Effect of ductus ligation on cardiopulmonary function in premature baboons

Pulmonary Function and Systolic Blood Pressure in Very Low Birth Weight Infants at 34 - 36 Weeks of Corrected Age

Purpose

Preterm infants are at increased risk of systemic hypertension compared to term infants. Bronchopulmonary dysplasia (BPD) has been shown to be associated with hypertension in preterm infants albeit with no causation reported. BPD is characterized by abnormal pulmonary function tests (PFTs), specifically elevated passive respiratory resistance (Rrs), decreased passive respiratory compliance (Crs) and decreased functional residual capacity (FRC). There have been no studies comparing PFTs in very low birth weight (VLBW) infants with and without hypertension. We hypothesized that stable VLBW infants with hypertension will have altered PFTs.

Patients and Methods

Retrospective cohort study of infants < 1500 grams at birth (VLBW) who had PFTs performed near 34-36 weeks of corrected gestational age (CGA). We excluded infants with congenital anomalies, known hypertensive disorders or those at risk of medication-induced hypertension. Data obtained included PFT parameters (Rrs, Crs, FRC) and mean systolic blood pressure (SBP).

Results

59 VLBW infants were identified for analysis, 14 with and 45 without hypertension. Hypertensive and normotensive patients were similar in terms of mean gestational age (26.6 vs 27.4 weeks), mean CGA at PFTs (36.1 vs 34.6 weeks) and proportion of BPD (36% vs 36%). The Rrs was significantly higher in hypertensive versus normotensive patients [median Rrs of 0.080 (0.069, 0.090) versus 0.066 (0.054, 0.083) cmH₂O/mL/sec; p = 0.04]. There was no difference in systolic blood pressure in the infants with and without BPD.

Conclusion

In this cohort of contemporary VLBW infants, those with hypertension had increased Rrs. This finding warrants a prospective study with a larger sample size and long-term follow-up.

Predictors of Respiratory Improvement 1 Week after Ligation of Patent Ductus Arteriosus in Preterm Infants

OBJECTIVE

To characterize preterm infants that demonstrates respiratory improvement 7 days after ligation of a patent ductus arteriosus (PDA).

STUDY DESIGN

We performed a 2-phase study of preterm infants (birthweight <1500 g between 2010 and 2016). We first did a retrospective analysis using regression modeling of ligation population. We then performed a case-control study comparing a ligation group with infants matched by gestational age, postnatal age, and preligation respiratory condition (ventilator mode, mean airway pressure [MAP], and fraction of inspired oxygen [FiO₂]). Respiratory improvement was defined as either extubation, downgrading of ventilatory mode, reduction in MAP >25%, or decrease in FiO₂ >25%.

RESULTS

Forty-five (42%) of 107 preterm infants (gestational age 25.5 ± 1.7 weeks) with ligation showed respiratory improvement at 7 days. Infants on high frequency ventilation (HFV) were more likely to have respiratory improvement (aOR 5.03, 95% CI [1.14-22.18]). In matched-control analysis of 89 pairs, there was no difference in respiratory improvement. Among infants on HFV, the ligation group had an increase in MAP during 3 days prior to ligation. For infants on conventional ventilation, the ligation group had higher MAP and FiO₂ than the control group during the first 2-3 postoperative days.

CONCLUSIONS

Among infants undergoing PDA ligation, those on HFV were more likely to have respiratory improvement in the first week, possibly because of the prevention of further respiratory deterioration. For infants on conventional ventilation, ligation was associated with higher respiratory support in the immediate postligation period without respiratory benefits at 7 days. As HFV was used as a rescue mode, our findings suggest that those with worse lung disease may achieve greater short term benefit from PDA ligation.

Lung function in very low birth weight infants after pharmacological and surgical treatment of patent ductus arteriosus - a retrospective analysis

BACKGROUND

The indications and strategies for treatment of patent ductus arteriosus (PDA) are controversial, and the safety and long-term benefits of surgical PDA closure remain uncertain. The aim of this study was to compare the lung function of very low birth weight (VLBW) infants after successful PDA treatment with a cyclooxygenase inhibitor or secondary surgical ligation.

METHODS

A total of 114 VLBW infants (birth weight < 1500 g), including 94 infants (82%) with a birth weight < 1000 g, who received treatment for hemodynamically significant PDA (hsPDA), were examined at a median postmenstrual age of 48 weeks. All infants were initially given pharmacological treatment, and 40 infants (35%) required PDA ligation. Lung function testing (LFT) included tidal breathing measurements, measurement of respiratory mechanics assessed by the occlusion test, whole-body plethysmography, SF₆ multiple breath washout, forced expiratory flow (V'max_FRC) by the rapid thoracoabdominal compression technique, exhaled NO (FeNO), and arterialized capillary blood gas analysis.

RESULTS

On the day of the LFT, the 2 groups had similar postconceptional age and body weight. However, the PDA ligation group was more immature at birth (p < 0.001) and had reduced respiratory compliance (p < 0.001), lower V'max_FRC (p = 0.006), increased airway resistance (R_aw) (p < 0.001), and impaired blood gases (p < 0.001). Multivariate analysis showed that PDA surgery was an independent risk factor for increased R_aw.

CONCLUSION

PDA ligation after failed pharmacological treatment is associated with impaired lung function as compared to successful pharmacological closure in infants at a postmenstrual age of 48 weeks. However, only Raw was independently affected by PDA ligation, while all other differences were merely explained by patient characteristics.

Mandatory Closure Versus Nonintervention for Patent Ductus Arteriosus in Very Preterm Infants

OBJECTIVE

To determine whether a nonintervention approach for treating hemodynamically significant patent ductus arteriosus (PDA) is associated with decreased mortality and/or morbidity compared with a mandatory closure approach in extremely low birth weight infants.

STUDY DESIGN

We reviewed the medical records of 178 infants of 23-26 weeks' gestational age with PDA, requiring ventilator treatment, and with hemodynamically significant PDA ≥2 mm in size. Mandatory closure was used during period I (July 2009 to December 2011, n = 81), and nonintervention was used during period II (January 2012 to June 2014, n = 97).

RESULTS

During period I, 64% of infants were first treated with indomethacin, and 82% were ultimately ligated surgically. During period II, no infant was treated with indomethacin and/or ligation. The average postnatal day of PDA closure was day 13 and day 44 during periods I and II, respectively. There was significantly more use of diuretics and fluid restriction during period II compared with period I. There was no difference in mortality or morbidities such as necrotizing enterocolitis or intraventricular hemorrhage. The incidence of bronchopulmonary dysplasia (BPD) and the propensity score adjusted OR of BPD were significantly lower during period II compared with period I.

CONCLUSIONS

Despite longer PDA exposure, nonintervention was associated with significantly less BPD compared with mandatory closure. Additional study is warranted to determine the benefits and risks of non-intervention for the hemodynamically significant PDA in extremely low birth weight infants.

Management of patent ductus arteriosus in preterm infants--where do we stand?

Patent ductus arteriosus (PDA) in preterm infants is a controversial topic in the management of preterm neonates. There are no generally accepted guidelines for diagnosis, treatment, and follow-up of PDA, and few publications have covered the whole topic or have been conclusively summarized to give a proper direction for the treating physician. Major issues remain to be clarified, both with respect to diagnosis and treatment. The definition of hemodynamic significance varies because of different use of echocardiographic criteria and uncertainty about the role of biomarkers. The detailed risks and benefits of available treatment alternatives are still under investigation. There has been a general shift in the management of PDA in preterm neonates from the "aggressive approach" to a more "conservative approach," but the effects of this strategy on morbidity in a longer time perspective are not fully known. An individualized therapeutic strategy with special emphasis on identification of hemodynamically significance seems to be the way forward. In this review we put forward the scientific background in favor of a seemingly growing body of evidence against active treatment, but we raise caution against shying away from all forms of treatment or instituting them too late. Finally, we try to integrate the current knowledge into suggestions for the management of PDA in premature infants.

Liver disease after intensive care of premature baboons: histopathologic observations

BACKGROUND AND OBJECTIVES

Cholestasis affects 50% of extremely low-birth-weight infants. Its etiology remains poorly understood and the extent of liver injury in these infants is unclear. The premature baboon model provides an opportunity to study neonatal liver disease. We characterize hepatic histopathologic changes in this model.

METHODS

Archival tissue and data were obtained from the Southwest Foundation for Biomedical Research Primate Center, San Antonio, TX. Animals were selected based on history of antenatal steroid therapy and absence of sepsis or necrotizing enterocolitis with a protocol duration of at least 21 days and no early death (n = 45). Baboons had been treated per protocol in the neonatal intensive care unit (NICU). At necropsy, liver tissue was harvested and stored. Tissues from fetal gestational controls at similar ages were used for comparison (n = 28). Histologic changes were scored by consensus of 2 pathologists blinded to treatment group. Descriptive and comparative statistics were performed.

RESULTS

Control fetal livers had extramedullary hematopoiesis (EMH) that decreased across the gestational range. There was evidence of hepatocyte iron storage and ongoing portal tract development. Livers of NICU-treated baboons had increased Kupffer cell hypertrophy and hemosiderosis. There was a shift away from erythroid EMH toward increased myeloid EMH. There was increased cholestasis, ductular proliferation, portal tract fibrosis, and steatosis in treated animals.

CONCLUSIONS

We found pathologic changes in NICU-treated baboons comparable with findings reported in human infants. The baboon model of prematurity may be a useful tool to explore cholestasis and liver dysfunction in extremely low-birth-weight infants.

The role of patent ductus arteriosus and its treatments in the development of bronchopulmonary dysplasia

A persistent left-to-right shunt through a patent ductus arteriosus (PDA) increases the rate of hydrostatic fluid filtration into the lung's interstitium, impairs pulmonary mechanics, and prolongs the need for mechanical ventilation. In preclinical trials, pharmacologic PDA closure leads to improved alveolarization and minimizes the impaired postnatal alveolar development that is the pathologic hallmark of the "new bronchopulmonary dysplasia (BPD)". Although early pharmacologic closure of the PDA decreases the incidence of pulmonary hemorrhage, intraventricular hemorrhage, and the need for PDA ligation, there is little evidence from controlled, clinical trials to support or refute a causal role for the PDA in the development of BPD. However, evidence from epidemiologic, preclinical, and randomized controlled clinical trials demonstrate that early ductus ligation is an independent risk factor for the development of BPD and may directly contribute to the neonatal morbidities it is trying to prevent.

Hyperglycemia increases the risk of death in extremely preterm baboons

BACKGROUND

Transient neonatal hyperglycemia (HG) has been reported in up to 80% of extremely preterm human infants. We hypothesize that severe HG is associated with increased morbidity and mortality in preterm baboons.

METHODS

Sixty-six baboons born at 67% of gestation were studied. HG was defined as serum glucose level ≥150 mg/dl during the first week of life. Animals were stratified into two groups: severe HG (≥8 events) and nonsevere HG (<8 events).

RESULTS

HG developed in 65 of the 66 (98%) baboons that were included. A total of 3,386 glucose measurements were obtained. The mean serum glucose level was 159 ± 69 mg/dl for the severe HG group and 130 ± 48 mg/dl for the nonsevere HG group during the first week of life. No differences were found in gender, birth weight, sepsis, patent ductus arteriosus, or oxygenation/ventilation indexes between groups. Severe HG was associated with early death even after controlling for sepsis, postnatal steroid exposure, and catecholamine utilization.

CONCLUSION

HG is common in preterm baboons and is not associated with short-term morbidity. Severe HG occurring in the first week of life is associated with early death in preterm baboons.

Transient decrease in PaCO(2) and asymmetric chest wall dynamics in early progressing pneumothorax

PURPOSE

Diagnosis of pneumothorax (PTX) in newborn infants has been reported as late. To explore diagnostic indices for early detection of progressing PTX, and offer explanations for delayed diagnoses.

METHODS

Progressing PTX was created in rabbits (2.3 ± 0.5 kg, n = 7) by injecting 1 ml/min of air into the pleural space. Hemodynamic parameters, tidal volume, EtCO(2), SpO(2), blood gas analyses and chest wall tidal displacements (TDi) on both sides of the chest were recorded.

RESULTS

(Mean ± SD): A decrease in SpO(2) below 90 % was detected only after 46.6 ± 11.3 min in six experiments. In contrary to the expected gradual increase of CO(2), there was a prolonged transient decrease of 14.2 ± 4.5 % in EtCO(2) (p < 0.01), and a similar decrease in PaCO(2) (p < 0.025). EtCO(2) returned back to baseline only after 55.2 ± 24.7 min, and continued to rise thereafter. The decrease in CO(2) was a mirror image of the 14.6 ± 5.3 % increase in tidal volume. The analysis of endotracheal flow and pressure dynamics revealed a paradoxical transient increase in the apparent compliance. Significant decrease in mean arterial blood pressure was observed after 46.2 ± 40.1 min. TDi provided the most sensitive and earliest sign of PTX, decreasing on the PTX side after 16.1 ± 7.2 min. The TDi progressively decreased faster and lower on the PTX side, thus enabling detection of asymmetric ventilation.

CONCLUSIONS

The counterintuitive transient prolonged decrease in CO(2) without changes in SpO(2) may explain the delay in diagnosis of PTX encountered in the clinical environment. An earlier indication of asymmetrically decreased ventilation on the affected side was achieved by monitoring the TDi.

Vocal cord paralysis post patent ductus arteriosus ligation surgery: risks and co-morbidities

OBJECTIVES

1. To determine the prevalence of left vocal cord paralysis (LVCP) post patent ductus arteriosus (PDA) ligation at a Tertiary Care Centre. 2. To identify risk factors associated with LVCP. 3. To identify co-morbidities associated with LVCP. 4. To determine the frequency of pre- and post-operative nasopharyngolaryngoscopic (NPL) examination in this patient population.

METHODS

Retrospective chart review of all infants who underwent PDA ligation surgery at a tertiary care academic hospital between July 2003 and July 2010. Data on patient age, gender, weight, method of PDA ligation, and results of NPL scoping were collected, as well as patient co-morbidities post PDA ligation.

RESULTS

One hundred and fifteen patients underwent PDA ligation surgery. Four patients were excluded due to bilateral vocal cord paralysis. Of the remaining 111 patients, nineteen patients (17.1%) were found to have LVCP. Low birth weight was identified as a significant risk factor for LVCP (p=0.002). Gastroesophageal reflux was identified as a significant co-morbidity associated with LVCP post PDA ligation (p=0.002). Only 0.9% of patients were scoped pre-operatively, and 27.9% were scoped postoperatively.

CONCLUSIONS

LVCP is associated with multiple morbidities. The authors strongly recommend routine post-operative scoping of all patients post PDA ligation surgery, and preoperative scoping when possible. A prospective study is warranted, in order to confirm the prevalence of LVCP as well as risk factors and associated co-morbidities.

Patent ductus arteriosus: are current neonatal treatment options better or worse than no treatment at all?

Although a moderate-sized patent ductus arteriosus (PDA) needs to be closed by the time a child is 1-2 years old, there is great uncertainty about whether it needs to be closed during the neonatal period. Although 95% of neonatologists believe that a moderate-sized PDA should be closed if it persists in infants (born before 28 weeks) who still require mechanical ventilation, the number of neonatologists who treat a PDA when it occurs in infants who do not require mechanical ventilation varies widely. Both the high likelihood of spontaneous ductus closure and the absence of randomized controlled trials, specifically addressing the risks and benefits of neonatal ductus closure, add to the current uncertainty. New information suggests that early pharmacologic treatment has several important short-term benefits for the preterm newborn. By contrast, ductus ligation, while eliminating the detrimental effects of a PDA on lung development, may create its own set of morbidities that counteract many of the benefits derived from ductus closure.

Relationship between circulating platelet counts and ductus arteriosus patency after indomethacin treatment

OBJECTIVE

To determine whether low platelet counts are related to the incidence of patent ductus arteriosus (PDA) after indomethacin treatment in preterm human infants.

STUDY DESIGN

Multivariable logistic regression modeling was used for a cohort of 497 infants, who received indomethacin (within 15 hours of birth).

RESULTS

Platelet counts were not related to the incidence of permanent closure after indomethacin constriction. There was a relationship between platelet counts and the initial degree of constriction; however, this relationship appeared to be primarily influenced by the high end of the platelet distribution curve. PDA incidence was similar in infants with platelet counts < 50 × 10⁹/L and those with platelet counts above this range. Only when platelet counts were consistently >230 ×10⁹/L was there a decrease in PDA incidence.

CONCLUSION

In contrast to the evidence in mice, low circulating platelet counts do not affect permanent ductus closure (or ductus reopening) in human preterm infants.

Impaired lung function after intubation and mechanical ventilation for surgical ligation of the ductus arteriosus in preterm infants

OBJECTIVE

Significant patent ductus arteriosus (PDA) in the preterm infant has been associated with pulmonary edema and impaired gas exchange. Therefore, surgical ligature of the DA may be required. However, the effects of intubation and mechanical ventilation on the PDA-induced lung dysfunction presently are unknown. The aim of the study was to investigate whether intubation and mechanical ventilation alter pulmonary function in the preterm infant with significant PDA.

DESIGN

A prospective study.

SETTING

The neonatal intensive care unit and department of anesthesiology in a university hospital.

PARTICIPANTS

Preterm infants <32 weeks' gestational age treated with nasal continuous positive airway pressure (NCPAP) and requiring mechanical ventilation for undergoing surgical DA ligature.

INTERVENTIONS

Respiratory, Doppler echocardiographic parameters, and chest x-ray transparencies of the lungs were measured during NCPAP and 2 hours after intubation and starting mechanical ventilation.

MEASUREMENTS AND MAIN RESULTS

Twenty preterm infants (gestational age = 27 ± 1 wk, birth weight = 950 ± 140 g) were included. Heart rate, O(2) need, PaCO(2), and plasma lactate concentrations were significantly higher after intubation. The mean oxygenation index increased from 1.5 ± 0.6 to 7.2 ± 3 (p < 0.05). The overall transparencies of the lungs decreased after intubation. DA diameter, shortening fraction of the left ventricle, left pulmonary artery blood flow velocities, and left atrium/aorta did not change.

CONCLUSION

In preterm infants with significant PDA, intubation and mechanical ventilation before surgical DA ligation may increase the O(2) need and PaCO(2) and may promote lung edema formation. Mechanical ventilation-induced impairment in lung function is not associated with a change in pulmonary or systemic circulation or DA flow. Special care should be taken to prevent respiratory failure when intubation and mechanical ventilation are required for undergoing surgical DA ligation in the preterm infant.

Patent ductus arteriosus ligation alters pulmonary gene expression in preterm baboons

Ibuprofen-induced ductus closure improves pulmonary mechanics and increases alveolar surface area in premature baboons compared with baboons with a persistent patent ductus arteriosus (PDA). Ibuprofen-treatment has no effect on the expression of genes that regulate pulmonary inflammation but does increase the expression of alpha-ENaC (the transepithelial sodium channel that is critical for alveolar water clearance). Although ligation eliminates the PDA, it does not improve pulmonary mechanics or increase alveolar surface area. We used preterm baboons (delivered at 67% of term gestation and ventilated for 14 d) to study whether the lack of beneficial effects, after PDA ligation, might be due to alterations in pulmonary gene expression. We found no differences in ventilation or oxygenation indices between animals that were ligated (n = 7) on day of life 6 and those that had a persistent PDA (n = 12) during the entire 14 d study. In contrast with no intervention, PDA ligation produced a significant increase in the expression of genes involved with pulmonary inflammation (COX-2, TNF-α, and CD14) and a significant decrease in alpha-ENaC sodium channel expression. We speculate that these changes may decrease the rate of alveolar fluid clearance and contribute to the lack of improvement in pulmonary mechanics after PDA ligation.

The effects of postnatal estrogen therapy on brain development in preterm baboons

OBJECTIVE

Estrogen receptors are present within the fetal brain, suggesting that estrogens may exert an influence on cerebral development. Loss of placentally derived estrogen in preterm birth may impair development.

STUDY DESIGN

Baboons were delivered at 125 days of gestation (term approximately 185 days), randomly allocated to receive estradiol (n = 10) or placebo (n = 8), and ventilated for 14 days. Brains were assessed for developmental and neuropathological parameters.

RESULTS

Body and brain weights were not different between groups, but the brain/body weight ratio was increased (P < .05) in estradiol-treated animals. There were no differences (P > .05) between groups in any neuropathological measure in either the forebrain or cerebellum. There were no intraventricular hemorrhages; 1 estradiol animal displayed ectactic vessels in the subarachnoid space.

CONCLUSION

Brief postnatal estradiol administration to primates does not pose an increased risk of injury or impaired brain development.

Patterns of gene expression in the ductus arteriosus are related to environmental and genetic risk factors for persistent ductus patency

Three independent risk factors (immature gestation, absence of antenatal glucocorticoid exposure, and presence of the rs2817399(A) allele of the gene TFAP2B) are associated with patent ductus arteriosus (PDAs) that fail to close during prostaglandin inhibition. We hypothesized that these three factors may affect a common set of genes that increase the risk of persistent PDA after birth. We studied baboon ductus from term, preterm, and glucocorticoid-treated preterm fetuses and found that both immature gestation and absence of antenatal glucocorticoid exposure decreased RNA expression of calcium- and potassium-channel genes involved in oxygen-induced constriction, and phosphodiesterase genes (that modulate cAMP/cGMP signaling). Ductus obtained from second trimester human pregnancies were genotyped for TFAP2B polymorphisms. When present, the rs2817399(A) allele also was associated with decreased expression of calcium- and potassium-channel genes. In contrast, alleles of two other TFAP2B polymorphisms, rs2817419(G) and rs2635727(T), which are not related to the incidence of PDA after birth, had no effect on RNA expression. In conclusion, three calcium- and potassium-channel genes (CACNA1G/ alpha1G, CACNB 2/CaL-beta2, and KCNA2/ Kv1.2) were similarly affected by each of the PDA risk factors. We speculate that these channels may play a significant role in closing the preterm ductus during prostaglandin inhibition and may be potential targets for future pharmacologic manipulations.

Early surgical ligation versus a conservative approach for management of patent ductus arteriosus that fails to close after indomethacin treatment

OBJECTIVE

To examine whether a more conservative approach to treating patent ductus arteriosus (PDA) is associated with an increase or decrease in morbidity compared with an approach involving early PDA ligation.

STUDY DESIGN

In January 2005, we changed our approach to infants born at age

RESULTS

The 2 periods had similar rates of perinatal/neonatal risk factors and indomethacin failure (24%), as well as ventilator management and feeding advance protocols. The conservative approach (period 2) was associated with decreased rates of duct ligation (72% vs 100%; P<.05). Even though infants subjected to this approach were exposed to larger PDA shunts for longer durations, the rates of bronchopulmonary dysplasia, sepsis, retinopathy of prematurity, neurologic injury, and death were similar to those in period 1. The overall rate of necrotizing enterocolitis was significantly lower in period 2 compared with period 1.

CONCLUSIONS

These findings support the need for new controlled, randomized trials to reexamine the benefits and risks of different approaches to PDA treatment.

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Key Words

• surgery
• ductus ligation
• indomethacin
• patent ductus arteriosus

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MESH Headings

• Ductus Arteriosus, Patent/drug therapy
• Ductus Arteriosus, Patent/surgery
• Female
• Humans
• Indomethacin/therapeutic use
• Infant, Newborn
• Ligation
• Male
• Prospective Studies
• Time Factors
• Treatment Failure

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Grants

• R01 HL046691 NHLBI NIH HHS
• R01 HL046691-16 NHLBI NIH HHS
• UL1 RR024131 NCRR NIH HHS
• HL46691 NHLBI NIH HHS

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Affiliation(s)

Nami Jhaveri Department of Pediatrics, University of California, San Francisco, CA 94143-0544, USA
Anita Moon-Grady
Ronald I Clyman

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Neuronal damage in the preterm baboon: impact of the mode of ventilatory support

We evaluated the impact of randomized ventilatory strategies on specific neuronal populations of the cerebral cortex of preterm baboons. In the first series, baboons (n = 5) were delivered at 125 days of gestation (dg; term, 185 days) and exposed to 14 days of positive pressure ventilation (PPV) and compared with 140 dg controls (n = 6). In the second series, baboons were delivered at 125 dg and ventilated by either i) PPV for 1 day, followed by 27 days of nasal continuous positive airway pressure (early [EnCPAP]; n = 6) or ii) PPV for 5 days, followed by 23 days of CPAP (delayed [DnCPAP]; n = 4). Gestational controls were delivered at 153 dg (n = 3). The density of immunoreactive neurons for calretinin and somatostatin was assessed in the primary and secondary visual cortices, cingulate and parietal cortices, and subiculum in paraffin sections. Compared with gestational controls, PPV for 14 days resulted in a reduction in the density of calretinin-positive cells in the visual cortex (Areas 17 and 18) but not in the other cortical areas. No effect of PPV was observed on somatostatin-positive cells. DnCPAP, but not EnCPAP, was associated with a reduction in the density of calretinin and somatostatin-positive cells in the visual cortical areas but not in the other cortical areas compared with gestational controls. Taken together, these data demonstrate that ventilatory strategies involving greater than 5 days of PPV have a regionally selective impact on cortical neuronal subpopulations within the visual area but not in areas of association cortex in a nonhuman primate model of prematurity.

Patent ductus arteriosus ligation is associated with impaired left ventricular systolic performance in premature infants weighing less than 1000 g

OBJECTIVE

Patent ductus arteriosus ligation is often complicated by systemic hypotension and oxygenation failure. The ability of the immature myocardium to compensate for altered afterload is poorly understood. The aim of this study was to characterize the effects of patent ductus arteriosus ligation on myocardial performance in preterm infants.

METHODS

Serial echocardiographic analysis was performed before and after patent ductus arteriosus ligation. Characteristics of the patent ductus arteriosus, myocardial performance (fractional shortening, mean velocity of circumferential fiber shortening, and left ventricular output) and left ventricular afterload (end-systolic wall stress) were assessed. The stress-velocity relationship was measured as a preload-independent, afterload-adjusted measure of myocardial contractility.

RESULTS

Forty-six preterm infants were assessed at 28.5 +/- 11.3 days and a weight of 1058 +/- 272 g. Patent ductus arteriosus ligation was followed by increased left ventricular exposed vascular resistance temporally coinciding with reduced left ventricular preload, decreased left ventricular contractility, and low left ventricular output. Neonates weighing 1000 g or less had a higher rate of low fractional shortening (<25%) or low left ventricular output (<170 mL x kg(-1) x h(-1)) and increased need for cardiotropes and demonstrated a trend toward an impaired stress-velocity relationship. Neonates with impaired left ventricular systolic performance were more likely to require cardiotropes and have low systolic arterial pressure, increased heart rate, and abnormal base deficit.

CONCLUSION

Patent ductus arteriosus ligation is sometimes associated with impaired left ventricular systolic performance, which is most likely attributable to altered loading conditions. Neonates weighing 1000 g or less are at increased risk of impaired left ventricular systolic performance, which might relate to maturational differences and decreased tolerance to altered loading conditions.

Pathophysiology of patent ductus arteriosus in premature neonates

Failure of complete postnatal closure of the ductus arteriosus is associated with various neonatal morbidities. Functional closure resulting from smooth muscle constriction and permanent anatomic closure due to vascular remodeling are the results of a complex interaction of different mechanisms. Prostaglandins, oxygen, nitric oxide and various other factors play a key role in ductal closure. An understanding of the role of these factors, involved both in maintenance of vascular tone of the ductus in fetal life as well as stimulation of ductal closure in postnatal life, and the cardiovascular and respiratory consequences of a patent ductus arteriosus, is important for the clinician involved in management of premature neonates.

Developmental and neuropathological consequences of ductal ligation in the preterm baboon

A patent ductus arteriosus (PDA) alters pulmonary mechanics and regional blood flow in the preterm infant. Its significance with respect to brain injury and brain development are unclear. We evaluated the effects of surgical ductal ligation on the preterm baboon brain. Baboons were delivered at 125 d of gestation (dg, term approximately 185 dg) and ventilated for 14 d (n = 12). The PDA was ligated 6 d after delivery (n = 7) or left untreated (n = 5). Animals were euthanized at 139 dg and brains compared histologically with gestational control fetuses (n = 7) at 140 dg. Brain and body weights were reduced (p < 0.05) in both groups of ventilated preterm animals; however, the brain to body weight ratio was increased (p < 0.01) in ligated, but not unligated newborns compared with gestational controls. No overt lesions were observed in either premature newborn group. Astrocyte density in the neocortex and hippocampus were greatest in the unligated newborns (p < 0.01). Myelination and oligodendrocytes were reduced (p < 0.05) in both premature newborn groups. The brain growth and development index was reduced, and the damage index was increased in prematurely delivered baboons. Surgical ligation of the PDA does not increase the incidence of brain injury and may be beneficial if the PDA is contributing to persistent pulmonary and hemodynamic instability.

Effects of a patent ductus arteriosus on postprandial mesenteric perfusion in premature baboons

BACKGROUND

Superior mesenteric artery flow increases after a feeding to meet the intestines' increased metabolic demands. Although a patent ductus arteriosus can affect superior mesenteric artery perfusion in nonfeeding infants, there is no information about its effects on the hyperemic response that follows a feeding.

OBJECTIVE

Our goal was to study the effects of a patent ductus arteriosus on superior mesenteric artery perfusion in preterm baboons.

DESIGN

Preterm baboons were delivered at 67% gestation and ventilated for 14 days. Enteral feedings were begun and advanced per protocol. Feeding studies were performed between days 10 and 14. Thirty-one studies were performed in animals with a closed ductus; 21 studies in those with a moderate patent ductus arteriosus shunt (pulmonary-to-systemic blood flow ratio>or=2:1). Two-dimensional echocardiographic and Doppler examinations were performed before and 10 and 30 minutes after a feeding. The groups were similar in birth weights, feeding volumes, and age at time of study.

RESULTS

During the preprandial period, baboons with a moderate patent ductus arteriosus had significantly lower blood pressures and systemic blood flows than animals with a closed ductus. Preprandial superior mesenteric artery-blood flow velocities did not differ between the open and closed ductus groups. Animals with a closed ductus increased their superior mesenteric artery-velocities (diastolic and mean) and decreased their superior mesenteric artery relative-vascular-resistance (mean blood pressure/mean superior mesenteric artery-velocity) by 10 minutes after the feeding. By 30 minutes after the feeding, the values were returning to their preprandial values. In contrast, in baboons in the patent ductus arteriosus group, there were no significant changes in superior mesenteric artery-velocity or resistance after the feeding, and superior mesenteric artery-velocities were significantly lower than those in the closed ductus group.

CONCLUSIONS

A moderate patent ductus arteriosus shunt limits the ability of the preterm newborn baboon to increase its postprandial mesenteric blood flow velocity. We speculate that this may interfere with its ability to meet increased intestinal metabolic demands and may contribute to feeding difficulties.

Postoperative cardiorespiratory instability following ligation of the preterm ductus arteriosus is related to early need for intervention

OBJECTIVE

To investigate the effect of postnatal age at patent ductus arteriosus (PDA) ligation on postoperative need for cardiotropic support.

STUDY DESIGN

A significant proportion of premature infants with a hemodynamically significant ductus arteriosus (HSDA) require surgical intervention. The relationship of postnatal maturation to postoperative cardiorespiratory stability is poorly understood. All preterm neonates who underwent PDA ligation between October 2002 and September 2004 were identified and divided according to postnatal age at ductal ligation, into early (<or=4 weeks, n=29) and late (>4 weeks, n=36) groups. Neonatal birth demographics and morbidities, characteristics of the HSDA and reason for ligation were reviewed. Indices of cardiorespiratory stability (for example heart rate, mean arterial pressure) were recorded before and 1, 4, 8, 12 and 24 h following ligation. Details of perioperative cardiovascular interventions (for example crystalloid boluses, cardiotropic agents) were recorded.

RESULT

There were no differences in baseline neonatal demographics between the groups although a greater number of babies requiring early ligation had contraindication to indomethacin as the main reason for ligation. Early PDA ligation was associated with increased postoperative cardiotrope requirement (27.6 vs 5.6%, P=0.02) and decreased systolic blood pressure 8 h after intervention (P<0.05). Although increased oxygenation index was observed in both groups during the first 12 h it was only sustained to 24 h in the early group (P<0.05). Age at ligation remained a significant risk factor for postoperative cardiotrope requirement on multiple logistic regression analysis.

CONCLUSION

Surgical ligation of the ductus arteriosus in preterm infants less than 28 days old is associated with oxygenation difficulties, decreased systolic arterial pressure and an increased need for cardiotropic support in the initial 24 postoperative hours. These data suggest the need to prospectively characterize perioperative cardiovascular physiology and identify predictive factors of clinical deterioration.

Ibuprofen-induced patent ductus arteriosus closure: physiologic, histologic, and biochemical effects on the premature lung

OBJECTIVE

The goal was to study the pulmonary, biochemical, and morphologic effects of a persistent patent ductus arteriosus in a preterm baboon model of bronchopulmonary dysplasia.

METHODS

Preterm baboons (treated prenatally with glucocorticoids) were delivered at 125 days of gestation (term: 185 days), given surfactant, and ventilated for 14 days. Twenty-four hours after birth, newborns were randomly assigned to receive either ibuprofen (to close the patent ductus arteriosus; n = 8) or no drug (control; n = 13).

RESULTS

After treatment was started, the ibuprofen group had significantly lower pulmonary/systemic flow ratio, higher systemic blood pressure, and lower left ventricular end diastolic diameter, compared with the control group. There were no differences in cardiac performance indices between the groups. Ventilation index and dynamic compliance were significantly improved with ibuprofen. The improved pulmonary mechanics in ibuprofen-treated newborns were not attributable to changes in levels of surfactant protein B, C, or D, saturated phosphatidylcholine, or surfactant inhibitory proteins. There were no differences in tracheal concentrations of cytokines commonly associated with the development of bronchopulmonary dysplasia. The groups had similar messenger RNA expression of genes that regulate inflammation and remodeling in the lung. Lungs from ibuprofen-treated newborns were significantly drier (lower wet/dry ratio) and expressed 2.5 times more epithelial sodium channel protein than did control lungs. By 14 days after delivery, control newborns had morphologic features of arrested alveolar development (decreased alveolar surface area and complexity), compared with age-matched fetuses. In contrast, there was no evidence of alveolar arrest in the ibuprofen-treated newborns.

CONCLUSIONS

Ibuprofen-induced patent ductus arteriosus closure improved pulmonary mechanics, decreased total lung water, increased epithelial sodium channel expression, and decreased the detrimental effects of preterm birth on alveolarization.

Fisioterapia em recém-nascidos com persistência do canal arterial e complicações pulmonares

OBJETIVOS: Revisar as complicações pulmonares e intervenções fisioterapêuticas disponíveis para recém-nascidos com persistência do canal arterial (PCA). FONTES DE DADOS: Artigos publicados nas fontes de dados Medline e Lilacs, além de capítulos de livros nos idiomas português e inglês, entre 1992 e 2006. As palavras-chave utilizadas para busca foram: "canal arterial", "prematuridade", "síndrome do desconforto respiratório", "complicações" e "pulmão". SÍNTESE DOS DADOS: A PCA é uma intercorrência freqüente em recém-nascidos pré-termos, que pode se associar a complicações pulmonares, tais como atelectasias, infecções pulmonares e falha na extubação, aumentando o tempo de ventilação mecânica e de internação na Unidade de Terapia Intensiva Neonatal. Os recursos fisioterapêuticos visam melhorar as condições pulmonares, propiciando o aumento da complacência pulmonar e a diminuição da resistência de vias aéreas, além de otimizar o mecanismo de depuração mucociliar e, dessa forma, reduzir o trabalho respiratório. CONCLUSÕES: A fisioterapia respiratória contribui para melhorar a evolução dos neonatos com complicações pulmonares por persistência de canal arterial, permitindo otimizar a mecânica respiratória, além de melhorar a oxigenação e a relação ventilação/perfusão.

Ductus arteriosus ligation and alveolar growth in preterm baboons with a patent ductus arteriosus

Premature newborn baboons [125 d (67%) gestation], exposed to a moderate-size patent ductus arteriosus (PDA) [pulmonary-to-systemic blood-flow-ratio (Qp/Qs) = 1.8] for 14 d, have impaired pulmonary function and arrested alveolar development and surface area when compared with age matched fetuses (140 d gestation). Pharmacologic closure of the PDA reduces the detrimental effects of preterm delivery on pulmonary function and surface area. We used preterm baboons (delivered at 125 d gestation and ventilated for 14 d) to study the effects of surgical PDA ligation on pulmonary function and alveolar surface area. After ligation (on day of life 6), ligated animals had lower Qp/Qs ratios [Qp/Qs (ligated, n = 10) = 1.00 +/- 0.04; (nonligated, n = 12) = 2.05 +/- 0.17; mean +/- SD] and higher systemic blood pressures than nonligated control animals. Ventilation and oxygenation indices did not differ between the groups, during either the pre- or postoperative periods. Alveolar surface area measurements were made by digital image analysis and compared with measurements made from fetal lungs at 125 d (n = 6) and 140 d (n = 7) gestation. PDA ligation failed to improve the postnatal arrest in alveolar surface area. In contrast with pharmacologic closure of the PDA, surgical closure failed to improve either pulmonary function or alveolar surface area in baboons with a moderate PDA shunt.

Patent ductus arteriosus: an overview

Patent ductus arteriosus (PDA) is one of the most common congenital heart defects, accounting for 5%-10% of all congenital heart disease in term infants. The occurrence of PDA is inversely related to gestational age and weight, with an even greater incidence in preterm infants. The maintenance of ductal patency is essential for the normal development of the fetus. In the neonate, however, persistent patency of the ductus arteriosus (DA) is associated with significant morbidity and mortality. Normally, at birth, the DA constricts, resulting in intraluminal ischemic hypoxia, which eventually leads to closure and remodeling of the ductus. PDA in term infants is usually associated with a functional defect, whereas in preterm infants it is associated with immaturity. Normal physiologic mechanisms contributing to closure - oxygen tension and decreased prostaglandins-are altered in prematurity. Clinical signs of ductal patency include murmur, tachycardia, bounding peripheral pulses, and congestive heart failure and associated symptoms. Symptoms are not always present; therefore, diagnostic imaging is critical if a PDA is suspected on clinical grounds. Three management strategies are currently available for PDA: fluid restriction and diuretics (as clinically appropriate), medical intervention, and surgical ligation. Pharmacologic closure can be achieved via administration of intravenous indomethacin or ibuprofen lysine. While both agents have shown similar efficacy, ibuprofen lysine has demonstrated an improved safety profile, particularly in terms of renal effects, compared to indomethacin.

Patent ductus arteriosus: an overview

Patent ductus arteriosus (PDA) is one of the most common congenital heart defects, accounting for 5%-10% of all congenital heart disease in term infants. The occurrence of PDA is inversely related to gestational age and weight, with an even greater incidence in preterm infants. The maintenance of ductal patency is essential for the normal development of the fetus. In the neonate, however, persistent patency of the ductus arteriosus (DA) is associated with significant morbidity and mortality. Normally, at birth, the DA constricts, resulting in intraluminal ischemic hypoxia, which eventually leads to closure and remodeling of the ductus. PDA in term infants is usually associated with a functional defect, whereas in preterm infants it is associated with immaturity. Normal physiologic mechanisms contributing to closure - oxygen tension and decreased prostaglandins-are altered in prematurity. Clinical signs of ductal patency include murmur, tachycardia, bounding peripheral pulses, and congestive heart failure and associated symptoms. Symptoms are not always present; therefore, diagnostic imaging is critical if a PDA is suspected on clinical grounds. Three management strategies are currently available for PDA: fluid restriction and diuretics (as clinically appropriate), medical intervention, and surgical ligation. Pharmacologic closure can be achieved via administration of intravenous indomethacin or ibuprofen lysine. While both agents have shown similar efficacy, ibuprofen lysine has demonstrated an improved safety profile, particularly in terms of renal effects, compared to indomethacin.

Changes in myocardial function and hemodynamics after ligation of the ductus arteriosus in preterm infants

OBJECTIVE

To characterize the changes in systemic hemodynamics and systolic, diastolic, and global myocardial performance after patent ductus arteriosus (PDA) ligation in very-low-birth-weight infants.

STUDY DESIGN

Echocardiograms were performed on 23 neonates (mean gestational age, 26.2 +/- 2.2 weeks) at 2.3 +/- 2.0 hours before PDA ligation (n = 23) and at 2.0 +/- 1.4 hours (n = 23) and 23.5 +/- 2.5 hours after (n = 11) PDA ligation.

RESULTS

Mean blood pressure, heart rate, load-independent contractility, shortening fraction, left ventricular (LV) afterload, and diastolic function did not change. Preload (early and atrial mitral inflow velocities) decreased immediately after ligation but remained unchanged thereafter. LV output decreased and systemic vascular resistance increased after surgery. The LV myocardial performance index (MPI), a measure of global myocardial performance, deteriorated acutely after ligation but improved by 23.5 hours after surgery. Changes in LV MPI were most closely correlated with changes in LV output.

CONCLUSIONS

After PDA ligation, LV output and MPI decrease, due primarily to a decrease in LV preload, although LV contractility and diastolic function do not change. However, the changes in LV MPI after ligation also reflect an acute deterioration followed by an improvement in global cardiac function, because LV loading conditions remained unchanged after surgery and thus cannot explain the improvement in MPI by 24 hours after ligation.

Patent ductus arteriosus and its treatment as risk factors for neonatal and neurodevelopmental morbidity

OBJECTIVES

The purpose of this work was to determine whether the reported association between neonatal morbidities and a patent ductus arteriosus is because of the left-to-right patent ductus arteriosus shunt itself, the therapies used to treat it, or the immaturity of the infants who are likely to develop a patent ductus arteriosus.

METHODS

A total of 446 infants (<28 weeks' gestation) were treated with the same patent ductus arteriosus care-oriented protocol, and logistic regression analysis was used to examine the effects of several patent ductus arteriosus-related variables (presence of a symptomatic patent ductus arteriosus, the number of indomethacin doses used, the ductus response to indomethacin, and the use of surgical ligation) on the incidence of retinopathy of prematurity, necrotizing enterocolitis, chronic lung disease, death, and neurodevelopmental impairment.

RESULTS

Most of the predictive effects that the presence of a patent ductus arteriosus and its treatment had on neonatal morbidity could be accounted for by the infants' immature gestation. Use of surgical ligation, however, was significantly associated with the development of chronic lung disease and was independent of immature gestation, other patent ductus arteriosus-related variables, or other perinatal and neonatal risk factors known to be associated with chronic lung disease.

CONCLUSIONS

These findings add to the growing uncertainty about the benefits and risks of surgical ligation during the neonatal period.

High levels of CXCL8 in tracheal aspirate samples taken at birth are associated with adverse respiratory outcome only in preterm infants younger than 28 weeks gestation

We investigated the relation between perinatal endotracheal colonization, the associated cytokine response and respiratory outcome in ventilated preterm neonates. Between September 1999 and March 2002, a cohort of 141 neonates with a gestational age <31 weeks requiring ventilation directly after birth, were followed prospectively. All were admitted to the Neonatal Intensive Care Unit, University Hospital of Antwerp, Belgium. A tracheal aspirate (TA) sample was collected soon after birth and was processed for microbiological examination, leukocyte count, and cytokine analysis (interleukins [IL] IL-1beta, IL-6, CXCL8 (formerly called IL-8), IL-10, IL-12p70 and tumor necrosis factor alpha [TNF-alpha]). Together with the prospectively registered patient's comorbidities and severity of disease, these inflammatory parameters were analyzed in a multivariate Cox proportional hazards model with time of extubation and duration of oxygen therapy as main outcome measures. Of the 141 patients included, 31 (22%) died before discharge from the unit and 37 (26%) had a positive TA culture. Independent predictors of duration of mechanical ventilation were: gestational age <28 weeks, degree of respiratory distress syndrome (RDS) at birth, significant patent ductus arteriosus (PDA), the SNAP-score, and high levels of CXCL8 (>4,153 pg/ml) in TA only in neonates with a gestational age <28 weeks. Variables associated with extended duration of oxygen therapy were gestational age <28 weeks, birth weight <1,000 g, degree of RDS at birth, and duration of mechanical ventilation.

Improved lung growth and function through hypoxia-inducible factor in primate chronic lung disease of prematurity

Bronchopulmonary dysplasia (BPD), a chronic lung disease affecting preterm neonates, is associated with significant childhood and adult health problems. Histopathologic features of BPD include impaired vascular and distal airway development. We previously showed that activation of hypoxia-inducible factors (HIFs) by inhibition of prolyl hydroxylase domain-containing proteins (PHDs) is feasible and that it stimulates vascular endothelial growth factor (VEGF)-dependent angiogenesis in vitro. We tested the hypothesis that enhancement of angiogenesis by activation of HIFs improves lung growth and function in prematurely born neonates in vivo. Preterm baboons (125 day+14 day pro re nata O2 model, corresponding to 27 human gestational weeks) were treated for 14 days with intravenous (i.v.) FG-4095, a PHD inhibitor. Notably, 77% of diminished total alveolar surface area in untreated controls was recovered by FG-4095 treatment. Functional significance of the structural changes was indicated by improved oxygenation and lung compliance in FG-4095-treated newborns. Surfactant proteins B and C and saturated phosphatidylcholine were unchanged. Incidence of spontaneous ductus arteriosus closure was increased, likely contributing to lower ratio of pulmonary to systemic blood flow in FG-4095 group. These findings indicate that HIF stimulation by PHD inhibition ameliorates pathological and physiological consequences of BPD.

Indomethacin prophylaxis, patent ductus arteriosus, and the risk of bronchopulmonary dysplasia: further analyses from the Trial of Indomethacin Prophylaxis in Preterms (TIPP)

OBJECTIVES

To determine the risk of bronchopulmonary dysplasia (BPD) in subgroups of infants with and without patent ductus arteriosus (PDA) who were randomized to indomethacin prophylaxis or placebo, and to examine whether adverse drug effects on edema formation and oxygenation may explain why indomethacin prophylaxis does not reduce BPD.

STUDY DESIGN

We studied 999 extremely low birth weight infants who participated in the Trial of Indomethacin Prophylaxis in Preterms (TIPP) and who survived to a postmenstrual age of 36 weeks.

RESULTS

The incidence of BPD in the 2 subgroups of infants with PDA was 52% (55/105) after indomethacin prophylaxis and 56% (137/246) after placebo. In contrast, rates of BPD in the 2 subgroups without a PDA were 43% (170/391) after indomethacin prophylaxis and 30% (78/257) after placebo (P [interaction] = .015). Logistic regression analysis with adjustment for prognostic baseline factors showed that adverse and independent effects of indomethacin prophylaxis on the need for supplemental oxygen and on weight loss by the end of the first week of life may increase the risk of BPD in infants without PDA.

CONCLUSIONS

Harmful side effects on oxygenation and edema formation may explain why indomethacin prophylaxis does not prevent BPD even though it reduces PDA.