disadvantages of N2O include diusion hypoxia, diusion into closed spaces, decreased methionine synthase activity, nausea and vomiting, occupational hazards on both a local and global scale, such as the possibility of teratogenicity and fortotoxicity, as well as an enhancement of the greenhouse eect. Vitamin B12 de®ciency is another strong argument against the use of N2O, because in most cases the anaesthesiologist will be unlikely to know about this condition in the patient. There are also accepted contraindications for the use of N2O including its use in neurosurgery or eye and ear surgery. Each operating room in which N2O is used should be equipped with scavenging systems and the workplace concentration of N2O should be monitored routinely. Actually, it seems easy to omit N2O in anaesthetic practice. There are recipes, such as the use of about 0.2±0.25 MAC in addition to the anaesthetic concentration that would have been used with N2O to overcome the missing eect of 60±70 vol% N2O. Furthermore there are now other alternatives such as mono-pharmacological anaesthesia using des¯urane or sevo¯urane, combination anaesthesia using the very short-acting opioid remifentanil, the use of total intravenous anaesthesia or, in the near future, the use of xenon. Most of these arguments will be discussed in detail in the following chapters of this volume. However, there are also bene®ts to the use of N2O which include its analgesic potency, its rapid kinetics and its low cost (although indirect costs have to be considered such as the rental cost of cylinders, the maintenance of pipe supplies, scavenging systems and cost of routine workplace monitoring). Furthermore, N2O seems to suppress memory and consciousness and thus decreases the incidence of awareness. Apart from the risk-bene®t ratio for N2O the bene®ts and downsides of alternative drug regimens should also be considered. This volume will address this question in the ®nal chapter by analysing xenon as a possible substitute for N2O. 1521±6896/01/03000vii02 $35.00/00
c 2001 Harcourt Publishers Ltd. *
viii Preface
At a recent meeting of the Working Group of the use of Nitrous Oxide in Europe (WGNOE) initiated by the European Academy of Anaesthesiologists (EAA), the current status of N2O was discussed. Although there were distinctive dierences in the assessment of the present and future use of N2O in anaesthesia it was clear that there are no guidelines for the minimum requirements for the safe use of N2O. Thus, one of the main tasks for the near future is to de®ne recommendations for the safe use of N2O at a national and an international level. In conclusion, this volume is not intended to support those who want to completely abandon N2O. Nevertheless we do not wish to state that N2O should be used as the routine carrier gas without taking into account any contraindications. Before turning the wheel one should consider the risks and bene®ts many of which are discussed in this volume, and then decide whether N2O will be of bene®t for the anaesthesia being performed. Peter H. Tonner Jens Scholz Department of Anaesthesiology and Intensive Care Medicine, University Hospital, Kiel, Germany.
doi:10.1053/bean.2001.0164, available online at http://www.idealibrary.com on
Preface: Nitrous oxide: time to say goodbye ± again? Nitrous oxide (N2O) has now been in use for more than 150 years, longer than any of the other modern anaesthetics. There thus exists considerable experience in using N2O including both the pros and cons. Recently, there has been a trend towards decreasing or even abandoning the use of N2O. This trend is mostly due to the transition from high-¯ow to low-¯ow or minimal-¯ow anaesthesia. When used under these reduced ¯ow conditions, N2O may be hazardous because it promotes the formation of a hypoxic gas mixture. However, there are other potential side eects of N2O that have, now and then, led to the request to completely abandon the use of N2O in anaesthetic practice. In some European countries such as Germany, there is at present a vigorous discussion about abandoning N2O. What are the arguments of those who advocate abandoning N2O in anaesthesia? One has to weigh the risks and bene®ts of a drug in order to reach a de®nite conclusion. The disadvantages of N2O include diusion hypoxia, diusion into closed spaces, decreased methionine synthase activity, nausea and vomiting, occupational hazards on both a local and global scale, such as the possibility of teratogenicity and fortotoxicity, as well as an enhancement of the greenhouse eect. Vitamin B12 de®ciency is another strong argument against the use of N2O, because in most cases the anaesthesiologist will be unlikely to know about this condition in the patient. There are also accepted contraindications for the use of N2O including its use in neurosurgery or eye and ear surgery. Each operating room in which N2O is used should be equipped with scavenging systems and the workplace concentration of N2O should be monitored routinely. Actually, it seems easy to omit N2O in anaesthetic practice. There are recipes, such as the use of about 0.2±0.25 MAC in addition to the anaesthetic concentration that would have been used with N2O to overcome the missing eect of 60±70 vol% N2O. Furthermore there are now other alternatives such as mono-pharmacological anaesthesia using des¯urane or sevo¯urane, combination anaesthesia using the very short-acting opioid remifentanil, the use of total intravenous anaesthesia or, in the near future, the use of xenon. Most of these arguments will be discussed in detail in the following chapters of this volume. However, there are also bene®ts to the use of N2O which include its analgesic potency, its rapid kinetics and its low cost (although indirect costs have to be considered such as the rental cost of cylinders, the maintenance of pipe supplies, scavenging systems and cost of routine workplace monitoring). Furthermore, N2O seems to suppress memory and consciousness and thus decreases the incidence of awareness. Apart from the risk-bene®t ratio for N2O the bene®ts and downsides of alternative drug regimens should also be considered. This volume will address this question in the ®nal chapter by analysing xenon as a possible substitute for N2O. 1521±6896/01/03000vii02 $35.00/00
c 2001 Harcourt Publishers Ltd. *
viii Preface
At a recent meeting of the Working Group of the use of Nitrous Oxide in Europe (WGNOE) initiated by the European Academy of Anaesthesiologists (EAA), the current status of N2O was discussed. Although there were distinctive dierences in the assessment of the present and future use of N2O in anaesthesia it was clear that there are no guidelines for the minimum requirements for the safe use of N2O. Thus, one of the main tasks for the near future is to de®ne recommendations for the safe use of N2O at a national and an international level. In conclusion, this volume is not intended to support those who want to completely abandon N2O. Nevertheless we do not wish to state that N2O should be used as the routine carrier gas without taking into account any contraindications. Before turning the wheel one should consider the risks and bene®ts many of which are discussed in this volume, and then decide whether N2O will be of bene®t for the anaesthesia being performed. Peter H. Tonner Jens Scholz Department of Anaesthesiology and Intensive Care Medicine, University Hospital, Kiel, Germany.