Pulmonary and ductal hemodynamics in studies of simulated diaphragmatic hernia of fetal and newborn lambs

A novel surgical toxicological-free model of diaphragmatic hernia in fetal rats

BACKGROUND

Teratogen-induced congenital diaphragmatic hernia (CDH) rat models are commonly used to study the pathophysiology. We have created a new and reliable surgically induced diaphragmatic hernia (DH) model to obtain a purely mechanical DH rat model, and avoid the confounding teratogen-induced effects on the lung development.

METHODS

Fetal DH was surgically created on fetuses at E18.5 and harvested at E21.5 in rats. Four groups were evaluated (n = 16): control (CONT), control exposed to Nitrofen (CONT NIT), DH surgically created (DH SURG), and CDH Nitrofen (CDH NIT). Body weight, total lung weights, and their ratio (BW, TLW, and TLBR) were compared. Air space (AS), parenchyma (PA), total protein, and DNA contents were measured to verify lung hypoplasia. Medial wall thickness (MWT) of pulmonary arterioles was also analyzed.

RESULTS

DH SURG showed significant hypoplasia (decreased in total protein and DNA) vs CONT (p < 0.05); DH SURG vs CDH NIT were similar in TLW and TLBR. DH SURG has less AS than CONT (p < 0.05) and similar PA compared to CONT NIT and CDH NIT, MWT were similarly increased in CONT NIT, DH SURG, and CDH NIT.

CONCLUSIONS

This novel surgical model generates fetal lung hypoplasia contributing to the study of the mechanical compression effect on fetal lung development in DH.

IMPACT

There is a critical need to develop a surgical model in rat to complement the findings of the well-known Nitrofen-induced CDH model. This experimental study is pioneer and can help to understand better the CDH pathophysiological changes caused by herniated abdominal viscera compression against the lung during the final stage of gestation in CDH fetuses, and also to develop more efficient treatments in near future.

Congenital diaphragmatic hernia: current management strategies from antenatal diagnosis to long-term follow-up

Congenital diaphragmatic hernia (CDH) is a developmental birth defect consisting of a diaphragmatic defect and abnormal lung development. CDH complicates 2.3-2.8 per 10,000 live births. Despite efforts to standardize clinical practice, management of CDH remains challenging. Frequent re-evaluation of clinical practices in CDH reveals that management of CDH is evolving from one of postnatal stabilization to prenatal optimization. Translational research reveals promising avenues for in utero therapeutic intervention, including fetoscopic endoluminal tracheal occlusion. These remain highly experimental and demand improved antenatal diagnostics. Timely diagnosis of CDH and identification of severely affected fetuses allow time for delivery planning or in utero therapeutics. Optimal perinatal care and surgical treatment strategies are highly debated. Improved CDH mortality rates have placed increased emphasis on identifying and monitoring the long-term sequelae of disease throughout childhood and into adulthood. We review the current management strategies for CDH, highlighting where progress has been made, and where future developments have the potential to revolutionize care in this vulnerable patient population.

Prenatal intervention for the management of congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is the result of incomplete formation of the diaphragm that occurs during embryogenesis. The defect in the diaphragm permits the herniation of abdominal organs into the thoracic cavity contributing to the impairment of normal growth and development of the fetal lung. In addition to the hypoplastic lung, anomalies of the pulmonary arterioles worsen the pulmonary hypertension that can have detrimental effects in severe cases. Most cases of CDH can be effectively managed postnatally. Advances in neonatal and surgical care have resulted in improved outcomes over the years. When available, extracorporeal membrane oxygenation can provide temporary cardiorespiratory support for those not effectively supported by mechanical ventilation. In spite of these advances, very severe cases of CDH still carry a very high mortality and morbidity rate. Advances in imaging and evaluation now allow for early and accurate prenatal diagnosis of CDH, thereby identifying those at greatest risk who may benefit from prenatal intervention. This review article discusses some of the surgical and non-surgical prenatal interventions in the management of isolated severe congenital diaphragmatic hernia.

New Insights into Congenital Diaphragmatic Hernia - A Surgeon's Introduction to CDH Animal Models

In recent decades, new research into the developmental defects and pathophysiological basis of congenital diaphragmatic hernia (CDH) has revealed opportunities for the development of innovative therapies. Importantly, the use of animal models to represent this anomaly in the laboratory has resulted in the discovery of many important genetic, epigenetic, and other molecular contributors to this condition. In this review, the most commonly used and newly devised animal models of CDH are presented to familiarize the reader with the latest innovations in the basic sciences.

The making of fetal surgery

Fetal diagnosis prompts the question for fetal therapy in highly selected cases. Some conditions are suitable for in utero surgical intervention. This paper reviews historically important steps in the development of fetal surgery. The first invasive fetal intervention in 1963 was an intra-uterine blood transfusion. It took another 20 years to understand the pathophysiology of other candidate fetal conditions and to develop safe anaesthetic and surgical techniques before the team at the University of California at San Francisco performed its first urinary diversion through hysterotomy. This procedure would be abandoned as renal and pulmonary function could be just as effectively salvaged by ultrasound-guided insertion of a bladder shunt. Fetoscopy is another method for direct access to the feto-placental unit. It was historically used for fetal visualisation to guide biopsies or for vascular access but was also abandoned following the introduction of high-resolution ultrasound. Miniaturisation revived fetoscopy in the 1990 s, since when it has been successfully used to operate on the placenta and umbilical cord. Today, it is also used in fetuses with congenital diaphragmatic hernia (CDH), in whom lung growth is triggered by percutaneous tracheal occlusion. It can also be used to diagnose and treat urinary obstruction. Many fetal interventions remain investigational but for a number of conditions randomised trials have established the role of in utero surgery, making fetal surgery a clinical reality in a number of fetal therapy programmes. The safety of fetal surgery is such that even non-lethal conditions, such as myelomeningocoele repair, are at this moment considered a potential indication. This, as well as fetal intervention for CDH, is currently being investigated in randomised trials.

Linking animal models to human congenital diaphragmatic hernia

BACKGROUND

Congenital diaphragmatic hernia (CDH) is a major life-threatening malformation, occurring in approximately 1 in 3,000 live births. Over the years, different animal models have been used to gain insight into the etiology of this complex congenital anomaly and to develop treatment strategies. However, to date the pathogenic mechanism is still not understood, and treatment remains difficult because of the associated pulmonary hypoplasia and pulmonary hypertension.

METHODS

In this review, data available from several animal models will be discussed. The retinoic acid signaling pathway (RA pathway, retinoid pathway) will be addressed as a developmental pathway that is potentially disrupted in the pathogenesis of CDH. Furthermore, genetic factors involved in diaphragm and lung development will be discussed.

CONCLUSIONS

With this review article, we aim to provide a concise overview of the current most important experimental genetic data available in the field of CDH.

Vitamin A deficiency (VAD), teratogenic, and surgical models of congenital diaphragmatic hernia (CDH)

Congenital diaphragmatic hernia (CDH) is a congenital malformation that occurs with a frequency of 0.08 to 0.45 per 1,000 births. Children with CDH are born with the abdominal contents herniated through the diaphragm and exhibit an associated pulmonary hypoplasia which is frequently accompanied by severe morbidity and mortality. Although the etiology of CDH is largely unknown, considerable progress has been made in understanding its molecular mechanisms through the usage of genetic, teratogenic, and surgical models. The following review focuses on the teratogenic and surgical models of CDH and the possible molecular mechanisms of nitrofen (a diphenyl ether, formerly used as an herbicide) in both induction of CDH and pulmonary hypoplasia. In addition, the mechanisms of other compounds including several anti-inflammatory agents that have been linked to CDH will be discussed. Furthermore, this review will also explore the importance of vitamin A in lung and diaphragm development and the possible mechanisms of teratogen interference in vitamin A homeostasis. Continued exploration of these models will bring forth a clearer understanding of CDH and its molecular underpinnings, which will ultimately facilitate development of therapeutic strategies.

Fetal surgery for congenital diaphragmatic hernia: the North American experience

The role for fetal surgery in treating fetuses with congenital diaphragmatic hernia (CDH) is unclear. Two decades of investigation have improved our understanding of the prenatal natural history, pathophysiology, and outcomes of these patients. During this same period, there have been advances in fetal surgery techniques including improvements in fetal monitoring, maternal-fetal anesthesia, tocolysis, and improved instrumentation to permit increased application of videoscopic approaches. Because of technical challenges, open fetal repair of CDH has been abandoned. Fetal tracheal ligation has shown promise, but a recently published prospective, randomized trial failed to show a benefit of fetoscopic tracheal ligation compared with expert postnatal treatment. Although there is evidence that postnatal outcomes for infants with this disease have improved with the adoption of gentilation ventilator management, high-frequency ventilation, and ECMO, there continues to be a subset of infants with severe CDH that die or suffer serious long-term morbidity despite advanced surgical care. The purpose of this article is to review issues related to prenatal diagnosis, patient selection, and outcomes for fetal surgery; and ultimately to assess whether there is a role for fetal surgery in treating fetuses with CDH.

Evaluation of the development of lung hypoplasia in the premature lamb

BACKGROUND

The death rate from human diaphragmatic hernia (CDH) ranges from 50 to 80%, mainly due to the associated lung hypoplasia. To prevent these irreversible pathological and physical defects, the question of intrauterine surgical intervention arises. The histological changes of the lung tissue after inducement of a diaphragmatic hernia were examined. Of special interest was the time elapsing until the development of lung hypoplasia.

METHODS

A model of intrauterine inducement of diaphragmatic hernia was established using five fetal lambs to study consecutive pulmonary hypoplasia. Inducement of a diaphragmatic hernia was undertaken between 105 and 108 days' gestation. Lung tissue was examined histologically on postoperative days 8, 17, 21, 22, and 25 after inducement of the defect.

RESULTS

On postoperative days 8, 17, and 21, no signs of pulmonary hypoplasia were found on histological examination. A pulmonary hypoplasia was found in two fetuses (on the 22nd and 25th postoperative day). The pathological and anatomical examination of a unilateral pulmonary hypoplasia after a short period of time shows that the artificially created diaphragmatic defect is a good model for producing a congenital diaphragmatic hernia.

DISCUSSION

The severity of the pulmonary hypoplasia is related to the duration of lung compression by the herniated organs. The time elapsing until the development of lung hypoplasia is shorter than expected. Tracheal occlusion seems to be an effective strategy for treatment of the defect CDH, but the best technique for achieving occlusion, and particularly the ideal point in time to carry out "Fetendo," are unknown. Further research into this congenital illness is required in order to treat it.

Expression and cDNA sequence of helix destabilizing protein (HDP) in rat lung

The current study was undertaken to investigate genes that show alteration in expression during late fetal rat lung development. Using the differential display (DD) method, an initially unknown transcript was found to be abundant on day 18 compared to day 22 of gestation. This finding was confirmed by RNA blot analysis. Subsequent screening of a rat lung cDNA library with the unknown DD cDNA as a probe revealed a clone that encodes helix destabilizing protein (HDP), similar to that reported in rat brain (J Biol Chem. 1986, 261:3536-3543). Although there were several differences between lung and brain cDNAs at the 3' untranslated region (UTR), the 5' end was well conserved. There was a gradual decrease in HDP mRNA content beyond day 18 of gestation, as lung maturation increased. Similarly, a lower content of HDP mRNA was observed in maternal heart and brain tissues than in fetal heart and brain tissues from day 18 of gestation. Maternal dexamethasone treatment that promotes lung maturation did not have an impact on HDP expression. Because of the much higher abundance of HDP mRNA during fetal organ development compared to adult tissues, we speculate that HDP plays an important role during lung development. A portion of this work was previously presented (FASEB J. 1996;10:A26).

Surfactant decreases pulmonary vascular resistance and increases pulmonary blood flow in the fetal lamb model of congenital diaphragmatic hernia

INTRODUCTION

Experiments using animal models of neonatal respiratory distress syndrome have shown a decrease in pulmonary vascular resistance (PVR) with surfactant replacement, whereas studies with the lamb model of congenital diaphragmatic hernia (CDH) have demonstrated improvement in oxygenation and lung mechanics with this therapy. The aim of the present study was to measure the effects of surfactant replacement therapy on the pulmonary hemodynamics of the lamb model of CDH.

METHODS

Ten lambs with surgically created CDH and five control lambs were instrumented at term, with the placental circulation intact. Ultrasonic flow probes were positioned around the main pulmonary artery and the common origin of the left and right pulmonary arteries to record total lung and main pulmonary artery blood flow. Catheters were inserted to record systemic, pulmonary, and left atrial pressure. Five CDH animals received 50 mg/kg of surfactant by tracheal instillation just before delivery. All 15 animals were then ventilated for 4 hours.

RESULTS

Correcting the surfactant deficiency in the CDH lamb resulted in a significant increase in pulmonary blood flow, a decrease in PVR, and a reduction in right-to-left shunting. These improvements in hemodynamics were associated with a significant improvement in gas exchange over 4 hours.

CONCLUSION

The fetal lamb model of CDH has elevated PVR in comparison to controls. Prophylactic surfactant therapy reduces this resistance and dramatically increases pulmonary blood flow while reducing extrapulmonary shunt. A surfactant deficiency may be partially responsible for the persistent pulmonary hypertension in neonates with CDH.

Congenital diaphragmatic hernia and associated anomalies: their incidence, identification, and impact on prognosis

The general concept of the association of congenital diaphragmatic hernia (CDH) with other anomalies has been well described. This study is aimed at assessing the distribution of the associated anomalies (AA) by organ system, their influence on prognosis, and the practical signs that should prompt a diagnostic search. One hundred and sixty-six high-risk patients with CDH (symptomatic within the first 6 hours of life) were treated in this institution in the past decade. Sixty-five patients (39.2%) were found to have one or more AA, and 101 had isolated CDH. Of patients with anomalies, cardiac (excluding patent foramen ovale and patent ductus arteriosus) was the most frequent type of AA (63%). Hypoplastic heart syndrome was the most common defect. Many patients had multiple AA. For purposes of analysis, the patients were divided into three groups: isolated CDH, cardiac anomalies, and all other anomalies. The groups were compared with respect to several common clinical and laboratory variables, as well as survival. The frequency and timing of antenatal diagnosis were also noted. The analysis led to the following conclusions. (1) AA are present in more than one third of high-risk patients with CDH; in this group, cardiac lesions predominate. (2) High-risk CDH infants with AA have significantly lower APGAR scores and a lower BPDPO2 (best postductal PO2 before ECMO or surgery) than those with isolated CDH. This is even more evident in the group with cardiac AA. In such patients, a careful search for an undetected AA, especially cardiac, is warranted.(ABSTRACT TRUNCATED AT 250 WORDS)

Surgically produced congenital diaphragmatic hernia in fetal rabbits

Animal models of congenital diaphragmatic hernia (CDH) still are indispensable for the evolution of knowledge related to this disease and to fetal surgery in general. The lamb has provided the most reliable experimental design thus far. Considering the possible advantages of using rabbits (rather than lambs) namely lower costs, no need of special veterinary facilities, smaller body size, year-round availability, higher number of fetuses per pregnancy, and shorter gestational period, a successful model of CDH was developed in fetal rabbits. Sixteen pregnant New Zealand rabbits underwent hysterotomy and fetal operation. Group 1 (6 does) underwent surgery on gestational day 20 and group 2 (10 does) on gestational day 24 or 25. The normal full gestation time is 31 to 33 days. In group 1, the CDH was created by transabdominal puncture and dilatation of the fetal diaphragm. In group 2, the CDH was created through open thoracotomy, either left or right. The fetuses were delivered by cesarean section on gestational day 30. The overall fetal survival rate was 0 for group 1 and 70% for group 2. All operated fetuses in group 2 that were born alive had CDH. The histological morphometric examinations (radial alveolar count after sustained lung expansion) of the normal and operated fetuses in group 2 showed pulmonary hypoplasia in all the lungs on the same side as the CDH (statistical analysis was performed using the Neuman-Keuls test and analysis of variance; the significance level was set at .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal lamb pulmonary hypoplasia: pulmonary vascular and myocardial abnormalities

Neonatal pulmonary hypoplasia resulting from a congenital diaphragmatic hernia (CDH) produces hemodynamic changes and morphologic abnormalities of the pulmonary vasculature. To characterize the myocardial and pulmonary vascular status of the fetus with pulmonary hypoplasia, we studied four chronically instrumented, near-term fetal lambs with pulmonary hypoplasia, induced by producing a diaphragmatic hernia. We found an elevation in the pulmonary arterial pressure (control, 43.8 +/- 5.9 mmHg; CDH, 58.8 +/- 9.1 mmHg; p < 0.05), an elevation in the systemic arterial pressure (control, 43.8 +/- 0.48 mmHg; CDH, 58.6 +/- 6.7 mmHg; p < 0.05), and an elevation in the pulmonary vascular resistance (control, 0.47 +/- 0.11; CDH, 3.87 +/- 1.9; p < 0.05). In addition, though the total pulmonary blood flow was reduced (control, 83.5 +/- 32.9 mL/min; CDH, 22.2 +/- 17.6 mL/min; p < 0.05), the blood flow reduction was proportional to the reduction in the lung mass (control, 79.8 +/- 28.1 [in flow per 100-g lung weight]; CDH, 85.4 +/- 71.7). The increase in the pulmonary vascular resistance in relation to the unit lung mass (control, 0.55 +/- 0.33; CDH, 0.99 +/- 0.5) was not as pronounced as its increase in relation to the total pulmonary blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Pulmonary hypertension in lambs with congenital diaphragmatic hernia: vasodilator prostaglandins, isoprenaline, and tolazoline

After antenatal induction of diaphragmatic hernias in fetal lambs, prostaglandins D2, E1, and I2 were compared to tolazoline, or isoprenaline, for the treatment of pulmonary hypertension. When rendered hypoxic, these, and normal lambs, showed an increase in pulmonary artery pressure, a decrease in systemic pressure, and a decrease in pulmonary blood flow. All of the drugs altered that response, but to different degrees. None of the drugs tested was consistently successful in reversing the adverse affects of hypoxia, but prostaglandin D2 came closest to the ideal vasodilator, decreasing the pulmonary artery pressure in all seven hypoxic lambs having a diaphragmatic hernia. There was a concomitant increase in pulmonary blood flow in six; in the remaining lamb the decrease in blood flow induced by the hypoxia was arrested. At the same time, there was an increase in systemic artery pressure in three, the decrease was arrested in two, but the decrease continued in the other two. Isoprenaline was a more effective drug than tolazoline, producing an increase in pulmonary blood flow in five of the seven lambs, with minor decreases in systemic pressure in five. Tolazoline improved blood flow in three of six lambs (not all lambs survived the full study), with a marked decrease in systemic pressure in four of them. Prostaglandin D2 seems to be a useful drug for the treatment of patients having diaphragmatic hernias and pulmonary hypertension, and warrants further study. Isoprenaline was the most effective of the readily available drugs tested in this animal model.

Experimentally induced congenital diaphragmatic hernia in rats

Experiments to induce congenital diaphragmatic hernia (CDH) in rats, by means of administering a single dose of 2,4-dichlorophenyl-P-nitrophenyl (Nitrofen) on the 10th day of gestation, are reported here. Previously, congenital diaphragmatic hernia has been induced in sheep late in fetal development, and in mice early in gestation. The rat model, including a control group, was used to evaluate lung development and the presence of lung hypoplasia by morphometrical analysis. It was found that the single dose of Nitrofen, given 5 days before the normal closure of the diaphragm in the rat, leads to a high incidence of diaphragmatic hernia, mainly on the right side, and highly abnormal lung development (hypoplasia) comparable to the human situation. Both the lung weight/body weight index as well as the radial alveolar count were significantly lower in animals with CDH (P less than .05). This animal model offers a good opportunity to study abnormal lung development in relation to ventilatory capacity and pulmonary vascular reactivity.

Correction of congenital diaphragmatic hernia in utero, V. Initial clinical experience

Review of our experience with 45 cases of prenatally diagnosed congenital diaphragmatic hernia (CDH) confirms that most fetuses (77%) will not survive despite optimal pre- and postnatal care. Polyhydramnios, associated anomalies, early diagnosis, and a large volume of herniated viscera (including liver) are associated with a particularly dismal prognosis. After extensive experimental work demonstrated the efficacy, feasibility, and safety of repair in utero, we attempted to salvage six highly selected fetuses with severe CDH by open fetal surgery. Five had liver incarcerated in the chest: three died at operation because attempts to reduce the liver compromised umbilical venous return. In one, a Goretex diaphragm was constructed around the liver, but the baby died after birth. The last two fetuses, one with incarcerated liver, were successfully repaired. Both demonstrated rapid growth of the lung in utero, had surprisingly good lung function after birth despite prematurity, had the abdominal patch removed at 2 weeks, and subsequently died of nonpulmonary problems (an unrelated nursery accident in one and intestinal complications in the other). The only maternal complication was amniotic fluid leak and preterm labor. All six women are well and four have had subsequent normal children. From this phase I experience, we conclude that fetal surgery appears safe for the mother and her reproductive potential, that fetal CDH repair is feasible in selected cases, and that the fetal lung responds quickly after decompression. However, fetal repair remains a formidable technical challenge.

Pulmonary barotrauma in congenital diaphragmatic hernia: experimental study in lambs

A left diaphragmatic hernia was created surgically in 20 fetal lambs between 93 and 110 days of gestation. Ten animals were alive with defects at cesarean section near term (135 to 140 days). These animals and two controls were submitted to various transpulmonary pressure gradients (inspiratory pressure minus pleural pressure). Hemodynamic and ventilatory studies were performed after the correction of the hernia. Morphometric analysis of the lung was carried out in all cases. The results showed a highly significant linear correlation between the transpulmonary pressure gradient employed and the pulmonary interstitial emphysema found at morphometry. Our data suggest that using low ventilatory pressures and not draining the pleural cavity results in less trauma to both lungs and may prevent one of the components of the pulmonary hypertension so often seen in newborns with congenital diaphragmatic hernia.

Consequences of antenatal diagnosis for pediatric surgery

Based on an increase from 6000 ultrasound examinations done at the First University Gynecological Hospital of Munich in 1969 to more than 13,000 in 1982, and on an increased rate of antenatally diagnosed malformation, the accuracy of antenatal ultrasound diagnosis was investigated. It turned out that correct diagnosis could be made in over 80% of cases. However, this was incomplete in approximately 40% of the cases, since associated malformations of the gastrico-intestinal tract, congenital heart disease, myelomeningocele in correctly diagnosed hydrocephalus, and others were not recognized. False-positive results were found in 17.5% of cases, false-negative ones in 12.7%. Because of the uncertainty of antenatal diagnosis and ignorance of many physiological parameters, intrauterine surgical treatment cannot be advocated at present. Intrauterine measures are still confined to punctures, administration of drugs, and diagnostic procedures. Further consequences such as termination of pregnancy, psychological aspects, and possible development of intrauterine therapy are discussed.

Congenital diaphragmatic hernia

Congenital diaphragmatic hernia continues to be a critical problem in neonatal surgery. Despite the apparent simplicity of the anatomic defect, the physiology is complex, and survival remains uncertain. Surgical success has been achieved, but we recognize that the barrier to survival is pulmonary parenchymal and vascular hypoplasia as well as the complex syndrome of persistent fetal circulation. In many ways the problem of diaphragmatic hernia is as much of an enigma to today's physician-scientist as it was to Bochdalek in the nineteenth century. The treatment of respiratory distress after repair of congenital diaphragmatic hernia has brought out the most creative and innovative efforts of pediatric surgeons in both the laboratory and the intensive care unit.

[New developments in pediatric surgery]

New concepts in pediatric surgery have been developed concerning inter-disciplinary problems such as ureter implantation or urinary undiversion as well as deformities of abdominal organs such as biliary atresia, anorectal malformations, adrenogenital syndrome and sinus urogenitalis. Considerable improvements in fetal surgery as a part of pediatric surgery were achieved. For diagnostic, surgical and ethical reasons, however, these efforts are, for the time being, only of theoretical interest.

Creation and repair of diaphragmatic hernia in the fetal lamb: lung development and morphology

Left-sided diaphragmatic hernias were created in 26 lambs at about 78 days' gestation and repaired at 106 to 124 days' gestation. Nine of these lambs were delivered at term and lived much longer than the nonrepaired lambs delivered at term. The normal development of the fetal lamb lung is compared and contrasted with the development of the lung after creation of a diaphragmatic hernia and also with the changes in morphology resulting from in-utero repair. Creation of a diaphragmatic hernia resulted in marked delay in the development of alveoli and at term the lung had small, thick-walled terminal air-spaces with few capillaries and no true alveoli when compared with the thin-walled alveoli in normal lungs. Another striking feature was an apparent increase in the frequency of type II alveolar cells in diaphragmatic hernia lungs. In-utero repair of the diaphragmatic hernia resulted in a more normal appearance with true alveoli developing by term, although capillaries appeared to be less numerous and type II cells more numerous than in normal lungs. Surprisingly, there appears to be little difference between the left and right lungs in lambs with diaphragmatic hernia.

Creation and repair of diaphragmatic hernia in the fetal lamb: techniques and survival

Diaphragmatic hernias were created in 54 fetal lambs at 72 to 82 days gestation via a left thoracotomy. The diaphragmatic hernia was repaired in 30 lambs at 106 to 123 days gestation, and 14 of these lambs subsequently aborted. The majority of those surviving to term were delivered for survival. Four lambs with an unrepaired diaphragmatic hernia were intensively resuscitated at delivery and their diaphragmatic hernias repaired; survival in these lambs ranged from 20 minutes to 89 hours. Nine lambs with repaired diaphragmatic hernia were resuscitated following delivery; survival times ranged from one hour, 45 minutes to 123 days, with three lambs surviving to be sacrificed at 43, 62, and 123 days. Three of the lambs that died before sacrifice, died of causes unrelated to their lung function. These results show that in-utero repair of the diaphragmatic hernia in the fetal lamb results in improved survival. We feel, however, that direct application of these results in humans would be premature.

Intrauterine cardiothoracic surgery: the fetal lamb model

We have developed fetal lamb models of congenital cardiothoracic lesions that have been allowed to progress through birth for physiological study. Simulated lesions, simulated repairs, actual lesions, and actual repairs have been performed in this model. Sixty-two fetal lambs comprised the study group, including 48 in which models were created and 14 controls. Models included pulmonary stenosis, aortic stenosis, and diaphragmatic hernia. Gestational age ranged from 90 to 120 days (0.6 of normal gestation). In each pregnant ewe, laparotomy and hysterotomy were performed under general anesthesia, with care taken to avoid placental vessels. The foreleg was exposed, the appropriate anterior chest wall was isolated, and a thoracotomy was done. Thoracic or cardiac procedures then were performed under controlled transplacental anesthesia and perfusion. Following completion of the procedure, the fetal thoracotomy was closed, sterile antibiotic solution was placed in the amniotic sac, and the hysterotomy and laparotomy were closed. Subsequently the fetus either was allowed to progress to birth and infant study or underwent subsequent intrauterine repair and then was allowed to progress to birth and neonatal study. This fetal lamb model provides reproducible anatomical and pathophysiological lesions to facilitate the development of techniques for repair of such lesions in early infancy. Further, it offers the potential for developing methods of intrauterine cardiothoracic surgical repair.

Correction of congenital diaphragmatic hernia in utero. III. Development of a successful surgical technique using abdominoplasty to avoid compromise of umbilical blood flow

Infants born with congenital diaphragmatic hernia (CDH) die because their lungs are hypoplastic. In the fetal lamb, the lung made hypoplastic by compression with an intrathoracic balloon can, if decompressed in utero, grow and develop enough to permit survival at term. To study the efficacy and feasibility of in utero repair of CDH, we created diaphragmatic hernias in fetal lambs at approximately 100 days gestation and corrected them surgically at approximately 120 days. Repair of the diaphragm with closure of the abdomen resulted in postoperative fetal death in six lambs. Acute studies demonstrated that increased intraabdominal pressure compromises blood flow in the umbilical vein and produces severe fetal distress. When a silastic patch was used to enlarge the abdomen after reduction of the viscera and repair of the diaphragm, six of nine lambs were viable after term delivery. In sacrificed lambs, the lungs were well expanded, mature histologically, and greatly increased in size. Correction of CDH in utero appears physiologically sound and technically feasible.

Congenital diaphragmatic hernia

Surgical intervention for congenital diaphragmatic hernia is urgent, but success depends more on preoperative and postoperative management of the associated physiologic derangements. Survival seems to depend on the condition of the lungs at birth. In the future, correction of congenital diaphragmatic hernia in utero may be possible.

Vasodilator response and prediction of survival in congenital diaphragmatic hernia

In an effort to find an accurate prediction of survival in congenital diaphragmatic hernia (CDH) patients with severe respiratory distress and persistent pulmonary hypertension, we reviewed the response to vasodilators and te clinical course of 13 patients with this condition. All patients had been operated upon within the first 24 hr of life and had postoperative descending aortic PaO2 values less than or equal to 50 torr on maximum ventilatory support. The only significant change in standard blood gas values after an intravenous test dose of 2 mg/kg of tolazoline was in the PaO2 (p less than 0.05). Patients with good response (PaO2 increase greater than 100 torr) survived. Patients with fair response (PaO2 increase between 20 and 100 torr) had equivocal survival. Patients with poor response (PaO2 increase less than 20 torr) died. There was a postoperative period up to several weeks of marked fluctuations in arterial oxygen tension in survivors before stability occurred. Vasodilator responsiveness appears to be an accurate, therapeutic indicator of the chances for survival in CDH patients with persistent pulmonary hypertension and right to left shunting.

Congenital diaphragmatic hernia

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.

Hemodynamics of congenital diaphragmatic hernia in lambs

Despite surgical treatment, congenital foramen of Bochdalek diaphragmatic hernia continues to carry a high mortality rate due to associated respiratory insufficiency. We studied the pathologic and hemodynamic changes that result from this condition in lambs. Surgical creation of diaphragmatic hernias in fetal lambs was performed in utero with subsequent delivery by cesarean section near term. Cardiac catheterization was performed on these newborn lambs immediately after delivery, before and after surgical repair of the defect. Data from five of these lambs were compared to data obtained from seven normal lambs. Pulmonary hypertension was found only in lambs with hernias. Pulmonary artery pressures and the mean ratio of pulmonary to systemic resistance were higher in experimental lambs. Oxygen saturation and average cardiac index were higher in normals. Lambs in the experimental group, but not in the control group, had large left-to-right shunts at the level of the ductus arteriosus in the early neonatal period. Arterial oxygen saturations were consistently low with no differences in pre- and post-ductal samples, which suggests right-to-left shunting at the atrial level or physiologic shunting across the unexpanded lungs. No further expansion of the hypoplastic lungs occurred following decompression by surgical hernia repair, but transient hemodynamic improvement was noted in some cases. Surgical ligation of the ductus arteriosus did not significantly alter the clinical condition of the lambs. Lungs in lambs with hernias were grossly abnormal, the left appearing more hypoplastic than the right.

Pulmonary artery pressure monitoring in persistent fetal circulation (PFC)

The use of the Swan-Ganz catheter to monitor pulmonary artery pressure in adults with cardiopulmonary failure has become commonplace. Our meager experience was with four neonates diagnosed as having persistent fetal circulation monitored by the use of this PA catheter. Tolazoline was infused directly into the pulmonary circulation via the catheter. Pulmonary artery pressure was temporarily reduced by tolazoline administration, with a marked increase in PaO2. More experience is required to define the role of the Swan-Ganz catheter in neonatal physiologic monitoring.

Management of pulmonary insufficiency in diaphragmatic hernia using extracorporeal circulation with a membrane oxygenator (ECMO)

Persistent fetal circulation (PFC) causes severe pulmonary insufficiency in patients who have demonstrated adequate lung function following diaphragmatic hernia repair. Patent ductus arteriosus (PDA) ligation corrects this condition, but carries the risk of sudden right ventricular failure. Pharmacologic reversal of PFC may be attempted, and if unsuccessful, prolonged venoarterial bypass becomes necessary to provide effective pulmonary support. PDA ligation can then be performed safely and maturation of the pulmonary vasculature allowed to occur. Pulmonary artery pressure monitoring is essential.