Prematurity; Respiratory distress syndrome; corticosteroids; neurodevelopmental outcomes
Purpose of Review
BPD remains the most common severe complication of preterm birth. A number of recent animal models and clinical studies provide new information about pathophysiology and treatment.
The epidemiology of BPD continues to demonstrate that birth weight or gestational age are most predictive of BPD. Correlations of BPD with chorioamnionitis are clouded by the complexity of the fetal exposures to inflammation. Excessive oxygen use in preterm infants can increase the risk of BPD, but low saturation targets may increase death. Numerous recent trials demonstrate that many preterm infants can be initially stabilized after delivery with CPAP and then be selectively treated with surfactant for RDS. The growth of the lungs of the infant with BPD through childhood remains poorly characterized.
Recent experiences in neonatology suggest that combining less invasive care strategies that avoid excessive oxygen and ventilation, decrease postnatal infections, and optimize nutrition may decrease the incidence and severity of BPD.
Ventilation; oxygen; prematurity; lung injury
Corticosteroids are used to improve lung function in infants who are progressing toward BPD. Corticosteroids facilitate extubation, but there is conflicting information about adverse effects on the developing brain. An approach to minimizing risk is to use low dose, short duration treatments in the highest risk ventilator dependent patients. Questions remain about which corticosteroid is the safest and how to dose that corticosteroid.
Lung Injury; Alveoli; Premature; Neurodevelopment; Mechanical Ventilation
We tested the hypothesis that interleukin 1 (IL-1) mediates intra-amniotic lipopolysaccharide (LPS)-induced chorioamnionitis in preterm fetal sheep. Time-mated Merino ewes with singleton fetuses received IL-1α, LPS, or saline (control) by intra-amniotic injection 1 to 2 days before operative delivery at 124 ± 1 days gestational age (N = 5-9/group; term = 150 days). Recombinant human IL-1 receptor antagonist (rhIL-1ra) was given into the amniotic fluid 3 hours before intra-amniotic LPS or saline to block IL-1 signaling. Inflammation in the chorioamnion was determined by histology, cytokine messenger RNA (mRNA), protein expression, and by quantitation of activated inflammatory cells. Intra-amniotic IL-1 and LPS both induced chorioamnionitis. However, IL-1 blockade with IL-1ra did not decrease intra-amniotic LPS-induced increases in pro-inflammatory cytokine mRNAs, numbers of inflammatory cells, myeloperoxidase, or monocyte chemotactic protein-1-expressing cells in the chorioamnion. We conclude that IL-1 and LPS both can cause chorioamnionitis, but IL-1 is not an important mediator of LPS-induced chorioamnionitis in fetal sheep.
fetal inflammatory response syndrome; prematurity; innate immunity; IL-1 receptor antagonist
There is increasing evidence linking in utero infection and inflammation to preterm birth. Many commensal urogenital tract microorganisms, including the Mycoplasmas and Ureaplasmas, are commonly detected in association with preterm birth. Using an ovine model of sterile fetal inflammation, we demonstrated previously that the fetal skin generates a robust inflammatory response following in utero exposure to lipopolysaccharides from Escherichia coli. The fetal skin’s response to colonization of the amniotic fluid by viable microorganisms remains unstudied. We hypothesised that in utero infection with Ureaplasma parvum serovar 3 would induce a proinflammatory response in the fetal skin. We found that (1) cultured fetal keratinocytes (the primary cellular constituent of the epidermis) respond to U. parvum exposure in vitro by increasing the expression of the chemotactant monocyte chemoattractant protein 1 (MCP-1) but not interleukin 1β (IL-1β), IL-6, IL-8, or tumor necrosis factor-α (TNF-α); (2) the fetal skin’s response to 7 days of U. parvum exposure is characterized by elevated expression of MCP-1, TNF-α, and IL-10; and (3) the magnitude of inflammatory cytokine/chemokine expression in the fetal skin is dependent on the duration of U parvum exposure. These novel findings provide further support for the role of the fetal skin in the development of fetal inflammation and the preterm birth that may follow.
preterm birth; uterine infection; inflammation
Bronchopulmonary dysplasia (BPD), associated with chorioamnionitis, results from the simultaneous effects of disrupted lung development, lung injury, and repair superimposed on the developing lung. Caveolins (Cavs) are implicated as major modulators of lung injury and remodeling by multiple signaling pathways, although Cavs have been minimally studied in the injured developing lung. We hypothesized that chorioamnionitis-associated antenatal lung inflammation would decrease the expression of Cav-1 in preterm fetal lungs. We tested whether changes occurred in the transcription factors Smad2/3, Smad1/5, Stat3, and Stat1, and we also studied the activation of acid-sphingomyelinase (a-SMase) with the generation of ceramide, along with changes in the expression of heme oxygenase–1 (HO-1) as indicators of possible Cav-1–mediated effects. Fetal sheep were exposed to 10 mg of intra-amniotic endotoxin or saline for 2, 7, or 2 + 7 days before preterm delivery at 124 days of gestation. The expression of Cav-1 and HO-1 and the phosphorylation of Smad and Stat were evaluated by real-time PCR, Western blotting, and/or immunohistochemistry. The activity of a-SMase and the concentrations of ceramide were measured. Intra-amniotic endotoxin decreased Cav-1 mRNA and protein expression in the lungs, with a maximum reduction of Cav-1 mRNA to 50% ± 7% of the control value (P < 0.05), and of Cav-1 protein expression to 20% ± 5% of the control value (P < 0.05). Decreased concentrations of Cav-1 were associated with the elevated phosphorylation of Smad2/3, Stat3, and Stat1, but not of Smad1/5. The expression of HO-1, a-SMase activity, and ceramide increased. Antenatal inflammation decreased the expression of Cav-1 in the preterm fetal lung. The decreased expression of Cav-1 was associated with the activation of the Smad2/3, Stat, and a-SMase/ceramide pathways, and with the increased expression of HO-1. The decreased concentrations of Cav-1 and changes in other signaling pathways may contribute to BPD.
bronchopulmonary dysplasia; TGF-β; a-SMase; ceramide; chorioamnionitis
The chorioamnionitis associated with preterm delivery is often polymicrobial with ureaplasma being the most common isolate. To evaluate interactions between the different pro-inflammatory mediators, we hypothesized that ureaplasma exposure would increase fetal responsiveness to LPS. Fetal sheep were given intra-amniotic injections of media (control) or Ureaplasma parvum serovar 3 either 7d or 70d before preterm delivery. Another group received an intraamniotic injection of E.coli lipo-polysaccharide (LPS) 2d prior to delivery. To test for interactions, intraamniotic U. parvum exposed animals were challenged with intraamniotic LPS and delivered 2d later. All animals were delivered at 124±1d gestation (Term=150d). Compared to the 2d LPS exposure group, the U. parvum 70d+LPS group had: 1) decreased lung pro and anti-inflammatory cytokine expression 2) fewer CD3+ T-lymphocytes, CCL2+, myeloperoxidase+, and PU.1+ cells in the lung. Interestingly, exposure to U. parvum for 7d did not change responses to a subsequent intraamniotic LPS challenge, and exposure to intraamniotic U. parvum alone induced mild lung inflammation. Exposure to U. parvum increased pulmonary TGFβ1 expression but did not change mRNA expression of either the receptor TLR4 or some of the downstream mediators in the lung. Monocytes from fetal blood and lung isolated from U. parvum 70d+LPS but not U. parvum 7d+LPS animals had decreased in vitro responsiveness to LPS. These results are consistent with the novel finding of down-regulation of LPS responses by chronic but not acute fetal exposures to U. parvum. The findings increase our understanding of how chorioamnionitis exposed preterm infants may respond to lung injury and postnatal nosocomial infections.
Prematurity; Chorioamnionitis; Fetal inflammatory response syndrome; endotoxin tolerance; lung inflammation
The multiple banded antigen (MBA) is a predicted virulence factor of Ureaplasma species. Antigenic variation of the MBA is a potential mechanism by which ureaplasmas avoid immune recognition and cause chronic infections of the upper genital tract of pregnant women. We tested whether the MBA is involved in the pathogenesis of intra-amniotic infection and chorioamnionitis by injecting virulent or avirulent-derived ureaplasma clones (expressing single MBA variants) into the amniotic fluid of pregnant sheep. At 55 days of gestation pregnant ewes (n = 20) received intra-amniotic injections of virulent-derived or avirulent-derived U. parvum serovar 6 strains (2×104 CFU), or 10B medium (n = 5). Amniotic fluid was collected every two weeks post-infection and fetal tissues were collected at the time of surgical delivery of the fetus (140 days of gestation). Whilst chronic colonisation was established in the amniotic fluid of animals infected with avirulent-derived and virulent-derived ureaplasmas, the severity of chorioamnionitis and fetal inflammation was not different between these groups (p>0.05). MBA size variants (32–170 kDa) were generated in vivo in amniotic fluid samples from both the avirulent and virulent groups, whereas in vitro antibody selection experiments led to the emergence of MBA-negative escape variants in both strains. Anti-ureaplasma IgG antibodies were detected in the maternal serum of animals from the avirulent (40%) and virulent (55%) groups, and these antibodies correlated with increased IL-1β, IL-6 and IL-8 expression in chorioamnion tissue (p<0.05). We demonstrate that ureaplasmas are capable of MBA phase variation in vitro; however, ureaplasmas undergo MBA size variation in vivo, to potentially prevent eradication by the immune response. Size variation of the MBA did not correlate with the severity of chorioamnionitis. Nonetheless, the correlation between a maternal humoral response and the expression of chorioamnion cytokines is a novel finding. This host response may be important in the pathogenesis of inflammation-mediated adverse pregnancy outcomes.
Inflammation is a defensive process by which the body responds to both localized and systemic tissue damage by the induction of innate and adaptive immunity. Literature from human and animal studies links inappropriate in utero inflammation to preterm parturition and fetal injury. The pathways by which such inflammation may cause labor, however, are not fully understood. Any proinflammatory agonist in the amniotic fluid will contact the fetal skin, in its entirety, but a potential role of the fetal skin in the pathways to labor have not previously been explored. We hypothesized that the fetal skin would respond robustly to the presence of intra-amniotic lipopolysaccharide (LPS) in our ovine model of in utero inflammation. In vitro and in utero exposure of fetal ovine keratinocytes or fetal skin to Escherichia coli LPS reliably induced significant increases in interleukin 1β (IL-1β), IL-6, tumor necrosis factor α (TNF-α), and IL-8 expression. We demonstrate that, in utero, this expression requires direct exposure with LPS suggesting that the inflammation is triggered directly in the skin itself, rather than as a secondary response to a systemic stimuli and that inflammation involves Toll-like receptor (TLR) regulation and neutrophil chemotaxis in concordance with an acute inflammatory reaction. We show that this response involves multiple inflammatory mediators, TLR regulation, and localized inflammatory cell influx characteristic of an acute inflammatory reaction. These novel data strongly suggests that the fetal skin acts as an important mediator of the fetal inflammatory response and as such may contribute to preterm birth.
skin; inflammation; preterm birth; uterine infection
Monocyte chemoattractant proteins (MCP-1 and MCP-2) mediate monocyte and T-lymphocyte chemotaxis, and IL-1 contributes to the pathogenesis of chorioamnionitis-induced lung inflammation and fetal inflammatory responses. We tested the hypothesis that IL-1 mediates the systemic and pulmonary induction of MCP-1 and MCP-2 in response to lipopolysaccharide (LPS) induced chorioamnionitis. MCP-1 mRNA, MCP-2 mRNA and MCP-1 protein expression were measured in two models: 1) intra-amniotic LPS and 2) intra-amniotic recombinant sheep IL-1α given at varying intervals prior to preterm delivery at 124d gestational age. Intra-amniotic LPS or IL-1α induced MCP-1 mRNA and protein and MCP-2 mRNA in fetal lung many fold at 1-2d. LPS induced intense MCP-1 expression in sub-epithelial mesenchymal cells and interstitial inflammatory cells in the lung. Inhibition of IL-1 signaling with recombinant human IL-1 receptor antagonist (rhIL-1ra) did not attenuate LPS induced increase in MCP-1 or MCP-2 expression. MCP-1 and MCP-2 were not induced in liver or chorioamnion, but MCP-1 increased in cord plasma. LPS or IL-1 can induce robust expression of MCP-1 or MCP-2 in the fetal lung. LPS induction of MCP-1 is not IL-1 dependent in fetal sheep. MCP-1 and MCP-2 may be significant contributors to fetal inflammation.
Ureaplasma species are the bacteria most frequently isolated from human amniotic fluid in asymptomatic pregnancies and placental infections. Ureaplasma parvum serovars 3 and 6 are the most prevalent serovars isolated from men and women. We hypothesized that the effects on the fetus and chorioamnion of chronic ureaplasma infection in amniotic fluid are dependent on the serovar, dose, and variation of the ureaplasma multiple-banded antigen (MBA) and mba gene. We injected high- or low-dose U. parvum serovar 3, serovar 6, or vehicle intra-amniotically into pregnant ewes at 55 days of gestation (term = 150 days) and examined the chorioamnion, amniotic fluid, and fetal lung tissue of animals delivered by cesarean section at 125 days of gestation. Variation of the multiple banded antigen/mba generated by serovar 3 and serovar 6 ureaplasmas in vivo were compared by PCR assay and Western blot. Ureaplasma inoculums demonstrated only one (serovar 3) or two (serovar 6) MBA variants in vitro, but numerous antigenic variants were generated in vivo: serovar 6 passage 1 amniotic fluid cultures contained more MBA size variants than serovar 3 (P = 0.005), and ureaplasma titers were inversely related to the number of variants (P = 0.025). The severity of chorioamnionitis varied between animals. Low numbers of mba size variants (five or fewer) within amniotic fluid were associated with severe inflammation, whereas the chorioamnion from animals with nine or more mba variants showed little or no inflammation. These differences in chorioamnion inflammation may explain why not all women with in utero Ureaplasma spp. experience adverse pregnancy outcomes.
After intra-amniotic inoculation of pregnant sheep with Ureaplasma parvum serovar 3 and serovar 6, infections persisted in utero for 70 days, causing high titer chorioamnion infections, while some chorioamnions showed no histological evidence of infection.
chorioamnionitis; immunology; multiple-banded antigen gene; pregnancy; ureaplasma species
Preterm and term infants are frequently exposed to high concentrations of oxygen for prolonged periods. In experimental models, high and prolonged oxygen exposures cause delayed alveolar septation and a bronchopulmonary dysplasia phenotype. Often, however, the oxygen exposure is tolerated in that the infants recover without severe lung or systemic injury. Multiple exposures change oxygen sensitivity in adult and newborn animals. Examples are antenatal corticosteroids, inflammatory mediators or preconditioning with oxygen, which will increase tolerance to oxygen injury. Intrauterine growth restriction or postnatal nutritional deficits will increase oxygen injury. Different infants probably have quite variable sensitivities to oxygen injury, but there are no biomarkers available to predict the risk of oxygen injury.
Bronchopulmonary dysplasia; Injury; Lung; Prematurity
Mechanical ventilation causes lung injury in premature infants. Hypothermia may protect against and hyperthermia may augment lung injury. We tested the effects of hypo- and hyperthermia on ventilation induced acute lung injury in preterm lambs.
Twin sheep fetuses at 128 d GA (term 150 d) were surgically delivered and randomized to unventilated control (UVC), normothermia (38-39 °C) without lung injury (NTNI), or to 1 of 3 injurious ventilation groups: hypothermic (33-34 °C, LT), normothermic (38-39 °C, NT) or hyperthermic (40-41 °C, HT). NT, LT and HT groups had 15 min of injurious ventilation (PEEP 0 cmH2O, VT escalation to 15 mL/kg) following delivery and prior to surfactant. The animals were then gently ventilated (PEEP 5 cmH2O, VT 7.5 mL/kg) for 2 h 45 min. NTNI lambs received surfactant at birth prior to gentle ventilation. The lambs were then euthanized, and bronchoalveolar lavage (BAL) fluid and lung tissue were used to evaluate lung injury, inflammatory cell counts, inflammatory markers and cytokine mRNA.
Target temperatures were achieved by 15 min of age and maintained for 3 h. All ventilated groups had increased BAL protein, lung inflammation and increased cytokine mRNA. HT animals developed acidosis, premature death, pneumothoraces, impaired lung function and increased inflammatory mRNA expression. LT animals remained clinically stable without pneumothoraces or death, had improved ventilatory efficiency and trended toward lower inflammatory mRNA expression than NT animals.
Hyperthermia exacerbated ventilator induced lung injury, while hypothermia may protect against lung injury in the preterm lamb.
Treg mediates homeostasis of the immune system and differentiate under the control of the transcription factor FoxP3 in the fetal thymus.
We asked if fetal inflammation caused by chorioamnionitis would modulate thymus development.
Fetal sheep were exposed to an intraamniotic injection (IA) of 10 mg LPS 5h, 1d, 2d or 5d before delivery at 123d gestation days. Cord blood lymphocytes, plasma cortisol and thymus weight were measured. Glucocorticoid receptor-, activated caspase-3-, Ki67-, PCNA-, NF-κB- and FoxP3-positive cells were immunohistochemically evaluated in thymus.
IA LPS decreased the number of circulating lymphocytes by 40% after 1d. Thymus-to-body weight ratios were reduced in all LPS groups by a maximum of 40% at 5d. LPS modestly increased plasma cortisol concentration, increased NF-κB immunostaining in fetal thymus and reduced the number of FoxP3-positive cells by 60% at 1d.
Intraamniotic exposure to LPS induced thymic changes and influenced thymic FoxP3 expression.
preterm; fetal inflammatory syndrome; immune development; T lymphoyctes; FoxP3; Treg
Premature infants exposed to ventilation are at risk of developing bronchopulmonary dysplasia (BPD) and persistent lung disease in childhood. We report where injury occurred within the lung following brief ventilation at birth. Preterm sheep (129d gestation) were ventilated with an escalating VT to 15mL/kg by 15 min to injure the lungs, with the placental circulation intact (Fetal) or after delivery (Newborn). Fetal lambs were returned to the uterus for 2h 45min, while Newborn lambs were maintained with gentle ventilatory support for the same period. The control group was not ventilated. Bronchoalveolar lavage fluid (BALF) and lung tissue were analysed. In both Fetal and Newborn lambs, ventilation caused bronchial epithelial disruption in medium-sized airways. Egr-1, MCP-1, IL-6, and IL-1β mRNA increased in lung tissue from Fetal and Newborn lambs. Egr-1, MCP-1 and IL-6 mRNA were induced in mesenchymal cells surrounding small airways, whereas IL-1β mRNA localized to the epithelium of medium/small airways. Ventilation caused loss of HSP70 mRNA from the bronchial epithelium, but induced mRNA in smooth muscle surrounding large airways. HSP70 protein decreased in lung tissue and increased in BALF with ventilation. Initiation of ventilation induced a stress response and inflammatory cytokines in small and medium-sized airways.
We hypothesized that fetal LPS exposures to the chorioamnion, lung or gut would induce distinct systemic inflammatory responses.
Groups of 5–7 time-mated ewes were used to surgically isolate the fetal respiratory and the gastrointestinal systems from the amniotic compartment. Outcomes were assessed at 124d gestational age, 2d and 7 d after LPS (10 mg, E.coli 055:B5) or saline infusions into the fetal airways or amniotic fluid.
LPS induced systemic inflammatory changes in all groups in the blood, lung, liver, and thymic lymphocytes. Changes in lymphocytes in the posterior mediastinal lymph node draining lung and gut, occurred only after direct contact of LPS with the fetal lung or gut.
Fetal systemic inflammatory responses occurred after chorioamnion, lung or gut exposures to LPS. The organ responses differed based on route of the fetal exposure.
fetal inflammation; innate immunity; maturation; chorioamnionitis; antigen exposure
We hypothesized that maternal treatments with betamethasone acetate (Beta-Ac) induce fetal lung maturation comparably to the betamethasone phosphate (Beta-PO4) + Beta-Ac (Celestone®) used clinically.
Ewes with singleton pregnancies were treated with single doses of 0.25 mg/kg or 0.5 mg/kg Beta-Ac, 4 doses of 0.25 mg/kg Beta-PO4, a single dose of 0.5 mg/kg Beta-Ac + 0.25 mg/kg Beta-PO4, 2 doses of 0.25 mg/kg Beta-Ac + 0.25 mg Beta-PO4 or vehicle beginning 48 h before preterm delivery. Fetal lung maturation was evaluated.
All treatments induced lung maturation relative to vehicle controls. The relatively insoluble Beta-Ac resulted in low maternal blood Beta and no detectable fetal blood Beta in 2 of 3 fetuses, but induced fetal lung maturation comparable to the 2 dose Beta-Ac + Beta-PO4 or 4 doses of Beta-PO4.
A single maternal dose of Beta-Ac effectively induces fetal lung maturation in sheep with minimal fetal exposure.
Corticosteroid; Fetal Therapy; Preterm; Respiratory Distress Syndrome; Sheep 7
Rationale: Chorioamnionitis frequently associates with preterm delivery and increased amniotic fluid IL-1, and causes fetal lung and systemic inflammation. However, chorioamnionitis is also associated with a paradoxical reduction in the incidence of surfactant deficiency–related respiratory distress syndrome in preterm infants.
Objectives: To identify the role of IL-1 signaling in the mediation of pulmonary and systemic inflammation and lung maturation in a fetal sheep model of lipopolysaccharide (LPS) induced chorioamnionitis.
Methods: After confirming the efficacy of recombinant human IL-1 receptor antagonist (rhIL-1ra), fetal sheep were exposed to intraamniotic (IA) injections of Escherichia coli LPS with or without prior IA injections of rhIL-1ra. Preterm lambs were delivered at 82% of term gestation.
Measurements and Main Results: rhIL-1ra decreased IA LPS–induced lung inflammation assessed by decreased lung neutrophil and monocyte influx, inducible nitric oxide synthase expression, lung IL-6 and IL-1β mRNA expression, and airway myeloperoxidase concentrations. rhIL-1ra inhibited IA LPS–induced fetal systemic inflammation assessed by decreased plasma IL-8, protein carbonyls, blood neutrophilia, and the expression of serum amyloid A3 mRNA in the liver. rhIL-1ra also partially blocked the lung maturational effects of IA LPS. Therefore blockade of IL-1 signaling in the amniotic compartment inhibited fetal lung and systemic inflammation and lung maturation in response to LPS-induced chorioamnionitis.
Conclusions: IL-1 plays a central role in the pathogenesis of chorioamnionitis-induced fetal inflammatory responses.
respiratory distress syndrome; bronchopulmonary dysplasia; preterm birth; interleukin-1 receptor; innate immunity
Prenatal exposure of very low birth weight infants to chronic indolent chorioamnionitis with organisms such as mycoplasma and ureaplasma is frequent. Chorioamnionitis is inconsistently associated with changed risks of respiratory distress syndrome (RDS) or bronchopulmonary dysplasia (BPD), probably because the diagnosis of chorioamnionitis does not quantify the extent or duration of the fetal exposures to infection and inflammation. The correlations between prenatal exposures and postnatal lung disease also are confounded by the imprecision of the diagnoses of RDS and BPD. In animal models, chorioamnionitis caused by pro-inflammatory mediators or live ureaplasma induces lung maturation, but also causes alveolar simplification and vascular injury. Intra-amniotic endotoxin administration also modulates the fetal innate immune system, resulting in maturation of monocytes to alveolar macrophages and the induction or paralysis of inflammatory responses depending on exposure history. Prenatal inflammation can have profound effects on the fetal lung and subsequent immune responses.
Bronchopulmonary dysplasia; Chorioamnionitis; Lung injury; Respiratory distress syndrome; Ureaplasma
To assess the efficacy of maternal betamethasone for improving preterm lung function, in the presence of inflammation induced by amniotic fluid ureaplasma colonization.
Ewes bearing single fetuses were randomized to receive an intra-amniotic injection of Ureaplasma parvum (serovar 6; 2×107 colony forming units) or vehicle at 86±2 days of pregnancy (mean±SD: term is 150d), followed by maternal intramuscular betamethasone (0.5mg/kg) or saline, either 2 or 7 days before delivery of lambs at 123±1d.
Amniotic fluid IL-8 was elevated by ureaplasmas (p=0.049) but unaffected by betamethasone. Lung inflammation induced by ureaplasmas was not affected by betamethasone. Lung compliance was increased by ureaplasma colonization (p=0.009) and betamethasone (p=0.042), and effects were additive. Lung surfactant was increased by ureaplasma colonization (p<0.001) and betamethasone 7 days (p=0.001), but not 2 days, before delivery.
Inflammation improves preterm lung function due to increases in surfactant. Antenatal corticosteroids further augment lung function, through an apparently independent mechanism.
betamethasone; intrauterine inflammation; infection; preterm birth
Initiation of ventilation using high tidal volumes in preterm lambs causes lung injury and inflammation. Antenatal corticosteroids mature the lungs of preterm infants and postnatal corticosteroids are used to treat bronchopulmonary dysplasia.
To test if antenatal or postnatal corticosteroids would decrease resuscitation induced lung injury.
129 d gestational age lambs (n = 5-8/gp; term = 150 d) were operatively delivered and ventilated after exposure to either 1) no medication, 2) antenatal maternal IM Betamethasone 0.5 mg/kg 24 h prior to delivery, 3) 0.5 mg/kg Dexamethasone IV at delivery or 4) Cortisol 2 mg/kg IV at delivery. Lambs then were ventilated with no PEEP and escalating tidal volumes (VT) to 15 mL/kg for 15 min and then given surfactant. The lambs were ventilated with VT 8 mL/kg and PEEP 5 cmH20 for 2 h 45 min.
High VT ventilation caused a deterioration of lung physiology, lung inflammation and injury. Antenatal betamethasone improved ventilation, decreased inflammatory cytokine mRNA expression and alveolar protein leak, but did not prevent neutrophil influx. Postnatal dexamethasone decreased pro-inflammatory cytokine expression, but had no beneficial effect on ventilation, and postnatal cortisol had no effect. Ventilation increased liver serum amyloid mRNA expression, which was unaffected by corticosteroids.
Antenatal betamethasone decreased lung injury without decreasing lung inflammatory cells or systemic acute phase responses. Postnatal dexamethasone or cortisol, at the doses tested, did not have important effects on lung function or injury, suggesting that corticosteroids given at birth will not decrease resuscitation mediated injury.
Positive end-expiratory pressure (PEEP) protects the lung from injury during sustained ventilation, but its role in protecting the lung from injury during the initiation of ventilation in the delivery room is not established. We aimed to evaluate whether PEEP and/or tidal volume (VT) within the first 15-minutes of ventilation are protective against lung injury. Operatively delivered preterm lambs (133±1d gestation) were randomly assigned to unventilated controls or to 1 of four 15 minute ventilation interventions: 1) VT15mL/kg, PEEP 0cmH2O, 2) VT15mL/kg, PEEP 5cmH2O, 3) VT8mL/kg, PEEP 0cmH2O and 4) VT8mL/kg, PEEP 5cmH2O. Each group was subsequently ventilated with VT <10mL/kg, PEEP 5cmH2O for 1h 45min. Lung function was assessed and measurements of lung injury were evaluated post-mortem. After the 15min ventilation maneuver, the VT15 groups were hypocarbic, had higher oxygenation and required lower pressures then the VT8 groups; no consistent effect of PEEP was found. Markers of lung injury were significantly elevated in all ventilation groups compared to unventilated controls; no effect of PEEP was found. Ventilation resulted in localization of IL-6 to the small airways. Initial ventilation of preterm lambs with PEEP and/or VT of 8mL/kg did not prevent an inflammatory injury to the lung.
Neonatal resuscitation; preterm; lung injury; inflammation; volutrauma
To determine effects in late gestation of U. parvum serovar 3 colonization, and effects, preterm, of U. parvum serovar 6.
Ewes received an intra-amniotic (IA) injection of U. parvum serovar 6 (20x106 cfu; n=9), U. parvum serovar 3 (20x103 cfu; n=6), vehicle (n=10) or saline (n=4) on day 80 of pregnancy (d). Lambs were delivered at 125d (ureaplasma, n=9; saline or media controls, n=9) or 145d (ureaplasma, n=6; media controls, n=5) for assessment of inflammation and lung maturation.
IA ureaplasmas caused histologic chorioamnionitis but not preterm delivery. Fetal lung epithelium was colonized with ureaplasmas at both gestational ages and pulmonary IL-8 levels had doubled in the ureaplasma-colonized animals compared to controls at 145d. Surfactant levels in bronchoalveolar lavage fluid had increased 8 fold and 2.5 fold at 125 and 145d, respectively after ureaplasma injection.
Fetal lung inflammation and altered development accompanies ureaplasma colonization regardless of age at delivery.
intrauterine infection; fetal inflammation; ureaplasmas
We evaluated lung maturation responses to the mixture of betamethasone phosphate (Beta-PO4) + betamethasone acetate (Beta-Ac) in comparison to Beta-PO4 or Beta-Ac in fetal sheep.
Ewes carrying singleton pregnancies at 122d gestation were randomized to: single doses of 0.5 mg/kg Beta-PO4 + Beta-Ac, 0.25 mg/kg Beta-PO4, 0.5 mg/kg Beta-PO4 or 0.25 mg/kg Beta-Ac given 48h before delivery. These treatments were compared to saline placebo and 2 doses of 0.5 mg/kg Beta-PO4 + Beta-Ac given 48 and 24h prior to delivery. Fetal lung maturation was evaluated.
The 2 doses of the Beta-PO4 + Beta-Ac mixture gave the best lung maturation. Single doses of the Beta-PO4 + Beta-Ac mixture and Beta-Ac also induced lung maturation. There were no consistent responses to either dose of Beta-PO4.
Beta-PO4 alone is ineffective with the dosing schedule used, while Beta-Ac can induce lung maturation. However, the best responses result from the mixture of Beta-PO4 + Beta-Ac.
Respiratory Distress Syndrome; preterm; corticosteroids; fetal sheep; lung development