Pilot study of milrinone for low systemic blood flow in very preterm infants

Should SVC flow be a routine measure when performing targeted neonatal echocardiography? A narrative review

Superior vena cava is commonly used in neonatal hemodynamics and is suggested to be the best available non-invasive marker for systemic circulation in preterm infants. Inter- and intra-observer variability remain to be an issue. Its association with neonatal outcomes is has not been established. This is a narrative review about this marker, its use, and its potential pitfalls.

OBJECTIVE

This is a narrative review about SVC flow in preterm infants, physiology, techniques of measurement and its potential association with outcomes.

SOURCES

Literature revie mainly PubMED.

SUMMARY OF THE FINDINGS

SVC flow measurement has some limitations and pitfalls.

CONCLUSIONS

SVC flow association with neonatal outcomes, still needs to be established in further research.

Predicting the effectiveness of drugs used for treating cardiovascular conditions in newborn infants

BACKGROUND

Cardiovascular support (CVS) treatment failure (TF) is associated with a poor prognosis in preterm infants.

METHODS

Medical charts of infants with a birth weight <1500 g who received either dopamine (Dp) or dobutamine (Db), were reviewed. Treatment response (TR) occurred if blood pressure increased >3rd centile for gestational age or superior vena cava flow was maintained >55 ml/kg/min, with decreased lactate or less negative base excess, without additional CVS. A predictive model of Dp and Db on TR was designed and the impact of TR on survival was analyzed.

RESULTS

Sixty-six infants (median gestational age 27.3 weeks, median birth weight 864 g) received Dp (n = 44) or Db (n = 22). TR occurred in 59% of the cases treated with Dp and 31% with Db, p = 0.04. Machine learning identified a model that correctly labeled Db response in 90% of the cases and Dp response in 61.4%. Sixteen infants died (9% of the TR group, 39% of the TF group; p = 0.004). Brain or gut morbidity-free survival was observed in 52% vs 30% in the TR and TF groups, respectively (p = 0.08).

CONCLUSIONS

New predictive models can anticipate Db but not Dp effectiveness in preterm infants. These algorithms may help the clinicians in the decision-making process.

IMPACT

Failure of cardiovascular support treatment increases the risk of mortality in very low birth weight infants. A predictive model built with machine learning techniques can help anticipate treatment response to dobutamine with high accuracy. Predictive models based on artificial intelligence may guide the clinicians in the decision-making process.

Reassessing the role of milrinone in the treatment of heart failure and pulmonary hypertension in neonates and children: a systematic review and meta-analysis

To evaluate milrinone's impact on pediatric cardiac function, focusing on its specific role as an inotrope and lusitrope, while considering its systemic and pulmonary vasodilatory effects. Search of PubMed, EMBASE, and the Cochrane Library up to August 2023. We included all studies that evaluated milrinone in children under 18 years old in neonatal, pediatric, or cardiac intensive care units. We excluded case reports, studies that did not provide tabular information on milrinone's outcomes, and studies focused on non-intensive care populations. We extracted data on the research design, objectives, study sample, and results of each study, including the impact of milrinone and any associated factors. We screened a total of 9423 abstracts and 41 studies were ultimately included. Milrinone significantly improved left ventricular ejection fraction (WMD 3.41 [95% CI 0.61 - 6.21]), left ventricle shortening fraction (WMD 4.25 [95% CI 3.43 - 5.08]), cardiac index (WMD 0.50 [95% CI 0.32 to 0.68]), left ventricle output (WMD 55.81 [95% CI 4.91 to 106.72]), serum lactate (WMD -0.59 [95% CI -1.15 to -0.02]), and stroke volume index (WMD 2.95 [95% CI 0.09 - 5.82]). However, milrinone was not associated with improvements in ventricular myocardial performance index (WMD -0.01 [95% CI -0.06 to 0.04]) and ventricular longitudinal strain (WMD -2.14 [95% CI -4.56 to 0.28]). Furthermore, milrinone was not associated with isovolumetric relaxation time reduction (WMD -8.87 [95% CI -21.40 to 3.66]).

CONCLUSION

Our meta-analysis suggests potential clinical benefits of milrinone by improving cardiac function, likely driven by its systemic vasodilatory effects. However, questions arise about its inotropic influence and the presence of a lusitropic effect. Moreover, milrinone's pulmonary vasodilatory effect appears relatively weaker compared to its systemic actions. Further research is needed to elucidate milrinone's precise mechanisms and refine its clinical applications in pediatric practice.

WHAT IS KNOWN

• Milrinone is a phosphodiesterase III inhibitor that has been used to treat a variety of pediatric and neonatal conditions. • Milrinone is believed to exert its therapeutic effects by enhancing cardiac contractility and promoting vascular relaxation.

WHAT IS NEW

• Milrinone may not have a significant inotropic effect. • Milrinone's pulmonary vasodilatory effect is less robust than its systemic vasodilatory effect.

Randomized Trial of Perfusion-Based Circulatory Management in Infants of Very Low Birth Weight

OBJECTIVE

To establish the superiority of blood flow (BF)-based circulatory management over conventional blood pressure (BP)-based management strategies used for preventing intraventricular hemorrhage (IVH) in infants of very low birth weight (VLBW).

STUDY DESIGN

We conducted a nonblinded, single-centered randomized trial with the aim to prevent IVH by managing BF. Infants with VLBW were assigned randomly to a BF-based group or BP-based (BP group) circulatory management group. The incidence of IVH was the outcome of interest. The IVH also data were compared among healthy patients and patients responsive and unresponsive to the intervention.

RESULTS

A total of 219 and 220 infants with VLBW were assigned to the BF and BP groups, respectively. The IVH incidence rate was lower in the BF group, but the difference was not statistically significant (BF group, 6.8% vs BP group, 10.9%; P = .14). In 21% of patients of the BP group and 20% of the BF group, the intervention failed. In BF group, the IVH incidence rate was significantly greater in infants with unsuccessful intervention when compared with healthy individuals (6% vs 23%, P = .001). Multivariate logistic regression analysis revealed a correlation between low blood flow and IVH (aOR 3.24; 95% CI 1.49-7.08, P = .003) but not between low BP and IVH (P = .73).

CONCLUSIONS

The BF management protocol did not significantly decrease the incidence of IVH. However, after further optimization, we speculate the treatment strategy holds promise in decreasing the incidence of IVH. Trial registration UMIN-CTR: UMIN000013296.

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.

Superior vena cava flow: Role, assessment and controversies in the management of perinatal perfusion

The superior vena cava (SVC) is a large vein responsible for the venous return of blood from structures located superior to the diaphragm. The flow in the SVC can be assessed with Doppler ultrasound and can be used as a proxy for cerebral perfusion. Early clinical research studies showed that low SVC flow, particularly if for a prolonged period, was associated with short term morbidity such as intraventricular hemorrhage, mortality, and poorer neurodevelopmental outcomes. However, these findings have not been consistently reported in more recent studies, and the role of SVC flow in early management and as a predictor of poor long-term neurodevelopment has been questioned. This paper provides an overview of SVC assessment, the expected range of findings, and reviews the role of SVC flow as a diagnostic and monitoring tool for the assessment of perinatal perfusion.

The Use of Cardiotonic Drugs in Neonates

There is a distinct lack of age-appropriate cardiotonic drugs, and adult derived formulations continue to be administered, without evidence-based knowledge on their dosing, safety, efficacy, and long-term effects. Dopamine remains the most commonly studied and prescribed cardiotonic drug in the neonatal intensive care unit (NICU), but evidence of its effect on endorgan perfusion still remains. Unlike adult and pediatric critical care, there are significant gaps in our knowledge on the use of various cardiotonic drugs in various forms of circulatory failure in the NICU.

Postnatal cardiovascular adaptation

The heart undergoes rapid transformations in function during the transition to extrauterine life. Our understanding of the adaptive physiology underlying this process is able to inform the clinical management of infants who are struggling to complete this complex transition. Much of our knowledge of the cardiac transition is derived from the preterm infant in whom the preparative adaptations are incomplete and clinical sequelae all too common. This review will re-examine the cardiac transition highlighting the physiology that drives it and suggest appropriate clinical intervention to support the process.

Correlations between near-infrared spectroscopy, perfusion index, and cardiac outputs in extremely preterm infants in the first 72 h of life

Haemodynamic assessment during the transitional period in preterm infants is challenging. We aimed to describe the relationships between cerebral regional tissue oxygen saturation (CrSO₂), perfusion index (PI), echocardiographic, and clinical parameters in extremely preterm infants in their first 72 h of life. Twenty newborns born at < 28 weeks of gestation were continuously monitored with CrSO₂ and preductal PI. Cardiac output was measured at H6, H24, H48, and H72. The median gestational age and birth weight were 25.0 weeks (24-26) and 750 g (655-920), respectively. CrSO₂ and preductal PI had r values < 0.35 with blood gases, lactates, haemoglobin, and mean blood pressure. Cardiac output significantly increased over the 72 h of the study period. Fifteen patients had at least one episode of low left and/or right ventricular output (RVO), during which there was a strong correlation between CrSO₂ and superior vena cava (SVC) flow (at H6 (r = 0.74) and H24 (r = 0.86)) and between PI and RVO (at H6 (r = 0.68) and H24 (r = 0.92)). Five patients had low SVC flow (≤ 40 mL/kg/min) at H6, during which PI was strongly correlated with RVO (r = 0.98).

CONCLUSION

CrSO₂ and preductal PI are strongly correlated with cardiac output during low cardiac output states. What is Known: • Perfusion index and near-infrared spectroscopy are non-invasive tools to evaluate haemodynamics in preterm infants. • Pre- and postductal perfusion indexes strongly correlate with left ventricular output in term infants, and near-infrared spectroscopy has been validated to assess cerebral oxygenation in term and preterm infants. What is New: • Cerebral regional tissue oxygen saturation and preductal perfusion index were strongly correlated with cardiac output during low cardiac output states. • The strength of the correlation between cerebral regional tissue oxygen saturation, preductal perfusion index, and cardiac output varied in the first 72 h of life, reflecting the complexity of the transitional physiology.

Objective cardiovascular assessment in the neonatal intensive care unit

Traditionally, cardiovascular well-being was essentially based on whether the mean blood pressure was above or below a certain value. However, this singular crude method of assessment provides limited insight into overall cardiovascular well-being. Echocardiography has become increasingly used and incorporated into clinical care. New objective modality assessments of cardiovascular status continue to evolve and are being evaluated and incorporated into clinical care. In this review article, we will discuss some of the recent advances in objective assessment of cardiovascular well-being, including the concept of multimodal monitoring. Sophisticated haemodynamic monitoring systems are being developed, including mechanisms of data acquisition and analysis. Their incorporation into clinical care represents an exciting next stage in the management of the infant with cardiovascular compromise.

Controversies in the identification and management of acute pulmonary hypertension in preterm neonates

It is increasingly recognized that the abnormal physiologic consequences of pulmonary hypertension (PH) may contribute to poor cardiopulmonary health in premature babies. Conflicting literature has led to clinical uncertainty, pathological misinterpretation, and variability in treatment approaches among practitioners. There are several disorders with overlapping and interrelated presentations, and other disorders with a similar clinical phenotype but diverse pathophysiological contributors. In this review, we provide a diagnostic approach for acute hypoxemic respiratory failure in the preterm neonate, outline the pathophysiological conditions that may present as acute PH, and discuss the implications of high pulmonary vascular resistance (PVR) on the cardiovascular system. Although PVR and respiratory management are highly interrelated, there may be a population of preterm neonates in whom inhaled nitric oxide may improve illness severity and may relate to outcomes. A management approach based on physiology that considers common clinical conundrums is provided. A more comprehensive understanding of the physiology may help in informed decision-making in clinical situations where conclusive scientific evidence is lacking. Regardless, high-quality research is required, and appropriate definition of the target population is paramount. A thoughtful approach to cardiovascular therapy may also provide an avenue to improve neurodevelopmental outcomes while awaiting more clear answers.

Milrinone in congenital diaphragmatic hernia - a randomized pilot trial: study protocol, review of literature and survey of current practices

Background

Congenital diaphragmatic hernia (CDH) is commonly associated with pulmonary hypoplasia and pulmonary hypertension (PH). PH associated with CDH (CDH-PH) is frequently resistant to conventional pulmonary vasodilator therapy including inhaled nitric oxide (iNO) possibly due to right and left ventricular dysfunction. Milrinone is an intravenous inotrope and lusitrope with pulmonary vasodilator properties and has been shown anecdotally to improve oxygenation in PH. We developed this pilot study to determine if milrinone infusion would improve oxygenation in neonates ≥36 weeks postmenstrual age (PMA) with CDH.

Methods/design

Data on pulmonary vasodilator management and outcome of CDH patients was collected from 18 university NICUs affiliated with the Neonatal Research Network (NRN) from 2011 to 2012. The proposed pilot will be a masked, placebo–controlled, multicenter, randomized trial of 66 infants with CDH with an oxygenation index (OI) ≥10 or oxygen saturation index (OSI) ≥5. The primary outcome is the oxygenation response, as determined by change in OI at 24 h after initiation of study drug. As secondary outcomes, we will determine oxygenation at 48 h and 72 h post-infusion, right ventricular pressures on echocardiogram and the incidence of systemic hypotension, arrhythmias, intracranial hemorrhage, survival without extracorporeal membrane oxygenation, and chronic lung disease (oxygen need at 28 days postnatal age). Finally, we will evaluate the pulmonary and nutritional status at 4, 8 and 12 months of age using a phone questionnaire.

Results

Three hundred thirty-seven infants with CDH were admitted to NRN NICUs in 2011 and 2012 of which 275 were ≥36 weeks PMA and were exposed to the following pulmonary vasodilators: iNO (39%), sildenafil (17%), milrinone (17%), inhaled epoprostenol (6%), intravenous epoprostenol (3%), and intravenous PGE1 (1%). ECMO was required in 36% of patients. Survival to discharge was 71%.

Discussion

CDH is an orphan disease with high mortality with few randomized trials evaluating postnatal management. Intravenous milrinone is a commonly used medication in neonatal/pediatric intensive care units and is currently used in 17% of patients with CDH within the NRN. This pilot study will provide data and enable further studies evaluating pulmonary vasodilator therapy in CDH.

Trial registration

ClinicalTrials.gov; NCT02951130; registered 14 October 2016.

Hemodynamic Assessment and Monitoring of Premature Infants

The management of the hemodynamic status of critically ill preterm infants, particularly around the periviable period, remains a significant challenge in the neonatal intensive care unit for a multitude of reasons. The causes of hemodynamic compromise in this population are heterogeneous and usually superimposed on the complex physiologic processes that occur during transition from fetal to neonatal life. This review outlines the unique nature of low blood flow states in this population and present an overview of the current methods for identification and assessment of hemodynamic compromise.

A review of superior vena cava flow measurement in the neonate by functional echocardiography

Neonatologists have begun using superior vena cava flow as assessed by functional echocardiography to facilitate real-time decision-making on cardiovascular care. This review aims to describe the basis of the technique, summarise the evidence for its use and compare the technique to existing clinical, biochemical and radiological techniques for assessing neonatal circulatory status.

CONCLUSION

Although echocardiographic measurements of superior vena cava flow, like other measures of perfusion, are not perfect, their noninvasive nature and ability to facilitate real-time decision-making means that at present, they remain the best available methodology of monitoring central perfusion in the neonatal population.

Hemodynamic instability in the critically ill neonate: An approach to cardiovascular support based on disease pathophysiology

Hemodynamic disturbance in the sick neonate is common, highly diverse in underlying pathophysiology and dynamic. Dysregulated systemic and cerebral blood flow is hypothesized to have a negative impact on neurodevelopmental outcome and survival. An understanding of the physiology of the normal neonate, disease pathophysiology, and the properties of vasoactive medications may improve the quality of care and lead to an improvement in survival free from disability. In this review we present a modern approach to cardiovascular therapy in the sick neonate based on a more thoughtful approach to clinical assessment and actual pathophysiology. Targeted neonatal echocardiography offers a more detailed insight into disease processes and offers longitudinal assessment, particularly response to therapeutic intervention. The pathophysiology of common neonatal conditions and the properties of cardiovascular agents are described. In addition, we outline separate treatment algorithms for various hemodynamic disturbances that are tailored to clinical features, disease characteristics and echocardiographic findings.

The diagnostic value of a single measurement of superior vena cava flow in the first 24 h of life in very preterm infants

Low superior vena cava (SVC) flow has been associated with intraventricular haemorrhage (IVH) in very preterm infants. We studied the diagnostic value of a single measurement of SVC flow within the first 24 h of life in very preterm infants and its association with occurrence or extension of IVH in a setting of limited availability of neonatal echocardiography. Preterm infants who were born at less than 30 weeks gestation and who had an echocardiogram within 24 h after birth were eligible. Baseline, clinical and ultrasound data were collected. A total of 165 preterm infants were included. Low SVC flow (<41 ml/kg/min) occurred in six infants and was associated with severe IVH and extension of IVH, although this was not significant after adjusting for confounders. The only independently associated variable with low SVC flow was admission temperature (odds ratio 0.27, p = 0.001). A review of SVC flow values shows that these are higher now than initially reported. This study does not show an association of low SVC flow and severe IVH or extension of IVH after adjusting for confounders as a single measurement of SVC flow did not add any diagnostic value in this cohort. Thus, the exact role of SVC flow measurements in the circulatory assessment of preterm infants remains to be elucidated. However, admission temperature may have an effect on systemic blood flow in very preterm infants.

Use of milrinone to treat cardiac dysfunction in infants with pulmonary hypertension secondary to congenital diaphragmatic hernia: a review of six patients

BACKGROUND

Pulmonary hypertension and secondary cardiac dysfunction are important contributors of morbidity and mortality in infants with congenital diaphragmatic hernia (CDH). Milrinone, a phosphodiesterase-3 inhibitor, may be useful in this setting for its combined actions as a pulmonary vasodilator and to improve systolic and diastolic function.

OBJECTIVES

This study aimed to assess the effects of milrinone on cardiac function and pulmonary artery pressure in infants with CDH.

METHODS

A retrospective review of echocardiograms performed on infants with CDH who received milrinone was performed. Tissue Doppler imaging velocities were used to assess systolic and diastolic function. Pulmonary artery pressure was assessed from the pattern and velocity of ductal shunting.

RESULTS

Six infants with CDH and severe pulmonary hypertension were identified. Systolic and diastolic myocardial velocities were reduced in the right ventricle (RV) and interventricular septum (IVS) at baseline. In the 72 h after commencement of milrinone, there was a significant increase in early diastolic myocardial velocities in the RV, accompanied by increasing systolic velocities in the RV and IVS. Oxygenation index was significantly reduced, blood pressure unchanged, and ductal shunt velocity minimally altered over the same time period.

CONCLUSIONS

Milrinone use was associated with an improvement in systolic and diastolic function in the RV, corresponding to an improvement in clinical status.

Newer inotropes in pediatric heart failure

In the cardiac setting in pediatrics, inotropic support is often employed based on the extrapolation from adult studies, the underlying pathophysiology, pharmacodynamics of inotropes, and anecdotal experience. Large pediatric critical care studies involving inotropic support are rare. Levosimendan, a calcium-sensitizing agent with inotropic and lusitropic properties, is a pyridazole dinitrate derivative with linear pharmacokinetics and a relatively short half life, although an active metabolite, namely, OR-1876, has a half life of 70-80 hours accounting for a prolonged effect. Albeit few, pediatric studies involving levosimendan suggest similar pharmacokinetics to adults with heart failure, an efficacy at least equal to that of milrinone, favorable myocardial oxygen effects, and an ability to decrease concomitant catecholamine dosing. Levosimendan may be a promising new agent in pediatrics, but further experience and study are warranted. Finally, istaroxime, a calcium cycling agent that is in the beginning of adult study, may be another inotrope with lusitropic properties that might be applicable to pediatric patients.

Haemodynamically unstable preterm infant: an unresolved management conundrum

While extremely low-birthweight infants are at a higher risk of haemodynamic instability, management strategies can be highly variable and may lack scientific validation. The aetiology of cardiovascular compromise can be diverse. Volume replacements, cardiotropes (dobutamine, dopamine, epinephrine and milrinone) and hydrocortisone supplementation are common interventions. Most often, therapy is driven by protocol, is based on poorly validated clinical information or is based on the premise that "one therapy fits all". A physiology-driven approach is most needed during transition from intrauterine to extrauterine life surrounding preterm birth, when rapid changes in cardiovascular adaptation occur. The physiologically important determinants of neonatal haemodynamics include cardiac output and systemic vascular resistance, blood pressure, as well as individual organ vascular resistances and blood flows. Three key variables with impact on neonatal haemodynamics, haemodynamically significant ductus arteriosus, systemic blood flow and left ventricular afterload, as well as related therapeutic dilemmas are addressed. Among the novel technologies and approaches presently available, targeted neonatal echocardiography performed by the clinician, used in conjunction with the clinical context, has the potential to better define pathophysiology. A framework for physiology-driven care is proposed, which has the potential to optimize care.

Use of milrinone in the management of haemodynamic instability following duct ligation

Haemodynamic instability affects 22% to 29% of very low birth weight infants in the acute period following ligation of the ductus arteriosus and contributes to the mortality seen in this group. Since the sudden elevation of systemic vascular resistance has been recognised to be one of the factors contributing to this instability, milrinone, an afterload reducing agent, might potentially be of significant therapeutic benefit. This report presents the clinical course of an infant born at 26 weeks gestation who required surgical ligation of a haemodynamically significant patent ductus arteriosus after two unsuccessful 6-day courses of intravenous indomethacin. The post-operative period was characterized by oxygenation failure, rising blood pressure and echocardiographic signs indicative of diastolic dysfunction. The infant was successfully managed with milrinone, a phosphodiesterase inhibitor, which acts both as an "inodilator" and has lusitropy properties. Post-duct ligation haemodynamic instability in a preterm infant was successfully managed with milrinone. The role of afterload-reducing agents such as milrinone in this setting should, therefore, be systematically analyzed.

Systemic and cerebral hemodynamics during the transitional period after premature birth

Little is known about the effect on clinically relevant outcomes of the complex hemodynamic changes occurring during adaptation to extrauterine life in preterm neonates, particularly in very low birth weight neonates. As cardiovascular adaptation in this extremely vulnerable patient population is complicated by immaturity of all organ systems, especially that of the cardiorespiratory, central nervous, and endocrine systems, maladaptation has been suspected, but not necessarily proven, to contribute to mortality and long-term morbidities. This article describes recent advances in the understanding of hemodynamic changes in very low birth weight neonates during postnatal transition, and reviews the complex and developmentally regulated interaction between systemic and cerebral hemodynamics and the effect of this interaction on clinically relevant outcomes.

Shock in the critically ill neonate

Shock is a clinical disorder that challenges caregivers in the neonatal intensive care unit. Critically ill neonates may develop shock due to a variety of causes but the predominant cause of shock in neonates is sepsis. This article provides the neonatal nurse with basic knowledge of the pathophysiology and the types of shock seen in the critically ill neonate. Treatment and supportive care of the neonate in shock is determined by the underlying cause of shock with the ultimate goal of treatment being adequate perfusion of tissues to deliver oxygen to the cells and remove metabolic waste products.

Support of the preterm circulation: keynote address to the Fifth Evidence vs Experience Conference, Chicago, June 2008

Hemodynamics is an area of neonatology that is marked more by what we do not know than what we do. What is clear is that it is much more complex than just measuring blood pressure (BP). Early postnatal preterm hemodynamic pathophysiology is characterized by low systemic blood flow (SBF), possibly relating to a mix of afterload compromise, left-to-right shunting through the unconstricted ductus and to the circulatory effects of ventilation. After approximately 24 h of age, vasodilatation seems to be the dominant pathology. In the face of this complexity, a one-size-fits-all approach to treatment that will be applicable in a large clinical trial may prove elusive. The possibility of using a measure of both BP and SBF to target an appropriate treatment needs to be explored.

Acute hemodynamic effects of caffeine administration in premature infants

OBJECTIVE

Administration of caffeine citrate (caffeine) has been a central component of the treatment of apnea of prematurity. However, given its multiple pharmacologic effects, caffeine might be expected to produce hemodynamic changes in heart rate, stroke volume, cardiac output and vascular resistance.

STUDY DESIGN

In this prospective observational study, we report the hemodynamic effects of intravenous caffeine administration in a population of premature infants who received caffeine to correct or prevent apnea of prematurity.

METHODS

Hemodynamic effects of caffeine were determined in 31 infants. Stroke volume was measured via echocardiogram, using velocity time integral at the aortic root diameter. Statistically univariate analyses were performed parametrically using paired t-test and nonparametrically (sign test). Multivariate linear regression models were used to identify subgroup covariate effects.

RESULTS

After intravenous caffeine, cardiac index increased in 31 of 31 trials, by an average of 14.6+/-16.3% (s.d.); stroke volume increased in 24 of 31 trials, by 7.8+/-12.2%; heart rate increased in 28 of 31 trials by 7.7+/-7.2 beats per min; and blood pressure increased in 25 of 31 trials, by 4.1+/-5.8 mm Hg (all P<0.001). Multivariate linear regression revealed no significant effect of dose, birth weight, gestational age or postnatal age.

CONCLUSIONS

Intravenous caffeine consistently increases cardiac output and blood pressure in relatively stable premature infants, when given to treat or prevent apnea of prematurity. We speculate that there may be a role for caffeine in the hemodynamic treatment of hypotensive/hypoperfused infants.

Randomized trial of milrinone versus placebo for prevention of low systemic blood flow in very preterm infants

OBJECTIVE

To assess the effectiveness of early prophylactic milrinone versus placebo for prevention of low systemic blood flow in high-risk preterm infants.

STUDY DESIGN

Double-blind randomized placebo controlled trial of milrinone (loading dose 0.75 microg/kg/min for 3 hours then maintenance 0.2 microg/kg/min until 18 hours after birth) versus placebo. Infants born <30 weeks gestational age and <6 hours of age were eligible and were monitored with serial echocardiography, head ultrasound scanning, and continuous invasive blood pressure. Primary outcome was maintenance of superior vena cava (SVC) flow > or =45 mL/kg/min through the first 24 hours. The exit criterion was hypotension unresponsive to volume and inotropes.

RESULTS

Ninety infants were enrolled, equal proportions maintained SVC flow > or =45 mL/kg/min after treatment commenced. No significant difference was observed in SVC flow, right ventricular output, and blood pressure during the first 24 hours; or grades 3 to 4 periventricular/intraventricular hemorrhage and death. Heart rate was higher and constriction of the ductus was slower in the infants randomized to milrinone.

CONCLUSIONS

Milrinone did not prevent low systemic blood flow during the first 24 hours in very preterm infants, and no adverse effects were attributable to milrinone. Use of a preventative treatment with rescue model allowed comparison of an inotrope with placebo in this high-risk group of infants.

Clinical practice parameters for hemodynamic support of pediatric and neonatal septic shock: 2007 update from the American College of Critical Care Medicine

BACKGROUND

The Institute of Medicine calls for the use of clinical guidelines and practice parameters to promote "best practices" and to improve patient outcomes.

OBJECTIVE

2007 update of the 2002 American College of Critical Care Medicine Clinical Guidelines for Hemodynamic Support of Neonates and Children with Septic Shock.

PARTICIPANTS

Society of Critical Care Medicine members with special interest in neonatal and pediatric septic shock were identified from general solicitation at the Society of Critical Care Medicine Educational and Scientific Symposia (2001-2006).

METHODS

The Pubmed/MEDLINE literature database (1966-2006) was searched using the keywords and phrases: sepsis, septicemia, septic shock, endotoxemia, persistent pulmonary hypertension, nitric oxide, extracorporeal membrane oxygenation (ECMO), and American College of Critical Care Medicine guidelines. Best practice centers that reported best outcomes were identified and their practices examined as models of care. Using a modified Delphi method, 30 experts graded new literature. Over 30 additional experts then reviewed the updated recommendations. The document was subsequently modified until there was greater than 90% expert consensus.

RESULTS

The 2002 guidelines were widely disseminated, translated into Spanish and Portuguese, and incorporated into Society of Critical Care Medicine and AHA sanctioned recommendations. Centers that implemented the 2002 guidelines reported best practice outcomes (hospital mortality 1%-3% in previously healthy, and 7%-10% in chronically ill children). Early use of 2002 guidelines was associated with improved outcome in the community hospital emergency department (number needed to treat = 3.3) and tertiary pediatric intensive care setting (number needed to treat = 3.6); every hour that went by without guideline adherence was associated with a 1.4-fold increased mortality risk. The updated 2007 guidelines continue to recognize an increased likelihood that children with septic shock, compared with adults, require 1) proportionally larger quantities of fluid, 2) inotrope and vasodilator therapies, 3) hydrocortisone for absolute adrenal insufficiency, and 4) ECMO for refractory shock. The major new recommendation in the 2007 update is earlier use of inotrope support through peripheral access until central access is attained.

CONCLUSION

The 2007 update continues to emphasize early use of age-specific therapies to attain time-sensitive goals, specifically recommending 1) first hour fluid resuscitation and inotrope therapy directed to goals of threshold heart rates, normal blood pressure, and capillary refill 70% and cardiac index 3.3-6.0 L/min/m.

Recent advances in sepsis and septic shock

Sepsis remains a common problem in all age groups. Recently surviving sepsis campaign has taken up a worldwide initiative by publishing international guidelines 2008 with a hope to disseminate information regarding management of sepsis for all age groups. This article presents a review of recent advances as they apply to pediatric age group supported by the available evidence with reference to standard definitions of pediatric sepsis and septic shock and management in the emergency room and pediatric intensive care unit.

Relationship between blood pressure and blood flow in newborn preterm infants

BACKGROUND

Arterial blood pressure remains the most frequently monitored indicator of neonatal circulatory status. However, studies of systemic perfusion in neonates have often shown only weakly positive associations with blood pressure.

OBJECTIVES

To examine the relationship between invasively monitored arterial blood pressure and four measurements of systemic perfusion: left and right ventricular outputs, superior vena caval (SVC) flow and descending aortic (DAo) flow.

DESIGN

Echocardiographic assessments of perfusion were performed four times in the first 48 h of postnatal life in a cohort of 34 preterm (<30 weeks) infants. Arterial blood pressure was monitored invasively over the exact duration of the echocardiogram.

RESULTS

In the first 48 h of postnatal life there was no evidence of a positive association between blood pressure and volume of blood flow in any of the four vessels studied. At 5 h postnatal age there was a weak but significant inverse correlation between volume of SVC flow and arterial blood pressure (p = 0.04). A similar but non-significant trend was seen at 12 h postnatal age.

CONCLUSIONS

Infants with reduced systemic perfusion tend to have normal or high blood pressure in the first hours of life, suggesting that a high systemic vascular resistance may lead to reduced blood flow. Low blood pressure does not correlate with poor perfusion in the first 48 h of postnatal life in sick preterm infants.

Treating hypotension in the preterm infant: when and with what: a critical and systematic review

A very large proportion of extremely preterm infants receive treatments for hypotension. There are, however, marked variations in indications for treatment, and in the interventions used, between neonatal intensive care units and between neonatologists.

METHODS

We performed systematic reviews of the literature in order to determine which preterm infants may benefit from treatment with interventions to elevate blood pressure (BP), and which interventions improve clinically important outcomes.

RESULTS

Our review was not able to define a threshold BP that was significantly predictive of a poor outcome, nor whether any interventions for hypotensive infants improved outcomes, nor which interventions were more likely to be beneficial.

CONCLUSIONS

There is a distinct lack of prospective research of this issue, which prevents good clinical care. It is possible that a simple BP threshold that indicates the need for therapy does not exist, and other factors, such as the clinical status or systemic blood flow measurements, may be much more informative. Such a paradigm shift will also require careful prospective study.

Population pharmacokinetics and dosing regimen design of milrinone in preterm infants

AIMS

To define the pharmacokinetics of milrinone in very preterm infants and determine an optimal dose regimen to prevent low systemic blood flow in the first 12 h after birth.

METHODS

A prospective open-labelled, dose-escalation pharmacokinetic study was undertaken in two stages. In stage one, infants received milrinone at 0.25 microg/kg/min (n = 8) and 0.5 microg/kg/min (n = 11) infused from 3 to 24 h of age. Infants contributed 4-5 blood samples for concentration-time data which were analysed using a population modelling approach. A simulation study was used to explore the optimal dosing regimen to achieve target milrinone concentrations (180-300 ng/ml). This milrinone regimen was evaluated in stage two (n = 10).

RESULTS

Infants (n = 29) born before 29 weeks gestation were enrolled. Milrinone pharmacokinetics were described using a one-compartment model with first-order elimination rate, with a population mean clearance (CV%) of 35 ml/h (24%) and volume of distribution of 512 ml (21%) and estimated half-life of 10 h. The 0.25 and 0.5 microg/kg/min dosage regimens did not achieve optimal milrinone concentration-time profiles to prevent early low systemic blood flow. Simulation studies predicted a loading infusion (0.75 microg/kg/min for 3 h) followed by maintenance infusion (0.2 microg/kg/min until 18 h of age) would provide an optimal milrinone concentration profile. This was confirmed in stage two of the study.

CONCLUSION

Population pharmacokinetic modelling in the preterm infant has established an optimal dose regimen for milrinone that increases the likelihood of achieving therapeutic aims and highlights the importance of pharmacokinetic studies in neonatal clinical pharmacology.

Left ventricular contractility in extremely premature infants in the first day and response to inotropes

The aim was to assess myocardial contractility in infants born <30 wk gestation developing low systemic blood flow (SBF) in the first day, and the effect of dobutamine versus dopamine. Superior vena cava (SVC) flow was used as a measure of SBF at 3, 10, and 24 h (n = 106). Infants with low SVC flow randomized to dopamine or dobutamine. Myocardial contractility was determined by the relationship between left ventricular (LV) mean velocity of circumferential fiber shortening (mVcfs) and wall stress. Infants who developed low SVC flow had significantly worse myocardial contractility at 3 h, but not 10 h. At 24 h, low-flow infants had lower than expected mVcfs for any given LV stress. In 37 infants randomized to inotrope, there was no significant difference in contractility at 10 microg/kg/min. At 20 microg/kg/min (n = 21), dopamine increased whereas dobutamine decreased LV stress. Infants on dobutamine had significantly lower than expected mVcfs for any given LV stress compared with infants on dopamine. Contractility was not improved by either inotrope at either dose. In conclusion, infants developing low SVC flow in the first day have worse myocardial contractility at 3 h. Neither inotrope increased contractility, but dopamine increased LV stress at 20 microg/kg/min.

Selected Proceedings of the NICHD/FDA newborn drug development initiative: Part II

BACKGROUND

In February 2003, the National Institute of Child Health and Human Development (NICHD) and the US Food and Drug Administration (FDA) created the Newborn Drug Development Initiative (NDDI), an ongoing program to determine gaps in knowledge in neonatal therapeutics and to explore clinical study designs for use in the newborn population. Working groups were established in 3 therapeutic areas: the central nervous, pulmonary, and cardiovascular systems. Three additional groups discussed pain control, drug prioritization, and ethics in neonatal clinical trials.

OBJECTIVE

The purpose of this article was to provide an overview of the 5 articles written by members of the Neurology, Cardiology, Drug Prioritization, and Ethics Groups.

METHODS

Information for the current article, as well as the 5 articles presented in this supplemental section, was gathered from the proceedings of a workshop cosponsored by the NICHD and the FDA. This workshop took place March 29 and 30, 2004, in Baltimore, Maryland.

RESULTS

The Neurology Group addressed the treatment of 2 common and interrelated conditions in the newborn population: neonatal seizures and hypoxic-ischemic encephalopathy. The unsubstantiated clinical preference for using phenobarbital to treat neonatal seizures, coupled with the development of several newer antiepileptic drugs with application in children, dictates the need for rigorous clinical trials of these drugs in the neonatal population. A number of pharmacologic agents currently undergoing extensive investigations in experimental animals and adult humans may have application in the newborn population. The Cardiology Group reviewed controversial approaches to the diagnosis and treatment of cardiovascular instability of preterm infants and identified gaps in knowledge. The group discussed issues of study design and developed 2 study proposals: (1) a placebo-controlled trial with a rescue arm for symptomatic infants; and (2) a targeted blood pressure (BP) trial. The Drug Prioritization Group focused on the fact that the uniqueness of the newborn population is due to distinctive and changing physiologic characteristics, conditions, and diseases that are different from those affecting older children, as well as the large differences in developmental patterns between 23 weeks of gestation and term. All of these factors help explain the lack of adequate trials and the sparseness of evidence regarding efficacy and toxicity risks of most drugs used in the newborn population. Unfortunately, the frequency of drug use and polypharmacy is highest in very-low-birth-weight infants. The large number of drugs requiring study and the uniqueness of the indications for those drugs preclude the use of the prioritization process used in older children. The focus of the Drug Prioritization Group was the determination of factors that identify which drugs are most important for study. The Ethics Group was unique in that its members were integrated into the therapeutic groups. This approach allowed for the identification of similarities and dissimilarities in the proposed clinical trial design framework. The summary report included here identifies common themes voiced in the various NDDI reports and deliberations.

CONCLUSIONS

The 5 articles included in this issue address different issues but share common themes: the need to develop innovative trial designs and biomarkers of efficacy, consideration of ethical concerns, and selection of appropriate drugs for study.

Assessment and support of the preterm circulation

There are no clinical outcome data on which to base recommendations on how to assess and support the preterm circulation. Current standards are derived from an assumed proportionality between systemic and organ blood flow and mean blood pressure. Our study of central measures of systemic blood flow suggests preterm haemodynamics are more complex than this. Low systemic blood flow is common in the first 24 h after birth in very preterm babies and is not necessarily reflected by low blood pressure. The causes of this low systemic blood flow are complex but may relate to maladaptation to high extrauterine systemic (and sometimes pulmonary) vascular resistance. After day 1, hypotensive babies are more likely to have normal or high SBF reflecting vasodilatation. Empirically, inotropes that reduce afterload (such as dobutamine) may be more appropriate in the transitional period, while those with more vasoconstrictor actions (such as dopamine) may be more appropriate later on. Defining the haemodynamic in an individual baby needs both blood pressure and echocardiographic measures of systemic blood flow. Research in this area needs to move beyond just demonstrating changes in physiological variables to showing improvements in important clinical outcomes.