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A 36-year-old female presented with seizures and transient dysphasia in her 31 week of pregnancy. Neuroradiological investigations revealed a large falx meningioma. A decision was taken to deliver the infant and excise the tumor before term because of the risk of an increase in the size of the tumour and the risk of sinus thrombosis. Therefore, she underwent in her 32 week of pregnancy an elective Caesarean section followed by a craniotomy to remove the meningioma. There were no neonatal complications and she made an uneventful recovery. The final pathology report confirmed the diagnosis of meningioma with progesterone positive receptors.

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We have performed a prospective randomised trial of 30 patients undergoing craniotomy to compare intramuscular codeine phosphate with patient-controlled analgesia using morphine 1 mg bolus with a 10-min lockout and no background infusion. For 24 h postoperatively, pain, nausea, Glasgow coma score, respiratory rate and sedation score were assessed. There was a wide variation in the amounts of morphine requested by the patients in the patient-controlled analgesia group in the first 24 h postoperatively (range 2-79 mg, median 17 mg). There was a small, but non-significant, reduction in pain scores in the patient-controlled analgesia group. There were no significant differences between the two groups in respect of nausea and vomiting, sedation score or respiratory rate. No major adverse effects were noted in either group. Patient-controlled analgesia with morphine is an alternative to intramuscular codeine phosphate in neurosurgical patients which merits further investigation.

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As part of an evaluation of post-operative analgesia for craniotomy patients, a postal questionnaire was sent to 183 consultant members of the Neuroanaesthesia Society of Great Britain and Ireland, inquiring about their current practices for post-operative neurosurgical analgesia. Replies were received from 110 neuroanaesthetists in 37 different neurosurgical centres. Intramuscular codeine phosphate or dihydrocodeine was the mainstay of post-operative analgesia for 97% of neuroanaesthetists despite the fact that over half of them thought that analgesia was inadequate. Only four neuroanaesthetists would ever consider using opioids post-operatively because of fears about respiratory depression and sedation, yet all except one used opioids per-operatively. Post-operative analgesia for craniotomy patients is perceived as inadequate by most neuroanaesthetists, yet traditional prejudice against opioid use prevents this being remedied. We suggest that patient-controlled analgesia with morphine could be a safe alternative to codeine phosphate.

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The changes in intracranial pressure which occur following a change in one of the constituent volumes within the skull are governed by the Monro-Kellie doctrine, stated in the late 18th century and describes how an increase in one of the constituent volumes must be reflected by a reciprocal decrease in another volume to avoid any change in pressure and that if this does not occur, there is a rapid rise in intracranial pressure. Cerebral blood flow is affected by many physiological and pharmacological factors, and is relevant as a change in cerebral blood flow results in a similar alteration in cerebral arterial volume which will affect intracranial dynamics. Another important concept to be understood is cerebral perfusion pressure, how it is related to intracranial and arterial pressures and its relevance during the conduct of any neuroanaesthetic. Both carbon dioxide and the volatile agents are potent vasodilating agents and will cause a catastrophic rise in intracranial pressure and fall in cerebral perfusion pressure if hypercapnia develops in the presence of more than one MAC of a volatile agent. The volatile agents are reviewed and it is stressed that while isoflurane may have advantages over the older volatile agents it is not without complication and nitrous oxide which has always been regarded as an innocuous agent may also have some significant intracranial affects. The use of propofol, as an infusion and the neuromuscular blocking agents and narcotics are described. Recently the use of induced hypotension during clipping of cerebral aneurysms has been questioned and this view and the treatment of vasospasm is discussed in some detail.(ABSTRACT TRUNCATED AT 250 WORDS)

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Invasive investigation of the brain and spinal cord started in the early part of the 20th century. With advances in the understanding of neurophysiology, improvements in anaesthetic technique and the advent of new drugs, general anaesthesia has become an acceptable alternative to local anaesthesia during these investigations.

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Brain surface oxygen tensions were measured, in sheep (n = 8), with a seven-barrelled mini-electrode polarized by sweep potentials. Mean arterial pressure was reduced to 30 mm Hg with either sodium nitroprusside or adenosine. At this value of mean arterial pressure, oxygen supply to cerebral tissue was impaired. There was no significant difference between the two agents in the degree to which the oxygen supply was reduced.

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In eight rabbits, the common carotid artery was ligated and multiple estimations of brain surface oxygen tension performed using a seven barrelled mini-electrode. In five rabbits ligation of the carotid artery resulted in impairment of cortical oxygenation. The remaining three rabbits showed no impairment in the supply of oxygen to the cerebral cortex after carotid occlusion. In the five rabbits who displayed a reduction in oxygen supply after carotid ligation, ventilation with 33% oxygen after the infusion of 15 ml/kg of Fluosol FC-43 produced an improvement in cortical oxygenation in only three of the five rabbits. When these animals were ventilated with 100% oxygen after carotid ligation and Fluosol infusion, oxygen supply in all five was commensurate with or greater than that during control conditions.

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A multitipped seven barrelled platinum electrode for brain surface oxygen measurements during neurosurgery is described. Its performance has been examined when employed under conditions of sweep potential polarography. Although there is no plateau within the oxygen polarogram, the electrode displays linear performance within the physiological range, gives reproducible results in practice, has an acceptable temperature coefficient and a fast response time.

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A multitipped oxygen electrode has been used to measure cortical surface oxygen tensions in the sheep. A histogram of the pattern of supply of oxygen to cortical tissue within the microcirculation during normal conditions is presented. Systemic arterial pressure was reduced to a mean of 30 mmHg with either Adenosine or ATP, and further oxygen tension measurements undertaken. The oxygen histogram was shifted to the left in these circumstances, and there was an increase in the frequency of occurrence of very low tissue oxygen tensions. This suggests that the use of these agents to induce profound hypotension may be associated with significant ischaemia within the microcirculation.

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An etomidate infusion was used to anaesthetise twelve patients for spinal surgery; six (group I) with 67% nitrous oxide and six (group II) with oxygen enriched air. Anaesthesia was induced with infused etomidate at a rate of 100 micrograms/kg/minute for 10 minutes and maintained at a rate of 10 micrograms/kg/minute. Recovery was assessed as the time to opening eyes on command (t1) and the time to giving correct date of birth (t2). In group I, mean value for t1 was 37.9 minutes and t2 59.1 minutes which is significantly longer than in group II where mean value for t1 was 9.0 minutes and t2 15.1 minutes. Blood was taken for estimation of etomidate levels. In group I the maintenance level was 501 ng/ml and the plasma clearance 20.9 ml/kg/minute. In group II the maintenance level was 367 ng/ml and plasma clearance 27.3 ml/kg/minute. Etomidate infusion appears to be a suitable alternative for neuroanaesthesia when nitrous oxide is contra-indicated.

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In conscious subjects breathing spontaneously the performance of the Lack semi-closed system resembled the Magill attachment in that rebreathing was only detected at fresh gas flows of less than resting minute volume. With the Bain semi-closed system rebreathing was detectable at fresh gas flows of the order of 2.5 times the minute volume. The two co-axial circuits behaved similarly for anaesthetised patients. In adults breathing spontaneously the Lack system is efficient and more economical than the Bain.

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Using an intramyocardial pH needle probe (21 gauge) to monitor myocardial metabolism during ischemia, we determined the effect of potassium cardioplegia at both moderate and deep hypothermia. Five groups of 5 dogs each were placed on cardiopulmonary bypass and the pH probe was inserted approximately 10 mm into the left ventricular free wall. Cardiac ischemia was achieved by cross-clamping the ascending aorta at 37 degrees C (Group 1), 27 degrees C (Group 2), or 17 degrees C (Group 3). In the remaining two groups, aortic cross-clamping was followed by the infusion of 600 to 800 ml of potassium cardioplegic solution adjusted to cardiac temperatures of 27 degrees C (Group 4) or 17 degrees C (Group 5). In each group, myocardial temperature was maintained constant, electrical and mechanical activity observed, and pH recorded until a plateau was reached or for 3 hours. Our results show a progressive and significant decrease in the metabolic rate with reduction in temperature over the 37 degrees to 17 degrees C range. By abolishing contractile activity, potassium cardioplegia markedly reduces the rate of hydrogen ion accumulation at 27 degrees C, but at 17 degrees C the additive effect of cardioplegia is much less pronounced. These observations support the principle of reducing contractile activity to a minimum during elective arrest of the heart but indicate that potassium cardioplegia does little to further reduce the rate of anaerobic metabolism, as shown by the measurement of intramyocardial pH, under conditions of deep hypothermia.

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At present, a practical method for continuous monitoring of the state of tissue metabolism in the individual patient's heart during cardiac operations is not available. We have explored the use of miniature electrode measurements of myocardial interstitial pH to provide this monitoring capability, making comparisons with intracellular pH in left ventricular biopsy specimens and with tissue PCO2 measured by mass spectrometry. The electrode system consisted of a hydrogen ion-sensitive glass miniature electrode, housed in the beveled end of a 21 gauge (0.8 mm diameter) hypodermic needle, and a 2 mm diameter reference electrode, with an internal silver-silver chloride electrode coupled to tissue through a saline bridge (150 mM/L sodium chloride) saturated with silver chloride. Accuracy in blood at 37 degrees C was compared with conventional instrumentation (Radiometer BMS-3 MK-2 Blood Micro System) over a pH range of 7.4 to 6.4 with linear regression analysis (n = 26) revealing a high correlation (r = 0.997) and a mean difference in paired observations of only 0.01 +/- 0.004 (mean +/- SEM) pH units. In two groups of dogs on cardiopulmonary bypass, the pH needle and reference electrodes were inserted into the anterior wall of the left ventricle. Ischemic arrest of the heart at 37 degrees C was used to vary myocardial pH. In Group 1 (n = 8), intracellular pH was estimated from left ventricular biopsy specimens (400 mg each) taken over a microelectrode pH range of 7.37 to 6.37, snap frozen, and homogenized. In Group II (n = 6), tissue PCO2 in the anterior wall of the left ventricle was determined by mass spectrometry (sampling catheter 1.3 mm diameter). Miniaturized electrode (interstitial) pH exceeded biopsy (intracellular) pH under control conditions by 0.28 +/- 0.025 pH units (p less than 0.001), but below an electrode pH of 6.8 the results of the two techniques did not differ significantly. The tissue PCO2 rose from 69 +/- 2 mm Hg to a final plateau of 419 +/- 25 mm Hg, which was similar to the predicted value of 427 +/- 28 mm Hg calculated from the pH change (7.37 +/- 0.01 to 6.01 +/- 0.07), providing a further independent check on the pH electrode technique. These data indicate that our intramyocardial pH measurements do reflect intracellular metabolism during elective arrest of the heart and may have potential for clinical use.

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Clobazam is a new 1,5 benzodiazepine which differs from the 1,4 benzodiazepines such as diazepam, in that it displays a wide separation of its tranquillising or anxiolytic effects from impairment of cortical arousal and psychomotor performance. Its potential advantages as a premedicant for day-case or outpatient surgery were evaluated in a placebo-controlled double-blind study in female patients undergoing minor day surgery. Anxiety reduction was evaluated clinically and by means of plasma cortisol estimations. The clinical evaluation, using an established portocol, did not differentiate either active drug from placebo or between the active drugs; the cortisol results permitted opposing conclusions depending on the statistical approach used. Potential fallacies inherent in the methodology current used for evaluating premedicant drugs are discussed.

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Twenty-six patients with severe coronary artery disease, receiving long term beta-adrenoceptor blocking drugs were anaesthetised for aorto-coronary bypass operations. Beta-adrenoceptor blocking drugs were withdrawn 2 to 8 days before surgery in ten patients only. In the remaining sixteen patients there were no serious complications due to the presence of a degree of beta-blockade during anaesthesia and surgery. The undesirable cardiovascular responses to laryngoscopy and tracheal intubation were diminished in these patients, and the rise in heart rate/systolic pressure product, and indicator of myocardial oxygen consumption, was less in this group. The need for peripheral vasodilators to treat systemic arterial pressure rises in response to surgery was also reduced. There appeared to be no contraindication to the continuation of beta-adrenoceptor blockade before operation in patients undergoing aorto-coronary bypass procedures when suitable anaesthetic agents were selected and when an appropriate blood volume was maintained.

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