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

Inactivation of exogenous surfactant in experimental respiratory failure induced by hyperoxia

Adult guinea pigs were exposed to 100% oxygen until, after 54-85 h, they developed severe respiratory insufficiency. One subgroup of animals was ventilated artificially with 100% oxygen for an additional 60-960 min. When the PaO2 was less than 15 kPa or the PaCO2 greater than 20 kPa, 1 ml of porcine surfactant (phospholipid concentration 80 mg.ml-1) was instilled via the trachea. These animals were ventilated for one more hour and then sacrificed. Surfactant instillation did not improve the blood gases, nor the pulmonary pressure-volume characteristics. All hyperoxia-exposed guinea pigs showed prominent histologic lung lesions, including intraalveolar edema and desquamation of airway epithelium. Compared to normal guinea pigs the volume density of intraalveolar "gas" was decreased and that of intraalveolar fluid increased. The alveolar expansion pattern in histologic sections was not improved in the surfactant-treated animals, compared to hyperoxia-exposed guinea pigs studied immediately after death. In hyperoxia-exposed animals, about 1.5 ml of edema fluid was sampled from the airways. Evaluated with pulsating bubble, our surfactant preparation had a minimum surface tension (gamma min) close to zero. However, the gamma min values of edema fluid from surfactant-treated and nontreated guinea pigs were both about 20 mN.m-1. the edema fluid thus seemed to inhibit the essential physical properties of exogenous surfactant. This, together with the prominent lung lesions, may explain the failure of surfactant replacement therapy at a late stage of hyperoxia-induced respiratory failure.

Changes in pulmonary mechanics after the administration of surfactant to infants with respiratory distress syndrome

We assessed pulmonary mechanics in 35 premature infants with respiratory distress syndrome just before and one hour after the administration of 90 mg of surfactant to each infant. Transpulmonary pressure was measured between the airway opening and an esophageal balloon with use of a differential transducer, and flow rates were measured by a pneumotachometer. Values for pulmonary mechanics were then calculated by microcomputer processing. The administration of surfactant produced a large decrease (56 percent) in the mean (+/- SEM) ratio of alveolar to arterial oxygen, from 7.1 +/- 0.5 to 3.1 +/- 0.2 (P less than 0.0001)--a change that indicates improvement in gas exchange. Associated changes in pulmonary mechanics were not demonstrable when 10 of the infants were studied during continuous mechanical ventilation. However, in the 25 infants examined during spontaneous breathing with continuous positive airway pressures (identical airway pressures before and after treatment), large and consistent improvements in pulmonary mechanics were found after the administration of surfactant. Tidal volume increased by 32 percent (P less than 0.03), minute ventilation by 38 percent (P less than 0.02), dynamic compliance by 29 percent (P less than 0.004), and inspiratory flow rates by 54 percent (P less than 0.01). We conclude that significant improvement in pulmonary mechanics results from surfactant-replacement therapy for respiratory distress syndrome, but that these mechanical changes are apparent only during spontaneous respiration and can be masked if measurements are made during mechanical ventilation.

Randomized trial of artificial surfactant (ALEC) given at birth to babies from 23 to 34 weeks gestation

Artificial surfactant (ALEC) composed of dipalmitoylphosphatidylcholine and unsaturated phosphatidylglycerol in a ratio of 7:3 (w/w) and a dose of 50-100 mg was suspended in 1 ml of cold saline and used at birth as a prophylaxis against the respiratory distress syndrome and its complications in a two centre randomized prospective trial involving 341 babies from 23 to 34 weeks gestation regardless of their antenatal problems. The surfactant had little effect in babies above 29 weeks gestation and was most beneficial in babies under 30 weeks gestation (67 controls and 69 surfactant treated babies). In this subgroup the artificial surfactant significantly reduced the inspired oxygen and peak ventilator pressure requirements during the first 96 h, the incidence of intraventricular haemorrhages from 40% to 19% (P less than 0.01), the overall mortality from 36% to 17% (P less than 0.02), the mortality due to RDS from 31% to 9% (P less than 0.01), the need for more than 28 days oxygen from 37% to 21% (P = 0.05) and the use of pancuronium in ventilated babies from 52% to 27% (P less than 0.01). There were no apparent side effects. This protein free, artificial surfactant should be a useful addition to the therapy of babies under 30 weeks gestation to reduce the severity of their RDS and the incidence of serious complications.

Use of human surfactant low molecular weight apoproteins in the reconstitution of surfactant biologic activity

Two low molecular weight (LMW) apoproteins were isolated from human pulmonary surfactant. SDS polyacrylamide gel analysis showed one protein (SP 18) to have an apparent molecular weight of 18,000 when unreduced and 9,000 D after reduction. The second protein (SP 9) migrated at approximately 9,000 D in the presence or absence of reducing agents. Both proteins contain a high number of hydrophobic amino acids. The NH2-terminal sequence of SP 18 was determined to be: NH2-phe-pro-ile-pro-leu-pro-tyr-. A cDNA clone isolated from a human adult lung cDNA library contained a long open reading frame encoding at an internal position the human SP 18 amino-terminal sequence. Mixtures of phospholipids (PL) and SP 9 and SP 18 were assessed for their capacity to reduce surface tensions on a pulsating bubble surfactometer. The addition of 1% apoprotein resulted in a reduction of surface tension after 15 s from 42.9 dyn/cm for PL alone to 16.7 and 6.3 dyn/cm for preparations containing SP 9 and SP 18, respectively. In vivo assessment of reconstituted surfactant activity was performed in fetal rabbits. Reconstituted surfactant consisting of PL + 0.5% SP 18 instilled intratracheally at delivery resulted in a marked increase in lung compliance, while the incorporation of 0.5% SP 9 yielded a moderate increase. These data show the ability to produce biologically active surfactant by the addition of isolated LMW apoproteins to defined PL.

Surfactant replacement therapy in neonatal respiratory distress syndrome. A multi-centre, randomized clinical trial: comparison of high- versus low-dose of surfactant TA

We conducted a prospective, randomized, controlled trial comparing the efficacy of two doses of a reconstituted bovine surfactant (Surfactant TA) in premature infants requiring mechanical ventilation shortly after birth for respiratory distress syndrome. Forty-six infants weighting 1000-1499 g were randomized into two groups: a low-dose group (23 infants given a single dose of 60 mg surfactant lipid/kg) and a high-dose group (23 infants given a single dose of 120 mg/kg). The mean (SD) age at which surfactant was given was 5.5 (+/- 1.2) h in the low-dose group and 6.0 (+/- 1.5) h in the high dose group. Both treatments improved oxygenation (increased arterial-alveolar PO2 ratio) with decreased mean airway pressure, the high-dose surfactant having a more beneficial effect in prolonging the response. Infants in the high-dose group had significantly less (P less than 0.05) incidence of both intraventricular haemorrhage and bronchopulmonary dysplasia. This prospective trial documents that a greater benefit can be obtained by increasing the dose of surfactant (120 mg/kg) beyond 60 mg/kg treatment of premature infants with severe respiratory distress syndrome (RDS).

Early treatment of patent ductus arteriosus in premature infants with severe respiratory distress syndrome

In 1983, a US National Collaborative Study (NCS) proposed criteria for the diagnosis of hemodynamically significant patent ductus arteriosus (PDA) in premature infants with respiratory distress syndrome (RDS), but the widespread use of pulsed Doppler cross-sectional echocardiography (PD-CSE) in neonatal intensive care units has made direct assessment of the ductus possible thus providing more timely therapy. We have compared the results in 30 premature infants with severe RDS, assessed according to the guidelines of the US NCS, with those in 51 infants whose PDA was diagnosed by PD-CSE. Together with a significant reduction in the age at treatment (7.8 +/- 3.9 vs 2.4 +/- 1.1 days), there was a reduced dependence on artificial ventilation (14.8 +/- 11.0 vs 7.8 +/- 2.7 days), a reduction in the number requiring surgical ligation of PDA (9 vs 2), a decreased incidence of bronchopulmonary-dysplasia (BPD) (40% vs 16%), and a reduction of unfavorable outcome of treatment (death or BPD) (76% vs 49%).

Surfactant treatment and incidence of intraventricular haemorrhage in severe respiratory distress syndrome

As part of a multicentre study of porcine surfactant administration in respiratory distress syndrome, 29 babies weighing 2000 g or less were studied in the neonatal intensive care unit of the Royal Maternity Hospital, Belfast. Fourteen babies of a mean gestational age of 28.1 weeks were randomly allocated to the treatment group (200 mg/kg phospholipid given intratracheally) and 15 babies of a mean gestational age of 28.7 weeks formed the control group. All babies had severe respiratory distress syndrome (oxygen requirement over 60%, mechanical ventilation, and age 15 hours or less). Almost immediate improvement in oxygenation was seen in the treated group so that oxygen concentrations could be reduced and remained significantly lower than those of control babies for the first seven days of life. Alveolar-arterial oxygen gradients were also significantly different for the first five days after treatment. More babies in the treatment group survived (79% v 40%) but the difference was not significant. The incidence of pneumothorax and of intraventricular haemorrhage, however, was significantly lower in treated babies compared with controls. For babies weighing less than 1200 g the risk of developing or extending intraventricular haemorrhage after entry to the study was also reduced in the treatment group (29% v 100%).

Severe neonatal respiratory distress syndrome treated with the isolated phospholipid fraction of natural surfactant

Ten newborn infants (795-1680 g) with severe respiratory distress syndrome (RDS) were treated with the isolated phospholipid fraction of bovine or porcine surfactant, which was administered via the airways (dose 200 mg/kg), at a median age of 10.5 h. Before receiving surfactant, all the infants were on artificial ventilation (FiO2 0.6-1.0). Within 2 h after surfactant replacement, the arterial-to-alveolar PO2 ratio increased from 0.1 to 0.35. There was a concomitant improvement in lung aeration on the chest roentgenograms and a significant reduction in the right-to-left shunt. Four patients died of cerebral hemorrhage; two of them also had a patent ductus arteriosus. One surviving infant developed bronchopulmonary dysplasia, and another succumbed 8 months later to the sudden infant death syndrome. No antibodies against surfactant were detected in the sera of the survivors. Since our results show a significant improvement in lung function after replacement therapy, the efficacy of this new surfactant preparation should be further tested in randomized clinical trials.

Lung function in prematurely delivered rabbits treated with a synthetic surfactant

We treated prematurely delivered rabbit pups with the synthetic surfactant that has been named Exosurf. By weight, Exosurf is 61.8% dipalmitoylphosphatidylcholine, 6.8% hexadecanol, 4.6% tyloxapol, and 26.7% NaCl. This simple mixture, suspended at 15 mg lipid X ml-1 water, has appropriate in vitro characteristics for a lung surfactant substitute. As determined by static pressure volume relationships performed after 30 min ventilation, lungs treated with Exosurf accepted significantly more gas at maximal inflation (36 versus 15 ml X kg-1 body weight) and had significantly greater volumes during deflation that did saline-treated control lungs; lungs treated with natural rabbit surfactant (SAM) had significantly larger volumes at maximal inflation (65 versus 35 ml X kg-1) and during deflation than did the Exosurf-treated lungs. After 30 min of ventilation with oxygen and fixation at 10 cm H2O pressure, the ratio of air space to tissue space was determined by a point-counting technique, and mean linear intercepts were measured for air spaces. Exosurf-treated lungs were intermediate between SAM and saline-treated lungs in both measurements. With positive pressure ventilation to maintain a tidal volume of 6.5 to 7.5 ml X kg-1, total compliance was significantly greater and inspiratory pressure significantly lower in both SAM- and Exosurf-treated animals than in saline-treated control animals, although the lungs of the SAM-treated animals were more compliant than the lungs of animals treated with Exosurf. During the first minute of positive pressure ventilation, lungs treated with SAM or Exosurf expanded equally rapidly, both expanding more rapidly than the saline-treated lungs.(ABSTRACT TRUNCATED AT 250 WORDS)

Biophysical activity of synthetic phospholipids combined with purified lung surfactant 6000 dalton apoprotein

This research studies the biophysical surface activity of synthetic phospholipids combined in vitro with purified lung surfactant apoprotein, having an Mr of 6000. Hydrophobic surfactant-associated protein (SAP-6) was delipidated and purified from both bovine and canine lung lavage, and was combined in vitro with a synthetic phospholipid mixture (SM) of similar composition to natural lung surfactant phospholipids. SM phospholipids were also combined and studied biophysically with another purified surfactant-associated protein, SAP-35. The biophysical activity of synthetic phospholipid-apoprotein combinants was assessed by measurements of adsorption facility and dynamic surface tension lowering ability at 37 degrees C. The SM-SAP-6 combinants had adsorption facility equivalent to natural lung surfactant, and to the surfactant extract preparations CLSE and surfactant-TA used in exogenous surfactant replacement therapy for the neonatal Respiratory Distress Syndrome (RDS). The synthetic phospholipid-SAP-6 combinants also lowered surface tension to less than 1 dyne/cm under dynamic compression in an oscillating bubble apparatus at concentrations as low as 0.5 mg phospholipid/ml. A striking finding was that this excellent dynamic surface activity was preserved as SAP-6 composition was reduced to values as low as 5 micrograms/5 mg SM phospholipid (0.1% SAP-6 protein), an order of magnitude less than the 1% protein content of CLSE and surfactant-TA. Mixtures of SM phospholipids plus SAP-35, the major surfactant glycoprotein, had significantly lower biophysical activity, which did not approach that of a functional lung surfactant. These results suggest that synthetic exogenous surfactants of potential utility for replacement therapy in RDS can be formulated by combining synthetic phospholipids in vitro with specifically purified, hydrophobic surfactant-associated protein, SAP-6.

Extracorporeal membrane oxygenation in pediatric respiratory failure

ECMO is capable of safely supporting respiration and circulation in newborns with severe respiratory failure and a moribund clinical presentation. The results thus far suggest that term infants with respiratory failure are the best candidates for ECMO, with a survival rate of 83 per cent. Infants under 35 weeks' gestation have a very high incidence of intracranial hemorrhage. Consequently, we do not currently accept them for ECMO treatment. The outcome of the survivors is largely determined by the clinical condition before ECMO and by major complications. Research must be directed toward cost effectiveness, timing and earlier use, alternative vascular access, cannula and circuit design, and expanded indications.

Natural surfactant substitution in respiratory distress syndrome

Natural surfactants consist of unique proteins and lipids. Their effectiveness in improving subnormal lung function in surfactant deficiency should be established prior to any clinical trials. Rigorous tests are required to document batch to batch variability in surface activity and to exclude toxic contaminants. Up to this date randomized clinical trials in small preterm infants have demonstrated a striking improvement in lung function, and a decrease in incidence of acute complications (pneumothorax, interstitial emphysema). Administration of human surfactant at birth or in severe RDS decreased deaths and incidence of bronchopulmonary dysplasia. Although homologous surfactant may not be more advantageous than the heterologous one in terms of its acute beneficial effects on lung function, the safety and efficacy of animal surfactant in improving the outcome remains to be established. Human surfactant may serve as a model for unlimited natural surfactant produced by gene technology. The pharmacodynamics aspects of surfactant substitution, the indications of exogenous surfactant, and the management of the patients undergoing surfactant substitution remain to be studied. Exogenous surfactant offers a potential to treat or prevent severe respiratory failure in infants, children and adults.

Respiratory distress syndrome and inositol supplementation in preterm infants

We report a randomised double blind trial of myo-inositol (inositol) supplementation for 10 days in 74 preterm infants with a birth weight less than 2000 g (mean gestational age 29.5 weeks and mean birth weight 1266 g). All infants required artificial ventilation for treatment of respiratory distress syndrome. Inositol (120-160 mg/kg/day) was administered by the ingastric or intravenous route. The 37 infants who received inositol supplementation required less mechanical ventilation during days 4-10, had less failures of indomethacin to close ductus arteriosus, and had less deaths or bronchopulmonary dysplasia, or both, than the infants treated with placebo. There were no detectable adverse effects. These preliminary results suggest that inositol is an important nutrient in immature preterm infants.

Prophylactic treatment of very premature infants with human surfactant

We undertook a randomized, controlled trial to determine whether human surfactant administered endotracheally at birth to very premature infants (gestational age, 24 to 29 weeks) would prevent the respiratory distress syndrome or reduce its severity. Thirty-one treated infants (birth weight, 938 +/- 286 g) were compared in a blinded fashion with 29 control infants (birth weight, 964 +/- 174 g). The lecithin/sphingomyelin ratio was less than 2 in all infants, and phosphatidylglycerol was not present in amniotic fluid or tracheal fluids at birth, indicating a deficiency of surfactant in the lungs. The principal dependent variables were neonatal death, the incidence of bronchopulmonary dysplasia, and the infant's requirement for respiratory support (and its complications). The surfactant-treated group had significantly fewer deaths than the control group (16 percent vs. 52 percent, P less than 0.001), fewer cases of bronchopulmonary dysplasia (16 percent vs. 31 percent), and significantly fewer cases of pulmonary interstitial emphysema (P less than 0.001) and pneumothorax (P less than 0.02). Prophylactic treatment with human surfactant also substantially reduced the period of neonatal intensive care. We conclude that treatment with human surfactant offers promise for improving the survival of very premature infants with a surfactant deficiency and for reducing the pulmonary sequelae of the respiratory distress syndrome.

Extracorporeal membrane oxygenation (ECMO) in neonatal respiratory failure. 100 cases

Extracorporeal membrane oxygenation (ECMO) was used in the treatment of 100 newborn infants with respiratory failure in three phases: Phase I (50 moribund patients to determine safety, efficacy, and risks); Phase II (30 high risk patients to compare ECMO to conventional ventilation); and Phase III (20 moderate to high risk patients, the current protocol). Seventy-two patients survived including 54% in Phase I, 90% in Phase II, and 90% in Phase III. The major complication was intracranial bleeding, which occurred in 89% of premature infants (less than 35 weeks) and 15% of full-term infants. Best survival results were in persistent fetal circulation (10, 10 survived), followed by congenital diaphragmatic hernia (9, 7 survived), meconium aspiration (44, 37 survived), respiratory distress syndrome (26, 13 survived), and sepsis (8, 3 survived). There were seven late deaths; in follow-up, 63% are normal or near normal, 17% had moderate to severe central nervous system dysfunction, and 8% had severe pulmonary dysfunction. ECMO is now used in several neonatal centers as the treatment of choice for full-term infants with respiratory failure that is unresponsive to conventional management. The success of this technique establishes prolonged extracorporeal circulation as a definitive means of treatment in reversible vital organ failure.

Growth and development two years after artificial surfactant replacement at birth

Two year follow-up of 80 surviving preterm babies from a controlled trial of surfactant replacement is reported. There were no statistically significant differences in rates of hospital admission, respiratory infections or antibiotic treatment. Wheezing, skin rashes and food intolerance were reported by parents with similar frequency in each group. Weight, length and occipito-frontal circumference were similar at all ages up to and including 2 years. Median developmental quotient (Griffiths scales) was 100 in the treated group and 95 in the control group (P = 0.053). Rates of cerebral palsy were similar in each group although milder forms predominated in the treated group. It is concluded that artificial surfactant (dipalmitoylphosphatidylcholine and high-density lipoprotein) replacement at birth is not associated with adverse long term effects on preterm babies.

Respiratory distress syndrome

Increasing knowledge of the pathophysiology of respiratory distress syndrome has led to improvements in clinical management. Future advances in prevention and therapy, including administration of agents to prevent prematurity or to accelerate lung maturation, provision of surfactant replacement, and new techniques of mechanical ventilation, will further decrease mortality and morbidity.

Human surfactant treatment of severe respiratory distress syndrome: pulmonary effluent indicators of lung inflammation

Pulmonary effluent from infants who received exogenous human surfactant for severe respiratory distress syndrome was evaluated for inflammatory changes previously identified with lung injury during the first 2 weeks after birth. The number of pulmonary effluent inflammatory cells was higher only on day 1 in infants given surfactant. No other evidence of enhanced inflammation was detected in cytologic assessment of tracheal secretions. The classical pathway of complement was not activated in infants given surfactant or in control infants 2 weeks after birth. Albumin content of airway secretions was higher on the first day but not significantly altered on subsequent days. Human surfactant treatment was not associated with increased proteolytic activity, measured as neutrophilic elastase per milligram of albumin in lung effluent, but was associated with significantly higher alpha 1-proteinase inhibitor levels than in control infants from days 2 to 7 after birth. These findings provide evidence that exogenous human surfactant instilled into the lungs of preterm infants with severe respiratory distress syndrome is not associated with enhanced lung inflammation, compared with conventional mechanical ventilation alone. These data support additional clinical trials using human surfactant.

Gas exchange and lung morphology after surfactant replacement in experimental adult respiratory distress syndrome induced by repeated lung lavage

Severe respiratory insufficiency was induced in adult guinea pigs by repeated lung lavage. The animals were then ventilated for 75 min with 100% O2, insufflation pressure 28/6-8 cmH2O (2.7/0.6-0.8 kPa), frequency 30/min, and 33% inspiration time. One group of animals (I) was treated with protein-depleted porcine surfactant, prepared by a combination of sucrose-gradient centrifugation, heating to 90 degrees C, and chloroform/methanol extraction. Another group (II) received the phospholipid fraction of porcine surfactant, isolated from minced lungs by chloroform/methanol extraction and liquid-gel chromatography. Surfactant was administered in two 1-ml doses (lipid concentration 90 mg/ml) instilled via the tracheal cannula about 15 and 45 min after the lavage procedure. Non-treated, lavaged animals served as controls. After 75 min of ventilation, control values for PaO2 and PaCO2 were 13.3 +/- 6.8 and 6.8 +/- 2.3 kPa (mean +/- s.d.), respectively. The corresponding values in Group I of surfactant-treated animals were 52.9 +/- 7.7 and 4.4 +/- 1.1 kPa, in Group II 53.5 +/- 7.3 and 4.8 +/- 1.3 kPa (P less than 0.02-0.002). The two groups of surfactant-treated animals also had significantly improved alveolar air expansion in histological sections, as reflected by increased alveolar volume density (0.67 +/- 0.05 and 0.62 +/- 0.11 vs 0.45 +/- 0.08 in controls; P less than 0.002). The benefits of surfactant replacement in this experimental model were thus similar to those previously observed in animal models of neonatal surfactant deficiency as well as in babies with respiratory distress syndrome (RDS). Our data suggest that surfactant replacement might have a therapeutic effect also in clinical adult RDS.

Proteolipid in bovine lung surfactant: its role in surfactant function

The chemical and biophysical properties of the proteins in the lipid extracts of lung surfactant have not clearly been determined. These proteins were isolated from lung surfactant lipids by Sephadex LH-20 chromatography and purified with silicic acid chromatography followed by dialysis against organic solvents. The proteolipid thus obtained had a protein to phospholipid ratio of 3 to 1 (w/w). The proteolipid apoprotein had a nominal molecular weight of ca. 5 kDa. We evaluated the functional role of this proteolipid by combining it with proteolipid-depleted surfactant lipids or synthetic dipalmitoylphosphatidylcholine (DPPC) and then measuring with a pulsating bubble surfactometer. The proteolipid and DPPC recombinant reproduced the surface activity of natural lung surfactant. We conclude that this 5 kDa proteolipid apoprotein is a functionally important constituent of lung surfactant.

Proximal high-frequency jet ventilation of the newborn

During a 14-month period 11 preterm infants were treated with high-frequency jet ventilation for severe respiratory failure that had been unresponsive to conventional mechanical ventilation. Primary indications included intractable air leaks (pulmonary interstitial emphysema, pneumothorax, or both), congenital diaphragmatic hernia, and progressive pneumonia. The Sechrist 990 HFV respirator, a solenoid-driven, pulse-generated high frequency jet ventilator, was used. This device delivers a volume of gas at a controlled pressure to a jet located in the patient connector proximal to a standard single lumen endotracheal tube. The ventilator was operated in tandem with a Sechrist IV-100B ventilator to provide a sigh effect and to improve humidification. Although only 3 of 11 patients survived, 9 displayed short-term benefits from HFJV with significant reduction in mean airway pressure and improvement in mean arterial blood pressure, and no concomitant adverse effects on oxygenation or ventilation. Preliminary results suggest short-term benefits of HFJV in infants who have severe respiratory failure that is unresponsive to conventional mechanical ventilation.