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SUMMARY General anaesthesia was given to 63 in-patients for electroconvulsive therapy. The relaxant-modified method, using thiopentone and suxamethonium, was used on 134 occasions. For 220 treatments methohexitone, without suxamethonium, was used a graded potential stimulus being applied instead of an instantaneous maximal electrical stimulus. Comparing the two methods it was found that there were significantly fewer increases in blood pressure and an absence of dental or oral trauma with the methohexitone technique. The results of arterial blood-gas analysis of 15 patients treated by this technique showed that there was neither a dangerous fall in arterial oxygen tension nor a marked rise in arterial carbon dioxide tension.

SUMMARY Various techniques of general anaesthesia were studied in sixty patients undergoing cerebral angiography to determine the separate influences of arterial carbon dioxide tension, controlled ventilation and trichloroethylene upon the quality of the films obtained. A low carbon dioxide tension and controlled ventilation both increased the probability of high quality films. The use of trichloroethylene did not appear to affect film quality. Anaesthesia for cerebral angiography is discussed and it is concluded that moderate hyperventilation under nitrous oxide and tubocurarine anaesthesia resulted in high quality films with the greatest diagnostic value.

SUMMARY Two patients are described who had suffered injuries both to the chest and the head. Both patients had evidence of impairment of ventilation-perfusion relationships, and were ventilated mechanically. The large minute volumes which were used to inflate the lungs and to restore normal arterial oxygen tensions severely reduced the arterial carbon dioxide tension, and produced an arterial alkalaemia. The insertion of a dead-space into the ventilation circuit increased the arterial carbon dioxide tension; the arterial oxygen tension was not further impaired, and the levels of consciousness of both patients improved. A suitable deadspace allows normal carbon dioxide tension to be maintained when increased ventilation volumes are required for adequate mechanical ventilation.

Hafnia A and Hafnia D anaesthetic systems are non-polluting modifications of the Mapleson A and D systems. The excess gas is vented in the Hafnia systems directly and continuously via a calibrated ejector flowmeter. Sixteen adult patients anaesthetized for abdominal surgery were ventilated with either Hafnia A or D systems at six different fresh gas flows. No difference between the Hafnia A and D systems could be demonstrated in the values of arterial carbon dioxide tension measured with the same fresh gas flow, despite gas flows in opposite directions.

A preliminary study was undertaken to assess the feasibility of increasing the arterial oxygen tension, and decreasing the arterial carbon dioxide tension, in intact animals, by means of peritoneal perfusion with the perfluorocarbon-containing, oxygen-transporting blood substitute, 20% Fluosol-DA. Perfusion was carried out in rabbits using a bubble oxygenator and circulator pump, delivering Fluosol at a rate of 25 ml min-1. Control blood-gas measurements were carried out at various FIO2 between 0.5 and (if the animal was not severely hypoxic) 0.16. The measurements were repeated during the intraperitoneal perfusion of Fluosol. At all values of FIO2, significant increases in PaO2 were seen (P less than 0.05). Significant decreases of PaCO2 (P less than 0.05) were seen if the animals were not hypoxic (PaO2 greater than 10 kPa).

A method of predicting arterial carbon dioxide tension in anaesthetized patients having controlled ventilation using a circle system without carbon dioxide absorption is described. Adequate mixing of circuit and alveolar gases is assumed when large minute volumes are provided, and the Nunn blood-gas predictor is utilized to choose the appropriate fresh gas flow. The method has been tested on forty-three patients.

Cerebral circulation and metabolism during Althesin anaesthesia were studied in seven healthy patients. Althesin was given in a single dose of 0.1 ml/kg and thereafter infused at a constant rate of 0.3 ml/kg/h. During Althesin infusion, the cerebral blood flow (CBF), the cerebral metabolic rate for oxygen (CMRo2) were 29 +/- 10 ml/100 g/min and 1.7 +/- 0.4 ml/133 g/min, respectively. These values were significantly different from those obtained in awake subjects in our laboratory (CBF: 46 +/- 7 ml/100 g/min; CMRo2: 3.1 +/- 0.6 ml/100 g/min). During CBF measurement, the mean cerebral perfusion pressure, cerebral vascular resistance (CVR) and arterial carbon dioxide tension (PaCO2) were 89 +/- 16 mm Hg, 3.4 +/- 1.3 mm Hg/ml/100 g/min, and 36 +/- 9 mm Hg, respectively. The relationship between CBF and PaCO2 were studied and it was found that during Althesin anaesthesia reactivity of cerebral vessels to the alteration of PaCO2 was maintained. It is concluded that Althesin caused cerebral metabolic depression which was accompaned by a decrease in CBF and an increase in CVR.

Greyhound dogs were given oleic acid i.v. to induce controlled pulmonary oedema. These animals were then studied using intermittent positive pressure ventilation (IPPV) with four different inspiratory flow waveforms, each at three different inspiratory times, in a fixed respiratory cycle of 4 s at a constant tidal volume. Although there were statistically significant differences in airway and oesophageal pressures between the different waveforms and times, there was little variation in the other physiological parameters studied except for arterial carbon dioxide tension. (PaCO2) which showed statistically significant improvement with reversed ramp and sine wave inputs and at the longer inspiratory time of 2.2s. Venous admixture (Qs/Qt) was also less with the longer inspiratory time of 2.2s.

SUMMARY In eight out of eleven patients investigated, the arterial carbon dioxide tension was higher in the period immediately after total cardiopulmonary bypass than before, although the minute volume delivered from the ventilator was unchanged. It was concluded that the increased carbon dioxide tension was due to an increase in physiological deadspace. Possible causes are discussed.

SUMMARY In a double-blind, between-patient study involving fifty-five patients undergoing neuroradiological investigations, pentazocine and phenopendine have been compared in the technique of neuroleptanalgesia. Subjective assessment has shown both drugs to be equally satisfactory. Cardiovascular changes were more marked after phenoperidine and this drug also caused a greater and more persistent increase in arterial carbon dioxide tension. It is concluded that pentazocine is a suitable alternative for phenoperidine in combination with droperidol in neuroleptanalgesia.

SUMMARY Ten patients were studied during air encephalography under general anaesthesia with controlled pulmonary ventilation. Arterial carbon dioxide tension was lowered by over-ventilation, or raised by adding carbon dioxide, and lumbar or cisternal cerebro-spinal fluid samples were taken for acid-base analysis. No consistent changes in the bicarbonate concentration of the cerebrospinal fluid were demonstrated. This suggests that changes in the bicarbonate concentration of large cavity cerebrospinal fluid, in response to a change in arterial carbon dioxide tension, may be slower in man than animals.

There are two main sources of error in the determination of Paco2 by an interpolation technique which utilizes bubble equilibrations. These are: The occurrence of metabolic acidosis during the process of storage and equilibration. Incomplete equilibration of the blood samples with the known carbon dioxide and oxygen mixture. Incomplete equilibration is particularly likely to occur if the blood has a high packed cell volume: in these circumstances there may be an underestimate of Pco2 of as much as 20 mm Hg. It is suggested that a Pco2 electrode is both more accurate and more convenient than the interpolation technique described. However, this too is subject to error and its accuracy should be repeatedly checked by tonometry.

Measurements of arterial carbon dioxide tensions (PaCO2) were made in children between nine months and twelve years of age, using a modification of the rebreathing technique of Campbell and Howell, during anaesthesia with halothane, nitrous oxide and oxygen, maintaining spontaneous respiration. The accuracy of this method was investigated by a series of double readings, in which the rebreathing times were varied, and by comparison with samples of arterial blood analyzed by the Astrup technique. The results of these experiments showed this basically simple method to be adequate for measuring PaCO2 in clinical anaesthesia.