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

Prediction of the acute response to surfactant therapy by pulmonary function testing

We tested the hypothesis that pretreatment pulmonary function values would be predictive of the response to the synthetic pulmonary surfactant, Exosurf (Burroughs Wellcome Co.) treatment of infants with respiratory distress syndrome (RDS). Pulmonary compliance and resistance were measured prior to Exosurf treatment in 40 infants with severe RDS. In 36 patients who survived for at least 24 hr the acute response to therapy was quantitated by calculated post-treatment/pretreatment ratios of ventilator efficiency index (VEI) and arterial/alveolar oxygen tension ratios [Pa/AO2]. The values of these calculated response ratios 24 and 48 hr after treatment varied widely among individual patients. The magnitude of the response was not related to birthweight, gestational age, age at treatment, pretreatment VEI, pretreatment Pa/AO2, or pretreatment pulmonary compliance. However, the response to Exosurf as measured by improvements in Pa/AO2 at 24 and 48 hr was related to pretreatment pulmonary resistance (r = -0.34, P less than 0.05 and r = -0.60, P less than 0.001), high pretreatment pulmonary resistance was associated with a poor response to Exosurf 24 and 48 hr after treatment.

A 2-year follow up of babies enrolled in a European multicentre trial of porcine surfactant replacement for severe neonatal respiratory distress syndrome. Collaborative European Multicentre Study Group

The postnatal growth, respiratory status and neurodevelopmental outcome of surviving babies enrolled in the first European multicentre trial of porcine surfactant (Curosurf) replacement for severe neonatal respiratory distress syndrome, were assessed at corrected ages of 1 and 2 years. Follow up rates of survivors were 93% at 1 year and 89% at 2 years. Treated and control groups were similar at both 1 and 2 years in terms of physical growth, the prevalence of persistent respiratory symptoms and the occurrence of major and minor disability. Serum antibodies recognising Curosurf and surfactant-anti-surfactant immune complexes were detected in both treated and control babies, the titres showing no difference between groups. Examination of histological lung sections from non-survivors revealed a higher incidence of severe pulmonary interstitial emphysema in control babies than in those treated with surfactant. Surfactant treatment for severe respiratory distress syndrome reduces neonatal mortality and air leaks and is not associated with an increase in disability 2 years later.

Controlled trial of a single dose of synthetic surfactant at birth in premature infants weighing 500 to 699 grams. The American Exosurf Neonatal Study Group I

In a multicenter, double-blind, placebo-controlled trial conducted at 23 hospitals in the United States, a single prophylactic 5 ml/kg dose of a synthetic surfactant (Exosurf Neonatal) or air placebo was administered shortly after birth to 215 infants with birth weights of 500 to 699 gm. Despite stratification at entry by birth weight and gender, by chance female infants predominated in the air placebo group and male infants predominated in the surfactant group. Among infants receiving synthetic surfactant, improvements in oxygen requirements were significant at 2 hours after birth (p = 0.014) and persisted for 3 days (p = 0.001); improvements in the alveolar-arterial partial pressure of oxygen gradient were significant at 6 hours after birth (p = 0.01) and persisted for 3 days (p = 0.008). Improvements in mean airway pressure were not significant at 2 or at 6 hours after birth (p = 0.622 and 0.083, respectively), but became significant thereafter and persisted for 3 days (p = 0.002). Pneumothorax was reduced by slightly more than half (25 vs 11; p = 0.014); death from respiratory distress syndrome (RDS) was also reduced (26 vs 15; p = 0.046). Overall neonatal mortality, however, was not significantly reduced (58 vs 46; p = 0.102). Other complications of RDS and prematurity were not altered, except that pulmonary hemorrhage occurred significantly more frequently in infants receiving synthetic surfactant (2 vs 12; p = 0.006). These findings indicate that a single prophylactic dose of synthetic surfactant in infants weighing 500 to 699 gm at birth improves lung function, incidence of air leak, and death from RDS but not overall mortality. The only safety problem identified was an increase in pulmonary hemorrhage.

Raised plasma hypoxanthine levels as a prognostic sign in preterm babies with respiratory distress syndrome treated with natural surfactant

Plasma hypoxanthine concentration was measured in twelve preterm babies with respiratory distress syndrome (RDS) treated with 200 mg/kg of a porcine surfactant (Curosurf). Five of the babies died within one week and seven survived the neonatal period. Surviving babies had no significant changes in plasma hypoxanthine concentration throughout a one hour study period following the administration of surfactant. By contrast, in nonsurvivors the mean plasma hypoxanthine concentrations increased from 6.8 mumol/l before surfactant administration to 14.2 mumol/l 15 minutes after surfactant treatment. Survivors had a mean maximal increase in plasma hypoxanthine of 1.9 mumol/l 15-30 min factor surfactant treatment compared with 9.4 mumol/l in nonsurvivors (p < 0.05). The babies who developed intracranial hemorrhage had significantly higher maximal plasma hypoxanthine increase (mean 9.6 mumol/l) compared with babies who did not develop intracranial hemorrhage (mean 1.1 mumol/l) (p < 0.01). The combination of high PaO2 and high hypoxanthine concentration could lead to an increased production of oxygen radicals which might be harmful. We conclude that plasma hypoxanthine concentration may serve as an indicator of the prognosis in preterm babies treated with natural surfactant. Further, it seems important to reduce oxygen supplementation as soon as surfactant is given to possibly limit oxygen radical production.

Importance of hydrophobic apoproteins as constituents of clinical exogenous surfactants

The biophysical properties and physiologic effects of a series of clinical exogenous pulmonary surfactants was compared to determine the importance of the hydrophobic apoproteins (SP-B and C) as constituents of these preparations. The three exogenous surfactants studied, calf lung surfactant extract (CLSE), Survanta (Surfactant-TA), and Exosurf, all contain dipalmitoyl phosphatidylcholine (DPPC) as their major constituent. CLSE and Survanta also contain 1 to 2% of SP-B,C but Exosurf has the additives hexadecanol and tyloxapol instead to enhance the activity of DPPC. In adsorption experiments, CLSE reached a final surface tension of 22 mN/m, and Survanta and Exosurf reached 28 and 38 mN/m, respectively. Addition of 1% by weight of an apoprotein isolate containing both SP-B and C to Exosurf slightly improved its adsorption. In oscillating bubble studies, CLSE and Survanta decreased surface tension to low values of less than 1 and 2 mN/m, respectively, but Exosurf achieved a minimum value of only 29 mN/m. Addition of SP-B,C to Exosurf improved this minimum to 1 mN/m and approached the behavior of mixtures of synthetic DPPC with SP-B,C. In both adsorption and pulsating bubble experiments, the minimum surface tensions found for Exosurf were almost identical to those generated by tyloxapol alone. In studies of physiologic activity, 20 mg of CLSE or Survanta restored the pressure-volume mechanics of lavaged, surfactant-deficient excised rat lungs to 95 and 50%, respectively, of normal prelavage levels. Instillation of Exosurf (37.5 mg) produced a minimal improvement of only 10% compared to 70% for mixtures containing 1% SP-B,C with either Exosurf or DPPC.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

Influence of intratracheal application of fluorocarbon 72 and different lipid-mixtures on mechanical behavior of isolated immature pig lungs

Substitution of surfactant in immature lungs has two functional targets: the reduction of the overall alveolar surface tension and the mechanical stabilization of the system of alveoli having different diameters. Indeed, the lowering of the surface tension facilitates the inflation of the lungs, but according to Laplace's law small and large alveoli are not in pressure equilibrium as long as the surface tension is equal in both small and large alveoli. In the present work, we tried to stabilize the lungs and to compare the effect of bolus surfactant substitution with the two-step substitution of fluorocarbons and surfactant. In all, 24 fetal immature lungs were used. For our experiments we used fluorocarbon 72 (FC-72) with a surface tension of 12 mN/m. In groups 1 and 2, a mixture of dipalmitoylphosphatidylcholine (DPPC): cholesterol 9:1 (molar ratio) or DPPC: phosphatidylglycerol (PG) 9:1 (molar ratio) was administered intratracheally as a bolus. In the case of groups 3 and 4, the immature lungs were rinsed first with FC-72. After removing the fluorocarbon, the lungs were artificially ventilated and the DPPC: cholesterol 9:1 (group 3) or DPPC:PG 9:1 mixture (group 4) was given in aerosol form. Static pressure-volume curves (p-v) of the mean values of the 6 lungs in each group were registered at the beginning (0 min) and after 20 and 40 min of artificial ventilation. Airway opening pressure, weight-specific end-inspiratory lung compliance, and phospholipid contents were investigated.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors affecting surfactant responsiveness

There is a wide variability in the therapeutic responsiveness to exogenous surfactant, a drug that has become generally available for the treatment of lung immaturity and respiratory distress syndrome. Recent studies have demonstrated evidence that therapies decreasing lung edema improve the effectiveness of surfactant substitution. In addition, exogenous surfactant may acutely decrease pulmonary perfusion since the airway pressures are effectively transmitted to airspaces, compressing alveolar capillaries, especially in hypovolemia. Therapies aimed at decreasing lung edema, improving cardiac output, and stepwise weaning from oxygen and ventilatory pressures are cornerstones in the successful management of patients undergoing surfactant therapy.

The use of dexamethasone in full-term infants with severe respiratory failure and pulmonary barotrauma

Eight full-term infants (mean gestation 39.9 weeks [range 37-42] and mean birthweight 3642 g [range 3060-4200]) with severe respiratory failure (median oxygenation index 28 [range 16-65] and median arterial/alveolar PO2 ratio (a/APO2) 0.094 [range 0.038-0.165]) and pulmonary barotrauma were treated with Dexamethasone, 0.5 mg/kg per day, from the median age of 5 days (range 3-22). Six of the eight (75%) infants survived. They were weaned from mechanical ventilation and extubated a median of 2.5 days after commencing treatment with Dexamethasone. Two infants died and one of them suffered recurrent pneumothoraces. There was a significant improvement in oxygenation in the seven infants who survived the 72 h period of observation. Their median oxygenation index was 24 when Dexamethasone was commenced compared with 8 after 12 h (P less than 0.05) and 10 after 36 h (P less than 0.025). Their a/APO2 ratio was 0.095 when Dexamethasone was commenced compared with 0.289 after 12 h (P less than 0.05) and 0.207 after 36 h (P less than 0.025). There was a significant increase in the infants' arterial mean blood pressure associated with Dexamethasone therapy and one infant developed Staphylococcus aureus septicaemia. In this uncontrolled study of eight full-term infants with severe respiratory failure and pulmonary barotrauma, the use of Dexamethasone was associated with significant improvement in oxygenation and rapid weaning from mechanical ventilation.

Development of a human lung surfactant, derived from extracted amniotic fluid

Using a surfactant preparation of human origin for the treatment of the respiratory distress syndrome (RDS) instead of an animal-derived surfactant will minimize immunological problems. Therefore we isolated surfactant material from human amniotic fluid. Protein and phospholipid fractions of extracted human amniotic fluid (HAFS) were separated by Lipidex 5000 or acidulated LH20 liquid chromatography systems. Fractions of HAFS, the phospholipid or the recombined phospholipid-protein fractions, were tested in the 27-day fetal rabbit model. The results were compared with the results of the corresponding fractions of extracted ovine lung lavage (EOS) and of the already clinically tested surfactant Curosurf. The in situ surface activity of HAFS, EOS, and of their combined phospholipid + protein fractions (200 mg/kg body wt.) resulted in a lung compliance which was significantly higher than the control (saline) values. The compliances of HAFS, EOS, their combined fractions, and Curosurf were similar, but the lung stability values (V5) differed significantly among these surfactant extracts. The best V5 values (greater than or equal to 0.020 ml/g body wt.) were found after installing EOS or its LH20 phospholipid + protein fractions. HAFS had a poor stabilizing capacity which increased significantly after Lipidex chromatography and even more after enrichment of the Lipidex material with 10% palmitic acid. The Lipidex HAFS + 10% palmitic acid surfactant is at present the best obtainable human surfactant extract. Further development is in progress for the clinical application of this surfactant in preterm neonates.

Surfactant analysis and replacement therapy: a future tool of the lung transplant surgeon?

From 1965 to 1974 extensive research was carried out concerning the effects of experimental lung reimplantation and allografting on the surface tension properties of pulmonary surfactant. Since then, surfactant has been more rigorously examined in terms of its composition and function, and the potential roles of three surfactant-associated proteins have been established. Furthermore, surfactant replacement therapy for neonatal respiratory distress syndrome has come of age. The efficacy of surfactant treatment for adult respiratory distress syndrome is currently under clinical scrutiny, and experimental work on alterations in surfactant after lung transplantation has resumed after a 15-year hiatus. This article reviews current knowledge of the pulmonary surfactant system, as well as previous studies of the changes in surfactant after experimental lung transplantation. The experience in surfactant replacement therapy for the neonatal and adult respiratory distress syndromes is briefly described. Suggestions are made concerning the potential experimental and clinical applications of surfactant analysis and replacement therapy in lung transplantation.

Pulmonary surfactant as a vehicle for intratracheal delivery of technetium sulfur colloid and pentamidine in hamster lungs

Tracheal instillation of pentamidine in a surfactant vehicle may be an effective direct method of antibiotic delivery to the lungs. In 10 healthy hamsters, we compared the pulmonary distribution of 99mTc sulfur colloid (TcSC) mixed with pentamidine, using as a vehicle either surfactant (n = 5) or saline (n = 5). Each animal was instilled with 0.25 ml/kg of suspension containing 0.0018 mCi TcSC and pentamidine mixed with either surfactant or saline. After 4 h of spontaneous respiration, the lungs were excised, inflated to TLC, dried, and sliced into 3-mm cross sections from apex to base. Autoradiographs were examined to evaluate 99mTc distribution. The surfactant group had detectable radioactivity in 93% of all slices compared with 72% in the saline group (p = 0.02). Six slices per animal (43% of total) and their corresponding autoradiographs were analyzed for distribution of radioactivity. Lung slice area was determined by planimetry, and autoradiograph area was determined by video densitometry. We calculated the fraction of each lung slice with detectable radioactivity. The surfactant group had 41% of the lung slice areas exposed compared with 21% in the saline group (p = 0.02). The coefficient of variation of radioactive intensities within each slice was used as an index of spatial uniformity. There was a trend towards more uniform distribution in the surfactant group, with a narrower range of variation of intensities (1.51 to 2.56) than the saline group (1.95 to 6.47). We conclude that a surfactant vehicle significantly increases airspace deposition of TcSC and pentamidine instilled intratracheally in normal hamster lungs, and may improve uniformity of spread.

Immediate improvement in lung volume after exogenous surfactant: alveolar recruitment versus increased distention

To determine whether changes in lung volume may be responsible for the clinical improvement in preterm infants given exogenous surfactant, we measured functional residual capacity (FRC), lung mechanics, and partial pressure of oxygen in seven ventilated neonates (birth weight 1080 +/- 361 gm (mean +/- SD); gestational age 28.3 +/- 2.6 weeks) less than 9 hours of age who had findings typical of hyaline membrane disease. All patients received 100 mg/kg calf lung surfactant extract. FRC was measured by a closed-circuit helium-dilution technique, and lung mechanics were determined by least mean squares analysis. FRC increased in all patients (range 56% to 330%; p less than 0.03). Dynamic lung compliance and total airway conductance did not change. Mean +/- SEM specific lung compliance (dynamic lung compliance/FRC) decreased 55.93% +/- 4.27% (p less than 0.02) and mean specific conductance (total airway conductance/FRC) decreased 45.91% +/- 9.74% (p less than 0.009). Mean alveolar/arterial partial pressure of oxygen ratio decreased 51.0% +/- 8.67% (p less than 0.01). These data indicate that the immediate improvement in oxygenation after surfactant administration is related to increased lung volumes. The decrease in specific lung compliance and specific airway conductance is suggestive of increased distention rather than recruitment of functional alveoli.

Lung surfactant in respiratory distress syndrome

Severe respiratory failure is always associated with a defect in the surfactant system. Surfactant substitution in newborn infants with respiratory distress syndrome (RDS) has gained worldwide acceptance. In the present study, we have evaluated whether surfactant diagnostics are of use in choosing recipients of exogenous surfactant. In addition, we studied whether factors apparently unrelated to surfactant influence the degree of respiratory failure and surfactant responsiveness. In small preterm infants, the surfactant indices in amniotic fluid (L/S ratio and phosphatidylglycerol), within 3 days of birth, predicted the risk of RDS with a sensitivity of 90-100%, and a specificity of 50-85%. The surfactant indices, measured in BAL, predicted the risk of ARDS (which became evident 1 to 7 days later) with a sensitivity of 50-60% and a specificity of 59-65%. In small preterm infants with RDS, the amount of fluids given during the first day correlated positively with the degree of respiratory failure and negatively with the degree of surfactant responsiveness. According to an experimental study, in hydrostatic lung edema, exogenous surfactant is diluted by edema fluid and becomes sensitive to inhibitors of surfactant function. Beside dosage, quality, and time of administration, the management of patients largely dictates the responsiveness to exogenous surfactant.

Advances in pediatric surgical critical care

The advances in pediatric intensive care outlined here point out the differences between children and adults that need to be considered when taking care of children with surgical diseases. In the past, advances in pediatric critical care have not kept pace with advances in adult care, but these and other new techniques have rapidly closed this gap in knowledge.

Effect of surfactant replacement on Pneumocystis carinii pneumonia in rats

The effect of intratracheal surfactant instillation on pulmonary function in rats with Pneumocystis carinii pneumonia (PCP) was investigated. In those animals which developed PCP with severe respiratory failure after administration of cortisone acetate s.c. over 8-12 weeks, pulmonary function was improved by surfactant instillation. PaO2 values 30 min after surfactant instillation were significantly higher compared to pretreatment values and also compared to PaO2 values of rats 30 min after receiving saline (482.9 mmHg +/- 44.7, 170.7 mmHg +/- 39.3 and 67.2 mmHg +/- 17.4, respectively). Histological examination showed that alveoli of rats with PCP which received no exogenous surfactant are filled with foamy edema, whereas after exogenous surfactant alveoli are stabilized and well-aerated. These results indicate that exogenous surfactant may help patients with severe PCP to overcome an acute stage of respiratory distress.

The impact of extracorporeal membrane support in the treatment of congenital diaphragmatic hernia

Neonates with congenital diaphragmatic hernia (CDH) treated by immediate surgical intervention and conventional ventilatory support have an overall poor survival. The potential of extracorporeal membrane oxygenation (ECMO) therapy to improve survival of infants with CDH remains controversial. Comparison was made in a single institution's pre-ECMO and post-ECMO survival statistics to establish efficacy of extracorporeal support for persistent pulmonary hypertension (PPH). This study was accomplished by stratifying patients by an oxygen index (OI). Sixty-eight patients were treated for CDH from 1977 to 1986 without ECMO. Fifty-eight patients underwent repair of CDH within the first 24 hours of life. Data could be retrieved for calculation of the OI in 46 patients. Nineteen patients developed an OI of 40 or greater; one survived (5%). Three of 27 patients with an OI less than 40 died (OIs = 34, 38, and 38). Thirty-one patients were treated from 1987 to 1989 and none were excluded from ECMO based on a minimum PO2. Fifteen had an OI less than 40 (range, 1 to 38), were treated conventionally, and 13 survived (87%). Sixteen patients had an OI greater than 40 and 13 qualified for ECMO. Nine of 13 survived (69%). Comparing pre-ECMO and post-ECMO survival for infants with an OI of 40 or greater (5% v 69%), there is a significant improvement in survival when ECMO is used (P less than .001). ECMO support offers a strong adjunct in management of neonates with CDH who develop PPH.

Collaborative European Multicentre Study Group. Factors influencing the clinical response to surfactant replacement therapy in babies with severe respiratory distress syndrome. Collaborative European Multicentre Study Group

Clinical data from a total of 164 babies with severe respiratory distress syndrome treated with a single dose of porcine surfactant (Curosurf, 200 mg/kg body weight) were subjected to multiple regression analysis in order to identify factors influencing the response to replacement therapy. At entry all babies were being treated with artificial ventilation, requiring at least 60% oxygen; the first 77 babies were part of a controlled trial, and an additional 87 babies were treated without controls once the benefit of surfactant therapy had been established. Both series of patients showed a sustained doubling of the mean arterial/alveolar oxygen tension ratio (a/APO2) after treatment with surfactant. Mortality was only 15% in the new series of treated patients, and the number of survivors without evidence of chronic lung disease after 28 days remained twice as high as that of the control group in the randomized study (55% vs. 26%; P less than 0.001). High fraction of inspired oxygen requirement at entry had a negative impact on a/APO2 6 h and 24 h after treatment. The duration of artificial ventilation and total time in greater than 21% oxygen were lower in heavier babies, who also had a lower mortality. Male and outborn babies had a higher mortality. Perinatal asphyxia (Apgar score less than 7 at 5 min) and high airway pressure requirement at entry were associated with increased mortality. Hospital allocation had a significant impact on all dependent variables. We also analysed the incidence of complications in relation to the therapeutic response pattern.(ABSTRACT TRUNCATED AT 250 WORDS)

Randomized, placebo-controlled trial of human surfactant given at birth versus rescue administration in very low birth weight infants with lung immaturity

A randomized, placebo-controlled trial of human surfactant given intratracheally at birth (prophylactic) versus rescue administration after the onset of severe respiratory distress syndrome (RDS) was conducted among preterm infants born at 24 to 29 weeks of gestation. Singleton fetuses were randomly assigned to receive (1) placebo (air), (2) prophylactic surfactant treatment, or (3) rescue surfactant treatment; infants of multiple births received either (1) prophylactic or (2) rescue treatment. Of 282 potentially eligible fetuses, 246 infants received treatments at birth and 200 infants had RDS. Outcomes are presented both as an intention-to-treat analysis (including infants who met exclusion criteria at or after birth) and as a full treatment protocol analysis for those infants with RDS and likely to benefit from surfactant. Preterm infants (mean 1.0 kg birth weight, 27 to 28 weeks of gestational age) randomly assigned to receive prophylactic treatment received surfactant soon after birth; those assigned to receive rescue surfactant had instillation at a mean age of 220 minutes if the lecithin-sphingomyelin ratio was less than or equal to 2.0 and no phosphatidylglycerol was detected in either amniotic fluid or initial airway aspirate, oxygen requirements were a fraction of inspired oxygen of greater than 0.5, and mean airway pressure was greater than or equal to 7 cm H2O from 2 to 12 hours after birth. Up to four treatment doses (or air) were permitted within 48 hours; approximately 60% of surfactant-treated infants required two or more doses. Surfactant-treated infants had significantly less pulmonary interstitial emphysema than placebo-treated infants (p = 0.02), but there were no other significant differences in mortality rates or morbidity. Indexes of oxygenation and ventilation were improved in surfactant recipients during the first 24 hours. An intention-to-treat analysis found no significant differences between infants given placebo and surfactant-treated infants or between prophylactic- and rescue-treated infants; an improved total mortality rate (p = 0.002) was found among surfactant-treated infants in Helsinki but not in San Diego. Among infants with RDS, the total mortality rate was significantly improved (p = 0.004) with surfactant treatment but not the proportion alive and without bronchopulmonary dysplasia at 28 days (p = 0.052), or the proportion alive and without bronchopulmonary dysplasia at 38 weeks of postconceptional age (p = 0.18) to adjust for differences in prematurity. Deaths caused by RDS or bronchopulmonary dysplasia were significantly reduced among surfactant recipients (p = 0.0001). Neither among singletons nor among multiple-birth infants was there a selective advantage to prophylactic versus rescue treatment.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of two rescue doses of a synthetic surfactant on mortality rate and survival without bronchopulmonary dysplasia in 700- to 1350-gram infants with respiratory distress syndrome. The American Exosurf Neonatal Study Group I

In a multicenter, double-blind, placebo-controlled rescue trial conducted at 21 American hospitals, two 5 ml/kg doses of a synthetic surfactant (Exosurf Neonatal) or air were administered to 419 infants weighing 700 to 1350 gm who had respiratory distress syndrome and an arterial/alveolar oxygen pressure ratio less than 0.22. The first dose was given between 2 and 24 hours of age; the second dose was given 12 hours later to those infants remaining on ventilatory support. Infants were stratified at entry by birth weight and gender. Among infants receiving synthetic surfactant, improvements in alveolar-arterial oxygen pressure gradient, arterial/alveolar oxygen pressure ratio, and oxygen and ventilator needs through 7 days of age were apparent. Death from respiratory distress syndrome was reduced by two thirds (21 vs 7; p = 0.007), and the overall neonatal mortality rate was reduced by half (50 vs 23; p = 0.001). Although there was no significant reduction in the incidence of bronchopulmonary dysplasia (39 vs 31; p = 0.107), the hypothesis that survival through 28 days without bronchopulmonary dysplasia would be enhanced by two rescue doses of synthetic surfactant was proved true (21% improvement, from 132 to 156 patients; p = 0.001). In addition, the incidence of pneumothorax was reduced by one third (62 vs 40; p = 0.022), and the incidence of pulmonary interstitial emphysema was reduced by half (102 vs 51; p = 0.001). The only side effect identified was an increase in the incidence of apnea (102 vs 134; p = 0.001). These findings indicate that rescue use of a synthetic surfactant can improve the morbidity and mortality rates for premature infants with respiratory distress syndrome.

A comparison of surfactant as immediate prophylaxis and as rescue therapy in newborns of less than 30 weeks' gestation

BACKGROUND

Exogenous pulmonary surfactants are administered into the trachea either to prevent respiratory distress syndrome in premature infants or to treat it. In a randomized, multicenter trial, we compared the results of surfactant therapy initiated as prophylaxis with the results of rescue therapy with surfactant.

METHODS

Before birth, 479 infants with an estimated gestational age of less than 30 weeks were randomly assigned to receive surfactant as prophylaxis (n = 235) or rescue therapy (n = 244). The infants in the prophylaxis group received a 90-mg intratracheal dose of an exogenous calf-lung surfactant extract at the time of delivery, whereas the infants in the rescue-therapy group received 90 mg of the surfactant several hours after delivery if the fractional inspiratory oxygen concentration was at least 0.40 or if the mean airway pressure was at least 0.686 kPa (7 cm of water), or both. Infants in both groups received additional doses of surfactant at intervals of 12 to 24 hours if these criteria were met.

RESULTS

The proportion of infants surviving until discharge to their homes was significantly higher in the prophylaxis group than in the rescue-therapy group (88 vs. 80 percent, P = 0.028). This difference was due primarily to the longer survival of very premature infants (less than or equal to 26 weeks' gestation) in the prophylaxis group than in the rescue-therapy group (75 vs. 54 percent, P = 0.006). According to proportional-hazards regression analysis, the distribution of survival times was better for all infants in the prophylaxis group (P = 0.007) and for the subgroup of infants in the prophylaxis group who were delivered at 26 weeks' gestation or earlier (P = 0.0048). Infants in the prophylaxis group who were delivered at 26 weeks' gestation or earlier had a lower incidence of pneumothorax than similar infants in the rescue-therapy group (7 vs. 18 percent, P = 0.03).

CONCLUSIONS

We found a significant advantage to the administration of the initial dose of surfactant as prophylaxis rather than as rescue therapy in very premature infants.

Surfactant replacement therapy for severe neonatal respiratory distress syndrome: implications for nursing care

This study, which was part of a European multicentre randomised controlled trial of surfactant administration for severe respiratory distress syndrome, monitored the progress and nursing care of the group of babies enrolled in Belfast. In total 33 preterm babies with birth weights between 700-2000 g were studied. Nineteen babies were treated with surfactant and fourteen acted as controls, receiving conventional therapy with mechanical ventilation alone. All the babies had severe respiratory distress syndrome requiring mechanical ventilation in oxygen concentrations greater than 60% by the age of fifteen hours. The aim of the study was to determine the effect on nursing workload of giving surfactant to babies with severe respiratory distress syndrome. The duration of care, such as the length of time the babies required intensive care and subsequent hospitalisation was calculated for each baby. The characteristics of the treated and control babies were similar but survival in the treated group was significantly greater (79% vs 36%, p less than 0.05). There were no significant differences between the groups for individual nursing requirements. However due to the increase in numbers of surviving surfactant treated babies there was a threefold increase in cumulative nursing workload. Surfactant replacement therapy effectively modifies the course of respiratory distress syndrome but also increases the nursing workload and the need for intensive care. This has implications for staffing and financial support of Neonatal Intensive Care Units once surfactant replacement becomes a routine treatment.

Neonatology in the 1990's: surfactant replacement therapy becomes a reality

It has been more than 35 years since the lung was discovered to be lined with a layer of surface-active material that is important in lung stability and mechanics of respiration. The absence of this "anti-atelectasis" factor was proposed by Avery and Mead in 1959 to be the cause of hyaline membrane disease of premature infants. An indepth historical review of pulmonary surfactant by Tierney was recently published. In the years since 1959, there has been an exhaustive amount of research aimed at elucidating the structure and function of pulmonary surfactant, the ultimate goal being a safe and effective exogenous surfactant for the treatment of the Respiratory Distress Syndrome (RDS). The days of surfactant research are far from over, but the era of surfactant replacement therapy is now upon us. The practitioner needs to be knowledgeable about surfactant and aware of his or her role in surfactant therapy for premature infants. The following is intended to clarify some of the important issue of surfactant replacement.

Neonatal surfactant deficiency and surfactant replacement therapy

For the past 25 years, attempts have been made to treat respiratory distress syndrome (RDS) by administration of surfactant into the airways. This practice is not yet an accepted form of therapy. Lack of generally available surfactant during the present era of prospective studies will hopefully decrease the therapeutic misuse of this novel medicine.

Early versus late surfactant replacement therapy in severe respiratory distress syndrome

26 preterm infants with severe respiratory distress syndrome (RDS) have been treated at different ages with a single dose of natural porcine surfactant (Curosurf, 200 mg/kg). Criteria for treatment included clinical and radiological signs of severe RDS (grade III-IV), requirement of artificial ventilation and an FiO2 greater than or equal to 0.6. Nineteen neonates have been subjected to early treatment (2-15 h of age, mean birth weight SD: 1201 +/- 387 g) and 7 patients to late treatment (greater than 15 h to 48 h of age, birth weight SD 1624 +/- 649 g). Average FiO2 before treatment was 0.88 in early-treated patients and 0.8 in late-treated patients, age at treatment was 4.6 h and 36 h, respectively (median). Both early- and late-treated infants exhibited an improvement in oxygenation (more than twofold increase of the PaO2/FiO2 ratio) within 5 minutes after initiation of therapy. Average duration of intermittent pressure ventilation was 15 days in the early treatment group and 19 days in the late treatment group. Total exposition to greater than 21% oxygen was 21 days in early-treated and 48 days in late-treated infants. Pneumothorax occurred in none of the patients. All early treated infants survived without signs of severe bronchopulmonary dysplasia (BPD greater than 21% O2, greater than 90 days plus radiological changes). However, two out of seven late-treated infants developed severe BPD; one patient died as a consequence of cardiopulmonary deterioration. Two patients in the early treatment group died of nonpulmonary complications. We conclude that surfactant replacement therapy should probably be initiated as soon as possible after manifestation of severe RDS.

European multicenter trials of curosurf for treatment of neonatal respiratory distress syndrome

Curosurf, a preparation of polar lipids and hydrophobic proteins isolated from porcine lungs by liquid-gel chromatography, is currently used in European multicenter trials for prevention and treatment of neonatal respiratory distress syndrome (RDS). In babies requiring artificial ventilation with 60-100% oxygen, tracheal instillation of a single dose of Curosurf (200 mg/kg) leads to a dramatic improvement of gas exchange and reduced mortality, without increasing the incidence of neurodevelopmental handicap among survivors. Several factors, including high ventilator pressure and oxygen requirements, have a negative impact on the therapeutic response, suggesting that the patients should be treated at a comparatively early stage of the disease. Clinical trials testing this hypothesis, as well as the effect of multiple treatment doses, are in progress.

A multicenter randomized controlled clinical trial of bovine surfactant for prevention of respiratory distress syndrome

Treatment with bovine surfactant (SF-RI 1) was shown to be efficacious in improving pulmonary function and in increasing survival rate without BPD in very premature infants. Surfactant therapy did not affect the risk of major complications of prematurity.

Immediate effects on lung function of instilled human surfactant in mechanically ventilated newborn infants with IRDS

We have studied the effects on lung volume, respiratory mechanics and ventilation during the first hours after instillation of 60 mg/kg of human surfactant into the trachea of 4 very preterm, newborn infants with severe IRDS under mechanical ventilation. Measurements were made with a "face-out" body plethysmograph and a modified nitrogen wash-out method. In addition to a transient decrease in total and alveolar ventilation immediately after the instillation we found an immediate rise in lung volume, but respiratory compliance decreased. These changes lasted less than two hours. Oxygen requirements fell in 3 out of 4 infants. The changes in lung volume and compliance are explained in terms of changes in the shape of the static recoil pressure characteristics of the diseased lungs after treatment. Mechanisms behind the short duration are sought in mode of instillation, dosage, age at treatment, and severity of disease.

Hydration during the first days of life and the risk of bronchopulmonary dysplasia in low birth weight infants

We conducted a case-control study of antecedents of bronchopulmonary dysplasia (BPD) in 223 infants enrolled in a prospective, randomized clinical trial of phenobarbital prophylaxis for intracranial hemorrhage. The trial took place at three Boston neonatal intensive care units between June 1981 and April 1984. The 76 babies with BPD had radiographic evidence of the condition and required oxygen therapy for 28 days or more. All 147 control babies survived until day 28 of life without meeting either of these criteria for BPD. Compared with control infants, those with BPD received greater quantities of total, crystalloid, and colloid fluids per kilogram per day in the first 4 days of life. In addition, infants with BPD generally had a net weight gain in the first 4 days of life in contrast to the normal pattern of weight loss seen in control infants. Finally, the infants with BPD were more likely to be given a clinical diagnosis of patent ductus arteriosus and to have received furosemide on days 3 and 4 of life. From these observations we infer that early postnatal phenomena such as excessive fluid therapy may be important in the pathogenesis of BPD.

The critical concentration of surfactant in fetal lung liquid at birth

Various doses (0-4.8 mg) of porcine surfactant were administered into the airways of immature newborn rabbits delivered at a gestational age of 26 days and 17-23 h. When the estimated concentration of exogenous surfactant in the lung liquid was less than or equal to 0.75 mg/ml (dose 0.6 mg), an average tidal volume of no more than a 3.0 ml/kg was obtained by mechanical ventilation with a peak insufflation pressure of 25 cm H2O, but when the estimated concentration was increased to 1.5 mg/ml (dose 1.2 mg), an average tidal volume of 17.7 ml/kg was attained, and the survival rate during a 30-min period of artificial ventilation improved significantly, from 14% to 53%. Even larger average tidal volumes, about 25 ml/kg, were recorded in animals with estimated surfactant concentrations of 3 and 6 mg/ml (doses 2.4 and 4.8 mg, respectively). In vitro observations revealed that the surface adsorption time of the surfactant suspension decreased non-linearly from 20 to 1 sec when the concentration was increased from 1 to 3 mg/ml. The minimum surface tension during cyclic film compression also decreased non-linearly from greater than 15 to less than 3 mN/m with the same increments in concentration. This led us to conclude that, under the present experimental conditions, the critical concentration of surfactant in fetal lung liquid at birth (about 3 mg/ml) is close to the concentration required in vitro for rapid adsorption and optimal dynamic surface properties.

Hydrophobic surfactant-associated polypeptides: SP-C is a lipopeptide with two palmitoylated cysteine residues, whereas SP-B lacks covalently linked fatty acyl groups

Pulmonary surfactant contains two hydrophobic polypeptides, SP-B and SP-C, with known amino acid sequences and with truncated subforms lacking the N-terminal residues. Treatment of SP-C with KOH releases fatty acids (palmitic acid to more than 85%) in molar ratios of 1.8-2.0 relative to the polypeptide. Furthermore, plasma-desorption mass spectrometry shows native SP-C of both the intact and truncated types to be monomers with masses about 500 units higher than those expected for the polypeptide chains. After treatment with KOH, trimethylamine, or dithioerythritol, the polypeptide masses are obtained. These results prove that native SP-C is a lipopeptide with two palmitoyl groups covalently linked to the polypeptide chain. The deacylation conditions, the presence of two cysteine residues in the polypeptide, and the absence of other possible attachment sites establish that the palmitoyl groups are thioester-linked to the two adjacent cysteine residues. In contrast, the major form of porcine SP-B is a dimer without fatty acid components. That SP-C is a true lipopeptide with covalently bound palmitoyl groups suggests possibilities for functional interactions. It gives a direct physical link between SP-C and surfactant phospholipid components. Long-chain acylation may constitute a means for association of proteins with membranes and could conceivably modulate the stability and biological activity of surfactant films.

Cumulative effects of repeated surfactant treatments in the rabbit

The responses of the adult rabbit lung to multiple doses of surfactant after intratracheal injections of either natural calf surfactant or Surfactant-TA were evaluated. For each surfactant, four groups of 1.4-kg rabbits were studied: group 1 received 100 mg of surfactant containing isotopically-labeled dipalmitoylphosphatidylcholine; group 2 received the same labeled surfactant and then three tracheal injections of vehicle; group 3 received labeled surfactant and then three doses (100 mg) of unlabeled surfactant; group 4 was treated in the same way as group 3 except that the final dose was of the labeled surfactant. All rabbits were killed, and alveolar washes were recovered 24 h after the labeled surfactant dose had been given. The amount of labeled palmitate-saturated phosphatidylcholine (Sat PC) in alveolar washes did not change after multiple doses of calf surfactant, indicating that subsequent doses did not alter the clearance of previous doses. The four doses of calf surfactant increased the alveolar Sat PC pool size by a factor of 2.5 only when measured 6 h after the last dose, but the total lung Sat PC pool size doubled, indicating a loss of most of the surfactant Sat PC to the lung tissue. In contrast, Surfactant-TA increased the alveolar pool size by a factor of 4 after the single dose and by a factor of 11 after the multiple doses, and the percentage clearance of labeled Sat PC from the lungs decreased with multiple doses, indicating an effect of subsequent doses on the initial dose. The quantity of Sat PC cleared from the lungs increased by about a factor of 2 after the multiple doses of Surfactant-TA. Although repetitive surfactant doses changed alveolar and lung Sat PC pool sizes the quantity of Sat PC cleared from the lungs increased, and the lungs accommodated the large amount of surfactant without short-term adverse effects.

A European multicenter randomized controlled trial of single dose surfactant therapy for idiopathic respiratory distress syndrome

We performed a multicenter prospective randomized controlled trial to determine the efficacy and safety of the surfactant preparation, Survanta (Abbott Laboratories, Chicago, USA), for 750-1750 g infants with idiopathic respiratory distress syndrome, (IRDS) receiving assisted ventilation with 40% or more oxygen. One hundred and six eligible infants from the eight participating centers were randomly assigned between March 1986 and June 1987 to receive either surfactant (100 mg phospholipid/kg, 4 ml/kg) or air (4 ml/kg) administered into the trachea within 8 h of birth (median time of treatment 6.2 h, range 3.2-9.1 h). The study was stopped before enrollment was completed at the request of the United States Food and Drug Administration when significant differences were observed in incidence of periventricular-intraventricular hemorrhage (PIH), between the surfactant treated and control infants. Surfactant treated infants had larger average increases in the arterial-alveolar oxygen ratio, (a/A ratio) (P less than 0.0001), and larger average decreases in FiO2 (P less than 0.0001) and mean airway pressure, (MAP) (P less than 0.017) than controls over the 48 h following treatment. The magnitude of the differences between the surfactant and control groups were 0.19 (SE = 0.03) for a/A ratio, -0.28 (SE = 0.04) for FiO2 and -1.7 cm H2O (SE = 0.70) for MAP. The clinical status on days 7 and 28 after treatment was classified using four predefined ordered categories: (1) no respiratory support; (2) supplemental O2 with or without continuous positive airway pressure (CPAP); (3) intermittent mandatory ventilation; and (4) death. There were no statistically significant differences in the status categories on days 7 or 28 between surfactant and control infants.(ABSTRACT TRUNCATED AT 250 WORDS)

A controlled trial of human surfactant replacement therapy for severe respiratory distress syndrome in very low birth weight infants

In a randomized, controlled study, human surfactant derived from amniotic fluid was administered within 12 hours of birth to infants with severe respiratory distress syndrome who were born at 24 to 32 weeks of gestation weighing less than or equal to 1500 gm. A second dose of surfactant was given to patients in the treatment group if they met ventilator requirements indicating relapse or lack of response to the initial dose. No significant improvement was observed in mortality rate (9/28 vs 15/31) or incidence of bronchopulmonary dysplasia (5/28 vs 3/31) when surfactant-treated infants were compared with control subjects, although there was a significant reduction in initial respirator and inspired oxygen requirements and the arterial/alveolar oxygen ratio improved. In addition, there was a significant reduction in pulmonary air leak in treated infants (10/28 vs 20/31; p less than 0.05). Retreatment was associated with an attenuated ventilatory response and with a higher mortality rate (7/14) than that of infants who did not require a second dose (2/14; p = 0.05), indicating a more severe form of disease. Multiple discriminant analysis, including eight independent variables, revealed that increasing birth weight, earlier age at surfactant treatment, and female gender were significantly associated with survival. These data suggest that early surfactant treatment may reduce mortality rates in very low birth weight infants with severe respiratory distress syndrome, as well as reduce ventilator requirements and the incidence of pulmonary air leaks.

Effects of exogenous surfactant therapy on dynamic compliance during mechanical breathing in preterm infants with hyaline membrane disease

In a prospective, randomized, controlled clinical trial, the immediate and the longitudinal effects of exogenous surfactant therapy on pulmonary mechanics were evaluated in extremely premature infants during mechanical respiration. Ninety-four infants weighing between 600 and 1250 gm received either exogenous surfactant or sham (air) therapy in the delivery room and up to three additional doses in the first 48 hours of life if they were ventilator-dependent, had fractional inspiratory oxygen requirements greater than or equal to 0.30, and radiographic findings consistent with hyaline membrane disease. Each infant underwent pulmonary mechanics assessment (dynamic compliance, total pulmonary resistance, tidal volume) immediately before and 1 hour after each dose, and at 24, 48, and 72 hours and 7 days of age. There were no significant differences in dynamic compliance, total pulmonary resistance, and tidal volume in the surfactant (n = 47) and control (n = 47) groups before and 1 hour after each dose. However, dynamic compliance was 50% greater in the surfactant group at 24 hours of age (p less than or equal to 0.009); this difference steadily increased to 94% at 7 days of age (p less than or equal to 0.009). Oxygenation, assessed by the ratio of alveolar to arterial oxygen pressure, was significantly greater in the surfactant group during the first 72 hours of life; the greatest difference was noted at 24 hours (p less than or equal to 0.001). Mean airway pressure requirements in the surfactant group were significantly less than in the control group at all times during the first week. We conclude that exogenous surfactant therapy, administered at birth and during the first 48 hours of life in extremely premature infants with hyaline membrane disease, improves dynamic compliance and gas exchange during mechanical breathing.

Effects of bovine surfactant in premature lambs after intra-tracheal application

Twenty-two premature lambs (gestational age 124-125 days, term 144-160 days) were intubated and supported by infant ventilators immediately after delivery. Respiratory rate was 60/min, inspiratory time 0.4 s, peak inspiratory pressure (PIP) 35 cm H2O, positive endexpiratory pressure (PEEP) 2 cm H2O, FiO2 1.0. 15 min after delivery 10 lambs (group 1) were treated with 35 mg/kg body weight bovine surfactant (SF-RI 1), whereas 1 ml/kg body weight saline was instilled in 12 lambs as controls (group 2). Sequential measurements of blood gases and acid base status (every 30 min) as well as continuous registration of PIP, PEEP, respiratory rate and tidal volume (TV) were performed in all lambs for 300 min. PIP was varied between 20 and 40 cm H2O in order to attain paCO2 values between 35 and 50 mm Hg. Significantly improved oxygenation was observed in group 1 lambs with maximum differences 30 min after delivery for 2 h. Ventilation was likewise affected: paCO2 and PIP values were significantly lower in the surfactant-treated animals (group 1). Total lung-thorax compliances (calculated from TV and delta P, i.e. PIP-PEEP) per kg body weight also significantly reflected the improvement of pulmonary function in group 1 compared to group 2 lambs. Intratracheal instillation of SF-RI 1 improved gas exchange in premature lambs, whereas control animals exhibited severe respiratory failure characteristic of respiratory distress syndrome (RDS).

The severity of RDS during the first two neonatal days in relationship to fluid intake

There are no generally accepted guidelines regarding the degree of hydration of small preterm infants with RDS. In the present prospective study, liquid intake (intravenous fluids, drugs, and enteral nutrition) during the first 48 h was correlated with the degree of respiratory failure at the age of two days in 120 consecutive, mechanically ventilated, small preterm infants with RDS (GA less than 30 w, BW less than 1,750 g). There was a positive linear relationship between the amount of liquids given and the degree of respiratory failure. Multiple regression analysis taking into consideration various perinatal factors revealed that the liquid intake explained the degree of respiratory failure (p less than 0.0001). The regression analysis revealed a similar dependence of respiratory failure on the liquid intake in the following groups of infants: GA less than 27 w (p = 0.023); GA 27-30 w (p = 0.005); SGA (p = 0.104); Non-SGA (p = 0.001); severe preeclampsia (p = 0.018); surfactant substitution (p = 0.002); liquid intake 127-240 ml/48 h (p less than 0.006); liquid intake 240-430 ml/48 h (p less than 0.047). The present results demonstrate the need to re-evaluate the optimal needs of hydration among infants with RDS during the very early neonatal period.

Impact of antenatal dexamethasone administration on respiratory distress syndrome in surfactant-treated infants

Neonatal lung disease is primarily responsible for the perinatal morbidity and mortality associated with preterm birth. Recently exogenous surfactant replacement therapy has been used to prevent or treat respiratory distress syndrome. As part of a multicenter, preventive trial between February 1986 and December 1988 using calf-lung surfactant extract, we treated 147 infants with single dose calf-lung surfactant extract. We analyzed this experience to evaluate the possibility that antenatal steroids may be additive (with calf-lung surfactant extract) in reducing both the incidence and severity of respiratory distress syndrome. Although a reduction in the incidence of respiratory distress syndrome was observed among the 33 neonates exposed to antenatal dexamethasone when compared with the 114 infants given calf-lung surfactant extract alone, the difference was not significant (37.7% vs. 24.2% p = 0.15). However, comparison of neonatal subsets previously shown to benefit most from steroid use revealed an additive effect between calf-lung surfactant extract and dexamethasone in reducing both the incidence and severity of respiratory distress syndrome. Of the 99 singleton pregnancies, only 2 of 16 infants treated with calf-lung surfactant extract and dexamethasone developed respiratory distress syndrome, compared with the 33 of 83 calf-lung surfactant extract cases (p less than 0.05). A similar reduction was observed in infants between 28 and 32 weeks' gestation (calf-lung surfactant extract, 21 of 79 vs. calf-lung surfactant extract and dexamethasone, 0 of 24; p less than 0.05). A reduction in disease severity was observed in male offspring (moderate or severe respiratory distress syndrome only; 22 of 63 vs. 2 of 22; p less than 0.05). Potential confounding variables (e.g., gestational age at birth, birth weight, exposure to tocolytics before delivery, fetal pH at birth) were similar in all comparisons. We conclude that an additive effect between dexamethasone and calf-lung surfactant extract is observed in selected cases. It may therefore be appropriate to maximize antenatal steroid use in centers where exogenous surfactant is available.

Nucleotide and deduced amino acid sequence of the hydrophobic surfactant protein SP-C from rat: expression in alveolar type II cells and homology with SP-C from other species

Pulmonary surfactant lowers surface tension in the lung. Its deficiency leads to the severe physiologic abnormalities seen in the respiratory distress syndrome. The hydrophobic surfactant proteins, SP-B and SP-C, appear to be especially important in the surface-spreading characteristics of pulmonary surfactant. We report the nucleotide sequence of cDNA clones for rat SP-C and compare the deduced amino acid sequence for SP-C from several species. A highly conserved domain exists within the confines of mature human SP-C. An Eisenberg plot of this region predicts a membrane-associated helix. We also demonstrate by Northern analysis the tissue-specific expression of SP-C. A comparison of signal strength between total lung RNA and RNA derived from isolated type II cells supports the idea that most SP-C messenger RNA in total lung can be accounted for by that present in alveolar type II cells.

A multicenter randomized, placebo-controlled trial of surfactant therapy for respiratory distress syndrome

We carried out a multicenter randomized, placebo-controlled trial to evaluate the efficacy and safety of surfactant in the treatment of respiratory distress syndrome. The study population was made up of newborn infants weighing 750 to 1750 g who were receiving assisted ventilation with 40 percent or more oxygen. The eligible infants received a single dose of either surfactant (100 mg of phospholipid per kilogram of body weight [4 ml per kilogram]) or an air placebo (4 ml per kilogram), administered into the trachea within eight hours of birth by an investigator not involved in the clinical care of the infant. When compared with the infants who received the placebo (n = 81), the infants who were treated with surfactant (n = 78) had a 0.12 greater average increase in the ratio of arterial to alveolar oxygen tension (P less than 0.0001), a 0.20 greater average decrease in the fractional inspiratory oxygen concentration (P less than 0.0001), and a 0.26-kPa greater average decrease in the mean airway pressure (P less than 0.0001) during the 72 hours after treatment. Pneumothorax was less frequent among the infants treated with surfactant than in the control group (13 percent vs. 37 percent; P = 0.0005). There were no statistically significant differences between the groups in the proportion of infants in each of five ordered clinical-status categories on day 7 (P = 0.08) or day 28 (P = 0.75) after treatment. There were also no significant differences between the groups in the frequency of bronchopulmonary dysplasia, patent ductus arteriosus, necrotizing enterocolitis, or periventricular-intraventricular hemorrhage. In each group, 17 percent of the infants died by day 28. We conclude that treatment with the single-dose surfactant regimen used in this study reduces the severity of respiratory distress during the 72 hours after treatment and decreases the frequency of pneumothorax, but that it does not significantly improve clinical status later in the neonatal period and does not reduce neonatal mortality. Further study of different surfactant regimens and patient-selection criteria will be required to determine whether this initial improvement can be translated into reductions in mortality or serious morbidity.

Inhibition of exogenous surfactant in ventilated immature newborn rabbits

Immature newborn rabbits were treated at birth by tracheal instillation of porcine surfactant (100 microliters, phospholipid concentration 80 mg.ml-1), to which [14C]dipalmitoylphosphatidylcholine had been added as a marker. They were kept in a body plethysmograph/pneumotachygraph system at 37 degrees C. During a 120 min period of artificial ventilation with a peak insufflation pressure of 20 cm H2O, there was a gradual decrease in tidal volumes (36%.h-1). This decrease was correlated to an elevation of minimum surface tension (r = 0.81; P less than 0.01) and to a prolongation of the adsorption rate (r = 0.80; P less than 0.01) of surfactant recovered by lung lavage from the same animals. There was also correlations between duration of ventilation and minimum surface tension (r = 0.56; P less than 0.01), and between duration of ventilation and adsorption rate (r = 0.73; P less than 0.01). The surface properties of phospholipids extracted from the lavage fluid were similar to those of the original surfactant preparation. Our data suggest that, in immature newborn rabbits subjected to artificial ventilation, exogenous surfactant may become inactivated, probably due to protein leakage into the airspaces.