Pseudomonas aeruginosa

Pseudomonas aeruginosa

LEADING ARTICLES 1139 necessarily sterile. Lately the organism has been responsible for several episodes of pulmonary infection derived from some of...

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LEADING ARTICLES

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necessarily sterile. Lately the organism has been responsible for several episodes of pulmonary infection derived from some of the many machines designed to assist respiration.1-3 These ventilators are marvels of ingenious design which, for good reasons, incorporate a device for adding water vapour to the air-and here the danger lies. If the water is contaminated with Ps. aeruginosa the whole machine will be contaminated within a short time, and in some instances the discharge itself is an aerosol suspension of the organism. Other sources of infection have been a steroid cream and lignocaine jelly used as an anaathetic lubricant for passing tracheal 5 not

THE LANCET LONDON

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1966

catheters.4 In both instances the emollient was dispensed in a way honoured by tradition but quite unsatisfactory. Repeated infections in a neurosurgical unit were traced to that horrid object, a shaving-brush, used on all patients who were being prepared for operation. In this hospital extensive investigations revealed the Pseudomonas aeruginosa organism on the floors, the sink, a shaving-bowl, the soap IN the days of innocence the medical student always tray, a pot of hand cream-et al.This is the occasion remembered Pseudomonas pyocyanea because of the blue- when the control-of-infection officer wishes he had sent in his resignation last month. green culture and because his teacher told him it was of There is no single measure which would have prelittle medical importance. Its name has now been vented all these catastrophes-except, perhaps, a more changed and its habits too-or so one might guess from the many reports of infections caused by it. This general understanding that " sterile " means free of apparent increase in incidence may be due to a wider viable bacteria of all kinds. The individual eyedrop to interest in bacterial infection; but the complexity of be used only once is an ideal which is not always posmuch of the medical apparatus used today and the fact sible, but no bottle should be used after the day on that Ps. aeruginosa is resistant to most of the antibiotics which it is opened, and in the operating-theatre a fresh in common use and to many antiseptics probably have bottle should be used for each patient. There is no something to do with it. The organism " appears " most practical difficulty in testing each bottle’s sterility often in the flora of infected wounds which have been before issue, but it takes time. The 1966 Supplement treated with antibiotics: whether it has arrived de novo to the British Pharmaceutical Codex sets out competely new formulations for all eyedrops previously preserved or was present in small numbers from the start can seldom be discovered, but it is a singularly difficult by the hydroxybenzoates, allowing a choice between organism to eradicate. Primary infections are less com- phenylmercuric nitrate or acetate (0-002%), benzalkonium chloride (0-01%), and chlorhexidine acetate mon but more serious. There have been several accounts of postoperative infection of the eye leading to panoph- (0-01%). The steroid cream which caused infections thalmitis, and these have not been limited to the smaller points to another danger. Although it contained 0-1% hospitals: the paper from the Birmingham Eye Hospital chlorocresol, most of this was in the watery phase. One customary feature of the casualty department at the front of this issue is not telling a new story. In one week the eyes of 15 out of 25 patients who had intraocular stands condemned-the stockpot of a medicament from operations became infected, and 6 lost an eye. None of which dollops are taken on a bit of gauze or even on a the patients who had extraocular operations was infected. finger. It is wide open to aerial contamination, it lasts The source of infection was " sterile " saline made up far too long, and its contents are never examined apparawith 0-06% ’Nipasept’ (a mixture of methyl and propyl bacteriologically. The humidifiers in breathing " Absolute " tus of all sorts present difficult problems. in and bottles. drop p-hydroxybenzoates) dispensed The strain of Ps. aeruginosa was found to survive in filters-those which prevent the passage of a single nipasept 0-06% for at least forty-eight hours, but where microbe-have been recommended, but used by themselves they soon get obstructed by dust or water. it came from was never discovered. A good many of us harbour Ps. aeruginosa in our They can be protected to some extent by a coarser filter bowels, and the organism is a not uncommon cause of proximal to them, but every filter impedes the flow of rather intractable urinary infections. Outside the body air to some extent. If a suitable antiseptic could be it is not " everywhere " (as are Bacillus spp.), but it found it might be incorporated in the water of the lingers in some unexpected places, such as kitchen sinks. humidifier, but a more useful suggestion is that the 1. Rubbo, S. D., Gardner, J. F., Franklin, J. C. J. Hyg., Camb. 1966, Its most dangerous quality is an ability to survive and 64, 121. even to multiply on a very meagre diet. The washing of 2. Phillips, I, Spencer, G. Lancet, 1965, ii, 1325. D. C. J., Thompson, S. A. S., Page, B. ibid. 1965, i, 781. syringes to be used for spinal injections in distilled water 3.4. Bassett, Noble, W. C., Savin, J. A. ibid. Feb. 12, 1966, p. 347. that had been chemically disinfected led to many cases of 5. Phillips, I. ibid. April 23, 1966, p. 903. G. A. J., Lowbury, E. J. L., Hamilton, J. G., Small, J. M., meningitis until it was realised that water so labelled was 6. Ayliffe, Asheshov, E. A., Parker, M. T. ibid. 1965, ii, 365.

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controlled heater.7 It is essential too that every part of these machines (including babies’ incubators) should be of a pattern and material which will withstand disinfection by a reliable method, and that this disinfection should be carried out frequently and as a matter of course. Perhaps the most important thing is that all doctors, nurses, pharmacists, and engineers should be aware that water which seems to be clear and clean can support bacterial growth and often does and that the most ingenious apparatus can be a source of unsuspected danger.

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Breathlessness A NORMAL person performing strenuous exercise is conscious of his breathing and knows that it is increased, but he recognises that it is appropriate to his activity and is not distressed by the act of breathing. A normal subject at high altitude or a patient with anxmia finds that his breathing is inappropriate to his activity on mild exercise or even at rest, but he is not distressed by the act of breathing. A patient with stiff lungs or obstructed airways may be distressed by the act of breathing. Are these sensations all related or are they produced in totally different ways ? A respiratory physiologist offering a unitary explanation for breathlessness should " arouse the same suspicions as a tattooed Archbishop offering a free ticket to heaven " and most respiratory physiologists, asked how these sensations come about, will be evasive. They will offer a list of possibilities: stimulation of chemoreceptors by disturbed blood gasesstimulation of vagally mediated receptors in the lungs; stimulation of nerve-endings in the chest wall; cortical irradiation from an overstimulated respiratory centre. They turn to the prototypes or models of simpler sensations they acquired as students: the specific ending, the specific pathway, the " centre ", the cortical localisation. This model has its place in clinical neurology, in deciding the site and nature of lesions, but it is stultifying when applied to visceral sensations. Understanding of thirst, hunger, lassitude, or fear is unlikely to be helped by using such a model. Breathlessness is different in that, although respiration is visceral, the act of breathing is somatic. Of all the actions employing skeletal muscles, breathing is the least optional in that the demands that respiration makes on the breathing cannot be evaded by unconsciousness nor, for more than a minute or so, can they be voluntarily

suppressed. In the past few years the range of possible mechanisms subserving the sensation of breathlessness seems to have narrowed, but those that remain seem more complicated than respiratory physiologists would have suspected. Clinical experience, supported by FowLER’s celebrated experiment9 on breath-holding, has excluded any direct role for disturbance of the blood gases. FOWLER showed that the distress of breath-holding was relieved by the 7. 8. 9.

Glover, W. J. ibid. Jan. 22, 1966, p, 203. Campbell, E. J. M., Howell, J. B. L. Br. med. J. 1963, ii, 868. Fowler, W. S. J. appl. Physiol. 1954, 6, 539.

of breathing even if the air was rich in carbon dioxide and low in oxygen so that the blood gases were not improved. Guz and his co-workers "’ have now shown that act

time is prolonged by vagal block in conscious normal man, and that the dyspnoea of one patient with pulmonary fibrosis was also relieved by vagal block. These observations would seem to point to vagal afferents as one source of dyspnoea. But the picture is more complex; Guz et al. found that the distress of breathing against resistance was unaffected by vagal block. NEWSOM DAVIS 11 has marshalled evidence that this sensation may arise in the thoracic cage. Although new work has convincingly shown that muscle spindles are operative in the intercostal muscles, they are unlikely to be the source of this sensation and NEWSOM DAVIS favours the joint receptors. One of the difficulties in an experimental approach to breathlessness is how to reproduce the sensation in the laboratory and study it quantitatively. Both Guz and NEWSOM DAVIS have made use of the ability of subjects to feel the presence of a resistance added to the breathing. The relevance of this sensation to breathlessness is uncertain, but it does allow the relationship between sensation and mechanical changes to be explored the

breath-holding

quantitatively. Another approach

to breathlessness side-steps strucand formulates its explanation in terms of function. It looks at the problem as one of control and turns to the systems engineer rather than the neuro-anatomist for its models. The best " explanation " for breathlessness from this standpoint at present seems to be that difficulty in breathing gives rise to a sensation of inappropriateness " between the volume of breath or rate of expansion of the chest which the respiratory centre demands and the volume or rate of expansion actually achieved. Whether or not this mechanism subserves the sensation of breathlessness when there is no mechanical difficulty in breathing is debatable. In the simple form of the hypothesis 12 it would seem not; but CAMPBELL 13 argues how an extension of the essential idea of inappropriateness might apply. Unfortunately, his suggestions are hard to test. Although both respiratory physiologists and neurophysiologists have contributed to these developments, they were not normally at home in each other’s territory until last year in Manchester they came together with clinicians for a two-day symposium which ranged widely over the whole topic of the act of breathing and its control, the sensation of breathing and its disturbance, clinical observation, and laboratory experiment. The proceedings 14 have now been published and make exciting reading for anyone concerned with this challenging symptom, whose elucidation promises much more than the satisfaction of a clinician’s curiosity.

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Guz, A., Noble, M. I. M., Widdicombe, J. G., Trenchard, D., Mushin, W. W., Makey, A. R. Clin. Sci. 1966, 30, 161. 11. Newsom Davis, J. in Breathlessness (edited by J. B. L. Howell and E. J. M. Campbell); p. 73. Oxford, 1966. 12. Campbell, E. J. M., Howell, J. B. L. Br. med. Bull. 1963, 19, 36. 13. Campbell, E. J. M. in Breathlessness (edited by J. B. L. Howell and E. J. M. Campbell); p. 55. Oxford, 1966. 14. Breathlessness: Proceedings of an International Symposium. Editors: J. B. L. HOWELL and E. J. M. CAMPBELL. Oxford: Blackwell Scientific Publications. 1966. Pp. 238. 63s. 10.