200 5 Tornetta FJ. Clinical studies with the new anti-

emetic metoclopramide. Ancsth Analg 1969; 48: 198-204. 6 Diamond M J, Keeri-Szanto M. Reduction of postoperative vomiting by preoperative administration of oral Metoclopramide. Can Anaesth Soc J 1980; 27: 36-8. 7 AssafRAE, Clarke RSJ, Dundee JW, Samuel 10.

8

9

10

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Studies of the drugs given before anaesthesia XXIV: Metoclopramide with morphine and pethidine. Br J Anaesth 1974; 46:514-9. Ellis FR, Spence AA. Clinical trial of metoclopramide as an anliemetic in anaesthesia. Anaesthesia 1970; 25: 368-71. Shah ZP, Wilson J. An evaluation of metoclopramidc as an anticmetic in minor gynaecological surgery. Br J Anaesth 1972; 44: 865-7. Korttila K, Kauste A, Auvinen J. Comparison of domperidone and metoclopramide in the prevention and treatment of nausea and vomiting after balanced general anaesthesia. Anesth Analg 1979; 58: 396-400. Kris MG, Tyson LB, Gralla RJ et al. Extrapyramidal reactions with high dose metoclopramide. N Engl J Med 1983; 309: 433.

CANADIAN ANAESTHETISTS' SOCIETY JOURNAL

three minutes, the child again reacted to the needle and then started coughing on the endotracheal tube. The smell of halothane from the fresh gas line was barely discemable. Since the child had been satisfactorily anaesthetized initially it was assumed that a fault had developed in the vapourizer and that this had produced the audible click. The anaesthetic was completed uneventfully using methoxyflurane. When the Fluotec Mark II vapourizer was examined after the case, it was found that the circlip had broken, cutting off the fresh gas flow through the vapourizer. J.R. Maltby MB FRCP(C) Department of Anaesthesia Foothills Hospital at the University of Calgary Calgary, Alberta REFERENCE

1 Lamberty JM, Lerman J. Intraoperative failure

of a Fluotee Mark 11 vapourizer. Can Anaesth Soc J 1984; 31: 687-9.

Intraoperative failure of a Fluotec Mark H Nitrous oxide analgesia and the vapourizer endogenous opioid system To the Editor: The description by Lamberty and Lerman I of the intraoperative breaking of the internal circlip of a Fluotec Mark II vapourizer is most interesting. A similar case occurred in our hospital in 1970. A two-year-old boy was scheduled for pneumoencephalogram under general anaesthesia. An inhalation induction was performed with nitrous oxide and halothane using a Jackson Rees circuit. Tracheal intubation was easy and did not cause coughing. Nitrous oxide was discontinued and the halothane concentration reduced from four to two per cent. A distinct click was heard from the direction of the anaesthetic machine. There was no obvious cause for this and the child was positioned for lumbar puncture. When the radiologist attempted the lumbar puncture the child reacted to the needle. The vapourizer dial was returned to four per cent but, after inhaling this higher concentration for two to

To the Editor: We read with interest the review by Milne and Jhamandas concerning new therapeutic roles for naloxone, i We would like to extend the scope of their article by referring to some of our own work using nitrous oxide. Firstly, as we have noticed in many cases, as with this review,1 anaesthesia and analgesia are lumped together, without any clear differentiation being made between these very different states. This probably adds to the controversy regarding the opioid effects of analgesic concentrations of nitrous oxide. During administration of nitrous oxide at analgesic concentration, the level of consciousness of the subject is such that full contact with the environment and co-operation with the investigator

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CORRESPONDENCE is possible. 2 This is of course not the case where anaesthetic concentrations of nitrous oxide are used, in which case the subject is rendered unconscious. In view of the considerable physiological differences found in the analgesic and anaesthetic states, it is conceivable and even likely that these two states may be caused by entirely different underlying mechanisms. For this reason it is vital to differentiate between analgesia and anaesthesia when comparing studies. This is particularly important when one is looking at the underlying pharmacological mechanisms which might be responsible for these two so different states. Furthermore, it is doubtful whether the mechanism of nitrous oxide analgesia or anaesthesia involves the release of endorphins because titres of these substances are not raised in the CSF 3 or discrete brain areas. 4 Since analgesic concentrations of nitrous oxide displace both tritiated dehydromorphine s and naloxone 6 at in vitro radioactive binding sites, there is now good evidence indicating the interaction of nitrous oxide with the mu opioid receptor. In vivo studies in which naloxone influences nitrous oxide analgesic responses in man add further support to the concept that nitrous oxide is an opioid receptor agonist. 2'7 M.A. Gillman F.J. Lichtigfeld South African Brain Research institute 8 Highlands House 173 Louis Botha Ave. Orange Grove, 2192, South Africa

In: Endogenous opiate agonists and antagonists, ed.

E.L. Way. Pergamon Press 1980; pp. 51-5. Daras C, CantrilI RC, Gillman MA. (3H) naloxone displacement: evidence for nitrous oxide as opioid receptor agonist. Europ I Pharmacol 1983; 89: 177-8. Gillman MA, LichtigfeM FJ. Comparison of the effects of morphine sulphate and nitrous oxide analgesia on chronic pain states in man. J Neurol Sci 1981; 49: 41-5.

Doppler crystal fixation with double-

stick discs For the past several years we have used the ultrasonic Doppler Flow Detector | to determine systolic blood pressure during anaesthesia. The main problem has been in maintaining the position of the Doppler crystal over the radial artery. In the past the crystal has been routinely fixed over the radial artery with stretch adhesive after the application of ultrasonic gel. However, frequently the signal is lost in spite of an adequate blood pressure, soon after surgery has begun. On reexamination of the crystal it is often noted that it had shifted slightly and therefore the pulse is no longer audible. The repositioning is often difficult once surgery has begun. We have routinely used double-stick discs for

REFERENCES

1 Milne B, Jhamandas K. Naloxone: New therapeutic

roles. Can Anaesth Soc J 1984; 31: 272-8. 2 Gillman MA, Kok L, Lichtigfeld FJ. Paradoxical

effect of naloxone on nitrous oxide in man. Europ J Pharm 1980; 61: 175-7. 3 Morris B, Livingston A. Effect of nitrous oxide: exposure on met-enkephalin levels in discrete areas of rat brain. Neuroscience Letters 1984; 45:1 I - 14. 4 Way WL, Hosobuchi Y, Johnson BH, Eger E1 H, Bloom FE. Anesthesia does not increase opioid

peptides in cerebrospinal fluid of humans. Anesthesiology 1984; 60: 45. 5 Ahmed MS, Byrne WL. Opiate receptor binding studies in influence of a reversible sulfhydryl reagent.

FIGURE 1 Doublestick disc applied over radial artery.