N E U R O L E P T A N A L G E S I A F O R C E R E B R A L B L O O D F L O W S T U D I E S I N P A T I E N T S

U N D E R G O I N G C A R O T I D L I G A T I O N

JOHN BARKER and W. BRYAN JENNETT

Neuroleptanalgesia has been recommended for certain surgical procedures, hitherto carried out under local anaesthesia alone or with other forms of sedation. Brown (1964) has reported a series of stereotaxic operations for Parkinsonism for which procedure a patient should be both tranquil and yet, when required, able to obey commands and carry out movements. He also stressed the need for analgesia since these patients have to lie for a considerable period on a hard operating table and to wear uncomfortable apparatus. Neuroleptanalgesia is also reported not to disturb the electrocardiogram and so to be suitable for open operations on the cerebral cortex for epilepsy as an adjunct to local anaesthesia.

We have been concerned with the measurement of cerebral blood flow during trial periods of carotid occlusion prior to carotid ligation (for ruptured aneurysms) under local anaesthesia. The radio-active inert gas clearance method is used which depends on an intracarotid injection of Xenon133 and then following the rate of decay of gamma emission detected through the intact skull using a collimated scintillation crystal; the head must be held still for ten to fifteen minutes during this counting period and the PaCO, must be kept constant if assessments of cerebral blood flow are to be comparable. The Xenon133 is excreted by the lungs and in order to carry this effluent away from the counting area and way from the theatre where personnel are exposed, the expired gases are led out of the theatre through a wide bore tube attached to the expiratory limb of a special mask. This is a modified Airline Pilot’s mask (Ledingham et al. 1965) and is a considerable discomfort to wear in the recumbent posture under a canopy of sterile drapes. The operative procedure involves retraction and manipulation about the trachea with inevitable apprehension about choking even although no pain should be felt if local anaesthesia is satisfactory. This combination of circumstances makes this procedure one which patients

Neurosurgical Unit, Killearn Hospital, Killearn by Glasgow, Scotland.

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tolerate poorly under local anaesthesia supplemented by conventional seda- tion with barbiturates or morphine derivatives. Even if the patients will lie still during the counting period emotional hyperventilation is usual and the resulting hypocapnia considerably reduces cerebral blood flow. Chlorpromazine is unacceptable on account of resulting hypotension and heavy sedation is unacceptable because the patient must be able to co-operate in tests for limb movement and dysphasia when the effect of temporary carotid occlusion on function in the cerebral hemisphere is being assessed.

M E T H O D

No pre-medication is given before arrival at the operating theatre. A Mit- chell needle is inserted in a hand vein on the side of the carotid exposure (the opposite limb is repeatedly tested for power later in the procedure). An initial intravenous injection of 3 mg of Droperidol and 1.5-2 mg of Phenoperidine or 0.1 mg of Fentanyl (cases 6 and 7) is given slowly and the patient is set up in theatre with the mask in position on the face. Local anaesthesia is infiltrated into the neck using not more than 50 ml of 0.5% Lignocaine containing 1 /200,000 adrenaline. The carotid bifurcation is then exposed and the internal carotid artery cannulated with a fine teflon catheter and blood withdrawn for measurement of pH and PaCO, by the interpolation technique for whole blood (Siggard Andersen et al. 1960). There follows a series of assessments of cerebral blood flow each one lasting 15 minutes after an injection of isotope; blood samples are taken before each estimation of cerebral blood flow. Incre- ments of 0.5 mg of Phenoperidine or 0.05 mg of Fentanyl are given if the respiratory rate starts to rise above 14 per minute. Any appearance of anxiety is taken as an indication for further supplements of 1 mg of Droperidol. The respiratory rate is estimated visually. The electro-encephalogram is recorded on an Offner Type 1 Portable 8 Channel machine from scalp leads fixed before the patient comes to theatre. Blood pressure is monitored by upper arm sphygmomanometry and the pulse rate by palpation.

R E S U L T S 1. Mental State

The operations lasted from 1 to 3% hours. In every case the whole procedure was successfully completed ; under previous regimes we had, on occasion, to abandon attempts to carry out cerebral blood flow studies because the patient was too restless and unco-operative. Only two patients in the present series were at all restless, and neither they nor any of the others would admit to any unpleasant memories of the operation. Co-operation and neurological testing including speech were satisfactory in all ; electro-encephalogram records showed a consistently normal record with occasional drifting into light sleep.

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opera-

systo-

&. mmHg

I 1 Total dosage mg

PH PaCO, m m ~ g

Respira- Systolic '". Pulse rate range

mm Hg

1 31/2 4.25 - 4

2 2 % 2 - 4

3 1 2 - 5

4 2y2 4 - 10

5 1y2 3 - 7

6 3 - 0.2 15

7 3 - 0.15 10

8 234 2 - 2

124 120-135

150 110-140

150 180-195

130 100-130

150 140-160

140 80-115

170 160-190

100 100-115

100-140

60-80

60-80

64-1 10

60-1 10

52-84

60-80

52-64

(1) 45.5 10-16 (2) 46.5

(3) 46.5

10-16 (2) 41.5

10-12 (1) 41.5

(1) 45.5

(1) 43

(3) 39 (4) 44

(2) 56 (1) 35.5

(3) 37.7

(1) 37

(3) 37.5

10-20 (1) 39.5

8-16 (2)42

10-18 (1)56

10-14 (2) 36.5

12-16 (2) 38

(4) 36.5

(2) 41

(1) 7.33 (2) 7.33 (3) 7.33

(1) 7.34 (2) 7.35

(1) 7.38

(1) 7.36 (2) 7.36 (3) 7.36 (4) 7.36

(1) 7.26 (2) 7.26

(1) 7.37 (2) 7.35 (3) 7.37

(2) 7.39 (3) 7.39 (4) 7.39

(1) 7.39 (2) 7.38

(1) 7.40

2. Cardiovascular

The blood pressure was well maintained in every case but one; in this case the pressure fell from 140 mm Hg to 80 mm Hg for 30 minutes after the administration of initial dose but thereafter regained a normal level (case 6). In all cases the systolic pressure varied only moderately around the patient's pre-operative level. The pulse rate tended to slow in most cases confirming the parasympathomimetic action of the analgesics. There seemed to be some vagal release mechanism in cases 4 and 5 because each showed a definite tachycardia towards the end of the procedure. Case 1 had a tachycardia throughout.

3. Respiratory Function

In every case respiratory rate was markedly slowed, commonly to between 10 and 12 per minute, and absence of any trace of emotional hyperventilation was most striking. The normal rate for these patients was between 16 and 20

50

per minute. The PaCO, values were remarkably constant during the period of sampling and were within the normal range in all but one (case 5 had a PaCO, of 56 mm Hg). In cases 1 and 3 the pre-operative PaCO, was 2.5 and 3.5 mm Hg lower than that recorded under neuroleptanalgesia. The mechanism of the ventilatory depression is not yet completely clear. Initial physiological studies in normal volunteers suggest that there is metabolic depression and an altered pattern of ventilation (Jennett and Barker 1966).

C O N C L U S I O N

Neuroleptanalgesia has proved successful in meeting the unusually exacting conditions demanded for carrying out cerebral blood-flow studies during carotid ligation under Iocal anaesthesia. In particular, emotional hyperventila- tion is prevented and a constant PaCO, maintained, making assessments of cerebral blood flow possible against a stable background.

REFERENCES

1. SIGGARD ANDERSEN o., ENGEL K., JBRGENSEN K., ASTRUP P. (1960) : Scand. J. Clin. Lab. Invest. 12, 172.

2. BROWN A. S. (1964): Neuroleptanalgesia for the Surgical Treatment of Parkin- sonism. Anaesthesia 19, 70.

3. LEDINGHAM I. McA., MCDOWALL D. G., JACOBSON I., NORMAN J. N. (1965) : Oxygen Administration and Measurement in Conscious Healthy Volunteers; Observations on Patients with Respiratory Disease. Hyperbaric Oxygenation. Ed. Ledingham I. McA. Livingstone, Edinburgh.

4. JENNETT S. M., BARKER J. (1966) : To be published.