Anaesthesia, 1979, Volume 34, pages 567-577 R E V 1 EW ARTICLE

Congenital diaphragmatic hernia

R.J. BRAY

Congenital diaphragmatic hernia (CDH) associated with pulmonary hypoplasia usually presents in early neonatal life. This defect is still the cause of a high mortality rate and is a major challenge to the doctors and nurses who are involved. A defect in the diaphragm occurs in cases of CDH, it may affect one or both sides and through this defect some of the abdominal contents herniate either with, or without, an enclosing sac. An eventration of the diaphragm is a failure of development of part of its muscle and tendon component but a continuous fibrous layer still remains to separate the chest from the abdomen, although it tends to arch upwards into the chest. This review is confined to congenital diaphragmatic hernia; eventrations, diaphragmatic hernias occurring at, or post, delivery and not associated with pulmonary hypoplasia, and hiatus hernias are not considered, The experience obtained in Newcastle is also reported. Hiktory

The first records of diaphragmatic hernia occurring in animals seem to have been made about 4000 years ago in Babylonian times.' Later, in 1575, Ambrose Pare described the condition in adults,2 and in 1804 Astley Cooper described the pathology and clinical presentation in the newborn.3 In 1848 Bochdalek described the embryology of the hernia which

still bears his name4 although his explanation is now thought to be erroneous. The operative treatment of CDH was not generally considered feasible until Ladd & Gross published their series in 1940. Classification Various classifications are described in the literature, based mainly on the position of the defect in the diaphragm. The postero-lateral defect (Bochdalek) is the most common and important, and occurs mainly on the left side. Retro-costosternal hernias (Morgagni) are infrequent in neonates and are usually of small size. Other types described are into the pericardium6*' and bilateral hernia^,**^*'^ both of these types are rare. Incidence The incidence of CDH was reported as 0.45 per 1000 live births in the British Perinatal Mortality Survey of 1958,'' 0.13 per lo00 live births by LeckI2 and 0.33 per loo0 live births by David.I3 There seems to be little geographical variation although it has been suggested that it is particularly common in Greenland.I4 In a survey of 143 cases from the Southwest of England from 1943 to 1974, David & IllingworthI3 concluded that CDH was aetiologically heterogeneous and appeared to be a nonspecific consequence of several teratological processes.

R.J. Bray, MB, BS, DRCOG. FFARCS. Consultant, Newcastle Area Health Authority (Teaching), Department of Anaesthesia, Hospital for Sick Children, Great North Road, Newcastle upon Tyne, NE2 3AX. 0003-2409/79/0600-0567$02.00

0 1979 Blackwell Scientific Publications

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Embryology

In the fetus the diaphragm develops from several different structures. In the 5-week embryo a thick mesodermal plate, called the septum transversum, occupies the space between the base of the thoracic cavity and the stalk of the yolk sac. This structure has large openings on each side called the pleural canals. The lung buds grow into the pleural canals during the sixth week and to allow space for this to continue, small bilateral outpocketing occurs at the level of the third, fourth and fifth cervical segments. These pockets are limited caudally by a crescent-shaped fold, the pleuroperitoneal fold. By the seventh week this fold has fused with the mesentery of the oesophagus and with the septum transversum, the right side usually closing before the left, in thisway separating the thoracic from the abdominal cavity and forming the diaphragm. In the normal course of events the diaphragm is complete before the gut returns from the umbilical coelom to the abdominal cavity at about 10 weeks. A CDH occurs, either because the gut returns to the abdominal cavity prematurely and pushes through the still-open pleural canals, a concept supported by the high incidence of malrotation reported in most series,13.15or by a failure of closure of the pleural canal allowing the normal gut to herniate into the chest, helped by the increasing abdominal muscle tone and fetal breathing movements. These abnormal developments seem to occur between the fifth and eighth week.

Anatomical dejkcts The site of the defect in the diaphragm was found, in David's survey,I3 to be most often posterolateral (approximately 90%), the most common side was the left (75%). a few were bilateral (3.5%) and even fewer retrocostosternal (2%). About half had other malformations, most commonly of the central nervous system (CNS) (28 %), e.g. spina bifida, hydrocephalus, anencephaly and iencephaly. Next most frequently involved was the gastrointestinal tract (20%) where malrotation was the most common defect but rectal and oesophageal atresias also occurred. Abnormalities of the genitourinary system occurred in 15% and 13 % had abnormalities of the cardiovascular system.

The lung on the side of the hernia is almost invariably small and this is not simply an atelectask but a true hypoplasia, which usually affects the other lung as well, although to a much lesser degree (Fig. I). The division of the affected lung into lobes is usually,16 but not always,I7 normal. The shape of the lobes, however, is abnormal and is determined by the structures pressing on them, the lower lobe usually being more affected.I6 The number of generations of airways is reduced by up to a half, the most distal airways being affected to the greatest extent.I6*I '* Sometimes the bronchioles are completely missing and alveoli open directly from the bronchi.16 These various changes can exist throughout a single lung and suggest, on average, a stage of development of the fetal lung normally reached at about 12 weeks,19 shortly after the time that the gut usually returns to the abdominal cavity. The cell types are, however, normal for the gestation of the fetus. Studies on lambs, using the presence of type I1 alveolar cells as an index of alveolar maturity,20have shown that the hypoplastic lungs produced by surgically created diaphragmatic hernias have type I 1 alveolar cells with their typical inclusion bodies.2' The airways terminate in alveoli which are smaller and fewer than n ~ r r n a I . ' ~ *Each '~ terminal bronchus or bronchiole has the usual number of small alveoli but as there are fewer terminal airways the total numbers of alveoli is less than n0rrna1.I~ Alveolar multiplication occurs mainly after birth and helps to account for the rapid growth of the hypoplastic lung which has been observed in survivors. The pulmonary artery is smaller than normal at the hilum but is in proportion to the size of the lung." There is a reduction in the number of pulmonary arteries and muscle is found in the media of much smaller diameter vessels than usual. However the extent of muscle development relative to the vessel distance from the periphery of the lung is Although there is no doubt that physical compression of the lung by the hernia does affect its development, partly by reducing the space available for its growth and partly by reducing the volume of lung liquor which appears necessary for normal development,22 it seems possible that the lungs also require the dynamic stimulus of breathing in utero for full development. Fetal breathing movementsz3 shift

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Fig. 1. A post-mortem specimen of heart and lungs from a case of left CDH, showing the hypoplastic left lung.

amniotic and lung fluid up and down the respiratory tract and in situations where these movements are decreased centrally, e.g. anencephaly, or by deficient amniotic fluid, e.g. renal agenesis, pulmonary hypoplasia occurs. I t is easy to suppose that the breathing movements of a fetus with CDH are rather less effective than normal and that this may influence the development of the lungs. Clinical presentation and diagnosis Over 30% of cases of CDH are associated with maternal hydramnios'2 and even if cases in which the associated CNS or gut malformations which are known to produce hydramnios them selves are eliminated, the association still remains high, being about 28%. There is no other significant obstetric abnormality associated with CDH although there may be features produced by associated fetal CNS abnormalities. There is no proven familial or epidemiological association.' CDH can be diagnosed antenatally by fetography. Contrast is injected into the amniotic fluid, 6-12 hr are allowed for the fetus to swallow it and then an outline of the alimentary tract can be obtained by X-ray.24 Afier birth the baby may establish spon-

taneous respiration but more often some difficulty occurs and active resuscitation is required. Even when respiration has been established spontaneously it soon becomes apparent that all is not well, signs of hypoxia develop and there is often sternal and intercostal recession which indicates a reduction in compliance of the lungs. The abdomen may look empty, or scaphoid, and the chest may appear full. With a left-sided hernia the heart sounds may be heard better on the right, a so-called dextroversion. Occasionally, with a right-sided hernia the liver is not palpable. Rarely, bowel sounds may be heard in the chest. Vomiting is uncommon and if present may indicate a gut complication such as strangulation. A chest X-ray usually provides confirmation of the diagnosis, showing gas-filled intestinal loops and possibly the liver or spleen in the chest. The lung on the side of the hernia may be seen compressed up into the apex and the heart and mediastinurn is pushed towards the opposite side. Unilateral lung cysts can cause confusion25 as can a hamartoma of the lung, a pneumothorax, staphylococcal lung cysts and a loculated haemopneumothorax secondary to haernorrhagic disease of the newborn.26-2The diagnosis in these doubtful cases can often be resolved by passing a nasogastric tube before the X-ray is

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taken and if the stomach is contained in the hernia the tube is seen to loop back into the chest and this may be even better demonstrated if radio-opaque dye is injected down the nasogastric tube.28 The recommendationz9 that air be injected down the nasogastric tube is not to be followed since rapid deterioration in the general condition of the patient due to further compression of the thoracic contents results. Unibilical arteriography30 and a liver scan3’ have been advocated as aids to diagnosis, but in the experience of most clinicians these are sophisticated methods which are not usually necessary and take valuable time to perform.

Management Transfir to a surgical unit

Once the diagnosis has been made, the considerable problem of keeping the child alive and transporting it to a neonatal surgical unit must be considered. Important factors which will determine the ability of the infant to survive are the seriousness of any associated congenital abnormalities, the size of the space-occupying lesion in the chest, the degree of pulmonary hypoplasia and the occurrence of a tension pneumo thorax. A tension pneumothorax is a common cause of death in these babies.j2 It can occur on the side of the hernia or on the contralateral side, during both spontaneous ventilation and intermittent positive pressure ventilation (IPPV). It has been shown in experimentally produced diaphragmatic hernias in lambs that hypoplastic lungs ruptured before they became fully inflated.2 ’ It follows from the Laplace equation that the pressure necessary to expand a small airway is greater than that required for a large one. The diameter of the airways varies between the two lungs and within the hypoplastic lung itself. The pressure necessary to expand the more hypoplastic areas appears to be higher than the rupture pressure of the more normal airways,’l hence the pneumothorax occurs more frequently on the side opposite to the hernia. In addition to a tension pneumothorax, sudden deterioration can also be produced by air swallowing which increases the volume of the gut within the hernia, thus compressing the lungs even further and may even obstruct the venous return to the heart.

Before and during transport the fact that a tension pneumothorax is likely to occur must always be remembered and prepared for and IPPV should probably be avoided unless absolutely necessary. The baby should be transported in 100% oxygen, breathing spontaneously if possible and a high Paco2accepted temporarily. If IPPV becomes unavoidable then low inflating pressures should be used (less than 20 cm H20) and a degree of hypoventilation accepted. The gut within the hernia should be kept decompressed as far as possible by continuous suction on the nasogastric tube and ventilation using a face-mask should be avoided. Elevation of the baby’s head and tilting towards the side of the hernia may help to reduce its size and allow maximum movements of the diaphragm on the normal ~ i d e . Transport ~ ~ * ~ ~ should be as rapid as possible, using a helicopter if necessary, due care being taken to maintain the baby’s body temperature by using an incubator and a heated v e h i ~ l e . ~The ~ - baby ~ ~ should be accompanied by an experienced nurse and the most appropriately experienced doctor who must be able to intubate and ventilate the baby and to drain a pneumothorax. Anaesthesia and operation

On arrival at the neonatal surgical unit the baby should be received into an area equipped for all aspects of resuscitation, including the ability to warm the baby. Although it has been claimed that the mortality rate can be predicted from the values of pre-operative blood gas m e a ~ u r e m e n t sand ~ ~ in - ~some ~ cases quite prolonged efforts have been made to improve these values by IPPV and alkali infusions,42 it seems preferable to proceed as rapidly as possible to surgical reduction of the hernia. Indeed some surgeons are prepared to reduce the hernia without anaesthesia in an acute situation.33 Blood should be taken so that values for haemoglobin level and haematocrit can be measured and to enable one unit of whole blood less than 3 days old to be crossmatched. The operation should be started without waiting for these examinations to be completed. It is our practice to intubate these babies without anaesthesia or relaxation and then to ventilate them with a low peak airway pressure (less than 20 cm H20) using nitrous oxide and oxygen and a low concentration of halothane

Congenital diaphragmatic hernia

(0.5% or less). The gases are delivered via an Ayre’s T-piece, to the reservoir limb of which is attached a fluidlogic-type ventilator,43 which has been adapted for neonatal use by the insertion of a parallel compliance. This allows mechanical IPPV to be started, although some clinicians prefer to continue to use manual ventilation, at least until the hernia has been reduced. During the induction period a surgeon or second anaesthetist is present in the operating theatre, ready to insert a chest drain should a pneumothorax be produced. When the airway has been secured an intravenous cannula is inserted percutaneously and a dextrose/saline infusion started. A non-depolarising relaxant (e.g. 0.5 mg of tubocurarine) is then injected intravenously. Considerable care is taken to maintain the baby’s body temperature during operation by raising the temperature of the operating theatre to about 25”C, by placing a circulating-water heating mattress under the baby and by heating and humidifying the fresh gas flow to the Tpiece.44 The effectiveness of these measures is assessed using a nasopharyngeal thermistor and any necessary adjustment can be made to the temperature of the inspired gas which is monitored using a second thermistor placed in the insulated fresh gas flow lineclose to the baby. The ECG is monitored continuously using either adhesive electrodes or a specially adapted oesophageal ~ t e t h o s c o p e , ~and ~ the arterial pressure is measured ultrasonically. The surgical repair

The surgical approach may be through the chest or abdomen, although most surgeons consider that the abdominal route makes the reduction of the hernia and the correction of any malrotation or other intestinal abnormality easier. The actual reduction of the hernia produces a rapid improvement in the ease of ventilation. Throughout surgery, however, it should be remembered that either lung can easily be ruptured if attempts are made to expand a markedly hypoplastic lung to any extent. Although a contralateral pneumothorax can be drained during surgery from the side of the hernia by passing a cannula through the anterior mediastinum, most often a conventional chest drain is employed. So great

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is this risk of a contralateral pneumothorax and the danger of failing to detect its presence that some workers prefer to insert a prophylactic chest drain on this side before operation. After the reduction of the hernia and, if using the abdominal approach, before the defect in the diaphragm is closed, a chest drain is inserted into the chest on the side of the hernia. Some authorities consider this chest drain to be optional when the abdominal approach is being but this would seem to be an unnecessary risk. It may be possible to close the defect in the diaphragm by suturing the edges together but if the defect is very large this may be impossible and various techniques have been used to overcome this difficulty, e.g. a hinged flap of muscle from the anterior abdominal wall4’ or from latissimus d o r ~ or i ~the ~ use, more recently, of ‘Silastic’ and ‘Teflon’ (Fig. 2). After repair of the diaphragmatic defect any malrotation or other intestinal abnormality or mishap such as ~ t r a n g u l a t i o ncan ~ ~ be corrected and the gut returned to the abdominal cavity. If this proves to be difficult because of a small abdominal cavity that has never before accommodated all the alimentary tract, then, in a manner analogous to the treatment of an exomphalos, a ventral hernia3 can be constructed or a ‘Silastic’ p o ~ c h ~ attached ~ - ~ ’ to the anterior abdominal wall so that the diaphragm is not raised by the excessive intra-abdominal pressure. Peroperative blood loss is usually small but there is often a need for relatively large volumes of plasma or plasma protein fraction (PPF) to be infused to maintain the arterial pressure and skin perfusion. This is probably the consequence of fluid loss from the vessels of the gut within the hernia which may have had a somewhat obstructed venous return.

Postoperative care

At the end of surgery a decision has to be made about the degree of respiratory assistance that the baby will require. Factors involved in this decision include the pre-operative state of the baby, the degree of pulmonary hypoplasia, the presence of a contralateral pneumothorax even though it has been drained, the size of the defect in the diaphragm, the tension of the

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Fig. 2. A ‘Teflon’ patch used in the repair of the diaphragmatic defect.

abdominal wall and the presence and type of other congenital defects. Mechanical ventilation will be required in the majority of cases and in a few the degree of pulmonary hypoplasia is so severe that effective gas exchange will prove to be impossible, but with the remainder a decision can only be made after a trial of spontaneous ventilation. In some cases continuous positive airway pressure (CPAP) has been thought to be helpfuL5* In Newcastle the policy in all cases at the end of surgery is to introduce a nasotracheal tube whose length has been decided by reference to Coldiron’s charts, which relates head circumference to the distance between the nares and the midtra~hea.~’ The tube is secured by means of the head set described by I n k ~ t e r . ’If~ IPPV is required a volume pre-set ventilator which delivers sterile, completely humidified and heated gas of a known oxygen ~ o n t e n t should ~ ~ e ~be~ employed. If a trial of spontaneous ventilation is to be carried out, then the inspiratory limb of the head set is supplied with gas of the same quality, so that the nurse can intervene and ventilate the baby by hand at any time simply by attaching an open-ended bag to the gas outflow limb of the head set. Blood gas measurements are carried out when the baby has settled on the intensive care unit in

order to provide a base line. Arterialised heel prick samples are employed in the belief that their pH, Pco2 and bicarbonate results have sufficient accuracy and repeatability for clinical without the hazards of repeated arterial puncture, indwelling arterial cannulaes9 or an umbilical artery catheter.60 Where possible the baby’s Por should be monitored continuously using a skin Por electrode.6’ The baby is then observed closely for clinical signs of respiratory distress, serial blood gases taken and IPPV started if indicated. The chest drain(s) must be carefully observed to ensure that they are working effectively. This is important because a pneumothorax must be prevented and the pleural exudate which often occurs around the hypoplastic lung must be allowed to drain. This pleural fluid loss can be quite considerable and it should be replaced intravenously with a protein-containing fluid such as PPF. The exudate continues for a few days and then abruptly diminishes, at which time the drain can be removed unless it is still required to drain air. Occasionally it may be necessary to aspirate loculated collections of fluid or air after removal of the drain. The hypoplastic lung usually grows rapidly over the first few postoperative days, largely by increase of size and in the number of alveoli

Congenital diaphragmatic hernia

although in some cases it may take a few weeks.52 During this period there have been several reports of increased alveolar to arterial Po, gradients as a result of right to left hunts,^^^ 62-65 indeed this has been used to predict mortality.66 The increased right to left shunt appears to be the result of arterial vasoconstriction in the hypoplastic lung presumably secondary to hypoxia. It has been investigated by measuring pulmonary artery pressure and pulmonary a n g i ~ g r a p h y ~in~ .patients ~ and in surgicallycreated CDH in lamb^.^^-^^ The shunt takes place through the foramen ovale and the ductus arteriosus, both being consequences of hypoxia and the effects of pulmonary hypertension on the neonatal cardiovascular system. The means to break this vicious circle would seem to be the use of a drug which causes pulmonary vasodilatation. Morphine, prednisolone, c h l o r p r ~ m a z i n e ,tolazoline, ~~ bradykinin and acetylcholine65have all been used with some success and on occasions combined with dopamine4‘ to increase the cardiac output and maintain the systemic arterial pressure. Recently sodium nitroprusside has been used to reduce hypoxic pulmonary vasoconstriction in the respiratory distress syndrome.71 It is possible that this drug could have a beneficial effect on the pulmonary blood flow in cases of diaphragmatic hernia although its use has, so far, proved disappointing in Newcastle. Another serious disorder of pulmonary mechanics which has been encountered in these patients during the postoperative period is due to poor or absent function of the affected side of the diaphragm. The degree of poor function seems to be related to the size of the original defect and the presence of a patch. Any part of the diaphragm without functions tends to move paradoxically during spontaneous ventilation, thus increasing the alveolar dead space by a ‘pendelluft’ type of mechanism. This poor function may also allow retention of bronchial secretions in the affected lung which may consequently become infected. The patch may become detached which re-creates the defect and allows abdominal organs to return to the chest. Another difficulty with the patch occurs when the tissue to which the patch has been sutured stretches and thus reduces the circumference and area of the original defect. The patch then ‘tents’, usually upwards because of the lower

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intra-thoracic pressure, reduces the volume of that side of the chest and causes, in effect, an eventration. WeaningfrornlPPV can take place after trials of spontaneous ventilation whilst the tracheal tube remains in place and progress is assessed with serial blood gases. When spontaneous ventilation has been established it is preferable to keep the baby intubated until there seems little chance of respiratory failure redeveloping and until it is no longer required for the aspiration of bronchial secretions. Laryngeal and tracheal damage appears to be rare provided that these structures were originally normal, the tube is of the correct composition and diameter and is securely The period of postoperative ventilation and intubation can last from a few days to several weeks and if tube or oral feeding cannot be established then intravenous nutrition must be started. Mortality rate

Many babies with CDH die before, or shortly after, birth and less than half survive long enough to reach a neonatal surgical centre. Most of the still-births and early neonatal deaths are due to major associated congenital abnormalities especially those of the central nervous system.” A recent survey in covering the years 1969-1975 revealed that from a total of seventy cases of CDH, recognised retrospectively, but probably still an underestimation, only thirty-three reached a neonatal surgical centre. Ten of these thirty-three died, which is a perioperative mortality rate of 30%. This compares well with other reported series15.42*64-66*75 where the mortality is variously reported as being between 30% and 60%. Much of this variation between series, however, arises from differences of definition, age of presentation and the small numbers in individual series. Long term results

There have been several reports of the long term results of the surgical repair of CDH76-80These are concerned almost entirely with respiratory function although there is an occasional mention of operations for intestinal obstruc-

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tion*" and of a 10% incidence of mental retardation thought to be a result of h y p o ~ i a The .~~ surveys cover children aged 6-18 years who were examined clinically, had chest X-rays and were given a battery of respiratory function tests. Clinically they were quite normal and led normal lives although some had a slight wheeze. Their chest X-rays showed various abnormalities of the diaphragm and some emphysematous changes but the most consistent finding was a decrease in the pulmonary vascular markings on the affected side. Supporting this was a consistent decrease of perfusion of the lung on this side as revealed by lung scans. Screening, where carried out, showed smaller, and delayed, respiratory excursions of the affected diaphragm. Measurements of lung volumes were largely normal but there was a suggestion of a minor degree of airways obstruction during forced expiration. These results suggest that although the lung looks largely normal on chest X-ray it continues to have a degree of hypoplasia in adult life, especially of the pulmonary blood vessels. This does not seem to be secondary to hypoxia and, where it has been possible to examine pulmonary blood flow gradients down the lung, the flow reduction was most marked in the lower zones.*" This is consistent with Areechon's'6 and Boyden's'8 findings that the lower zones were more affected anatomically in the newborn.

The results in Newcastle The neonatal surgical unit moved to its present location during 1971 and only the cases treated since then are reported here. There have been twenty-four cases of CDH with hypoplastic lungs, presenting within 24 hr of delivery and of these thirteen (54%) have died. The number of cases admitted and dying each year is shown in Fig. 3 with each year's percentage mortality shown in Fig. 4. Four cases died before or during operation but the remainder twenty stayed intubated postoperatively, the average duration of intubation being about 12 days (282 hr). Of these, seventeen were ventilated and three were allowed to breathe spontaneously. The average period of ventilation was about 10 days (238 hr). Two babies died from bleeding during operation, possibly caused by pre-operative hypoxia, and one died from associated congenital

0

Total number

6-

1

54-

Cares

Number dying

321-

0-

1

Year

Fig. 3. Cases of congenital diaphragmatic hernia in Newcastle 1971-1 978. 1O O r

80 -

-

60

%

-

20 -

40

0-

-

7 Year Fig. 4. Percentage mortality rate of congenital diaphragmatic hernia in Newcastle 1971-1978.

abnormalities. All the other ten deaths were directly caused by hypoxia. Two died from the effects of a postoperative pneumothorax, one on the side of the hernia which was caused by the chest drain becoming blocked with blood and one on the contralateral side. Seven died from the consequences of a pre-operative tension pneumothorax, one on the side of the hernia, four on the other side and two on both sides. One baby's endotracheal tube fell out during transport and was not replaced. Over half (57%) of the deaths of these babies was caused by a tension pneumothorax, especially on the side opposite to that of the hernia, which occurred before or during transport to the neonatal surgical unit. Most of these deaths could have been avoided by relatively simple means. The ten babies who survived the neonatal period have not been specially investigated but

Congenital diaphragmatic hernia

three have been re-admitted between the ages of 6 and 8 months because of chest infections; one required IPPV for 3 weeks, one appears to have resolving behaviour problems and one required a laparotomy for division of adhesions a t the age of one month. Discussion It seems likely that C D H will continue to provide difficulties in management and will always have a relatively high mortality. The most obvious area for improvement seems to lie in a reduction of the number of babies dying before they reach the neonatal surgical unit. Greater awareness of the likelihood of tension pneumothorax especially o n the side opposite to that of the hernia, and greater care during transport should reduce the mortality. The babies who survive the neonatal period appear to have a good prognosis although the 10% incidence of mental subnormality is a matter for concern. Summary A description of the pathology, clinical presentation and management of congenital diaphragmatic hernia is given together with the results obtained in Newcastle during the last seven years. Some suggestions are made for improved management.

Key words MUSCLE, skeletal, diaphragm. GENETIC FACTORS, diaphragm, hernia. ANAESTHESIA, paediatric. Acknowledgments The author gratefully acknowledges the help and guidance of D r J.S. Inkster in the preparation of this manuscript. Figure 1 is reproduced by the courtesy of Mr J. Wagget, Fig. 2 by the courtesy of Dr J.S. Inkster and the Department of Photography, University of Newcastle upon Tyne. Figs 3 and 4 were prepared by the Department of Graphics, University of Newcastle upon Tyne. References I . WA R KANY, J. (1971) Congenital Malformations. Notes and comments, 1st edn, p. 10. Year Book Medical Publishers, Chicago.

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2. PARE,A. (1575) Les Oeuures. Buon, Paris. (English edn (1634). p. 388. Thomas Johnson, London.) 3. COOPER,Sir A. (1804) The Anatomy & Surgical Treatment of Inguinal and Congenital Hernia, p. 76. T. Cox. London. 4. BOCHDALEK, V. (1848) Einige Betrachtungen uber die Einstcllung des angeborenen Zwerchfellbruches als Beitrag zur pathologischen Anatomie der Hernien. Vierteljahrschrifi fur die praktische Heilkrtnde, 19, 89. 5 . LADD, W.E. & GROSS, R.E. (1940) Congenital diaphragmatic hernia. New England Journal of Medicine, 223, 9 17. G., VESTERDAL. J. & WINKEL SMITH, C.C. 6. THOMSON, (1954) Diaphragmatic hernia into the pericardium. Acta Paediatrica Scandinaoica, 43, 485. 7. SMITH,L. & LIPPERT,K.M. (1958) Peritoneopericardial diaphragmatic hernia. Annals of ' Surgery, 148, 798. 8. FITCHETT, C.W. & TAVAREZ, v. (1965) Bilateral congenital diaphragmatic herniation. Surgery, 57, 305. 9. LEVY,J.L., GUYNES, W.A., LOUIS,J.E. & LINDER, L.H. (1969) Bilateral congenital diaphragmatic hernias through the foramina of Bochdalek. Journal of Pediatric Surgery, 4, 557. 10. THOMAS, M.P., STERN, L.M. & MORRIS, L.L. (1976) Bilateral congenital diaphragmatic hernias in 2 siblings. Journal of Pediatric Surgery, 11, 465. 11. BUTLER, N. & CLAIREAUX, A.E. (1962) Congenital diaphragmatic hernia as a cause of perinatal mortality. Lancet, 1, 659. 12. LECK, I., RECORD, R.G., MCKEOWN,T. & EDWARDS, J.H.(1968) The incidence of malformations in Birmingham, England. 195C1959. Teratology, 1, 263. T.J. & ILLINGWORTH, C.A. (1976) Diaphrag13. DAVID, matic hernia in the Southwest of England. Journal of Medical Genetics, 13, 253. 14. RBNN,G . & ANDERSEN, S . (1971) Diaphragmatic hernias in Greenland. Scandinavian Journal of Thoracic and Cardiovascular Surgery, 5, 284. 15. ALLEN,M.S. & THOMSON, S.A. (1966) Congenital diaphragmatic hernias in children under one year of age: A 24 year review. Journal of Pediatric Surgery, 1, 157. W. & REID, L. (1963) Hypoplasia of 16. AREECHON, lung with congenital diaphragmatic hernia. British Medical Journal, 1, 230. 17. KITAGAWA,M., HISLOP, A., BOYDEN,E.A. & REID, L. (1971) Lung hypoplasia in congenital diaphragmatic hernia. A quantitative study of airway, artery and alveolar development. British Journal of Surgery, 58, 342. 18. BOYDEN, E.A. (1972) The structure of compressed lungs in congenital diaphragmatic hernia. American Journal of Anatomy, 134,497. U. & REID,L. (1961) Development of the 19. BUCHER, intrasegmental bronchial tree: the pattern of branching and development of cartilage at various stages of intra-uterine life. Thorax, 16, 207. 20. KIKKAWA, Y., MOTOYAMA, E.K. & COOK,C.D. (1965) The ultrastructure of the lungs of lambs. The relation of osmiophilic inclusions and alveolar

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