Exogenous human surfactant for treatment of severe respiratory distress syndrome: a randomized prospective clinical trial

The new obstetrics: its integration into neonatal clinical practise, teaching and research

Most neonatologists have not yet incorporated into their teaching, clinical service and research the advances in high risk obstetrics particularly as it relates to fetal surveillance. This brief review emphasizes some of the "new obstetrics" from the viewpoint of perinatal medicine, particularly in terms of neonatal teaching and the design of future neonatal research. The information that can be obtained about an infant prenatally by the use of ultrasound. power doppler, computerized fetal heart rate monitoring, cordocentesis, etc is extensive and yet, has rarely been utilized in the design of neonatal research protocols. It is becoming imperative that the "new obstetrics" be recognized and utilized in modern neonatal thinking if a truly "perinatal medicine" is to be practised.

Changes in oxygenation and pulmonary haemodynamics in preterm infants treated with inhaled nitric oxide

AIM

To investigate changes in various cardiorespiratory variables with inhaled nitric oxide (NO), as part of a randomised controlled trial.

METHODS

Infants were treated with inhaled NO for 72 hours. Changes in oxygenation were assessed using the oxygenation index (OI). Serial changes in pulmonary artery pressure (PAP) were assessed using the Doppler derived acceleration time to right ventricular ejection time ratio (AT:RVET). Doppler measurements of right ventricular output, pulmonary blood flow, and systolic PAP was performed in a subset of infants.

RESULTS

Twenty infants received inhaled NO and 22 acted as controls. Infants were treated at a median dose of 5 (range 5 to 20) ppm. There was a fall in median OI by 17% in treated infants within 30 minutes of treatment. The fall in OI in treated infants was significantly different from the response in controls until 96 hours. Infants treated with inhaled NO showed a rapid response with a median rise in AT:RVET of 0.04 (range -0.06 to 0.12) within 30 minutes. The change in AT:RVET was significantly different from controls until 4 hours. Median systolic PAP also fell in treated infants by 6.1 (range -14.4 to -4.4) mm Hg within 1 hour. Changes in OI were significantly associated with changes in PBF (r = 0.44), but not with changes in AT:RVET.

CONCLUSION

Treatment with inhaled NO rapidly improves oxygenation and lowers PAP in preterm infants. However, these effects are transient and treatment does not influence long term outcome.

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.

Outcome of very low birth weight infants at 12 to 18 months of age in Soweto, South Africa

OBJECTIVE

To describe the long-term outcome of very low birth weight infants growing up in poor socioeconomic conditions in Soweto, South Africa.

METHODS

A stratified sample of infants weighing < 1500 g surviving to hospital discharge was enrolled. Group 1 consisted of 49 infants 1000 to 1499 g who required mechanical ventilation; group 2 consisted of 39 infants 1000 to 1499 g who did not require mechanical ventilation; and group 3 consisted of 25 infants < 1000 g (such infants are not routinely ventilated). Growth and neurological status were recorded at follow-up visits at 3, 6, and 12 months' corrected age and the infants were evaluated further using the Bayley scales of infant development between 12 and 18 months.

RESULTS

Fifteen infants died during the period between hospital discharge and 1 year corrected age, and 12 others were lost to follow-up. Although some catch-up growth was noted in the early months, all group means for weight and length were below the 25th percentile at 1 year. Cerebral palsy was diagnosed in nine infants (8 from group 1). Periventricular leukomalacia and/or porencephaly was diagnosed in eight of the nine infants during their initial hospital stay and was also the strongest negative predictor of the Bayley scores. Higher maternal education and better intrauterine growth were associated with higher Bayley scores.

CONCLUSIONS

Mortality after hospital discharge in this study cohort was extremely high. However, despite marked differences in socioeconomic conditions and tertiary care facilities, the handicap rates were comparable with recent studies from developed countries, and some of the predictors of handicap, eg, periventricular leukomalacia and porencephaly, were also similar.

Factors affecting the neonatal response to artificial surfactant

OBJECTIVE

To define the individual neonatal response to the artificial surfactant, Exosurf, and factors that may influence the response.

METHODOLOGY

Eighty-two consecutive, preterm neonates with respiratory distress syndrome, who received Exosurf at < 12 h of age were studied. Their response was categorized from the graphical change in the oxygenation index with postnatal age, for 12 h after each of two doses of surfactant and assessed independently by two observers. Clinical factors were analysed for their effect on the four pre-defined categories of response, namely: none; mild; good: relapsed; and good: sustained.

RESULTS

Within the first 12 h, 11% of the neonatas showed no response, 5% a mild response and 84% a good response, but 34% relapsed. By 24 h, 6% still showed no response (all died), 11% showed a mild response and 83% a good response, of whom half relapsed. At 24 h, no response was significantly associated with low gestational age and asphyxia, mild response with less severe lung disease. According to the response there was a gradation in the risk of death during the first week.

CONCLUSIONS

The response to Exosurf can be individually and reproducibly categorized and demonstrated that 83% of neonates had a good response but half relapsed. No response was associated with extreme prematurity and asphyxia.

Improved outcomes following the introduction of surfactant to an Australian neonatal unit

OBJECTIVE

To study the impact of the introduction of artificial surfactant therapy for hyaline membrane disease (HMD) in an Australian neonatal intensive care unit.

METHODOLOGY

Infants < 32 weeks gestation admitted between June 1991 and Dec 1993 who received treatment with artificial surfactant were compared with infants admitted during the preceding 30 months who would have been candidates for such treatment.

RESULTS

For treated infants with gestations in the range 24-27 weeks, there was a significant reduction in neonatal death (adjusted odds ratio 0.28) and a significant increase in the incidence of chronic lung disease (CLD) (adjusted odds ratio 3.4). With gestations in the range 28-31 weeks, there was no significant change in neonatal death or CLD, but there was a significant reduction in incidence of pneumothorax (adjusted odds ratio 0.32).

CONCLUSIONS

A reduced incidence of pneumothorax and neonatal death following the introduction of artificial surfactant therapy was readily demonstrable in the Australian setting.

Invasive monitoring in infants with respiratory syncytial virus infection

OBJECTIVE

Coincident with a change in the physician staff in our pediatric intensive care unit (PICU), the frequency and duration of invasive monitoring were decreased. We examined the impact of this change on outcomes, complications, and hospital charges in infants admitted to the PICU with respiratory syncytial virus (RSV) infection.

STUDY DESIGN

We reviewed medical records of all children less than 1 year of age who were admitted to the PICU from January 1989 to July 1993 with confirmed RSV infection. Patient characteristics, therapeutic interventions, outcomes, and hospital charges were extracted and compared.

RESULTS

Seventy-eight patients were identified, 38 admitted from January 1989 through July 1991 (group 1) and 40 from July 1991 through July 1993 (group 2). The groups were well matched in age, preexisting disease, and cardiorespiratory status on admission. Group 1 had significantly greater use of invasive monitoring, pharmacologic paralysis, inotropes, blood products, antibiotics, and parenteral nutrition. Outcomes were not different, but group 1 patients had significantly longer stays, more complications, and higher hospital charges.

CONCLUSIONS

Routine use of invasive monitoring of PICU patients with RSV disease was associated with increased laboratory testing, overtreatment, and significant increases in costs and morbidity without improvement in outcome.

Respiratory mechanics before and after late artificial surfactant rescue

OBJECTIVE

To assess the effect of late administration of synthetic surfactant (Exosurf) on the ventilatory function of premature infants with hyaline membrane disease (HMD).

METHODOLOGY

Prospective non-randomized study in the Neonatal Intensive Care Unit (NICU) of a major referral hospital. The patients included two groups of premature infants with a birthweight between 750 and 2000 g who developed HMD. In group 1 with moderate to severe HMD, 2 x 5 mL/kg doses of Exosurf were given 12 h apart (first dose given at a mean age of 18.7 +/- 3.4 h [mean +/- s.e.m.]). In group 2 with milder HMD, no surfactant was given.

RESULTS

Significant reductions (P < 0.05) in the fraction of inspired oxygen (FIO2) occurred 6 h after surfactant administration (24 h of life) and by 48 h (64 h of life) in group 2. These improvements in gas exchange preceded improvements in passive respiratory compliance which occurred 24 h after surfactant (42 h of life) and by 72 h (88 h of life) in group 2 (P < 0.01). In both groups pulmonary resistance increased and was significant (P < 0.05) by 48 h (66 h of life) in group 1.

CONCLUSIONS

Synthetic surfactant given as late as a mean age 18.7 +/- 3.4 h still improves gas exchange but these early improvements cannot be completely explained by modifications of respiratory compliance.

Efficacy of surfactant therapy in infants managed with CPAP

Surfactant rescue therapy can be utilized effectively early in the course of respiratory distress syndrome (RDS) in infants weighing > 1,000 g and treated exclusively with continuous positive airway pressure (CPAP) therapy. Thirteen infants (BW, 1,774 +/- 580 g; GA, 31 +/- 3 weeks) comprising the CPAP/SURFACTANT group were compared with 12 infants (BW, 1,753 +/- 556 g; GA, 31 +/- 2 weeks) who comprised the intermittent mandatory ventilation (IMV)/surfactant group, and with 14 infants (BW, 1,776 +/- 332 g; GA, 32 +/- 2 weeks) treated with CPAP before surfactant was clinically available. A 5 mL/kg dose of Exosurf Neonatal (Burroughs-Wellcome) was administered to infants intratracheally when the FiO2 requirement reached 0.40 to maintain the PO2 above 50 torr. Infants in the CPAP/surfactant group were intubated solely for surfactant administration and extubated within 18 +/- 6 min of treatment. The CPAP/surfactant group was treated at a mean age of 12.3 +/- 9.3 h, and the IMV/surfactant group at 10.2 +/- 9.8 h. Alveolar-arterial oxygen gradient (AaDO2), oxygenation index (OI), and mean airway pressure (MAP) were determined immediately before and after surfactant therapy, and at comparable times for the CPAP-only group. A significant difference was found in pre-treatment AaDO2, OI and MAP between the CPAP/surfactant group and IMV/surfactant group, but not between the CPAP/surfactant group and the CPAP-only group. Similarly, a significant difference in AaDO2, OI and MAP continued post-treatment was noted. However, a significant difference was also found at this time between the CPAP/surfactant group and the CPAP-only group. In addition, a significant difference was noted in AaDO2 and OI pre- and post-treatment within each surfactant-treated group. Furthermore, in the CPAP-only group AaDO2 and OI actually worsened (212 +/- 70 vs. 239 +/- 68; 4.0 +/- 1 vs. 4.5 +/- 2, respectively). There was a significant reduction in the duration of oxygen therapy (3 +/- 2 vs. 5 +/- 2 vs. 4.5 +/- 2 days, respectively) as well as in the total days of hospitalization (30 +/- 10 vs. 42 +/- 15 vs. 43 +/- 12 days, respectively). We conclude that in this small group of infants surfactant administration was effective and safe. It appeared to improve the course of RDS and shorten the duration of oxygen exposure and days of hospitalization.

Pulmonary haemodynamics after surfactant replacement in severe neonatal respiratory distress syndrome

Aortopulmonary pressure difference and pulmonary blood flow velocity were studied during the first 48 hours of life in 12 premature neonates with severe respiratory distress syndrome (RDS), treated by natural surfactant, and in 25 premature neonates with mild RDS. A non-invasive Doppler ultrasound method was used to estimate aortopulmonary pressure difference and pulmonary blood flow velocity from the left pulmonary artery. Aortopulmonary pressure difference was significantly lower at 6 hours of age in the infants with severe RDS and was not increased one hour after surfactant therapy. Aortopulmonary gradient started to rise at 24 hours of age and was equal to that of neonates with mild RDS at 48 hours. Pulmonary blood flow velocity was significantly lower, initially in the severe RDS group, and was not increased one hour after surfactant therapy. Left pulmonary artery flow velocity began to rise after 24 hours and reached the values of the mild RDS group at 48 hours. These data indicate that aortopulmonary pressure difference and pulmonary blood flow are low in the acute phase of RDS and that surfactant treatment does not seem to affect these values.

Double-blind, randomized trial of one versus three prophylactic doses of synthetic surfactant in 826 neonates weighing 700 to 1100 grams: effects on mortality rate. American Exosurf Neonatal Study Groups I and IIa

At 33 hospitals in the United States, a double-blind, randomized clinical trial was performed to compare one versus three prophylactic doses of synthetic surfactant in 700 to 1100 gm inborn infants. All 826 infants received an initial prophylactic dose of surfactant within 30 minutes of birth. Subsequently 410 infants received two doses of placebo (air) 12 and 24 hours later, and 416 infants received two additional doses of surfactant. By the age of 28 days, 70 infants who received one dose of surfactant and 40 infants who received three doses were dead, a 43% relative reduction in the mortality rate (30 fewer deaths; p = 0.002). By the age of 1 year after term, 87 infants who received one dose and 62 infants who received three doses were dead: a 29% relative reduction in the mortality rate (25 fewer deaths; p = 0.027). Infants who received three doses of surfactant required significantly less oxygen and less mean airway pressure for the first week of life. Necrotizing enterocolitis (9 vs 25 infants; p = 0.005), and use of high-frequency ventilation (13 vs 26 infants; p = 0.037); pancuronium (43 vs 62 infants; p = 0.045); and leukocyte transfusions (0 vs 4 infants; p = 0.042) were less frequent in the three-dose group, but air leak, bronchopulmonary dysplasia, intraventricular hemorrhage, patent ductus arteriosus, pulmonary hemorrhage, and infections were not different. These results indicate that physiologic findings, mortality rates, and probably morbidity rates are improved by two additional prophylactic doses of synthetic surfactant.

Effect of maternal glucocorticoid exposure on risk of severe intraventricular hemorrhage in surfactant-treated preterm infants

OBJECTIVE

To determine whether the reduced risk of severe intraventricular hemorrhage (SIVH) that follows antenatal maternal glucocorticoid (AMG) receipt is mediated by an AMG effect on blood pressure or improved respiratory function in infants who receive artificial surfactant as rescue therapy.

DESIGN

Retrospective cohort study.

SETTING

Two level III neonatal intensive care units, Boston, Mass.

PARTICIPANTS

Two hundred twenty-five infants < or = 32 weeks of gestational age and < or = 1.7 kg birth weight, treated with surfactant.

MAIN FINDINGS

SIVH occurred in 10% (10/102) of infants who were exposed to AMG, compared with 23% (25/111) of infants not exposed (odds ratio, 0.4; 95% confidence interval, 0.2 to 0.8). Hypotension and need for colloid or dopamine were associated with both SIVH and the absence of AMG exposure (p < or = 0.03). Logistic regression models of SIVH risk and AMG exposure, with adjustment for antenatal potential confounders, were altered by the addition of measures of hypotension. Most clinical measures of pulmonary function, both before and after surfactant receipt, were not associated with reduced risk of SIVH and did not appear to account for the increased risk of SIVH in babies not exposed to AMG.

CONCLUSION

The reduced risk of SIVH in preterm newborn infants whose mothers received AMG was associated with normal blood pressures. The association between AMG and SIVH was not consistently enhanced by respiratory function improvement after surfactant therapy.

A new radiographic scoring system for bronchopulmonary dysplasia. Newborn Lung Project

OBJECTIVES

To develop a simple, clinically meaningful radiographic score for bronchopulmonary dysplasia (BPD). To investigate its reliability, validity, and usefulness and to compare it to the Edwards score.

WORKING HYPOTHESIS

Our radiographic scoring of BPD is reliable, correlates with respiratory support, and provides a necessary standardization in comparing severity of respiratory disease between hospitals.

STUDY DESIGN

Prospective cohort study.

PATIENT SELECTION

The study included all neonates (n = 366) with birth weight below 1501 g admitted to 7 neonatal intensive care units, who had chest radiographs taken at age 25-35 days.

METHODOLOGY

A simple radiographic scoring system was developed. Scores ranging from 0 to 6 were assigned based on standard radiographs and descriptors of degree of abnormality. All radiographs taken between days 25 and 35 of age (n = 1087) were graded by a radiologist and a neonatologist. Radiographs from a stratified random sample of 37 neonates (10%) were also scored by the method of Edwards (n = 128 radiographs). A respiratory support index was constructed for days 25-35 and correlated with the radiographic score.

RESULTS

Between-reader correlation was r = 0.87 for our score and r = 0.88 for the Edwards score. The two scores correlated with each other at r = 0.94. The respiratory support index correlated with our radiographic score at r = 0.75 overall, and r = 0.56 to 0.88 within hospitals. Higher postnatal corticosteroid use was found at the hospitals with the lower correlations.

CONCLUSIONS

Our radiographic scoring is reliable, valid, and gives results similar to the Edwards score. Radiographs play a standardizing role in assessing severity of BPD between hospitals.

Prognostic value of the immediate response to surfactant

AIM

To evaluate the association between the immediate response to surfactant treatment and morbidity and mortality in infants with severe respiratory distress syndrome.

METHODS

The response to surfactant was defined as the difference in the arterial:alveolar (delta a:A) ratio before and one hour after the first surfactant dose. Measurements were obtained from 253 Israeli infants participating in the multi-centre Curosurf 4 trial of surfactant replacement therapy.

RESULTS

Delta a:A ratios ranged from -0.115 to 0.8 and were significantly related to both birth weight and gestational age. Among infants weighing 1001-1500 g mortality decreased from 40% among very bad responders to zero among good responders. The incidence of pneumothorax decreased with better response. Logistic regression analysis showed a hierarchy of predictive power for mortality: birth weight or gestational age; immediate response to surfactant; severity of initial disease.

CONCLUSION

The immediate response to surfactant treatment is a significant prognostic indicator for mortality and morbidity.

Failure of acute perinatal asphyxia or meconium aspiration to produce persistent pulmonary hypertension in a neonatal baboon model

OBJECTIVE

Our purpose was to determine whether perinatal asphyxia or meconium aspiration, or both, can produce the physiologic and histologic pulmonary vascular changes associated with the meconium aspiration syndrome.

STUDY DESIGN

Twenty neonatal baboons were studied in four groups: 1, control; 2, meconium aspiration; 3, asphyxia (intermittent cord compression); and 4, asphyxia with meconium aspiration. Animals were ventilated for 24 hours under ketamine, diazepam, and pancuronium. Data were analyzed by means of mixed model analysis of measures.

RESULTS

Meconium significantly impaired oxygenation (p < 0.001), whereas concurrent asphyxia moderated this effect (p < 0.034). Meconium also increased the need for ventilatory support (p < 0.002). No animal had persistent pulmonary hypertension; neither systemic nor pulmonary systolic pressures differed statistically between the groups. No animal showed evidence of abnormal pulmonary arteriolar muscularization.

CONCLUSION

Sublethal perinatal asphyxia or meconium aspiration were insufficient to produce either the physiologic or histologic changes of severe meconium aspiration syndrome. It is unlikely that intrapartum fetal distress alone can produce this syndrome in human neonates.

Pathology of the lung in surfactant-treated neonates

Respiratory distress syndrome (RDS) is associated with prematurity-related deficiency of surfactant. Surfactant replacement therapy has been used in premature infants to prevent RDS or reduce its severity. In this study we describe the pathology of the lungs after surfactant replacement therapy. All the neonatal autopsies during the years 1989 and 1990 (n = 235) were examined. Infants > or = 31 weeks gestation, with congenital anomalies or who lived more than 2 weeks were excluded from the study. Infants who had received intratracheal Survanta, a modified surfactant extracted from cow lung (n = 14), were compared with infants who did not receive exogenous surfactant (n = 20). The two groups were statistically comparable in terms of weight, gestational and postnatal age, gender, and clinical management. H&E-stained lung sections were examined independently by two pathologists without knowledge of surfactant treatment status; any discrepancies in histological evaluation were resolved by joint review. Nine histological features were evaluated including hyaline membranes, necrosis of the epithelium, hemorrhage, edema, inflammation, metaplasia, arteriolar muscular hyperplasia, interstitial fibrosis, and pulmonary interstitial emphysema (PIE). Histological changes were graded from 0 to 3+. When it was present, cerebral periventricular-intraventricular hemorrhage (PVH-IVH) was graded 1-4. The presence or absence of sepsis and necrotizing enterocolitis (NEC) were also determined. Comparisons between patient groups were performed using the Mann-Whitney U, Student's t and chi 2 tests. The severity of hyaline membrane disease, PIE, and epithelial necrosis was less severe in the surfactant-treated group than in the untreated group. There were no differences between the two groups in the degree of pulmonary hemorrhage or in the incidence of PVH-IVH, sepsis, or NEC.

Extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation has now evolved into standard therapy for patients unresponsive to conventional ventilatory and pharmacological support. This article presents a clinical review of extracorporeal life support and its application to neonatal and pediatric patients as well as children requiring circulatory support after open heart surgery.

The fate of exogenous surfactant in neonates with respiratory distress syndrome

Respiratory distress syndrome (RDS) in newborn neonates is characterised by deficient secretion of surfactant from type III alveolar cells. Administration of surfactant to airways acutely decreases the degree of respiratory failure and increases the survival rate in neonates with RDS. Clinically available surfactants are lipid extracts derived from animal lung lavage or from whole lung. Synthetic surfactants contain phospholipids or additional spreading agents. An optimal exogenous surfactant would be efficacious, nontoxic and nonimmunogenic, resistant to oxidants and proteolytic agents, widely available at reasonable cost and manufactured with little batch-to-batch variability. Surfactant has been instilled into the airways as a bolus infusion through the endotracheal tube. In addition, surfactant may be given by aerosolisation or continuous infusion into the airways. Suggested dosages range from 50 to 200 mg/kg. Exogenous surfactant is cleared from the epithelial lining fluid (ELF) mainly by alveolar epithelial cells, although alveolar macrophages and the central airways may also contribute to clearance of the drug. Only small quantities of surfactant actually enter the blood stream. A significant fraction of surfactant is taken up, processed, and secreted back into the alveolar space by type II alveolar cells. This process is termed recycling. Phosphatidylglycerol, given to small premature neonates as a component of exogenous human surfactant, has an apparent pulmonary half-life of 31 +/- 3 hours (n = 11). The apparent pulmonary half-life of the main surfactant component dipalmitoyl phosphatidylcholine is 45 hours (n = 3) and that of surfactant protein A is about 9 hours (n = 4). A relationship between the dose of exogenous surfactant and its concentration in the ELF has been demonstrated. Some neonates with RDS respond poorly to surfactant therapy. The reasons for this include insufficient levels of surfactant in the ELF, uneven distribution of exogenous surfactant, inability of exogenous surfactant to enter the metabolic pathways, inhibition of surface activity by plasma-derived proteins, or inactivation of surfactant as a result of proteases, phospholipases, or oxygen free radicals. In addition, surfactant therapy may be ineffective in neonates with respiratory failure caused by factors other than surfactant deficiency. The efficacy of exogenous surfactant can be improved by increasing the dosage of surfactant and by administration of surfactant very early in respiratory failure.

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.

Effect of dexamethasone on protein metabolism in infants with bronchopulmonary dysplasia

Corticosteroids result in protein wasting in human adults and rats. To determine to what extent this therapy affects protein metabolism in preterm infants, we studied 10 very low birth weight infants before a gradually tapered dexamethasone regimen was started and at day 4 of treatment (dexamethasone dosage 0.35 +/- 0.09 mg.kg-1.day-1), and seven infants at day 19 of treatment (dexamethasone dosage, 0.10 +/- 0.01 mg.kg-1.day-1). Protein breakdown and turnover rates were increased at day 4 of treatment but not any more at day 19 of treatment. Protein synthesis rate was not significantly affected during dexamethasone therapy. Weight gain was severely diminished during the first week of treatment but not during the next 2 weeks. We conclude that nitrogen balance during high dosages of dexamethasone is significantly lower because of an increase in proteolysis and not because of a suppression of synthesis.

In vivo evaluation of the inhibitory capacity of human plasma on exogenous surfactant function

OBJECTIVE

The adult respiratory distress syndrome (ARDS) and neonatal respiratory distress syndrome (RDS) are characterized by high permeability pulmonary edema which contains plasma-derived proteins inhibiting pulmonary surfactant function. Currently, discussion continues as to what dose of surfactant is required for treatment of these syndromes.

DESIGN

The purpose of this study was to investigate the amount of exogenous surfactant needed to overcome the inhibitory components in human plasma. Male adult rats suffering from respiratory failure due to surfactant depletion after whole-lung lavage received human plasma (4 ml/kg body weight) mixed with surfactant at different concentrations, intratracheally. Rats receiving surfactant only at different concentrations served as controls. Blood gas analysis was performed.

MEASUREMENTS AND RESULTS

It was demonstrated that plasma (4 ml/kg-273 mg plasma proteins/kg) mixed with surfactant at 300 mg/kg was able to increase and maintain PaO2 at normal values. Plasma mixed with surfactant at 100 mg/kg, after initial restoration of blood gases, showed deterioration of PaO2 values. Plasma mixed with surfactant at a dose of 50 mg/kg did not improve PaO2 whereas surfactant at 50 mg/kg, without plasma, restored blood gases to pre-lavage values.

CONCLUSION

It is concluded that approximately 1 mg surfactant phospholipids is required to overcome the inhibitory effect of approximately 1 mg plasma proteins. For clinical practice this means that an excess of surfactant should be given, or repeatedly be substituted ("titrated") at low concentrations, until blood gases improve.

Surfactant replacement therapy in neonates less than 32 weeks gestation: effect on neonatal intensive care resource utilization

The effect of synthetic surfactant (Exosurf) replacement on complications from hyaline membrane disease (HMD) in infants < 32 weeks gestation and their resource utilization within a neonatal intensive care unit was studied in 1991-92. A control group was selected from infants admitted to the same unit during the preceding 3 years when Exosurf was not available. The infants were controlled for gestation, weight and severity of HMD. Infants given Exosurf had a significant reduction in the incidence of pulmonary interstitial emphysema (PIE), and a marginal decrease in the incidence of pneumothorax. They required fewer days on the ventilator and consumed less of the scarce financial resources. There was no difference in the mortality rate among the two groups. The changes seen were more evident among those infants between 30 and 31 weeks gestation, compared to those < 28 weeks.

Developmental outcome in extremely premature infants. Impact of surfactant

Advances in neonatology, particularly surfactant, have enabled us to significantly improve mortality in the extremely low-birth-weight prematurely born infant. The impact on morbidity remains less clear but decidedly optimistic as the preponderance of the data currently available suggests that although we have not improved outcome in this high-risk group of infants, neither have we increased the percentage of infants with significant impairments. But overall morbidity remains high, especially for the smallest and earliest survivors. There is a growing body of research that supports the idea that with modification of the stressful impact of the NICU environment on the physiologically unstable and vulnerable premature infant, we may be able to improve developmental outcome. We are already seeing even very small infants extubated at a younger age and ready for discharge home well before their originally anticipated "due date." Within this setting we have unequalled opportunity to positively impact development by caring for the infants in a supportive environment that integrates parents as primary caretakers who are comfortable and competent at the time of the infant's discharge home. Further research endeavors should be enlightening in this regard.

Pulmonary hemorrhage and exogenous surfactant therapy: a metaanalysis

A metaanalysis of surfactant clinical trials was carried out to assess whether or not an association exists between exogenous surfactant therapy and pulmonary hemorrhage. Trials that reported the pulmonary hemorrhage occurrence (group 1) and those that did not (group 2) were analyzed. Thirty-three treatment strategies were tested in 29 publications from 1980 through 1992. Eleven of these were group 1 trials, which reported a 3% overall incidence of pulmonary hemorrhage. The rates were significantly higher in both the treated and the control groups of natural surfactant trials than in synthetic surfactant trails (5.87% and 5.36% in the natural surfactant trials vs 2.51% and 1.04% in the synthetic surfactant trials, respectively). The pooled estimate of relative risk for pulmonary hemorrhage with any surfactant therapy was 1.47 (95% confidence interval 1.05, 2.07; p < 0.05). Logistic regression modeling revealed that the nature of surfactant, treatment strategy, and lower mean birth weight had a significant influence on the relative risk of pulmonary hemorrhage; a similar trend was seen with higher mortality rates. Variation in the rates of patent ductus arteriosus did not have an independent effect on the estimated pulmonary hemorrhage risk. Most group 2 trials were published before 1990, and the median total sample size was 73, compared with 402 for the group 1 trials (p < 0.05), most of which were published in the 1990s. In 10 (50%) of 20 group 2 trials, pulmonary hemorrhage data were collected methodically, in comparison with all group 1 trials, most of which collected data prospectively. We conclude that pulmonary hemorrhage is a rare complication of respiratory distress syndrome. An awareness of the possible association of pulmonary hemorrhage with surfactant use in later trials and the differences in definitions and reporting practices probably explain variations in the reported incidence among the trials. The risk of pulmonary hemorrhage increases slightly, on an average of 47%, with any surfactant therapy. This increased risk is small compared with the documented benefits of surfactant therapy in respiratory distress syndrome.

Surfactant replacement therapy for pulmonary diseases

Surfactant therapy has clearly been a meaningful addition to the therapeutic armamentarium in the management of premature infants with RDS. Pediatricians and others involved in the care of newborn infants should familiarize themselves with the various surfactant preparations, the indications for their use, the techniques of administration, and the possible side effects. All such care provides should also be skilled in endotracheal intubation and ventilation of neonates; recognition of the clinical and radiographic signs of RDS; and have the appropriate equipment to monitor cardiopulmonary status, oxygenation, and ventilation in these infants until transport to a tertiary care facility can be accomplished. In addition to the two current FDA-approved surfactants, several other surfactants are in various stages of evaluation. When administered to infants with established RDS, both natural and synthetic surfactants have clearly been shown to improve survival, decrease requirements for ventilatory support, and reduce the incidence of air leak complications. Although by no means conclusively demonstrated, certain infants, particularly those delivered at < 30 week gestation, may benefit from immediate treatment in the delivery room. It should be emphasized that, except under extenuating but controlled circumstances and except in the hands of an experienced physician, surfactant treatment should not be viewed as an integral part of neonatal resuscitation. Adequate treatment requires the administration of a minimum of two surfactant doses, although some infants may benefit from additional doses or treatment with an alternative preparation. Massive pulmonary hemorrhage, although rare, is observed with prophylactic and rescue treatment protocols and may result from hemorrhagic pulmonary edema due to a hemodynamically significant PDA. Currently there are no data to recommend the use of one surfactant preparation over another. The short- and long-term benefits may be similar with different products. Therefore, we must await results of trials with then necessary power (large number of subjects) and unbiased design to discern any clinically relevant differences. Results of studies directly comparing the relative efficacy of Survanta and Exosurf, conducted under the auspices of the National Institutes of Health, are expected in 1993. Multicenter trials comparing prophylactic and rescue administration of Exosurf versus CLSE and Survanta versus CLSE are currently underway. It is encouraging to note that follow-up studies up to 2 years of age do not reveal an increase in physical or neurodevelopmental handicaps, BPD, or other problems in preterm infants who received surfactant preparations either for prophylaxis or rescue therapy. Results of long-term follow-up studies, however, are not yet available.(ABSTRACT TRUNCATED AT 400 WORDS)

Optimizing alveolar expansion prolongs the effectiveness of exogenous surfactant therapy in the adult rabbit

We evaluated four ventilator patterns after the administration of 80 mg/kg bovine lipid extract surfactant (LES) to anesthetized, paralyzed, saline-lavaged New Zealand white rabbits. Two ventilator types were compared: high frequency oscillatory ventilation (HFO) versus conventional mechanical ventilation (CMV), each at high (HI) and low (LO) end-expiratory lung volumes (EELV); n = 6, each group; treatment duration = 4 h. Target PaO2 ranges were > 350 mm Hg for groups with high EELV (i.e., HFO-HI and CMV-HI) and 70 to 100 mm Hg for those with low EELV (i.e., HFO-LO and CMV-LO). Ventilator pressures were limited to < or = 39/9 cm H2O in the CMV-HI group. Five of six CMV-HI-treated animals did not maintain target PaO2 levels. Both ventilator type and strategy influenced outcome significantly. Animals managed with HFO had higher mean arterial pressures (p = 0.004), lower mean airway pressures (Paw) (p < 0.00008) and HCO3- requirements (p < 0.02), larger inflation (p = 0.003) and deflation (p < 0.00001) respiratory system volumes at 10 cm inflation pressure, and higher lung lamellar body (p = 0.0006) and lavage fluid (p = 0.003) phospholipid quantities than did CMV-treated animals. The deflation P-V curve (p = 0.0004), lamellar body (p < 0.00001) and lavage fluid (p = 0.0002) phospholipid levels were superior after the high EELV strategy. We conclude that ventilator pattern strongly influences exogenous surfactant efficacy. Benefits arise from keeping EELV high enough to prevent atelectasis and using small (approximately 2 ml/kg) tidal volumes to prevent overdistension.(ABSTRACT TRUNCATED AT 250 WORDS)

Ureaplasma urealyticum in a neonatal intensive care population

The incidence of Ureaplasma colonization at birth and its effect on the development of chronic lung disease (CLD) and on mortality was studied in a neonatal intensive care population. Ureaplasma colonization was associated with a birthweight < 1000 g (odds ratio [OR] 3.45 confidence intervals [CI] 2.13-5.60) and a gestational age < 30 weeks (OR 2.54 CI 1.71-3.79). In a case-controlled study of 112 infants, significant associations with Ureaplasma colonization were maternal pyrexia in labour (n = 38 vs 21; P = 0.015), the requirement for antibiotics in labour (n = 39 vs 16; P = 0.0005) and vaginal delivery (n = 78 vs 58; P = 0.009). Risk factors associated with the development of CLD were birthweight < 1000 g (OR 3.77 CI 2.53-5.62) and delivery by Caesarean section (OR 1.65 CI 1.11-2.43). Within the group delivered by Caesarean section. Ureaplasma colonization was also associated with an increased risk of CLD (OR 1.97 CI 1.08-3.62). Ureaplasma colonization of infants at birth is associated with factors suggestive of maternal chorioamnionitis as well as preterm birth and low birthweight. In infants delivered by Caesarean section, Ureaplasma colonization is associated with an increased risk of chronic lung disease.

Perinatal factors influencing survival at twenty-four weeks' gestation

OBJECTIVE

Our objective was to identify those obstetric and neonatal factors associated with survival in infants delivered at 24 weeks' gestation.

STUDY DESIGN

The obstetric and pediatric data bases from the two hospitals in our perinatal center were examined to ascertain all infants delivered between 1987 and 1989 whose gestational age was 24 weeks to 24 weeks 6 days. This time interval was chosen to coincide with the introduction of prophylactic exogenous surfactant. Data were abstracted from the maternal antepartum and intrapartum records and the neonatal records, with specific attention to objective risk factors related to survival.

RESULTS

Forty-five pregnant patients were identified and delivered of 52 infants. Seventeen newborn infants survived (33%). Univariate comparisons between survivors and nonsurvivors revealed more aggressive intrapartum care in the former cohort as represented by the frequencies of internal fetal heart rate monitoring (p = 0.005), maternal oxygen therpay (p = 0.003), and maternal position change to remediate decelerations (p = 0.001). Planned exclusion of cesarean delivery was more common in those pregnancies that ended in fetal or neonatal death (29/35 vs 7/17; p = 0.006). Although a greater proportion of infants delivered by cesarean section survived (6/11 vs 11/41), this difference was not significant (p = 0.17). With the use of logistic regression, the best predictor of survival was gestational age at delivery. Neonatal care was more aggressive among survivors, as measured by the relative frequencies of resuscitation and surfactant administration. Respiratory distress syndrome was either absent (n = 6) or mild (n = 6) in a majority of the survivors, and respiratory insufficiency was the major cause of neonatal death.

CONCLUSION

Perinatal outcome at 24 weeks' gestation appears most dependent on gestational age at delivery. The intensity of intrapartum care and neonatal support, as well as clinical biases regarding survivability, may also influence outcome.

Stable microbubble test for predicting the risk of respiratory distress syndrome: I. Comparisons with other predictors of fetal lung maturity in amniotic fluid

With the advent of surfactant replacement therapy, there is an increasing need for a rapid test of predicting the development of respiratory distress syndrome (RDS). We evaluated the clinical usefulness of the stable microbubble (SM) test in predicting the development of RDS by comparison with other tests in amniotic fluid samples obtained within 12 h before delivery from 40 pregnancies between 23-35 weeks of gestation. These tests included the lecithin/sphingomyelin (L/S) ratio, disaturated phosphatidylcholine/sphingomyelin (DSPC/S) ratio, concentrations of lecithin, DSPC, and surfactant-associated proteins A and B, C (SP-A, SP-B,C). The cut-off value of each test for predicting RDS was determined at a point of maximum diagnostic accuracy. The overall diagnostic accuracy of the SM test was similar to that of other tests. However, both the SM test and the SP-B,C concentration had positive predictive values of 100%. We conclude that the rapid (< 10 min) and reliable information obtained by this test should encourage its use in defining a population of neonates with surfactant deficiency in a multicentre trial of prophylactic surfactant therapy.

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.

Efficacy of venovenous extracorporeal membrane oxygenation for neonates with respiratory and circulatory compromise

We report a 12-month experience at Egleston Children's Hospital in Atlanta, Ga., with a protocol under which venovenous extracorporeal membrane oxygenation (ECMO) was used instead of venoarterial ECMO. Fifty-five newborn infants were referred for ECMO, four of whom had disqualifying conditions (all four died). Thirty-one infants were supported without recourse to ECMO, one of whom died. Of the 20 remaining patients, three were placed on a venoarterial ECMO regimen because of our early uncertainty about the efficacy of venovenous ECMO or because of technical constraints. All other patients (n = 17), including three with congenital diaphragmatic hernia, were supported with venovenous perfusion. No patient begun on a venovenous ECMO regimen required conversion to venoarterial bypass. Before ECMO, venovenous patients required an average dopamine dose of 16 micrograms/kg per minute and an average dobutamine dose of 6 micrograms/kg per minute. Of 15 patients studied before ECMO, three had significantly impaired contractility, and all had evidence of pulmonary hypertension on an echocardiogram. Mean blood pressure did not change while heart rate fell from 172 to 146 beats/min during the first 2 hours of ECMO and vasoactive drug doses were reduced. Of the 17 venovenous ECMO patients, 15 (88%) survived. We conclude that neonatal patients with severe hypoxia and substantial circulatory compromise can be effectively supported by venovenous ECMO in most cases.

Comparison of clinical responses to natural and synthetic surfactants

The clinical responses to both natural and synthetic surfactants were observed in two District General Hospital Neonatal Units who were centrally randomised as part of two separate multicentre trials (OSIRIS and Curosurf 4). Forty five infants were enrolled consecutively in the OSIRIS trial using synthetic surfactant (Exosurf), while 21 infants were subsequently enrolled in the Curosurf 4 trial using natural surfactant (Curosurf). There were no significant differences between the groups for mean birth weight, gestational age, inspired oxygen (FiO2), or arterial: alveolar oxygen ratio (a/A) prior to surfactant administration. Oxygen requirements fell significantly more rapidly within the first 24 hours for patients treated with Curosurf compared to Exosurf (p < 0.001). Mean duration of > 40% oxygen requirement was significantly shorter in the Curosurf group (2.6 days) compared to 8.0 days in the Exosurf group (p < 0.01). Mean duration of oxygen therapy was also significantly shorter in the Curosurf group (10.2 days) compared to 17.1 days in the Exosurf group (p < 0.05). Ten infants (24%) in the Exosurf group developed intraventricular haemorrhage (IVH) compared to none in the Curosurf group (p < 0.05). As oxygen requirements appear to decrease more rapidly following administration of Curosurf compared to Exosurf a large prospective randomized multicentre trial needs to be performed to compare the effects of these surfactants on both short and long-term outcome.

Mortality prediction in infants with congenital diaphragmatic hernia: potential criteria for ECMO

Over the last ten years the survival of infants born with congenital diaphragmatic hernia who reach the Intensive Care Unit of the Royal Children's Hospital, Melbourne has been constant at 56 +/- 6%. Experimental therapies such as extracorporeal membrane oxygenation, high-frequency oscillation and lung transplantation are now being considered as therapeutic options, and as such the ability to predict survival or death of these infants is increasingly important. The records of all infants with congenital diaphragmatic hernia admitted to the Intensive Care Unit between 1 January 1980 and 30 April 1989 were reviewed; blood gas, ventilatory details, and outcome information was obtained. Receiver operating curve analysis was used to determine the best predictor of death. An oxygenation index (MAP x FiO2/PaO2) > 0.3 or ventilation index (PIP x RR x CO2/1000) > 70 predicted a 94% mortality with a specificity of 96% and a sensitivity of 82%.

Secondary structure and orientation of the surfactant protein SP-B in a lipid environment. A Fourier transform infrared spectroscopy study

Attenuated total reflection Fourier transform infrared spectroscopy was used to investigate the secondary structure of the surfactant protein SP-B. Nearly half of the polypeptide chain is folded in an alpha-helical conformation. No significant change of the secondary structure content was observed when the protein is associated to a lipid bilayer of dipalmitoylphosphatidylcholine (DPPC)/phosphatidylglycerol (PG) or of dipalmitoylphosphatidylglycerol (DPPG). The parameters related to the gamma w(CH2) vibration of the saturated acyl chains reveal no modification of the conformation or orientation of the lipids in the presence of SP-B. A model of orientation of the protein at the lipid/water interface is proposed. In this model, electrostatic interactions between charged residues of SP-B and polar headgroups of PG, and the presence of small hydrophobic alpha-helical peptide stretches slightly inside the bilayers, would maintain SP-B at the membrane surface.

Lung mechanics and gas exchange in ventilated preterm infants during treatment of hyaline membrane disease with multiple doses of artificial surfactant (Exosurf)

Eight premature infants ventilated for hyaline membrane disease and enrolled in the OSIRIS surfactant trial were studied. Lung mechanics, gas exchange [PaCO2, arterial/alveolar PO2 ratio (a/A ratio)], and ventilator settings were determined 20 minutes before and 20 minutes after the end of Exosurf instillation, and subsequently at 12-24 hour intervals. Respiratory system compliance (Crs) and resistance (Rrs) were measured by means of the single breath occlusion method. After surfactant instillation there were no significant immediate changes in PaCO2 (36 vs. 37 mmHg), a/A ratio (0.23 vs. 0.20), Crs (0.32 vs. 0.31 mL/cm H2O/kg), and Rrs (0.11 vs. 0.16 cmH2O/mL/s) (pooled data of 18 measurement pairs). During the clinical course, mean a/A ratio improved significantly each time from 0.17 (time 0) to 0.29 (time 12-13 hours), to 0.39 (time 24-36 hours) and to 0.60 (time 48-61 hours), although mean airway pressure was reduced substantially. Mean Crs increased significantly from 0.28 mL/cmH2O/kg (time 0) to 0.38 (time 12-13 hours), to 0.37 (time 24-38 hours), and to 0.52 (time 48-61 hours), whereas mean Rrs increased from 0.10 cm H2O/mL/s (time 0) to 0.11 (time 12-13 hours), to 0.13 (time 24-36 hours) and to (time 48-61 hours) with no overall significance. A highly significant correlation was found between Crs and a/A ratio (r = 0.698, P less than 0.001). We conclude that Exosurf does not induce immediate changes in oxygenation as does the instillation of (modified) natural surfactant preparations. However, after 12 and 24 hours of treatment oxygenation and Crs improve significantly.(ABSTRACT TRUNCATED AT 250 WORDS)

Early treatment of respiratory distress syndrome with bovine surfactant in very preterm infants: a multicenter controlled clinical trial

OBJECTIVE

To determine the effect of bovine surfactant (SF-RI 1, Alveofact) administered during the first hour following birth to very premature infants [gestational age (GA), 25-30 weeks] in a multicenter, controlled trial.

HYPOTHESIS

Survival without bronchopulmonary dysplasia (BPD; definition: ventilator dependency or FiO2 greater than 0.3 during spontaneous respiration) at day 28 is increased in surfactant-treated infants (sequential analysis).

PATIENTS AND METHODS

Thirty-four infants [GA 28.0 +/- 1.5 SD weeks, birth weight (BW), 1,048 +/- 299 g] received 50 mg/kg BW surfactant, whereas 35 infants (GA, 27.6 +/- 1.5 weeks, BW 969 +/- 269 g) served as controls. Retreatment with surfactant (up to three identical doses) 12-24 hours after the previous dose was permitted if FiO2 was greater than 0.5.

RESULTS

Survival without BPD was significantly higher in surfactant treated infants (26/34) compared to controls (14/35; P = 0.003), but in the incidence of pulmonary air leaks, patent ductus arteriosus, intracranial hemorrhage, and nosocomial infections they were not different.

CONCLUSION

Bovine surfactant treatment improves survival without BPD in very premature infants at risk for neonatal respiratory distress syndrome (RDS).

Immunogenicity and immunomodulatory activity of bovine surfactant (SF-RI 1)

Respiratory distress syndrome in preterm infants can be treated successfully by endotracheal administration of a bovine surfactant preparation (SF-RI 1). Before the routine use of xenogenic surfactant preparations can be recommended, their immunogenicity as well as their in-vivo and in-vitro immunomodulatory activity have to be investigated. High titers of anti-surfactant antibodies were detected by a sensitive ELISA after immunizing rats, rabbits and mice with SF-RI 1. Repeated endotracheal administration of SF-RI 1 resulted in a humoral antibody response in three out of eight rabbits. After treatment of 34 preterm infants with SF-RI 1 (50-200 mg/kg), a humoral immune response to SF-RI 1 could not be detected. In-vitro restimulation of peripheral blood lymphocytes with SF-RI 1 after primary in-vivo administration did not result in cell proliferation as measured by 3H-thymidine incorporation. SF-RI 1 did not stimulate peripheral blood lymphocytes of neonates in vitro. The mitogenic response of these cells to stimulation with PHA, ConA or PWM was heavily impaired in the presence of SF-RI 1 concentrations increasing from 0.04 to 4 mg/ml. These data indicate that SF-RI 1 is immunogenic and that it may have an influence on lymphocyte proliferation in vivo.