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CORRESPONDENCE
533
tinal obstruction. Furthermore, there can be no guarantee that the level of residual fluid will remain below the level of the fistula, even though a head-up position is maintained, when the patient is placed in the lateral position for surgery. These authors state that, except in patients with a small fistula, "the need to aspirate caused frequent interruptions in the course of anaesthesia". In two of their patients gross spillover of pleural fluid into the lung did occur, and in one the operation had to be stopped as the patient's condition deteriorated. This is an incidence of 2 in 22 cases (9 per cent) and in view of the potentially lethal consequences of such a complication, entirely unacceptable. That no more serious sequelae occurred was indeed fortunate. As stated by the authors, the general condition of most patients was poor—such patients are more susceotible to the effects of aspiration of infected pleural fluid. T have witnessed fluid flooding out of an endotracheal tube (a sight never to be forgotten) in a patient with a bronchopleural fistula as he was turned into the lateral position on the operating table; this was accompanied by considerable aspiration and cardiac arrest Even when using blocking techniques such as advocated by Dennison and Lester (Brit. J. Anaesth. (1%1), 33, 655) and Dr. Glennie Smith and myself (Brit. J. Anaeslh. (1962), 34, 817) one never feels entirely free from these hazards until the operation has been safely completed; one at least has the satisfaction of knowing that all reasonable precautions have been taken and that the patient has not been subjected to unnecessary risks. I would contend that the results of the series reported by Drs. Khurana and Sharma, rather than showing that blocking techniques are unnecessary, strongly support the case for their adoption. J. G. FRANCIS
London
pain threshold, as measured by the tibial pressure technique, in two of the subjects to the same degree as that produced by white sound. The third subject showed no rise in pain threshold doing this exercise nor did he with white sound. We then tried to sec whether we could add the effects of white sound on to the effects produced by distraction. We produced white sound by the method described by Moore, McClurc Browne and Hill, and were unable to detect any further effect by the white sound over and above that shown by distraction. It would seem that their experiments, despite the elegant statistical treatment of their results, would be most unlikely to show any analgesic effects from white sound. Moor, McClure Browne and Hill also say that the intensity of sound from the headphones was measured with a standard sound level meter made by Dawc Instruments. We should be interested to know what coupler was used here between the earphones and the microphone of the sound level meter—the coupler most usually used being, of course, a standard artificial ear. Messrs Dawe Instruments Ltd. inform us that proper coupling between headphones and their standard sound level meter is impossible. The whole question of the production of white sound and the measurement of its intensity has been gone into in some detail by Hesse (1962), reference to which article was made by Moore, McClure Browne and Hill. In the article by Hesse is also shown the response curve of a pair of S. G. Brown super "K" headphones, as presented by the manufacturers, which does not agree with that given by Moore, McClurc Browne and Hill. It is not the purpose of this letter to suggest that white sound is a useful means of providing analgesia but to suggest that our knowledge of white sound has not been enlarged by the article by Moore and his colleagues. JOHN CLUTTON-BROCK
Bristol REFERENCES EFFECT OF WHITE SOUND ON PAIN THRESHOLD
Sir,—-I was interested in the article bv Moore. McClurc Browne and Hill (Brit. J. Anaesth. 0964), 36, 268) on the effect of white sound on the pain threshold. While understanding their wish to use the ischaemic Dain technique described by Hewer and Keele (1948) there would appear to be a very serious objection to the use of this techniaue for investigating the effects of white sound. As mentioned in this article we (CluttonBrock, 1962), using the tibial pressure techniaue, were able to show that white sound of reasonable intensities produced an elevation of the pain threshold very similar to that produced bv distraction. The difference between white sound and distraction presumably is that the effect of white sound does not depend on a voluntary effort on the part of the subiect. With the ifchaemic nain technique the subject has to do a certain amount of work in a given time and it seemed that the concentration reauired to do this properly might well act as a form of distraction. We therefore investigated the effect on the Dain threshold as measured bv the tibial pressure technique, of squeezing the bulb of a manometer in time with a metronome at 60 beats Der minute with sufficient force to measure 150 mm He on a manometer, this being the technique used by Moore, McClure Browne and Hill. This was done on three subjects. The distraction produced a rise in the
Clutton-Brock. J. (1962). Analsesia produced by white sound. Anaesthesia, 17, 87. Hesse. G. E. (1962). Observations on the production of white sound. World Med. Electron.. 1, 55. Hewer. A. J. H., and Keele, C. A. (1948). A method of testing analgesics in man. Lancet, 2. 6F3 Moore. W. M. O.. Browne, J. C. McClure, and Hill. I. D. (1964) Effect of white sound on pain threshold. Brit. J. Anaeslh., 36, 268. RESPIRATORY OBSTRUCTION DUE TO IMPACTION OF THE EPIGLOTTIS TN AN ADULT
Sir,—Since publication of the case report of respiratorv obstruction from impaction of the epielottis (Brit. J. Anaeslh. (1964), 36, 314), Dr. H. J. V. Morton has kindly drawn my attention to two earlier papers on this subject. Pokrzywnicki (1953) reported a patient anaestized with thiopentone, nitrous oxide and oxygen with ether. At second plane of the third stage, prior to intubation, obstruction occurred. Careful larvngoscopv revealed the epielottis being alternately sucked in and blown out of the larvngeal aditus with respiration. This was demonstrated to those present. Caiger and Sichel (1954) describe laryngeal obstruction from this cause in throat surgery. The precipitating factors they regard as being the hyperextension of the head, and
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