Relationship between blood pressure and cardiac output in preterm infants requiring mechanical ventilation

A Theoretical and Practical Approach to Defining "Adequate Oxygenation" in the Preterm Newborn

John Scott Haldane recognized that the administration of supplemental oxygen required titration in the individual. Although he made this observation in adults, it is equally applicable to the preterm newborn. But how, in practice, can the oxygen requirements in the preterm newborn be determined to avoid the consequences of too little and too much oxygen? Unfortunately, the current generation of oxygen saturation trials in preterm newborns guides saturation thresholds rather than individual oxygen requirements. For this reason, we propose an alternate model for the description of oxygen sufficiency. This model considers the adequacy of oxygen delivery relative to simultaneous consumption. We describe how measuring oxygen extraction or the venous oxygen reservoir could define a physiologically based definition of adequate oxygen. This definition would provide a clinically useful reference value while making irrelevant the absolute values of both oxygen delivery and consumption. Additional trials to test adjunctive, noninvasive measurements of oxygen status in high-risk preterm newborns are needed to minimize the effects of both insufficient and excessive oxygen exposure.

Hemodynamic and metabolic effects of a new pediatric dobutamine formulation in hypoxic newborn pigs

BACKGROUND

The aim of our study was to measure drug-related changes in hemodynamics and oxygen metabolism in response to different doses of an age-appropriate dobutamine formulation in hypoxic pigs. A secondary aim was to validate superior vena cava flow (SVCF) as a marker of cardiac index (CI) for subsequent clinical trials of this formulation in humans.

METHODS

Newborn pigs (n = 18) were exposed to 2-h hypoxia (10-15% oxygen) followed by reoxygenation (21-30% oxygen 4 h). After 1-h reoxygenation, pigs were randomized to: control group (no treatment), dobutamine infusion at a rate of 10-15 or 15-20 µg/kg/min. Dobutamine groups received two dobutamine doses during 30 min with a 60 min washout period between doses. Cardiovascular profile and oxygen metabolism were monitored. In four animals, an ultrasonic perivascular flow probe was placed around superior vena cava to measure SVCF.

RESULTS

Hypoxia significantly decreased CI, systemic vascular resistance and mean arterial blood pressure (MABP). Dobutamine doses significantly increased heart-rate, CI, and oxygen-delivery without changes in stroke-volume and MABP. Only 10-15 µg/kg/min increased oxygen consumption and peripheral tissue oxygenation measured by Near-infrared spectroscopy. A positive correlation was observed between SVCF and CI.

CONCLUSION

The new pediatric dobutamine formulation improved hemodynamic status, with dose-specific differences in metabolic response. SVCF may be a useful surrogate for CI in subsequent clinical trials.

What Should We Do about Low Blood Pressure in Preterm Infants

The management of preterm infants with low blood pressure soon after birth remains unresolved. The definition of what constitutes low blood pressure is uncertain. At birth, mean blood pressure appears to be gestation specific and increases in the first few days of life. Antenatal steroids, delayed cord clamping, and the avoidance of mechanical ventilation are all associated with higher mean blood pressure and less hypotension after birth. Rates of hypotension of 15-50% have been reported in various studies of extremely preterm infants. However, only about 10% of all extremely preterm infants receive inotropes, suggesting that clinicians take into account other factors such as clinical, biochemical, and echocardiographic findings before deciding to intervene. The exact role of functional echocardiography in assessing the need for treatment of low blood pressure in extremely preterm infants remains to be determined. Near- infrared spectroscopy to assess cerebral perfusion may also have a role to play. Volume expansion (usually 10 mL/kg of saline) remains the most commonly used intervention for low blood pressure but evidence of benefit is lacking and there may be safety concerns. Whilst dopamine is the most commonly used inotropic drug, dobutamine, epinephrine, corticosteroids, milrinone, and vasopressin have also been utilised in preterm infants with low blood pressure. Clinical trials with long-term outcomes are needed to determine the most suitable inotrope and when to use it. Early hypotension differs from late hypotension with regard to cause, treatment, and outcome. A number of recent studies aimed at improving the evidence base for the treatment of early hypotension in extremely preterm infants have been terminated early because of poor recruitment. Currently, the answer to the question of what to do about low blood pressure in preterm infants remains unclear.

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.

Developing an objective method for analyzing vital signs changes in neonates during general anesthesia

BACKGROUND

Commonly used general anesthetics are considered to be neurotoxic to the developing rodent brain, leading to poor long-term outcome. However, it is unclear whether these rodent studies can be extrapolated to the human neonate. Given that anesthesia for urgent neonatal surgery cannot be avoided, it is vitally important to assess other factors that may impact neurological outcome following anesthesia and surgery.

OBJECTIVE

The purpose of this study is to identify thresholds for detecting vital sign deviations, which may have the potential for affecting neurological outcome following anesthesia and surgery in neonates. These data may be suitable to identify targets for prospective quality improvement projects and guide future research for strategies to reduce detrimental neurocognitive outcomes.

METHODS

A retrospective analysis of vital sign data was performed for neonates (age ≤28 days), undergoing noncardiac surgery over a 4-year period (2010-2013). Thresholds for detecting bradycardia, tachycardia, hypothermia, hyperthermia, hypertension, hypotension, hypocarbia, hypoxemia, significant changes in mean arterial blood pressure, and periods of high inspired oxygen concentration, were proposed. Selected chart review, to identify additional risk factors, and identify sources of data artifact, was performed for 224 cases.

RESULTS

Data from 435 procedures in neonates, with median (IQR [range]) ages of 6 (2-16 [0-28]) days were available for analysis. Five (3-6 [0-12]) rule deviations per case were observed; only 11 cases had no rule deviations. Hypothermia was observed in 285/435 (70%), moderate hypocapnia in 298/430 (69%), and severe hypotension in 270/435 (62%) cases.

CONCLUSION

An objective method of comparing cases has been created with a method to automatically identify neonatal vital sign deviations. With further validation the method has the potential to be a powerful tool to drive future quality improvement projects in neonatal anesthesia.

Fetal Physiology and the Transition to Extrauterine Life

The physiology of the fetus is fundamentally different from the neonate, with both structural and functional distinctions. The fetus is well-adapted to the relatively hypoxemic intrauterine environment. The transition from intrauterine to extrauterine life requires rapid, complex, and well-orchestrated steps to ensure neonatal survival. This article explains the intrauterine physiology that allows the fetus to survive and then reviews the physiologic changes that occur during the transition to extrauterine life. Asphyxia fundamentally alters the physiology of transition and necessitates a thoughtful approach in the management of affected neonates.

Artificial placenta: Recent advances and potential clinical applications

Lung immaturity remains a major cause of morbidity and mortality in extremely premature infants. Positive-pressure mechanical ventilation, the method of choice for respiratory support in premature infants, frequently promotes by itself lung injury and a negative impact in the circulatory function. Extracorporeal lung support has been proposed for more than 50 years as a potential alternative to mechanical ventilation in the treatment of severe respiratory failure of extremely premature infants. Recent advances in this field included the development of miniaturized centrifugal pumps and polymethylpentene oxygenators, as well as the successful use of pump-assisted veno-venous extracorporeal gas exchange systems in experimental artificial placenta models. This review, which includes studies published from 1958 to 2015, presents an update on the artificial placenta concept and its potential clinical applications. Special focus will be devoted to the milestones achieved so far and to the limitations that must be overcome before its clinical application. Notwithstanding, the artificial placenta stands as a promising alternative to mechanical ventilation in extremely premature infants. Pediatr Pulmonol. 2016;51:643-649. © 2016 Wiley Periodicals, Inc.

Hemodynamic Effects of Nasal Intermittent Positive Pressure Ventilation in Preterm Infants

Nasal intermittent positive pressure ventilation (NIPPV) and nasal continuous positive airway pressure (NCPAP) have proven to be effective modes of noninvasive respiratory support in preterm infants. Although they are increasingly used in neonatal intensive care, their hemodynamic consequences have not been fully evaluated. The aim of this study was to investigate the hemodynamic changes between NIPPV and NCPAP in preterm infants.This prospective observational study enrolled clinically stable preterm infants requiring respiratory support received NCPAP and nonsynchronized NIPPV at 40/minute for 30 minutes each, in random order. Cardiac function and cerebral hemodynamics were assessed by ultrasonography after each study period. The patients continued the study ventilation during measurements.Twenty infants with a mean gestational age of 27 weeks (range, 25-32 weeks) and birth weight of 974 g were examined at a median postnatal age of 20 days (range, 9-28 days). There were no significant differences between the NCPAP and NIPPV groups in right (302 vs 292 mL/kg/min, respectively) and left ventricular output (310 vs 319 mL/kg/min, respectively), superior vena cava flow (103 vs 111 mL/kg/min, respectively), or anterior cerebral artery flow velocity.NIPPV did not have a significant effect on the hemodynamics of stable preterm infants. Future studies assessing the effect of NIPPV on circulation should focus on less stable and very preterm infants.

Transitional Hemodynamics in Preterm Neonates: Clinical Relevance

BACKGROUND

Each newborn enters this world facing tremendous respiratory, hemodynamic and neuroendocrine challenges while going through drastic physiological changes during the process of adaption from fetal to postnatal life. Even though the vast majority of term infants transition smoothly without apparent consequences, this task becomes increasingly arduous for the extremely preterm infant.

METHODS & RESULTS

This article reviews the physiology and pathophysiology of cardiovascular adaptation of the very preterm neonate. In particular it describes the physiology of fetal circulation, summarizes the hemodynamic changes occurring during preterm births and discusses the impact of the most frequently seen clinical scenarios that place additional burden on the premature infant during immediate transition. Finally an emphasis is placed on discussing common clinical dilemmas and practical aspects of developmental hemodynamics such as neonatal hypotension and patent ductus arteriosus; clinical presentations the neonatologist encounters on a daily basis.

CONCLUSION

The review provides a physiology-based view on the hemodynamics of the immediate postnatal transitional period.

Functional Neonatal Echocardiography: Indian Experience

INTRODUCTION

Functional echocardiography, as opposed to echocardiography as performed by the cardiologist, is the bedside utilization of cardiac ultrasound to take after functional and haemodynamic changes longitudinally. Information reflecting cardiovascular capacity and systemic and pulmonary blood flow in sick preterm and term neonates can be observed utilizing this strategy. Information is lacking on its use in neonatal units in India.

AIM

To characterize the impact of Functional neonatal echocardiography (FnECHO) programme on decision making in a tertiary care centre in India by evaluating its frequency of use, patient characteristics, and indications.

MATERIALS AND METHODS

Prospective observational study of neonates in a tertiary Neonatal Intensive Care Unit (NICU) in Pune (India) from February 2014 to January 2015. All the neonates undergoing FnECHO during this 12 month period based on clinical findings were included in the study. Data extracted from the review of the clinical notes included gestational age, birth-weight, mode of delivery, Apgar scores, details of respiratory and cardiovascular support, timing of FnECHO and any other clinical diagnosis. The findings of echocardiography were recorded and correlated with the clinical and other laboratory or X-ray findings. If these findings indicated a change in management, it was instituted.

RESULTS

A total of 348 echocardiographic studies were performed in 187 neonates (mean 1.86; SD 2.02). The most frequent indication was Patent Ductus Arteriosus (PDA) assessment (n= 174, 50%), followed by haemodynamic instability (n=43, 12.36%). The results of FnECHO modified treatment in 148 cases (42.50%) in the form of addition and/or change in the treatment or avoidance of unnecessary intervention.

CONCLUSION

FnECHO is frequently used in the NICU setting and may be a useful tool to guide treatment. PDA assessment and haemodynamic instability are the most frequent indications. To validate its usefulness, well co-ordinated large prospective studies are needed.

Chest shielding for prevention of a haemodynamically significant patent ductus arteriosus in preterm infants receiving phototherapy

BACKGROUND

Patent ductus arteriosus (PDA) is associated with mortality and morbidity in preterm infants. Phototherapy is a common treatment for jaundice in preterm infants. However, phototherapy has been associated with failure of closure of the ductus arteriosus in preterm infants.

OBJECTIVES

To determine if chest shielding of preterm infants receiving phototherapy reduces the incidence of clinically and/or haemodynamically significant PDA and reduces morbidity secondary to PDA.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (the Cochrane Library; 2015, Issue 3), MEDLINE, EMBASE, CINAHL, previous reviews, cross-references, abstracts, proceedings of scientific meetings, and trial registries through March 2015.

SELECTION CRITERIA

Randomised controlled trials (RCTs), cluster-RCTs, or quasi-RCTs of chest shielding during phototherapy compared to sham shielding or no shielding for the prevention of a haemodynamically or clinically significant PDA in preterm infants.

DATA COLLECTION AND ANALYSIS

Three review authors independently assessed studies for eligibility and quality and extracted data. We defined a clinically significant PDA as the presence of a PDA with clinical signs of an effect on organ function attributable to the ductus arteriosus. We defined a haemodynamically significant PDA as clinical and/or echocardiographic signs of a significant ductus arteriosus effect on blood flow.

MAIN RESULTS

We included two small trials enrolling very preterm infants (Rosenfeld 1986; Travadi 2006). We assessed both as at high risk of bias. No study reported clinically significant PDA, defined as the presence of a PDA with clinical symptoms or signs attributable to the effect of a ductus arteriosus on organ function. Rosenfeld 1986 reported a non-significant reduction in haemodynamically significant PDA with left atrial to aortic root ratio greater than 1.2 (risk ratio (RR) 0.23, 95% confidence interval (CI) 0.05 to 1.01; 74 infants) but a statistically significant risk difference (RD -0.18, 95% CI -0.34 to -0.03; number needed to treat for an additional beneficial outcome (NNTB) 5, 95% CI 3 to 33). Rosenfeld 1986 reported a significant reduction in PDA detected by murmur (RR 0.50, 95% CI 0.29 to 0.88; RD -0.30, 95% CI -0.52 to -0.08; NNTB 3, 95% CI 2 to 12; 74 infants). Rosenfeld 1986 reported a significant reduction in treatment with indomethacin (RR 0.12, 95% CI 0.02 to 0.88; RD -0.21, 95% CI -0.35 to -0.06; NNTB 5, 95% CI 3 to 17; 74 infants), and only one infant had a ductal ligation in the no-shield group. There were no other significant outcomes, including mortality to discharge or 28 days, days in oxygen, days on mechanical ventilation, days in hospital, intraventricular haemorrhage, retinopathy of prematurity, or exchange transfusion.

AUTHORS' CONCLUSIONS

The available evidence is very low quality and insufficient to assess the safety or efficacy of chest shield during phototherapy for prevention of PDA in preterm infants. Further trials of chest shielding are warranted, particularly in settings where infants are not receiving prophylactic or early echocardiographic targeted cyclo-oxygenase inhibitors for PDA.

Management of Shock in Neonates

Shock is characterized by inadequate oxygen delivery to the tissues, and is more frequent in very low birth weight infants, especially in the first few days of life. Shock is an independent predictor of mortality, and the survivors are at a higher risk of neurologic impairment. Understanding the pathophysiology helps to recognize and classify shock in the early compensated phase and initiate appropriate treatment. Hypovolemia is rarely the primary cause of shock in neonates. Myocardial dysfunction is especially common in extremely preterm infants, and in term infants with perinatal asphyxia. Blood pressure measurements are easy, but correlate poorly with cerebral and systemic blood flows. Point-of-care cardiac ultrasound can help in individualized assessment of problems, selecting appropriate therapy and monitoring response, but may not always be available, and long-term benefits need to be demonstrated. The use of near-infrared spectroscopy to guide treatment of neonatal shock is currently experimental. In the absence of hypovolemia, excessive administration of fluid boluses is inappropriate therapy. Dobutamine and dopamine are the most common initial inotropes used in neonatal shock. Dobutamine has been shown to improve systemic blood flow, especially in very low birth weight infants, but dopamine is better at improving blood pressure in hypotensive infants. Newer inodilators including milrinone and levosimendan may be useful in selected settings. Data on long-term survival and neurologic outcomes following different management strategies are scarce and future research efforts should focus on this.

Physiology of the fetal and transitional circulation

The fetal circulation is an entirely transient event, not replicated at any point in later life, and functionally distinct from the pediatric and adult circulations. Understanding of the physiology of the fetal circulation is vital for accurate interpretation of hemodynamic assessments in utero, but also for management of circulatory compromise in premature infants, who begin extrauterine life before the fetal circulation has finished its maturation. This review summarizes the key classical components of circulatory physiology, as well as some of the newer concepts of physiology that have been appreciated in recent years. The immature circulation has significantly altered function in all aspects of circulatory physiology. The mechanisms and significance of these differences are also discussed, as is the impact of these alterations on the circulatory transition of infants born prematurely.

Challenges in Treating Low Blood Pressure in Preterm Infants

Whilst the prevalence of low blood pressure in preterm infants seems to have fallen over the last number of years, the problem is still frequently encountered in the neonatal intensive care unit and many babies continue to receive intervention. Great variability in practice persists, with a significant number of extremely low gestational age newborns in some institutions receiving some form of intervention, and in other units substantially less. A great degree of this variability relates to the actual criteria used to define hypotension, with some using blood pressure values alone to direct therapy and others using a combination of clinical, biochemical and echocardiography findings. The choice of intervention remains unresolved with the majority of centres continuing to administer volume followed by dopamine as a first line inotrope/vasopressor agent. Despite over 40 years of use there is little evidence that dopamine is of benefit both in the short term and long-term. Long-term follow up is available in only two randomised trials, which included a total of 99 babies. An under recognized problem relates to the administration of inotrope infusions in very preterm infants. There are no pediatric specific inotrope formulations available and so risks of errors in preparation and administration remain. This manuscript outlines these challenges and proposes some potential solutions.

In preterm infants, ascending intrauterine infection is associated with lower cerebral tissue oxygen saturation and higher oxygen extraction

BACKGROUND

Placental lesions are associated with neurological morbidity but the mechanism leading to morbidity is unclear. To provide insight into such a possible mechanism, we determined whether placental lesions were associated with regional cerebral tissue oxygen saturation (rcSO2) and fractional tissue oxygen extraction (FTOE) in preterm infants during their first 5 d after birth. We hypothesized that as a result of cerebral hypoperfusion, rcSO2 would be lower and FTOE would be higher.

METHOD

In a prospective, observational study of 42 preterm infants (gestational age <32 wk), the infants' placentas were examined for histopathology. We measured rcSO2 and transcutaneous arterial oxygen saturation (SpO2) on days 1-5. FTOE was calculated as FTOE = (transcutaneous SpO2 - rcSO2)/transcutaneous SpO2.

RESULTS

Only three placentas showed no pathology. Ascending intrauterine infection (AIUI) (n = 16) was associated with lower rcSO2 and higher FTOE values on days 2, 3, and 4 (P ≤ 0.05). Other placental lesions were not associated with rcSO2 and FTOE.

CONCLUSION

AIUI is associated with lower rcSO2, and higher FTOE shortly after birth. The effect it has on cerebral oxygenation might be the mechanism leading to neurodevelopmental problems.

Prenatal Exposure to Angiotensin II Receptor Blockers and Hemodynamic Effects on the Newborn

Angiotensin II receptor blockers (ARBs) are potent antihypertensive agents that block the renin angiotensin aldosterone system (RAS). Their use in pregnancy may cause malformations, oligoanuria, hypotension, and death. Hypotension is observed up to 15% of cases and is described as refractory to volume and inotropic support, although its pathophysiology is unknown. We present a case of prenatal exposure to ARBs in order to characterize the hemodynamic compromise in the newborn, help in decision-making, and guide the therapeutic approach to these patients.

Endogenous angiotensins and catecholamines do not reduce skin blood flow or prevent hypotension in preterm piglets

Endocrine control of cardiovascular function is probably immature in the preterm infant; thus, it may contribute to the relative ineffectiveness of current adrenergic treatments for preterm cardiovascular compromise. This study aimed to determine the cardiovascular and hormonal responses to stress in the preterm piglet. Piglets were delivered by cesarean section either preterm (97 of 115 days) or at term (113 days). An additional group of preterm piglets received maternal glucocorticoids as used clinically. Piglets were sedated and underwent hypoxia (4% FiO₂ for 20 min) to stimulate a cardiovascular response. Arterial blood pressure, skin blood flow, heart rate and plasma levels of epinephrine, norepinephrine, angiotensin II (Ang II), angiotensin‐(1–7) (Ang‐(1‐7)), and cortisol were measured. Term piglets responded to hypoxia with vasoconstriction; preterm piglets had a lesser response. Preterm piglets had lower blood pressures throughout, with a delayed blood pressure response to the hypoxic stress compared with term piglets. This immature response occurred despite similar high levels of circulating catecholamines, and higher levels of Ang II compared with term animals. Prenatal exposure to glucocorticoids increased the ratio of Ang‐(1‐7):Ang II. Preterm piglets, in contrast to term piglets, had no increase in cortisol levels in response to hypoxia. Preterm piglets have immature physiological responses to a hypoxic stress but no deficit of circulating catecholamines. Reduced vasoconstriction in preterm piglets could result from vasodilator actions of Ang II. In glucocorticoid exposed preterm piglets, further inhibition of vasoconstriction may occur because of an increased conversion of Ang II to Ang‐(1‐7).

This study aimed to determine if immature hormonal control of the cardiovascular system contributes to preterm cardiovascular compromise. Physiological and hormonal responses of preterm piglets to hypoxia are immature compared with term piglets. This is not due to a lack of endogenous catecholamines or angiotensin II, but may be due to the differences in cardiovascular actions of the renin–angiotensin system.

Heart rate passivity of cerebral tissue oxygenation is associated with predictors of poor outcome in preterm infants

AIM

Near-infrared spectroscopy (NIRS) and transcranial Doppler (TCD) allow non-invasive assessment of cerebral haemodynamics. We assessed cerebrovascular reactivity in preterm infants by investigating the relationship between NIRS- and TCD-derived indices and correlating them with severity of clinical illness.

METHODS

We recorded the NIRS-derived cerebral tissue oxygenation index (TOI) and TCD-derived flow velocity (Fv), along with other physiological variables. Moving correlation coefficients between measurements of cerebral perfusion (TOI, Fv) and heart rate were calculated. We presumed that positivity of these correlation coefficients - tissue oxygenation heart rate reactivity index (TOHRx) and flow velocity heart rate reactivity index (FvHRx) - would indicate a direct relationship between cerebral perfusion and cardiac output representing impaired cerebrovascular autoregulation.

RESULTS

We studied 31 preterm infants at a median age of 2 days, born at a median gestational age of 26 + 1 weeks. TOHRx was significantly correlated with gestational age (R = -0.57, p = 0.007), birth weight (R = -0.58, p = 0.006) and the Clinical Risk Index for Babies II (R = 0.55, p = 0.0014). TOHRx and FvHRx were significantly correlated (R = 0.39, p = 0.028).

CONCLUSION

Heart rate has a key influence on cerebral haemodynamics in preterm infants, and TOHRx may be of diagnostic value in identifying impaired cerebrovascular reactivity leading to adverse clinical outcome.

Use of ultrasound in the haemodynamic assessment of the sick neonate

Clinician performed ultrasound (CPU) by the clinician caring for a sick patient is increasingly used in critical care specialties. The real-time haemodynamic information obtained helps the clinician to understand underlying physiology, target treatment and refine clinical decision-making. Neonatologists are increasingly using ultrasound to assess sick neonates with a range of clinical presentations and demand for training and accreditation programmes is increasing. This review discusses the current expanded uses for CPU in the haemodynamic assessment of the sick neonate.

Respiratory support for premature neonates in the delivery room: effects on cardiovascular function and the development of brain injury

The transition to newborn life in preterm infants is complicated by immature cardiovascular and respiratory systems. Consequently, preterm infants often require respiratory support immediately after birth. Although aeration of the lung underpins the circulatory transition at birth, positive pressure ventilation can adversely affect cardiorespiratory function during this vulnerable period, reducing pulmonary blood flow and left ventricular output. Furthermore, pulmonary volutrauma is known to initiate pulmonary inflammatory responses, resulting in remote systemic involvement. This review focuses on the downstream consequences of positive pressure ventilation, in particular, interactions between cardiovascular output and the initiation of a systemic inflammatory cascade, on the immature brain. Recent studies have highlighted that positive pressure ventilation strategies are precursors of cerebral injury, probably mediated through cerebral blood flow instability. The presence of, or initiation of, an inflammatory cascade accentuates adverse cerebral blood flow, in addition to being a direct source of brain injury. Importantly, the degree of brain injury is dependent on the nature of the initial ventilation strategy used.

Neonatal hypotension: dopamine or dobutamine?

Controversy surrounds the assessment of perfusion and the methods currently utilised to define hypotension, especially blood pressure. There is growing agreement to assess heart function when selecting inotropic therapy and use bedside tools such as echocardiography for assessing at-risk infants. Both dopamine and dobutamine have comparative efficacy, and in certain disease states with immature myocardium there could be potential advantages in using dobutamine. The concomitant use of hydrocortisone has been shown to be beneficial when escalating doses of first-line inotropes are used. Other inotropes require further study through randomised trials for their safety and efficacy to be established.

Management of hypotension in preterm infants (The HIP Trial): a randomised controlled trial of hypotension management in extremely low gestational age newborns

BACKGROUND

Extremely preterm babies (delivered at <28 completed weeks of gestation) are frequently diagnosed with hypotension and treated with inotropic and pressor drugs in the immediate postnatal period. Dopamine is the most commonly used first-line drug. Babies who are treated for hypotension more frequently sustain brain injury, have long-term disability or die compared to those who are not. Despite the widespread use of drugs to treat hypotension in such infants, evidence for efficacy is lacking, and the effect of these agents on long-term outcomes is unknown.

HYPOTHESIS

In extremely preterm babies, restricting the use of dopamine when mean blood pressure (BP) values fall below a nominal threshold and using clinical criteria to determine escalation of support ('restricted' approach) will result in improved neonatal and longer-term developmental outcomes. RESEARCH PLAN: In an international multi-centre randomised trial, 830 infants born at <28 weeks of gestation, and within 72 h of birth, will be allocated to 1 of 2 alternative treatment options (dopamine vs. restricted approach) to determine the better strategy for the management of BP, using a conventional threshold to commence treatment. The first co-primary outcome of survival without brain injury will be determined at 36 weeks' postmenstrual age and the second co-primary outcome (survival without neurodevelopmental disability) will be assessed at 2 years of age, corrected for prematurity.

DISCUSSION

It is essential that appropriately designed trials be performed to define the most appropriate management strategies for managing low BP in extremely preterm babies.

Cerebral blood flow in the neonate

Ensuring adequate oxygenation of the developing brain is the cornerstone of neonatal critical care. Despite decades of clinical research dedicated to this issue of paramount importance, our knowledge and understanding regarding the physiology and pathophysiology of neonatal cerebral blood flow are still rudimentary. This review primarily focuses on currently available human clinical and experimental data on cerebral blood flow and autoregulation in the preterm and term infant. Limitations of systemic blood pressure values as surrogates for monitoring adequate cerebral oxygen delivery are discussed. Particular emphasis is placed on the high interindividual variability in cerebral blood flow values, vasoreactivity, and autoregulatory thresholds making the applications of normative values highly questionable. Technical and ethical difficulties to conduct such trials leave us with a near complete lack of knowledge on how pharmacological and surgical interventions impact on cerebral autoregulation. The ensemble of these works argues for the necessity of highly individualized care by taking advantage of continuous bedside monitoring of cerebral circulation. They also point to the urgent need for further studies addressing the exciting but difficult issue of cerebral blood flow autoregulation in the neonate.

Measuring physiological changes during the transition to life after birth

The transition to life after birth is characterized by major physiological changes in respiratory and hemodynamic function, which are predominantly initiated by breathing at birth and clamping of the umbilical cord. Lung aeration leads to the establishment of functional residual capacity, allowing pulmonary gas exchange to commence. This triggers a significant decrease in pulmonary vascular resistance, consequently increasing pulmonary blood flow and cardiac venous return. Clamping the umbilical cord also contributes to these hemodynamic changes by altering the cardiac preload and increasing peripheral systemic vascular resistance. The resulting changes in systemic and pulmonary circulation influence blood flow through both the oval foramen and ductus arteriosus. This eventually leads to closure of these structures and the separation of the pulmonary and systemic circulations. Most of our knowledge on human neonatal transition is based on human (fetal) data from the 1970s and extrapolation from animal studies. However, there is renewed interest in performing measurements directly at birth. By using less cumbersome techniques (and probably more accurate), our previous understanding of the physiological transition at birth is challenged, as well as the causes and consequences for when this transition fails to progress. This review will provide an overview of physiological measurements of the respiratory and hemodynamic transition at birth. Also, it will give a perspective on some of the upcoming technological advances in physiological measurements of neonatal transition in infants who are unable to make the transition without support.

Cardiac blood flow measurements in stable full term small for gestational age neonates

BACKGROUND

Cardiac blood flow measurements are useful in the haemodynamic management of neonates. Cardiac blood flows can be estimated with functional echocardiography as follows; flow in Superior Vena Cava (SVC), Right Ventricular Outflow (RVO) and Left Ventricular Outflow (LVO). Studies in preterm infants have shown that abnormal superior vena cava flow is associated with poor neurodevelopmental outcomes. To date, normative data on LVO, RVO and SVC flows has been established for term appropriate for gestational age neonates and preterm neonates, but no data is available on RVO, LVO and SVC flows for term small for gestational age neonates.

OBJECTIVE

To determine Right Ventricular Output (RVO), Left Ventricular Output (LVO) and Superior Vena Cava (SVC) flow after the transitional period in stable full term Small for Gestational Age (SGA) neonates.

DESIGN

Observational study.

SETTING

A tertiary care, perinatal centre in western Maharashtra, India.

PARTICIPANTS

Full term (37 to 41 weeks) small for gestational age (weight below 10th percentile for gestational age) infants who were born during the study period.

METHODS

RVO, LVO and SVC flows were measured by functional echocardiography on day 7 of life in stable full term SGA neonates from January 2011 to August 2011. Infants who required respiratory or cardiovascular support and intensive care unit admissions for any indication and those with a clinical suspicion of an infection within 48 hours after data collection were excluded from the study.

STATISTICAL ANALYSES

Unpaired t-test was used to compare SVC flow between symmetric and asymmetric SGA neonates.

MAIN OUTCOME MEASURE

Measurements of RVO, LVO and SVC in term SGA neonates on day 7 of life.

RESULTS

We performed measurements in 52 term SGA neonates with a median (range) birth weight of 2.190 (1.600-2.410) kg. Fifty two measurements were analyzed on day 7. The mean (SD) RVO, LVO and SVC flows were 255.59 (57.42) , 214.61 (52.04) and 126.28 (31.23) mL/kg/min.

CONCLUSION

This study provides RVO, LVO and SVC flow values in a cohort of stable term SGA neonates after the transitional period.

The SafeBoosC phase II randomised clinical trial: a treatment guideline for targeted near-infrared-derived cerebral tissue oxygenation versus standard treatment in extremely preterm infants

Near-infrared spectroscopy-derived regional tissue oxygen saturation of haemoglobin (rStO2) reflects venous oxygen saturation. If cerebral metabolism is stable, rStO2 can be used as an estimate of cerebral oxygen delivery. The SafeBoosC phase II randomised clinical trial hypothesises that the burden of hypo- and hyperoxia can be reduced by the combined use of close monitoring of the cerebral rStO2 and a treatment guideline to correct deviations in rStO2 outside a predefined target range.

AIMS

To describe the rationale for and content of this treatment guideline.

METHODS

Review of the literature and assessment of the quality of evidence and the grade of recommendation for each of the interventions.

RESULTS AND CONCLUSIONS

A clinical intervention algorithm based on the main determinants of cerebral perfusion-oxygenation changes during the first hours after birth was generated. The treatment guideline is presented to assist neonatologists in making decisions in relation to cerebral oximetry readings in preterm infants within the SafeBoosC phase II randomised clinical trial. The evidence grades were relatively low and the guideline cannot be recommended outside a research setting.

Renovascular reactivity measured by near-infrared spectroscopy

Hypotension and shock are risk factors for death, renal insufficiency, and stroke in preterm neonates. Goal-directed neonatal hemodynamic management lacks end-organ monitoring strategies to assess the adequacy of perfusion. Our aim is to develop a clinically viable, continuous metric of renovascular reactivity to gauge renal perfusion during shock. We present the renovascular reactivity index (RVx), which quantifies passivity of renal blood volume to spontaneous changes in arterial blood pressure. We tested the ability of the RVx to detect reductions in renal blood flow. Hemorrhagic shock was induced in 10 piglets. The RVx was monitored as a correlation between slow waves of arterial blood pressure and relative total hemoglobin (rTHb) obtained with reflectance near-infrared spectroscopy (NIRS) over the kidney. The RVx was compared with laser-Doppler measurements of red blood cell flux, and renal laser-Doppler measurements were compared with cerebral laser-Doppler measurements. Renal blood flow decreased to 75%, 50%, and 25% of baseline at perfusion pressures of 60, 45, and 40 mmHg, respectively, whereas in the brain these decrements occurred at pressures of 30, 25, and 15 mmHg, respectively. The RVx compared favorably to the renal laser-Doppler data. Areas under the receiver operator characteristic curves using renal blood flow thresholds of 50% and 25% of baseline were 0.85 (95% CI, 0.83–0.87) and 0.90 (95% CI, 0.88–0.92). Renovascular autoregulation can be monitored and is impaired in advance of cerebrovascular autoregulation during hemorrhagic shock.

Cardiovascular support in preterm infants: a survey of practices in Australia and New Zealand

AIM

Management of haemodynamic instability in premature neonates and selection of inotropic therapy are protocol driven, and therapeutic choices lack scientific validation. The aim of this study was to characterise practices related to the management of haemodynamic instability in premature infants.

METHODS

An electronic web-based questionnaire was emailed to all neonatologists and advanced trainees in Australia and New Zealand. Respondents were presented with a series of questions related to the management of hypotension in a 1-day-old, extremely low birthweight infant, and opinions were collected.

RESULTS

Survey response rate was 65% (114/176). Haemodynamically significant ductus arteriosus, systemic blood flow and left ventricular afterload were considered the most important physiologic concepts by 81, 68 and 50%, respectively. After initial crystalloid replacement, the next step in management reported included a second bolus (35%), dobutamine (28%), dopamine (17%) or clinician-performed cardiac ultrasound (CPCU) (20%). In the setting of hypotension resistant to dobutamine and dopamine, the most common strategies were to perform CPCU (57%), or administer hydrocortisone (39%), epinephrine (3.5%) or milrinone (<1%). The majority (66%) of respondents felt that premature infants are over-treated on the basis of presumed hypotension, while 83% felt that performing a CPCU would enhance clinical decision-making.

CONCLUSIONS

Wide variation in the approach to management of haemodynamic instability in extremely low birthweight infants was identified. Haemodynamic information provided by a CPCU was considered highly desirable by the majority of the respondents.

Corticosteroids for treating hypotension in preterm infants

BACKGROUND

Systemic hypotension is a relatively common complication of preterm birth and is associated with periventricular haemorrhage, periventricular white matter injury and adverse neurodevelopmental outcome. Corticosteroid treatment has been used as an alternative or an adjunct to conventional treatment with volume expansion and vasopressor/inotropic therapy.

OBJECTIVES

To determine the effectiveness and safety of corticosteroids used either as primary treatment of hypotension or for the treatment of refractory hypotension in preterm infants.

SEARCH METHODS

Randomized or quasi-randomised controlled trials were identified by searching the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 2, 2011), MEDLINE (1996 to Jan 2011), EMBASE (1974 to Jan 2011), CINAHL (1981 to 2011), reference lists of published papers and abstracts from the Pediatric Academic Societies and the European Society for Pediatric Research meetings published in Pediatric Research (1995 to 2011).

SELECTION CRITERIA

We included all randomised or quasi-randomised controlled trials investigating the effect of corticosteroid therapy in the treatment of hypotension in preterm infants (< 37 weeks gestation) less than 28 days old. Studies using corticosteroids as primary treatment were included as well as studies using corticosteroids in babies with hypotension resistant to inotropes/pressors and volume therapy. We included studies comparing oral/intravenous corticosteroids with placebo, other drugs used for providing cardiovascular support or no therapy in this review.

DATA COLLECTION AND ANALYSIS

Methodological quality of eligible studies was assessed according to the methods used for minimising selection bias, performance bias, attrition bias and detection bias. Studies that evaluated corticosteroids (1) as primary treatment for hypotension or (2) for refractory hypotension unresponsive to prior use of inotropes/pressors and volume therapy, were analysed using separate comparisons. Data were analysed using the standard methods of the Neonatal Review Group using Rev Man 5.1.2. Treatment effect was analysed using relative risk, risk reduction, number needed to treat for categorical outcomes and weighted mean difference for outcomes measured on a continuous scale, with 95% confidence intervals.

MAIN RESULTS

Four studies were included in this review enrolling a total of 123 babies. In one study, persistent hypotension was more common in hydrocortisone treated infants as compared to those who received dopamine as primary treatment for hypotension (RR 8.2, 95% CI 0.47 to 142.6; RD 0.19, 95% CI 0.01 to 0.37). In two studies comparing steroid versus placebo, persistent hypotension (defined as a continuing need for inotrope infusion) was less common in steroid treated infants as compared to controls who received placebo for refractory hypotension (RR 0.35, 95% CI 0.19 to 0.65; RD -0.47, 95% CI - 0.68 to - 0.26; NNT = 2.1, 95% CI 1.47, 3.8). There were no statistically significant effects on any other short or long-term outcome. A further two studies that have only been published in abstract form to date, may be eligible for inclusion in a future update of this review.

AUTHORS' CONCLUSIONS

Hydrocortisone may be as effective as dopamine when used as a primary treatment for hypotension. But the long term safety data on the use of hydrocortisone in this manner is unknown.Steroids are effective in treatment of refractory hypotension in preterm infants without an increase in short term adverse consequences. However, long term safety or benefit data is lacking. With long term benefit or safety data lacking steroids cannot be recommended routinely for the treatment of hypotension in preterm infants.

Effect of antihypotensive treatment on cerebral oxygenation of preterm infants without PDA

BACKGROUND

Preterm infants with hypotension (mean arterial blood pressure [MABP] < gestational age [GA]) are treated with volume expansion and/or dopamine to ensure adequate cerebral perfusion/oxygenation. We used near-infrared spectroscopy to analyze the effects of volume expansion and dopamine on cerebral oxygenation in hypotensive preterm infants without patent ductus arteriosus (PDA).

PATIENTS AND METHODS

Among 390 infants, 71 (GA < 32 weeks) were hypotensive and eligible for inclusion. Thirty-three infants received volume expansion only (NaCl 0.9%; 20 mL/kg), and 38 received additional dopamine (5 μg/kg per minute). Nine and 11 infants initially treated with dopamine subsequently needed 7.5 and 10 μg/kg per minute, respectively. Seventy-one infants without hypotension were individually matched to serve as controls. MABP, regional cerebral oxygen saturation (rSco(2)), fractional tissue oxygen extraction (cFTOE), and arterial saturation (Sao(2)) were monitored 15 minutes before and 30 and 60 minutes after volume or dopamine and at comparable postnatal ages in controls.

RESULTS

No changes in MABP, rSco(2), or cFTOE were found 30 minutes after volume expansion. MABP increased 60 minutes after 5 μg/kg per minute dopamine (median [range]: 28 [19-32] vs 33 [23-46] mm Hg; P < .001). There was a small increase and decrease, respectively, in rSco(2) (63 [43-84] vs 66 [46-87]%; P < .05) and cFTOE (0.33 [0.14-0.56] vs 0.31 [0.07-0.54]1/1; P < .05). However, no differences were found at any time point between controls and infants treated with volume or additional dopamine (5, 7.5, and 10 μg/kg per minute) for rSco(2) or cFTOE.

CONCLUSIONS

Volume expansion and additional dopamine do not cause any significant change in rSco(2) or cFTOE in hypotensive preterm infants without PDA. We speculate that very preterm infants with hypotension but without signs of a compromised cerebral oxygenation and systemic perfusion might not be in need of antihypotensive therapy.

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.

Functional cardiac MRI in preterm and term newborns

OBJECTIVE

To use cardiac MRI techniques to assess ventricular function and systemic perfusion in preterm and term newborns, to compare techniques to echocardiographic methods, and to obtain initial reference data.

DESIGN

Observational magnetic resonance and echocardiographic imaging study.

SETTING

Neonatal Unit, Queen Charlotte's and Chelsea Hospital, London, UK. Patients 108 newborn infants with median birth weight 1627 (580-4140) g, gestation 32 (25-42) weeks.

RESULTS

Mean (SD) flow volumes assessed by phase contrast (PC) imaging in 28 stable infants were left ventricular output (LVO) 222 (46), right ventricular output (RVO) 219 (47), superior vena cava (SVC) 95 (27) and descending aorta (DAo) 126 (32) ml/kg/min, with flow being higher at lower gestational age. Limits of agreement for repeated PC assessment of flow were LVO ±50.2, RVO ±55.5, SVC ±20.9 and DAo ±26.2 ml/kg/min. Mean (SD) LVO in 75 stable infants from three-dimensional models were 245 (47) ml/kg/min, with limits of agreement ±58.3 ml/kg/min. Limits of agreement for repeated echocardiographic assessment of LVO were ±108.9 ml/kg/min.

CONCLUSIONS

Detailed magnetic resonance assessments of cardiac function and systemic perfusion are feasible in newborn infants, and provide more complete data with greater reproducibility than existing echocardiographic methods. Functional cardiac MRI could prove to be a useful research technique to study small numbers of newborn infants in specialist centres; providing insights into the pathophysiology of circulatory failure; acting as an outcome measure in clinical trials of inotropic intervention and so guiding clinical practice in the wider neonatal community.

Neonatologist-performed functional echocardiography in the neonatal intensive care unit

The use of point-of-care functional ultrasound to assess cardiovascular function is gaining interest in the neonatal intensive care unit (NICU). The modality has been in use in adult intensive care units for some time and has often guided management. Clinical signs such as heart rate, blood pressure, and capillary refill time, which physicians traditionally have relied upon, provide limited insight into the adequacy of systemic blood flow and organ perfusion. Enhanced cardiovascular imaging and hemodynamic evaluation offers novel insights regarding the contribution of the ductus arteriosus, myocardial performance and pulmonary hemodynamics to ongoing clinical instability. In addition, it allows more accurate delineation of the nature of the underlying disease process and facilitates the evaluation of response to therapeutic intervention. This review examines the potential clinical role of ultrasound methods in the NICU; specifically, its applications in different disease states, and how the technology may be introduced safely in the NICU.

Functional echocardiography in assessment of the cardiovascular system in asphyxiated neonates

Perinatal asphyxia commonly results in multi-organ damage, and cardiovascular dysfunction is a frequent association. Myocardial damage, right ventricular dysfunction, abnormal circulatory transition, and impaired autoregulation may all contribute to postnatal neurological damage. Adequate monitoring and appropriate targeted treatment therefore are essential after an asphyxial insult. Standard methods of cardiovascular monitoring in the neonate have limitations. Point of care ultrasound scanning or functional echocardiography offers extra information to assist the clinician in identifying when there is significant cardiovascular impairment, classifying the underlying abnormal physiology and potentially targeting appropriate therapy, thereby optimizing the post-insult cerebral blood flow and oxygen delivery.

Validation of a preterm infant cardiovascular system model under baroreflex control with heart rate and blood pressure data

In this paper we present an autonomic cardiovascular model of a preterm infant of 28 weeks of gestation with a birth weight of 1000 g and a closed ductus arteriosus by the end of the first week, that is capable of describing the complex interactions between heart rate, blood pressure and respiration. The hemodynamic model consists of a pulsatile heart and several vascular compartments, and is regulated by a baroreflex control system. The model is relatively simple to allow for a mathematical analysis of the dynamics but sufficiently complex to provide a realistic representation of the underlying physiology. The model provides (beat-to-beat) values of R-R interval and blood pressure that resemble realistic signals of preterm infants. The model is validated with experimental data obtained in preterm infants.

Changes in cerebral perfusion in extremely LBW infants during the first 72 h after birth

Cerebral perfusion and its relation with systemic circulation in extremely LBW (ELBW) infants in the early neonatal period are not well understood. The cerebral tissue oxygenation index (TOI) and cerebral fractional tissue oxygen extraction (FTOE) were monitored in stable 16 ELBW infants (GA <29 wk) using near-infrared spectroscopy (NIRS) at 3-6, 12, 18, 24, 36, 48, and 72 h after birth. The left ventricular end-systolic wall stress (ESWS), left ventricular ejection fraction (LVEF), left ventricular cardiac output (LVCO), and superior vena cava (SVC) flow were also measured simultaneously using echocardiography. The ESWS increased till 18 h and then decreased; LVEF, LVCO, and SVC flow decreased till 12 h and increased thereafter. The TOI decreased till 12 h and correlated with SVC flow; FTOE increased until 12 h and then decreased. These changes in variables of NIRS and echocardiographic measurements contrasted to changes in mean arterial blood pressure (MABP), which showed trends of continuous and gradual increase after birth. We conclude that even stable ELBW infants undergo evident transitional changes in cerebral oxygenation and perfusion in the early postnatal period, which may reflect changes in cardiac function and cardiac output.

Pathophysiology and treatment of septic shock in neonates

Neonatal septic shock is a devastating condition associated with high morbidity and mortality. Definitions for the sepsis continuum and treatment algorithms specific for premature neonates are needed to improve studies of septic shock and assess benefit from clinical interventions. Unique features of the immature immune system and pathophysiologic responses to sepsis, particularly those of extremely preterm infants, necessitate that clinical trials consider them as a separate group. Keen clinical suspicion and knowledge of risk factors will help to identify those neonates at greatest risk for development of septic shock. Genomic and proteomic approaches, particularly those that use very small sample volumes, will increase our understanding of the pathophysiology and direct the development of novel agents for prevention and treatment of severe sepsis and shock in the neonate. Although at present antimicrobial therapy and supportive care remain the foundation of treatment, in the future immunomodulatory agents are likely to improve outcomes for this vulnerable population.

Peripheral haemodynamics in newborns: best practice guidelines

Peripheral haemodynamics refers to blood flow, which determines oxygen and nutrient delivery to the tissues. Peripheral blood flow is affected by vascular resistance and blood pressure, which in turn varies with cardiac function. Arterial oxygen content depends on the blood haemoglobin concentration (Hb) and arterial pO2; tissue oxygen delivery depends on the position of the oxygen-dissociation curve, which is determined by temperature and the amount of adult or fetal haemoglobin. Methods available to study tissue perfusion include near-infrared spectroscopy, Doppler flowmetry, orthogonal polarisation spectral imaging and the peripheral perfusion index. Cardiac function, blood gases, Hb, and peripheral temperature all affect blood flow and oxygen extraction. Blood pressure appears to be less important. Other factors likely to play a role are the administration of vasoactive medications and ventilation strategies, which affect blood gases and cardiac output by changing the intrathoracic pressure.

Clinical monitoring of systemic hemodynamics in critically ill newborns

Circulatory failure is a major cause of mortality and morbidity in critically ill newborn infants. Since objective measurement of systemic blood flow remains very challenging, neonatal hemodynamics is usually assessed by the interpretation of various clinical and biochemical parameters. An overview is given about the predictive value of the most used indicators of circulatory failure, which are blood pressure, heart rate, urine output, capillary refill time, serum lactate concentration, central-peripheral temperature difference, pH, standard base excess, central venous oxygen saturation and colour.

Noninvasive cerebral perfusion imaging in high-risk neonates

Advances in medical and surgical care of the high-risk neonate have led to increased survival. A significant number of these neonates suffer from neurodevelopmental delays and failure in school. The focus of clinical research has shifted to understanding events contributing to neurological morbidity in these patients. Assessing changes in cerebral oxygenation and regulation of cerebral blood flow (CBF) is important in evaluating the status of the central nervous system. Traditional CBF imaging methods fail for both ethical and logistical reasons. Optical near infrared spectroscopy (NIRS) is increasingly being used for bedside monitoring of cerebral oxygenation and blood volume in both very low birth weight infants and neonates with congenital heart disease. Although trends in CBF may be inferred from changes in cerebral oxygenation and/or blood volume, NIRS does not allow a direct measure of CBF in these populations. Two relatively new modalities, arterial spin-labeled perfusion magnetic resonance imaging and optical diffuse correlation spectroscopy, provide direct, noninvasive measures of cerebral perfusion suitable for the high-risk neonates. Herein we discuss the instrumentation, applications, and limitations of these noninvasive imaging techniques for measuring and/or monitoring CBF.

The effect of adenoidectomy on right ventricular performance in children

OBJECTIVE

Several studies have shown a reduction in pulmonary artery pressure (PAP) after adenoidectomy in children suffering form upper airway obstruction caused by adenoid hypertrophy (AH). However, it is not clear whether this would be significantly reflected on right ventricle output (RVO).

METHODS

Our aim was to determine if there were any detectable changes in RV performance parameters after adenoidectomy in children with AH. Thirty children with AH (female/male: 11/19) aged between 2.5 and 12 years (median: five years) were included in this study. Adenoidectomy was performed under sinuscopic guide using adenoid curette and microdebrider. All children were examined by echocardiography one day before and one month after adenoidectomy. Velocity time integral of tricuspid valve flow (VTItv) and pulmonary valve flow (VTIpa); E/A ratio of tricuspid valve flow; RV end-diastolic diameter (RVEDd) and left ventricle fraction shortening (FS) were measured. Heart rate (HR) was also recorded.

RESULTS

Preoperatively VTItv, VTIpa, E/A ratio, RVEDd, FS, and HR were 18.6+/-3.0 cm, 20.8+/-3.1 cm, 1.21+/-0.31, 11.5+/-2.1 mm, 35.1+/-4.3%, and 112+/-19, respectively. Postoperatively VTItv, VTIpa, E/A ratio, RVEDd, FS, and HR were 21.5+/-2.5 cm, 24.4+/-4.3 cm, 1.44+/-0.32, 9.3+/-2.6 mm, 33.9+/-3.5%, and 104+/-28, respectively. There were significant differences between preoperative and postoperative VTItv (p=0.03), VTIpa (p=0.01), E/A ratios (p=0.04), and RVEDd (p=0.01). FS and HR were not significantly different.

CONCLUSIONS

This study illustrated that in children suffering from AH, relieving upper airway obstruction by adenoidectomy may result in improvement of RV filling and RVO, associated with the reduction in PAP.

The role of systemic hemodynamic disturbances in prematurity-related brain injury

Premature infants who experience cerebrovascular injury frequently have acute and long-term neurologic complications. In this article, we explore the relationship between systemic hemodynamic insults and brain injury in this patient population and the mechanisms that might be at play.

Carbon monoxide is a significant mediator of cardiovascular status following preterm birth

OBJECTIVE

With male gender as a strong predictor of cardiovascular instability, we hypothesized that gender-specific differences in circulating carbon monoxide levels contributed to dysregulated microvascular function in preterm male infants.

METHODS

Infants born at 24 to 34 weeks of gestation (N = 84) were studied in a regional tertiary neonatal unit. Carboxyhemoglobin levels were measured through spectrophotometry in umbilical arterial blood and at 24, 72, and 120 hours after birth. Microvascular blood flow was determined through laser Doppler flowmetry.

RESULTS

Carboxyhemoglobin levels demonstrated a strong inverse relationship with gestational age (r = -0.636; P < .001) and were higher in boys (P = .032). Repeated-measures analysis of variance showed a significant decrease in arterial carboxyhemoglobin levels over time (P < .001), with significant between-subjects effects for gestational age (P = .011) and gender (P = .025). Positive correlations with microvascular blood flow at 24 hours of age (r = 0.495; P < .001) and 120 hours of age (r = 0.548; P < .001) were observed. With controlling for gestational age, carboxyhemoglobin levels at 72 hours were greater for infants who died in the first week of life (P = .035).

CONCLUSIONS

The gestational age- and gender-specific differences in carboxyhemoglobin levels and the relationship with dysregulated microvascular blood flow, a state related to greater illness severity and hypotension, are novel findings not confined solely to sick preterm infants. Both inducible heme oxygenase-dependent and non-heme oxygenase-dependent pathways may initially play a central role in carbon monoxide production, inducing pathophysiologic processes in a gender-specific manner.

Elevated cerebral pressure passivity is associated with prematurity-related intracranial hemorrhage

OBJECTIVES

Cerebral pressure passivity is common in sick premature infants and may predispose to germinal matrix/intraventricular hemorrhage (GM/IVH), a lesion with potentially serious consequences. We studied the association between the magnitude of cerebral pressure passivity and GM/IVH.

PATIENTS AND METHODS

We enrolled infants <32 weeks' gestational age with indwelling mean arterial pressure (MAP) monitoring and excluded infants with known congenital syndromes or antenatal brain injury. We recorded continuous MAP and cerebral near-infrared spectroscopy hemoglobin difference (HbD) signals at 2 Hz for up to 12 hours/day and up to 5 days. Coherence and transfer function analysis between MAP and HbD signals was performed in 3 frequency bands (0.05-0.25, 0.25-0.5, and 0.5-1.0 Hz). Using MAP-HbD gain and clinical variables (including chorioamnionitis, Apgar scores, gestational age, birth weight, neonatal sepsis, and Score for Neonatal Acute Physiology II), we built a logistic regression model that best predicts cranial ultrasound abnormalities.

RESULTS

In 88 infants (median gestational age: 26 weeks [range 23-30 weeks]), early cranial ultrasound showed GM/IVH in 31 (37%) and parenchymal echodensities in 10 (12%) infants; late cranial ultrasound showed parenchymal abnormalities in 19 (30%) infants. Low-frequency MAP-HbD gain (highest quartile mean) was significantly associated with early GM/IVH but not other ultrasound findings. The most parsimonious model associated with early GM/IVH included only gestational age and MAP-HbD gain.

CONCLUSIONS

This novel cerebrovascular monitoring technique allows quantification of cerebral pressure passivity as MAP-HbD gain in premature infants. High MAP-HbD gain is significantly associated with GM/IVH. Precise temporal and causal relationship between MAP-HbD gain and GM/IVH awaits further study.

Cerebral blood flow velocities in extremely low birth weight infants with hypotension and infants with normal blood pressure

OBJECTIVE

To determine whether extremely low birth weight (ELBW) infants with hypotension have similar cerebral hemodynamics when compared with control subjects with normal blood pressure. We hypothesized that ELBW infants with low or normal blood pressure have similar cerebral blood flow (CBF) velocity.

STUDY DESIGN

In this case control study, CBF velocity (with Doppler ultrasound scanning), PCO2, and mean arterial blood pressure (MABP) were continuously monitored twice daily before intensive care procedures. If an infant became hypotensive (MABP < or = gestational age in weeks), additional monitoring was performed for 10 to 20 minutes, before treatment with dopamine. Thirty ELBW infants were enrolled (637 +/- 140 g, 24.2 +/- 1.1 weeks); 15 had hypotension, and 15 were gestational age/birth weight-matched control subjects with normal blood pressure. CBF velocity was compared by use of the Mann-Whitney U test.

RESULTS

The groups did not differ significantly in gestational age, birth weight, race, sex, PCO2, Apgar scores, or occurrence of severe intraventricular hemorrhage. There was no difference in mean CBF velocity (P = .934) in infants with hypotension (MABP: 23 [20-24.9] mm Hg) compared with infants with normal blood pressure (MABP: 32.6 [27.5-35.7] mm Hg).

CONCLUSION

Despite having hypotension, ELBW infants (before treatment) had similar CBF velocity compared with control subjects with normal blood pressure. On the basis of these results, hypotension may not indicate decreased CBF.

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.

Cardiovascular and pulmonary consequences of airway recruitment in preterm lambs

Increases in positive end-expiratory pressure (PEEP) improve arterial oxygenation in preterm infants, but the effects on cardiopulmonary hemodynamics are understood poorly. We aimed to determine the effect of increased PEEP on cardiopulmonary hemodynamics and to compare measurements from indwelling flow probes with Doppler echocardiography. Preterm lambs (129 ± 1 days) were ventilated initially with a tidal volume of 7 ml/kg and 4 cmH2O of PEEP. In ramp lambs ( n = 7), PEEP was increased by 2-cmH2O increments to 10 cmH2O and then in decrements back to 4 cmH2O. PEEP was unchanged in controls ( n = 6). Doppler echocardiographic flow measurements in the left pulmonary artery (LPA) and ductus arteriosus (DA) were correlated with flow probe measurements. Compared with controls, high PEEP reduced LPA flow from baseline (10-cmH2O PEEP: 43 ± 8% vs. control: 83 ± 21%; P = 0.029). High PEEP increased the proportion of right-to-left (R-L) shunting through the DA, with a trend to an increased oxygenation index compared with controls (oxygenation index: 44.5 ± 13.5 at 10-cmH2O PEEP vs. 19.4 ± 4.5 in controls; P = 0.07). Increasing PEEP decreased heart rate (17 beats/min; P = 0.03) and tended to lower systolic arterial pressure (5.0 mmHg; P = 0.052) compared with controls. Doppler echocardiography measurement of LPA flows correlated strongly with indwelling flow probe ( r2 = 0.73, P < 0.001), except during highly turbulent flows. Increases in PEEP have significant cardiopulmonary consequences in preterm lambs, including reduced LPA flow and increased R-L shunt through the DA. These changes are likely due to the concomitant increase in downstream pulmonary vascular resistance and increased cardiovascular constraint induced by PEEP.