Lung injury from oxygen in lambs: the role of artificial ventilation

Bronchopulmonary dysplasia-A historical perspective

Bronchopulmonary dysplasia (BPD) was first described by Northway et al in 1967. This article describes the evolution of our understanding of the pathophysiology of BPD and the approaches to treatments of this illness developed over the past fifty years. These interventions had their roots in the understanding of the principles of the surface tension present at air-liquid interfaces, which were developed over 150 years before BPD's initial description. Improving outcomes in neonatal care have led to greater survival of preterm and very preterm infants, and to an evolution of the pathogenesis and pathology of BPD, from an illness caused primarily by barotrauma and oxygen toxicity to one of interruption of lung development. While the incidence of BPD has remained about the same in recent decades, this is because survival of infants born at lower gestational ages is increasing. Understanding of molecular, genetic and physiologic mechanisms has led to newer treatments that have mitigated some of the harmful effects of prolonged mechanical ventilation. Recognition of BPD as a chronic multi-system disease has resulted in further improvements in care after discharge from neonatal intensive care. Since many of the origins of chronic obstructive lung disease in adults are based in childhood respiratory illnesses, improving outcomes of BPD in infancy and childhood will undoubtedly lead to improved respiratory outcomes in the adults that these children will become.

Mary Ellen Avery's Research Career - Remembrance of Things Past

Mary Ellen Avery's research is recognized as a milestone in biomedical research. She had discovered the underlying cause of hyaline membrane disease, surfactant deficiency, fostering ever more vigorous efforts to reduce neonatal mortality in the burgeoning practice of Neonatology. Neonatology is the only clinical discipline that began as an experiment, making it a model for biomedical research. Avery knew that the concerted effort to treat preterm newborns could potentially do more harm than good, violating her oath to Hippocrates, if not held to the highest scientific standards. She remained true to that pledge throughout her career, as recounted in this Review.

Hyperoxic acute lung injury

Prolonged breathing of very high F(IO(2)) (F(IO(2)) ≥ 0.9) uniformly causes severe hyperoxic acute lung injury (HALI) and, without a reduction of F(IO(2)), is usually fatal. The severity of HALI is directly proportional to P(O(2)) (particularly above 450 mm Hg, or an F(IO(2)) of 0.6) and exposure duration. Hyperoxia produces extraordinary amounts of reactive O(2) species that overwhelms natural anti-oxidant defenses and destroys cellular structures through several pathways. Genetic predisposition has been shown to play an important role in HALI among animals, and some genetics-based epidemiologic research suggests that this may be true for humans as well. Clinically, the risk of HALI likely occurs when F(IO(2)) exceeds 0.7, and may become problematic when F(IO(2)) exceeds 0.8 for an extended period of time. Both high-stretch mechanical ventilation and hyperoxia potentiate lung injury and may promote pulmonary infection. During the 1960s, confusion regarding the incidence and relevance of HALI largely reflected such issues as the primitive control of F(IO(2)), the absence of PEEP, and the fact that at the time both ALI and ventilator-induced lung injury were unknown. The advent of PEEP and precise control over F(IO(2)), as well as lung-protective ventilation, and other adjunctive therapies for severe hypoxemia, has greatly reduced the risk of HALI for the vast majority of patients requiring mechanical ventilation in the 21st century. However, a subset of patients with very severe ARDS requiring hyperoxic therapy is at substantial risk for developing HALI, therefore justifying the use of such adjunctive therapies.

Oxidative Stress in Critically Ill Children with Sepsis

Sepsis is one of the leading causes of death in critically ill patients in the intensive care unit. Sepsis accounts for significant morbidity and mortality in critically ill children as well. The pathophysiology of sepsis is characterized by a complex systemic inflammatory response, endothelial dysfunction, and alterations in the coagulation system, which lead to perturbations in the delivery of oxygen and metabolic substrates to the tissues, end-organ dysfunction, and ultimately death. Oxidative stress plays a crucial role as both a promoter and mediator of the systemic inflammatory response, suggesting potential targets for the treatment of critically ill children with the sepsis syndrome. Herein, we will provide a brief review of the role of oxidative and nitrosative stress in the pathophysiology of sepsis.

Chronic lung disease of prematurity: a short history

Chronic lung disease of prematurity (CLD) is commonly considered to be a consequence of assisted ventilation. However, prior to the description in 1967 of bronchopulmonary dysplasia (BPD), following ventilator therapy for respiratory distress syndrome, Wilson-Mikity syndrome (WMS) had been described in very preterm infants on minimal oxygen supplementation. In the 1970s and 1980s, many infants treated with assisted ventilation required prolonged mechanical ventilation after developing radiographic features of coarse infiltrates, severe hyperinflation, and microcystic changes, associated with hypercarbemia and the need for increased inspired oxygen concentrations. Some infants died and showed evidence of pulmonary fibrosis, obstructive bronchiolitis, and dysplastic change. The role of supplemental oxygen, positive pressure ventilation, and the immaturity of the lung have long been considered important in the etiology of CLD/BPD. More recently, the role of inflammation (particularly antenatal exposure to cytokines) and individual susceptibility (genetic predisposition) have assumed greater etiologic importance. The historical setting into which corticosteroid treatment for BPD was introduced is also discussed. After the licensing of exogenous surfactant to treat RDS in the early 1990s and more widespread use of prenatal corticosteroids in the mid-1990s, severe BPD became an unusual event. Gradually, the diagnosis of CLD, still often referred to as BPD, was based on an oxygen requirement at 36 weeks postmenstrual age. However, it is not clear that this 'new BPD' is substantially different from WMS. It is difficult to make prognostications about long-term lung function of these infants based on oxygen 'requirement' at 36 weeks, since supplemental oxygen is frequently used unnecessarily.

Saturated Phosphatidylcholine Secretion and the Effect of Natural Surfactant on Premature and Term Lambs Ventilated for 2 Days

Lambs prematurely delivered by cesarean section and term lambs were supported on ventilators and studied over a period of 2 days. Sequential measurements of ventilatory requirements, lung compliance, and arterial pH, pO2, and pCO2 values documented the course of the lung disease. In five premature lambs the pCO2 increased to 77 +/- 5 mm Hg (mean +/- SE) by 40.5 +/- 3.1 hr of age, at which time treatment with 50 mg natural sheep surfactant lipid/kg body weight by tracheal instillation resulted in improvements in pH, pO2, and pCO2 measurements. Radiolabeled palmitic acid was injected systemically after birth to detect the appearance of endogenously synthesized and secreted saturated phosphatidylcholine in sequential airway samples. Radiolabeled saturated phosphatidylcholine specific activity increased in a relatively linear fashion for about 30 hr in lambs treated with natural surfactant, in untreated premature lambs, and in term lambs. The study demonstrates that surfactant therapy can improve the ventilatory status of premature lambs despite many hours of ventilation for pulmonary immaturity. The overall kinetics of secretion of saturated phosphatidylcholine is similar in lambs with and without pulmonary immaturity.

Effects of Hyperoxia and Beta-Adrenergic Stimulation on Pulmonary Surfactant in Neonatal Rabbits

To study the effects of hyperoxia and beta-adrenergic stimulation on pulmonary surfactant in the neonatal lung, we measured disaturated phosphatidylcholine (DSPC) and [14C]choline incorporation into DSPC, obtained from alveolar lavage and lung tissue. We used an isolated salt-perfused rabbit lung preparation from neonatal rabbits exposed to room air or greater than 95% oxygen for 3 days. There were four experimental groups: room air, basal condition; room air, beta-adrenergic stimulation; hyperoxia, basal conditions; and hyperoxia, beta-adrenergic stimulation. Hyperoxia caused a significant decrease in lavage and intracellular [14C]DSPC specific activity, and a decrease in intracellular DSPC suggesting depressed surfactant synthesis. Beta-stimulation in room air caused a decrease in lavage DSPC, an increase in DSPC, and [14C]DSPC fraction released, consistent with increased uptake for reutilization. With hyperoxia and beta-stimulation, there is an increase in total DSPC in the lavage; lavage [14C]DSPC specific activity is similar to that of the basal hyperoxia group (i.e., depressed compared with the room air state); intracellular [14C]DSPC specific activity does not differ from basal, hyperoxia, or beta-stimulated, room air groups, all being depressed compared with basal, room air conditions. Intracellular DSPC in the beta-stimulated group is less affected by hyperoxia than the basal groups. It appears that prolonged exposure to hyperoxia is manifested primarily by a decrease in [14C]DSPC specific activity suggesting alterations in surfactant synthesis, though DSPC in the lavage is not altered. Beta-adrenergic stimulation may enhance release of newly synthesized surfactant into the alveoli, and possibly enhances uptake for reutilization. The enhancement of surfactant release seems to be preserved after prolonged hyperoxia.

Bombesin-like peptides modulate alveolarization and angiogenesis in bronchopulmonary dysplasia

RATIONALE

The incidence of bronchopulmonary dysplasia (BPD), a chronic lung disease of newborns, is paradoxically rising despite medical advances. We demonstrated elevated bombesin-like peptide levels in infants that later developed BPD. In the 140-day hyperoxic baboon model of BPD, anti-bombesin antibody 2A11 abrogated lung injury.

OBJECTIVES

To test the hypothesis that bombesin-like peptides mediate BPD in extremely premature baboons (born at Gestational Day 125 and given oxygen pro re nata [PRN], called the 125-day PRN model), similar to "modern-day BPD."

METHODS

The 125-day animals were treated with 2A11 on Postnatal Day 1 (P1), P3, and P6. On P14 and P21, lungs were inflation-fixed for histopathologic analyses of alveolarization. Regulation of angiogenesis by bombesin was evaluated using cultured pulmonary microvascular endothelial cells.

MEASUREMENTS AND MAIN RESULTS

In 125-day PRN animals, urine bombesin-like peptide levels at P2-3 are directly correlated with impaired lung function at P14. Gastrin-releasing peptide (the major pulmonary bombesin-like peptide) mRNA was elevated eightfold at P1 and remained high thereafter. At P14, 2A11 reduced alveolar wall thickness and increased the percentage of secondary septa containing endothelial cells. At P21, 2A11-treated 125-day PRN animals had improved alveolarization according to mean linear intercepts and number of branch points per millimeter squared. Bombesin promoted tubulogenesis of cultured pulmonary microvascular endothelial cells, but cocultured fetal lung mesenchymal cells abrogated this effect.

CONCLUSIONS

Early bombesin-like peptide overproduction in 125-day PRN animals predicted alveolarization defects weeks later. Bombesin-like peptide blockade improved septation, with the greatest effects at P21. This could have implications for preventing BPD in premature infants.

Optimum oxygen therapy in preterm babies

Oxygen is the most commonly used therapy in neonatal nurseries as an integral part of respiratory support. The goal of oxygen therapy is to achieve adequate delivery of oxygen to the tissue without creating oxygen toxicity. Oxygen must have been given to newborn preterm babies more than any other medicinal product in the past 60 years. Despite this, we still know very little about how much oxygen these babies actually need, or how much oxygen is safe to give, especially in the first few weeks of life. Recent observational studies have raised concerns that giving oxygen to target the saturation at "physiological" levels in newborn preterm babies may do more harm than good, but to date, clinicians have not been able to resolve the uncertainties surrounding optimum oxygen therapy.

Bombesin-like peptide and receptors in lung injury models: diverse gene expression, similar function

We previously demonstrated that bombesin-like peptide (BLP) mediates lung injury in premature infants with bronchopulmonary dysplasia (BPD). We now investigate gene expression and function of BLP (gastrin-releasing peptide, GRP) and BLP-receptors (GRP-R and BRS-3) in lung from two baboon BPD models. In the "interrupted gestation model," only GRP mRNA was up-regulated. In the "hyperoxic model," GRP-R mRNA was up-regulated. In lung explants from O2-treated animals, all BPD animals responded to 1nM bombesin, whereas non-BPD animals did not; the opposite effect was observed with a BLP blocking antibody. Cumulatively, these observations suggest that novel BLPs and/or BLP receptors are likely to be implicated in the pathogenesis of BPD.

Bombesin-like peptide mediates lung injury in a baboon model of bronchopulmonary dysplasia

The etiology of bronchopulmonary dysplasia (BPD), a chronic lung disease of infants surviving respiratory distress syndrome, remains fundamentally enigmatic. BPD is decreasing in severity but continues to be a major problem in pediatric medicine, being especially prevalent among very premature infants. Increased numbers of pulmonary neuroendocrine cells containing bombesin-like peptide (BLP) have been reported to occur in human infants with BPD. We tested the hypothesis that BLP mediates BPD using the hyperoxic baboon model. Urine BLP levels increased soon after birth only in 100% O2-treated 140-d animals which developed BPD, correlating closely with severity of subsequent chronic lung disease. Similar elevations in urine BLP were observed in the 125-d baboon "interrupted gestation" model of BPD. Postnatal administration of anti-BLP antibody attenuated clinical and pathological evidence of chronic lung disease in the hyperoxic baboon model. Urine BLP could be a biological predictor of infants at risk for BPD, and blocking BLP postnatally could be useful for BPD prevention.

Pre mortem analysis of lung injury and lung function in oxygen toxic rabbits

OBJECTIVES

To determine whether respiratory system mechanics measurements could detect lung injury in oxygen toxic rabbits before clinical deterioration. To determine whether respiratory system mechanics measurements, using a power analysis, have the statistical power to detect significant reductions in hyperoxic lung injury due to an intervention when compared with traditional post mortem measurements of lung injury, extravascular lung water, and bronchoalveolar lavage protein concentration.

DESIGN

Prospective, controlled study.

SETTING

Institutional animal laboratories.

SUBJECTS

Adult New Zealand white rabbits.

INTERVENTIONS

Spontaneously breathing adult New Zealand white rabbits were exposed continuously to either > 95% oxygen or room air.

MEASUREMENTS AND MAIN RESULTS

We measured arterial pH, blood gas tensions, and respiratory system mechanics in rabbits twice, both before exposure to > 95% oxygen, and after the rabbits developed symptoms of mild lung dysfunction. After the second set of respiratory system mechanics measurements, we measured extravascular lung water and bronchoalveolar lavage protein concentration in the hyperoxia-exposed rabbits and compared the values with those values obtained in animals that breathed room air only. Our hyperoxia-exposed rabbits developed symptoms of mild respiratory impairment at 69 +/- 2 hrs. In these hyperoxia-exposed rabbits, measurements of static compliance, quasi-static compliance and resistance all changed significantly (p < .05) when compared with baseline measurements. Functional residual capacity and arterial blood gas values did not change significantly. Furthermore, assuming that an intervention reduced hyperoxic lung injury by a given amount, we performed a power analysis and found that the measurement of static compliance had at least equivalent power to detect a reduction in lung injury from an intervention when compared with measurement of extravascular lung water and bronchoalveolar lavage protein concentration.

CONCLUSIONS

Measurements of respiratory system mechanics can detect lung injury in hyperoxic rabbits before the onset of severe clinical deterioration or death. Furthermore, measurement of static compliance of the respiratory system is likely to be a powerful tool to detect a reduction in lung injury produced by an intervention.

Pathophysiology and treatment of bronchopulmonary dysplasia. Current issues

Although much has been learned about BPD in the 25 years since its initial description, BPD remains a significant complication of prematurity. Substantial advances into the understanding of its pathophysiology and pathogenesis have been made and are reflected in new therapeutic interventions. Much current research is directed towards the role of prevention, exploring new approaches for accelerating lung maturation with combined maternal steroid and thyrotropin releasing hormone (TRH) therapy, surfactant replacement therapy, high frequency oscillatory ventilation, antioxidant administration, manipulation of endogenous antioxidants, and other pharmacologic strategies to minimize lung injury. The impact of other technologies, such as synchronized intermittent mandatory ventilation, perfluorocarbon (liquid) ventilation, and perhaps inhaled nitric oxide therapy may become additional parts of the clinical regimen for some cases of severe neonatal respiratory failure. Less information is available on mechanisms which can hasten lung healing. Ongoing studies of inflammatory products, growth factors, and cytokines may lead to new therapies which will favorably influence the fibroproliferative phase of disease. In the meantime, the medical and social impact of BPD continues to remain a significant problem not only during infancy but also throughout life. Mildred Stahlman, MD, recently wrote that (a)s sanguine as the future looks for surfactant therapy, it may leave us with more very low-birth weight infants who survive, whose potential for normal pulmonary growth and development is unknown, and whose very immature organ systems, besides the lung, are still susceptible to metabolic, neurologic, and other problems. As more survivors are reaching young adulthood, respiratory and neurodevelopmental complications persist. Thus, as advances in the care of the premature newborn with respiratory distress have dramatically improved survival, the management of chronic lung disease and related problems remains a continuing challenge.

Histopathologic pulmonary changes from mechanical ventilation at high peak airway pressures

We investigated the histopathologic pulmonary changes induced by mechanical pulmonary ventilation (MV) with a high peak airway pressure and a large tidal volume in healthy baby pigs. Eleven animals were mechanically ventilated at a peak inspiratory pressure (PIP) of 40 cm H2O, a respiratory rate (RR) of 20 min-1, a positive end-expiratory pressure (PEEP) of 3 to 5 cm H2O, and an FIO2 of 0.4. High airway pressure MV was terminated in 22 +/- 11 h because of severe hypoxemia in the animals. Five of the baby pigs were killed for gross and light microscope studies. The pulmonary changes consisted of alveolar hemorrhage, alveolar neutrophil infiltration, alveolar macrophage and type II pneumocyte proliferation, interstitial congestion and thickening, interstitial lymphocyte infiltration, emphysematous change, and hyaline membrane formation. Those lesions were similar to that seen in the early stage of the adult respiratory distress syndrome (ARDS). The remaining six animals were treated for 3 to 6 days with conventional respiratory care with appropriate ventilator settings. Prominent organized alveolar exudate in addition to lesions was also found in the five animals. These findings were indistinguishable from the clinical late stage of ARDS. Six control animals were mechanically ventilated at a PIP of less than 18 cm H2O, a RR of 20 min-1, a PEEP of 3 to 5 cm H2O, and an FIO2 of 0.4 for 48 h. They showed no notable changes in lung functions and histopathologic findings. Aggressive MV with a high PIP is often applied to patients with respiratory distress to attain adequate pulmonary gas exchange.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of oxygen and barotrauma on lung injury in the neonatal piglet

In order to differentiate the effects of hyperoxia and barotrauma in the pathogenesis of acute neonatal lung injury, piglets were either hyperventilated (Paco2, 15-20 torr) for 48 hours with 100% oxygen (Group I), hyperventilated with 21% oxygen (Group II), normally ventilated (Paco2, 40-45 torr) with 100% oxygen (Group III), or normally ventilated with 21% O2 (Group IV) and compared to unventilated controls. Pulmonary function was tested, and biochemical indicators of lung injury were analyzed in tracheo-bronchial aspirates at 0, 24, and 48 hours. Bronchoalveolar lavage fluid was analyzed for surfactant composition and activity at the end of the study. At 48 hours, hyperoxic, hyperventilated piglets had significantly decreased dynamic lung compliance (30%) and increased pulmonary resistance (16%), aspirate cell count (190%), elastase activity (88%), albumin (214%), and total protein (150%) concentration. Qualitative light microscopy showed moderate to severe atelectasis, fibrinous exudate, edema, and inflammation. Normoxic, hyperventilated animals had comparable changes in pulmonary mechanics, but significantly milder cellular, biochemical, and morphologic changes. In hyperoxic, normocarbic animals pulmonary physiologic, cellular, and biochemical variables changed comparably to hyperoxic, hyperventilated animals; the pathologic changes were intermediate between hyperoxic, hyperventilated and normoxic, hyperventilated piglets. Normoxic, normocarbic animals had no significant changes in most variables over 48 hours; on morphologic examination their lungs were similar to unventilated controls and showed only mild edema. Surfactant had normal biophysical activity in all animals. Our results demonstrate that hyperoxia causes more significant physiologic, inflammatory, and histologic changes than barotrauma alone. Future attempts to prevent lung injury in neonates should be directed primarily at oxygen toxicity.

Bronchopulmonary dysplasia: a correlative study by light, scanning, and transmission electron microscopy

The sequential stages of bronchopulmonary dysplasia occurring in 18 infants after intensive respiratory therapy supplemented by oxygen in high concentrations were studied by correlative light, scanning, and transmission electron microscopy. Infant survival ranged from 3 to 225 days. The earliest stage was an exudative reaction with a predominance of hyaline membranes. This merged with a subacute reparative response that was replaced by a chronic fibroproliferative stage in infants of longest survival; this stage was complicated by pulmonary fibrosis and emphysema. Correlative scanning and transmission electron microscopy demonstrated that type 2 pneumocytes contributed significantly to the reparative fibroproliferative response by organization of hyaline membranes and reepithelialization of damaged septal walls.

Oxygen toxicity in the infant rhesus monkey: effects on regulatory peptides in lung and blood

A total of ten 6-month-old male rhesus monkey (Macaca mulatta) infants, born full-term, were positive-pressure ventilated with greater than 95% oxygen or room air (controls). A protocol was used which closely simulated pediatric intensive care. To test if regulatory peptides were affected by the oxygen treatment, and to search for an early marker of oxygen toxicity, lung tissue samples and systemic mixed venous blood were collected at 6, 12 and 24 hours after onset of treatment. The peptides, gastrin releasing peptide (GRP), calcitonin gene-related peptide (CGRP), peptide YY (PYY), vasoactive intestinal peptide (VIP) and somatostatin (SOM), were quantitated in lung tissue extracts and plasma using radioimmunoassay. Lung tissue GRP, CGRP, and PYY levels appeared to decrease gradually with time, perhaps as a result of the positive pressure ventilation procedure. GRP and CGRP levels decreased less among monkey infants ventilated with oxygen, thus they were significantly higher at 24 hours than in air ventilated controls. VIP levels were significantly lower among tests compared to controls at that time. Blood peptide levels did not change with oxygen treatment. These results suggest that tissue concentrations of certain pulmonary regulatory peptides can become altered by ventilation with greater than 95% oxygen. A blood borne peptide marker was not identified.

Pulmonary function at 1 year of age in survivors of neonatal respiratory distress: a multivariate analysis of factors associated with sequelae

We studied pulmonary function 1 year after neonatal respiratory distress (RD) in 54 infants who had been treated at birth in the same neonatal intensive care unit. RD was related to hyaline membrane disease in 36 cases (group I) and to other causes in 18 cases (group II). Compared with predicted values, dynamic lung compliance (CL) was lower (less than -2 SD) and total pulmonary resistance (RL) was higher (+2 SD) in 18 (33%) and 12 (22%) infants, respectively. The relationships between these functional abnormalities at 1 year of age and the characteristics of the neonatal respiratory disease were assessed using a multifactorial analysis (multiple correspondences analysis). We found that elevated RL (greater than +2 SD) at 1 year of age was very significantly related with hyaline membrane disease, involving both high rate of positive pressure ventilation and prolonged intubation, and with the presence of both tachypnea and abnormal chest X rays at the time of discharge. Compared with elevated RL, the relationships between low CL (less than -2 SD) and the same neonatal characteristics were less significant; in particular, there was no strong link between low CL and hyaline membrane disease. Finally, birth before 30 weeks gestation was an index of severity.

Bronchopulmonary dysplasia

Bronchopulmonary dysplasia has become the most common pulmonary sequelae in neonates receiving mechanical ventilation. The pathogenesis of BPD is multifactorial, but prematurity, positive pressure ventilation, oxygen toxicity and pulmonary edema are some of the most important factors in its development. By minimizing these factors, it is possible to reduce the incidence and severity of BPD.

Bronchopulmonary dysplasia. Chronic pulmonary disease following neonatal respiratory failure

Infants with respiratory failure in the first weeks of life may develop a chronic pulmonary condition called bronchopulmonary dysplasia. Their lungs have areas of atelectasis and areas of air trapping from variable obstruction of the airways. These infants may be dependent on supplemental oxygen or a ventilator and may require hospitalization for months, and have symptoms of airway obstruction which last for years. They require meticulous medical management to avoid a number of common complications such as patent ductus arteriosus, cor pulmonale, tracheal stenosis, recurrent aspiration, and death. The condition of most infants improves over the first two years. Preliminary studies suggest that their exercise and pulmonary function is usually close to normal by school-age. The long-term implications for the increasing number of children with this disease who will soon reach adulthood are still unknown.

Variability in lung collagen amounts after prolonged support of acute respiratory failure

In order to identify correlates of fibrosis in acute respiratory failure, autopsies were performed on 16 patients who died after an episode of more than two weeks' duration, and the left lower lung lobe was obtained for biochemical measurements. The average amount of lobar collagen in one group of patients was nearly three times that in another group. Both groups had been mechanically ventilated for the same length of time and could not be distinguished by primary diagnosis. However, the group with increased collagen had received nearly twice the level of positive end-expiratory pressure and had received an inspired oxygen fraction of more than 0.4 for twice as long as the normal collagen group. Examination of complications and other aspects of therapy did not reveal clearcut differences between the groups. Examination of the same clinical data in a group of patients who had survived an episode of similar duration indicated that survivors differed from the high collagen group in inspired oxygen levels.

Cellular interactions in pulmonary oxygen toxicity in vitro: I. Hyperoxic induction of fibroblast factors which alter growth and lipid metabolism of pulmonary epithelial cells

Pulmonary fibroblasts exposed to hyperoxic conditions in vitro release factors into their culture medium which influence the growth and lipid synthesis of tumor and nontumor pulmonary epithelial cells, but not pulmonary fibroblasts. These factors may be either inhibitory or stimulatory, depending on the degree and duration of hyperoxic exposure. Two stimulatory heat-labile factors have been tentatively identified by gel filtration. A growth-stimulating factor induced by hyperoxia has an apparent molecular weight approximately 20,000-26,000 daltons; a factor tht stimulates lipid synthesis has an apparent molecular weight approximately 8000 daltons. These factors appear distinct from other pneumocyte-specific peptides which occur in response to steroid therapy or pneumonectomy.

Iatrogenic disease in the newborn

The role of intrapartum asphyxia and cerebral birth trauma as an important cause of perinatal mortality is well known and its contribution to perinatal morbidity as a cause of cerebral palsy is widely appreciated. This has led to more careful monitoring of pregnancy and labour, although monitoring techniques are not without hazard. The widespread availability of intensive care facilities for the newborn has resulted in the survival of many infants, particularly those of low birth weight, who might previously have died. Efficacious modes of treatment may, unfortunately, bring in their wake serious problems in the form of iatrogenic disease which may cause or contribute to rapid demise or whose effects may be fully apparent for many years. Ante natal investigations have also become frequently used and have their own hazards.

Bronchopulmonary dysplasia: possible relationship to pulmonary edema

The pathogenesis of bronchopulmonary dysplasia is controversial. Oxygen toxicity, mechanical trauma to the lung secondary to respirator therapy, and congestive heart failure with a left to right shunt through a patent ductus arteriosus have all been implicated. Our data suggest that in addition to these three conditions, all of which are edemagenic, infants with bronchopulmonary dysplasia have a significantly greater mean fluid intake in the first five days of life when compared with infants with respiratory distress syndrome or patent ductus arteriosus alone. We suggest that the addition of a fluid load may potentiate the effects of other factors and increase the risk of bronchopulmonary dysplasia in infants with respiratory distress syndrome who require respiratory support.

Bronchopulmonary dysplasia in premature infants. A radiological and pathological correlation

In a group of 70 premature and newborn infants, treated with artificial ventilation, 24.3% developed bronchopulmonary dysplasia (BPD). Only in a very few cases did the typical radiological stages, as described by Northway, succeed each other in a chronological order. It is impossible to differentiate BPD stage I or II from RDS stage III and IV without a knowledge of the clinical course and of the duration of artificial ventilation. The lower the gestational age, the more severe and earlier do the radiological and histological changes occur. The radiological differential diagnosis of BPD includes Wilson-Mikity-syndrome, congenital pulmonary lymphangiectasia, neonatal tuberculosis, cystic fibrosis and Hamman-Rich-syndrome.

Oxygen toxicity in premature infants

With the current state of our knowledge regarding uses, hazards, and dangers, the cavalier offhanded attitude which in the past has all too frequently characterized oxygen use in the premature is no longer acceptable. Sufficient knowledge and technical expertise now exist in spezialized centers which will allow maximal benefit at minimum risk from oxygen usage. Where such centers are readily accessible, the need for oxygen therapy should be considered as a major criterion for transfer from a lesser to a more sophisticated newborn care unit.

Improved prognosis of infants mechanically ventilated for hyaline membrane disease

The results of mechanical ventilation for severe hyaline membrane disease (HMD), and the changes in technique which took place, during the 6-year period 1967-72 are described. A pilot study of the effect of hydrocortisone among the most severely affected infants showed no benefit. After the introduction at the beginning of 1970 of a regimen for ventilating the infants at low peak airway pressures, slow respiratory frequencies, and high inspiration: expiration ratios, there was a sudden increase in survival rate which was largely accounted for by a reduction in the incidence of bronchopulmonary dysplasia. Evidence is presented that in infants with HMD mechanical factors are more important than oxygen toxicity in the pathogenesis of this condition.

Pulmonary fibroplasia in newborn babies treated with oxygen and artificial ventilation

A retrospective clinicopathological study was carried out on newborn babies who had died over a 5-year period, had received oxygen therapy, and had lived for 48 hours or longer. 23 of 81 babies had pulmonary fibroplasia at necropsy. Prolonged therapy in oxygen concentrations above 60% and prolonged artificial ventilation were associated with the development of pulmonary fibroplasia. All babies developing pulmonary fibroplasia had been treated in over 60% oxygen for at least 46 hours and the condition was invariably present in those who had over 60% oxygen for more than 123 hours or above 80% oxygen for more than 105 hours. The relation of pulmonary fibroplasia to mechanical ventilation was less constant. Hyaline membrane disease was associated with the development of fibroplasia in babies who lived for 3 days or longer, and the most severe histological changes were almost always associated with HMD. There was no correlation between gestational age and development of pulmonary fibroplasia. It is concluded that oxygen toxicity was probably the most important cause of pulmonary fibroplasia in the babies studied, though some histological features may be more closely related to artificial ventilation. The implications of these findings for oxygen and ventilator therapy in the newborn are discussed.