Vital capacity rapid inhalation induction technique: comparison of sevoflurane and halothane

Masaki Yurino MDPhl) 0 Hitomi Kirnura 0 0 From the Asahikawa Medical College, Department of Anaesthesia , 4-5-3-11,Nishikagura, Asahikawa-city,Hokkaido 078, Japan . College , Department of Anaesthesia , 4-5-3-11 Nishikagura, Asahikawa-city, Hokkaido 078, Japan . Acceptedfor publication 30th April , 1991 Induction o f anaesthesia using the vital capacity rapid inhalation induction (VCRI1) technique with either sevoflurane or halothane was compared. The induction time, characteristics, and acceptability were assessed. Thirty-two volunteers were given one o f the vapours: 17 received sevoflurane and 15 halothane. Subjects were unpremedicated and breathed approximately 2.6 minimum alveolar concentration (MAC) equivalent o f either agent. There were no differences in the patients' cardiovascular or respiratory variables. The mean time for induction o f anaesthesia with halothane (153 + 46 sec, SD) was slower than with sevoflurane (81 + 22 sec, SD, P < 0.05), reflecting its higher blood:gas solubility. There were fewer induction complications such as coughing and movement in the sevoflurane than in the halothane group. Subjects in the sevoflurane group found the smell o f anaesthetic more acceptable than those in the halothane group (65% vs 13%, respectively). Subjects in both groups had no objection to undergoing the procedure again. It is concluded that both halothane and sevoflurane are effective in VCRII o f anaesthesia without premedication. However, the slower speed o f induction with halothane frustrated the anaesthetist because o f the longer induction time, and may increase the chance o f pronounced excitatory phenomena occurring. Cette dtude compare l'induction ~ I'halothane d celle du sdvoflurane avec la technique d'induction rapide par inhalation jusqu'h la capacitd vitale. Trente-deux volontaires ontfait l'objet - de cette dpreuve et chacun d'eux a refu un des deux agents: 17 ont refu le sdvoflurane et 15, l~alothane. Non pr~m~diquds, ils ont inspir~ approximativement 2,6 fois l~quivalent de la concentration alvdolaire minimum (CAM) de l'un ou de l'autre des agents. II n'y avait de differences entre lesparambtres cardiovasculaires et respiratoires. La dur~e moyenne de l'induction de l'anesth~sie avec l'halothane (153 + 46 sec, SD) a dtd plus lente que celle produite par le s~voflurane (81 + 22 sec, SD, P < 0,05), ce qui reflbte son coefficient de solubilit$ sang:gaz plus dlev~. L~ncidence des complications telles que la toux et les mouvements a dt~ moindre avec s$voflurane qu'avec l~alothane. Les sujets du groupe sdvoflurane ont trouv~ son odeur plus acceptable que ceux de lhalothane (63% et 13% respectivement). Les sujets des deux groupes n'auraient pas eu dbbjection d r~pdter l~preuve. En conclusion, lhalothane et le s~voflurane se pr~tent tous deux d cette technique d'induction rapide. La lenteur de l'induction d lhalothane a dt~frustrante pour l'anesth~siste et pourrait augmenter l~ncidence des phdnombnes d'excitation. Two previous studies, in over 200 healthy volunteers, demonstrated the safety and acceptability of using the vital capacity rapid inhalation induction (VCRII) technique to induce anaesthesia with halothane and oxygen. 1,2 In 1986, Wilton and Thomas 3 modified the technique by using halothane in nitrous oxide and oxygen and confirmed, in 100 patients, the acceptability of the technique for rapid inhalation induction of anaesthesia. The VCRII technique has certain advantages over conventional inhalational or intravenous induction of anaesthesia, which include prompt induction without a prolonged excitatory phase, and full recovery without "hangover.'4 We assessed the use of the newly developed agent, sevoflurane, as an alternative to halothane for VCRII. Methods The study was approved by the Hospital Human Research Committee, and informed consent was obtained from each volunteer. Thirty-two healthy adult volunteers, who had no previous experience of anaesthesia induction, were randomly designated to receive either 4.5% sevof l u m e (S) or 2.0% halothane (H). These concentrations represent approximately 2.6 X minimum alveolar concentration (MAC) equivalent of each agent. Seventeen subjects were assigned to the S Group and 15 to the H Group. The selected inhalational agent, in oxygen, was delivered from an Ohmeda anaesthetic machine fitted with Ohmeda calibrated vaporisers and a circle system with an approximate volume of eight litres. In each experiment, the circle system was flushed with oxygen for more than four minutes at 8 L . min -] with the vaporiser set at the desired concentration. Excess gas was vented through the popoff valve and breathing hoses. Volunteers received no premedication and breathed air before induction of anaesthesia. They were instructed to breathe out to residual volume, their faces were covered by the mask connected to the primed circle system, and then they were asked to take a vital capacity breath (VCB) and to hold their breath for as long as they were comfortable. Following the VCB, the volunteers, through spontaneous respiration, were given the same anaesthetic mixture for up to five minutes. Then, they breathed oxygen until they regained consciousness. Loss of consciousness (LOC) was defined as failure to respond to the command "open your eyes." Commands were repeated at ten-second intervals until the subjects failed to respond. Induction time and the presence of excitatory phenomena were recorded by an independent observer. Induction time was defined as the interval from the time at which the subject's lung volume reached total lung capacity (the end of the vital capacity inspiration) until LOC Anaesthetic induction was defined as "complicated" if one or more of the five categories established by Lamberty occurred, s A single cough, laryngospasm, breath holding, movement of a limb, or excessive salivation (enough secretions to wet our hands) were recorded. As it is difficult to assess such observations objectively, the observer who was "blind" to the agent used, asked the subjects, immediately after emergence from anaesthesia, to recall how many commands they heard during induction of anaesthesia, to characterise the smell of the anaesthetic agent into three categories (pleasant: subjects liked, or did not mind smell, unpleasant: very pungent or not tolerable, no comment: others), and whether they would have any objection to undergoing VCRII again. Monitoring included an automatic noninvasive blood pressure recorder with an ECG oscilloscope, pulse oximeter (Colin, Japan) and multi-gas monitor (Datex, USA). The gas monitor was calibrated every day before Time from Start of Induction FIGURE End-tidalconcentration(ex/rendas MAC multiple)of sevotlurane(O) increasedmorerapidlywithVCRIIthan halothane(13). the experiment and three or four subjects were sequentially studied in a day. Respiratory gases were sampled from the elbow connector with the mask, at a flow rate of 150 ml. min -l, to monitor end-tida (...truncated)