The anaesthetic management of 350 consecutive patients with congenital hypertrophic pyloric stenosis over an 8-year period is reviewed. The anaesthetic technique is discussed and the complications encountered reviewed. The morbidity rate was 15.9%. The anaesthetic related morbidity rate was 3.7%. One patient in the series died (0.27%) 8 weeks after pyloromyotomy, as a result of an underlying myopathy.

A method is described for the direct determination of the volatile anaesthetics halothane and isoflurane in blood by gas chromatography with flame-ionisation detection. The method is accurate and precise and allows rapid measurements of blood levels of anaesthetic agents. Headspace concentrations of anaesthetic agents in the concentration range 0-3% V/V are determined with an accuracy of +/- 0.01% V/V. The relative standard deviation of these results is less than 4.0%. A relatively small volume of blood is required for each determination, a factor of great significance in the treatment of children. The need for separate blood calibration graphs for each patient is discussed, further emphasising the need for a rapid calibration procedure. The results from the clinical application of this method show conclusively its suitability for the management of anaesthetised subjects.

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The effect of changing the composition of the carrier gas from 66% nitrous oxide in oxygen to 100% oxygen was examined in three halothane vaporizers (Fluotec Mk 3, Drager Vapor 19 and Abingdon halothane vaporizer). All showed a transient increase in output following the discontinuation of the nitrous oxide. The effect was minor (2-8% of indicated output) and short-lived (1-4 min) at the fresh gas flows used. The steady-state output of the vaporizers, once the transient response was over, was found to be lower with 100% oxygen as carrier gas than it had been with 66% nitrous oxide in oxygen. The difference was minor in the case of the Drager Vapor 19 (1% of indicated output) and Fluotec Mk 3 (5% of indicated output), but greater in the case of the Abingdon (15% of indicated output).

The characteristics of induction with and recovery from isoflurane anaesthesia were studied in 248 children. The mean time to loss of consciousness was 1.5 min (SD 0.5). Tracheal intubation. without interruption ofspontaneous ventilation, was accomplished in a mean time of 4.2 min (SD 54 seconds). Movement andexcitement, of 20-30 secondr duration. occurred in 23.9% children and22patients coughed during induction; 15 (12.6%) during the first 124 inductions; 7 (5.6%) subsequently. The mean hawtimes of reduction of alveolar isoflurane concentrations in 28 children whose lungs were ventilated with isoflurane and in 13 children who breathed isoflurane spontaneously during anaesthesia were: 45 sec after exposure for one hour, 70 sec after exposure of 2-3 hours and 110 second following exposures of 4-8 hours. The mean recovery times of the three groups were 6.5, 9.5 and 11.5 min respectively. In two further groups of nine children the mean h a y times of elimination of halothane and isoflurane were 220 secondr and 54 secondr respectively; recovery from isojlurane was markedly faster.Isoflurane is well accepted by children; induction is more rapid than with halothane, and the markedflexibility in the control of its efl'ects are due to its relative insolubility. It has wide application in paediatric anaesthesia.

SummaryThe mathematical relationship between peak ventilator breathing system pressure displayed on the digital meter of

The effects of the withdrawal of nitrous oxide from the inspired gas mixture were studied in 10 spontaneously breathing children during nitrous oxide-halothane anaesthesia, before and during surgery, using a computerized system for the measurement, recording and analysis of data. Before surgery the decline in the alveolar nitrous oxide concentration was associated with an increase in minute ventilation (32.7%, P less than 0.05), and a decrease in alveolar carbon dioxide concentration (8.4%, P less than 0.05). These effects were produced solely by an increase in tidal volume (42.7%, P less than 0.001), as no significant change in respiratory rate was observed. The hypoventilation produced by an alveolar mixture of 60% nitrous oxide and 0.9% halothane, a reduction of VE by 50%, exceeded the hypoventilation caused by 0.9% halothane alone, which reduced VE by 36.6%; and the hypoventilation produced by nitrous oxide and halothane was rapidly reversed by the withdrawal of nitrous oxide from the inspired gas mixture. During surgery all indices of ventilation were stimulated, and there was greater variability of response, but the pattern and degree of change in response to nitrous elimination, VE increased by 33.3%, VT by 33.8%, closely resembled the changes before surgery. Five children had received papaveretum as premedication, and five thiopentone per rectum; the depression of carbon dioxide responsiveness was more severe in the group who received papaveretum, and their responses to nitrous oxide elimination were less than, and occurred later than the responses in the group given thiopentone.

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