Lung ultrasonography to diagnose meconium aspiration syndrome of the newborn

Objective To investigate the diagnostic value of lung ultrasonography for neonatal meconium aspiration syndrome (MAS). Methods This prospective observational study enrolled patients diagnosed with MAS based on medical history, clinical manifestations and chest X-ray and control newborns without MAS. During ultrasonography, each lung was divided into three regions (front, lateral, and back), using anterior and posterior axillary lines as the boundary. While scanning each region of the lungs, the hand piece was perpendicular or parallel to the ribs. Results This study enrolled 117 newborns with MAS and 100 controls. The main lung ultrasonographic findings in patients with MAS were: (i) pulmonary consolidation with air bronchogram was found in all patients; (ii) pleural line anomalies and the disappearance of the A-line was found in all patients; (iii) atelectasis was found in 19 (16.2%) severe cases, who demonstrated severe massive atelectasis and visible lung pulse; (iv) pleural effusion was found in 16 patients (13.7%); and (v) alveolar-interstitial syndrome or B-line in the non-consolidation area was found in all patients with MAS. Conclusion Ultrasonography can be used routinely to diagnose MAS in an accurate, reliable, convenient, and non-invasive manner.

A case of meconium aspiration syndrome in a bottlenose dolphin (Tursiops truncatus) calf

Stillbirth and neonatal mortality are significant problems in captive breeding of dolphins, however, the causes of these problems are not fully understood. Here, we report a case of meconium aspiration syndrome (MAS) in a male neonate of bottlenose dolphin (Tursiops truncates) who died immediately after birth. At necropsy, a true knot was found in the umbilical cord. The lungs showed diffuse intraalveolar edema, hyperemic congestion and atelectasis due to meconium aspiration with mild inflammatory cell infiltration. Although the exact cause of MAS in this case was unknown, fetal hypoxia due possibly to the umbilical knot might have been associated with MAS, which is the first report in dolphins. MAS due to perinatal asphyxia should be taken into account as a possible cause of neonatal mortality and stillbirth of dolphin calves.

Combination of budesonide and aminophylline diminished acute lung injury in animal model of meconium aspiration syndrome

Combination of low-dose budesonide and low-dose aminophylline may improve lung function in reduced adverse effects compared with high-dose monotherapy. Adult rabbits intratracheally received 4 ml/kg of saline or meconium (25 mg/ml). Meconium-injured rabbits were treated at 0.5 and 2.5 h after meconium instillation by intravenous aminophylline (1.0 mg/kg), by intratracheal budesonide (0.125 mg/kg) followed by intravenous aminophylline (1.0 mg/kg), or were untreated. Although aminophylline improved some respiratory parameters, budesonide+aminophylline more effectively reduced intrapulmonary shunts and improved gas exchange, without significant cardiovascular effects. Combined treatment reduced lung edema and number of lung neutrophils to a higher extent than aminophylline alone. Both treatments reduced lung peroxidation and in vitro airway reactivity to histamine, with a better effect after aminophylline alone. Combination of budesonide and aminophylline enhanced respiratory parameters more effectively, having fewer side effects than aminophylline alone. However, no additive effect of budesonide was observed on lung peroxidation and in vitro airway reactivity.

Morphological changes in the lungs of meconium-stained piglets

Meconium staining of the skin is a common event associated with fetal hypoxia, stillbirths, weak-born piglets, and neonatal mortality. Aspiration of meconium leads to meconium aspiration syndrome (MAS). This study was undertaken to assess the relationship between the degree of meconium staining of the skin at birth, meconium aspiration, and pulmonary changes in porcine neonates. A total of 353 farrowing sows and 3,693 born piglets were monitored during parturition and for 15 days after delivery. Umbilical cords were classified as normal or ruptured. Meconium staining in the skin was graded as nonstained, mildly, moderately, and severely stained. Mortality from birth to 15 days of age was 8.4%. The lungs from 60 meconium-stained piglets and 60 lungs from nonstained piglets were collected and microscopically examined for meconium aspiration and inflammation. Rupture of the umbilical cord was significantly higher (P < 0.01) in meconium-stained piglets. Microscopically, 32% and 40% of the lungs had evidence of meconium for the stained and nonstained groups, respectively. The microscopic grade of meconium aspiration and inflammatory cells was not different between nonstained and meconium-stained piglets. Aspiration of meconium induced a granulomatous response in the lungs. It was concluded that the grade of meconium staining is a good indicator of fetal hypoxia, but not a good predictor for meconium aspiration and MAS in piglets.

Effects of surfactant replacement on irregular overdistension of meconium-injured lungs in rats

BACKGROUND

Overdistension of the lungs is a cause of ventilator-induced lung injury. In meconium aspiration syndrome, irregular overdistension of the lungs often occurs.

OBJECTIVES

We investigated whether surfactant replacement could restore the terminal airspaces in the lungs that had been distended after meconium aspiration.

METHODS

Meconium aspiration was induced by injecting meconium (50 mg x kg(-1)) into the airways of adult rats anesthetized with pentobarbital and ventilated with pressure-preset mode. The animals were further ventilated with or without surfactant replacement (100 mg x kg(-1)), and the sizes of the terminal airspaces were determined after fixing the lungs at an airway pressure of 10 cm H2O on deflation.

RESULTS

Approximately 75 min after aspiration (early analysis point), alveolar ducts were widened and the mean ratio of the largest terminal airspace size class (> or =63,000 microm(2)) was 38.7% (n = 7), which was significantly higher than that of controls (6%, n = 7). Three hours after the early analysis point, the ratio increased to 50.2% (n = 7, p < 0.05), but surfactant replacement reversed the ratio to 18.8% (n = 7, p < 0.05).

CONCLUSIONS

In rats with meconium aspiration, surfactant replacement restored the distended terminal airspaces of the lungs and kept the spaces from irregular overdistension.

Inflammatory markers in meconium induced lung injury in neonates and effect of steroids on their levels: A randomized controlled trial

PURPOSE

To determine the levels of TNFa and IL-1beta in tracheal aspirates of neonates with meconium aspiration syndrome (MAS) and to ascertain whether the use of steroids by systemic or nebulized routes suppresses the levels of these inflammatory markers.

METHODS

This was a double blind, randomized, controlled, prospective, interventional study done over one year period in the neonatal unit of the Lady Hardinge Medical College. Fifty-one babies of MAS which were randomly distributed into three groups; control, systemic and nebulized steroids; were included in the study. Methyl prednisolone was given intravenously in the dosage of 0.5 mg/kg/day in two divided doses while nebulized budecort was given in a dosage of 50 mcg/dose twice daily. Tracheal aspirates were taken on day 1, 3 and 4 and were analyzed for TNFa and IL-1b by ELISA technique.

RESULTS

TNFa in tracheal aspirates showed an increasing trend in babies of MAS in first four days, thereby signifying an inflammatory process underlying the condition. The levels of TNFa were suppressed by use of steroids. Higher levels of TNFa were associated with longer stay in hospital. IL-1b did not show any significant correlation.

CONCLUSIONS

TNFa is associated with meconium-associated inflammation. Its level is suppressed with the use of steroids and can also be used to assess prognosis of neonates with MAS.

Pancreatic phospholipase A2 contributes to lung injury in experimental meconium aspiration

To investigate the role of pancreatic (group I) secretory PLA2 (sPLA2-I) in the pathogenesis of meconium aspiration syndrome, human particulate meconium or its supernatant either before or after extraction of PLA2-I was insufflated into rat lungs. In addition, the pulmonary effects of intra-tracheal human and bovine PLA2-I were studied. Lungs with saline instillation served as controls. Intrapulmonary particulate meconium (both before and after PLA2-I extraction), unlike meconium supernatant, resulted in markedly elevated lung tissue PLA2 catalytic activity and human PLA2-I concentrations when compared with controls. On the other hand, tissue concentrations of the group II PLA2 remained unchanged in all meconium lungs. Pulmonary PLA2-I concentrations further correlated positively with lung injury scores. Instillation of meconium-derived human PLA2-I, at a concentration of one-third of that in particulate meconium, did not raise PLA2 activity or concentrations of PLA2-I or PLA2-II in the lung tissue from the control level, but still resulted in significantly elevated lung wet/dry ratio and injury score. In contrast, insufflation of bovine pancreatic PLA2 increased the lung tissue enzyme activity and wet/dry ratio from the control level, but had no effect on the type II PLA2 concentration or lung injury score. Our data thus indicate that human pancreatic PLA2, introduced in high amounts within aspirated meconium especially in particulate form, is a potent inducer of lung tissue inflammatory injury.

Meconium aspiration induces neuronal injury in piglets

AIM

Meconium aspiration-induced hypertensive lung injury, especially when connected with perinatal asphyxia, has been associated with brain damage. We aimed to determine the neuronal injury induced by pulmonary meconium contamination alone and with concurrent asphyxia.

METHODS

36 anaesthetized and ventilated newborn piglets were haemodynamically monitored for 6 h. Seven piglets without concurrent asphyxia and seven piglets with asphyxia were instilled with a bolus of human meconium intratracheally. Seven piglets had only asphyxia and 15 piglets served as controls. The brains were studied histologically.

RESULTS

Meconium aspiration did not change systemic haemodynamics acutely, while its combination with asphyxia diminished the abrupt postasphyxic systemic hypertensive peak and resulted in a transient increase in carotid artery flow, not seen after isolated asphyxia. Systemic pressure declined after 4 h in all insulted groups, but only isolated asphyxia was associated with a sustained decrease in carotid artery flow. Arterial oxygenation remained normal, except during the acute insults. Brain examination after meconium instillation indicated neuronal injury, especially in the CA3 region of the hippocampus. Asphyxia resulted in neuronal injury in the cortical, cerebellar and hippocampal hilus regions.

CONCLUSION

Severe meconium aspiration itself may result in hippocampal neuronal injury.

Meconium inhibits phagocytosis and stimulates respiratory burst in alveolar macrophages

The meconium aspiration syndrome is an important cause of respiratory distress in newborn infants. Alveolar macrophages (AMs) provide a first line of defense in the lower respiratory tract against inhaled pathogens and particles such as meconium. In this study, we examined the effect of meconium on two primary macrophage functions: phagocytosis and respiratory burst. Short-term exposure of rat NR8383 AMs to sterile meconium from human or equine neonates (1.2-24 mg/mL) produced a dose-dependent decrease in phagocytosis of fluorescent latex beads. This effect was not due to decreased cell viability or to an elevation of intracellular cAMP. The effect of short-term exposure to meconium on the respiratory burst response in AMs was quantified using flow cytometry to measure oxidation of dichlorofluorescin diacetate. A robust respiratory burst was triggered when AMs were exposed to 12 or 24 mg/mL meconium. This effect was attenuated but not eliminated by filtration of the meconium. However, subsequent to meconium exposure, AMs had a reduced respiratory burst in response to stimulation with phorbol myristate acetate. In addition, AMs that were exposed to meconium for an extended period (24 h) showed DNA fragmentation indicative of apoptosis. Meconium therefore may interfere with AM function by inducing oxidative stress and apoptosis. Tissue injury from release of reactive oxygen species by AMs may be important in the pathophysiology of the meconium aspiration syndrome.

Meconium passage in utero: mechanisms, consequences, and management

Meconium passage in newborn infants is a developmentally programmed event normally occurring within the first 24 to 48 hours after birth. Intrauterine meconium passage in near-term or term fetuses has been associated with fetomaternal stress factors and/or infection, whereas meconium passage in postterm pregnancies has been attributed to gastrointestinal maturation. Despite these clinical impressions, little information is available on the mechanism(s) underlying the normal meconium passage that occurs immediately after birth or during the intrauterine period of fetal development. Birth itself is a stressful process and it is possible that fetal stress-mediated biochemical events may regulate the meconium passage occurring either during labor or after birth. Aspiration of meconium during intrauterine life may result in or contribute to meconium aspiration syndrome (MAS), representing a continued leading cause of perinatal death. This article reviews aspects of meconium passage in utero, its consequences, and management.

Pulmonary function after surfactant lung lavage followed by surfactant administration in infants with severe meconium aspiration syndrome

OBJECTIVE

The effect of surfactant lung lavage (SLL) on pulmonary function was examined in neonates with severe form of meconium aspiration syndrome (MAS) (mean +/- standard deviation: birth weight, 3178.1 +/- 237.6 g; gestational age, 37.7 +/- 1.8 weeks).

METHODS

The infants were on mechanical ventilation and were subjected to SLL with Survanta. Dynamic compliance (Cdyn), airway resistance (Raw) and mean airway pressure (MAP) were obtained with use of the pneumotachometric method. Measurements of Cdyn, Raw, MAP and time constant (Tc) were compared in the study and control groups and between the groups before SLL and 24 and 48 h after SLL.

RESULTS

A significant increase in Cdyn (from 1.06 +/- 0.23 to 2.12 +/- 0.99 (ml/cmH(2)O)/kg) (p < 0.05) and a drop in both Raw (from 264.7 +/- 41.5 to 146.6 +/- 39.4 (cmH(2)O/l)/s) and MAP (from 12.4 +/- 3.6 to 5.4 +/- 2.1 cmH(2)O) were observed 48 hours after SLL.

CONCLUSIONS

These data suggest that SLL is associated with a rapid and significant improvement in pulmonary mechanics, together with an improvement in oxygenation, in newborns with severe MAS. We found that the beneficial effects of SLL on pulmonary mechanics persisted for at least 48 h after introduction of the procedure.

Apoptosis of airway epithelial cells in response to meconium

Meconium aspiration syndrome (MAS) is common among newborn children but its mechanism is unclear. The syndrome is known to produce a strong inflammatory reaction in the lungs resulting in massive cell death. In this work we studied lung cell death by apoptosis after meconium aspiration in forty two-week-old rabbit pups. Analyzing lung samples by ISEL-DNA end labeling demonstrated the specific spread of apoptotic bodies throughout the lungs. These bodies were shrunken and smaller in size compared to normal cells and many of them were lacking cell membranes. About 70% of all apoptotic bodies were found among the airway epithelium cell eight hours after meconium instillation. In comparison, among lung alveolar cells, only about 20% cells were apoptotic in the same animals. In meconium-treated lungs and A549 cells, a significant increase of angiotensinogen mRNA and Caspase-3 expression were observed. The pretreatment of cells with Caspase-3 inhibitor ZVAD-fmk significantly inhibited meconium-induced lung cell death by apoptosis. These findings demonstrate the apoptotic process in meconium-instilled lungs or A549 cells in culture. Our results show lung airway epithelial and A549 cell apoptosis after meconium instillation. We suggest that studies of lung airway epithelial cell death are essential to understanding the pathophysiology of MAS and may present a key point in future therapeutic applications.

Lavage administration of dilute surfactant in a piglet model of meconium aspiration

Maldistribution of exogenous surfactant may preclude any clinical response in acute lung injury associated with surfactant dysfunction. Our previous studies have shown the effectiveness of surfactant lavage after homogenous lung injury. The present study utilizes a histologically confirmed non-homogeneous lung injury model induced by saline lung-lavage followed by meconium injected into a mainstem bronchus. Piglets were then treated with Infasurf or Exosurf by lavage (I-LAVAGE, n = 7; E-LAVAGE, n = 5) or bolus (I-BOLUS, n = 8; E-BOLUS, n = 5), or went untreated (CONTROL, n = 4). Lavage administration utilized a dilute surfactant (35 ml/kg; 4 mg phospholipid/ml) instilled into the lung, followed by gravity drainage. The retained doses of the respective surfactant in the lavage and bolus groups were similar. Results showed that the surfactant distribution was more uniform in the lavage groups compared to the bolus groups. Significant and consistent increases in PaO2 were observed in the lavage groups compared to the bolus groups and the controls. PaO2 (mmHg) at 240 min posttreatment: I-LAVAGE = 297 +/- 54, E-LAVAGE = 280 +/- 57; I-BOLUS = 139 +/- 31; E-BOLUS = 152 +/- 29; C = 119 +/- 73 (mean +/- SEM). Other improved pulmonary function parameters favored lavage administration. We conclude that better surfactant distribution achieved by lavage administration can be more effective than bolus administration in this type of non-homogeneous lung injury.

Complement C5a is a key mediator of meconium-induced neutrophil activation

Meconium aspiration syndrome is a serious condition of the newborn characterized by pulmonary inflammation with substantial neutrophil infiltration. We recently showed that meconium is a potent activator of complement. The aim of the present study was to investigate a possible role for complement in meconium-induced neutrophil activation. Meconium was incubated in human whole blood anticoagulated with lepirudin, a specific thrombin inhibitor that does not affect complement activation. Complement activation was detected by measuring the terminal complement complex. Neutrophil oxidative burst and changes in CD11b and L-selectin expression were measured by flow cytometry. Complement was inhibited using the MAb 166-32 and 137-26, which block factor D and neutralize C5a, respectively. Meconium markedly activated the neutrophils, as revealed by up-regulation of CD11b, accentuation of L-selectin shedding, and induction of oxidative burst. Complement inhibition using the anti-factor D antibody completely (95-100%) blocked meconium-induced changes in CD11b and L-selectin expression, whereas oxidative burst was reduced by 60-70%. The anti-C5a antibody inhibited the neutrophil activation to the same extent as anti-factor D. The data suggest that complement activation is largely responsible for the neutrophil inflammatory responses induced by meconium in vitro and that C5a is a key mediator of this response.

Cardiopulmonary and inflammatory changes in adult rabbits with meconium aspiration

BACKGROUND

Pulmonary inflammation and vasoconstriction are important pathogenetic factors in neonatal meconium aspiration syndrome (MAS).

OBJECTIVES

Study was performed to evaluate cardiopulmonary and inflammatory changes in adult rabbits after meconium administration.

METHODS

Animals were anesthetized and ventilated with room air. Initial values of cardiopulmonary parameters were recorded and blood samples taken. Three animals were then sacrifice and used as controls. The others were administered saline (4 ml/kg, n = 4) or meconium (25 mg/ml, 4 ml/kg, n = 5) and were further ventilated with 100% oxygen. When respiratory failure developed, parameters were recorded and animals were ventilated for additional 5 hours. Rabbits were then sacrifice and lungs excised. Right lungs were dried to determine wet/dry weight ratio and left lungs were lavaged with saline. Differential leukocyte count in the blood and lavage fluid sediment, and total blood leukocyte count were evaluated.

RESULTS

Instillation of meconium significantly decreased lung compliance, ventilation efficiency index and gas exchange, and increased right-to-left pulmonary shunts in comparison with saline group. No significant differences between groups were observed in mean blood pressure, heart rate, and central venous pressure. Meconium caused higher fluid and polymorphonuclear accumulation in the lungs, linked with decreased neutrophil and increased eosinophil counts in the blood.

CONCLUSIONS

Adult rabbits may be used for experimental testing of drugs influencing lung inflammation and vasoconstriction in MAS (Tab. 1, Fig. 4, Ref. 16).

Postmortem findings in term neonates

Neonatal deaths in infants born at term are relatively rare in the USA, occurring in 0.9/1000 live births. Congenital malformations, perinatal asphyxia, infections and inborn errors of metabolism are the leading causes. Chromosomal malformation syndromes, congenital heart disease, pulmonary hypoplasia and severe neural tube defects comprise the majority of lethal malformations. Several skeletal dysplasias are lethal in the newborn infant. Group B Streptococcus still plays a major role in neonatal mortality while deaths due to other infectious agents have decreased. Hypoxic ischaemic encephalopathy is a significant cause of neonatal death. Inborn errors of metabolism have variable presentations but some, such as the fatty acid oxidation disorders, may present in neonates and cause sudden death.

Intratracheal albumin reduces interleukin-8 in tracheobronchial aspirates in piglets after meconium aspiration

Meconium aspiration induces pulmonary inflammation and reduces surfactant function. We hypothesized that albumin mixed with meconium attenuates pulmonary inflammation and improves surfactant function after meconium aspiration. We measured the concentration of free fatty acids (FFA) in the meconium (110 mg dry weight/mL) and added albumin to provide a molar FFA:albumin ratio of 1:1. Newborn piglets, 0-2 day of age, artificially ventilated and exposed to hypoxemia by ventilation with 8% O2, were randomized to group A receiving meconium (n = 12), or group B receiving meconium + albumin (n = 12), 3 ml/kg intratracheally. The animals were reoxygenated for 8 h. Reoxygenation was started when mean arterial blood pressure was < 20 mm Hg or base excess was < -20 mmol/L. During 8 h of reoxygenation the interleukin-8 concentrations in tracheobronchial aspirates increased 5-fold more in the meconium vs. the meconium + albumin groups (93 +/- 56 vs. 18 +/- 4 pg/mL, p < 0.005). There were no differences between the groups for tumor necrosis factor alpha in tracheobronchial aspirates, recruitment of inflammatory cells in the airspaces or surfactant function in bronchoalveolar lavage fluid. In conclusion, albumin significantly decreased interleukin-8 concentrations in tracheobronchial aspirates after meconium aspiration.

Angiotensin II receptor blockade inhibits pneumocyte apoptosis in experimental meconium aspiration

Lung tissue inflammation and apoptosis are implicated in the pathogenesis of meconium aspiration-induced lung injury in the newborn, but the mechanisms of these reactions are still poorly known. We investigated the time-dependent leukocyte influx and appearance of apoptosis, as well as the contribution of angiotensin (ANG) II receptor action on these processes in the meconium-induced lung injury. Experimental meconium aspiration was induced by intratracheal instillation of human meconium in 18 rats, and eight rats were further pretreated with an unspecific ANG II receptor inhibitor saralasin. Rats were ventilated with 60% oxygen for 1, 3, or 5 h, and the lungs were then studied histologically for tissue injury and with DNA nick-end labeling and electron microscopy for apoptotic cell death. Lung tissue myeloperoxidase activity and expression of angiotensinogen mRNA and endothelial monocyte-activating polypeptide (EMAP) II protein were also analyzed. The meconium-instilled lungs showed increasing neutrophil migration and histologic injury after the first hour, whereas the number of epithelial apoptotic cells was elevated from the control level throughout the study. Myeloperoxidase activity was high, and the angiotensinogen mRNA and EMAP II protein was up-regulated at 5 h after the meconium insult. Pretreatment with saralasin significantly prevented the increase in lung tissue myeloperoxidase activity, EMAP II, and lung epithelial apoptosis. The results suggest that pulmonary meconium insult rapidly results in epithelial apoptosis, before significant neutrophil sequestration into the lungs. Apoptotic cell death is further connected with ANG II receptor action in the meconium-contaminated lung tissue.

Ultrastructural changes in the lungs of neonatal rats intratracheally inoculated with meconium

Meconium aspiration syndrome has been for many years an important cause of neonatal respiratory distress in newborn babies and sporadically reported in animals. This investigation was designed to study the ultrastructural and morphometric changes in the lungs of neonatal rats following the intratracheal inoculation of meconium. Seven-day-old Fischer-344 rats (n = 24) were randomly allocated in two groups. One group was intratracheally inoculated with saline solution and the second group received homologous meconium. Neonates were euthanatized at 1, 3 and 7 postinoculation days (PID) and lungs were examined by light and electron microscopy. Saline solution did not induce any ultrastructural changes in the lung. In contrast, meconium induced deciliation, recruitment of neutrophils and pulmonary alveolar macrophages to the bronchoalveolar space, intravascular sequestration of neutrophils and aggregation of platelets at PID 1 and 3. Other ultrastructural changes at PID 1 and 3 included interstitial edema and escape of red cells and fibrin into the alveolar space and interstitium. Interstitial edema and sequestration of neutrophils were responsible for the significant increase in thickness of alveolar septa. At PID 7 there was hyperplasia and enlargement of type II pneumocytes as well as interstitial proliferation of mesenchymal cells with intra-alveolar fibrosis. It was concluded that intratracheal inoculation of meconium in neonatal rats induces acute ultrastructural changes followed by a reparative response.

Meconium induces only localized inflammatory lung injury in piglets

Neonatal meconium aspiration often produces severe respiratory distress due to an inflammatory pulmonary injury, but the extension of this damaging reaction to the noncontaminated lung regions is still uncertain. To investigate the presence of generalized pulmonary inflammatory response, 31 anesthetized and ventilated neonatal piglets (1-3 d) were studied. Meconium (n = 16) or saline (n = 15) was instilled unilaterally into the right lung, and analysis of the lung tissue or bronchoalveolar lavage (BAL) fluid from both lungs was performed after 12 h. Meconium increased the wet/dry weight ratio, histologic tissue injury score and tissue myeloperoxidase activity as well as BAL fluid total cell count in the contaminated lung. Tumor necrosis factor-alfa concentrations in BAL fluid did not however differ significantly. Furthermore, in the meconium-instilled lungs the tissue and lavage fluid catalytic activity of phospholipase A2 (PLA2) and tissue PLA2 group-I and group-II concentrations were significantly elevated. Although BAL fluid catalytic activity of PLA2 was moderately increased also in the meconium noninstilled lung, significant inflammatory injury in this lung was absent. The results thus indicate that meconium aspiration induces severe local inflammation and lung injury, but significant generalized pulmonary inflammatory damage in the pathogenesis of meconium aspiration syndrome is unlikely.

The effects of prednisolone and serum malondialdehyde levels in puppies with experimentally induced meconium aspiration syndrome

The aim of this study was to investigate the effect of different doses of prednisolone in puppies experimentally induced with meconium aspiration syndrome (MAS). Meconium was collected from human babies in the first day of life and was released into the trachea of 11 newborn puppies to induce MAS. Puppies were treated with 2 mg/kg prednisolone (standard dose), 30 mg/kg prednisolone (megadose) or 0.9% saline, all administered intravenously. The study ended 20 h after meconium aspiration and the lungs were then scored for histopathology. Animals not treated with prednisolone deteriorated after 8 h while respiration rate, oxygenation, pH and partial pressure of carbon dioxide values were better in the prednisolone-treated groups. Histopathology scores were better in the treatment groups compared with the control group, with megadose giving the best result. At the end of the study, serum malondialdehyde levels were significantly higher in the megadose prednisolone group compared with the other two groups. In conclusion, we determined that prednisolone reduced physiological and histological changes in puppies with MAS and that a 30 mg/kg dose was more effective than 2 mg/kg.

Meconium aspiration produces airway hyperresponsiveness and eosinophilic inflammation in a murine model

Meconium aspiration syndrome is a cause of significant morbidity and mortality in the perinatal period and has been implicated in the pathogenesis of airway dysfunction. In this study, we developed a murine model to evaluate the effects of meconium aspiration on airway physiology and lung cellular responses. Under light anesthesia, BALB/c mice received a single intratracheal instillation of meconium or physiological saline. Respiratory mechanics were measured in unrestrained animals and expressed as percent increase in enhanced pause to increasing concentrations of methacholine (MCh). Furthermore, we assessed the changes in cells and cytokines into the bronchoalveolar lavage fluid (BALF). We found meconium aspiration produced increased airway responsiveness to MCh at 7 days. These functional changes were associated with lymphocytic/eosinophilic inflammation, goblet cell metaplasia, and increased concentrations of IL-5 and IL-13 in the BALF. Our findings suggest meconium aspiration leads to alterations of airway function, lung eosinophilia, goblet cell metaplasia, and cytokine imbalance, thus providing the first evidence of meconium-induced airway dysfunction in a mouse model.

Comparison of effects of perflubron and surfactant lung lavage on pulmonary gas exchange in a piglet model of meconium aspiration

In a piglet model of meconium aspiration we compared lavage with surfactant with that with perflubron (PFOB) and a control group. A human meconium suspension was instilled into piglets which were randomized in 3 (n = 6 each) groups. After lung injury, the control group was ventilated with high-frequency oscillatory ventilation (HFOV) without suctioning and lavage. A second group was lavaged with 10 ml/kg diluted surfactant, a third with 10 ml/kg pre-oxygenated PFOB. Thereafter, the animals of both groups were ventilated with HFOV. After lung injury by instillation of meconium, no further improvement in oxygenation was possible in animals of the control group and 3 piglets died during the ventilation. The subjects of the surfactant group improved promptly, and at the end of the study the arterial pO(2) was significantly better than immediately after injury as compared with the other groups. Lavage with PFOB had intermediate effects in gas exchange and oxygenation compared to surfactant lavage. No differences were observed in arterial blood pressure and heart rate as well as in histological lung injury score between all groups. Lavage with exogenous surfactant as well as with PFOB improve pulmonary gas exchange in a piglet model of meconium aspiration.

Transoral intratracheal inoculation method for use with neonatal rats

BACKGROUND AND PURPOSE

Studying the effects of toxic and infective compounds on the respiratory system requires a reliable method for delivering inoculum into the distal region of the lung. Although transoral intratracheal inoculation methods have been well documented for adult rats, to the authors' knowledge, a reliable method has not been validated for neonatal rats. The purpose of the study reported here was to develop a simple method for transoral inoculation in rat neonates.

METHODS

Seven-day-old Fischer 344 rats were anesthetized with halothane, and a spinal needle was inserted in the tracheal lumen, by use of illumination and a modified otoscope. Meconium was injected into the lungs as a marker, and the neonates were kept under close observation. After euthanasia at 24 h, lungs were removed and fixed in formalin, and the microscopic distribution of the inoculum was assessed in the left, right cranial, middle, median, and caudal lung lobes.

RESULTS

Microscopic examination of lungs indicated that intratracheal inoculation was achieved in 100% of neonatal lungs and the inoculum was consistently distributed in the alveoli of all pulmonary lobes. Important complications or mortality were not observed in the neonates.

CONCLUSIONS

Intratracheal inoculation of neonatal rats is possible by use of a modified otoscope for transoral illumination. This technique is simple and reproducible and ensures, without complications, widespread distribution of inoculum in the lungs of neonatal rats.

Surfactant and surfactant inhibitors in meconium aspiration syndrome

Surfactant indices and inhibitors were measured in lung lavage fluid from 8 infants with meconium aspiration syndrome (MAS) who were receiving mechanical ventilation and 11 healthy control subjects. Surfactant phospholipid and surfactant protein A content in MAS was not different from that of control subjects, but concentrations of total protein, albumin, and membrane-derived phospholipid were elevated. All infants with MAS had hemorrhagic pulmonary edema. These findings reinforce the notion of MAS as a toxic pneumonitis with epithelial disruption and proteinaceous exudation.

Surfactant tracheobronchial lavage for the management of a rabbit model of meconium aspiration syndrome

We evaluated the effect of tracheobronchial lavage with diluted surfactant solution (bovine lipid extract surfactant, bLES) in a rabbit model of meconium aspiration. All animals were anaesthetized, tracheotomized and given 3-4 ml/kg of 25% slurry of human meconium into the endotracheal tube and mechanically ventilated for 1 h. The animals were then randomly assigned to surfactant lavage (n = 12) with 15 ml/kg of diluted surfactant at a concentration of 5.4 mg phospholipid/ml administered in aliquots of 2 ml; or simple endotracheal suction (control n = 12) when the oxygenation index (OI) was >/=15. Changes in the arterial blood gases and the histomorphological and radiological appearances of the lungs were recorded. The OI and arterial/alveolar oxygen tension (a/A PO2) of the surfactant lavage group improved significantly at 5 min post-treatment, and these improvements were observed throughout the ensuing 4 h of ventilation. There was significantly more solid content recovered by surfactant lavage compared with the control group (p = 0.0001). Radiologically, the post-treatment air space opacification scores of the lavage group were significantly lower compared with the control (p = 0.002). The post-treatment radiographs of the lavage-treated rabbits were rated by the radiologist, who was blinded to the treatment groups, as much improved in 5 and improved in 4, whereas the control rabbits were rated as much worse in 3 and worse in 4. Histological examination showed the lungs of the lavaged rabbits had significantly more normal airway (p < 0.0001), more fields showing completely normal airspace (p = 0.0001) and less fields showing severe overdistension with meconium (p = 0.0005). We concluded that lavage with diluted surfactant solution effectively washed out the meconium, improved gases exchanges, and improved the histological and radiological appearances in the rabbit model of MAS.

Polymer-surfactant treatment of meconium-induced acute lung injury

Substances (for example, serum proteins or meconium) that interfere with the activity of pulmonary surfactant in vitro may also be important in the pathogenesis or progression of acute lung injury. Addition of polymers such as dextran or polyethylene glycol (PEG) to surfactants prevents and reverses surfactant inactivation. The purpose of this study was to find out whether surfactant/polymer mixtures are more effective for treating one form of acute lung injury than is surfactant alone. Acute lung injury in adult rats was created by tracheal instillation of human meconium. Injured animals, which were anesthetized, paralyzed, and ventilated with 100% oxygen and not treated with surfactant mixtures, remained hypoxic and required high ventilator pressures to maintain Pa(CO(2)) in the normal range over the 3 h of the experiment. Uninjured animals maintained normal values for oxygen and compliance of the respiratory system. The greatest improvement in both oxygenation (178%) and compliance (42%) occurred in animals with lung injury that were treated with Survanta and PEG (versus untreated control animals; p < 0.01), whereas little improvement was found after treatment with Survanta alone. Similar results were found when postmortem pulmonary pressure-volume curves and histology were examined. We conclude that adding PEG to Survanta improves gas exchange, pulmonary mechanics, and histologic appearance of the lungs in a rat model of acute lung injury caused by meconium.

Chronic intrauterine meconium aspiration causes fetal lung infarcts, lung rupture, and meconium embolism

Three neonates with chronic intrauterine meconium aspiration are reported. All had distinctive subpleural plate-infarcts of the lungs caused by meconium-induced vasoconstriction of peripheral preacinar arteries. These vessels showed plexogenic arteriopathy with medionecrosis and obliterative hyaline sclerosis. Organized thrombi and systemic-pulmonary arterial anastomoses were numerous. The infarcts contained inspissated meconium with a granulomatous reaction. In one case, lung rupture occurred, causing meconiumthorax and meconium embolism to hilar lymphatics and lymph nodes; this suggests that particulate meconium may enter the circulation. This fetus had rubella and probable acute twin-twin transfusion following the intrauterine death of the co-twin. The cause of the hypoxia that led to intrauterine passage of meconium in the other cases is unknown. Meconium-stained amniotic fluid was noted in only one case.

Mouse ATF-2 null mutants display features of a severe type of meconium aspiration syndrome

Mouse null mutants of transcription factor ATF-2 were generated by the gene targeting method. They died shortly after birth and displayed symptoms of severe respiratory distress with lungs filled with meconium. These features are similar to those of a severe type of human meconium aspiration syndrome. The increased expression of the hypoxia inducible genes suggests that hypoxia occurs in the mutant embryos and that it may lead to strong gasping respiration with consequent aspiration of the amniotic fluid containing meconium. A reduced number of cytotrophoblast cells in the mutant placenta was found and may be responsible for an insufficient supply of oxygen prior to birth. Using the cDNA subtraction and microarray-based expression monitoring method, the expression level of the platelet-derived growth factor receptor alpha gene, which plays an important role in the proliferation of trophoblasts, was found to be low in the cytotrophoblasts of the mutant placenta. In addition, ATF-2 can trans-activate the PDGF receptor alpha gene promoter in the co-transfection assay. These results indicate the important role of ATF-2 in the formation of the placenta and the relationship between placental anomalies and neonatal respiratory distress. The ATF-2 null mutants should enhance our understanding of the mechanism of severe neonatal respiratory distress.

Combined effects of high-frequency ventilation and surfactant treatment in experimental meconium aspiration syndrome

BACKGROUND

Deterioration of lung function in meconium aspiration syndrome may in part be due to inactivation of endogenous surfactant. We evaluated the efficacy of high-frequency ventilation (HFV) and the combination of HFV and surfactant therapy in the management of respiratory failure induced by experimental meconium aspiration in adult rats.

METHODS

Animals were anesthetized and tracheotomized, and received via the tracheal cannula a suspension of human meconium (25 mg/ml, dose 4 or 5 ml/kg). After 30 min of conventional ventilation (CV) with 100% oxygen, animals were in respiratory failure as indicated by a decrease in lung-thorax compliance of > or = 30% and PaO2 < 10 kPa. They were then ventilated for an additional 3 h with either CV (frequency 40/min, inspiration time 50%) or HFV (frequency 15 Hz, inspiration time 50%) using comparable mean airway pressures (about 20 cmH2O) and variable FiO2. Subgroups of animals were treated with Curosurf (80 mg/ml, dose 200 mg/kg) 30 min after meconium aspiration; no additional material was instilled in controls.

RESULTS

From 30 min onwards, values for PaO2/FiO2 were significantly higher in animals ventilated with HFV without receiving surfactant than in control animals subjected to CV alone (at 120 min; 18 +/- 7.3 vs. 7.4 +/- 0.8 kPa, P < 0.05). Additional improvement in oxygenation was seen in HFV-treated animals receiving Curosurf (at 120 min: 39 +/- 16 kPa: P vs. HFV alone < 0.01). Relative lung volumes at a deflation pressure of 10 cmH2O, expressed as percent of maximum volume, were larger in animals ventilated with HFV than in those undergoing CV (41 +/- 12 vs. 33 +/- 10%; P < 0.05), and were further increased in the groups of animals treated with surfactant and ventilated with HFV (55 +/- 9.9%; P vs. animals ventilated with HFV not receiving surfactant < 0.01) or CV (49 +/- 9.6%; P vs. animals ventilated with CV without receiving surfactant < 0.05). Hyaline membranes, granulocytes in cytospin preparations from lung lavage fluid, and vascular-to-alveolar leak of albumin were less prominent in the HFV than in the CV group, particularly in animals treated with surfactant.

CONCLUSION

Our data indicate that HFV, especially in combination with surfactant therapy, may be superior to CV for treatment of respiratory failure in this animal model of meconium aspiration syndrome.

Liquid ventilation for treatment of meconium aspiration syndrome in a piglet model

We tested the hypothesis that liquid ventilation (LV) with perfluorocarbon (PFC) can remove aspirated meconium and improve lung function in experimental meconium aspiration syndrome (MAS). PFC (FC-77) was used as the medium in LV. Sixteen piglets were divided into control and LV groups (8 animals/group). All animals received slurry meconium (20% in normal saline) via endotracheal instillation at baseline. Thirty minutes later, the LV group received 15 cycles of LV. Pulmonary mechanics, arterial blood gases, and hemodynamic values were recorded at baseline, and 30, 60, 120, 180, and 240 minutes after meconium instillation. Chest radiographs and lung sections were taken and scored at the end of the study. The percentage of meconium cleared by LV was calculated as the ratio of the dry weight of washings to that of meconium instilled, multiplied by 100. The procedure was tolerated well by the animals. LV cleared 25% +/- 7% of the instilled meconium. Tidal volume (9.5 +/- 2.0 vs 7.1 +/- 0.8 mL/kg, p = 0.012), respiratory system compliance (2.32 +/- 0.60 vs 1.60 +/- 0.24 mL/cmH2O, p = 0.01), PaO2 (65 +/- 7 torr vs 55 +/- 6 torr, p = 0.0067), and arterial to alveolar oxygen ratio (0.14 +/- 0.01 vs 0.12 +/- 0.01, p = 0.0077) were improved in the LV group at 60 minutes after meconium instillation compared with those of the control group. The scores of exudative debris (1.7 +/- 0.3 vs 2.1 +/- 0.2) and visible meconium (1.4 +/- 0.5 vs 2.1 +/- 0.5) were significantly lower in the LV group. In conclusion, short-term L.V with FC-77 can partially remove aspirated meconium from the lungs and improve pulmonary function transiently.

Meconium aspiration syndrome complicated by massive intravascular thrombosis

Fetal aspiration of meconium in amniotic fluid during fetal distress by newborn infants can induce the meconium aspiration syndrome (MAS), a form of neonatal respiratory distress. Should this event occur, admission to a Neonatal Intensive Care Unit and vigorous airway management and monitoring are required. We present a term gestation resulting in MAS complicated by a massive intravascular thrombosis. Despite airway management considered appropriate, the infant developed respiratory distress a few hours after birth and died 5 days later. Postmortem examination showed a diffuse alveolar damage of the lungs with alveoli filled with meconium and amniotic epithelial cells as well as disseminated thrombi in the pulmonary vascular tree, portal system, suprahepatic veins, and peripheral arterial vascular tree.

Perfluorocarbon broncho-alveolar lavage and liquid ventilation versus saline broncho-alveolar lavage in adult guinea pig experimental model of meconium inhalation

OBJECTIVE

This study compares perfluorocarbon broncho-alveolar lavage (PFC-BAL) with isotonic saline broncho-alveolar lavage (saline-BAL) in an experimental model of meconium aspiration in adult guinea pigs.

DESIGN

Prospective controlled experimental study.

PATIENTS AND METHODS

Ten male guinea pigs were given 1 ml of human meconium, diluted to 10% in isotonic saline, via tracheostomy and then artificially ventilated. After stabilization, five animals (control group) underwent BAL with 10 ml/ kg isotonic saline solution. After bronchial suctioning, a further BAL with 2 ml/kg saline was performed. The other five animals (study group) underwent BAL with 100 ml/kg of PFC (RIMAR 101). Bronchosuction was effected at 5 min and then a BAL with PFC 2 ml/kg was performed. Both groups received conventional mechanical ventilation during the lavage procedures. Within 20 min all the saline-BAL treated animals died, whereas the PFC-BAL treated animals survived and were then treated with total liquid ventilation (TLV) by gravity.

MEASUREMENTS AND RESULTS

After meconium inhalation in both groups, a large alveolar-arterial oxygen difference, hypercarbia, severe acidosis and tachycardia were noticed. In PFC treated animals, an improvement in blood gases was noted and acid-base balance remained stable compared to saline-BAL treated animals. No haemodynamic change was observed during or after PFC-BAL, while during saline-BAL there was evidence of bradycardia, hypotension and respiratory failure, which led to the death of the animals. The histological lung sections in the PFC-BAL group showed evidence of normal alveolar expansion with a minimal presence of meconium debris in the small bronchioles. In saline-BAL treated animals, the lung structure appeared severely compromised with the presence of meconium in bronchioles and alveoli, intra-alveolar oedema and haemorrhagic areas.

CONCLUSIONS

This study confirms the detrimental effects of meconium aspiration and the impairment of lung function following saline-BAL. By contrast, PFC-BAL and TLV by gravity seemed to prevent absorption of meconium, facilitate its removal, improve gas exchange and reduce lung barotrauma.

Exudative lung injury is associated with decreased levels of surfactant proteins in a rat model of meconium aspiration

OBJECTIVE

Meconium aspiration syndrome remains a common cause of respiratory failure in neonates. The acute effects of meconium aspiration are inactivation of lung surfactant in vivo and in vitro. This study investigated the delayed effects of meconium on alveolar surfactant phospholipids and protein levels in spontaneously breathing animals.

METHODS

Twenty-two adult rats were given 4.3 mg of dry weight human meconium after endotracheal intubation. Rats were briefly mechanically ventilated in room air, extubated, then killed after 16 (n = 6), 24 (n = 6), 48 (n = 6), and 72 hours (n = 4). Control animals received the same volume of normal saline (n = 7) or no meconium (n = 7). Bronchoalveolar lavage and tissue specimens were evaluated for inflammatory cells, total proteins, surfactant phospholipids, and surfactant proteins.

RESULTS

Meconium caused exudative lung injury that was reflected in increased cell counts and proteins in alveolar lavage fluid. The peak injury occurred at 16 hours after instillation, whereas recovery occurred by 72 hours. Although total lavage fluid phospholipids did not change over time, phospholipid and dipalmitoyl phosphatidylcholine in large aggregates tended to decrease at 24 hours. Western blot analysis demonstrated time-dependent qualitative decreases in surfactant proteins A and B (SP-A, SP-B) in meconium-instilled animals compared with the controls. ELISA for SP-B confirmed the Western blot findings with total SP-B in large aggregate decreasing from 25 +/- 4 microg in controls to 6.6 +/- 0.8 microg at 24 hours of injury.

CONCLUSIONS

Our study suggests that the exudative lung injury with meconium instillation is associated with decreased levels of SP-A and SP-B in the large aggregate fraction of lung surfactant. We speculate that decreased secretion and/or increased degradation accounts for lower levels of SP-B in bronchoalveolar lavage fluid.

[Analysis of the causes of neonatal deaths at term in pregnancy induced hypertension patients]

OBJECTIVE

To study the neonatal developmental status, its causes of death and their possible correlation in women complicated with pregnancy induced hypertension (PIH).

METHODS

46 autopsies of neonatal death at term with PIH and their clinical data were collected. The developmental status was evaluated by body weight, body length, and the weights of lungs, kidneys, liver and brain. The causes of death were reviewed by the clinicopathologic findings.

RESULTS

The neonatal development features for mild PIH in term pregnancy approached to the normal levels of 37 to 38 gestation weeks. In the infants with moderate and severe PIH, the body weights, the weights of lungs and liver were significantly decreased in comparison with those of the mild PIH, respectively (P < 0.05), while the weights of kidneys and brain were not significantly decreased. The causes of death showed that pulmonary hypoplasia accounted for 23.9%, primary pulmonary atelectasis 10.9%, pulmonary hyaline membrane disease 21.7%, massive pulmonary hemorrhage 13.0%, the meconium aspiration 19.6% and others 10.9%. There was no difference in sex among the dead infants.

CONCLUSIONS

The PIH syndrome had retarded the process of fetal growth and development, and associated with the severity of PIH, mostly involving the lung and the liver. The pulmonary hypoplasia and immaturity were the primary causes for neonatal death in PIH women.

Fatal meconium aspiration in spite of appropriate perinatal airway management: pulmonary and placental evidence of prenatal disease

OBJECTIVE

Our purpose was to summarize eight cases of fatal meconium aspiration syndrome where pathologic review showed evidence of chronic prenatal disease and to compare these findings with those of a group of control infants and fetuses who died of other causes.

STUDY DESIGN

A 15-year retrospective chart review identified the infants who died of meconium aspiration within 48 hours of life and who also had autopsies performed. Neonatal pulmonary and available placental pathologic findings are described from these study infants and are compared with published norms and with autopsy results from a group of control infants and fetuses.

RESULTS

Seven of the eight study infants underwent suctioning of the trachea immediately after birth. In all eight cases the neonatal lungs demonstrated histologic evidence of significant hypoxic changes of a chronic nature with onset before birth. The available placentas showed variable but significant abnormalities that support a case for subacute or chronic in utero compromise.

CONCLUSIONS

As in other reports, there is evidence that meconium aspiration may be a prenatal rather than a postnatal disease. However, this is the first study that presents evidence on the basis of both pulmonary and placental pathologic findings and reinforces the importance of placental examinations in complicated pregnancies.

Exogenous surfactant improves ventilation efficiency and alveolar expansion in rats with meconium aspiration

The pathogenesis of neonatal meconium aspiration syndrome (MAS) may involve inactivation of endogenous surfactant, and data from clinical pilot studies indicate that treatment with exogenous surfactant may alleviate respiratory failure in babies with MAS. We studied ventilation efficiency after treatment with a modified porcine surfactant in experimental meconium aspiration. Adult rats were anesthetized and tracheotomized, and received via a tracheal cannula from 4 to 6 ml/kg body weight of a saline suspension of human meconium (25 mg [dry weight]/ml). After 30 min of ventilation with 100% oxygen, the animals were in respiratory failure, with dynamic lung-thorax compliance < 0.5 ml/cm H2O/kg and PaO2 < 8 kPa (60 mm Hg). Animals were then allocated to: (1) immediate treatment with surfactant (200 mg/kg); (2) treatment with surfactant (200 mg/kg 3 h later; or (3) a control group not receiving surfactant. All animals were ventilated for 6 h with variable FIO2 and peak inspiratory/positive end-expiratory pressure (PIP/PEEP). In the control group, six of 12 animals died of respiratory failure with hypoxemia and acidosis despite ventilation with 100% oxygen and high mean airway pressure (> 20 cm H2O). The lungs of all animals in this group showed severe atelectasis, influx of neutrophils, edema, and hyaline membranes. In contrast, animals allocated to immediate or late surfactant treatment had lower mortality (one of seven and two of eight, respectively), a reduction of oxygen supply by 30%, and a decrease in mean airway pressure of 3 to 4 cm H2O. This was associated with a > 50% increase in static lung volume at 40 cm H2O inflation and 10 cm H2O deflation pressure and improved alveolar expansion in histologic sections. Hyaline membranes tended to be less prominent in surfactant-treated animals than in controls. We conclude that both early and late treatment with surfactant is effective in this animal model of MAS.

Liquid assisted ventilation: an alternative ventilatory strategy for acute meconium aspiration injury

Evidence of surfactant inactivation by meconium has led to the use of exogenous surfactant therapy in the management of meconium aspiration syndrome (MAS). Liquid assisted ventilation has been shown to improve the cardiopulmonary function in lungs with high surface tension. We compared exogenous surfactant therapy with liquid assisted ventilation in the management of experimental acute meconium aspiration injury. Thirty-two newborn lambs were ventilated at peak inspiratory pressures of 13-16 cm H2O, positive end expiratory pressure of 3-4 cm H2O, fractional inspired oxygen concentration (FiO2) of 1.0, and a respiratory frequency range between 30 and 35 breaths/min. Baseline arterial blood gases, pulmonary function, and arterial blood pressure measurements were taken. All lambs were given 2-3 ml/kg of an unfiltered 25% meconium solution. Lambs were then randomized into either gas-ventilated meconium control, or one of three treatment groups: 1) surfactant; 2) partial liquid ventilation (PLV); or 3) total liquid ventilation (TLV) for 4 hours after meconium injury. All treated groups demonstrated a significant increase in arterial oxygenation (P < 0.05); surfactant and PLV-treated lambs demonstrated significantly decreased arterial PCO2 (P < 0.05). Compliance in all groups increased compared with injury values; compliance of the TLV group increased more than in all other treatment groups (P < 0.05). In addition, lung histology of the TLV group demonstrated clear, intact alveolar epithelium and homogeneously expanded alveoli, while no such improvement was evident in the other groups. These data suggest roles for both exogenous surfactant therapy and liquid assisted ventilation techniques in the management of MAS.

Patterns and implications of MR contrast enhancement in perinatal asphyxia: a preliminary report

PURPOSE

To determine the presence and location of MR contrast enhancement in infants with perinatal asphyxia and to evaluate the utility of enhancement in assessing extent of brain damage.

METHODS

Precontrast and postcontrast MR examinations within the first 10 days of life were evaluated in 10 infants with suspected hypoxic-ischemic birth injury. Findings were correlated with clinical birth history and short-term neurologic follow-up.

RESULTS

All four infants with MR signal abnormalities and contrast enhancement in the basal ganglia and brain stem had early seizures and profound neurologic deficits at early follow-up. Two infants had abnormal scans but no contrast enhancement; one with MR signal abnormality within the basal ganglia is neurologically healthy at 10-month follow-up, whereas the other, in status epilepticus at the time of imaging at age 2 days, died. Two infants with minimal parasagittal subcortical white matter enhancement had no early seizure activity and only mild developmental delay at early follow-up. Two infants with normal precontrast and postcontrast MR had no early seizures and remain healthy at early follow-up, despite initial clinical parameters similar to more severely injured infants.

CONCLUSION

Although the number of patients is small, our results indicate that the presence of contrast enhancement in asphyxiated neonates may indicate more severe brain damage and, hence, a poorer prognosis.

Exogenous surfactant improves lung compliance and oxygenation in adult rats with meconium aspiration

We studied the effects of exogenous surfactant on lung function and morphology in an adult rat model of severe meconium aspiration syndrome. Animals ventilated with 100% oxygen received 4-6 ml of human meconium (25 mg/ml) intratracheally. After 30 min, lung-thorax compliance had decreased by > 30% and arterial PO2 was < 10 kPa. Animals were then treated with no material (MECO group), 0.9% NaCl (MECO-saline group), natural porcine surfactant (NPS group) at a dose of 100 mg/kg, or modified porcine surfactant at a dose of either 100 (MPS100 group) or 200 mg/kg (MPS200 group) and were ventilated for another 180 min. Immediate and sustained improvement of arterial PO2 and compliance was observed in the MPS200 group, whereas the MPS100 and NPS groups showed less pronounced effects. There was a significant improvement of quasi-static lung volumes at maximum insufflation pressure and during deflation in the MPS200, MPS100, and NPS groups. Recordings with Wilhelmy balance showed that minimum surface tension of bronchoalveolar lavage fluid from animals receiving either type or dose of surfactant was significantly lower than in the MECO and MECO-saline groups. Meconium aspiration induced diffuse and prominent atelectasis, intra-alveolar edema, and hyaline membranes. These morphological abnormalities were reversed by exogenous surfactant, especially by the high-dose regimen.

Surfactant therapy and high-frequency jet ventilation in the management of a piglet model of the meconium aspiration syndrome

In vitro data have shown a concentration-dependent inhibition of surfactant by meconium, while anecdotal reports demonstrate improved oxygenation after surfactant replacement in babies with meconium aspiration syndrome, particularly in conjunction with high-frequency jet ventilation. We randomized 70 newborn piglets to either conventional or high-frequency jet ventilation, followed by insufflation of 3 mL/kg of a 33% meconium solution. Each group was further randomized to one of five surfactant therapies: 1) control, 2) 4 mL/kg Survanta, 3) 8 mL/kg Survanta, 4) 5 mL/kg Exosurf, or 5) 10 mL/kg Exosurf. We followed arterial blood gases and ventilator requirements over 6 h of ventilation. Aspirates of airway fluids were obtained for surface tension measurements, as well as total protein and phospholipid concentrations. Using a previously established scoring system, a pathologist blinded to treatment evaluated four sections of lung per animal for histologic changes of meconium aspiration syndrome. There were no differences noted between groups in any physiologic parameter measured (mean airway pressure, arterial partial pressure of oxygen/alveolar partial pressure of oxygen ratio, etc.) during the 6 h of ventilation. Airway fluid aspirate total protein concentrations increased significantly after meconium instillation (4- to 5-fold, p < 0.007) and remained elevated in spite of surfactant therapy. There was an initial decline in airway phospholipid concentrations after meconium instillation followed by a rise to levels equal to or greater than premeconium levels. Surface tension measurements increased in all groups after meconium insufflation (p < 0.012) and did not decline thereafter, despite standard and twice-standard surfactant doses of both types.(ABSTRACT TRUNCATED AT 250 WORDS)

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

OBJECTIVE

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

STUDY DESIGN

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

RESULTS

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

CONCLUSION

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

Improved oxygenation with exogenous surfactant administration in experimental meconium aspiration syndrome

Fifteen adult New Zealand white rabbits were used to determine if exogenous surfactant immediately improves oxygenation in experimental meconium aspiration syndrome (MAS). They were ventilated with 100% O2 before insufflating 3 mL/kg of 40% filtered meconium. Arterial blood gases, dynamic lung compliance (CLdyn) and resistance (RL) were monitored for 2 hours before and 1 hour after the intratracheal administration of calf lung surfactant extract or air placebo. The arterial/alveolar O2 tension ratio [P (a/A)O2] increased 133% within 1 hour of surfactant therapy but CLdyn did not change. The increase of RL was comparable in the surfactant and control groups after meconium instillation. A further increase of 44% in RL occurred after surfactant administration with no change in the controls. Qualitative histologic analysis confirmed the presence of alveolar meconium as well as inflammation and atelectasis. Persistently elevated RL suggested airway obstruction in both groups throughout the study. Most likely no increase in CLdyn occurred with surfactant administration or it could not be detected because it was measured only with ventilator-induced breaths and ventilator settings were held constant. In the face of airway obstruction CLdyn is an inadequate reflection of pulmonary elasticity. We conclude that exogenous surfactant therapy improves oxygenation in this model of MAS. Further studies are needed to understand the mechanism of this improvement.

Meconium aspiration syndrome: physiological and inflammatory changes in a newborn piglet model

In order to evaluate further the physiological and inflammatory changes of meconium aspiration syndrome (MAS), 25 newborn piglets (1-2 days old, 1.5 +/- 0.4 kg) were studied. Piglets were briefly ventilated with 100% oxygen and then received an intratracheal bolus of 3 mL/kg of a 20% suspension of human meconium. They were then further ventilated, keeping PaCO2 at approximately 40 torr and PaCO2 at 70 torr during 4, 12, 24, and 48 h studies. Pulmonary function studies and tracheal aspirates were obtained at time zero and serially throughout the study. Bronchoalveolar lavage was performed at the end of the study to examine endogenous surfactant function. Control piglets received 3 mL/kg of intratracheal saline and were then ventilated for 48 h at an inspired oxygen concentration and mean airway pressure matched to the meconium treated group (to control for the effects of hyperoxia and barotrauma on the lung). MAS caused acute decreases in gas exchange and dynamic lung compliance, which returned toward baseline by 48 h (P < 0.001, ANOVA). Tracheal aspirate absolute neutrophil count, neutrophil chemotactic activity, albumin, and total protein concentrations also increased significantly over time (P < 0.001). Endogenous surfactant function appeared to be significantly inhibited by the meconium. All variables of lung injury were significantly higher in the meconium group compared to the saline control group over the 48 h study. Newborn piglets provide a clinically relevant model of MAS, demonstrating physiological and inflammatory changes with apparent alterations in endogenous surfactant function. Effective therapies for MAS may require interventions directed at all of these components of lung injury.

Surfactant inhibition in experimental meconium aspiration

Human meconium components were separated into a water-methanol soluble phase containing mainly proteins and bilirubin and a chloroform soluble phase containing free fatty acids, triglycerides and cholesterol. Various amounts of original meconium, the water-methanol soluble fraction or the chloroform soluble fraction were added to standard suspensions of porcine surfactant (Curosurf). In a pulsating-bubble or Wilhelmy-balance system, meconium and its subfractions inhibited surfactant activity, but the chloroform soluble fraction had the highest specific inhibitory activity. Original meconium in saline (130 or 65 mg/ml) was instilled into the airways of ventilated near-term newborn rabbits (dose 6 ml/kg). Lung-thorax compliance was reduced by 38% in animals aspirating the higher dose and by 27% in the low-dose group. Histological sections showed intra-alveolar accumulation of fine meconium particles in experimental animals, but no plugging of larger airways. We conclude that respiratory failure from meconium aspiration may be mediated, in part, by inactivation of surfactant.

Surfactant improves lung function and morphology in newborn rabbits with meconium aspiration

Nearly mature newborn rabbits (gestational age 29.5 days) were tracheotomized at birth and received, via the tracheal cannula, 6 ml/kg body weight of a filtered saline suspension of human meconium, 65 or 130 mg/ml. Animals were kept in body plethysmographs and ventilated for 60 min with standardized tidal volume (8-10 ml/kg). Aspiration of meconium caused, in both groups, a statistically significant reduction in lung-thorax compliance, elevated PCO2 in heart blood and reduced alveolar volume density (VV) in histological sections. Both groups responded to treatment with exogenous surfactant (Curosurf, 200 mg/kg) with a moderate, statistically significant improvement in lung-thorax compliance, PCO2 and alveolar VV. Our data indicate that respiratory failure after neonatal meconium aspiration may be influenced favorably by treatment with exogenous surfactant.

Management of a piglet model of the meconium aspiration syndrome with high-frequency or conventional ventilation

OBJECTIVE

To assess the usefulness of three methods of high-frequency ventilation in the early management of a piglet model of the meconium aspiration syndrome.

DESIGN

Randomized, block design.

SETTING

Animal research facility.

SUBJECTS

Fifty-six mixed-breed newborn piglets aged 1 to 4 days and weighing 1.8 to 2.7 kg.

INTERVENTIONS

After instillation of a 2.2-mL/kg solution of 25% meconium, 56 piglets were randomized to receive treatment with (1) a conventional positive-pressure infant ventilator, (2) the Bunnell Life Pulse high-frequency jet ventilator, (3) the Bird model VDR high-frequency flow interruptor, or (4) the Infant Star high-frequency flow interruptor. We adjusted ventilator settings to maintain partial pressures of arterial oxygen (PaO2) of 80 to 120 cm H2O and partial pressures of arterial carbon dioxide (PaCO2) of 30 to 50 cm H2O during the 6 hours of ventilation.

MEASUREMENTS AND MAIN RESULTS

We compared pulmonary histologic alterations and four physiologic parameters: (1) mean airway pressure, (2) PaCO2, (3) ratio of PaO2 to partial alveolar oxygen pressure (PAO2), and (4) oxygenation index ([(fraction of inspired oxygen)(mean airway pressure)(100)]/PaO2). The two measures of oxygenation were similar for all four devices except at 4 hours, when the PaO2/PAO2 ratio on positive-pressure ventilation was significantly higher than that on high-frequency jet ventilation (P = .008). The histologic changes on positive-pressure ventilation (atelectasis, inflammation, presence of meconium, and exudative debris) were significantly worse than those on high-frequency jet ventilation or flow interruption (P < .0001).

CONCLUSIONS

The finding of less severe pathologic alterations with various types of high-frequency ventilators justifies further investigations into the management of the meconium aspiration syndrome with these devices.