556

KuNIN’s observations indicate that, if we can preventa recurrence for a year or two, the prospect of long-term success is good. Thereby, the unpleasantsymptoms and sequelse of acute urinary infectionsmay be avoided. More speculatively, the incidenceof chronic pyelonephritis and renal failure may alsobe reduced.

AT WHAT TEMPERATURE SHOULD YOU KEEPA BABY?

THE human baby, even if he is born before term, hasconsiderable ability to regulate his temperature. 1, 2When exposed to an environment below that ofthermal neutrality, he increases his metabolic rate,consuming more oxygen and metabolic fuel, and heshows a tendency to metabolic acidosis 3 and lowarterial oxygen tension.4 Thus, there are good reasonsfor expecting that a cool environment might jeopardisehis life, and clinical observations and experience con-firm this.5,6 His range of neutral thermal environmentis less wide than that of an adult, because a baby hasthe disadvantages of a relatively large surface area fromwhich to exchange heat and a small mass to act as aheat sink.The neutral thermal environment appropriate for

the naked baby has been widely studied in the past tenyears.1,2,7,8 Most investigations have been conductedin specially constructed incubators where air tempera-ture and incubator-wall temperature are within a

degree of each other, so that the air temperature is a notunreasonable statement of thermal environment. The

temptation to extrapolate the findings to babies nursedin clinical incubators has dangers, for here air tempera-tures and the temperature of the inside skin of the

transparent canopy are usually very different. This

disparity was emphasised by Hey and Mount 9 whocalculated that a baby may lose half his heat dissipationto the skin of the canopy by radiant heat loss. Theydescribe a simple device, a ’ Perspex ’ heat-shield,which helps control this channel of heat-loss; when itis in place, the air temperature becomes a reasonablemeasure of thermal environment.

In temperate climates air temperatures rarely exceeda baby’s body temperature, so that the commonthermal stress a baby experiences is that of cold. Moststudies therefore have been concerned with the lower

margin of the neutral temperature zone, the so-calledcritical temperature.10 In thermal surroundings whichare close to or warmer than body temperature, heatdissipation must take place by evaporation of waterfrom the respiratory tract or from the skin. From aknowledge of the factors affecting thermal balance,1. Bruck, K. Biol. Neonat., Basle, 1961, 3, 65.2. Scopes, J. W. Scientific Basis of Medicine: Annual Reviews 1970.

London, 1970.3. Gandy, G. M., Adamsons, K., Jr., Cunningham, N., et al. J. clin.

Invest. 1964, 43, 751.4. Stephenson, J. M., Du, J. N., Oliver, T. K. J. Pediat. 1970, 76, 848.5. Mann, T. P., Elliot, R. I. K. Lancet, 1957, i, 229.6. Silverman, W. A., Fertig, J. W., Berger, A. P. Pediatrics, Springfield,

1958, 22, 876.7. Hill, J. R., Radimtulla, K. A. J. Physiol. 1965, 180, 239.8. Hey, E. N., Katz, G. Archs Dis. Childh. 1970, 45, 328.9. Hey, E. N., Mount, L. E. ibid. 1967, 42, 75.

10. Scopes, J. W., Ahmed, I. ibid. 1966, 41, 407.

including measurement of a baby’s capacity to

increase evaporative water loss, Hey and Katz 8

calculated temperatures which are too hot, and thusdefine both the upper and the lower margins of theneutral range. Within such a range, body temperatureremains normal while oxygen consumption and

evaporative heat loss are both at a minimum. Their

findings emphasise that there is no single temperaturethat is appropriate for all sizes of baby. A temperatureappropriate for a term baby may be far too cold for a1500 g. baby, and a temperature which is right for the1500 g. baby could be dangerously warm for a 2500 g.child. (Needless to say, all temperatures suitable fornaked newborn babies are unpleasantly warm for theadult.) It is possible to make an informed guess of theproper temperature for a particular naked baby in anincubator (with a heat-shield in place). Since there issome biological variation this guess may always be wrong,so it is still essential to monitor the baby’s owntempera-ture to ensure that he does not overheat or become toocold. This procedure is, of course, a form of servo-control, and a logical extension is to use the incubatoritself a a monitoring device as in ihe servo-controlincubatorAs soon as a baby is clothed 01 b waddled, most of the

channels of heat-loss are partially occluded. The airtemperature within the clothing of a baby in an

ordinary room is in the order of 35°C.11 Hey andO’Connell 12 examined the neutral zone and responseto cold in clothed babies. They found, of course, lowercritical temperatures than in naked babies, and theyconclude that a draught-free environment of 24°C

(75 °F) is necessary to provide neutral thermal condi-tions for most cot-nursed babies in the first month oflife. Here, at last, is a scientifically based recoinmenda-tion for room temperatures which apply in the usualclinical situation. In a temperature below the criticalone the metabolic cost to a clothed baby is less than toa naked baby, and in hot conditions a cot-nursed baby,whose face is inevitably exposed, can dissipate heatfrom this area. Thus, the clothed baby in a cot is saferthermally than the naked baby in an incubator in thesense that his attendants need not control the environ-ment so precisely. Clearly, control is still needed,since extremes are dangerous, but the latitude is

greater. Added advantages are that coolness on theface is a stimulus to respiration and the face and headare important sweating areas for heat dissipation whenthat is necessary. It is notable that adults prefer theface to be cooler than the rest of the body.

ADDING DRUGS TO INTRAVENOUSINFUSIONS

IT is commonplace for patients to take severaldifferent drugs concurrently. Thoughtful recipientssometimes wonder " what is going on inside" or

suspect that one preparation may react with or

neutralise another. The wise doctor should also givethought to this matter; and, in general, care is takento ensure that drugs swallowed by or injected into

11. Scopes, J. W. Br. med. Bull. 1966, 22, 88.12. Hey, E. N., O’Connell, B. Archs Dis. Childh. 1970, 45, 335.

557

patients are properly administered. Increasing atten-tion is being paid to the interaction of drugs whichmay be incompatible. Whether the same care isobserved when drugs are injected not into a vein butinto an infusion bottle is hard to judge, but it is likelythat insufficient attention is paid to this subject, whichis discussed 1 in a recent issue of the Drug andTherapeutics Bulletin. Solutions for infusion of sugarand electrolytes, and particularly bottles of blood,provide excellent media for the growth of micro-

organisms, the opportunity for which is enhanced byimperfect asepsis during injection, storage of the fluid,or prolonged infusion. The stability of substances insolution may be affected by change in environmentaltemperature, exposure to light, alteration of pH of thefluid, or storage. Mixing drugs with certain solutionsmay produce frank physical change (such as precipita-tion) when the constituents are incompatible. It iscommon, for instance, to give infusions of certainantibiotics but it is not generally realised that somesemisynthetic penicillins and other antibacterial drugsmay break down rapidly in acidic solutions such asdextrose. Heparin is unstable in acid solutions and

incompatible with hydrocortisone. Preparations ofvitamin-B compounds and vitamin C may interactwith many drugs, as may tetracyclines.Few doctors have sufficient knowledge of chemistry

to appreciate all the possible risks, and scanty informa-tion is available from manufacturers about thebehaviour or loss of activity which may follow injectionof substances into solutions of various kinds. The

problem is compounded by a lack of liaison with thepharmacist, when instructions for the addition of

drugs to infusion bottles (often done by nurses) arewritten not on suitable prescription sheets but onfluid-balance charts. The Bulletin acknowledges thatit is sometimes necessary to give drugs by intravenousinfusion but points out how certain precautions wouldreduce the risks. All drugs given by nurses shouldbe precisely prescribed on suitable forms, complexmixtures should be avoided, and drugs should notnormally be added to blood, aminoacids, or fatemulsions. Giving-sets should be changed before

infusing a drug solution, particularly when blood is

being given. Another necessary precaution is the

training of nurses to give drugs into drip tubing; and,perhaps most important of all, closer liaison must beestablished with hospital pharmacists so that drug andintravenous-fluid mixtures can be prepared in thepharmacy under the best conditions shortly before use.

LEFT VENTRICULAR HYPERTROPHY ANDISCHÆMIC HEART-DISEASE

THE natural history of ischaemic heart-disease is

incompletely understood, largely on account of thedifficulty in following a general population for a longenough time. The Framingham study in which fivethousand men and women have been followed forfourteen years, has made outstanding contributions

1. Drug Ther. Bull. July 3, 1970.2. Framingham Study. U.S. Government Printing Office, Washington

D.C., 1968.

in defining factors relating to the development ofischaemic heart-disease. Kannel et al.3 discuss leftventricular hypertrophy (L.V.H.) diagnosed by electro-cardiograms (E.C.G.S) in this study population anddraw attention to its unsuspected importance as a

warning sign of overt coronary-artery disease or suddendeath.

Using generally accepted criteria for " definite"

E.C.G./L.v.H. (increased R-wave voltage with S-TT-

segment changes) and "

possible "

E.C.G./L.V.H. (in-creased R-wave voltage), these workers show that thedevelopment of definite E.C.G./L.v.H. augments therisk of clinically evident ischxmic heart-disease three-fold after adjusting for the known influence of hyper-tension. Possible E.C.G./L.v.H. was associated with atwofold increase in risk, but this was almost whollyaccounted for by the risk relating to associated hyper-tension.

In patients with definite E.c.G./L.v.H., there was anexcess of sudden deaths in patients dying of ischaemicheart-disease; this was true at all ages. Under age 55at entry to the study, 83% of deaths from ischaemicheart-disease in those with definite E.c.G./L.v.H. weresudden. Of the men with definite E.c.G./L.v.H. whodeveloped some manifestation of ischaemic heart-

disease, in about 29% this presented as suddendeath compared with 10% in those without the

abnormality. The overall risk of sudden death waseight times that of the population without the E.c.G.abnormality.That an E.c.G. pattern of L.v.H. does to some degree

reflect anatomical hypertrophy of the left ventricle issupported by necropsy and X-ray findings.4-’ How-ever, there is not a good correlation between heart-weight and the E.c.G. Accordingly the E.C.G. changesare suspected of being produced not simply by anincreased muscle mass, but by a closely associatedfactor-perhaps an altered sequence of electrical acti-vation. In a study of the evolution of the E.c.G. patternof L.V.H., Cosby et al. concluded that the increase inQRS voltage alone reflected primarily pure work hyper-trophy, whereas that associated with prominent s-TT-segment abnormality was related to coronary-arteryinsufficiency. Such a thesis is in keeping with theFramingham findings.From a practical viewpoint the pattern of E.C.G./

L.V.H. must be regarded as a grave prognostic sign,carrying a high risk of clinically overt ischaemic heart-disease and of premature death-particularly suddendeath. In the general population, sudden death is verydifficult to predict and in previously well patientsprodromal events may be limited to non-specific symp-toms of unusual malaise and fatigue within a week orso before death. Owing to the difficulty in identifyingpatients at risk, general long-term prophylaxis with

3. Kannel, W. B., Gordon, T., Castelli, W. P., Margolis, J. R. Ann.intern. Med. 1970, 72, 813.

4. Dawber, T. R., Meadors, G. F., Moore, F. E. Am. J. publ. Hlth,1951, 41, 279.

5. Allenstein, B. J., Mori, H. Circulation, 1960, 21, 401.6. Carter, W. A., Estes, E. H. Am. Heart J. 1964, 68, 173.7. Selzer, A., Ebnother, C. L., Packard, P., Stone, A. O., Quinn, J. E.

Circulation, 1958, 17, 255.8. Cosby, R. S., Herman, L. M., Mayo, M. Am. Heart J. 1962,

63, 180.9. Lown, B., Ruberman, W. Mod. Concepts cardiovasc. Dis. 1970,

39, 97.