The embryonic diaphragm has six major components—septum transversum, pleuroperitoneal membrane, thoracic mesoderm, and retroglandular, aortic, and mesogastric mesoderm. In the fourth postconceptual week, the septum transversum appears as a derivative of the pericardial sac and begins to divide the peritoneal and pleuropericardial cavities. The large pleuroperitoneal canals eventually form a membrane that separate the thoracic and coelomic cavities by the eighth week.

In the third month, retroglandular (perinephric) and aortic mesenchyme move in a dorsal to ventral direction to fuse with the septum transversum, with additional contributions to the eventual dorsal musculature coming from mesogastric mesoderm. Anterolaterally, costal myoblasts separate as an inner muscular layer from the thoracic wall (perhaps explaining the dual musculature of the thorax as opposed to the treble layers of the abdomen) to move centrally and join with the transverse septum. It is uncertain whether the lumbocostal trigone is the last remnant of this pleuroperitoneal membrane or is a junction of the anterolateral and dorsal musculature; current thought favours the latter explanation. By the time of parturition, the neonatal diaphragm has four major regions, defined by the central tendon, the dorsal musculature through which the various foramen pass, the posterolateral lumbocostal triangle, and the anterolateral muscle.

The cervical innervation of the diaphragm by the phrenic nerve may be a muscular contribution to the diaphragm derived from the infrahyoid mesoderm as myoblasts migrating to the transverse septum. Embryologically, a muscular component of the septum is not identified. A more likely explanation may be found in the gradual relocation of the dorsal alignment of the transverse septum from a cervical to lumbar orientation. During this period of accelerated craniothoracic growth, the diaphragm appears to ‘descend’. During these fetal stages and by the eighth embryonic week, the phrenic innervation is complete.

Although a deficiency in any of the mesodermal contributions may create a hernia, the most frequent congenital defect is through the posterolateral aspect of the diaphragm (the hernia of Bochdalek) (Fig. 1) 1971. The closure of the pleuroperitoneal canal at the eighth week only shortly precedes the rapid return of the intestine from the yolk sac to the abdomen at the tenth embryological week. Moreover, during these fetal stages the muscular formation of the diaphragm is proceeding. An imbalance between the speed of the diaphragmatic closure (as a membrane and as a muscle) and the increasing pressure in the peritoneal cavity may provide an opportunity for the intestine to intrude itself into the newly forming hemithorax. The left hemidiaphragm closes at a slightly later fetal stage than does the right diaphragm. A combination of earlier closure and the protection to the right hemidiaphragm afforded by the hepatic anlage may explain the overall predominance of left-sided posterolateral diaphragmatic defects.

One of the most challenging experiences for the practising physician is the infant with the congenital diaphragmatic hernia and immediate respiratory distress. Despite advances in neonatal intensive care and respiratory support, infants who present with respiratory distress in the first 6 h have a predicted 50 to 80 per cent mortality rate. Pulmonary hypoplasia and a reactive pulmonary artery vasculature accentuate the risk. The hernia of Bochdalek, or posterolateral diaphragmatic hernia, has an incidence of 1 in 4400 live births and a predicted incidence of approximately 1 in 2200 conceptions. Many of these fetuses have associated congenital and chromosomal anomalies that are incompatible with life and result in early fetal loss or stillbirth. The severity and frequencies of these congenital anomalies must be weighed in evaluating new therapies designed to address the problem of diaphragmatic defects, particularly those demanding in-utero intervention.

A left-sided diaphragmatic defect occurs in 80 to 90 per cent of babies with respiratory distress at birth. Right-sided defects are found in 15 per cent of cases; bilateral herniae are rare. The male to female ratio is 1:1.36. In diaphragmatic defects that manifest themselves late the right to left ratio tends towards an equal distribution.

A high index of suspicion for diaphragmatic hernia must be raised when an infant has respiratory distress. While other causes of respiratory distress need to be eliminated, the classic clinical presentation of a scaphoid abdomen and barrel chest with a right-sided cardiac impulse suggests the presence of an underlying diaphragmatic defect. Many children with diaphragmatic herniae are term infants with no other obvious anomaly.

Once the problem is recognized, intubation is mandatory. Continued mask ventilation makes matters worse by causing insufflation and distension of the intrathoracic abdominal viscera with worsening hypoxia and hypercarbia. The underlying pulmonary hypoplasia prevents dynamic chest motion and if there is a possibility of a diaphragmatic defect, low pressure, high frequency ventilation is recommended at peak inflation pressures of 30 cmH&sub2;O and respiratory rates of 60 to 120 cmH&sub2;O. Once the child is intubated, a nasogastric tube should be passed to prevent further distension of the distal bowel and worsening pulmonary compression.

Intravenous fluid adminstration is started. Acidosis needs to be corrected aggressively with a sodium bicarbonate drip (0.5–2 mEq/kg.h). A child in respiratory distress should be paralysed with pancuronium and sedated with fentanyl (which may have some beneficial pulmonary vasodilatory effects).

Immediate operative reduction does not improve the mortality rate. Evisceration of the infant in the delivery room has been universally fatal. A period of stabilization may be of some benefit. Predictors of survival have been proposed, based on radiographic criteria, level of preoperative acidosis, and on the arterial CO&sub2; and the ventilatory index (respiratory rate × mean airway pressure). Using these standards, aggressive support need not be continued for the infant who remains hypercarbic in the face of a high ventilatory index: this indicates a degree of pulmonary hypoplasia that precludes survival. Nonetheless, the newer treatment modalities available make it possible for some infants in this group to survive.

After stabilization, the child is taken to the operating room, where the incarcerated viscera are removed from the thoracic cavity through a subcostal incision. The majority of neonates do not have a sac if a large diaphragmatic defect is found. A posterior rim of muscle is frequently found; this needs to be freed from the retroperitoneum and the adrenal gland and approximated to the larger anterior leaf. If possible, a two-layer closure in performed, always using a non-absorbable suture. Occasionally, the defect is so large that synthetic material must be used: any of the prosthetic materials that are currently available are suitable, although Gore-Tex is our preferred material. Muscular flaps have also been used to close a large defect but, if extracorporeal membrane oxygenation is being considered, extensive dissection should be minimized and a patch should be used.

Non-rotation of the gastrointestinal tract is a universal finding in the neonate with a left-sided diaphragmatic defect. If the child's condition is sufficiently stable, division of duodenal and colic bands (Ladd's procedure) is performed to open the small bowel mesentery widely. An incidental appendectomy is performed.

Postoperative care in directed to minimizing the onset of persistent pulmonary hypertension of the newborn. The pulmonary vasculature of the infant with diaphragmatic defects in the neonatal period has a diminished cross-sectional area as well as extension of medial hypertrophy out to terminal arterioles. The best means of preventing return of the ‘fetal’ circulation appears to be a combination of mild alkalosis with normal oxygenation. The use of alkalinizing agents, including sodium bicarbonate or tromethamine, is of some benefit. If a respiratory alkalosis can be induced, there may be a benefit to reaching that CO&sub2; tension at which pulmonary artery hypertension reverts. The combination of acidosis and hypoxia, however, causes severe, unrelenting pulmonary hypertension and right to left shunting through the patent foramen ovale and the patent ductus arteriosus.

Ventilator management is crucial. Changes tolerated by a normal infant or adult can result in reversal of the pulmonary vasodilatation and return to the vasoconstricted state. A switch from this normally perfused pulmonary bed to the vasoconstricted state, with increased right to left shunting, has been termed the ‘honeymoon’ period. Initial ventilator changes gradually lower the FIo&sub2; and then decrease the peak inflation pressure to a normal range. High peak inflation pressure increases barotrauma and eventually results in the formation of interstitial emphysema and late bronchopulmonary dysplasia.

High frequency jet ventilation and oscillatory ventilation have been used in the medical management of neonates with persistent pulmonary hypertension. This type of ventilation depends on a diffusion of CO&sub2; out in small increments while oxygenation is maintained at much lower mean airway pressures. Although early experience has failed to demonstrate significant success, continued investigation in this therapy is ongoing because of the apparent diminution of barotrauma.

The only pharmacological agent of benefit in reversing pulmonary hypertension is tolazoline. Tolazoline appears to act as a mild vasodilator, but inhibits the activation of native vasoconstrictors of the arachidonic acid pathway (thromboxane, leukotriene). This pharmacological support is effective in only 30 per cent of cases. Additionally, there is appreciable gastrointestinal morbidity, including massive bleeding and infarction. Before initiating tolazoline, a bolus of crystalloid or albumin should be given intravenously to avert these complications. Tolazoline is initially given as a 0.5 to 1 mg/kg bolus over 15 min. If reversal of the hypoxia occurs (with a rise in postductal Pao&sub2; of more than 13 kPa), the drip is continued at a rate of 1 to 2 mg/kg.h until the child can be weaned from the ventilator. Other agents, including nitroglycerine, nitroprusside, and isuprel, have not had much effect on pulmonary hypertension.

If medical therapy fails, extracorporeal oxygenation has been used in infants with sporadic reversal of the previously seen 100 per cent mortality rate. The criteria for use of this therapy varies from hospital to hospital, but commonly include prolonged Aao&sub2; gradient greater than 78 kPa for over 12 h, oxygenation index (OI) greater than 40 (OI =(FIo&sub2; × MAP/postductal Pao&sub2; (in torr)) × 100) or evidence of severe barotrauma. An infant whose condition meets these criteria has a predicted mortality rate from 80 to 90 per cent. Extracorporeal membrane oxygenation, which consists of bypass through a membrane oxygenator, can reverse pulmonary hypertension. In the neonate, extracorporeal support is provided by placing a venous drainage catheter into the right atrium and an arterial catheter in the right common carotid artery. Once the catheters are in place, the blood is passed through a membrane oxygenator, through a heat exchanger, and is then returned to the infant's arterial side. The infant needs to be heparinized, and there is a risk of bleeding. Intracranial haemorrhage occurs in 10 to 15 per cent of neonates: bypass needs to be urgently terminated, as extension of the bleeding can be fatal.

Sixty-two per cent of neonates with diaphragmatic hernia and unrelenting persistent pulmonary hypertension survive following treatment with extracorporeal membrane oxygenation. There is less of an impact on the incidence of bronchopulmonary dysplasia.

Perhaps the most exciting new venture in surgery is the use of in-utero surgery to correct diaphragmatic defects. Although there is a high incidence of congenital anomalies, and despite the fact that 25 to 50 per cent of children with diaphragmatic hernias have a good outcome with conventional therapy, if a population of fetuses can be identified with a high risk of a fatal outcome, in-utero intervention may be indicated. The presence of an intrathoracic stomach and evidence of maternal polyhydramnios are potential indicators. Diaphragmatic hernia identified before 24 weeks of gestation is frequently associated with other severe congenital anomalies. Successful in-utero intervention with reduction of in carcerated viscera and repair of left-sided diaphragmatic herniae has been reported in two children. This remains an experimental therapy but may become a major treatment modality.

Infants and children with diaphragmatic herniae who do not have respiratory distress in the first 6 to 12 h of life have a more favourable prognosis. These children with late-presenting posterolateral diaphragmatic herniae do not have the complicating feature of pulmonary hypoplasia, and their perioperative mortality in this group is low, and should theoretically approach zero. The differential diagnosis includes pneumatoceles secondary to staphylococcal pneumonias (Fig. 3) 1973 and the macrocystic variant of cystic adenomatoid malformation. Contrast studies can help delineate the presence of intestine in the thoracic cavity.

Surgical repair can be accomplished through the abdomen in almost all instances. Even right-sided diaphragmatic defects are generally easily approached and repaired through the abdomen, although a thoracic extension is occasionally necessary. A thoracic approach can be successfully used, but reduction of the intestine may not be easily accomplished.

Of special note is the presentation of right-sided diaphragmatic herniae with group B streptococcal infection. While streptococcal infections are common in the neonatal period (estimated at 1 in 300 births), the presence of a right-sided ‘pneumonia’ that fails to respond to appropriate antibiotic coverage should alert the physician to the presence of a right-sided diaphragmatic defect.

Isolated anterior diaphragmatic defects through the retrosternal space of Larrey create the Morgagni hernia. The defect is most frequently noted as an unexpected radiographic finding. Repair is easily accomplished and should be performed to avoid the potential complications of incarceration or gastric volvulus. The anterior diaphragmatic defect associated with the pentalogy of Cantrell is more complex. This defect is a remnant of the pericardioperitoneal canal and is associated with epigastric omphalocele, crescentic anterior diaphragmatic defect, pericardial defect, ectopia cordis, distal sternal cleft, and ventriculoseptal defect.

Para-oesophageal hernia in the neonate is secondary to the failure of dorsal musculature to form from the posterior mesoderm. These defects are rare and generally present because the children eat poorly and do not grow. Pulmonary hypoplasia does not complicate either the Morgagni or congenital para-oesophageal herniae.

Diaphragmatic eventration can be congenital or acquired. The congenital form presents with moderate respiratory distress. Although attempts at medical management are occasionally successful, additional ventilatory support is often indicated. If the child is dependent on a respirator for more than 5 days, the eventration is best addressed by diaphragmatic plication. Plication usually increases the functional residual capacity and allows rapid weaning from the ventilator.

The acquired forms of eventration are secondary to phrenic nerve damage or entrapment. If respiratory distress does not intervene, observation alone is indicated. If symptoms are present, plication through a low thoracic approach can be beneficial. In the special instance of an intraoperative phrenic nerve injury, immediate plication of the diaphragm, particularly in infants, seems to avoid postoperative respiratory problems. In over 80 per cent of patients treated with immediate plication, diaphragmatic motion appears to return to normal when studied fluoroscopically.

The most common type of diaphragmatic hernia is the hiatal hernia. Three types of hiatal herniae have been described. The classic sliding hiatal hernia (type I) is the passage of the gastro-oesophageal junction and variable amounts of cardia above the diaphragm. In type II hiatal hernia, commonly referred to as paraesophageal or rolling hernia, the gastro-oesophageal junction remains below the diaphragm but the fundus rolls up, generally in an anterior location, next to the oesophagus. The type III hiatal hernia is a combination of a sliding and para-oesophageal hernia.

Hiatal herniae by themselves may be asymptomatic. Increased intra-abdominal pressure during routine upper gastrointestinal contrast studies frequently discloses a small sliding herniae in the normal population. Nonetheless, 20 per cent of hiatal hernia become symptomatic, primarily because of problems related to oesophageal reflux.

In contrast, para-oesophageal herniae can be associated with upper abdominal discomfort. Occasionally, fatigue and malaise are symptoms of chronic blood loss, which may be secondary to engorgement of the entrapped gastric mucosa. Reports of incarceration followed by strangulation have appeared.

Asymptomatic sliding hiatal herniae do not require surgical exploration. Patients with symptomatic type I hiatal herniae and oesophageal reflux should initially be managed medically with antacids or H&sub2;-receptor antagonists to diminish the acidity of the gastric efflux, and with metoclopramide, which promotes gastric emptying and tightens the lower oesophageal sphincter. Simethicone tablets may relieve symptoms. If medical management is unsuccessful or if complications such as oesophageal ulceration, stricture, stenosis, or Barrett's oesophagus intervene, surgical repair is indicated. Repair can be accomplished satisfactorily by a transthoracic or transabdominal approach. Nissen fundoplication, Belsey-Mark IV fundoplication, and the Hill gastropexy all produce excellent results when properly performed.

Large para-oesophageal hiatal herniae in otherwise healthy individuals should be repaired, even when asymptomatic. Incarceration, strangulation, or haemorrhage of such a hernia is an indicator for urgent repair.

Traumatic diaphragmatic injuries may result from either penetrating or blunt trauma, usually of the lower chest or upper abdomen. The location of the injury to the diaphragm is variable and is associated with injuries to other anatomic structures, particularly the ribs, spleen, long bones, the cranium and its contents, and the liver (Fig. 4) 1974.

Diaphragmatic injury is frequently difficult to diagnose and is often an unexpected finding at exploration in a patient who has suffered penetrating trauma. A high index of suspicion for the presence of diaphragmatic injury is necessary. Symptoms directly related to this injury are due to the effects of encroachment and entrapment of herniated viscera within the affected hemithorax; dyspnoea and pain related to the injured thorax or abdominal wall are common. Physical findings relate to thoracic or abdominal injury and to those specific to the diaphragmatic injury (dullness and diminished breath sounds over the affected hemithorax). The initial chest film is often normal or shows no specific findings. Non-specificity occurs more frequently following blunt injury: apparent elevation or irregularity of the diaphragm or extraneous shadows above the diaphragm suggest the diagnosis. In a stable patient, a contrast study of the stomach may establish the diagnosis, as may ultrasonic examination or CT scan with visceral contrast. Since diaphragmatic rents do not heal spontaneously, all injuries should be surgically repaired. The operative approach is largely determined by the condition of the patient and the nature of the suspected injury. Haemodynamically stable patients may be approached on a semi-urgent basis, the abdominal approach being used because of the frequency of associated occult intra-abdominal injuries. If suspected injuries to thoracic organs dictate thoracotomy, diaphragmatic repair can be accomplished through either the thoracotomy or via a laparotomy. Most diaphragmatic injuries can be closed with simple non-absorbable sutures.

The chronic presentation of diaphragmatic rupture represents the effect of entrapment of stomach, colon, or small bowel within the thorax, or the consequence of long-standing pulmonary collapse from encroachment on the affected lung. Early satiety, postprandial distress, productive sputum, or dyspnoea are the presenting symptoms. A chest radiograph with subsequent contrast examination of the gastrointestinal tract will usually secure the diagnosis. A thoracotomy is usually appropriate to allow separation of adhesions between the trapped viscera and lung, with subsequent repair of the diaphragmatic injury through this exposure.

Diaphragmatic pacing in adults is usually performed for quadriplegia and secondary diaphragmatic muscle paresis. In infants, congenital central alveolar hypoventilation syndrome (Ondine's curse) and Arnold–Chiari II malformation respond well to the use of the pacemaker. An electrode is placed about the phrenic nerve in the chest of an infant and in the neck of an adult: such a pacemaker can free at least partially over 90 per cent of patients from ventilator dependence.

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