Surfactant treatment for premature babies--a review of clinical trials

Proteomics reveals region-specific hemostatic alterations in response to mechanical ventilation in a preterm lamb model of lung injury

INTRODUCTION

Preterm infants often require assisted ventilation, however ventilation when applied to the immature lung can initiate ventilator-induced lung injury (VILI). The biotrauma which underscores VILI is largely undefined, and is likely to involve vascular injury responses, including hemostasis. We aimed to use a ventilated, preterm lamb model to: (1) characterize regional alterations in hemostatic mediators within the lung and (2) assess the functional impact of protein alterations on hemostasis by analyzing temporal thrombin generation.

MATERIALS AND METHODS

Preterm lambs delivered at 124 to 127 days gestation received 90 min of mechanical ventilation (positive end-expiratory pressure = 8 cm H₂O, V_T = 6-8 ml/kg) and were compared with unventilated control lambs. At study completion, lung tissue was taken from standardized nondependent and gravity-dependent regions, and Orbitrap-mass spectrometry and KEGG were used to identify and map regional alterations in hemostasis pathway members. Temporal alterations in plasma thrombin generation were assessed.

RESULTS

Ventilation was distributed towards the nondependent lung. Significant changes in hemostatic protein abundance, were detected at a two-fold higher rate in the nondependent lung when compared with the gravity-dependent lung. Seven proteins were uniquely altered in non-dependent lung (SERPINA1, MYL12A, RAP1B, RHOA, ITGB1, A2M, GNAI2), compared with a single proteins in gravity-dependent lung (COL1A2). Four proteins were altered in both regions (VTN, FGG, FGA, and ACTB). Tissue protein alterations were mirrored by plasma hypocoagulability at 90-minutes of ventilation.

CONCLUSIONS

We observed regionally specific, hemostatic alterations within the preterm lung together with disturbed fibrinolysis following a short period of mechanical ventilation.

Inspired by lipids: the Morton Lecture Award Presentation

Lipids are key molecules for membranes, energy storage and signalling. I have been privileged to have worked in such a diverse field and in organisms from microbes to humans. Here I will describe some of those contrasting areas which range from environmental impacts to food production and on to human health. It has been a fascinating journey which still continues to excite me.

Real-time pulmonary graphics

Real-time pulmonary graphics now enable clinicians to view lung mechanics and patient-ventilator interactions on a breath-to-breath basis. Displays of pressure, volume, and flow waveforms, pressure-volume and flow-volume loops, and trend screens enable clinicians to customize ventilator settings based on the underlying pathophysiology and responses of the individual patient. This article reviews the basic concepts of pulmonary graphics and demonstrates how they contribute to our understanding of respiratory physiology and the management of neonatal respiratory failure.

Evaluation of a computerized system for mechanical ventilation of infants

OBJECTIVE

To evaluate a computerized system for mechanical ventilation of infants.

METHODS

FLEX is a computerized system that includes the features of a patented mode known as adaptive-support ventilation (ASV). In addition, it has many other features including adjustment of positive end-expiratory pressure (PEEP), fraction of inspired oxygen (F(IO2)), minute ventilation, and control of weaning. It is used as an open-loop decision support system or as a closed-loop technique. Blood gas and ventilation data were collected from 12 infants in the neonatal intensive care at baseline and at the next round of evaluation. This data were input to open-loop version of FLEX. The system recommendations were compared to clinical determinations.

RESULTS

FLEX recommended values for ventilation were on the average within 25% and 16.5% of the measured values at baseline and at the next round of evaluation, respectively. For F(IO2) and PEEP, FLEX recommended values were in general agreement with the clinical settings. FLEX recommendations for weaning were the same as the clinical determinations 50% of the time at baseline and 55% of the time at the next round of evaluation. FLEX did not recommend weaning for infants with weak spontaneous breathing effort or those who showed signs of dyspnea.

CONCLUSIONS

A computerized system for mechanical ventilation is evaluated for treatment of infants. The results of the study show that the system has good potential for use in neonatal ventilatory care. Further refinements can be made in the system for very low-birth-weight infants.

Preterm outcomes research: a critical component of neonatal intensive care

While early preterm outcome studies described the lives of preterm survivors to justify the efforts required to save them, subsequent studies demonstrated their increased incidence of cerebral palsy, mental retardation, sensory impairments, minor neuromotor dysfunction, language delays, visual-perceptual disorders, learning disability and behavior problems compared to fullterm controls. Because infants born at the lower limit of viability require the most resources and have the highest incidence of neurodevelopmental disability, there is concern that resources have gone primarily to neonatal intensive care and are not available for meeting the followup, health, educational and emotional needs of these fragile infants and their families. Despite many methodological concerns, preterm outcome studies have provided insight into risk factors for and causes of CNS injury in preterm infants. Nevertheless, it remains difficult to predict neurodevelopmental outcome for individual preterm infants. Perinatal and neonatal risk factors are inadequate proxies for neurodevelopmental disability. Recent randomized controlled trials with one to five year neurodevelopmental followup have provided valuable information about perinatal and neonatal treatments. Recognizing adverse longterm neurodevelopmental effects of pharmacological doses of postnatal steroids is a sobering reminder of the need for longterm neurodevelopmental followup in all neonatal randomized controlled trials. Ongoing longterm preterm neurodevelopmental studies, analysis of changes in outcomes over time and among centers, and evaluation of the longterm safety, efficacy and effectiveness of many perinatal and neonatal management strategies and proposed neuroprotective agents are all necessary for further medical and technological advances in neonatal intensive care.

Extreme prematurity and school outcomes

The purpose of this study was to assess the impact of extreme prematurity on three global measures of school outcomes. Using a matched cohort design, exposed infants comprised all surviving singleton infants < or = 28 weeks gestation born at one regional neonatal intensive care hospital between 1983 and 1986 (n = 132). Unexposed infants comprised randomly selected full-term infants (> or = 37 weeks gestation) frequency matched on date of birth, zip code and health insurance. All children were selected from a regional tertiary children's centre serving western New York population. Standardised telephone interviews elicited information on grade repetition, special education placement and use of school-based services. Unconditional logistic regression was used to estimate odds ratios (OR) and corresponding 95% confidence intervals (CI) adjusted for potential confounders for children without major handicaps. Extreme prematurity was associated with a significant increase in risk of grade repetition (OR = 3.22; 95% CI = 1.63, 6.34), special education placement (OR = 3.16; 95% CI = 1.14, 8.76) and use of school-based services (OR = 4.56; 95% CI = 1.82, 11.42) in comparison with children born at term, even after controlling for age, race, maternal education, foster care placement and the matching factors. These findings suggest that survivors of extreme prematurity remain at risk of educational underachievement.

Pulmonary distribution and clearance of two beclomethasone liposome formulations in healthy volunteers

The pulmonary distribution and clearance of 99mTc-labelled beclomethasone dipropionate (Bec) dilauroylphosphatidylcholine (DLPC) and dipalmitoylphosphatidylcholine (DPPC) liposomes were compared in 11 healthy volunteers using gamma scintigraphy. As delivered by using the Aerotech jet nebulizer both liposome aerosols had a suitable droplet size (mass median aerodynamic diameter 1.3 microm) allowing deep pulmonary deposition. However, in the total drug output during the inhalation there was a relatively large difference between DLPC and DPPC of 11.4 and 3.1 microg, respectively. In a gamma camera study no significant differences existed in the central/peripheral lung deposition between the DLPC and DPPC formulations. Progressive clearance of both Tc-labelled Bec liposomes was seen: 24 h after inhalation, 79% of the originally deposited radioactivity of DLPC liposomes and 83% of that of DPPC liposomes remained in the lungs. Thus there was slightly slower clearance of inhaled liposomes using DPPC instead of DLPC. We conclude that both liposome formulations are suitable for nebulization, although aerosol clouds were more efficiently made from the DLPC liposome suspension. Our results support the view that liposome encapsulation of a drug can offer sustained release and drug action in the lower airways.

Pulmonary function at school-age in surfactant-treated preterm infants

A follow-up study was conducted in 40 children who had been enrolled in a prospective randomized study of exogenous surfactant therapy for respiratory distress syndrome (RDS) (n = 22; S) or placebo (n = 18; P) to determine long-term pulmonary sequelae of surfactant treatment in premature infants with RDS. At follow-up, mean (SD) age was 6.63 (0.18) and 6.55 (0.23) years for S and P, respectively. Complete lung function tests (LFT) were attempted in all patients. Satisfactory data were obtained in 17/22 surfactant-treated and in 12/18 control children. There was no significant difference between groups for any of the parameters measured. Mean (SD) functional residual capacity (FRC) was 92% (16%) and 90% (21%) predicted, mean (SD) airway resistance (R(aw,exp)) was 122% (25%) and 127% (61%), and mean (SD) forced expiratory volume in 1 s (FEV1) was 104% (12%) and 99% (17%) predicted for S and P. Only maximal expiratory flow at 25% vital capacity (L/s) was significantly below the predicted range in S and P groups, with 74% (23%) and 77% (28%), respectively. To test bronchial hyperreactivity, a simple standardized running test was performed: 4 children in S and 5 in P showed a significant response as defined by clinical airway obstruction or changes in FEV1 and/or R(aw), with no significant difference between groups. Although we found no major abnormalities in lung function and no difference between S and P at early school-age, lack of cooperation during lung function tests makes further follow-up necessary.

A simplified surfactant dosing procedure in respiratory distress syndrome: the "side-hole" randomized study. Spanish Surfactant Collaborative Group

The aim of this study was to compare the incidence of acute adverse events and long-term outcome of two different surfactant dosing procedures in respiratory distress syndrome (RDS). The effects of two surfactant dosing procedures on the incidence of transient hypoxia and bradycardia, gas exchange, ventilatory requirements and 28 d outcome were compared. The patients, comprising 102 infants (birthweight 600-2000 g) with RDS on mechanical ventilation with FiO2 > or = 0.4, were randomized at 2-24 h to receive 200 mg kg(-1) of Curosurf; in 56 it was given by bolus delivery, and in 55 by a simplified technique (dose given in 1 min via a catheter introduced through a side-hole in the tracheal tube adaptor. The baby's position was not changed and ventilation was not interrupted). Two additional surfactant doses (100 mg kg(-1)) were also given, by the same method, if ventilation with FiO2 > or = 0.3 was needed 12 and 24 h after the initial dose. The number of episodes of hypoxia and/or bradycardia was similar in both groups. A slight and transient increase in PaCO2 was observed in the side-hole group. The efficacy of the surfactant, based on oxygenation improvement, ventilator requirements, number of doses required and incidence of air leaks, was similar. No differences were observed in the incidence of intraventricular haemorrhage, patent ductus arteriosus, bronchopulmonary dysplasia or survival. In conclusion, a simplified surfactant dosing procedure not requiring fractional doses, ventilator disconnection, changes in the baby's position or manual bagging was found to be as effective as bolus delivery. The number of dosing-related transient episodes of hypoxia and bradycardia was not decreased by the slow, 1 min, side-hole instillation procedure.

Strategies to prevent chronic neonatal lung disease

The pathogenesis of chronic neonatal lung disease involves the combined iatrogenic insults of oxygen toxicity and barotrauma in addition to lung inflammation. Newer ventilator strategies using smaller tidal volumes (3-7 mL/kg) in order to avoid overdistension, higher positive end-respiratory pressure and lower peak inspiratory pressures decrease barotrauma. Earlier reduction of FiO2 through the use of surfactant, high frequency ventilation and nitric oxide reduce oxygen toxicity. Other measures include careful fluid balance, avoidance of prolonged paralysis and early steroids to decrease inflammation.

Plasminogen activator activity in preterm infants with respiratory distress syndrome: relationship to the development of bronchopulmonary dysplasia

Respiratory distress syndrome (RDS) is characterized by the presence of fibrin-rich exudates in the alveoli. Fibrin and its degradation products may play an important role in the pathogenesis of bronchopulmonary dysplasia (BPD). The purpose of this study was to test the hypothesis that preterm neonates with RDS have depressed alveolar fibrinolytic activity and that those with RDS progressing to BPD have an even greater impairment in alveolar fibrinolysis. Serial tracheal aspirate (TA) samples from intubated neonates--9 control and 46 with RDS--were analyzed for fibrinolytic activity. In neonates with RDS, 26 resolved, 18 progressed to BPD, and 2 died before 28 d. Plasminogen activator (PA) and its inhibitor (PAI) were identified in TA by reverse fibrin autography and immunoblotting. Net PA/plasmin activity in TA was significantly depressed on d 1 of life in patients with self-resolved RDS (median = 20.85 ng/mL, p < 0.05) and RDS progressing to BPD (median = 4.97 ng/mL, p < 0.001) compared with control patients (median = 87.1 ng/mL). In addition, neonates progressing to BPD had significantly lower PA/plasmin activity on day one of life compared with neonates with self-resolved RDS (p < 0.001). ELISA for specific PA and PAI were not significantly different. We speculate that depressed fibrinolytic activity may place preterm neonates at risk for RDS and that the degree of this depression may predict the progression to BPD. In infants < or = 30 wk of gestation at birth with RDS, a PA/plasmin activity < or = 10.0 ng/mL on the 1st d of life had a positive predictive value of 80% (12/15) and a negative predictive value of 82% (9/11) for the progression to BPD.

Prophylaxis of respiratory distress syndrome by treatment with modified porcine surfactant at birth: a multicentre prospective randomized trial

The objective of this prospective, multicentre trial, carried out at 18 third level hospitals in Italy, was to evaluate efficacy of modified porcine surfactant (Curosurf), administered at birth to prevent the development of respiratory distress syndrome (RDS) in premature infants. 287 babies with a gestational age of 24-30 weeks were randomized to prophylactic treatment with Curosurf (80 mg/ml; dose 20 mg/kg) or to a control group receiving no surfactant treatment in the delivery-room. Babies in both groups were eligible for rescue treatment with surfactant (200 mg/kg) if they developed clinical symptoms of RDS and required mechanical ventilation. The main end-point was to obtain, in the prophylaxis group, a 30% reduction in the incidence of grade 3-4 RDS. Median gestational age was 28 weeks in both groups and mean birth weight 1010 and 1002 g, respectively for prophylaxis and control babies. There was a 32% reduction in the incidence of grade 3-4 RDS in the prophylaxis group (p < 0.05). This was associated with a significant reduction in mean maximum fraction of inspired oxygen (0.57 vs 0.66%; p < 0.01), a decreased incidence of pulmonary interstitial emphysema (7 vs 14%; p < 0.05) and a lowered mortality (21 vs 35%; p < 0.01). Combined unfavourable outcome (mortality + bronchopulmonary dysplasia and/or grade 3-4 intraventricular hemorrhage and/or grade 2-4 retinopathy of prematurity) was significantly lower in the prophylaxis than in the second group (41 vs 58%; p < 0.01). The favourable effects of prophylactic treatment were equally recorded in all the age groups, including the babies with the lowest gestational age (24-25 weeks). Multiple and logistic regression analysis confirmed that high gestational age and surfactant prophylaxis were, independently, associated with a lower degree of RDS (p = 0.0001 and p = 0.0008, respectively) and a lower mortality (p = 0.0001 and p = 0.0045, respectively). We conclude that prophylaxis with modified natural surfactant effectively prevents RDS in newborn babies between 24 and 30 weeks' gestation.

Neonatal technology, perinatal survival, social consequences, and the perinatal paradox

Exogenous surfactant therapy for premature infants with respiratory distress syndrome has had a significant impact on infant mortality and on some complications of prematurity. Yet the total number of low-birthweight infants has not declined, resulting in a high-risk population who would require surfactant therapy and long-term child care. Surviving low-birthweight infants (despite surfactant therapy) remain at risk for the consequences of premature birth, such as neurosensory impairment, cerebral palsy, and chronic lung disease. In addition, because of the close association between poverty and low birthweight, surviving premature infants are at increased risk for the new morbidities such as violence, homelessness, child abuse and neglect, and addictive drug use. A goal should be to reduce the risk of being born with a low birthweight, rather than having to treat the consequences of premature gestation. Despite the marvelous advances that permit us to treat respiratory distress syndrome, the continuing high low-birthweight rate places a significant strain on our health care system. The goal should be redirected to identifying large population-based efforts to reduce the number of low-birthweight infants.

Respiratory distress syndrome of the newborn infant

Pulmonary immaturity, including deficiency in the surfactant system, incomplete structural/functional development of lungs and high chest wall compliance contribute to the pathogenesis of respiratory distress syndrome (RDS). Pulmonary edema and overperfusion, resulting from a patent ductus arteriosus, may further worsen the respiratory failure, and aggravate the surfactant deficiency. Infants born prematurely present with respiratory distress within the first few minutes of life. This quickly becomes life-threatening, and may result in death from severe respiratory failure if appropriate respiratory and general supportive therapy are not immediately instituted. The oxygenation deficit in RDS is secondary to V/Q mismatch and right-left shunting of blood via pulmonary and extrapulmonary routes. Hypoxemia induced pulmonary vasoconstriction further contributes to V/Q mismatch and R-L shunting. Hypoventilation in RDS is due to decreased tidal volume, increased dead space ventilation, and finally, decreased minute ventilation. Characteristically, pulmonary compliance, both static and dynamic, are greatly reduced resulting in a high work of breathing, whereas airway resistance is normal or only slightly increased. This combination of abnormal pulmonary mechanics results in lower respiratory time constant in respiratory units, and helps in achieving ventilation and oxygenation by using low inspiratory time in the ventilator. Management of RDS starts with prenatal identification of the risk, prolongation of pregnancy by tocolysis and prenatal administration of pharmacological agents, like betamethasone. These agents increase the pulmonary gas exchange surface area and induce endogenous pulmonary surfactant in the fetus. Advances in ventilatory and general management techniques have strikingly improved the outcome and prognosis of children suffering from RDS since the 1960s. Recent advancements in the prevention and treatment of RDS, e.g., acceleration of lung development by prenatal pharmacological manipulations and postnatal provision of exogenous surfactant, have significantly contributed to the decrease in mortality from RDS. Pharmacological induction of lung maturation by drugs in combination, and improved technology in lung ventilation are expected to further improve the course and outcome of the disease in future.

Lung volume and pulmonary blood flow measurements following exogenous surfactant

Lung function in eight infants with clinical and radiological features of surfactant deficiency treated with exogenous porcine surfactant was studied before and at 15 min, 2h and 6h after the intratracheal administration of porcine surfactant. We measured alveolar-arterial oxygen tension difference, dynamic lung compliance, lung volume and effective pulmonary blood flow in all infants. The alveolar-arterial oxygen tension difference fell from a mean (SD) 43.3 (14.5) kPa before treatment to 8.8 (8.8) kPa at 1 h and 12.2 (6.8) kPa 6h after treatment (P < 0.001). There was no change in mean (SD) dynamic compliance (0.39 [0.10] ml/cmH2O/kg pre dose; 0.36 [0.13] ml/cmH2O/kg 6h post treatment). Accessible functional residual capacity and effective pulmonary blood flow were measured using an adaptation of the argon/freon rebreathing method and showed an increase in mean (SD) functional residual capacity from 7.5 (1.4) ml/kg predose to 10.8 (3.3) ml/kg within 15 min of treatment, 11.4 (3.4) ml/kg 2h later and 12.7 (3.1) ml/kg 6h after treatment (P = 0.009). Mean (SD) effective pulmonary blood flow values did not differ significantly, changing from 78.2 (20.9) ml/kg per min predose to 88.7 (24.1) ml/kg per min 15 min post dose, 87.6 (21.7) ml/kg per min 2h post dose and 90.0 (22.7) ml/kg per min 6h post dose (P = 0.711).

CONCLUSION

The improvement in oxygenation after surfactant treatment is associated with an increase in lung volume but is not related to an improvement in dynamic lung compliance or effective pulmonary blood flow. The change in lung volume is detectable within 15 min of administration of the surfactant.

Pathophysiology of congenital diaphragmatic hernia. XII: Amniotic fluid lecithin/sphingomyelin ratio and phosphatidylglycerol concentrations do not predict surfactant status in congenital diaphragmatic hernia

Abnormal development of the lung in congenital diaphragmatic hernia (CDH) results in a dysfunctional surfactant system. In premature newborns at risk for respiratory distress syndrome, amniotic fluid lecithin/sphingomyelin (L/S) ratios and phosphatidylglycerol (PG) status have been successfully used to predict the surfactant status in the fetus. The objective of this study was to assess the accuracy of L/S ratios and PG in predicting the surfactant status in CDH. The surgically created lamb CDH model was used. Animals were delivered at 140 days' gestation (term 145) and immediately killed. Before delivery amniotic fluid was collected and L/S ratios and PG status were measured. Bronchoalveolar lavage (BAL) was performed and analyzed for total phospholipid and percent phosphatidylcholine (PC). Analysis of the BAL showed that the CDH lungs had both significantly less total phospholipid (CDH 0.10 +/- 0.03 mg/g versus control (CON) 0.76 +/- 0.28 mg/g) and PC (CDH 38 +/- 7.3% versus CON 70 +/- 3.4%) when compared with controls. In contrast the L/S ratios (CDH 2.44 +/- 0.26 versus CON 2.01 +/- 0.32) and PG status (CDH 8.75 +/- 1.01 nmol versus CON 10.2 +/- 0.9) were the same in CDH and control animals. The BAL from the CDH lamb model has a significant surfactant deficiency. Amniotic fluid L/S ratios and PG status were, however, not different between the control and CDH lambs. These results indicate that amniotic fluid L/S ratios and PG do not accurately predict the surfactant status of a fetus with CDH.

Evaluation of two commercial jet nebulisers and three compressors for the nebulisation of antibiotics

Nebulised antibiotics have been shown to be beneficial in the treatment of lung infections in cystic fibrosis. Studies on the efficiency of nebuliser systems are constantly required in view of the large number of compressor/drug/nebuliser combinations which are possible and the development of new systems and drugs. Six combinations of three commercially available compressors were compared (PortaNeb 50 (Medic-Aid; 5.4-6.1 l/min), Turboneb (Medix; 8.3-9.1 l/min), and CR 60 (Medic-Aid; 7.3-7.8 l/min)) and two jet nebulisers (Microneb III (Lifecare) and System 22 Acorn (Medic-Aid)) for the nebulisation of colomycin, gentamicin, and ciprofloxacin. Aerosol droplet size, nebulisation time, and aerosol output were determined. Turboneb and CR 60 reduced the nebulisation time and produced higher proportions of 'respirable' (< 5 microns diameter) antibiotic aerosols. The residual volume of the Microneb III was lower than that of the System 22 Acorn. It was found that the Turboneb and CR 60, when coupled with either Microneb III or System 22 Acorn, were suitable for the nebulisation of all three antibiotics. Of the equipment tested, Turboneb coupled with Microneb III was the most efficient combination. Even with this combination, only around 50% of the nominal dose was released as respirable aerosol.

Prediction of chronic neonatal lung disease in very low birthweight neonates using clinical and radiological variables

There are good theoretical reasons for earlier intervention in neonates likely to develop chronic neonatal lung disease (CNLD). Very low birthweight (VLBW) neonates who receive artificial ventilation are at high risk of CNLD. A test was therefore developed to predict CNLD based on clinical and radiological information readily available at 7 days of age in VLBW neonates. Logistic regression analysis was used to identify those factors significantly and independently associated with CNLD. For each neonate it was possible to insert the value of the independent factors into the equation, providing a probability value between 0 and 1. By selecting different cut off values between 0 and 1, and knowing which neonates had developed CNLD, it was possible to assess the use of varying probability values as a predictive test for CNLD. The variation in these two parameters was graphically represented by a receiver operator characteristic (ROC) curve. The area under the ROC curve was used to represent the discriminatory capacity of the test over its full range of values. The maximum area under an ROC curve is unity. The area under the ROC curve was similar in a model with and without radiographic information (0.926 and 0.913 respectively) and was 0.937 in neonates from another hospital.

High-dose versus low-dose bovine surfactant treatment in very premature infants

The aim of the study was to determine if high-dose bovine surfactant (Alveofact, initially 100 mg/kg birth weight) would improve oxygenation compared with low-dose surfactant (50 mg/kg birth weight) administered intratracheally within 1 h after birth. Inclusion criteria included gestational age 24-29 weeks and birth weight 500-1500 g, intubation and mechanical ventilation, absence of congenital malformations and bacterial infections. Retreatment was considered if the fraction of inspired oxygen (FiO2) was > 0.4 (dose 50 mg/kg birth weight). The primary endpoint was level of oxygenation (PaO2/FiO2) 2 h after treatment. The study design was a sequential analysis using a triangular test with alpha = 0.05 and 95% power to detect a 25% improvement in the endpoint. Oxygenation was improved significantly with high-dose (n = 42) compared to low-dose treatment (n = 48): 30.9 +/- 15.0 kPa (231.5 +/- 112.7 mmHg) versus 24.1 +/- 15.7 kPa (180.6 +/- 118.0 mmHg) (mean +/- SD). The survival rate was 83% in both groups and the incidence of pulmonary interstitial emphysema was 33% versus 14% with the high-dose treatment. We conclude that high-dose surfactant significantly improved oxygenation and reduced lung barotrauma. An initial dose greater than 50 mg/kg birth weight of surfactant is required for optimal acute response.

Pathophysiology of congenital diaphragmatic hernia. V. Effect of exogenous surfactant therapy on gas exchange and lung mechanics in the lamb congenital diaphragmatic hernia model

The aim of this study was to assess the impact of surfactant deficiency on the pathophysiology of congenital diaphragmatic hernia (CDH). Pregnant ewes were operated on at 80 days of gestation for creation of a diaphragmatic hernia in the lambs. Twenty-one lambs survived to be delivered by cesarean section and were studied. Compliance was improved when surface tension effects were removed by saline solution in lungs of both control animals and lambs with CDH; however, the lungs of the lambs with CDH still had significantly impaired compliance. In a second series of experiments, two groups were studied: a surfactant-treated and a control, nontreated group. Surfactant was given prophylactically into the liquid-filled lungs before the first breath. All lambs were paralyzed and sedated and their lungs mechanically ventilated with 100% oxygen for 30 minutes; gas exchange was then assessed, pressure-volume data were obtained, and compliance was calculated. Surfactant significantly improved gas exchange; arterial oxygen pressure increased from 39 +/- 11.4 to 316 +/- 53.6 mm Hg, arterial carbon dioxide pressure decreased from 148 to 63 mm Hg, and pH increased from 6.87 to 7.16 (p < 0.001). Lung volume at 25 cm H2O, functional residual capacity, and compliance were all increased (p < 0.02). Thus, in the CDH lamb model, pulmonary mechanics are impaired by both parenchymal and surfactant abnormalities. Both lung mechanics and gas exchange are markedly improved by exogenous surfactant therapy.

Advances in the critical care of poisoned paediatric patients

Recent improvements in paediatric intensive care may potentially improve outcome for severely poisoned children. The application of advanced techniques of critical care to the poisoned paediatric patient encompasses a wide variety of therapeutic and technical innovations that are primarily directed towards support of the cardiopulmonary system and removal of toxins. New extracorporeal removal techniques such as continuous arterio-venous haemofiltration have not substantively increased our ability to remove toxins except in rare instances. Exotic techniques such as extracorporeal membrane oxygenation remain in the background for use in rare instances only, with little clear data on the relative risks and benefits of applying them.

Correlations between radiological and cytological findings in early development of bronchopulmonary dysplasia

Sequential chest radiographs from 40 newborn infants requiring assisted ventilation for respiratory distress syndrome or other conditions were evaluated with a new scoring system aiming at identifying abnormal expansion patterns and interstitial infiltrates representing an early stage of bronchopulmonary dysplasia (BPD). Age at examination ranged from 3 to 23 days. Tracheal effluent samples obtained from the babies during the same period of observation were examined cytologically for evidence of regenerating airway epithelium with squamous metaplasia, indicating BPD. According to the radiological scoring system 24 babies (60%) developed BPD, first diagnosed at a median age of 9 days. By cytological criteria 20 babies (50%) developed BPD, first diagnosed at a median age of 10.5 days. The results from radiological and cytological diagnosis of BPD were concordant in 16 babies (P < 0.05 by chi-square test). Using oxygen dependency at the age of 28 days as evidence of established BPD, the radiological scoring system alone had a sensitivity of 93% and a specificity of 53%. The corresponding figures for cytological assessment alone were 73% and 58%, respectively. By combining radiological and cytological findings, values for sensitivity and specificity were 67% and 68%, respectively.

Randomised controlled trial of plasma protein fraction versus dopamine in hypotensive very low birthweight infants

Around 20% of very low birthweight infants admitted to a neonatal intensive care unit become hypotensive within 24 hours of their admission. Standard treatment is either expansion of the circulating volume by the infusion of plasma protein fraction or by using dopamine to improve cardiac function. The purpose of this study was to investigate by a randomised controlled trial which was the most appropriate treatment. Thirty nine infants were randomised to receive either plasma protein fraction or dopamine as first line treatment if they became hypotensive within 24 hours of admission to the neonatal intensive care unit. Seventeen of 19 (89%) infants responded to dopamine, whereas only 9/20 (45%) responded to plasma protein fraction. The median dose of dopamine needed to increase the blood pressure to at least the 10th centile was 7.5 micrograms/kg/min and was infused for a median duration of 18 hours. These observations suggest that dopamine should be used earlier in the treatment of these infants than has previously been recommended.

Respiratory function at follow-up after neonatal surfactant replacement therapy

Respiratory function was assessed at a median of 7 months (range 6-12) in 17 preterm infants who, in the neonatal period, had been entered into a multi-centre randomized placebo-controlled trial of prophylactic surfactant replacement therapy. Seven infants (median gestational age 28 weeks) received surfactant and the remaining ten infants (median gestational age 27 weeks) placebo. Respiratory function was assessed by measuring functional residual capacity (FRC), thoracic gas volume (TGV) and airways resistance (RAW). Specific conductance (SGAW) was calculated from RAW and TGV. There was no significant difference in FRC or TGV between the two groups. RAW, however, was significantly lower in the surfactant (median 41, range 21-48 cmH2O l-1 s-1) compared to the placebo group (median 57, range 40-68 cmH2O l-1 s-1), P < 0.05 and SGAW significantly higher in the surfactant (median 0.136, range 0.063-0.289 l cmH2O-1 s-1) compared to the placebo group (median 0.081, range 0.062-0.134 l cmH2O-1 s-1), P < 0.05. These results suggest that surfactant replacement therapy improves lung function at follow-up.

Induction of lipid peroxidation of pulmonary surfactant by plasma of preterm babies

Respiratory distress syndrome of the preterm baby is believed to be caused by a deficiency of pulmonary surfactant and leakage of plasma into the alveolar spaces. Since the two pathogenetic factors seem to be inter-related, we postulated that peroxidation of surfactant by plasma iron could be the linking mechanism. We obtained cord blood samples from 22 preterm babies (mean gestational age 32.2 [SD 2.7] weeks) and 24 term babies (40.1 [1.6] weeks), and venous blood samples from 18 healthy adults. No adult had detectable non-protein-bound iron in the plasma, but 10/21 (48%) preterm babies and 6/24 (25%) term babies had detectable concentrations (rate difference 23% [95% Cl -5 to 51%], p = 0.20). Transferrin and haptoglobin concentrations were higher and free haemoglobin concentrations lower in adults than in babies (p < 0.005). Only transferrin differed significantly between term and preterm babies. Plasma from all 18 adults and from 23 (96%) term babies inhibited iron-catalysed lipid peroxidation of pulmonary surfactant liposomes. By contrast, plasma from 11 (50%) preterm babies stimulated such peroxidation (difference in stimulation rate 46% [20-71%], p < 0.005 for preterm vs term babies); the ability to stimulate peroxidation was related to the presence of non-protein-bound iron (p < 0.001). Peroxidation decreased in the babies when apotransferrin was added to plasma and in all subjects when alpha-tocopherol was incorporated into the surfactant liposomes. Lipid peroxidation of surfactant may contribute to the pathogenesis of respiratory distress syndrome. Possible therapeutic approaches are increasing babies' iron-binding capacity by plasma transfusions and increasing the antioxidant capacity of commercial surfactant.

Randomized multicentre trial of treatment with porcine natural surfactant for moderately severe neonatal respiratory distress syndrome. The Collaborative European Multicentre Study Group

A randomized trial comparing outcome of babies treated with a natural surfactant (Curosurf) for moderately severe respiratory distress syndrome (RDS) with corresponding data from babies treated at a more advanced stage of the disease is reported. A total of 182 newborn babies (mean gestational age 29.8 weeks) requiring mechanical ventilation and a fraction of inspired oxygen (FiO2) in the range of 0.40-0.59 for RDS were randomized to immediate ("early") treatment (No = 86) with surfactant (200 mg/kg), or to a control group (No = 96). According to the protocol 49 controls (51%) qualified for a "late" surfactant treatment at an FiO2 requirement of > or = 0.60. In both groups of treated patients administration of surfactant led to a rapid improvement of oxygenation, but the peak value for PaO2 and the variability of the response tended to be lower in babies given immediate treatment. In comparison with the total control group, babies treated immediately had lower incidence of grade III-IV intraventricular hemorrhage (7% vs 18%; p < 0.05), lower mortality (9% vs 23%; p < 0.05), and lower incidence of unfavourable outcome--defined as death or bronchopulmonary dysplasia--(18% vs 34%; p < 0.05) at 28 days. Also significant reductions of time in oxygen > 21% and time on mechanical ventilation were observed. Our data suggest that treatment with surfactant when RDS is moderately severe prevents or reverses the natural progression of the disease in at least 50% of the cases and lowers the risk of serious complications.

Synthetic surfactant (Exosurf) inhibits endotoxin-stimulated cytokine secretion by human alveolar macrophages

Tumor necrosis factor-alpha (TNF), interleukin-1 beta (IL-1), interleukin-6 (IL-6), and interleukin-8 (IL-8) are inflammatory cytokines produced by alveolar macrophages (AMs) and implicated in sepsis-related adult respiratory distress syndrome (ARDS). Preliminary findings from clinical trials suggest that aerosolized delivery of the synthetic surfactant Exosurf (Burroughs Wellcome Co.) reduces mortality in patients with sepsis-induced ARDS. The purpose of the present study was to examine the effect of Exosurf on inflammatory cytokine secretion from AMs in vitro. AMs were obtained from normal nonsmoking adult volunteers. Secreted TNF, IL-1, IL-6, and IL-8 were measured by enzyme-linked immunoassays in 24 h culture fluids of AMs. Exosurf inhibited LPS-stimulated TNF, IL-1, and IL-6 secretion in a dose-dependent fashion. IL-8 secretion was not affected by Exosurf under these conditions. However, if AMs were preincubated for 24 h in media and then LPS-stimulated, IL-8 secretion was inhibited by Exosurf. Regulation of IL-8 production may differ from TNF, IL-1, and IL-6. Unstimulated cytokine secretion was not affected by any of the tested concentrations of Exosurf. The inhibitory effect of Exosurf on endotoxin-induced cytokine secretion by human AMs suggests that Exosurf may modulate inflammatory cytokine production in the lung.

Neonatal intensive care. When and where is it justified?

There is a wide panorama of disorders in the newborn infant where neonatal intensive care has been proven effective in reducing mortality. Although modern neonatal intensive care can be very costly, short and simple interventions for support and resuscitation still can be highly beneficial. In reviewing the field of neonatal intensive care during the 1980s, it becomes evident that a major challenge for the future will be to apply physiological principles of great and proven value for the newborn baby to more simple devices. Only thereby can the technology of neonatal care defined as a complex of actions-not only equipment and techniques-become justified for future generations.

Natural surfactant for neonatal respiratory distress syndrome in very premature infants: a 1992 update

Natural surfactant (Surfactant TA, Survanta, CLSE, SF-RI 1, Curosurf and human surfactant obtained from amniotic fluid) therapy for RDS in very premature infants has been evaluated in 17 controlled clinical trials. Uniformly intratracheal surfactant administration caused a decreased intensity of mechanical ventilation during the first hours (reduced inspiratory pressure, reduced oxygen requirements) as an immediate effect of surfactant administration. Metanalysis reveals barotraumatic pulmonary complications mainly, pneumothorax and pulmonary interstitial emphysema to occur less frequently in surfactant-treated infants in virtually all trials; an increased incidence of survival without bronchopulmonary dysplasia following surfactant treatment was observed in 10 controlled clinical trials. The incidence of other complications of prematurity (intracranial hemorrhage, patent ductus arteriosus and necrotizing enterocolitis) was unchanged following natural surfactant treatment. Dosing of natural surfactant is still under investigation, however recent data indicate that the initial dose should not be less than 100 mg/kg b.w. and retreatment should be given to infants with unsatisfactory response (i.e. fraction of inspired oxygen (FiO2) > 40%). Timing of surfactant treatment still remains controversial. Prophylactic treatment shortly following birth has been compared with rescue-treatment, i.e. surfactant administration to infants suffering from manifest RDS in most studies 4-8 h after birth. Conflicting data from 5 controlled trials may be interpreted as follows: prophylactic treatment seems to be favourable for extremely premature infants (GA < or = 26 weeks) and rescue treatment seems to be adequate for infants of 27-30 weeks of gestation. Intratracheal surfactant instillation in very premature infants did not result in an improved lung function for 24 h to 48 h in all patients. Ten--25% of study infants were reported to be "non-responders", i.e. infants without sustained decrease in oxygen requirements (i.e. FiO2 > 40%). Various factors may be operative including congenital bacterial infections (sepsis or pneumonia), lung hypoplasia and cardiac failure. Inactivation of surface properties of natural surfactant caused by a leakage of proteins across the alveolar-capillary membrane was observed in experimental and clinical studies. Current investigations focus on a combination of postnatal steroids and surfactant treatment to improve lung function and outcome in "non-responders". As long as any controlled clinical studies are being published, this approach remains experimental. Up to now, any controlled clinical trials have been performed to assess different modes of artificial ventilation (e.g. high frequency oscillating ventilation versus conventional ventilation) combined with surfactant therapy. Data obtained from premature animals given natural surfactant indicate any advantage with respect to gas exchange and lung histology to result from high frequency ventilation.(ABSTRACT TRUNCATED AT 400 WORDS)