Asphyxia aggravates systemic hypotension but not pulmonary hypertension in piglets with meconium aspiration

Comorbidity associated to Ascaris suum infection during pulmonary fibrosis exacerbates chronic lung and liver inflammation and dysfunction but not affect the parasite cycle in mice

Ascariasis is considered the most neglected tropical disease, and is a major problem for the public health system. However, idiopathic pulmonary fibrosis (IPF) is a result of chronic extracellular deposition of matrix in the pulmonary parenchyma, and thickening of the alveolar septa, which reduces alveolar gas exchange. Considering the high rates of ascariasis and pulmonary fibrosis, we believe that these two diseases may co-exist and possibly lead to comorbidities. We therefore investigated the mechanisms involved in comorbidity of Ascaris suum (A. suum) infection, which could interfere with the progression of pulmonary fibrosis. In addition, we evaluated whether a previous lung fibrosis could interfere with the pulmonary cycle of A. suum in mice. The most important findings related to comorbidity in which A. suum infection exacerbated pulmonary and liver injury, inflammation and dysfunction, but did not promote excessive fibrosis in mice during the investigated comorbidity period. Interestingly, we found that pulmonary fibrosis did not alter the parasite cycle that transmigrated preferentially through preserved but not fibrotic areas of the lungs. Collectively, our results demonstrate that A. suum infection leads to comorbidity, and contributes to the aggravation of pulmonary dysfunction during pulmonary fibrosis, which also leads to significant liver injury and inflammation, without changing the A. suum cycle in the lungs.

Ascariasis is considered a major problem for the public health system, which has an estimated 800 million infected people worldwide. It occurs in the United States, Africa, Asia, and Latin America, and is generally associated with poverty and precarious health conditions. Pulmonary fibrosis affects 14–63 people per 100,000 habitants/year, and is characterized by collagen deposition and alveolar wall thickening. The comorbidities caused by infections are commonly associated with pulmonary fibrosis exacerbations, poor prognosis, and high mortality. Despite the comorbidities caused by helminth infections, which display a pulmonary parasitic cycle such as that of Ascaris, there is no evidence relating to pulmonary fibrosis progression, possibly because Ascariasis is considered a neglected disease. We evaluated the role of Ascaris during pulmonary fibrosis. We considered two simple questions: (1) Whether Ascaris infection could protect or aggravate fibrosis (comorbidities) and (2) whether pulmonary fibrosis could change the cycle of Ascaris as a result of increased alveolar thickening, larvae retention, and the limitation of influx into airways. We answered both questions as follows: (1) Ascaris infection exacerbates pulmonary and liver injury and inflammation, but not fibrosis; and (2) Pulmonary fibrosis did not alter the course of Ascaris cycle in lungs during transmigration into airways, because Ascaris preferentially seeks and penetrates into the lung areas, which are thought to be preserved, but not into fibrotic areas.

Optimal Chest Compression Rate and Compression to Ventilation Ratio in Delivery Room Resuscitation: Evidence from Newborn Piglets and Neonatal Manikins

Cardiopulmonary resuscitation (CPR) duration until return of spontaneous circulation (ROSC) influences survival and neurologic outcomes after delivery room (DR) CPR. High quality chest compressions (CC) improve cerebral and myocardial perfusion. Improved myocardial perfusion increases the likelihood of a faster ROSC. Thus, optimizing CC quality may improve outcomes both by preserving cerebral blood flow during CPR and by reducing the recovery time. CC quality is determined by rate, CC to ventilation (C:V) ratio, and applied force, which are influenced by the CC provider. Thus, provider performance should be taken into account. Neonatal resuscitation guidelines recommend a 3:1 C:V ratio. CCs should be delivered at a rate of 90/min synchronized with ventilations at a rate of 30/min to achieve a total of 120 events/min. Despite a lack of scientific evidence supporting this, the investigation of alternative CC interventions in human neonates is ethically challenging. Also, the infrequent occurrence of extensive CPR measures in the DR make randomized controlled trials difficult to perform. Thus, many biomechanical aspects of CC have been investigated in animal and manikin models. Despite mathematical and physiological rationales that higher rates and uninterrupted CC improve CPR hemodynamics, studies indicate that provider fatigue is more pronounced when CC are performed continuously compared to when a pause is inserted after every third CC as currently recommended. A higher rate (e.g., 120/min) is also more fatiguing, which affects CC quality. In post-transitional piglets with asphyxia-induced cardiac arrest, there was no benefit of performing continuous CC at a rate of 90/min. Not only rate but duty cycle, i.e., the duration of CC/total cycle time, is a known determinant of CC effectiveness. However, duty cycle cannot be controlled with manual CC. Mechanical/automated CC in neonatal CPR has not been explored, and feedback systems are under-investigated in this population. Evidence indicates that providers perform CC at rates both higher and lower than recommended. Video recording of DR CRP has been increasingly applied and observational studies of what is actually done in relation to outcomes could be useful. Different CC rates and ratios should also be investigated under controlled experimental conditions in animals during perinatal transition.

Effects of pulmonary acid aspiration on the lungs and extra-pulmonary organs: a randomized study in pigs

Introduction

There is mounting evidence that injury to one organ causes indirect damage to other organ systems with increased morbidity and mortality. The aim of this study was to determine the effects of acid aspiration pneumonitis (AAP) on extrapulmonary organs and to test the hypothesis that these could be due to circulatory depression or hypoxemia.

Methods

Mechanically ventilated anesthetized pigs were randomized to receive intrabronchial instillation of hydrochloric acid (n = 7) or no treatment (n = 7). Hydrochloric acid (0.1 N, pH 1.1, 2.5 ml/kg BW) was instilled into the lungs during the inspiratory phase of ventilation. Hemodynamics, respiratory function and computer tomography (CT) scans of lung and brain were followed over a four-hour period. Tissue samples of lung, heart, liver, kidney and hippocampus were collected at the end of the experiment.

Results

Acid instillation caused pulmonary edema, measured as increased extravascular lung water index (ELWI), impaired gas exchange and increased mean pulmonary artery pressure. Gas exchange tended to improve during the course of the study, despite increasing ELWI. In AAP animals compared to controls we found: a) cardiac leukocyte infiltration and necrosis in the conduction system and myocardium; b) lymphocyte infiltration in the liver, spreading from the periportal zone with prominent areas of necrosis; c) renal inflammation with lymphocyte infiltration, edema and necrosis in the proximal and distal tubules; and d) a tendency towards more severe hippocampal damage (P > 0.05).

Conclusions

Acid aspiration pneumonitis induces extrapulmonary organ injury. Circulatory depression and hypoxemia are unlikely causative factors. ELWI is a sensitive bedside parameter of early lung damage.

The pulmonary circulation in neonatal respiratory failure

The pulmonary circulation rapidly adapts at birth to establish lungs as the site of gas exchange. Abnormal transition at birth and/or parenchymal lung disease can result in neonatal hypoxemic respiratory failure. This article reviews the functional changes in pulmonary hemodynamics and structural changes in pulmonary vasculature secondary to (1) normal and abnormal transition at birth, and (2) diseases associated with neonatal hypoxemic respiratory failure. Various management strategies to correct respiratory failure are also discussed.

Pulmonary hypertension and the asphyxiated newborn

Persistent pulmonary hypertension of the newborn may occur with perinatal asphyxia, either because of direct effects of hypoxia/ischemia on pulmonary arterial function or indirectly because both are associated with meconium aspiration syndrome or perinatal sepsis/pneumonia. Therapies for persistent pulmonary hypertension of the newborn have the potential to affect cerebral function and cerebral perfusion in infants with hypoxic ischemic encephalopathy. Our literature review concludes that hyperventilation should be avoided, bicarbonate therapy is unproven, and hypoxia and hyperoxia should both be avoided. Nitric oxide improves pulmonary artery pressure and systemic perfusion. The effects of inotropic agents on cerebral perfusion or outcomes are uncertain.

Meconium aspiration delays normal decline of pulmonary vascular resistance shortly after birth through lung parenchymal injury

BACKGROUND

Persistent pulmonary hypertension of the newborn is often associated with meconium aspiration syndrome (MAS) or perinatal asphyxia.

OBJECTIVE

To determine the effect of meconium or asphyxia on pulmonary arterial pressure and circulating levels of vasoactive substances, we conducted a prospective study of 54 term infants, including infants with meconium-stained amniotic fluid with normal (MSAF) or abnormal (MAS) chest X-ray findings, infants with perinatal asphyxia, and controls. The purpose of this study was to determine the group most likely to have elevated pulmonary arterial pressure and a disturbed balance between vasoactive substances.

METHODS

To estimate the pulmonary arterial pressure by echocardiography, we used the ratio of the right to left systolic ventricular pressure (RVP/LVP ratio). We measured the plasma concentrations of endothelin-1 (ET-1), cyclic guanosine monophosphate (cGMP) as an indicator of nitric oxide (NO) production, and 6-keto-prostaglandin F(1)α (6-keto-PGF(1)α) for the estimation of prostacyclin concentration. We also measured KL-6 as a marker of lung injury.

RESULTS

The RVP/LVP ratio was significantly higher in the MAS group than the other groups on day 0. Although ET-1 and 6-keto-PGF(1)α levels were comparable among all groups, the cGMP level on days 3-5 and the KL-6 level throughout the first postnatal week were significantly higher in the MAS group.

CONCLUSIONS

It is possible that meconium aspiration delays normal decline of pulmonary vascular resistance shortly after birth through lung parenchymal injury. The subsequent increase of cGMP in MAS may be an adaptive response to prevent further elevation of pulmonary arterial pressure by inducing NO.

Changes in pulmonary arterial pressure in term-infants with hypoxic-ischemic encephalopathy

BACKGROUND

Hypoxic-ischemic encephalopathy (HIE) is an important complication that results from birth asphyxia or some other adverse conditions and has a high risk of neonatal morbidity and mortality. It is unclear, however, whether the elevated pulmonary arterial pressure (PAP) can aggravate the condition and prognosis of HIE. The purpose of the present study was to investigate the relationship between the changes of PAP and HIE in term infants after birth asphyxia.

METHODS

The left/right ventricle pre-ejection phase (LPEP/RPEP), left/right ventricle ejection time (LVET/RVET) and the ratios of LPEP/LVET and RPET/RVET were evaluated in 40 term infants with HIE and 40 healthy controls on days 1, 3, 7, and 12-14 after birth using echocardiogram. PAP such as pulmonary arterial diastolic pressure (PADP, mmHg), pulmonary arterial resistance (PAR, mmHg), and pulmonary arterial resistance/systemic resistance ratio (PAR/RS) was calculated using these indexes. Patient mortality was also evaluated.

RESULTS

PADP, PAR, and PAR/RS were significantly higher in HIE patients than in healthy controls during the first week after birth, particularly in severe-degree HIE patients. And until the end of the first week of life, these indexes may return to the levels of healthy controls. Persistent fetal circulation (PFC) was found in nine patients (7/16 severe, 2/12 moderate HIE patients), and non-PFC was found in mild HIE patients. Two patients with PFC died. No patients without PFC died. The course of HIE was longer in patients with pulmonary hypertension than in those without.

CONCLUSION

Increased PAP is an important pathophysiological process that may influence the course and prognoses of HIE in infants after birth asphyxia, particular in severe HIE patients who often have PFC. Thus it is important to assess changes in PAP using echocardiography.

Meconium aspiration syndrome (MAS) - Where do we go? Research perspectives

The pathogenetic cascade of meconium aspiration syndrome (MAS) in newborn infants is complex and still incompletely studied. The variable clinical presentation of MAS is basically connected with variation of the amount and consistency of aspirated meconium and also its distribution within the affected lungs. The contributing role of other factors, like intrauterine fetal compromises, lung maturity at the time of insult as well as direct and indirect effects of meconium and its components on the lung alveolar and vascular integrity and development, remains to be studied in further detail. Better understanding of the lung injury processes in MAS, specifically inflammatory injury and non-inflammatory apoptosis and their interplay, may offer new possibilities to treat the severely affected infants, and needs therefore to be explored. Systemic dispersion of intrapulmonary meconium and its components may further induce inflammatory circulatory changes and injurious effects in distant organs, but the mechanisms and clinical significance of these systemic complications are still poorly known. It is thus evident that lung injury processes and potent long-term consequences in various extrapulmonary organs, specifically the brain, as well as development of new approaches to their treatment and prevention form great challenges for future research of MAS.

The role of complement in meconium aspiration syndrome

The complement system is part of the host defense with a number of biological effects, most of which contribute to the inflammatory reaction by activation of cells like leukocytes and endothelial cells. An intact complement system is required for protection against infection and for maintaining internal inflammatory homeostasis. However, the system is a double-edged sword as improperly or uncontrolled activation is disadvantageous and potentially harmful for the host. Meconium aspiration syndrome (MAS) is associated with a local inflammatory reaction in the lungs, frequently described as a chemical pneumonitis. Cytokines, arachidonic acid metabolites and reactive oxygen species are involved in this reaction. We have recently documented that meconium is a potent activator of complement in vitro and in an experimental piglet model of MAS, the latter presenting with an inflammatory profile closely resembling systemic inflammatory response syndrome. We postulate that complement activation may contribute to the pathogenesis of MAS.

Bronchoalveolar lavage plus surfactant in a piglet model of meconium aspiration syndrome

INTRODUCTION

Meconium aspiration produces airway obstruction and surfactant inhibition. Bronchoalveolar lavage (BAL) and surfactant replacement have been proposed as treatments for the syndrome.

OBJECTIVE

To evaluate the effect of BAL with normal saline followed by a supplementary dose of surfactant in a piglet model of meconium aspiration syndrome.

METHODS

15 newborn piglets were used in the study. The animals were ventilated with fixed settings. After inhalation of 4 ml/kg of diluted meconium, the piglets were randomized into three groups: group I (n = 5) - tracheal aspiration without BAL; group II (n = 5) - BAL with normal saline (15 ml/kg), and group III (n = 5) - BAL with normal saline (15 ml/kg) followed by a supplementary dose of surfactant (Curosurf(R) 100 mg/kg). Arterial blood gas samples were obtained 30 min and 6 h after the inhalation of meconium.

RESULTS

A significant increase of PaO(2 )values at 6 h after treatment was only observed in group III (from 51 +/- 13 to 189 +/- 115 mm Hg; p = 0.04). At this time, PaO(2) in group III was significantly higher compared to group II (189 +/- 115 and 37 +/- 11 mm Hg, respectively; p = 0.023) and showed a borderline significance when compared to group I (p = 0.066).

CONCLUSION

BAL with normal saline followed by a supplementary dose of surfactant may improve oxygenation in an experimental piglet model of meconium aspiration syndrome.

Inhaled nitric oxide treatment inhibits neuronal injury after meconium aspiration in piglets

BACKGROUND

Meconium aspiration-induced hypertensive lung injury is frequently associated with neuronal damage. Inhaled nitric oxide (iNO) is widely used in the treatment of pulmonary hypertension, but its effects on the brain are poorly known.

AIMS

The aim of this study was to determine the effects of iNO treatment on the neuronal tissue after meconium aspiration.

STUDY DESIGN

71 anesthetized, catheterized and ventilated newborn piglets were studied for 6 h. Thirty-five piglets were instilled with a bolus of human meconium intratracheally and 36 piglets with saline instillation served as controls. Nineteen meconium piglets and 17 control piglets were continuously treated with 20 ppm of iNO, started at 30 min after the insult. The extent of neuronal injury was analysed histologically, and the levels of brain tissue lipid peroxidation products, reduced glutathione (GSH), myeloperoxidase activity and oxidized DNA were analysed as indicators of oxidative stress.

RESULTS

iNO treatment diminished the pulmonary hypertensive response caused by meconium aspiration, but did not change systemic or carotid hemodynamics. NO administration was associated with reduced neuronal injury and diminished amount of oxidized DNA in the hippocampus of the meconium piglets. Further, iNO treatment was associated with decreased level of GSH in the cortex, but no change in lipid peroxidation production or myeloperoxidase activity was detected in any of the studied brain areas.

CONCLUSIONS

Our results suggest that iNO treatment may inhibit DNA oxidation and neuronal injury in the hippocampus, associated with newborn meconium aspiration.

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 aspiration induces oxidative injury in the hippocampus of newborn piglets

BACKGROUND

Meconium aspiration-induced hypertensive lung injury has been associated with neuronal damage in the newborn, but the mechanisms of the injury are poorly known.

AIMS

The aim of the study was to determine the contribution of oxidative stress to the brain damage after pulmonary meconium contamination.

STUDY DESIGN

Sixteen anesthetized and ventilated newborn piglets were studied for 6 h. Eight piglets were instilled with a bolus of human meconium intratracheally and eight piglets with saline instillation served as controls. Brain tissue lipid peroxidation products (TBARS), reduced glutathione (GSH), myeloperoxidase activity and oxidized DNA were analyzed as indicators of oxidative stress.

RESULTS

Meconium aspiration did not change the systemic or carotid hemodynamics, but caused a well-established pulmonary hypertensive response. Sustained increase in additional oxygen demand was also observed after meconium insult, but no actual hypoxemia or hypercarbia was evident during the whole study period. Myeloperoxidase activity was elevated in the cerebellum after pulmonary meconium instillation, whereas concentrations of peroxidation products and glutathione were similar in the cortical, cerebellar and hippocampal regions of the two groups. Still, the amount of oxidized DNA was increased in the hippocampus of the meconium-aspirated piglets when compared to controls.

CONCLUSIONS

Our data thus suggest that oxidative injury associated with pulmonary, but not systemic, hemodynamic disturbances may contribute to hippocampal damage after meconium aspiration in newborns.

Meconium Aspiration Syndrome Induces Complement-Associated Systemic Inflammatory Response in Newborn Piglets

The pathophysiology of meconium aspiration syndrome (MAS) is complex. We recently showed that meconium is a potent activator of complement. In the present study, we investigated whether the complement activation occurring in experimental MAS is associated with a systemic inflammatory response as judged by granulocyte activation and cytokine and chemokine release. MAS was induced by the instillation of meconium into the lungs of newborn piglets (n = 8). Control animals (n = 5) received saline under otherwise identical conditions. Haemodynamic and lung dynamic data were recorded. Complement activation, revealed by the terminal sC5b-9 complex (TCC), and cytokines [interleukin (IL)-6 and IL-8] were measured in plasma samples by enzyme immunoassays. The expression of CD18, CD11b and oxidative burst in granulocytes was measured in whole blood by flow cytometry. Plasma TCC increased rapidly in the MAS animals in contrast with controls (P < 0.0005). The TCC concentration correlated closely with oxygenation index (r = 0.48, P < 0.0005) and ventilation index (r = 0.57, P < 0.0005) and inversely with lung compliance (r = -0.63, P < 0.0005). IL-6 and IL-8 increased in MAS animals compared with the controls (P = 0.002 and P < 0.001, respectively). Granulocyte oxidative burst declined significantly in the MAS animals compared with the controls (P < 0.02). TCC correlated significantly with IL-6 (r = 0.64, P < 0.0005) and IL-8 (r = 0.32; P = 0.03) and inversely with oxidative burst (r = -0.37; P = 0.02). A systemic inflammatory response associated with complement activation is seen in experimental MAS. This reaction may contribute to the pathogenesis of MAS.