Pulmonary surfactant therapy

Survival and long-term neurodevelopmental outcome of extremely premature infants born at 23-26 weeks' gestational age at a tertiary center

OBJECTIVE

Long-term outcome, including school-age function, has been infrequently reported in infants born at ages as young as 23-26 weeks' gestation. The objective of this study is to report outcome on a large cohort of these infants to understand better the risks and factors that affect survival and long-term prognosis.

METHODS

Records from 1036 infants who were born between January 1, 1986, and December 31, 2000, were analyzed retrospectively by logistic regression to correlate multiple factors with both survival and long-term outcome. A total of 675 surviving infants were analyzed at a mean age of 47.5 months for developmental outcome. A subset of 147 surviving infants who were born before 1991 were followed through school-age years using the University of Vermont Achenbach Child Behavioral Checklist and Teachers Report Form. Longitudinal follow-up was performed comparing 1-year outcome with school-age performance.

RESULTS

Gestational age and recent year of birth correlated highly with survival. Maternal nonwhite race, female sex, inborn status, surfactant therapy, single gestation, and secondary sepsis also correlated positively with survival. Normal cranial ultrasound results, absence of chronic lung disease, female sex, cesarean delivery, and increased birth weight correlated favorably with long-term outcome. Infants who were born at 23 weeks were more likely to have severe impairments compared with those who were born at 24-26 weeks. Early follow-up identified most subsequent physical impairments but correlated poorly with school-age function.

CONCLUSIONS

Survival continues to improve for infants who are born at extremely early gestational ages, but long-term developmental concerns continue to be prevalent. Early outcomes do not reliably predict school-age performance. Strategies that reduce severe intraventricular hemorrhage and chronic lung disease will likely yield the best chances to improve long-term outlook.

Distribution dynamics of perfluorocarbon delivery to the lungs: an intact rabbit model

Motivated by the goal of understanding how to most homogeneously fill the lungs with perfluorocarbon for liquid ventilation, we investigate the transport of liquid instilled into the lungs using an intact rabbit model. Perfluorocarbon is instilled into the trachea of the ventilated animal. Radiographic images of the perfluorocarbon distribution are obtained at a rate of 30 frames/s during the filling process. Image analysis is used to quantify the liquid distribution (center of mass, spatial standard deviation, skewness, kurtosis, and indicators of homogeneity) as time progresses. We compare the distribution dynamics in supine animals to those in upright animals for three constant infusion rates of perfluorocarbon: 15, 40, and 60 ml/min. It is found that formation of liquid plugs in large airways, which is affected by posture and infusion rate, can result in a more homogeneous liquid distribution than gravity drainage alone. The supine posture resulted in more homogeneous filling of the lungs than did upright posture, in which the lungs tend to fill in the inferior regions first. Faster instillation of perfluorocarbon results in liquid plugs forming in large airways and, consequently, more uniform distribution of perfluorocarbon than slower instillation rates in the upright animals.

High-frequency oscillation and exogenous surfactant administration in lung-injured adult sheep

OBJECTIVE

To evaluate the effects of high-frequency oscillation on the response to exogenous surfactant in lung-injured adult sheep.

DESIGN

A prospective, controlled, in vivo, animal laboratory study.

SETTING

Animal research facility of a health sciences university.

SUBJECTS

Twenty-eight adult sheep.

INTERVENTIONS

Animals were anesthetized and instrumented with a tracheostomy and vascular catheters. Following whole lung saline lavage, animals were randomized to one of four groups: Group S-CMV received surfactant and was ventilated for 4 hrs using a conventional mechanical ventilation strategy, group S-HFOV/CMV received surfactant and was ventilated with a high-frequency oscillation technique for 2 hrs and a conventional mechanical strategy for 2 hrs, group HFOV/CMV underwent the latter ventilatory strategies without receiving surfactant, and group HFOV was ventilated with high-frequency oscillation only for 4 hrs. At the end of the ventilatory period, the distributions of ventilation and surfactant were evaluated in animals that received surfactant.

MEASUREMENTS AND MAIN RESULTS

Animals in the S-CMV group had a significantly greater mean PaO2 value at the end of the experimental period than animals in the S-HFOV/CMV or HFOV/CMV groups. Evaluation of the distribution of ventilation relative to surfactant demonstrated that animals ventilated with high-frequency oscillation followed by conventional mechanical ventilation had a significantly greater disproportionate distribution of ventilation relative to surfactant compared with the CMV-only group.

CONCLUSIONS

A period of high-frequency oscillation, as used in this study, immediately following exogenous surfactant administration mitigates the host's response to surfactant when subsequently switched to conventional mechanical ventilation.

Aerosolized surfactant and dextran for experimental acute respiratory distress syndrome caused by acidified milk in rats

BACKGROUND

Inhibition of pulmonary surfactant by plasma-derived proteins is an important pathogenetic factor of acute respiratory distress syndrome (ARDS). Inhalation of aerosolized surfactant may be suitable for early treatment of ARDS. However, requirement of a high dose is a drawback. Because dextran reverses surfactant inhibition, we examined whether dextran improves the therapeutic effects of aerosolized surfactant in rats with experimental ARDS.

METHODS

Acidified milk (pH 1.8, 1.5 ml kg(-1)) was injected into the trachea of the rats ventilated with pure oxygen using 2.45 kPa peak inspiratory pressure and 0.74 kPa positive end-expiratory pressure. When PaO2 decreased to <13 kPa, the rats were assigned to four groups: control group (n = 8), receiving no material; D-only group (n = 6), receiving aerosolized dextran for 45 min; S-only group (n = 8), receiving aerosolized modified natural surfactant (MNS) for 30 min; and S-plus-D group (n = 9), receiving aerosolized MNS for 30 min followed by aerosolized dextran for 15 min.

RESULTS

In the control group and D-only groups, the mean PaO2 remained at <10 kPa for 180 min. In the S-only and S-plus-D groups, the PaO2 increased to 50 kPa (P < 0.01 vs. untreated). The PaO2 of the surfactant-only group gradually decreased to <17 kPa at 180 min, whereas the PaO2 of the S-plus-D group was maintained at >38 kPa for 180 min (P < 0.01 vs. S-only group).

CONCLUSION

Inhalation of aerosolized dextran potentiates the effects of aerosolized surfactant by prolonging the therapeutic response.

Surfactant driven flows overlying a hydrophobic epithelium: film rupture in the presence of slip

Both for tear films and along the airways within the lung, one has an extremely thin fluid layer overlying a biological substrate; in both cases surfactants either of natural origin, or artificially introduced, are important in driving fluid flows. There is evidence that slip can occur when hydrophilic liquids, similar to mucus or aqueous tear films, overlie hydrophobic epithelium. Utilizing results from recent experimental findings we examine the possible influence of slip upon tear film rupture, important in so-called dry eye, and upon surfactant-induced flows within the lung, used in surfactant replacement therapy.

Comparison of three treatment regimens of natural surfactant preparations in neonatal respiratory distress syndrome

The aim of the study was to compare the treatment regimen of three natural surfactants of different extraction and formulation (Alveofact [Surfactant A = SA], Poractant [Surfactant B = SB] and Beractant [Surfactant C = SC]) in neonatal respiratory distress syndrome (RDS). Premature infants of </=32 weeks' gestation with birth weight of </=2,000 g and with established RDS requiring artificial ventilation with a FiO2 >/=0.3 were randomly assigned to receive at least two doses of SA, SB or SC (100 mg/kg per dose). Infants who remained dependent on artificial ventilation with a FiO2 >/=0.3 received up to two additional doses. There were no differences among the groups regarding the necessity for more than two doses. The SA and the SB groups spent fewer days on a ventilator (p-value SA/SB 0.7, SA/SC 0.05, SB/SC 0.043) compared with the SC group, needed fewer days of oxygen administration (p-value SA/SB 0.14, SA/SC 0.05, SB/SC 0.04) and spent fewer days in hospital (p-value SA/SB 0.65, SA/SC 0.04, SB/SC 0.027). There were no statistically significant differences in the incidence of mortality, chronic lung disease, air leaks, necrotising enterocolitis, retinopathy of prematurity and intraventricular haemorrhage among the three groups.

CONCLUSION

The Alveofact and Poractant groups spent fewer days on the ventilator, needed fewer days of oxygen administration and spent fewer days in hospital compared with the Beractant group but no differences were observed among the three groups with regards to mortality and morbidity.

Treatment of acute respiratory distress syndrome with recombinant surfactant protein C surfactant

We performed a phase I/II trial in North America of a recombinant surfactant protein C-based surfactant (Venticute) as treatment for the acute respiratory distress syndrome. Patients were prospectively randomized to receive either standard therapy or standard therapy plus one of two doses of exogenous surfactant given four times over 24 hours. Surfactant administration was well tolerated. No significant treatment benefit was associated with surfactant treatment. Bronchoalveolar lavage of treated patients at 48 hours reflected the presence of exogenous surfactant components, did not show evidence of improved surface tension lowering function, and had interleukin-6 concentrations that were significantly lower than control group values, consistent with an antiinflammatory treatment effect. The presence of exogenous surfactant was not detected in lavage fluid obtained at 120 hours. Future studies might rationally employ larger surfactant doses and a more prolonged dosing schedule.

Pulmonary surfactant for neonatal respiratory disorders

Surfactant therapy has revolutionized neonatal care and is used routinely for preterm infants with respiratory distress syndrome. Recent investigation has further elucidated the function of surfactant-associated proteins and their contribution toward surfactant and lung immune defense functions. As the field of neonatology moves away from intubation and mechanical ventilation of preterm infants at birth toward more aggressive use of nasal continuous positive airway pressure, the optimal timing of exogenous surfactant therapy remains unclear. Evidence suggests that preterm neonates with bronchopulmonary dysplasia and prolonged mechanical ventilation also experience surfactant dysfunction; however, exogenous surfactant therapy beyond the first week of life has not been well studied. Surfactant replacement therapy has been studied for use in other respiratory disorders, including meconium aspiration syndrome and pneumonia. Commercial surfactant preparations currently available are not optimal, given the variability of surfactant protein content and their susceptibility to inhibition. Further progress in the treatment of neonatal respiratory disorders may include the development of "designer" surfactant preparations.

Impact of ECMO on neonatal mortality in Michigan (1980-1999)

PURPOSE

Although extracorporeal membrane oxygenation (ECMO) is a potentially lifesaving intervention, the effect of ECMO on neonatal mortality has never been evaluated. In this study, we examined the relationship between increased ECMO utilization and its effect on the neonatal mortality rate in the state of Michigan.

METHODS

Neonatal mortality data were obtained from the Michigan State Department of Community Health. Data included total annual live births, total neonatal deaths, and deaths from respiratory causes in neonates > or =35 weeks' gestational age (ie, potential ECMO candidates). Pooled ECMO patient data from Michigan's 3 ECMO centers were obtained from the Extracorporeal Life Support Organization (ELSO) Registry. Associations between ECMO volume and neonatal mortality rates were assessed using simple linear regression. A scatterplot of ECMO volume and mortality rates was created, and the resulting fitted regression lines were superimposed on the plots. Statistical significance of the associations (ie, difference in slope of the regression line from zero) were based on a standard 2-sided Wald test for the regression slope parameter.

RESULTS

From 1980 through 1999, 1,061 neonates were treated with ECMO in Michigan, and 875 (82.5%) survived. When annual neonatal mortality rate (from all causes) and the rate from respiratory causes versus ECMO volume (cases per year) are superimposed with fitted regression lines, both are significantly different from zero (P =.041 and P =.002, respectively). The model predicts that for every 100 neonates treated with ECMO in Michigan, 38 lives are saved. The model also can be used to predict the annual neonatal mortality rate in Michigan if ECMO had not been utilized.

CONCLUSIONS

A strong association exists between ECMO volume and observed reductions in neonatal mortality seen in Michigan over the last 2 decades. This is the first study to show an association between ECMO and neonatal mortality rate at the population level.

Bronchopulmonary dysplasia: changes in pathogenesis, epidemiology and definition

Bronchopulmonary dysplasia (BPD) continues to be one of the most common long-term complications associated with preterm birth. Its incidence is increasing as the survival of extreme premature infants improves, but its clinical presentation is milder than the original description of Northway and collaborators. In contrast to the classic BPD that was strongly related to mechanical injury and oxygen toxicity, current forms of the condition are more related to immaturity, perinatal infection and inflammation, persistent ductus arteriosus and disrupted alveolar and capillary development. Many different definitions of BPD have been proposed, most of which are based on the duration of supplemental oxygen requirement. The different definitions can produce strikingly different incidence figures, which may account for the wide variations in the condition reported in the literature. Some of the limitations of the criteria most commonly used to diagnose BPD are discussed in this article.

Syringes with rubber-coated plungers and inactivation of surfactant

Injectable drugs are generally administered to newborns with 1 mL syringes. During in-vitro measurements of surface tension with a pulsating bubble surfactometer, we noticed that surfactant was inactivated after repeated aspiration into a 1 mL syringe with a rubber-coated plunger. Inactivation did not take place, however, when we used rubber-free two-part syringes with polyethylene pistons. Results of further studies showed that the silicone fluid used to lubricate the rubber surface of the syringe was inactivating the surfactant. Our findings suggest that contact with rubber surfaces should be avoided in the handling of surfactant material for biophysical assessment or clinical use.

Outcome of very-low-birth-weight infants in a developing country: a prospective study from the western region of Turkey

OBJECTIVE

To illustrate neonatal outcomes, including morbidity, birth weight and gestational age-specific mortality, and care practices for very-low-birth-weight infants admitted to our tertiary neonatal intensive care unit in Turkey and compare these with the corresponding data from recent reports from developed countries.

METHODS

Perinatal data were collected prospectively from January 1996 to December 2000. Perinatal events and the neonatal course to 120 days of life, discharge, or death were evaluated.

RESULTS

Of 173 infants, 82% survived until discharge to home or to 120 days of life. Survival was 13% for infants of 501-750 g at birth, 74% for those of 751-1000 g, 92% for those of 1001-1250 g and 87% for those of 1251-1500 g. Mortality rates were greater for male than for female infants (25% vs. 12%). The mean birth weight was 1218 (450-1500) g and the mean gestational age was 29.8 (23-36) weeks. The birth weight and gestational age distributions showed that the majority of infants (48%) weighed 1251-1500 g and were between 28 and 31 weeks' gestation (57%). Antenatal steroids were administered to only 19% of mothers. The overall Cesarean section rate was 77%. Respiratory distress syndrome was diagnosed in 36% and surfactant was administered to 98% of these infants. The rate of ventilator support was 54% for a mean duration of 9 days. Air leak syndromes were diagnosed in only nine infants (5%). Severe intracranial hemorrhage (grade > II) and periventricular leukomalacia developed in 9% of infants. Four infants had evidence of chronic lung disease. Retinopathy of prematurity (stage > II) was noted in only one infant, and proven necrotizing enterocolitis (Bell's classification stage > 2) was not observed. The rate of survival without major morbidity was 91%. The mean hospital stay was 40 days for survivors and 19 days for infants who died.

CONCLUSION

Despite marked differences in socioeconomic conditions and tertiary care facilities, the mortality (except in the smallest babies) and morbidity rates were comparable with those of recent studies from developed countries.

Hemorrhagic-ischemic cerebral injury in the preterm infant: current concepts

PV-IVH and adjacent white matter injury remains a significant problem in the premature infant. The potential mechanisms contributing to injury are complex and involve factors related to blood flow and its regulation, as well as cellular mediators including cytokines, free radical formation, and excitotoxin release. Although a reduction in the occurrence of severe IVH can be achieved with indomethacin, it does translate into long-term neurodevelopmental benefit. This reinforces the concept of a more diffuse injury to brain in sick premature infants than is apparent from the appearance of current neuroimaging techniques.

Congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a lethal human birth defect. Hypoplastic lung development is the leading contributor to its 30-50% mortality rate. Efforts to improve survival have focused on fetal surgery, advances in intensive care and elective delivery at specialist centres following in utero diagnosis. The impact of abnormal lung development on affected infants has stimulated research into the developmental biology of CDH. Traditionally lung hypoplasia has been viewed as a secondary consequence of in utero compression of the fetal lung. Experimental evidence is emerging for a primary defect in lung development in CDH. Culture systems are providing research tools for the study of lung hypoplasia and the investigation of the role of growth factors and signalling pathways. Similarities between the lungs of premature newborns and infants with CDH may indicate a role for antenatal corticosteroids. Further advances in postnatal therapy including permissive hypercapnia and liquid ventilation hold promise. Improvements in our basic scientific understanding of lung development may hold the key to future developments in CDH care.

Surfactant phosphatidylcholine half-life and pool size measurements in premature baboons developing bronchopulmonary dysplasia

Because minimal information is available about surfactant metabolism in bronchopulmonary dysplasia, we measured half-lives and pool sizes of surfactant phosphatidylcholine in very preterm baboons recovering from respiratory distress syndrome and developing bronchopulmonary dysplasia, using stable isotopes, radioactive isotopes, and direct pool size measurements. Eight ventilated premature baboons received (2)H-DPPC (dipalmitoyl phosphatidylcholine) on d 5 of life, and radioactive (14)C-DPPC with a treatment dose of surfactant on d 8. After 14 d, lung pool sizes of saturated phosphatidylcholine were measured. Half-life of (2)H-DPPC (d 5) in tracheal aspirates was 28 +/- 4 h (mean +/- SEM). Half-life of radioactive DPPC (d 8) was 35 +/- 4 h. Saturated phosphatidylcholine pool size measured with stable isotopes on d 5 was 129 +/- 14 micro mol/kg, and 123 +/- 11 micro mol/kg on d 14 at autopsy. Half-lives were comparable to those obtained at d 0 and d 6 in our previous baboon studies. We conclude that surfactant metabolism does not change during the early development of bronchopulmonary dysplasia, more specifically, the metabolism of exogenous surfactant on d 8 is similar to that on the day of birth. Surfactant pool size is low at birth, increases after surfactant therapy, and is kept constant during the first 2 wk of life by endogenous surfactant synthesis. Measurements with stable isotopes are comparable to measurements with radioactive tracers and measurements at autopsy.

Development of chronic lung disease in preterm infants treated with surfactant

BACKGROUND

Chronic lung disease (CLD) is generally known to develop among preterm infants who have severe respiratory distress syndrome (RDS) at birth. Many clinical trials have established the efficacy of surfactant replacement therapy to treat RDS at birth with differing doses. In this study, the preterm infants diagnosed to have RDS at birth and treated with one or two doses of surfactant, depending on the severity of the RDS, were studied to evaluate the effect of surfactant on the later development of CLD.

METHODS

A retrospective examination of case records of preterm infants who were born at < or = 28 weeks gestation period were studied. The subjects received a natural surfactant product (survanta) between September 1994 and April 1996 at the Monash Medical Center, Australia.

RESULTS

Despite less severe initial lung disease, the subsequent respiratory outcome of infants who received one dose of surfactant, showed a trend towards being poorer compared to those who were diagnosed as having severe RDS at birth and received two doses of surfactant. At the corrected gestational age of 36 weeks, 54% of those infants began with mild RDS required oxygen, while only 44% of those who started with a severe RDS required supplemental O2.

CONCLUSION

This study reports the infants with severe RDS at birth had responded slightly better or equally, compared to those with mild RDS, in terms of later development of CLD under surfactant treatment proportional to the severity.

Specific mode of interaction between components of model pulmonary surfactants using computer simulations

Atomistic molecular dynamics simulations and structural bioinformatics tools enable the identification of the exact mode of interaction between model pulmonary surfactant components. Two nanosecond long simulations of the N-terminal region of human surfactant protein-B (SP-B(1-25)) in dipalmitoylphosphatidylcholine (DPPC) and dipalmitoylphosphatidylglycerol (DPPG) monolayers of different lipid surface densities reveal the preferential affinity of SP-B(1-25) for anionic phospholipids. In particular, arginine 12 and lysine 24 interact strongly and with high specificity with the phosphate group of the DPPG lipids, stabilizing the position, the orientation, and the secondary structure of the peptide in the monolayer. The peptide lies at an oblique angle to the interfacial plane, ranging between 47 degrees and 62 degrees, increasing with decreasing lipid surface density. In DPPC monolayers the interaction is largely determined by hydrophobic interactions. The non-specific nature of DPPC-SP-B(1-25) interactions allows for significant flexibility in the topology of the peptide in the lipid matrix. Bioinformatics tools are employed to generalize the simulation results to the sequences of SP-B(1-25) in other organisms. The importance of specific residues, and the role of the largely helical and amphiphilic nature of the peptide in the functionality of SP-B(1-25) are established. The synergy of classical mechanics tools with bioinformatics methods greatly enhances the molecular-level interpretation of pulmonary surfactant action and facilitates the development of design rules for synthetic surfactant analogues.

Regulation of 1-cys peroxiredoxin expression in lung epithelial cells

1-cys peroxiredoxin (1-cys Prx), the only member of a Prx subfamily that contains a single conserved cysteine residue, is abundant in lung. This bifunctional protein has both glutathione peroxidase and phospholipase A2 activities compatible with a role both in protection against lung oxidant injury and also in lung phospholipid metabolism. Here we studied the developmental expression of 1-cys Prx in rat lungs and hormonal effects on protein expression in human and rat lung cells. There was little change in 1-cys Prx expression during the prenatal period, but a marked increase in expression immediately after birth. Enzymatic (peroxidase and phospholipase) activities increased gradually after birth and reached adult level at 7-14 postnatal days. Expression of the protein was induced in the presence of dexamethasone (Dex) in cultured human and rat lung epithelial cells and also was upregulated in neonatal rat lung in vivo. cAMP treatment had no effect on expression, although there was a modest synergistic effect when combined with Dex in human fetal lung epithelial cells. The increased expression of 1-cys Prx at birth may be important for surfactant phospholipid turnover related to the phopholipase A2 activity of the protein and for antioxidant defense based on its peroxidase function.

Trends in mortality and morbidity for very low birth weight infants, 1991-1999

BACKGROUND

Medical care for very low birth weight (VLBW) infants and their mothers has changed dramatically during the 1990s, yet it is unclear how these changes have affected mortality and morbidity.

OBJECTIVE

We used the Vermont Oxford Network Database to identify trends in clinical practice and patient outcomes for VLBW infants born from 1991 to 1999.

METHODS

Logistic regression was used to evaluate temporal trends in practices and outcomes while adjusting for patient characteristics and accounting for clustering of cases within hospitals.

RESULTS

There were 118 448 infants 501 to 1500 g from 362 neonatal intensive care units enrolled in the Network Database from 1991 to 1999. Prenatal care, cesarean section, multiple births, antenatal steroids, and 1-minute Apgar scores increased during this period, as did the use of nasal continuous positive airway pressure, high-frequency ventilation, surfactant, and postnatal steroids. The proportion of white infants decreased; the proportions of Hispanic infants and those of other races increased. The crude and adjusted rates of mortality, pneumothorax, intraventricular hemorrhage (IVH), and severe IVH declined from 1991 to 1995, whereas from 1995 to 1999, the rates of mortality, IVH, and severe IVH did not change significantly, and pneumothorax increased.

CONCLUSIONS

There have been major changes in both obstetric and neonatal care during the 1990s. These changes were associated with decreases in mortality and morbidity for VLBW infants during the first half of the decade. However, since 1995, no additional improvements in mortality or morbidity have been seen, ending a decades-long trend of improving outcomes for these infants.

In vitro and in vivo intrapulmonary distribution of fluorescently labeled surfactant

OBJECTIVE

To determine the distribution of endotracheally administered surfactant at the alveolar level in an animal model of acute respiratory distress syndrome.

DESIGN

Prospective, randomized animal study.

SETTING

Research laboratory of a university hospital.

SUBJECTS

Seventy-one male Sprague-Dawley rats, weighing 330-370 g.

INTERVENTIONS

To measure surfactant distribution in vitro, a glass trough mimicking dichotomic lung anatomy was used to determine the spreading properties of bovine lung surfactant extract supplemented with fluorescent Bodipy-labeled surfactant protein B. To measure surfactant distribution in vivo, rats were anesthetized, and lipopolysaccharide was aerosolized (12 mg/kg body weight) to induce lung injury resembling acute respiratory distress syndrome; in control rats, buffered saline was aerosolized. Twenty-four hours later rats were anesthetized, tracheotomized, and mechanically ventilated (peak airway pressure = 20 mbar; positive end-expiratory pressure = 6 mbar; inspiration time = expiration time = 0.6 sec; Fio2 = 50%). Surfactant (bovine lung surfactant extract, supplemented with fluorescent Bodipy-labeled surfactant protein B; 50 mg/kg body weight) was applied as a bolus; in control rats, saline was administered as a bolus. Rats were ventilated for 5, 15, 30, or 60 mins (n = 8 or 9 for each group). Then, lungs were excised and sliced. Lung slices, divided into aerated (open), underinflated (dystelectatic), or collapsed (atelectatic) alveolar areas, were examined by both light and fluorescence microscopy.

RESULTS

In vitro experiments revealed that surfactant spread independent of glass trough geometry and lowered the surface tension to equilibrium values (25 mN/m) within a few seconds. In vivo experiments showed that administered surfactant distributed preferentially into underinflated and aerated alveolar areas. Furthermore, surfactant distribution was not affected by length of mechanical ventilation.

CONCLUSIONS

When conventional mechanical ventilation was used in lipopolysaccharide-induced lung injury, surfactant preferentially distributed into underinflated and aerated alveolar areas. Because surfactant rarely reached collapsed alveolar areas, methods aiding in alveolar recruitment (e.g., open lung concept or body positioning) should precede surfactant administration.

Comparative randomized study: administration of natural and synthetic surfactant to premature newborns with respiratory distress syndrome

BACKGROUND

The respiratory distress syndrome (RDS) in premature newborns has been etiologically correlated to immature lungs and specifically with surfactant deficiency. Exogenous administration of surfactant is nowadays considered to be the treatment of choice. In this paper we attempt a comparison of clinical results from the administration of natural Alveofact and synthetic Exosurf surfactants in premature newborns with respiratory distress syndrome.

METHODS

The study subjects were 92 premature newborns who had been hospitalized in the Department of Neonatology, of the University of Crete. A total of 42 subjects received synthetic surfactant and 50 subjects received natural surfactant. The surfactant was administered in one to three doses, depending on respiratory support requirements.

RESULTS

The time of administration was a little longer for the natural surfactant group. The duration of mechanical ventilatory support, requiring oxygen, the duration of hospitalization and the percentage of increase of arterial alveolar partial pressure oxygen ratio (a/APO2) were slightly higher for the synthetic surfactant group. The mortality rate during the neonatal period (28th day) was higher for the synthetic surfactant group than for the natural surfactant group (38.1 vs 24%). A similar tendency was noticed also as regards to complications, e.g. pneumothorax (11.2 vs 5.2%; relative risk (RR) 0.27) intraventricular hemorrhage (34.6 vs 21.1%; RR 0.61), septicemia (11.5 vs 5.2%; RR 0.46) and bronchopulmonary dysplasia (12.5 vs 2.8%; RR 0.22).

CONCLUSION

The use of natural surfactant seems to offer more advantages in comparison with its synthetic counterpart.

A randomized trial of moderately early low-dose dexamethasone therapy in very low birth weight infants: dynamic pulmonary mechanics, oxygenation, and ventilation

OBJECTIVE

Dexamethasone is used in very low birth weight (VLBW) ventilator-dependent infants to prevent or decrease the severity of chronic lung disease. We reported a significant increase in respiratory compliance during a 7-day weaning course of moderately early dexamethasone therapy (0.5 mg/kg/d) in VLBW infants, along with a shorter duration of mechanical ventilation and O2 supplementation. Although 0.5 mg/kg/d has been the most commonly used dose in preterm infants, the use of a lower dose of dexamethasone may reduce potential adverse effects of steroid therapy. Quantification of dynamic pulmonary mechanics in VLBW infants who receive low-dose dexamethasone has not been reported. The objective of this study was to compare the effect of 2 dose regimens of dexamethasone on dynamic pulmonary mechanics, mean airway pressure (MAP), and fractional inspired oxygen concentration (Fio2) in intubated VLBW infants who were at risk for chronic lung disease.

METHODS

We studied 47 VLBW (birth weight: 550-1290 g; gestational age: 24-30 weeks) ventilator-dependent infants at 7 to 14 days of age. Twenty-three infants were randomized to receive dexamethasone at 0.5 mg/kg/d intravenously for 3 days (high dose), 0.25 mg/kg/d for 3 days, and 0.1 mg/kg/d during the 7th day; 24 infants received low-dose dexamethasone as 0.2 mg/kg/d for 3 days and 0.1 mg/kg/d for 4 days. Respiratory compliance (Crs) and resistance were measured before and on days 2, 5, and 7 of dexamethasone therapy. We recorded airway pressure, flow, and tidal volume, and mechanical breaths were analyzed.

RESULTS

Crs significantly increased during dexamethasone therapy in both groups of infants when compared with baseline (74% increase in the high-dose group and 66% increase in the low-dose group). Dexamethasone increased tidal volume and significantly reduced Fio2 and MAP in both groups of infants. A transient increase in blood pressure was noted in both groups.

CONCLUSIONS

Our findings indicate that 1) comparable significant increases in Crs are present in the low-dose dexamethasone as well as the high-dose dexamethasone groups on days 2, 5, and 7 of steroid therapy; and 2) MAP and Fio2 are significantly decreased during dexamethasone therapy in both groups of infants. We conclude that low-dose and high-dose dexamethasone, as used in this study, have comparable beneficial effects on dynamic pulmonary mechanics and subsequently on oxygen requirement and applied ventilatory support in VLBW infants.

Persistent fetal circulation

Persistent fetal circulation (PFC), also known as persistent pulmonary hypertension of the newborn, is defined as postnatal persistence of right-to-left ductal or atrial shunting, or both in the presence of elevated right ventricular pressure. It is a relatively rare condition that is usually seen in newborns with respiratory distress syndrome, overwhelming sepsis, meconium and other aspiration syndromes, intrauterine hypoxia and ischemia, and/or neonatal hypoxia and ischemia. This condition causes severe hypoxemia, and, as a result, has significant morbidity and mortality. Improved antenatal and neonatal care; the use of surfactant; continuous monitoring of oxygenation, blood pressure and other vital functions; and early recognition and intervention have made this condition even more rare. In modern neonatal intensive care units, anticipation and early treatment of PFC and its complications in sick newborns are commonplace. Thus, severe forms of PFC are only seen on isolated occasions. Consequently, it is even more imperative to revisit PFC compared with the time when there were occasional cases of PFC seen in neonatal intensive care units, and to discuss evolving treatment and management issues that pertain to this syndrome.

Surfactant alteration and replacement in acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) is a frequent, life-threatening disease in which a marked increase in alveolar surface tension has been repeatedly observed. It is caused by factors including a lack of surface-active compounds, changes in the phospholipid, fatty acid, neutral lipid, and surfactant apoprotein composition, imbalance of the extracellular surfactant subtype distribution, inhibition of surfactant function by plasma protein leakage, incorporation of surfactant phospholipids and apoproteins into polymerizing fibrin, and damage/inhibition of surfactant compounds by inflammatory mediators. There is now good evidence that these surfactant abnormalities promote alveolar instability and collapse and, consequently, loss of compliance and the profound gas exchange abnormalities seen in ARDS. An acute improvement of gas exchange properties together with a far-reaching restoration of surfactant properties was encountered in recently performed pilot studies. Here we summarize what is known about the kind and severity of surfactant changes occurring in ARDS, the contribution of these changes to lung failure, and the role of surfactant administration for therapy of ARDS.

Epidemiology of neonatal respiratory failure in the United States: projections from California and New York

We wanted to determine the incidence, cost, outcome, and patterns of care for neonates requiring mechanical ventilation (MV) in the United States. Using 1994 state hospital discharge data from California and New York, we conducted an observational study of all neonatal hospitalizations (n = 16,405) with MV, comparing outcomes at centers of different technological capability, and generating national projections using census and natality reports. The MV rate was 18 per 1,000 live births. Although the incidence was much higher in lower birth weight (BW) babies, one-third had normal BW. The incidence was higher in boys (20 versus 15.6 per 1,000) and in blacks (29 per 1,000). Hospital mortality was 11.1%, higher in minority groups, and associated with low BW, congenital anomalies, and major hemorrhage. Mean hospital length of stay and costs were 31.1 d and $51,700. Half of all deaths occurred at lower level centers. There are 80,000 cases per year in the United States with 8,500 deaths and total hospital costs of $4.4 billion. We conclude neonatal respiratory failure is common, expensive, and frequently fatal. There are a surprisingly large number of normal BW cases and there are large racial differences.

Volutrauma. What is it, and how do we avoid it?

Lung injury can be initiated at birth with the delivery room resuscitation. Adequate tidal volume must be achieved gradually and adjusted with each subsequent breath to achieve adequate, but not excessive, tidal volume delivery. Time constants vary greatly within the lung because some alveoli are collapsed, and some are inflated. Excessive pressure or volume may lead to high stretch injury when already open alveoli are overdistended. Sufficient alveoli must be recruited to establish the optimal functional residual capacity. This establishes an inflation history of the lung that tends to resist alveolar collapse at the end of expiration, provided that adequate mean airway pressure is provided throughout the ventilatory cycle. The best volume of inflation is achieved at the lowest pressure cost. Maintaining alveolar recruitment with the use of exogenous surfactant and positive end-expiratory pressure avoids alveolar collapse and injury with succeeding distending breaths. Although there have been significant advances in neonatal respiratory care, further improvement in outcomes may be expected by successfully avoiding ventilator-induced lung injury.

Current surfactant use in premature infants

Exogenous surfactant therapy has been a significant advance in the management of preterm infants with RDS. It has become established as a standard part of the management of such infants. Both natural and synthetic surfactants lead to clinical improvement and decreased mortality, with natural surfactants having additional advantages over currently available synthetic surfactants. The use of prophylactic surfactant administered after initial stabilization at birth to infants at risk for RDS has benefits compared with rescue surfactant given to treat infants with established RDS. In infants who do not receive prophylaxis, earlier treatment (before 2 hours) has benefits over later treatment. The use of multiple doses of surfactant is a superior strategy to the use of a single dose, whereas the use of a higher threshold for retreatment seems to be as effective as a low threshold. Adverse effects of surfactant therapy are infrequent and usually not serious. Long-term follow-up of infants treated with surfactant in the neonatal period is reassuring. In the future we are likely to see the development of new types of surfactants. Further research is required to determine the optimal use of surfactant in conjunction with other respiratory interventions.

Genetic disorders of neonatal respiratory function

Genetic risk for respiratory distress in infancy has been recognized with increasing frequency in neonatal intensive care units. Reports of family clusters of affected infants and of ethnic- and gender-based respiratory phenotypes point to the contribution of inheritance. Similarly, different outcomes among gestationally matched infants with comparable exposures to oxygen, mechanical ventilation, or nutritional deficiency also suggest a genetic risk for respiratory distress. Examples of inherited deficiency of surfactant protein B in both humans and genetically engineered murine lineages illustrate the importance of identifying markers of genetic risk. In contrast to developmental, inflammatory, or nutritional causes of respiratory distress that may resolve as infants mature, genetic causes result in both acute and chronic (and potentially irreversible) respiratory failure. The availability of clinically useful genetic markers of risk for respiratory distress in infancy will permit development of rational strategies for treatment of genetic lung disorders of infancy and more accurate counseling of families whose infants are at genetic risk for development of respiratory distress at birth or during early childhood. We review examples of genetic variations known to be associated with or cause respiratory distress in infancy.

Resistance of different surfactant preparations to inactivation by meconium

A disease similar to acute respiratory distress syndrome may occur in neonates after aspiration of meconium. The aim of the study was to compare the inhibitory effects of human meconium on the following surfactant preparations suspended at a concentration of 2.5 mg/mL: Curosurf, Alveofact, Survanta, Exosurf, Pumactant, rabbit natural surfactant from bronchoalveolar lavage, and two synthetic surfactants based on recombinant surfactant protein-C (Venticute) or a leucine/lysine polypeptide. Minimum surface tension, determined with a pulsating bubble surfactometer, was increased >10 mN/m at meconium concentrations >or=0.04 mg/mL for Curosurf, Alveofact, or Survanta, >or=0.32 mg/mL for recombinant surfactant protein-C, >or=1.25 mg/mL for leucine/lysine polypeptide, and >or=20 mg/mL for rabbit natural surfactant. The protein-free synthetic surfactants Exosurf and Pumactant did not reach minimum surface tension <10 mN/m even in the absence of meconium. We conclude that surfactant activity is inhibited by meconium in a dose-dependent manner. Recombinant surfactant protein-C and leucine/lysine polypeptide surfactant were more resistant to inhibition than the modified natural surfactants Curosurf, Alveofact, or Survanta but less resistant than natural lavage surfactant containing surfactant protein-A. We speculate that recombinant hydrophobic surfactant proteins or synthetic analogs of these proteins can be used for the design of new surfactant preparations that are relatively resistant to inactivation and therefore suitable for treatment of acute respiratory distress syndrome.

Alveolar recruitment promotes homogeneous surfactant distribution in a piglet model of lung injury

Uneven distribution of exogenous surfactant contributes to a poor clinical response in animal models of respiratory distress syndrome. Alveolar recruitment at the time of surfactant administration may lead to more homogeneous distribution within the lungs and result in a superior clinical response. To investigate the effects of three different volume recruitment maneuvers on gas exchange, lung function, and homogeneity of surfactant distribution, we studied 35 newborn piglets made surfactant deficient by repeated airway lavage with warm saline. Volume recruitment was achieved by either a temporal increase in tidal volume or an increase in end-expiratory pressure during surfactant administration, yielding an increase in dynamic compliance of the respiratory system of 77% in the first group and an increase in functional residual capacity of 108% in the second group. A third group of piglets (all n = 7) received a combination of both volume recruitment maneuvers, with increases in dynamic compliance of the respiratory system of 100% and in functional residual capacity of 192%. Those animals subjected to increased tidal volume showed an improved surfactant response in terms of oxygenation, ventilation, lung volumes, lung mechanics, and homogeneity of surfactant distribution. Increased end-expiratory volume augmented the surfactant effect only to some extent. The combination of both volume recruitment maneuvers, however, needed lung volumes beyond total lung capacity (approximately 56 mL/kg), thus probably inducing early sequelae of ventilator-induced lung injury. We conclude that volume recruitment by means of increased tidal volumes at the time of surfactant administration leads to a superior surfactant effect owing to more homogeneous surfactant distribution within a collapsed lung.

Lung salvage and protection ventilatory techniques

Physicians are in the beginning of an era in intensive care medicine in which they finally are starting to see improved outcomes in patients with AHRF. At the same time, intensivists are presented with a bewildering choice of ventilator options and adjunctive therapies. Trying to sort out which are "cosmetic," that is, improve the blood gases as opposed to influencing the outcome, remains a challenge and will be resolved only with additional RCTs. Principles of ventilator management that are driven by mimicking normal physiology are inappropriate and must be rethought.

Surfactant proteins: role in lung physiology and disease in early life

Pulmonary surfactant is an amalgam of proteins and phospholipids which serves to maintain a low surface tension within the alveolar regions of the lungs during changes in lung volume. Recently, two of the surfactant proteins--A and D--have been characterised within the collectin family and found to play important roles in the non-specific host defence of the lung. The field of surfactant biology has attracted the attention of physiologists, biochemists, molecular biologists and clinical scientists in an effort to describe the nature and role of pulmonary surfactant in health and disease. This paper will review the history and content of discoveries in the field of surfactant biology together with pulmonary diseases related to surfactant deficiency or dysfunction.

Altered stability of pulmonary surfactant in SP-C-deficient mice

The surfactant protein C (SP-C) gene encodes an extremely hydrophobic, 4-kDa peptide produced by alveolar epithelial cells in the lung. To discern the role of SP-C in lung function, SP-C-deficient (-/-) mice were produced. The SP-C (-/-) mice were viable at birth and grew normally to adulthood without apparent pulmonary abnormalities. SP-C mRNA was not detected in the lungs of SP-C (-/-) mice, nor was mature SP-C protein detected by Western blot of alveolar lavage from SP-C (-/-) mice. The levels of the other surfactant proteins (A, B, D) in alveolar lavage were comparable to those in wild-type mice. Surfactant pool sizes, surfactant synthesis, and lung morphology were similar in SP-C (-/-) and SP-C (+/+) mice. Lamellar bodies were present in SP-C (-/-) type II cells, and tubular myelin was present in the alveolar lumen. Lung mechanics studies demonstrated abnormalities in lung hysteresivity (a term used to reflect the mechanical coupling between energy dissipative forces and tissue-elastic properties) at low, positive-end, expiratory pressures. The stability of captive bubbles with surfactant from the SP-C (-/-) mice was decreased significantly, indicating that SP-C plays a role in the stabilization of surfactant at low lung volumes, a condition that may accompany respiratory distress syndrome in infants and adults.

Exogenous surfactant changes the phenotype of alveolar macrophages in mice

Alveolar macrophages are essential for the maintenance of surfactant homeostasis. We asked whether surfactant treatment would change alveolar macrophage number and whether the alveolar macrophage phenotype would become activated or apoptotic when challenged in vivo with exogenous surfactant. Surfactant pool size in mice was increased by repetitive surfactant treatments containing 120 mg/kg (110 micromol/kg) saturated phosphatidylcholine. The number of alveolar macrophages recovered by alveolar lavage decreased after the first dose by 49% and slightly increased after the second and third doses. Up to 28.5% of the macrophages became large and foamy, and their appearance normalized within 12 h. Surfactant treatment did not increase the percent of apoptotic or necrotic cells. The alveolar macrophages were not activated as indicated by no change in expression of CD14, CD16, CD54, CD95, and scavenger receptor class A types I and II after surfactant treatment. Surfactant treatment in healthy mice transiently changed the phenotype of alveolar macrophages to large and foamy without indications of changes in the surface markers characteristic of activation.

Development of inhalational agents for oncologic use

Because regional chemotherapy has been useful in treatment and palliation of many cancer types, the concept of delivering drugs by inhalation for the treatment of cancers in the lung is attractive. Much higher local drug exposure can be achieved with total doses considerably lower than those required for systemic administration, resulting in lower exposure of nonrespiratory tract tissues to potentially toxic drugs. Regional delivery of chemotherapy to the respiratory tract has been shown to have activity in preclinical and clinical studies. Technical improvements in delivery methods have now made it possible to conduct trials of inhalational agents, both to treat cancers affecting the respiratory tract and to deliver other drugs used in cancer patients. This review discusses the rationale of drug delivery by the inhalational route, its technical challenges, preclinical and clinical experiences, limitations, and promise.

Cerebral hemodynamics after exogenous surfactant administration for respiratory distress syndrome in piglet model

OBJECTIVE

The rapid improvement of lung function after exogenous surfactant treatment for respiratory distress syndrome (RDS) can affect the functions of several other systems, which includes cerebral blood flow volume (CBF). To evaluate the change in CBF after treatment with exogenous surfactant, we measured CBF in a newborn piglet model with RDS.

METHOD

After the lung lavage with normal saline, ten animals under mechanical ventilation were administered either 120 mg/kg surfactant-TA (Surfacten) or air placebo. Heart rate, blood pressure, dynamic lung compliance (Cdyn), PaO2, PaCO2, and CBF were recorded before and every 15 min after surfactant treatment up to 120 min.

RESULTS

Cdyn was improved significantly at 45 min and later after treatment; that of the control group remained unchanged. PaO2 increased and PaCO2 decreased significantly after surfactant treatment in both groups. However, the improvement was significantly less in the control group. CBF significantly decreased by about 30% in the control group, and by about 50% in the treated group at 120 min, with a significant difference between groups. Almost 70% of the changes in CBF were attributable to changes in PaCO2 by multivariate regression analysis.

CONCLUSIONS

Treatment with exogenous surfactant improves lung compliance, and has little effect on CBF itself. The drop in levels of PaCO2 after treatment, however, had a strong relationship with decreases in CBF.

Treatment and prevention of acute respiratory failure: physiological basis

Acute respiratory failure is caused by many factors and remains one of the most common reasons for admission to the intensive care unit (ICU). In all cases of acute respiratory failure, there is a shortage of surfactant at the alveolar level. This deficit of surfactant leads to an increase in alveolar surface tension that increases the retraction forces of the lung, leading to end-expiratory alveolar collapse, finally resulting in respiratory dysfunction, which includes hypoxemia, low lung compliance, increase of intrapulmonary shunts, low functional residual capacity, atelectasis, and pulmonary edema. The goal of the treatment and prevention of acute respiratory failure is therefore based on the following three main items: re-opening the collapsed alveolar units; preserving the active surfactant component in the remaining functional alveolar units, and preventing end-expiratory collapse. The following strategies can be used to prevent and/or treat acute respiratory failure: counterbalancing the retraction forces of the lung by applying sufficiently high external pressures; and/or decreasing the surface tension at the air-liquid interface by means of exogenous surfactant, and/or eliminating the air-liquid interface by filling the lung with perfluorocarbons. By applying these therapeutic strategies in routine clinical practice, we should achieve a reduction in the mortality rate of patients suffering from acute respiratory failure.

A critical review of cost reduction in neonatal intensive care. I. The structure of costs

Neonatal intensive care is expensive. In the current era of intense cost containment in hospital care, neonatologists and hospital administrators are under intense pressure to find strategies for cost reduction for neonatal services. Few neonatal clinicians are trained in economics, management, or accounting, and few hospital administrators are familiar with neonatal intensive care. In this review, we describe the structure and sources of hospital costs and the accounting systems needed to isolate and measure such costs. We discuss where efficiencies might be found and consider specific issues in capitated settings such as health maintenance organizations in the United States, the Canadian health care system and the National Health System in the United Kingdom.

In vivo diffusion measurements as an indication of fetal lung maturation using echo planar imaging at 0.5T

The aim of this study was twofold: First, to establish the normal range of fetal lung diffusion values measured during healthy pregnancy; and second, to determine whether fetal lung diffusion could be used as an indication of fetal lung maturity. The apparent diffusion coefficient (ADC), averaged over all 26 subjects with an average gestational age of 29 +/- 6 weeks (mean +/- sd), was found to be 2.0 +/- 0.6 x 10(-9) m(2)/sec (mean +/- sd), but a trend was found indicating that ADC increased with gestational age at the rate of 0.07 x 10(-9) m(2)/sec per week (P = 4 x 10(-5)). To determine the usefulness of this data in predicting lung maturity, a simple three-compartment model was proposed which was comprised of intra-lung amniotic fluid, intra-tissue water, and vascular blood. The relative proportions of each compartment were taken from the literature, and exchange between the compartments was assumed to be minimal. This model predicted the in vivo data reasonably well, and indicated that MR measurements of fetal lung diffusion are a marker for the degree of vascularization of the terminal tubules. Magn Reson Med 45:247-253, 2001.

A multicenter, randomized open study of early corticosteroid treatment (OSECT) in preterm infants with respiratory illness: comparison of early and late treatment and of dexamethasone and inhaled budesonide

AIM

To compare early (<3 days) with late (>15 days) steroid therapy and dexamethasone with inhaled budesonide in very preterm infants at risk of developing chronic lung disease.

METHODS

Five hundred seventy infants from 47 neonatal intensive care units were enrolled. Criteria for enrollment included gestational age <30 weeks, postnatal age <72 hours, and need for mechanical ventilation and inspired oxygen concentration >30%. Infants were randomly allocated to 1 of 4 treatment groups in a factorial design: early (<72 hours) dexamethasone, early budesonide, delayed selective (>15 days) dexamethasone, and delayed selective budesonide. Dexamethasone was given in a tapering course beginning with 0.50 mg/kg/day in 2 divided doses for 3 days reducing by half until 12 days of therapy had elapsed. Budesonide was administered by metered dose inhaler and a spacing chamber in a dose of 400 microg/kg twice daily for 12 days. Delayed selective treatment was started if infants needed mechanical ventilation and >30% oxygen for >15 days. The factorial design allowed 2 major comparisons: early versus late treatment and systemic dexamethasone versus inhaled budesonide. The primary outcome was death or oxygen dependency at 36 weeks and analysis was on an intention-to-treat basis. Secondary outcome measures included death or major cerebral abnormality, duration of oxygen treatment, and complications of prematurity. Adverse effects were also monitored daily.

RESULTS

There were no significant differences among the groups for the primary outcome. Early steroid treatment was associated with a lower primary outcome rate (odds ratio [OR]: 0.85; 95% confidence interval [CI]: 0.61,1.18) but even after adjustment for confounding variables the difference remained nonsignificant. Dexamethasone-treated infants also had a lower primary outcome rate (OR: 0.86; 95% CI: 0.62,1.20) but again this difference remained not significant after adjustment. For death before discharge, dexamethasone and early treatment had worse outcomes than budesonide and delayed selective treatment (OR: 1.42; 95% CI: 0.93,2.16; OR: 1.51; 95% CI: 0.99,2.30 after adjustment, respectively) with the results not quite reaching significance. Duration of supplementary oxygen was shorter in the early dexamethasone group (median: 31 days vs 40-44 days). Early dexamethasone was also associated with increased weight loss during the first 12 days of treatment (52 g vs 3 g) compared with early budesonide, but over 30 days there was no difference. In the early dexamethasone group, there was a reduced incidence of persistent ductus arteriosus (34% vs 52%-59%) and an increased risk of hyperglycemia (55% vs 29%-34%) compared with the other 3 groups. Dexamethasone was associated with an increased risk of hypertension and gastrointestinal problems compared with budesonide but only the former attained significance.

CONCLUSIONS

Infants given early treatment and dexamethasone therapy had improved survival without chronic lung disease at 36 weeks compared with those given delayed selective treatment and inhaled budesonide, respectively, but results for survival to discharge were in the opposite direction; however, none of these findings attained statistical significance. Early dexamethasone treatment reduced the risk of persistent ductus arteriosus. Inhaled budesonide may be safer than dexamethasone, but there is no clear evidence that it is more or less effective.

Fetal and placental volumetric and functional analysis using echo-planar imaging

Recent and past work using echo-planar imaging (EPI) in pregnancy has allowed important anatomic and physiological information to be obtained, giving advantages over conventional radiological methods such as ultrasound. EPI is a quick, convenient method of measuring organ volumes. The volumetric estimates throughout gestation correlate well with known fetal weight at these gestations. Relaxation time measurements also can be made in the placenta and lungs. By combining the changes in relaxation and volume with gestation in the future, it may be possible to develop an "index of maturity." This could be used to accurately reflect lung maturation. T1 and T2 parameters in the placenta decreased with gestational age and with abnormal placentation. EPI can be used to assess perfusion in the placenta and flow in the uterine arteries because of its rapid acquisition times. These techniques have been applied to assess perfusion within the fetal brain.

Endogenous surfactant turnover in preterm infants with respiratory distress syndrome studied with stable isotope lipids

We studied surfactant kinetics on Day 1 of life in 11 preterm infants on mechanical ventilation by infusing stable isotope labeled palmitic (PA) and linoleic acid (LLA). Six infants received exogenous surfactant for the treatment of respiratory distress syndrome (RDS) and five did not meet treatment criteria because of minimal or no disease. The isotopic enrichment of plasma free PA and LLA and of surfactant phosphatidylcholine PA (PC-PA) and LLA (PC-LLA) from tracheal aspirates was measured by mass spectrometry. Significant isotopic enrichment could be measured in PC-PA and PC-LLA from all patients. The fractional synthesis rate (FSR) of PC-LLA was higher than that of PC-PA (22.7 +/- 15.9 versus 12.1 +/- 7.7% per day, p = 0.018). Half-life (HL) of PC-PA was longer than that of PC-LLA (94.7 +/- 18.8 versus 46.6 +/- 32.6 h, p = 0.028). Patients who received exogenous surfactant had longer secretion times (ST) and delayed peak times (PK) but FSR and HL were unaffected. We concluded that: (1) surfactant kinetics can be measured in preterm infants with stable isotope labeled lipids; (2) surfactant FSR and HL calculated with PA and LLA gave different results; (3) patients treated with exogenous surfactant had similar FSRs compared with the nontreated subjects but had longer ST and delayed PK; (4) FSR from plasma free fatty acids (present study) was higher than that from plasma glucose in our previous work (Bunt JEH, Zimmermann LJI, Wattimena D, van Beek R, Sauer PJJ, Carnielli VP. Am J Respir Crit Care Med 1998;157:810-814) in a comparable population of preterm infants with RDS.

Alpha-1 proteinase inhibitor (a1PI) for preventing chronic lung disease in preterm infants

BACKGROUND

Inflammation of the pulmonary parenchyma is one of the important mechanisms implicated in development of chronic lung disease (CLD) in preterm neonates. Release of enzymes and other anti - oxidants following cell damage is considered to be responsible for the damage to lung tissue. Various strategies have been attempted to counteract enzymatic damage to pulmonary parenchyma and to prevent CLD.

OBJECTIVES

This review examines the effectiveness of alpha 1 proteinase inhibitor (a1PI) for the prevention of CLD defined as requirement of supplemental oxygen at 36 weeks post menstrual age (PMA) in preterm neonates.

SEARCH STRATEGY

A literature search was performed using the following databases: MEDLINE (1966 - February 2001), EMBASE (1980 -February 2001), CINAHL (1982 - February 2001), Cochrane Controlled Trials Register (Issue 1, 2001 of Cochrane Library) and abstracts from the annual meetings of the Society of Pediatric Research, American Pediatric Society and Pediatric Academic Societies published in Pediatric Research (1991-2000). No language restrictions were applied.

SELECTION CRITERIA

Selection criteria applied to the clinical trials were: 1. The population had to be preterm neonates 2. The intervention had to be administration of a1PI compared to placebo or no treatment within the first week of life 3. The eligible studies had to include any of the following outcomes: a. prevention of CLD b. reduction in duration of assisted ventilation c. reduction in the duration of oxygen requirement d. reduction in the need for systemic antiinflammatory therapy e. reduction in mortality or f. reduction in long term adverse neurological sequelae. 4. The trial had to be randomized or quasi-randomized.

DATA COLLECTION AND ANALYSIS

The methodological quality of the trials was assessed using the information provided in the studies and by personal communication with the authors. Data on relevant outcomes were extracted and the effect size was estimated and reported as pooled relative risk (RR), risk difference (RD) and weighted mean difference (WMD) as appropriate. Two strategies were used for analysis : 1. Comparison of 60 mg/kg/dose of a1PI administered for 4 days in first 2 weeks after birth, versus placebo and 2. Comparison of any dose of a1PI administered in first 2 weeks after birth, versus placebo.

MAIN RESULTS

Two eligible studies were identified. The methodological qualities of identified studies were good. One study randomized infants to either placebo, or a1PI 60 mg/kg/dose for four doses while in the second study the same investigators explored the efficacy of different dose regimens of a1PI compared to placebo. There was no statistically significant difference in the development of CLD at 36 weeks PMA amongst all randomized infants. For 60 mg/kg/dose for four doses of a1PI compared to placebo the pooled RR was 0.64 [95% CI 0.35, 1.18] and RD was -0.10 [95% CI -0.23, 0.03] while for any doses of a1PI the pooled RR was 0.79 [95% CI 0.44, 1.41], RD was -0.05 [95% CI -0.17, 0.06]. There was a trend towards reduced risk of development of oxygen dependency at 28 days postnatal age, pooled RR 0.81 [95% CI 0.64, 1.01], RD -0.14 [95% CI -0.29, 0.00] for 60 mg/kg/dose for four doses of a1PI compared to placebo. The pooled RR was statistically significant, RR 0.80 [95% CI 0.65, 0.98], RD -0.15 (95 % CI -0.29, -0.01) when any doses of a1PI were combined. The number of patients needed to treat (NNT) with a1PI to prevent one infant developing oxygen dependency at 28 weeks was 7. The benefits of short-term outcomes did not remain for long-term outcomes such as CLD and/or death at 36 weeks post menstrual age (pooled RR 0.84 [95% CI 0.53, 1.34], RD -0.06 [95% CI -0.20, 0.09] for 60 mg/kg/dose and pooled RR 0.95 [95% CI 0.61, 1.49], RD -0.02 [95% CI -0.15, 0.12] for any dose) or risk of development of long term neurodevelopmental abnormalities (pooled RR 1.29 [95% CI 0.43, 3.90], RD 0.03 [95% CI -0.11, 0.18]). In addition, no statistically significant difference was noted in other respiratory parameters such as duration of oxygen requirement or respiratory support.

REVIEWER'S CONCLUSIONS

Prophylactic administration of a1PI did not reduce the risk of CLD at 36 weeks or long term adverse developmental outcomes in preterm neonates.

Strategies for prevention of neonatal chronic lung disease

Chronic lung disease (CLD) of prematurity remains a substantial problem despite modern perinatal and neonatal care. CLD remains related to gestational age and lung immaturity, although it has become clear that severe initial lung disease is not a prerequisite for CLD to develop. Attempts to prevent CLD to date have not adequately addressed the multifactorial nature of the complex pathophysiology that leads to CLD. Thus, results have been modest at best. Prevention of CLD will require a multifaceted approach with specific interventions and care practices focused on different aspects of the pathway that leads to CLD. This review considers new information related to causation of CLD and the magnitude of the effect of prevention strategies tested to date. This article also advances the hypothesis that CLD is preventable with a global strategy of minimizing inciting events, optimizing management, and specific therapies aimed at intrinsic vulnerabilities.