SINGLE BREATH INDUCTION OF ANAESTHESIA WITH ISOFLURANE

Transcription

1 Br. J. Anaesth. (987), 59, SINGLE BREATH INDUCTION OF ANAESTHESIA WITH ISOFLURANE J. M. LAMBERTY AND I. H. WILSON Two studies have demonstrated that the induction of anaesthesia using a single breath of either halothane and oxygen alone (Ruffle et al., 9) or halothane, nitrous oxide and oxygen (Wilton and Thomas, 9) is effective, safe and acceptable to patients. However, as concern has been expressed recently over the dangers associated with repeated halothane anaesthesia (Editorial, 9a), we have assessed the suitability of isoflurane for use as an alternative to halothane in a single breath induction technique. PATIENTS AND METHODS Seventy-two patients (ASA grade I or II) aged between and 65 yr, who consented to an inhalation induction of anaesthesia, were divided randomly into a control group and single breath induction group. The patients were scheduled to undergo minor outpatient surgery under general anaesthesia. In the control group anaesthesia was induced via a Mapleson A breathing system, using an initial mixture of 0.5% isoflurane with 66% nitrous oxide in oxygen. A fresh gas flow of approximately 00 ml kg" was delivered through a calibrated vaporizer (Mark 3 Fluotec). The isoflurane was increased by 0.5 % after every fifth breath, unless some complication, such as coughing, warranted a modification of the technique. The maximum concentration of isoflurane was 4%. The single breath induction group inhaled a vital capacity breath of 2 % isoflurane with 66 % nitrous oxide in oxygen. This was administered SUMMARY This study has compared a single breath induction technique and a conventional inhalation induction technique using isoflurane in nitrous oxide and oxygen. Each group consisted of 36 unpremedicated patients. Single breath induction was associated with fewer problems on induction, but required more patient co-operation. Ninety-four percent of patients were willing to repeat the single breath induction technique, compared with 74% of patients receiving a conventional inhalation induction. from a modified Mapleson A breathing system to which an extra 2-litre reservoir bag had been added (fig. ). The choice of 2% isoflurane was initially empirical but, having been found to be satisfactory, was used throughout the study. The technique was explained to the patient who was then given a mask with a right-angled connector attached. After becoming familiar with breathing through the mask, the patient was asked to exhale fully whilst the breathing system was attached to the right-angled connector by the Fresh gas flow -/WV\ ww J. M. L A M B E R T Y, * M.B. B.S., F.F.A.R.C.S. J I. H. WlLSON, M.B. CH.B., F.F-AJJ.CS; Department of Anaesthesia, Freedom Fields Hospital, Plymouth PL4 8QQ. Accepted for Publication: May 7, 987. *Present address, for correspondence: The Sir Humphry Davy Department of Anaesthesia, Bristol Royal Infirmary, Bristol BS2 8HW. FIG.. Modified Mapleson A breathing system.

2 SINGLE BREATH INDUCTION OF ANAESTHESIA 25 anaesthetist. A fresh gas flow of not less than 8 litre min" and light thumb occlusion of the outlet of the breathing system were maintained to ensure both 2-litre bags were full, but not under tension. The patient was instructed to inhale fully and to hold the breath for as long as was comfortable. Following loss of consciousness, and after the development of regular breathing, the concentration of isoflurane was increased by 0.5 % every fifth breath to a maximum of 4%. Monitoring in both groups was identical: arterial pressure (Dinamap 5XT Critikon) and the ECG were recorded before induction, and then at 60-s intervals for 5 min after the loss of consciousness. We assessed an induction as complicated if one or more problems occurred. All problems could be categorized into one of the five groups shown in table II. As it is difficult to assess such observations objectively, we were very strict in our definition. We included a single cough, or movement of a limb; excessive salivation was recorded when our hands became wet. Usually the sequence of events was unequivocal, with excess salivation including coughing and breath-holding. We categorized patients' performance of the manoeuvres requested of them as good, moderate or poor. Good performance implied full compliance with the technique. Moderate performance was recorded when the patient did not fully comply with the instructions, for example by not taking a full vital capacity breath after maximum expiration but when induction was achieved satisfactorily. Poor performance was recorded when the patient was unable to complete the manoeuvres requested. Finally, when seen after operation, the patients were asked how they would describe the induction procedure, whether they would be willing to undergo a similar induction technique again, and how many breaths they remembered taking. Statistical analyses were carried out using the chi-square test, Fisher's exact test, and the Mann-Whitney U test, as appropriate. {n = 36) TABLE I. Demographic data of patients Males 9 2 Females 7 5 Median (mean) 36 (36.3) 32 (34.2) Age (yr) Range TABLE II. Incidence of complications during induction of anaesthesia. **P < 0.0 Induction Complicated Uncomplicated Coughing Laryngospasm Breath holding Movements Secretions Abandoned 8(50%) 8(50%) 8(22%) 8(8%) 9(25%) (30%) 8(22%) 7(9%)** 29 (8 %) 5(4%) (3%) 5(4%) between the two groups in table II. There were less complicated inductions in the single breath group. The most troublesome complications, coughing, laryngospasm and excessive salivation were also less common in the single breath induction group. Cardiovascular stability and the incidence and types of arrhythmia were similar in both groups (table III). Patients' performance of the single breath technique was inferior to the conventional inhalation technique. Conversely, patients preferred the single breath technique, and more of the patients in the single breath group indicated that they would be willing to have that induction technique repeated. When asked how many breaths they remembered taking before loss of consciousness, patients in the single breath group remembered taking significantly fewer breaths (table IV). RESULTS Anaesthesia was successfully induced by the selected technique in 35 patients in each group; one induction in each group had to be abandoned. The demographic data of the two groups are shown in table I. The most common complications of any inhalation technique are compared DISCUSSION Two studies have determined the safety and acceptability of using a single vital capacity breath of halothane in oxygen for the rapid induction of anaesthesia (Ruffle, Latta and Snider, 982;

3 26 BRITISH JOURNAL OF ANAESTHESIA TABLE III. Comparison of cardiovascular stability between techniques. Mean values (SD). -[Excludes abandoned inductions After induction (min) induction (n = 35f) Systolic pressure Diastolic pressure Heart rate (beat min" ) Arrhythmias (n = 35t) Systolic pressure Diastolic pressure Heart rate (beat min" ) Arrhythmias (9) 0 36 (6) () 82 (2) (2) (26) 35 (3) Atria! ectopic Nodal rhythrri Ventricular ectopics 3 32 (20) 87 (6) 88 3 (9) 92 (3) 29 (2) (2) Atria! ectopic Nodal rhythrri 27 (8) (2) (2) Ventricular ectopics 2 32 (24) (9) 80 (3) TABLB IV. Patient co-operation and acceptability. ^Excludes abandoned inductions. *P < 0.05; ***P < 0.00 Co-operation Good Fair Poor Same induction again? tyes No Breaths remembered (median)* 3(%) 4(%) (3%) 26(74%) 9(26%) 5 27(77%) 5(4%) 33(94%)* 2(6%) 2*** Ruffle et al., 9). These studies used healthy volunteers, and the authors used the technique successfully in more than 200 patients. In 9 Wilton and Thomas modified the technique by using halothane in nitrous oxide and oxygen. Their study of 00 patients again attested to the acceptability of the technique for the rapid induction of anaesthesia. The use of a single vital capacity breath technique for the rapid induction of and recovery from anaesthesia is particularly attractive for minor day-case, and accident and emergency, surgery. These patients will usually be unpremedicated and, therefore, at their most co-operative. The lack of premedication and the avoidance of an i.v. induction agent, should assure that the patient has the best chance of being alert in the postoperative period. The conclusions of a symposium on halothane and the liver have been reported (Blogg, 9; Editorial, 9a), and policy outlined by the Committee on Safety of Medicines (9). Another editorial in the Lancet (Editorial, 9b) acknowledged the advantages of a single breath technique, and emphasized again the problems associated with repeated halothane anaesthesia. We have assessed the suitability of isoflurane using the recently described single breath induction technique. We chose isoflurane rather than enflurane because a pilot study indicated that

4 SINGLE BREATH INDUCTION OF ANAESTHESIA 27 TABLE V. Vapour characteristics Isoflurane Enflurane Halothane Molecular weight MAC in oxygen Partition coefficients (37) Blood-gas Oil-gas Percentage biotransforraed % % % isoflurane was, surprisingly, acceptable to patients. Our clinical impression was that isoflurane would have been less acceptable because of its pungent odour, as in the case with conventional inhalation induction techniques (Pandit, Steude and Leach, 9). Pandit and colleagues have, however, suggested that isoflurane may become more acceptable for outpatient anaesthesia with the introduction of different techniques of induction. When the physical characteristics of the three vapours are compared, it is apparent that isoflurane should have a more rapid induction and emergence, and be less accumulative than the other two (table V). Isoflurane has a low percentage of biotransformation (0.2 %) and it has been suggested that the problems of pollution could be less than with the other vapours (Blogg, 9). Therefore, not only could isoflurane become a useful alternative to halothane when repeat anaesthesia is contemplated, it could also become the agent of choice for day-case surgery. However, when multibreath induction of anaesthesia with isoflurane has been used in outpatient anaesthesia, it has been found to be less satisfactory than halothane (Pandit, Steude and Leach, 9). Our study with isoflurane compared the two techniques of inhalation anaesthetic induction for complications and acceptability to patients. In our control group the findings confirm previous studies that isoflurane causes excitatory movements and an excessive amount of salivation, and that, although safe, it is less acceptable to both patient and anaesthetist than is halothane. This upper airway irritability (Jones, 9) has been attributed to the etheral odour of isoflurane (Editorial, 9b). In our single vital capacity breath group the complications were all less frequent than with a conventional induction (tables II, IV). The patients found the technique to be more acceptable, and 94% of them would have accepted the technique again. Although there was a greater incidence of moderate and poor compliance with the single breath technique in our study, than found by Wilton and Thomas, this did not reach statistical significance. The median number of breaths remembered by the single breath group was two, compared with five in the control group (table IV). The superiority of the single breath technique with isoflurane is surprising (Editorial, 9b), but may be explained by the low blood-gas solubility coefficient, causing the onset of anaesthesia to be relatively fast. The patient may pass through the conventional stages of light anaesthesia in much the same manner as occurs with i.v. induction agents. We believe that, with this technique of induction, isoflurane can be used more successfully for gaseous induction of anaesthesia. However, it should be noted that isoflurane is not superior to halothane for smoothness of induction, and had a higher complication rate when compared with the results of Wilton and Thomas. However, it is a reasonable alternative for the many situations in which halothane may be undesirable. The editorial in the Lancet (Editorial, 9b), suggested that the physical characteristics of isoflurane would lead to a prolonged and unsatisfactory single breath induction. Our study suggests that this is not so, and that a single breath induction with isoflurane is a practical alternative to halothane. In each group there was one patient in whom coughing and salivation were such that the technique had to be abandoned. In both patients the trachea was intubated subsequently to facilitate control of the airway. It was noted that both of these patients were smokers, and it is our clinical impression that possible difficulties on induction should be anticipated where there is coexistent upper airway irritability, whether from a recent upper respiratory tract infection or smoking, and that in these patients the single breath induction with isoflurane should not be attempted.

5 28 BRITISH JOURNAL OF ANAESTHESIA In conclusion, we believe that isoflurane is a useful alternative to halothane for use in a single vital capacity breath induction, when the latter agent is unsuitable. The use of isoflurane in daycase and casualty surgery is attractive and, when inhalation induction is planned, single breath induction is more acceptable to the patient. REFERENCES Blogg, C. E. (9) Halothane and the liver: the problem revisited and made obsolete. Br. Med. J., 292, 69. Committee on Safety of Medicines (9). Current Problems, 8,. Editorial (9a). Halothane associated liver damage. Lancet,, 25. Editorial (9b). Inhalations] induction of anaesthesia new inspiration? Lancet, 2,. Jones, R. M. (9). Recent Advances in Anaesthesia and Analgesia, vol. IS, p. 8. Edinburgh: Churchill Livingstone. Pandit, U. A., Steude, G. M., and Leach, A. B., (9). Induction and recovery characteristics of isoflurane and halothane anaesthesia for short outpatient operations in children. Anaesthesia, 40, 226. Ruffle, J. M., Latta, W. B., and Snider M. T. (982). Single breath halothane oxygen induction in man. Anesthesiology, 57, A46. Ruffle, J. M., Snider, M. T., Rosenberger, J. L., and Latta, W. B. (9). Rapid induction of halothane anaesthesia in man. Br. J. Anaesth., 57, 607. Wilton, N. C. T., and Thomas V. L. (9). Single breath induction of anaesthesia, using a vital capacity breath of halothane, nitrous oxide and oxygen. Anaesthesia, 4, 472.