general anaesthesia with halothane for surgical interventions and electrocorticography in cases of...

Acta anaesth. Scandinav. 1962, 6, 13-28.

GENERAL ANAESTHESIA WITH HALOTHANE FOR SURGICAL

INTERVENTIONS AND ELECTROCORTICOGRAPHY I N CASES OF FOCAL EPILEPSY

BY

E. GORDON and L. WIDEN

Until a few years ago the majority of intracranial operations were performed under local anaesthesia. The recent improvements in anaesthetic tech- niques and the availability of new drugs, as well as the greater number of skilled anaesthetists, however, have now made it possible to employ general anaesthesia in nearly all neurosurgical procedures and thereby solved many problems for both patient and surgeon.

Patients undergoing surgery for focal epilepsy, however, present special anaesthetic problems. General anaesthesia is generally considered undesirable in these cases for two reasons: (1) it may interfere with the electrical activity of the brain, and (2) it prevents communication with the patient. Therefore, in most neurosurgical clinics, the operative treatment of focal epilepsy is still carried out under local anaesthesia. In children and unco-operative, anxious and agitated adults, however, some form of general anaesthesia or at least heavy sedation is unavoidable.

Heavy premedication with barbiturates or opiates often causes respiratory depression and interferes with the electrical activity of the brain and should therrfore be avoided. Consequently, it was important to find an anaesthetic agent which does not suppress, or interfere with the interpretation of, the epileptogenic and other electrical activity. At the Neurosurgical Clinic at Serafimerlasarettet, various methods have been tried to attain this goal. At an early stage it was decided to abandon further attempts to find a form of combined regional and light general anaesthesia from which the patient could be roused for the electrocorticographic recording, and which permitted communication with him. General anaesthesia without intubation was considered too great a risk. The method described by W. PENFIELD and A. PASQUET (1954)16*14 for use in children and unco-operative adults, consisting of local anaesthesia

From the Department of Anaesthesia, Neurosurgical Clinic, and the Department of Clinical Neurophysiology, Serafimerlasarettet, Stockholm. The majority of the operations were performed by Professor Herbert Olivecrona. Received August 17, 1961.

14 E. GORDON AND L. WIDBN

combined with Pentothal anaesthesia, without intubation, during the initial stages of the operation and during electrographic recording, followed by blind nasal intubation after recording was completed, was not considered safe enough. Moreover, we as well as several earlier workers (for references see D. H. INCVAR et al. (1959)lO) have found that even short-acting barbiturates, such as Pento- thal@ and Thiogenalm have a profound effect on the electrogram, which tends to obscure focal abnormalities. Children, in particular, are very sensitive to barbiturates, and it can be extremely difficult to put them to sleep with doses small enough to prevent interference with the electrical activity. Even adult patients, however, may become so excited after small doses of barbiturates that it is necessary in all haste to deepen the level of anaesthesia with further doses, a measure which increases the difficulty of interpreting the electrogram.

D. H. INCVAR et al. (1959)’O described a form of anaesthesia consisting of regional anaesthesia in combination with nitrous oxide administered with 25 ?(, oxygen through an endotracheal tube. A perforated cuff on the tube permitted repeated administration of a local anaesthetic for the trachea. The administration of nitrous oxide was interrupted for periods of 10 to 30 minutes for electrocorticographic recording. During these periods the patient awakened, and it was possible to establish contact with him although he was unable to speak. The authors state that the effects of the nitrous oxide disappeared rapidly and “a stable, reactive electrical cortical pattern was then obtained” (cf. also D. S. BICKERS and L. RUMBLE (1958)2). This is in contradiction to the observation of H. JASPER (cited by A. PASQUET (1954)14) that after the administration of nitrous oxide in 65 7, concentration the electrical activity requires hours to return to normal. We have no systematic experience of this particular problem but it seems to us that, despite the convincing results of D. H. INGVAR et al., their method involves certain risks, the importance of which, especially in neurosurgery, should not be underestimated. To obtain a completely satisfactory anaesthesia during a long operation with nitrous oxide as the sole anaesthetic is exceedingly difficult, and the risk of an insidious hypoxia and carbon dioxide accumulation cannot, even in the hands of a skilled and experienced anaesthetist, be completely eliminated. Moreover, this method requires a certain degree of co-operation from the patient, which renders its use difficult in children and unco-operative adults.

RAVENT~S’ ( 1956)’’ report of a new volatile anaesthetic-Halothane-early aroused our interest in the use of this agent during surgical interventions and electrical recordings in patients with epilepsy. Despite the relatively short time that has elapsed since the discovery of Halothane, the literature contains a large number of detailed descriptions of the action and physical characteristics of this drug. I t is not our purpose to enter into a detailed discussion of these facts. We shall mention only those features which have a bearing on this study.

Halothane is a colourless, volatile liquid with a characteristic but not unpleasant odour. I t is non-inflammable and, when mixed with oxygen,

ELECTROCORTICOGRAPHY DURING HALOTHANE ANAESTHESIA 15

its vapours are not explosive. I t is stable when in contact with soda lime. From the point of view of this study, however, the most important characteristic of Halothane is its short action. Shortly after the withdrawal of the anaesthetic, the patient awakens, regardless of the duration of the anaesthesia, a characteristic which, along with its other properties, in our experience gives results superior to those of any other existing method.

Since December 1957, Halothane has been used in this Clinic as the prin- cipal anaesthetic in all neurosurgical procedures, including those for focal epilepsy with electrocorticography. The possibility of localising the focal (epileptogenic) abnormalities with electrocorticography and the therapeutic effects of the surgical interventions in this series of epileptics were at least as good as in earlier series operated upon under local anaesthesia.

C L I N I C AL M A T E R I A L

The present series consists of 46 patients (22 males and 24 females) with frequent epileptic seizures uncontrollable by large doses of anti-epileptic drugs of any kind. Two of the patients were operated upon twice. The age distribution is shown in table 1. A diagnosis of focal epilepsy accessible to operative treatment was made on the basis of focal changes in the EEG in all except three of the patients. Most of the patients had also seizures indicative of a focal cerebral lesion corresponding to the site of the EEG changes. In three patients the pre-operative EEG showed generalised abnormality (see table 2), but the clinical history and the type of seizure strongly suggested a focus in either temporal lobe.

TABLE 1 . Distribution of patients according to age.

NO. or patients

5-10 ......................... 3 11-15 ......................... 8 16-20 ......................... 10 21-30 ......................... 12 31-40 ......................... 7 41-50 ......................... 5 51-60 ......................... 1

Total.. ....................... 46 -

Patients with epilepsy in whom radiography revealed a lesion, such as a brain tumour or an arteriovenous aneurysm, since electrocorticography is not performed in these cases.

gross anatomical are not included,

16 E. GORDON AND L. W I D ~ N

In nine of the patients, operation disclosed a localised macroscopic abnormality; an astrocytoma in two, a “cortical scar” in six (in two of known post- traumatic origin and in two following an earlier operation for tumour and abscess, respectively), and an arteriovenous aneurysm in the meninges over- lying the epileptic focus in one. In the remaining patients, no definite structural abnormality was found at operation, but microscopic examination of the removed tissue disclosed variable degrees of gliosis in 12, and pyknosis with a reduction of the number of ganglion cells in 22. In two patients no abnormality was found, and in one biopsy was not performed. It should be pointed out that the histological examinations were very incomplete ; the hippocampus, for example, was usually not examined.

M E T H O D S

Premeditation.-All patients were given an intramuscular injection of 0.25-0.75 mg atropine and 25-50 mg pethidine, according to age and sex, one hour before the operation.

Anaesthesia.-Induction was accomplished by intravenous injection of 200-400 mg of 5 % Pentothal solution in a single dose, the effect of which had in all probability disappeared at the time of electrical recording, 60 to 90 minutes after induction. Succinylcholine (30-50 mg) was then given intra- venously and the trachea and larynx were sprayed with 4% Xylocain”, followed by endotracheal intubation with a flexometallic tube. The tube was connected to a Ruben non-rebreathing valve and a semi-closed system, the so-called Magill attachment. In young children, usually those under 8 years of age, Ayre’s “T” piece was substituted for the Ruben valve and Magill’s attachment. Anaesthesia was maintained by the administration of 0.25-1 yo Halothane with equal concentrations of nitrous oxide and oxygen or, in three cases, pure oxygen.*) A gas flow of 8 to 10 litres per minute was used in adults and about 6 litres per minute in children.

Before commencing the operation the line of proposed incision on the scalp was locally infiltrated with 1 yo procaine with adrenaline.

EEG examinations.-The 46 patients underwent a total of 137 pre-operative EEG examinations, including hyperventilation, and photic stimulation. Sphenoidal leads were used in 20 instances, and chlorpromazine activation (L. F. STEWART ( 1957)21 in 15. In 26 patients a pre-operative EEG was recorded during all stages of Halothane anaesthesia. Twenty-one electrodes were used. The electrode placements and recording technique were in accordance with the recommendations of the Committee on Methods of Clinical Examination in Electro-encephalography ( 1958)18. Recording was done with an 8 or 16 channel

*) The presence of nitrous oxide (in this concentration) had no detectable effect on the electrocorticogram. When pure oxygen was used, a slightly higher Halothane concentration was necessary.


Grass electro-encephalograph. A focus was seen in the anterior temporal region in 34 patients, posterior temporal in one, anterior frontal in onej posterior frontal in three, parietal in one, and the sensory motor region in six.

Electrocorticographic procedure.-The recording technique was conventional (see W. PENFIELD and H. JASPER (1954)'s). The recording equipment consisted of a Grass cortical electrode assembly and a 6 or 8 channel Grass EEG instrument. "Wick" electrodes were used for recording from the surface of the cortex and specially designed depth electrodes for recording from the tip, lower surface and depths of the temporal lobe.

The Halothane and nitrous oxide administration was generally interrupted about 5 minutes before the recording commenced and withheld for a period of 5 to 20 minutes. In patients in whom a longer exploration was necessary, Halothane was sometimes given for a few minutes at intervals of 5 to 10 minutes. This method seems preferable to the administration of succinylcholine for the prevention of movements on the part of the patient. In some of the patients on whom succinylcholine was tried, it appeared to influence the electrogram, in some instances increasing the amount of slow activity and in others tending to mask the focal abnormalities present. To our knowledge, these central effects of succinylcholine have not earlier been described and will form the subject of a later study. When the epileptogenic area had been mapped out, the anaesthesia was resumed until further recording was necessary to check that all epileptogenic tissue had been removed.

R E S U L T S

General anaesthetic considerations.-During Halothane anaesthesia the patient's breathing was quiet and regular, the pulse rate and blood pressure were slightly lower than normal, but remained at an almost constant level throughout the operation, even when Halothane was interrupted for electrographic recording. A remarkable feature is that although the patients were fully awake or under a very superfical level of anaesthesia during the recording, they moved very little and were completely amnesic for the entire procedure. Coughing and bucking on the endotracheal tube were rare, factors of extreme importance once the dura has been opened. There was no brain oedema or excessive bleeding during the Halothane anaesthesia, which is in good agreement with observations made during other intracranial interventions with this form of anaesthesia.

Postoperative vomiting was rare. The patient wakened a few minutes after extubation, readily answered questions and obeyed instructions, e.g. to move his limbs, which rendered it possible to check the presence or absence of vital signs and symptoms. If left alone they willingly fell asleep or into a state of drowsiness, from which they could easily be roused.

18 E. GORDON AND L. WIDBN

From the anaesthesiologic point of view, the postoperative treatment presents no problems.

Effects on the EEG.-The 26 patients in whom a pre-operative EEG was taken before, during and after Halothane anaesthesia (stage 111, plane 3, Guedel's classification) presented good opportunities for studying the influence of Halothane on the EEG in general, and on focal epileptic and non-epileptic abnormalities in particular, during the various phases of the anaesthesia. Premedication and anaesthesia were the same as for operation, except that pentothal was omitted and anaesthesia was administered through a face mask instead of an endotracheal tube.

At a very early stage, generally within 30 to 60 seconds, after the commence- ment of the anaesthesia, the normal rhythms disappeared and were substituted by 12-16 cycles per second activity of moderate amplitude, diffusely distributed in all scalp leads.*) I t could also be picked up in the sphenoidal leads. Focal epileptogenic discharges, when present at the beginning of the anaesthesia, generally tended to diminish and often disappeared completely. This also applied to slow focal activity. I t is quite possible that the reaction and sensitivity of focal abnormal activity is, to some extent, dependent on the type and site of the activity, but no overt differences or relationships were found in this rather limited patient material.

As the anaesthesia deepened (beyond plane 1 of stage 111), the high- frequency activity decreased and was replaced by irregular slow activity (cf. E. A. GAIN and S. G. PALETZ (1957)s).

The effects of Halothane anaesthesia rapidly disappeared after its withdrawal. Within one or two minutes the slow wave activity faded and fast activity appeared. After a further one to three minutes, most of the fast activity had disappeared and the EEG pattern was similar to that characterising the waking or slightly drowsy state; focal abnormalities reappeared and were often very pronounced. Despite the appearance of the EEG, the patient was clearly somnolent; he reacted to sensory stimulation and answered to his name, but was disoriented and usually slightly euphoric. This state lasted for a period of some minutes, for which the patient appeared to be amnesic.

As will appear from the foregoing, the focal (epileptogenic) abnormalities generally diminished or disappeared at a very early stage of the anaesthesia, but reappeared when the patient was wakening, even if sometimes he still appeared to be at a deeper level of anaesthesia than when the focal discharges disappeared. In two patients, a focal epileptogenic abnormality, not present in the pre-anaesthetic record, appeared when the patient was wakening but was still under the influence of the drug (fig. 1). In these patients Halothane

*) It has long been known that fast cortical rhythms appear in the earlier stages of anaesthesia induced by volatile agents (E. D. ADRIAN and D. H. C. MATTHEWS (1934)', F. BREMER ( 1935)a) and the mechanism of their production has been repeatedly studied (see e.g. G . F. Ross1 and A. ZIRONDOLI (1955)1°, J. SCHLAC and H. BRAND (1958)m).


3

1

Fig. -P.R., female, age1 20

EEG. A, Before administration of ; Halothane, showing slight gene- 6

ralised abnormality and focal 7 slow waves over the right tem-

poral region. B, During the early 8 stages of anaesthesia, showing

diffusely spread 15-20 c/s activity, predominant over the left hemisphere, and considerable de- crease in the amount of slow activity over the right temporal

2 2 area. C, Approximately 5 minutes after withdrawal of Halothane,

3

and a right-sided abnormality

waves in the anterior temporal region.

5 c_y_ K- - years. EJects of Halothane on the

I. . - - - Y

C d

WCC the fast waves have disappeared

b - - - - -

5

has appeared with focal sharp - -

5

7

0

20 E. GORDON AND L. WIDEN

2

6 7-

.4.--4- 8 v-k.+h*-

, lsec. , IlOOpV Fig. 2.-L. L., female, aged 19 years. Agvrnmetry of “Halothane activily.” The pre-anaesthetic EEG showed a sharp wave focus in the right anterior temporal area. During the early stage of anaesthesia (see figure) this was substituted by fast (14-18 c/s) activity which,

however, is of much lower amplitude in the right temporal area than in the left.

acted as a “sleep activator” (cf. e.g. E. L. GIBBS and F. A. GIBBS (1947)’, B. FUSTER et al. ( 1948)5, P. GLOOR et al. ( 1958)8).

In 10 patients the fast Halothane activity was asymmetrical and definitely less prominant in leads over the hemisphere ipsilateral to the focus, particularly over the focal area (figs. 1 B and 2), a phenomenon analogous to the asymmetry of the fast pentothal activity described, among others, by G. PAMPICLIONE (1952)13, B. FUSTER (1953)4, and W. A. KENNEDY and D. HILL (1958)”. In seven of these patients the epileptogenic focus was in the anterior temporal region, and in three in the sensory motor area. One patient had an astrocytoma, and one had macroscopic cortical atrophy. The other eight patients had only microscopic changes.

Electrocorticogrulhy.-As shown in table 2, the electrocorticographic (ECoG) findings were in good agreement with the pre-operative EEG findings. The EEG classification in each case was generally based on more than one EEG examination, in some on five to seven recordings. If only one of the records showed a focal abnormality, the EEG was classified as focal.


TABLE 2. Comparison between the pre-operative EEG and the ECoG in 48 operations on 46 patients.

1 Generalised 1 Generalised 1 Focal 1 Focal 1 non-specific epileptogenic non-specific epileptogenic Total

EEG . . . . . . . . . . . . . 2 1 4 411) 48 ECoG . . . . . . . . . . . . 1 - 2 45**) 48

*) One of these was classified as "focal non-specific" in the ECoC at operation. ''1 The pre-operative EEG was classified as generalised abnormality in two (epileptogenic in one, and non-

specific in one), and focal non-specific in three.

In five patients, the ECoG revealed a focal epileptic activity not present in the pre-operative EEG. In three of these, the EEG showed a focal abnormality, but no activity characteristic of epilepsy (i.e. no spikes, sharp waves, or spike- and-wave activity), and in one patient, a paroxysmal, bilaterally synchronous epileptic activity (irregular, slow spike-and-wave discharges) with a maximum over the posterior temporal regions and slight right-sided predominance. In this patient operation revealed a large, old brain contusion in the posterior

Fig. 3.-G.A., male, aged 18 years. Electrocorticogram 2 to 3 minutes after interruption of Halothane anaesthesia, showing a continuous focal discharge of high-voltage spikes and slow waves from the anterior parts of the superior temporal gyrus, against a background

of remaining 12-14 c/s "Halothane activity."


part of the right temporal lobe. This area was excised under ECoG control. The postoperative EEG showed no epileptic activity on either the right or the left side.

In every case in which the pre-operative EEG showed a focal abnormality, this was recorded also in the ECoG. In one of the patients with a focal EEG abnormality consisting of mixed sharp and slow waves, however, the ECoG showed only focal slow wave activity.

Figures 3 to 5 illustrate some typical electrocorticographic findings in patients anaesthetised with Halothane. In figure 3, recorded 2 to 3 minutes after interruption of the anaesthesia, there is still some fast Halothane activity in the temporal areas, but a continuous focal discharge of high-voltage spikes and slow waves is recorded from the anterior parts of the superior temporal gyrus.

4-5

7-0 +

Fig. 4.-G. Z., male, aged 17 years. Electrocorticogram 5 minutes after interruption of Halothane anaesthesia, showing focal sharp waves and slow activity recorded from a depth electrode (6) in the region of the anterior hippocampus. Some spiking is also seen from the tip of the temporal lobe (electrode 1). The fast activity from the central region is beta

activity and not due to the Halothane anaesthesia.


Fig. 5.-O.S., male, aged 60 years. Electrocorticogram 3 to 4 minutes after interruption of Halothane anaesthesia, showing focal high-voltage sharp waves and slow activity from the meditemporal convolution (electrodes 2 and 3). An astrocytoma (grade 1-11) was

found in this area.

Figure 4, recorded from a depth electrode (insulated except for the tip) inserted through the meditemporal gyrus towards the anterior region of the hippocampus, shows a continuous, irregular, slow activity mixed with spikes and sharp waves. Some spike activity is also picked up from an electrode on the tip of the temporal lobe. The fast activity from the electrodes in the central region was in all probability not due to the Halothane anaesthesia; it persisted unchanged throughout the period of recording and was confined to the Rolandic area. The pre-operative EEG also contained a large amount of “beta” activity.

Figure 5, recorded 3 to 4 minutes after interruption of the anaesthesia, shows sharp waves and slow activity from electrodes (2 and 3) over the meditemporal gyrus. This area was pale and the gyrus was slightly broader than normal and somewhat hard on palpation. A diagnosis of astrocytoma was made and confirmed by histological examination.

Comparison of Results of Operations under Local and General Anaesthsia In order to determine whether the therapeutic effects of the operation

were influenced by the type of anaesthesia used, a comparison was made between 25 randomly selected patients operated upon under local anaesthesia and 25 patients operated upon under Halothane anaesthesia. The comparison was based on follow-up reports from the patients or their relatives one year


TABLE 3. Comparison of clinical results of operations under local and Halothane anaesthesia. 1 No 1 Considerable1 Slight 1 No 1

seizures improvement improvement change Total

Local anaesthesia.. . . . . . . . . . . . 7 3 9 6 25 General (Halothane)

anaesthesia.. . . . . . . . . . . . . . . 9 8 6 2 25

TABLE 4. Comparison of postopcrative EEG between patients opcrated upon under local and Halo-

thane anaesthesia.

r

Epileptogenic activity

Absent 1 Decreased I Unchanged 1 Increased Total ~~ ~-

Local anaesthesia.. . . . . . . . . . . . 13 8 15 1 37 General (Halothane)

anaesthesia.. . . . . . . . . . . . . . . 22 7 6 2 37

or more after the operation. As will be seen from table 3, the clinical results in the two groups showed no significant difference.

A comparison was also made between the postoperative EEG records of 37 patients in each group, based on the amount of focal epileptogenic changes present as compared with the pre-operative EEG. Table 4 shows that the number of “improved” records was slightly higher in the Halothane group. The series is too small, however, for the diffkrence to be significant.

DISCUSSION

The results show that focal epileptogenic abnormalitites present in the waking EEG record disappear during deep Halothane anaesthesia, but reappear within 2 to 3 minutes after its withdrawal. In the present series, good agreement was found between the electrocorticographic findings during operations performed under Halothane anaesthesia and the pre-operative EEG findings. Thus, from the electrophysiological point of view, this form of anaesthesia raises no objections; with the technique used, it does not reduce the possibility of accurately localising an epileptogenic focus. Some evidence is also provided that the chances of finding an active epileptogenic focus are greater when the patient is wakening from the anaesthetic than when he is awake. This is to be expected with focal abnormalities that are sensitive to arousal (C-L. Lr,


H. JASPER and L. HENDERSON (1952)’2) and accordingly may be expected to be blocked in the alert patient under local anaesthesia. This blocking effect has been assumed to affect chiefly discharges projected to the cortex from the diencephalon or brain stem. Since, however, the discharges from a cortical epileptogenic focus may not be spontaneous, but abnormally exaggerated responses to corticopetal impulses, it is reasonable to expect that a focus would be less active in the alert state under local anaesthesia, with its supposed “inhibition” of ascending impulses (cf. K.-E. HACBARTH and S. HOJEBERC (1957) O), than in the postanaesthetic drowsy state.

It may be argued that the use of general anaesthesia implies “chemical dissection” of the nervous system, permitting function of only the simplest and most strongly activated pathways, which carries with it the risk of missing foci that are less active but important for the patient’s symptoms. In our experience, however, there is no difference in the location and distribution of focal epileptogenic activity between the EEG recorded in the waking state and that recorded in the drowsy state following withdrawal of Halothane anaesthesia, even though the focus may be more active in the latter state (cf. B. FUSTER 1953)4). Furthermore, the postoperative results with respect to improvement in the clinical status and the EEG records were at least as good in patients operated upon under Halothane anaesthesia as in those operated upon under local anaesthesia. Admittedly, the two series are too small to permit a detailed evaluation of the results, and the clinical follow-ups are based on the written reports of the patients or their relatives, but if Halothane anaesthesia involved the risk of systematic errors in electrocorticographic diagnosis, this fact would have been reflected in the clinical results.

From the technical-surgical point of view, no adverse effects of the Halothane anaesthesia have been reported from our colleagues in the Neurosurgical Clinic. As mentioned earlier, Halothane anaesthesia is used for practically all neurosurgical procedures in this hospital. An overt disadvantage of the method is that it prevents communication with a conscious patient. The co- operation of the patient is necessary in any attempt to delineate the epileptogenic area by electrical stimulation in the hope of reproducing the characteristic auras in patients prone to such phenomena. The value of this method, however, is somewhat limited by more or less unpredictable factors, such as spread of after-discharge, refractory state, distant response, hyperstimul- ability, hypostimulability and the effects of repeated stimulation (W. PENFIELD and H. JASPER (1954)’s).

Although the compilation and analysis of the results of large series of cranial operations in which cortical stimulation was systematically employed- as performed by the Montreal school-have contributed greatly to our knowledge of brain function, this method does not appear to be indispensable for the successful surgical treatment of focal epilepsy, an opinion shared by G. VOURC’H et al. ( 1957)22). At least, the therapeutic results obtained in this Clinic do not


appear to differ significantly from those of other clinics where electrical stimulation is a routine procedure.

On the other hand, the co-operation and alertness of the patient may be necessary while the surgeon is tentatively interfering with functionally important brain areas, for example, areas of speech representation or the precentral motor cortex. In such cases local anaesthesia may still be necessary, but in most other cases general anaesthesia with Halothane seems to us to be preferable, especially since the patient is spared unnecessary anxiety and discomfort, and the pain which is sometimes unavoidable in operations performed under local anaesthesia.

S U M M A R Y

1. A method of general anaesthesia with Halothane which does not depress the electrographic evidence of epileptic abnormality is described.

2. In 26 patients a pre-operative EEG was recorded before, during and after Halothane anaesthesia. Focal epileptogenic abnormalities which were present in the waking EEG record disappeared during the early and deep stages of the anaesthesia, but reappeared within 2 to 5 minutes after its withdrawal, when the patient was wakening but still in the drowsy state.

3. Halothane anaesthesia was employed in 48 operations, with electrocorticography, performed on 46 patients with focal epilepsy. The electrocorticographic findings were in good agreement with the pre-operative EEG findings.

4. The therapeutic effects of the operations on the clinical symptoms and EEG in this group of patients operated upon under Halothane anaesthesia and in a group operated upon unaer local anaesthesia showed no significant differences.

5. The results are discussed with special reference to possible disadvantages of the method. It is concluded that Halothane is the anaesthesia of choice for the surgical treatment of most cases of focal epilepsy.

c

Z U S A M M E N FAS S U N G

1. Es wird eine Narkosemethode mit Halothan beschrieben, die nicht die abnormen elektrographischen Zeichem der Epilepsie verwischt.

2. Bei 26 Patienten wurde vor, wahrend und nach der Halothannarkose ein praeoperatives EEG aufgezeichnet. Die im Wach-EEG aufscheinenden Abnormalitaten der Fokalepilepsie verschwanden in oberflachlichen und tie- fen Stadien der Anaesthesie, traten aber innerhalb von 2-5 Minuten nach Ab- setzen des Mittels, wahrend der Patient beim Aufwachen jedoch noch einem schlafrigen Zustand war wieder auf.

ELECTROCORTICOGRAPHY DURING HALOTHANE ANAESTIIESIA 27

3. Halothannarkose wurde bei 48 Operationen mit Elektrocorticographie, an 46 Patienten mit fokaler Epilepsie, angewendet. Die Befunde der Elektro- kortikographie stimmten mit dem praeoperativen EEG-Befunden gut uberein.

4. Der therapeutische Effekt der Operationen auf die klinischen Symptome und das EEG zeigte keinen auffalligen Unterschied zwischen der Gruppe von Patienten, die in Halothannarkose und einer anderen, die in Lokalanaesthesie operiert wurde.

5. Die Ergebnisse werden besonders im Hinblick auf die moglichen Nach- teile dieser Methode diskutiert. Es wird der Schluss gezogen, dass Halothan die Narkose der Wahl fur die chirurgische Behandlung der meisten Faille fokaler Epilepsie darstellt.

During the first part of this work, Halothane (Fluothane@) was kindly supplied by MEDA, of Gothenburg, Sweden.

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