842

or cooking; substances other than N-nitroso

compounds may be involved. Preoccupation with thediet should not exclude the possibility of a

contribution from inhaled carcinogens, especially inindustrial rather than domestic contexts.16 On a morefundamental level, there is the challenge of integratingHo’s three sets of aetiological factors into a singleunifying hypothesis.

ULTRASOUND AND BONE FRAGILITY

THERE is growing interest in the use of simple non-invasive techniques for assessing skeletal status and forhelping to estimate fracture risk,1-3 especially in

postmenopausal and older women. Among the considerableadvances in bone densitometry techniques and their clinicalapplication,4 is the possible use of ultrasound.’*"

Strength of bones in the human skeleton is related notonly to the amount of bone present (mass or density) but alsoto its structure (architecture) .7 ’ Architectural factors may beespecially important in trabecular bone in the primaryfracture sites (vertebrae and proximal femur). Whilstlow-dose radiation techniques can be used to measure bonemass or density, and their changes,4 ultrasoundmeasurements can also give an indication of bone structure,since ultrasound is attenuated in bone’ and the velocity ofultrasound in that tissue is related to density and structure.9 9The two main areas of ultrasound research are use ofbroad-band ultrasound attenuation (BUA)3°5 s andmeasurement of the apparent velocity of ultrasound (AVU)in bone.6,9

In the BUA technique, measurements are made of theattenuation of a short burst of ultrasound by the

predominantly trabecular bone of the os calcis.3,5 The slopeof the linear portion of the attentuation curve (200-600kHz), in dB/MHz, is used as an index of bone status. Thisquantity may also be adjusted for bone thickness.Correlations have been reported between BUA results andquantitative computerised tomography measurements ofthe os calcis in vitro,1O and between BUA values for the oscalcis in vivo and bone mass measured at the wrist, lumbarspine, and proximal femur, with low-dose radiation

techniques.3,11 Mean BUA values for osteoporotic patientsare generally lower than for healthy individuals, and there is

1. Browner WS, Cummings SR, Genant HK, et al. Bone mineral density and fractures ofthe wrist and humerus in elderly women: a prospective study. J Bone Min Res 1989;4 (suppl 1): 171.

2. Ross PD, Wasnich RD, Davis JW, Vogel JM. Estimating remaining lifetime fractureprobability (RLFP) from bone mineral measurements, age, and other factors.J Bone Min Res 1989; 4 (suppl 1): 185.

3. Palmer SB, Langton CM, eds. Ultrasonic studies of bone. IOP short meetings seriesno 6. Bristol: IOP Publishing, 1987.

4. Tothill P. Methods of bone mineral measurement. Phys Med Biol 1989; 34: 543-72.5. Langton CM, Palmer SB, Porter RW. The measurement of broadband ultrasonic

attenuation in cancellous bone. Eng Med 1984; 13: 89-91.6. Greenfield MA, Craven JD, Huddleston A, Kehrer ML, Wishko D, Stern R.

Measurement of the velocity of ultrasound m human cortical bone in vivo.Radiology 1981; 138: 701-10.

7. Bell GH, Dunbar O, Beck JS, Gibb A. Variations in strengh of vertebrae with age andtheir relation to osteoporosis. Calcif Tiss Res 1967; 1: 75-86.

8. Heaney RP Osteoporotic fracture space an hypothesis. Bone Min 1989; 6: 1-13.9 Heaney RP, Avioli LV, Chesnut CH, Lappe J, Recker RR, Brandenburger GH.

Osteoporotic bone fragility. Detection by ultrasound transmission velocity. JAMA1989; 261: 2986-90.

10. McKelvie ML, Fordham J, Clifford C, Palmer SB In vitro comparison of quantitativecomputed tomography and broadband ultrasonic attenuation of trabecular bone.Bone 1989, 10: 101-04.

11 Baran DT, Kelly AM, Karellas A, et al. Ultrasound attenuation of the os calcis inwomen with osteoporosis and hip fractures Calcif Tiss Int 1988, 43: 138-42.

a preliminary report on the possible use of BUA forpredicting risk of hip fractures.3 AVU has been used byHeaney et al for measurements on the patella.9 In their studyosteoporotic women tended to have lower AVU values thandid normal women, and the researchers thought that thetechnique might be useful in screening for osteoporotic bonefragility.Although these ultrasound techniques avoid exposure to

ionising radiation, have the potential for obtaining quantitiesinfluenced by bone structure, and are less expensive thanmost of the low-dose radiation techniques, they cannot yetbe used to measure the main fracture sites (spine, proximalfemur, and wrist). Even for measurements of the os calcis,precision needs to be improved if changes are to bemeasured. Moreover, some of the low-dose radiation

techniques are capable of high-precision measurements atthe sites of fracture risk, with an effective dose equivalent(EDE) of less than 1 % of the annual EDE from naturalbackground radiation.4

Thus, although ultrasonic techniques are not yet preciseor versatile enough to follow the skeletal response to

treatment, their use for screening warrants seriousconsideration.

NOT ALL UPSIDE DOWN

IT seems a long time ago now, but many obstetricians stillin practice will remember at least witnessing, if not actuallyperforming, external cephalic version under generalanaesthesia. Vaginal breech delivery had long been

acknowledged to be more hazardous than vaginal vertexdelivery, and external version was among the most time-honoured of obstetric manoeuvres. That heroic attemptswere made to rectify breech malpresentation antenatally wasnot remarkable but logical. What was remarkable andarcanely illogical is that when the attempted external

cephalic version under general anaesthesia was unsuccessfulthe patient was often allowed to deliver naturally if shecould. The increasing use of caesarean section to obviatevaginal breech delivery saw the end of this folly, whileexternal cephalic version, if not exactly falling into

disrepute, became decidedly demode.But not all obstetricians were willing to abandon external

cephalic version altogether, feeling that the gentle attemptsthey make in the antenatal clinic to coax breech babies toturn upside down should not be tarred with the same brushas more formal and more determined attempts made withand without anaesthesia. These obstetricians now have an

objective assessment of their sort of external cephalicversion. Van Veelen and colleagues1 in Rotterdam attemptexternal cephalic version for breech presentation from 33 to40 weeks and will often repeat the procedure several timeson the same patient. Ultrasound scanning is used to confirmthe diagnosis and to exclude gross fetal anomalies,oligohydramnios, and placenta praevia. Women who arerhesus negative and those with an anterior placenta are notexcluded. The operators work as a pair, with the patientrelaxed in a slight Trendelenberg position. Anaesthesia,analgesia, tocolysis, or vaginal manipulation are not used,

1. Van Veelan AJ, Van Cappellen AW, Flu PK, Straub MJPF, Wallenburg HCS. Effectof external cephalic version in late pregnancy on presentation at delivery: a

randomised controlled trial. Br J Obstet Gynaecol 1989; 96: 916-21

843

and if the version is not easy the attempt is abandoned. In arandomised controlled evaluation of their practice in 180patients the emphasis upon gentleness may be judged fromthe fact that only 25% of attempted versions were

successful. Nonetheless, in 50% of the 89 patients in theversion group, the baby was presenting by the head at thetime of delivery. In the control group of 91 patients in whomno versions were attempted only 23 babies were presentingby the head at the time of delivery. In both primigravidaeand multigravidae external cephalic version was better thannature in effecting rectification of the malpresentation-andwithout complications. Because no elective caesarean

sections were done in this study and the outcome of labourwas similar in the two groups of patients, no benefit tomother or baby was shown. In units where the practice is todeliver all patients with persistent breech presentation bycaesarean section, a 20-25% reduction in the caesareansection rate for this indication seems readily attainable.

SPONTANEOUS PNEUMOTHORAX

THE incidence of spontaneous pneumothorax in patientswithout obvious underlying lung disease is over 7/ 100 000per year in men, and about six times less in women.1 In

patients with tension pneumothorax, or much pleural fluid,or when the pneumothorax complicates chest trauma orartificial ventilation, intercostal tube drainage is an urgentpriority. Which treatment is best for patients with non-tension primary pneumothorax?

Factors that influence management include the size of the

pneumothorax, the perceived morbidity of whatever

procedure is adopted, and whether the procedure has anyinfluence on recurrence. 20-50% of primary spontaneouspneumothoraces recur, depending on patient selection, typeof treatment, and duration of follow-up.2,3 Whilst a

pneumothorax can resolve spontaneously with time,absorption of air is very slow (1-25% in 24 hours’), so await-and-see policy is appropriate only for very small

pneumothoraces in patients who have ready access to

medical help and are not planning to travel by air (orundergo other pressure changes). Moreover, an apparently"small" pneumothorax, usually judged by area on theradiograph, may represent a large volume of air, sincevolume is proportional to the cube of the radius; a 1 cm rimof air round a lung with a normal 5 cm radius reduces itsvolume by up to 50%, and this amount of air will take severalweeks to be fully absorbed.

Pleural intubation, with underwater seal drainage, is theaccepted treatment for spontaneous pneumothorax of anydegree; surgeons tend to favour a Malecot catheter insertedwith a Tudor-Edwards trochar and cannula. Argyle-typecatheters may be simpler to use but carry some risks,

1. Melton JL, Hepper NGG, Offord KP. Incidence of spontaneous pneumothorax mOlmstead County, Minnesota; 1950 to 1974. Am Rev Respir Dis 1979; 120:1379-82.

2. Ruckley CV, McCormack RJM. The management of spontaneous pneumothorax.Thorax 1966, 21: 139-44.

3 Almind M, Lange P, Viskum KAJ. Spontaneous pneumothorax: comparison ofsimple drainage, talc pleurodesis, and tetracycline pleurodesis. Thorax 1989; 44:627-30.

4. Kircher LT Jr, Swartzel RL Spontaneous pneumothorax and its treatment. JAMA1954; 155: 24-29.

5 Walesby RK How to insert a chest drain and aspirate a pleural effusion. Br J HospMed 1981; 25: 198-201.

especially if inserted by inexperienced operators without aguard to prevent penetration of lung or other organs. 5Whatever the technique, pleural intubation is generallyuncomfortable and wearisome for the patient, and interest insimple aspiration has increased since Hamilton and Archeradvocated this approach in 1983.6,7 Simple aspiration, withan intravenous-type cannula, a three-way tap, and a syringe(it may even be possible to resurrect an artificial

pneumothorax apparatus from the cupboards of the oldtuberculosis clinic8) can satisfactorily treat perhaps 70% ofprimary pneumothoraces. This procedure causes very littledisturbance for the patient, but will not affect the rate ofrecurrence. Patients in whom aspiration fails to re-expandthe lung will require pleural intubation.The contribution of pleural intubation alone to the

prevention of recurrence is difficult to assess, and manyforms of pleurodesis have been added to the procedure toobliterate the pleural space, including silver nitrate,tetracycline, and talc. A report from Copenhagen comparesthe morbidity and recurrence rate following simple tubedrainage alone, talc pleurodesis, and tetracyclinepleurodesis.3 Over an 8-year period, 96 patients with a firstepisode of spontaneous pneumothorax (including 25

patients with pneumothorax secondary to lung disease) wererandomised to one of the three treatments; for the sclerosingagents, tetracycline in 20 ml water or talc in 250 ml salinewas instilled, the drain was clamped for 2 hours, and thepatient was moved about to disperse the solution in thecavity. Duration of drainage was the same in the threegroups (about 4 days), as was length of hospital stay (6-7days). As many patients as possible were traced 2 years afterthe last patient had been treated, giving a total of 73 patientsfollowed for a mean of 4-6 years. 9 of 25 treated by simpletube drainage had a recurrence of pneumothorax on thesame side, compared with 2 of 24 treated with talc-asignificant difference. 3 of 23 given tetracycline had arecurrence, but this figure was not significantly differentfrom the other two groups.

Thoracoscopy was done in 88 % of the original patients totry to predict those who might be at greatest risk of arecurrence; although 16% of these patients had visible cystsor bullae, they were no more likely to have a recurrence thanwere those without such lesions. About two-thirds of all

patients had pain during the period of intubation, withoccasional brief lance-like chest pains being more commonat follow-up in the talc group. Anxieties about the chroniceffects of talc can be substantially allayed by results of earlierlong-term studies.9no The Danish workers conclude that talcpleurodesis with tube drainage offers the best chance ofpreventing recurrence, and that it is no more inconvenientfor the patient than are the other techniques. Thus, thisprocedure reduces the risk of recurrence from 20%-50% toabout 10%, but will have been an unnecessary procedure inthe 50-80% who would not have had a recurrence anyway.In patients who have a recurrence after medical pleurodesis,thoracotomy with parietal pleurectomy or pleural abrasion

6. Hamilton AAD, Archer GJ. Treatment of pneumothorax by simple aspiration.Thorax 1983; 38: 934-36

7. Editorial. Simple aspiration of pneumothorax. Lancet 1984; i: 434-35.8. Spencer Jones J. A place for aspiration in the treatment of spontaneous pneumothorax.

Thorax 1985; 40: 66-679. Research Committee of the British Thoracic Association and the Medical Research

Council Pneumoconiosis Unit. The survey of long-term effects of talc and kaolinpleurodesis. Br J Dis Chest 1979, 73: 285-88.

10. Lange P, Mortensen J, Groth S. Lung function 22-35 years after treatment ofspontaneous pneumothorax with talc poudrage or simple drainage. Thorax 1988;43: 559-61.