Cardiac abnormalities in birth asphyxia

Change over time in internal cerebral vein pulsation in premature infants at risk of intraventricular hemorrhage

BACKGROUND

Prolonged continuation of augmented internal cerebral vein (ICV) pulsation may be related to the development of premature intraventricular hemorrhage (IVH). However, the characteristics of ICV flow patterns in premature infants are unclear.

AIM

To investigate the changes over time in ICV pulsation in premature infants at risk of IVH.

STUDY DESIGN

A 5-year retrospective observational study of a single-center trial.

SUBJECTS

In total, 112 very-low-birth-weight infants with gestational age of ≤32 weeks.

OUTCOME MEASURES

ICV flow was measured every 12 h until 96 h after birth and thereafter on days 7, 14, and 28. The ICV pulsation index (ICVPI), which is a ratio of the minimum/maximum speed of ICV flow, was calculated. We recorded longitudinal ICVPI change and compared ICVPI among three groups classified according to gestational age.

RESULTS

ICVPI started declining after day 1 and reached the minimum median value in 49-60 h after birth (1.0 during 0-36 h, 0.9 during 37-72 h, and 1.0 after 73-84 h). ICVPI was significantly lower during 25-96 h than during 0-24 h and on days 7, 14, and 28. ICVPI in the 23-25-week group was significantly lower between 13-24 h and day 14 than that in the 29-32-week group, and the same was observed for the 26-28-week group between 13-24 h and 49-60 h.

CONCLUSIONS

ICV pulsation was affected by time after birth and gestational age, and this ICVPI fluctuation may reflect a postnatal circulatory adaptation.

Hemodynamic optimization for neonates with neonatal encephalopathy caused by a hypoxic ischemic event: Physiological and therapeutic considerations

Neonatal encephalopathy due to a hypoxic-ischemic event is commonly associated with cardiac dysfunction and acute pulmonary hypertension; both therapeutic hypothermia and rewarming modify loading conditions and blood flow. The pathophysiological contributors to disease are complex with a high degree of clinical overlap and traditional bedside measures used to assess circulatory adequacy have multiple confounders. Comprehensive, quantitative echocardiography may be used to delineate the relative contribution of lung parenchymal, pulmonary vascular, and cardiac disease to hypotension and/or hypoxemic respiratory failure. In this review, we provide a detailed overview of the contributors to hemodynamic instability following perinatal hypoxic-ischemic injury. Our proposed approach to therapy focuses on physiopathological considerations with interventions individualized to this potentially complex condition and considers the pharmacological idiosyncrasies, which may occur among neonates with NE presenting with multiorgan dysfunction while undergoing therapeutic hypothermia.

Cardiovascular Supportive Therapies for Neonates With Asphyxia - A Literature Review of Pre-clinical and Clinical Studies

Asphyxiated neonates often have hypotension, shock, and poor tissue perfusion. Various "inotropic" medications are used to provide cardiovascular support to improve the blood pressure and to treat shock. However, there is incomplete literature on the examination of hemodynamic effects of these medications in asphyxiated neonates, especially in the realm of clinical studies (mostly in late preterm or term populations). Although the extrapolation of findings from animal studies and other clinical populations such as children and adults require caution, it seems appropriate that findings from carefully conducted pre-clinical studies are important in answering some of the fundamental knowledge gaps. Based on a literature search, this review discusses the current available information, from both clinical studies and animal models of neonatal asphyxia, on common medications used to provide hemodynamic support including dopamine, dobutamine, epinephrine, milrinone, norepinephrine, vasopressin, levosimendan, and hydrocortisone.

Understanding the Full Spectrum of Organ Injury Following Intrapartum Asphyxia

Birth asphyxia is a significant global health problem, responsible for ~1.2 million neonatal deaths each year worldwide. Those who survive often suffer from a range of health issues including brain damage-manifesting as cerebral palsy (CP)-respiratory insufficiency, cardiovascular collapse, and renal dysfunction, to name a few. Although the majority of research is directed toward reducing the brain injury that results from intrapartum birth asphyxia, the multi-organ injury observed in surviving neonates is of equal importance. Despite the advent of hypothermia therapy for the treatment of hypoxic-ischemic encephalopathy (HIE), treatment options following asphyxia at birth remain limited, particularly in low-resource settings where the incidence of birth asphyxia is highest. Furthermore, although cooling of the neonate results in improved neurological outcomes for a small proportion of treated infants, it does not provide any benefit to the other organ systems affected by asphyxia at birth. The aim of this review is to summarize the current knowledge of the multi-organ effects of intrapartum asphyxia, with particular reference to the findings from our laboratory using the precocial spiny mouse to model birth asphyxia. Furthermore, we reviewed the current treatments available for neonates who have undergone intrapartum asphyxia, and highlight the emergence of maternal dietary creatine supplementation as a preventative therapy, which has been shown to provide multi-organ protection from birth asphyxia-induced injury in our preclinical studies. This cheap and effective nutritional supplement may be the key to reducing birth asphyxia-induced death and disability, particularly in low-resource settings where current treatments are unavailable.

Short term outcome of term newborns with unexpected umbilical cord arterial pH between 7.000 and 7.100

BACKGROUND

The relationship between cord arterial pH (CA-pH) > 7.000 and the neonatal outcome is not clear.

AIMS

To evaluate if asymptomatic infants born with unexpected cord arterial pH (CA-pH) between 7.000 and 7.100 develop clinical, biochemical, and instrumental signs of hypoxic cerebral, renal, and heart failure more frequently than symptomatic infants.

STUDY DESIGN

Term infants with CA-pH of 7.000-7.100 and appropriate birth weight were prospectively and consecutively enrolled and classified as asymptomatic, when they had no resuscitation, early respiratory distress or early abnormal neurologic signs, and symptomatic infants. Clinical, biochemical, and instrumental signs of hypoxic cerebral, renal, and heart failure were evaluated in the two groups.

RESULTS

A total of 53 infants were enrolled. Twenty-eight (53%) were asymptomatic. CA-pH was similar in both the groups, while the cTnI serum concentration in the first day of life and the occurrence of poor feeding were higher in the symptomatic than in asymptomatic infants. An arterial lactate level of ≥ 4.1 mmol/l measured in the first hour of life was an independent risk factor for the development of a symptomatic course.

CONCLUSIONS

In our population the majority of infants born with a CA-pH between 7.000 and 7.100 were asymptomatic and would not have needed immediate admission to the neonatal care unit. Symptomatic infants showed a higher occurrence of subclinical heart injury and poor feeding.

Propofol administration to the fetal-maternal unit reduces cardiac injury in late-preterm lambs subjected to severe prenatal asphyxia and cardiac arrest

BACKGROUND

Cardiac dysfunction is reported to occur after severe perinatal asphyxia. We hypothesized that anesthesia of the mother with propofol during emergency cesarean section (c-section) would result in less cardiac injury (troponin T) in preterm fetuses exposed to global severe asphyxia in utero than anesthesia with isoflurane. We tested whether propofol decreases the activity of proapoptotic caspase-3 by activating the antiapoptotic AKT kinase family and the signal transducer and activator of transcription-3 (STAT-3).

METHODS

Pregnant ewes were randomized to receive either propofol or isoflurane anesthesia. A total of 44 late-preterm lambs were subjected to in utero umbilical cord occlusion (UCO), resulting in asphyxia and cardiac arrest, or sham treatment. After emergency c-section, each fetus was resuscitated, mechanically ventilated, and supported under anesthesia for 8 h using the same anesthetic as the one received by its mother.

RESULTS

At 8 h after UCO, the fetuses whose mothers had received propofol anesthesia had lower plasma troponin T levels, and showed a trend toward a higher median left ventricular ejection fraction (LVEF) of 84% as compared with 74% for those whose mothers had received isoflurane. Postasphyxia activation of caspase-3 was lower in association with propofol anesthesia than with isoflurane. Postasphyxia levels of STAT-3 and the AKT kinase family rose 655% and 500%, respectively with the use of propofol anesthesia for the mother.

CONCLUSION

The use of propofol for maternal anesthesia results in less cardiac injury in late-preterm lambs subjected to asphyxia than the use of isoflurane anesthesia. The underlying mechanism may be activation of the antiapoptotic STAT-3 and AKT pathways.

Embryonic defects and growth alteration in mice with homozygous disruption of the Patz1 gene

PATZ1 is an emerging cancer-related gene coding for a POZ/AT-hook/kruppel Zinc finger transcription factor, which is lost or misexpressed in human neoplasias. Here, we investigated its role in development exploring wild-type and Patz1-knockout mice during embryogenesis. We report that the Patz1 gene is ubiquitously expressed at early stages of development and becomes more restricted at later stages, with high levels of expression in actively proliferating neuroblasts belonging to the ventricular zones of the central nervous system (CNS). The analysis of embryos in which Patz1 was disrupted revealed the presence of severe defects in the CNS and in the cardiac outflow tract, which eventually lead to a pre-mature in utero death during late gestation or soon after birth. Moreover, the Patz1-null mice showed a general growth retardation, which was consistent with the slower growth rate and the increased susceptibility to senescence of Patz1(-/-) mouse embryonic fibroblasts (MEFs) compared to wild-type controls. Therefore, these results indicate a critical role of PATZ1 in the control of cell growth and embryonic development.

Is myocardial performance index useful in differential diagnosis of moderate and severe hypoxic-ischaemic encephalopathy? A serial Doppler echocardiographic evaluation

INTRODUCTION

The aim of this study was to investigate the importance of myocardial performance index as an additive criterion to Sarnat criteria in differential diagnosis of newborn babies with moderate and severe hypoxic-ischaemic encephalopathy.

METHODS

Our study group included 50 healthy term newborn babies and 20 newborn babies with hypoxic-ischaemic encephalopathy. The 20 newborn babies with hypoxic-ischaemic encephalopathy were scored using Sarnat grades. Left and right ventricular functions were determined on the first day and thereafter in the 1, 3-4, 6-7, and 11-12 months of life by M-Mode and pulsed Doppler.

RESULTS

Myocardial performance indexes of the left ventricle were significantly higher in the severe hypoxic-ischaemic encephalopathy group than in the control group during the first, second, and third analyses (p = 0.01, p = 0.02, p = 0.02, respectively) and only during the first analysis (p = 0.01) in the moderate hypoxic-ischaemic encephalopathy group. In addition, the myocardial performance indexes of the right ventricle were significantly higher during the first, second, and third analyses in both severe and moderate hypoxic-ischaemic encephalopathy groups than in the control group (p = 0.01, all). Hypoxia-induced alterations last longer in the right ventricle than in the left ventricle in the moderate group, as during the second and third analyses myocardial performance index continues to be higher than the control group.

CONCLUSION

Myocardial performance indexes for the left and right ventricles were significantly higher in both severe and moderate hypoxic-ischaemic encephalopathy groups than in the control group during the first analysis, and myocardial performance index greater than or equal to 0.5 can be used in order to distinguish moderate and severe hypoxic-ischaemic encephalopathy babies according to Sarnat grades as a discriminative additive criterion.

Cardiac troponin T as a marker of myocardial injury in a group of asphyxiated African neonates

BACKGROUND

In caucasian newborns, troponin T (cTnT) is a specific marker for myocardial injury in perinatal asphyxia. This is the first such study in negroid neonates.

AIMS

To evaluate myocardial injury in a group of asphyxiated African newborns and determine the influence of mode of delivery on cTnT levels.

METHODS

Serum cTnT and clinical parameters in 40 asphyxiated and 40 healthy negroid neonatal controls were measured within the first 72 hours of life by chemiluminescence immune-assay. Perinatal asphyxia was assessed by APGAR score. The infants were followed up until discharge or death.

RESULTS

Mean (SD) cTnT values were significantly higher in asphyxiated infants [0.03 (0.04) ng/ml] than in healthy controls [0.01 (0.006) ng/ml, P = 0.002]. Asphyxiated infants delivered by forceps and vacuum extraction had significantly higher levels of cTnT [0.04 (0.018) ng/ml] than those born by caesarian section [0.02 (0.008) ng/ml] and by normal delivery [0.03 (0.01) ng/ml, P = 0.003]. cTnT levels were higher in infants who died (P = 0.037).

CONCLUSION

In the asphyxiated infants, mean cTnT levels were significantly higher than in controls. They were also significantly higher in those born by vacuum and forceps delivery and asphyxiated infants who died.

Differential hemodynamic effects of levosimendan in a porcine model of neonatal hypoxia-reoxygenation

BACKGROUND

Neonatal asphyxia can be complicated by myocardial dysfunction with secondary alterations in pulmonary and regional hemodynamics. Levosimendan is a calcium-sensitizing inotrope that may support cardiac output, but little is known regarding its differential hemodynamic effects in asphyxiated neonates.

METHODS

Mixed breed piglets (1-4 days old, weight 1.6-2.3 kg) were acutely instrumented. Normocapnic alveolar hypoxia (10-15% oxygen) was induced for 2 h, followed by reoxygenation with 100% (1 h) and then 21% oxygen (3 h). At 2 h of reoxygenation, after volume loading (Ringer's lactate 10 ml/kg), either levosimendan (0.1 or 0.2 μg/kg/min) or D(5)W (placebo) was infused for 2 h in a blinded, block-randomized fashion (n = 7-8/group). The systemic, pulmonary and regional (carotid, superior mesenteric and renal) hemodynamics were compared.

RESULTS

At 0.1 and 0.2 μg/kg/min, levosimendan significantly increased cardiac output (121 and 123% of pretreatment, respectively) and heart rate, and decreased systemic vascular resistance without causing hypotension. Pulmonary arterial pressure and estimated pulmonary vascular resistance were significantly increased from pretreatment baseline in 0.1 but not 0.2 μg/kg/min levosimendan. Levosimendan infusion had no effects on regional hemodynamics. Myocardial efficiency but not oxygen consumption increased with 0.1 μg/kg/min levosimendan without significant effects on plasma troponin and myocardial lactate levels.

CONCLUSIONS

In newborn piglets following hypoxia-reoxygenation injury, levosimendan improves cardiac output but has no marked effects in carotid, superior mesenteric and renal perfusion. It appears that various doses of levosimendan increase the cardiac output through different mechanisms. Further investigations are needed to examine the effectiveness of levosimendan as a cardiovascular supportive therapy either alone or in conjunction with other inotropes in asphyxiated neonates.

Myocardial response in preterm fetal sheep exposed to systemic endotoxinaemia

Exposure of the fetus to antenatal inflammation can occur from chorioamnionitis, which may progress to a fetal inflammatory response syndrome (FIRS) and to fetal sepsis. We tested whether the fetal myocardium responded to systemic Gram-negative endotoxinaemia. We hypothesized that the myocardium would respond to inflammation by changes in hypoxia-inducible factor-α (HIF-1α), inducible NO-synthase (iNOS), Toll-like receptors 2 and 4 (TLR2 and TLR4), IL-6, and phosphorylated signal transducer and activator of transcription-3 (pSTAT3). To model systemic endotoxinaemia, fetal sheep were exposed to Gram-negative endotoxin or saline i.v. 3 d before preterm delivery at 113 d of gestation (term = 147 d). All endotoxin-exposed animals developed cardiac dysfunction within these 72 h. Cardiac mRNA and protein levels of HIF-1α and TLR2 and TLR4 mRNA increased, whereas STAT3 phosphorylation decreased significantly. IL-6 and iNOS mRNA remained unchanged. Fetal systemic endotoxinaemia induced myocardial inflammation by activating TLR2 and 4. The following cardiac dysfunction seems not to be mediated via cardiac iNOS.

Early left ventricular diastolic dysfunction in premature infants born to preeclamptic mothers

AIM

To evaluate the cardiac function in premature infants born to preeclamptic mothers and its clinical consequences.

METHODS

This was a prospective observational cohort study performed in a tertiary neonatal intensive care unit. Fifty-three premature infants born to preeclamptic mothers comprising the study group were evaluated and compared with 42 premature infants born to normotensive mothers (control group). Relationship between echocardiographic measures and neonatal morbidity were assessed as the main outcome measures.

RESULTS

Left ventricle end-diastolic dimension (LVEDD), peak flow velocities during early diastole (peak E wave), peak flow velocities during atrial contraction (peak A wave), and peak E/A ratio were significantly lower in the study group. Within the study group, these parameters were also significantly lower in infants with respiratory problems. LVEDD was significantly smaller in preeclamptic infants with intrauterine growth retardation (IUGR).

CONCLUSION

Left ventricle diastolic dysfunction (LVDD) was detected in premature infants born to preeclamptic mothers in the first week after delivery. LVDD was associated with higher incidence of respiratory problems, transient tachypnea of the newborn, longer duration of oxygen requirement, and IUGR.

Functional echocardiography; from physiology to treatment

Functional echocardiography (fECHO) is the bedside use of ultrasound to longitudinally assess myocardial function, systemic and pulmonary blood flow, and intra and extracardiac shunts. This review will focus on fECHO as a tool for the clinician to assess the hemodynamic condition of sick neonates and describe situations where fECHO can help determine a pathophysiological choice for cardiovascular support. The very low birth weight infant with hypotension during the first 24h of life, assessment and monitoring of the ductus arteriosus, assessment and response to treatment of infants with pulmonary hypertension, the infant with perinatal asphyxia and the infant with sepsis and cardiovascular compromise are reviewed. Close cooperation with pediatric cardiology, proper logistics and training programs are mandatory to achieve a 24h a day fECHO service run by bedside clinicians.

Left ventricular systolic function of newborns with asphyxia evaluated by tissue Doppler imaging

The aim of the study was to evaluate the left ventricular systolic function of newborns with asphyxia using tissue Doppler imaging (TDI). Newborns with a history of asphyxia were divided into severe and mild groups based on their Apgar scores; normal newborns without asphyxia served as the controls. Left ventricular ejection fraction (LVEF), fraction shortening (FS), and stroke volume (SV) were measured by M-mode echocardiography at 24, 48, and 72 h after birth. The peak systolic velocity of the anterior mitral valve leaflet (Sm wave) was measured with TDI. Cardiac troponin I (CTnI) was measured. The results revealed that the LVEF and FS of the severe asphyxia group at 24 h were significantly lower than those at later time points (P < 0.01). These parameters were also significantly lower than those of the mild and control groups (P < 0.01). SV was not significantly different among the three groups. Sm wave of asphyxia groups was significantly lower than that of control group (P < 0.001). In the severe asphyxia group, Sm wave at 24 h was significantly lower than that at 48 or 72 h (P < 0.001). CTnI values of the severe asphyxia group were remarkably higher than those of the other two groups (P < 0.01). The findings of this study indicate decreased left ventricular systolic function of newborn children after asphyxia. Sm by TDI is a more sensitive indicator of left ventricular systolic function than LVEF, FS, or SV by M-mode echocardiography.

A prediction score model for risk factors of mortality in neonate with pulmonary hemorrhage: the experience of single neonatal intensive care unit in Southwest China

AIM

To establish a prediction score model for mortality of neonates with pulmonary hemorrhage (PH).

METHODS

Mortality risk factors of PH were analyzed by logistic regression analysis in 244 neonates retrospectively. A prediction score model was developed according to regression coefficients of risk factors. The receiver operating characteristic curve (ROC) was also constructed and the cutoff was determined.

RESULTS

The overall mortality rate of PH was 74.59% (182/244). More patients from multiple pregnancies were found in the death group than in the survivor group (20.1% vs. 3.2%, P = 0.023). The survivor group infants had higher birth weight in average than death group infants (2,787 g vs. 2,339 g, P = 0.000). Significant differences were found between survivor and death groups in the rates of intraventricular hemorrhage (IVH) (25.8% vs. 53.8%, P = 0.000), heart failure (22.6% vs. 48.9%, P = 0.000) and sepsis (3.2% vs. 16.5%, P = 0.008). Birth weight, IVH, heart failure and sepsis were identified as independent mortality risk factors by logistic regression analysis. A score model predicting death was developed according to the regression coefficients, with a sensitivity of 0.846, a specificity of 0.661, a positive predictive value of 0.88 and a negative predictive value of 0.594 at a cutoff of 9 points. The low risk group, with a score of 9 or less, had a lower mortality rate as compared with the high risk group (40.6% vs. 88%, P = 0.000).

CONCLUSIONS

Low birth weight, IVH, heart failure and sepsis were the risk factors for mortality of PH. Those infants with a predictive score of more than 9 were at high risk for death.

The hemodynamic effects of dobutamine during reoxygenation after hypoxia: a dose-response study in newborn pigs

Asphyxiated neonates usually have myocardial stunning and hypotension and require inotropic support. A randomized controlled study was designed to examine the dose-response effect of dobutamine (5-20 microg x kg(-1) x min(-1)) on systemic and regional circulations and oxygen metabolism in a neonatal swine model of hypoxia/reoxygenation. Thirty-eight anesthetized newborn piglets were acutely instrumented for continuous monitoring of heart rate, systemic and pulmonary arterial pressures, and pulmonary (surrogate for cardiac index), right common carotid, and superior mesenteric and left renal arterial flows. After stabilization, they were exposed to normocapnic alveolar hypoxia (10%-15% oxygen) for 2 h followed by reoxygenation with 100% oxygen for 1 h, then 21% for 3 h. Piglets were block randomized to receive dobutamine infusion (5, 10, or 20 microg x kg(-1) x min(-1)) or saline (control) at 2 to 4 h of reoxygenation (n = 8 each). A nonasphyxiated, sham-operated group was included (n = 6). Blood samples were collected for blood gas analysis, arterial and venous co-oximetry, and plasma lactate concentration determination. At 2-h reoxygenation after hypoxia, there was hypotension (systemic arterial pressure, 27 to 36 mmHg) and myocardial dysfunction (cardiac index from 178-209 to 134-156 mL x kg(-1) x min(-1)). Cardiac index improved significantly with 20 microg x kg(-1) x min(-1) of dobutamine (P < 0.05) and modestly in the treatment groups of 5 and 10 microg x kg(-1) x min(-1) (P < 0.1) (at 120 min, 172 +/- 35, 160 +/- 30, and 158 +/- 56 mL x kg(-1) x min(-1) vs. 119 +/- 33 mL x kg(-1) x min(-1) of controls, respectively), with corresponding increases in stroke volume. Pulmonary vascular resistance was lower in all dobutamine-treated groups (vs. controls, P < 0.05) There were no differences in heart rate, systemic and pulmonary arterial pressures, systemic vascular resistance, and regional flows between groups. The group of 20 mug.kg.min of dobutamine also had higher systemic oxygen delivery (at 120 min, 18 +/- 5 vs. 11 +/- 3 O(2) mL x kg(-1) x min(-1) of controls, P < 0.05) with no significant differences in systemic oxygen consumption and regional oxygen delivery between groups. After the reoxygenation of newborn piglets with severe hypoxia, high dose of dobutamine is effective to treat myocardial stunning and low cardiac output with no significant effect on blood pressure or regional circulation. Further clinical studies are needed to confirm these findings in the human neonate.

Cardiac troponin T: a useful early marker for cardiac and respiratory dysfunction in neonates

BACKGROUND

Cardiac troponin T (cTnT) has been proposed as specific biochemical marker for myocardial infarction in adults. Cardiac function in neonates could be influenced by the severity of respiratory distress and its ventilatory management.

OBJECTIVES

To establish a normal range of cTnT in healthy neonates, compare troponin concentrations among healthy neonates and those in respiratory distress (sick) and detect whether any correlation occurs between severity of respiratory distress and troponin concentrations.

METHODS

Concentrations of cTnT were compared between sick and healthy infants, accounting for confounding variables in a prospective investigation manner. Age at sampling, need for ventilation, duration of respiratory support, and inotropic use in addition to neonatal and maternal characteristics were assessed.

RESULTS

Samples were collected from 164 neonates (116 healthy and 48 sick). The medians [interquartile ranges] of cTnT in healthy and sick infants were 0.044 [0.027-0.073]mug/l and 0.121 [0.065-0.238] microg/l, respectively, with p < 0.0001. The 99th percentile for healthy neonates was 0.244 microg/l. Comparing both groups, there were significant differences concerning gestation, birth weight, Apgar at 5 min and admission to neonatal intensive care unit. Troponin concentrations in subgroups of sick infants including hypotensive, ventilated and dead infants were higher than other infants of the same subgroup. CTnT was positively correlated to the duration of respiratory support in ventilated neonates.

CONCLUSION

CTnT may prove to be a useful early marker for cardiac and respiratory dysfunction in newborns.

Reduced left ventricular function in hypoxemic newborn pigs: a strain Doppler echocardiographic study

Myocardial dysfunction, hypotension, and increased pulmonary artery pressure are induced by asphyxia in neonates. We sought to define left ventricular (LV) systolic function by measuring longitudinal and radial contraction by strain Doppler echocardiography (SDE) in hypoxemic newborn pigs. Hypoxemia was induced in 11 anesthetized and instrumented newborn pigs by ventilation with 8% O2 in nitrogen. When mean arterial blood pressure (BP) decreased to 15 mm Hg or arterial base excess reached -20 mmol/L or less, the pigs were reoxygenated and ventilated for 150 min. Echocardiography was performed at baseline and during hypoxemia and reoxygenation. Baseline measurements of myocardial peak systolic strain demonstrated normal longitudinal shortening and radial thickening. During hypoxemia, systolic longitudinal shortening in the mid-posterior and septal segments changed to systolic stretching. Peak strain in the mid-lateral and anterior segments decreased but without signs of paradox wall motion. Short-axis peak strain remained positive during hypoxemia, although the amplitude was reduced and delayed with respect to timing. In the newborn pig heart, we found a complex and heterogeneous systolic pattern with distinct regional differences during global hypoxemia. Rapid changes in LV function during hypoxemia and reoxygenation are assessable by SDE, and the results indicate that longitudinal systolic contraction is more vulnerable to hypoxemic changes than radial contraction. To explore the full picture of a global hypoxemic injury, both long- and short-axis functions have to be considered.

Restoration of cardiopulmonary function with 21% versus 100% oxygen after hypoxaemia in newborn pigs

OBJECTIVE

To assess the consequences of hypoxaemia and resuscitation with room air versus 100% O(2) on cardiac troponin I (cTnI), cardiac output (CO), and pulmonary artery pressure (PAP) in newborn pigs.

DESIGN

Twenty anaesthetised pigs (12-36 hours; 1.7-2.7 kg) were subjected to hypoxaemia by ventilation with 8% O(2). When mean arterial blood pressure fell to 15 mm Hg, or arterial base excess was < or = -20 mmol/l, resuscitation was performed with 21% (n = 10) or 100% (n = 10) O(2) for 30 minutes, then ventilation with 21% O(2) for 120 minutes. Blood was analysed for cTnI. Ultrasound examinations of CO and PAP (estimated from tricuspid regurgitation velocity (TR-Vmax)) were performed at baseline, during hypoxia, and at the start of and during reoxygenation.

RESULTS

cTnI increased from baseline to the end point (p<0.001), confirming a serious myocardial injury, with no differences between the 21% and 100% O(2) group (p = 0.12). TR-Vmax increased during the insult and returned towards baseline values during reoxygenation, with no differences between the groups (p = 0.11) or between cTnI concentrations (p = 0.31). An inverse relation was found between increasing age and TR-Vmax during hypoxaemia (p = 0.034). CO per kg body weight increased during the early phase of hypoxaemia (p<0.001), then decreased. Changes in CO per kg were mainly due to changes in heart rate, with no differences between the groups during reoxygenation (p = 0.298).

CONCLUSION

Hypoxaemia affects the myocardium and PAP. During this limited period of observation, reoxygenation with 100% O(2) showed no benefits compared with 21% O(2) in normalising myocardial function and PAP. The important issue may be resuscitation and reoxygenation without hyperoxygenation.

Increased myocardial matrix metalloproteinases in hypoxic newborn pigs during resuscitation: effects of oxygen and carbon dioxide

BACKGROUND

Perinatal asphyxia is associated with cardiac dysfunction, and it is important to prevent further tissue injury during resuscitation. There is increasing evidence that myocardial matrix metalloproteinases (MMPs) are involved in myocardial hypoxaemia-reoxygenation injury.

OBJECTIVE

To assess MMPs and antioxidant capacity in newborn pigs after global ischaemia and subsequent resuscitation with ambient air or 100% O(2) at different PaCO(2)-levels.

METHODS

Newborn pigs (12-36 h of age) were resuscitated for 30 min by ventilation with 21% or 100% O(2) at different PaCO(2) levels after a hypoxic insult, and thereafter observed for 150 min. In myocardial tissue extracts, MMPs were analyzed by gelatin zymography and broad matrix-degrading capacity (total MMP). Total endogenous antioxidant capacity in myocardial tissue extracts was measured by the oxygen radical absorbance capacity (ORAC) assay.

RESULTS

Matrix metalloproteinase-2 more than doubled from baseline values (P < 0.001), and was higher in piglets resuscitated with 100% O(2) than with ambient air (P = 0.012). The ORAC value was considerably decreased (P < 0.001). In piglets with elevated PaCO(2), total MMP-activity in the right ventricle was more increased than in the left ventricle (P = 0.008). In the left ventricle, total MMPactivity was higher in the piglets with low PaCO(2) than in the piglets with elevated PaCO(2) (P = 0.013).

CONCLUSION

In hypoxaemia-reoxygenation injury the MMP-2 level was highly increased and was most elevated in the piglets resuscitated with 100% O(2). Antioxidant capacity was considerably decreased. Assessed by total MMP-activity, elevated PaCO(2) during resuscitation might protect the left ventricle, and probably increase right ventricle injury of the myocardium.

Cardiac output, pulmonary artery pressure, and patent ductus arteriosus during therapeutic cooling after global hypoxia-ischaemia

OBJECTIVE

To assess by Doppler echocardiography the effects of 24 hours of whole body mild hypothermia compared with normothermia on cardiac output (CO), pulmonary artery pressure (PAP), and the presence of a persistent ductus arteriosus (PDA) after a global hypoxic-ischaemic insult in unsedated newborn animals.

DESIGN

Thirty five pigs (mean (SD) age 26.6 (12.1) hours and weight 1.6 (0.3) kg) were anaesthetised with halothane, mechanically ventilated, and subjected to a 45 minute global hypoxic-ischaemic insult. At the end of hypoxia, halothane was stopped; the pigs were randomised to either normathermia (39 degrees C) or hypothermia (35 degrees C) for 24 hours. Rewarming was carried out for 24-30 hours followed by 42 hours of normothermia. Unanaesthetised pigs were examined with a VingMed CFM 750 ultrasound scanner before and 3, 24, 30, and 48 hours after the hypoxic-ischaemic insult. Aortic valve diameter, forward peak flow velocities across the four valves, and the occurrence of a PDA were measured. Tricuspid regurgitation (TR) velocity was used to estimate the PAP. Stroke volume was calculated from the aortic flow.

RESULTS

Twelve animals (seven normothermic, five hypothermic) had a PDA on one or more examinations, which showed no association with cooling or severity of insult. There were no differences in stroke volume or TR velocity between the hypothermic and normothermic animals at any time point after the insult. CO was, however, 45% lower at the end of cooling in the subgroup of hypothermic pigs that had received a severe insult compared with the pigs with mild and moderate insults. CO and TR velocity were transiently increased three hours after the insult: 0.38 (0.08) v 0.42 (0.08) litres/min/kg (p = 0.007) for CO; 3.0 (0.42) v 3.4 (0.43) m/s (p < 0.0001) for TR velocity (values are mean (SD)).

CONCLUSIONS

The introduction of mild hypothermia while the pigs were unsedated did not affect the incidence of PDA nor did it lead to any changes in MABP or PAP. Stroke volume was also unaffected by temperature, but hypothermic piglets subjected to a severe hypoxic-ischaemic insult had reduced CO because the heart rate was lower. Global hypoxia-ischaemia leads to similar transient increases in CO and estimated PAP in unsedated normothermic and hypothermic pigs. There were no signs of metabolic compromise in any subgroup, suggesting that 24 hours of mild hypothermia had no adverse cardiovascular effect.