Effects of catecholamines on the pulmonary circulation in the ovine fetus

Hemodynamic effects of noradrenaline in neonatal septic shock: a prospective cohort study

BACKGROUND

The incidence of neonatal septic shock in low-income countries is 26.8% with a mortality rate of 35.4%. The evidence of the hemodynamic effects of noradrenaline in neonates remains sparse. This study was carried out to evaluate the effects of noradrenaline in neonates with septic shock.

METHODS

This was a single-center prospective cohort study in a tertiary care hospital's level III neonatal intensive care unit. Neonates with septic shock and those who received noradrenaline as a first-line vasoactive agent were included. Clinical and hemodynamic parameters were recorded before and after one hour of noradrenaline infusion. The primary outcomes were: response at the end of one hour after starting noradrenaline infusion and mortality rate.

RESULTS

A total of 21 babies were analyzed. The cohort comprised 17 preterm neonates. The mean age of presentation with septic shock was 74.3 h. Resolution of shock at one hour after starting noradrenaline was achieved in 76.2% of cases. The median duration of hospital stay was 14 days. The mean blood pressure improved after the initiation of noradrenaline from 30.6 mm of Hg [standard deviation (SD) 6.1] to 37.8 mm of Hg (SD 8.22, p < 0.001). Fractional shortening improved after noradrenaline initiation from 29% (SD 13.5) to 45.1% (SD 21.1, p < 0.001). The mortality rate was 28.6% in our study.

CONCLUSION

Noradrenaline is a potential drug for use in neonatal septic shock, with improvement in mean blood pressure and fractional shortening; however, further studies with larger sample sizes are needed to confirm our findings before it can be recommended as first-line therapy in neonatal septic shock.

The use of milrinone in neonates with persistent pulmonary hypertension of the newborn - a randomised controlled trial pilot study (MINT 1)

OBJECTIVE

To assess the impact of milrinone administration on time spent on nitric oxide (iNO) in infants with acute pulmonary hypertension (aPH). We hypothesized that intravenous milrinone used in conjunction with iNO would reduce the time on iNO therapy and the time spent on invasive ventilation in infants ≥34 weeks gestation with a diagnosis of aPH. We aimed to assess the practicality of instituting the protocol and contributing to a sample size calculation for a definitive multicentre study.

STUDY DESIGN

This was a multicentre, randomized, double-blind, two arm pilot study, with a balanced (1:1) allocation. Infants with a gestation ≥34 weeks and a birth weight ≥2000 grams aPH, an oxygenation index of ≥10, and commenced on iNO were eligible. Participants on iNO were assigned to either a milrinone infusion (intervention) or a normal saline infusion (placebo) for up to 35 h. The primary outcome was time on iNO and feasibility of conducting the protocol.

RESULTS

The trial was terminated early after 4 years of enrollment due to poor recruitment. Four infants were allocated to the intervention arm and 5 to the placebo arm. The groups were well matched for baseline variables. No differences were seen in any of the primary or secondary outcomes.

CONCLUSION

Conducting an interventional trial in the setting of acute pulmonary hypertension in infants is not feasible using our current approach. Future studies in this area require alternative trial design to improve recruitment as this topic remains understudied in the neonatal field.

TRIAL REGISTRATION

www.isrctn.com ; ISRCTN:12949496; EudraCT Number:2014-002988-16.

Gestational long-term hypoxia induces metabolomic reprogramming and phenotypic transformations in fetal sheep pulmonary arteries

Gestational long-term hypoxia increases the risk of myriad diseases in infants including persistent pulmonary hypertension. Similar to humans, fetal lamb lung development is susceptible to long-term intrauterine hypoxia, with structural and functional changes associated with the development of pulmonary hypertension including pulmonary arterial medial wall thickening and dysregulation of arterial reactivity, which culminates in decreased right ventricular output. To further explore the mechanisms associated with hypoxia-induced aberrations in the fetal sheep lung, we examined the premise that metabolomic changes and functional phenotypic transformations occur due to intrauterine, long-term hypoxia. To address this, we performed electron microscopy, Western immunoblotting, calcium imaging, and metabolomic analyses on pulmonary arteries isolated from near-term fetal lambs that had been exposed to low- or high-altitude (3,801 m) hypoxia for the latter 110+ days of gestation. Our results demonstrate that the sarcoplasmic reticulum was swollen with high luminal width and distances to the plasma membrane in the hypoxic group. Hypoxic animals were presented with higher endoplasmic reticulum stress and suppressed calcium storage. Metabolically, hypoxia was associated with lower levels of multiple omega-3 polyunsaturated fatty acids and derived lipid mediators (e.g., eicosapentaenoic acid, docosahexaenoic acid, α-linolenic acid, 5-hydroxyeicosapentaenoic acid (5-HEPE), 12-HEPE, 15-HEPE, prostaglandin E3, and 19(20)-epoxy docosapentaenoic acid) and higher levels of some omega-6 metabolites (P < 0.02) including 15-keto prostaglandin E2 and linoleoylglycerol. Collectively, the results reveal broad evidence for long-term hypoxia-induced metabolic reprogramming and phenotypic transformations in the pulmonary arteries of fetal sheep, conditions that likely contribute to the development of persistent pulmonary hypertension.

Milrinone Use in Persistent Pulmonary Hypertension of the Newborn

Failure of the normal transition from in utero to ex utero physiology leads to "persistent" pulmonary hypertension of the newborn (PPHN). PPHN is frequently associated with low systemic blood pressure and low cardiac output because of increased right ventricular afterload and myocardial dysfunction. The general management of newborns with PPHN is geared toward maintenance of normothermia, normal serum electrolytes, normal intravascular volume, correction of acidosis, adequate sedation/analgesia, adequate ventilation and oxygenation with optimal lung recruitment, and avoidance of hyperoxia. Inotropic and vasoactive agents are commonly initiated early to increase cardiac output, maintain adequate systemic blood pressure, and enhance oxygen delivery to the tissue. Unfortunately, there is not much evidence on the choice, timing of initiation, dosing, monitoring, and titrating of vasoactive agents in this patient population. In this review, we will discuss the pathophysiology of PPHN and review the use of inotropic, lusitropic, and vasoactive agents in the management of PPHN, with particular attention to milrinone.

The use of milrinone in neonates with persistent pulmonary hypertension of the newborn - a randomised controlled trial pilot study (MINT 1): study protocol and review of literature

Persistent pulmonary hypertension of the newborn (PPHN) is a relatively common condition which results in a mortality of up to 33%. Up to 40% of infants treated with nitric oxide (iNO) either have a transient response or fail to demonstrate an improvement in oxygenation. Milrinone, a selective phosphodiesterase 3 (PDE3) inhibitor with inotropic and lusitropic properties may have potential benefit in PPHN. This pilot study was developed to assess the impact of milrinone administration on time spent on iNO in infants with PPHN. This is a multicentre, randomized, double-blind, two arm pilot study, with a balanced (1:1) allocation of 20 infants. In this pilot study, we hypothesise that infants ≥34 weeks gestation and ≥ 2000 g with a clinical and echocardiography diagnosis of PPHN, intravenous milrinone used in conjunction with iNO will result in a reduction in the time spent on iNO. In addition, we hypothesise that milrinone treatment will lead to an improvement in myocardial performance and global hemodynamics when compared to iNO alone. We will also compare the rate of adverse events associated with the milrinone, and the pre-discharge outcomes of both groups. The purpose of this pilot study is to assess the feasibility of performing the trial and to obtain preliminary data to calculate a sample size for a definitive multi-centre trial of milrinone therapy in PPHN. Trial registration: www.isrctn.com; ISRCTN:12949496; EudraCT Number:2014-002988-16.

Circulatory Insufficiency and Hypotension Related to the Ductus Arteriosus in Neonates

The biological role of the ductus arteriosus (DA) in neonates varies from an innocent bystander role during normal postnatal transition, to a supportive role when there is compromise to either systemic or pulmonary blood flow, to a pathological state in the presence of hemodynamically significant systemic to pulmonary shunts, as occurs in low birth weight infants. Among a wide array of clinical manifestations arising due to the ductal entity, systemic circulatory insufficiency and hypotension are of significant concern as they are particularly challenging to manage. An understanding of the physiologic interplay between the DA and the circulatory system is the key to developing appropriate targeted therapeutic strategies. In this review, we discuss the relationship of systemic hypotension to the DA, emphasizing the importance of critical thinking and a precise individual approach to intensive care support. We particularly focus on the variable states of hypotension arising directly due to a hemodynamically significant DA or seen in the period following successful surgical ligation. In addition, we explore the mechanistic contributions of the ductus to circulatory insufficiency that may manifest during the transitional period, states of maladapted transition (such as acute pulmonary hypertension of the newborn), and congenital heart disease (both ductal dependent and non-ductal dependent lesions). Understanding the dynamic modulator role of the ductus according to the ambient physiology enables a more precise approach to management. We review the pathophysiology, clinical manifestations, diagnosis, monitoring, and therapeutic intervention for the spectrum of DA-related circulatory compromise.

Factors relating caesarean section to persistent pulmonary hypertension of the newborn

BACKGROUND

Several studies have clearly demonstrated a significantly higher incidence of persistent pulmonary hypertension of the newborn (PPHN) in neonates delivered by caesarean section (CS) compared to those delivered vaginally. The pathophysiological factors underlying the link between CS and PPHN are still poorly understood. In this review, we describe the mechanisms that could explain the association between CS delivery and subsequent PPHN, as well as potential preventive measures.

DATA SOURCES

A literature search was conducted by electronic scanning of databases such as PubMed and Web of Science using the key words "persistent pulmonary hypertension of the newborn", "caesarean section", "iatrogenic prematurity", "oxidative stress", "late preterm", "labor" and "vasoactive agents".

RESULTS

Iatrogenic prematurity, higher rates of late preterm delivery and lack of physiological changes of labor play an important role in the association between CS and PPHN. CS delivery also results in limited endogenous pulmonary vasodilator synthesis and lower levels of protective anti-oxidants in the neonates. In addition, CS delivery exposes infants to a higher risk of respiratory distress syndrome and its concomitant increase in endothelin-1 levels, which might indirectly lead to a higher risk of developing PPHN. We believe that neonates delivered by CS are exposed to a combination of these pathophysiological events, culminating in an endpoint of respiratory distress, hypoxia, acidosis, and delayed transition and thereby increased risks of PPHN. The use of antenatal corticosteroids prior to elective CS in late preterm deliveries, promoting accurate informedconsent process, delaying elective CS to 39 weeks of gestation or beyond and antenatal maternal anti-oxidant supplementation could potentially mitigate the effects of CS delivery and minimize CS-related PPHN.

CONCLUSIONS

The link between CS delivery and PPHN is complex. In view of the rising rates of CS worldwide, there is an urgent need to further explore the mechanisms linking CS to PPHN and experimentally test therapeutic options in order to allow effective targeted interventions.

Management of Neonatal Hypotension

Hypotension is a common problem in neonates with complex underlying pathophysiology. Although treatment of low blood pressure is common, clinicians must use all available information to target neonates with compromised perfusion. Pharmacotherapy should be tailored to the specific physiologic perturbations of the individual neonate. Dopamine is the most commonly utilized agent and may be the most appropriate agent for septic shock with low diastolic blood pressure. However, alternative therapies should be considered for other etiologies of hypotension, including milrinone and vasopressin for persistent pulmonary hypertension of the newborn and dobutamine for patent ductus arteriosus. Additional studies are required to refine the approach to neonatal hypotension and document the long-term outcomes of treated neonates.

The effect of milrinone on right and left ventricular function when used as a rescue therapy for term infants with pulmonary hypertension

INTRODUCTION

Milrinone may be an appropriate adjuvant therapy for infants with persistent pulmonary hypertension of the newborn. We aimed to describe the effect of milrinone administration on right and left ventricular function in infants with persistent pulmonary hypertension not responding to inhaled nitric oxide after 4 hours of administration.

MATERIALS AND METHODS

This is a retrospective review of infants born after or at 34 weeks of gestation with persistent pulmonary hypertension who received milrinone treatment. The primary endpoint was the effect of milrinone on myocardial performance and haemodynamics, including right and left ventricular outputs, tissue Doppler velocities, right ventricle and septal strain, and strain rate. Secondary endpoints examined included duration of inhaled nitric oxide and oxygen support.

RESULTS

A total of 17 infants with a mean (standard deviation) gestation and birth weight of 39.8 (2.0) weeks and 3.45 (0.39) kilograms, respectively, were included in the study. The first echocardiogram was performed 15 hours after the commencement of nitric oxide inhalation. Milrinone treatment was started at a median time of 1 hour after the echocardiogram and was associated with an increase in left ventricular output (p=0.04), right ventricular output (p=0.004), right ventricle strain (p=0.01) and strain rate (p=0.002), and left ventricle s` (p<0.001) and a` (p=0.02) waves. There was a reduction in nitric oxide dose and oxygen requirement over the subsequent 72 hours (all p<0.05).

CONCLUSION

The use of milrinone as an adjunct to nitric oxide is worth further exploration, with preliminary evidence suggesting an improvement in both oxygenation and myocardial performance in this group of infants.

Endocrine and other physiologic modulators of perinatal cardiomyocyte endowment

Immature contractile cardiomyocytes proliferate to rapidly increase cell number, establishing cardiomyocyte endowment in the perinatal period. Developmental changes in cellular maturation, size and attrition further contribute to cardiac anatomy. These physiological processes occur concomitant with a changing hormonal environment as the fetus prepares itself for the transition to extrauterine life. There are complex interactions between endocrine, hemodynamic and nutritional regulators of cardiac development. Birth has been long assumed to be the trigger for major differences between the fetal and postnatal cardiomyocyte growth patterns, but investigations in normally growing sheep and rodents suggest this may not be entirely true; in sheep, these differences are initiated before birth, while in rodents they occur after birth. The aim of this review is to draw together our understanding of the temporal regulation of these signals and cardiomyocyte responses relative to birth. Further, we consider how these dynamics are altered in stressed and suboptimal intrauterine environments.

Persistent pulmonary hypertension of the newborn: recent advances in pathophysiology and treatment

OBJECTIVES

Although recognized for decades, little is known about the etiology, physiopathology, and prevention of persistent pulmonary hypertension of the newborn (PPHN), and its treatment remains a major challenge for neonatologists. In this review, the clinical features and physiopathology of the syndrome will be addressed, as well as its general and specific treatments.

DATA SOURCE

A review was carried out in PubMed, Cochrane Library, and MRei consult databases, searching for articles related to the syndrome and published between 1995 and 2011.

DATA SYNTHESIS

Risk factors and the physiopathological mechanisms of the syndrome are discussed. The clinical presentation depends on the different factors involved. These are related to the etiology and physiopathology of the different forms of the disease. In addition to the measures used to allow for the decrease in pulmonary vascular resistance after birth, in some instances pulmonary vasodilators will be required. Although inhaled nitric oxide has proved effective, other vasodilators have been recently used, but clinical evidence is still lacking to demonstrate their benefits in the treatment of PPHN.

CONCLUSIONS

Despite recent technological advances and new physiopathological knowledge of this disease, mortality associated with PPHN remains at 10%. More clinical research and evidence-based experimental results are needed to prevent, treat, and reduce the morbidity/mortality associated with this neonatal syndrome.

Pathophysiology of persistent pulmonary hypertension of the newborn: impact of the perinatal environment

The main cause of pulmonary hypertension in newborn babies results from the failure of the pulmonary circulation to dilate at birth, termed 'persistent pulmonary hypertension of the newborn' (PPHN). This syndrome is characterized by sustained elevation of pulmonary vascular resistance, causing extrapulmonary right-to-left shunting of blood across the ductus arteriosus and foramen ovale and severe hypoxaemia. It can also lead to life-threatening circulatory failure. There are many controversial and unresolved issues regarding the pathophysiology of PPHN, and these are discussed. PPHN is generally associated with factors such as congenital diaphragmatic hernia, birth asphyxia, sepsis, meconium aspiration and respiratory distress syndrome. However, the perinatal environment-exposure to nicotine and certain medications, maternal obesity and diabetes, epigenetics, painful stimuli and birth by Caesarean section-may also affect the maladaptation of the lung circulation at birth. In infants with PPHN, it is important to optimize circulatory function. Suggested management strategies for PPHN include: avoidance of environmental factors that worsen PPHN (e.g. noxious stimuli, lung overdistension); adequate lung recruitment and alveolar ventilation; inhaled nitric oxide (or sildenafil, if inhaled nitric oxide is not available); haemodynamic assessment; appropriate fluid and cardiovascular resuscitation and inotropic and vasoactive agents.

Hemodynamic effects of fluid restriction in preterm infants with significant patent ductus arteriosus

OBJECTIVE

To determine the hemodynamic impact of fluid restriction in preterm newborns with significant patent ductus arteriosus.

STUDY DESIGN

Newborns ≥24 and <32 weeks' gestational age with significant patent ductus arteriosus were eligible for this prospective multicenter observational study. We recorded hemodynamic and Doppler echocardiographic variables before and 24 hours after fluid restriction.

RESULTS

Eighteen newborns were included (gestational age 24.8 ± 1.1 weeks, birth weight 850 ± 180 g). Fluid intake was decreased from 145 ± 15 to 108 ± 10 mL/kg/d. Respiratory variables, fraction of inspired oxygen, blood gas values, ductus arteriosus diameter, blood flow-velocities in ductus arteriosus, in the left pulmonary artery and in the ascending aorta, and the left atrial/aortic root ratio were unchanged after fluid restriction. Although systemic blood pressure did not change, blood flow in the superior vena cava decreased from 105 ± 40 to 61 ± 25 mL/kg/min (P < .001). The mean blood flow-velocity in the superior mesenteric artery was lower 24 hours after starting fluid restriction.

CONCLUSIONS

Our results do not support the hypothesis that fluid restriction has beneficial effects on pulmonary or systemic hemodynamics in preterm newborns.

Effects of environmental tobacco smoke on the pulmonary circulation in the ovine fetus

OBJECTIVE

Epidemiologic studies have highlighted an association between maternal smoking and persistent pulmonary hypertension of the newborn infant. However, the impact of exposure to tobacco smoke on the perinatal pulmonary circulation is currently unknown. The purpose of this study was to assess the pulmonary vascular effects of environmental tobacco smoke in the fetus.

STUDY DESIGN

We performed surgery on 16 fetal lambs and placed catheters in the main pulmonary artery, aorta, and left atrium to measure pressures. An ultrasonic blood flow transducer was placed around the left pulmonary artery to measure blood flow. The ewes were exposed to tobacco smoke for 2 hours. In another set of experiments, the pulmonary vascular response to increased fetal O(2) tension has been assessed after 2 hours of tobacco smoke inhalation or not (control group).

RESULTS

Exposure to tobacco smoke decreased pulmonary blood flow by 30% and elevated pulmonary vascular resistance by 40%. The vasodilator response to increased O(2) tension was blunted after smoke inhalation compared with control animals. Smoke inhalation was associated with a decrease in fetal PaO(2) and SaO(2).

CONCLUSION

Exposure to environmental tobacco smoke in pregnant ewes impairs both basal tone and vascular reactivity of the fetal lung.

Hypotension in preterm infants with significant patent ductus arteriosus: effects of dopamine

OBJECTIVE

To study the effects of dopamine on systemic arterial pressure (SAP) and systemic blood flow (SBF) (estimated with the superior vena cava [SVC] flow) in preterm infants with hypotension and patent ductus arteriosus (PDA).

STUDY DESIGN

Clinical and echocardiographic variables were measured before and 2 hours after starting dopamine in premature infants <32 weeks gestational age with PDA and systemic hypotension.

RESULTS

Seventeen premature infants were included (gestational age, 28+/-2 weeks; birth weight, 1030 +/- 400 g). A mean rate of 8 +/- 2 microg/kg/min of dopamine raised SAP from 30 +/- 3 to 41 +/- 5 mm Hg (P < .05), and the pulmonary artery pressures from 25 +/- 5 to 32 +/- 8 mm Hg (P < .05). The SVC flow increased by 30% (from 130 +/- 40 to 170 +/- 44 mL/kg/min; P < .05). The left ventricular output and the end-diastolic and mean left pulmonary artery blood flow velocities did not change despite the increase in pulmonary artery pressure.

CONCLUSION

In preterm infants with hypotension and PDA, dopamine (<10 microg/kg/min) increases the systemic blood pressure and the systemic blood flow. Our results suggest that dopamine decreases left-to-right shunting across ductus arteriosus, caused by a rise in pulmonary vascular resistances.

Dynamic relationships between catecholamine-induced shifts of pressure and blood flow in pulmonary artery

Experiments on cats showed that catecholamines produced maximum changes in pulmonary artery blood pressure during 12-16 sec postinjection, while blood flow in this artery attained maximum only to 40 sec postinjection, i.e. changes in blood flow attained maximum and ended later than blood pressure shifts. Intravenous epinephrine produced bidirectional changes in blood pressure, while norepinephrine always elevated blood pressure in the pulmonary artery; pulmonary circulation increased after injection of both catecholamines.

Pulmonary circulatory effects of norepinephrine in newborn infants with persistent pulmonary hypertension

OBJECTIVE

To evaluate the respiratory and the pulmonary circulatory effects of norepinephrine in newborn infants with persistent pulmonary hypertension (PPHN)-induced cardiac dysfunction.

STUDY DESIGN

Inclusion criteria were: 1) Newborn infants >35 weeks gestational age; 2) PPHN treated with inhaled nitric oxide; and 3) symptoms of circulatory failure despite adequate fluid resuscitation. Lung function and pulmonary hemodynamic variables assessed with Doppler echocardiography were recorded prospectively before and after starting norepinephrine.

RESULTS

Eighteen newborns were included (gestational age: 37 +/- 3 weeks; birth weight: 2800 +/- 700 g). After starting norepinephrine, systemic pressure and left ventricular output increased respectively from 33 +/- 4 mm Hg to 49 +/- 4 mm Hg and from 172 +/- 79 mL/kg/min to 209+/-90 mL/kg/min (P < .05). Although the mechanical ventilatory variables have not been changed, the post-ductal transcutaneous arterial oxygen saturation increased from 89% +/- 1% to 95% +/- 4%, whereas the oxygen need decreased from 51% +/- 24% to 41% +/- 20% (P < .05). The pulmonary/systemic pressure ratio decreased from 0.98 +/- 0.1 to 0.87 +/- 0.1 (P < .05). Mean left pulmonary artery blood flow velocity increased by 20% (P < .05).

CONCLUSION

Norepinephrine may improve lung function in newborn infants with PPHN through a decrease in pulmonary/systemic artery pressure ratio and improved cardiac performance.

Noradrenaline for management of septic shock refractory to fluid loading and dopamine or dobutamine in full-term newborn infants

AIM

To determine the effects of noradrenaline in full-term newborns with refractory septic shock.

METHODS

Newborns of >35 weeks' gestation with persistent septic shock, despite adequate fluid resuscitation and high dose of dopamine/dobutamine were eligible. In this prospective observational study, we recorded respiratory and hemodynamic parameters prior to and 3 h after starting noradrenaline infusion.

RESULTS

Twenty-two newborns were included (gestational age [GA] 39 +/- 1.7 weeks, birth weight (BW) 3110 +/- 780 g). Before starting noradrenaline, the infants received a mean volume expansion of 31 +/- 15 mL/kg and a mean infusion rate of dopamine of 14 +/- 5 microg/kg/min or dobutamine of 12 +/- 6 microg/kg/min. Three hours after starting noradrenaline (rate 0.5 +/- 0.4 microg/kg/min), the mean arterial blood pressure rose from 36 +/- 5 to 51 +/- 7 mmHg (p < 0.001). Urine output increased from 1 +/- 0.5 to 1.7 +/- 0.4 mL/kg/h (p < 0.05). Blood lactate concentration decreased from 4.8 +/- 2.3 to 3.3 +/- 1.8 mmol/L (p < 0.01). Despite an initial correction of hypotension, four infants died later.

CONCLUSION

Noradrenaline was effective in increasing systemic blood pressure. An increase in urine output and a decrease in blood lactate concentration suggest that noradrenaline may have improved cardiac function and tissue perfusion.

Early hemodynamic consequences of patent ductus arteriosus in preterm infants with intrauterine growth restriction

OBJECTIVE

To test the hypothesis that significant patent ductus arteriosus (PDA) may occur very early after birth in preterm infants with intrauterine growth restriction (IUGR), we compared the longitudinal changes in left-to-right shunting through DA between eutrophic and preterm infants with IUGR.

STUDY DESIGN

The preterm infants -26 to 32 weeks gestational age (GA), admitted in our neonatal intensive care unit from February to May 2004 were included. They were separated into an "IUGR of placental origin" group and an "eutrophic" group. Significant PDA was assessed by Doppler echocardiography at 6, 24, and 48 hours of age.

RESULTS

Thirty-one eutrophic (GA = 29 +/- 1.4 weeks; birth weight [BW] = 1300 +/- 160 g) and 17 infants with IUGR (GA = 29.3 +/- 1.5 weeks; BW = 810 +/- 140 g) were studied. Six hours after birth, the rate of significant PDA was higher in the IUGR than in the eutrophic group (10/17 [60%] vs 5/31 [15%]; P < .05). More DA became significant in infants with IUGR (11/17 [65%]) than in eutrophic infants (12/31 [40%]) (P < .05) within the 48 hours after birth.

CONCLUSION

Markers of high pulmonary blood flow and systemic vascular steal occur more frequently and earlier after birth in IUGR of placental origin than in eutrophic preterm infants. The management of preterm infants with severe IUGR of placenta origin should include early echocardiographic monitoring to assess for markers of significant PDA.

The Mechanisms of Pain-Induced Pulmonary Vasoconstriction: An Experimental Study in Fetal Lambs

BACKGROUND

Nociceptive stimulation induces pulmonary vasoconstriction in fetuses and newborns. The mechanism of this response is not fully understood. As the systemic hemodynamic response to pain is mainly mediated by sympathetic stimulation, we hypothesized that pain-induced pulmonary vasoconstriction results from the activation of catecholaminergic receptors. To test this hypothesis, we studied the pulmonary vascular response to nociceptive stimuli in fetal lambs before and after alpha-adrenoceptor blockade.

METHODS

Surgery was performed in fetal lambs. Catheters were placed into the ascending aorta, superior vena cava, and main pulmonary artery. An ultrasonic flow transducer was placed around the left pulmonary artery, and subcutaneous catheters were placed in the limb. The hemodynamic responses to (1) subcutaneous injection of formalin (which is used as nociceptive stimulus in experimental studies), (2) prazosin (specific alpha(1)-adrenoceptor antagonist), and (3) formalin during prazosin infusion were evaluated. Plasma cortisol and catecholamine concentrations were measured.

RESULTS

Pulmonary vascular resistance (PVR) increased by 50% (P < 0.01) after the formalin test. PVR did not change after the formalin test during prazosin infusion or during prazosin infusion alone. Catecholamine and cortisol levels did not change during any of the protocols.

DISCUSSION

Our results indicate that the fetal pulmonary vasoconstrictive response to pain involves alpha(1)-adrenoceptors activation. As plasma catecholamine concentrations did not change after the formalin test, we speculate that the pulmonary vascular response to nociceptive stimuli could be triggered by a local release of catecholamine induced by sympathetic stimulation.

Effects of Phosphodiesterase 5 Inhibitor on Pulmonary Vascular Reactivity in the Fetal Lamb

BACKGROUND

Nitric oxide released by pulmonary vascular endothelium is a potent vasodilator related to increased cyclic guanosine monophosphate (cGMP) content. Hydrolysis of cGMP is achieved predominately by cGMP-specific phosphodiesterases. Sildenafil is a selective phosphodiesterase-5 (PDE5) inhibitor. The purpose of the study is to assess the effects of sildenafil on pulmonary vascular circulation during the perinatal period.

METHODS

Thirty-two pregnant ewes were operated on at the end of gestation, and fetal lambs were prepared with catheters placed into the aorta, vena cava, pulmonary artery, and left atrium. An ultrasonic flow transducer and an inflatable vascular occluder were placed respectively around the left pulmonary artery and the ductus arteriosus. Fetal lambs were randomly divided into two groups: (1) sildenafil group, infused continuously with sildenafil for 24 hours at a rate of 1 mg/h; or (2) control group, infused with saline for 24 hours. After 24 hours of infusion, we compared basal pulmonary vascular resistance and the pulmonary vascular responses to increase in fetal PaO2 and to acute ductus arteriosus compression causing "shear stress."

RESULTS

Sildenafil infusion did not change mean aortic and pulmonary artery pressures, increased mean left pulmonary blood flow by 160%, and decreased pulmonary vascular resistance by 60% (p < 0.05). However, both mean flow (Q) and pulmonary vascular resistance returned to baseline values after 2 hours of sildenafil infusion. Despite similar baseline values, pulmonary vascular resistance during maternal O2 inhalation was lower in the sildenafil group than in the control group (0.21 +/- 0.03 versus 0.33 +/- 0.03 mm Hg.mL(-1).min(-1), respectively; p < 0.01). Furthermore, drop in pulmonary vascular resistance during acute ductus arteriosus compression was greater in the sildenafil group (from 0.56 +/- 0.06 to 0.26 +/- 0.04 mm Hg.mL(-1).min(-1)) than in the control group (from 0.55 +/- 0.05 to 0.39 +/- 0.03 mm Hg.mL(-1).min(-1); p < 0.01).

CONCLUSIONS

Although sildenafil induces a transient pulmonary vasodilation, it mediates a sustained change in vascular reactivity, especially to birth-related stimuli in the ovine fetal lung. These data suggest that PDE5 is involved in the regulation of pulmonary vascular reactivity during the perinatal period and may potentiate birth-related pulmonary vasodilator stimuli.

Influence of sympathetic tone on heart rate during vagal stimulation and nitroprusside induced hypotension in ovine fetus

OBJECTIVE

To characterize effects of sympathetic tone on fetal heart rate (FHR) reflex responses and FHR variability in late gestation.

DESIGN/METHODS

Changes in FHR and autonomic tones were studied (i) after electrical vagal stimulation and (ii) during nitroprusside-induced hypotension, in seven late gestation ovine fetus in control condition (ctrl), after dobutamine (beta1-activation) and atenolol (beta1-blockade). Results are expressed as mean +/- SEM.

RESULTS

(i) Minimal FHR after vagal stimulation was not influenced by atenolol or dobutamine but dobutamine accelerated FHR normalization. (ii) During nitroprusside induced hypotension atenolol inhibited the initial increases in FHR and FHR variability (measured by SD and LFnu) but not the bradycardia occurring below a mean arterial pressure of 38 +/- 2 mmHg. Dobutamine did not abolish the depressor reflex. During hypotension the positive chronotropic effect of sympathetic tone increased from 15 +/- 2 to 42 +/- 7 bpm then decreased at a rate of -7.6 +/- 1.5 bpm mmHg(-1), vagal negative chronotropic influence steadily increased at a rate of 1.9 +/- 0.4 bpm mmHg(-1). Changes in FHR variability were not correlated with vagal or sympathetic chronotropic effects.

CONCLUSIONS

beta1-stimulation does not affect sinus-node response to vagal stimulation but improves the speed of FHR normalization. FHR response to hypotension depends on an initial increase in both sympathetic and parasympathetic chronotropic effects that is associated with a sympathetic dependent increase in FHR variability and is followed by a withdrawal of sympathetic tone.

Effects of Antenatal Glucocorticoids on Circulatory Adaptation at Birth in the Ovine Fetus

OBJECTIVE

Adaptation to extra-uterine life requires dramatic increase in pulmonary blood flow. Mechanisms that induce pulmonary vasodilatation at birth are incompletely understood but include alveolar ventilation, increase in PaO2, and production of vasoactive mediators. We hypothesized that antenatal glucocorticoids (GC) increase pulmonary vasodilatation to birth-related stimuli.

STUDY DESIGN

To test this hypothesis, we studied the pulmonary hemodynamic response at birth to mechanical ventilation with low (<10%) and then with high (100%) FiO2 in chronically prepared late-gestation fetal lambs treated or not by antenatal maternal steroids.

RESULTS

Basal mean aortic and pulmonary artery pressure (PAP), left pulmonary blood flow, pulmonary vascular resistance (PVR), and blood gas were similar between control and dexamethasone-treated animals (GC group). During mechanical ventilation with low FiO2, mean PVR decreased by 40% in the control group (from 0.44 +/- 0.01 to 0.25 +/- 0.01 mm Hg/ml/min) and by 60% in the GC group (from 0.44 +/- 0.02 to 0.19 +/- 0.02 mm Hg/ml/min) (p < 0.01). When subsequently ventilated with 100% O2, there was no difference in PVR decrease between groups (0.15 +/- 0.02 mm Hg/ml/min in the GC group vs. 0.14 +/- 0.01 mm Hg/ml/min in the control group).

CONCLUSION

Antenatal GC enhance pulmonary vasodilatation induced by alveolar ventilation at birth but do not alter the pulmonary vascular response to O2. We speculate that antenatal steroids exposure improve adaptation at birth through acceleration of both parenchymal and vascular lung maturation.

Effects of nociceptive stimuli on the pulmonary circulation in the ovine fetus

The fetus is able to exhibit a stress response to painful events, and stress hormones have been shown to modulate pulmonary vascular tone. At birth, the increased level of stress hormones plays a significant role in the adaptation to postnatal life. We therefore hypothesized that pain may alter pulmonary circulation in the perinatal period. The hemodynamic response to subcutaneous injection of formalin, which is used in experimental studies as nociceptive stimulus, was evaluated in chronically prepared, fetal lambs. Fetal lambs were operated on at 128 days gestation. Catheters were placed into the ascending aorta, superior vena cava, and main pulmonary artery. An ultrasonic flow transducer was placed around the left pulmonary artery. Three subcutaneous catheters were placed in the lambs' limb. The hemodynamic responses to subcutaneous injection of formalin, to formalin after fetal analgesia by sufentanil, and to sufentanil alone were recorded. Cortisol and catecholamine concentrations were also measured. Pulmonary vascular resistances (PVR) increased by 42% ( P < 0.0001) after formalin injection. Cortisol increased by 54% ( P = 0.05). During sufentanil infusion, PVR did not change significantly after formalin. Cortisol increased by 56% ( P < 0.05). PVR did not change during sufentanil infusion. Norepinephrine levels did not change during any of the protocols. Our results indicate that nociceptive stimuli may increase the pulmonary vascular tone. This response is not mediated by an increase in circulating catecholamine levels. Analgesia prevents this effect. We speculate that this pulmonary vascular response to nociceptive stimulation may explain some hypoxemic events observed in newborn infants during painful intensive care procedures.

Effects of BAY 41-2272, a soluble guanylate cyclase activator, on pulmonary vascular reactivity in the ovine fetus

Nitric oxide (NO)-cGMP signaling plays a critical role during the transition of the pulmonary circulation at birth. BAY 41-2272 is a novel NO-independent direct stimulator of soluble guanylate cyclase that causes vasodilation in systemic and local circulations. However, the hemodynamic effects of BAY 41-2272 have not been studied in the perinatal pulmonary circulation. We hypothesized that BAY 41-2272 causes potent and sustained fetal pulmonary vasodilation. We performed surgery on 14 fetal lambs (125-130 days gestation; term = 147 days) and placed catheters in the main pulmonary artery, aorta, and left atrium to measure pressures. An ultrasonic flow transducer was placed on the left pulmonary artery (LPA) to measure blood flow, and a catheter was placed in the LPA for drug infusion. Pulmonary vascular resistance (PVR) was calculated as pulmonary artery pressure minus left atrial pressure divided by LPA blood flow. BAY 41-2272 caused dose-related increases in pulmonary blood flow up to threefold above baseline and reduced PVR by 75% (P < 0.01). Prolonged infusion of BAY 41-2272 caused sustained pulmonary vasodilation throughout the 120-min infusion period. The pulmonary vasodilator effect of BAY 41-2272 was not attenuated by N(omega)-nitro-l-arginine, a NO synthase inhibitor. In addition, compared with sildenafil, a phosphodiesterase 5 inhibitor, the pulmonary vasodilator response to BAY 41-2272 was more prolonged. We conclude that BAY 41-2272 causes potent and sustained fetal pulmonary vasodilation independent of NO release. We speculate that BAY 41-2272 may have therapeutic potential for pulmonary hypertension associated with failure to circulatory adaptation at birth, especially in the setting of impaired NO production.

Could the consequences of premature delivery be further attenuated by means of new prenatal strategies?

The last 10 years have already seen improvements in the short- and long-term prognosis for premature neonates. Nevertheless, progress in the prenatal evaluation of predictive factors for neonatal diseases and more detailed and reliable knowledge of fetal physiology could allow the development of new treatments with consequent expectations of further improvements in the prognosis for such premature newborns. Global strategies for the management of preterm labour, ranging from a policy for prenatal transfer to centres offering the appropriate level of perinatal care, should continue to be expanded, and long-term evaluations must also be continued.

Effects of antenatal glucocorticoids on pulmonary vascular reactivity in the ovine fetus

OBJECTIVES

Although mechanisms of glucocorticoids-induced parenchymal lung maturation have been largely studied, little is known about the pulmonary vascular effects of antenatal glucocorticoids (GCs). We therefore hypothesized that antenatal GCs may alter the hemodynamic response to vasodilatory agents in the fetal lung.

STUDY DESIGN

We tested the hemodynamic response to acetylcholine, increased PaO(2), and norepinephrine infusion before and after maternal GC administration in chronically prepared, late-gestation fetal lambs (135-137 days of gestational age, term = 147 days).

RESULTS

We found that antenatal GCs (1). do not change the basal pulmonary vascular tone and (2). do not alter the vasodilatory response to acetylcholine and increased PaO (2) but enhanced the norepinephrine-mediated pulmonary vasodilation.

CONCLUSION

Our results indicate that antenatal GCs alter the pulmonary vascular reactivity to catecholamines. We speculate that the benefits of antenatal GCs on the cardiovascular adaptation at birth may be related to potentiation of catecholamines vascular effects.