The haemodynamic effects of dopamine and volume expansion in sick preterm infants

Comparative efficacy of volume expansion, inotropes and vasopressors in preterm neonates with probable transitional circulatory instability in the first week of life: a systematic review and network meta-analysis

BACKGROUND

There exists limited agreement on the recommendations for the treatment of transitional circulatory instability (TCI) in preterm neonates OBJECTIVE: To compare the efficacy of various interventions used to treat TCI METHODS: Medline and Embase were searched from inception to 21st July 2023. Two authors extracted the data independently. A Bayesian random effects network meta-analysis was used. Recommendations were formulated using the Grading of Recommendations, Assessment, Development, and Evaluations (GRADE) framework.

INTERVENTIONS

Dopamine, dobutamine, epinephrine, hydrocortisone, vasopressin, milrinone, volume and placebo.

MAIN OUTCOME MEASURES

Mortality, major brain injury (MBI) (intraventricular haemorrhage > grade 2 or cystic periventricular leukomalacia), necrotising enterocolitis (NEC) ≥stage 2 and treatment response (as defined by the author).

RESULTS

15 Randomized Controlled Trials (RCTs) were included from the 1365 titles and abstracts screened. Clinical benefit or harm could not be ruled out for the critical outcome of mortality. For the outcome of MBI, epinephrine possibly decreased the risk when compared to dobutamine and milrinone (very low certainty). Epinephrine was possibly associated with a lesser risk of NEC when compared with dopamine, dobutamine, hydrocortisone and milrinone (very low certainty). Dopamine was possibly associated with a lesser risk of NEC when compared with dobutamine (very low certainty). Vasopressin possibly decreased the risk of NEC compared with dopamine, dobutamine, hydrocortisone and milrinone (very low certainty). Clinical benefit or harm could not be ruled out for the outcome response to treatment.

CONCLUSIONS

Epinephrine may be used as the first-line drug in preterm neonates with TCI, the evidence certainty being very low. We suggest future trials evaluating the management of TCI with an emphasis on objective criteria to define it.

What Inotrope and Why?

Primary function of cardiovascular system is to meet body's metabolic demands. The aim of inotrope therapy is to minimise adverse impact of cardiovascular compromise. Current use of inotropes is primarily guided by the pathophysiology of cardiovascular compromise and anticipated actions of inotropes. Lack of significant reduction in morbidity and mortality associated with cardiovascular compromise despite inotrope use, highlights major gaps in our understanding of circulatory targets, thresholds and choices of inotrope therapy. Thus far, prevention of cardiovascular compromise remains the most effective strategy to optimize outcomes. Studies of alternative design are needed for further advancement in cardiovascular therapy in neonates.

Fluid Therapy: Friend or Foe?

Many questions surround fluid bolus therapy and subsequent fluid management in neonatal critical care as they do in pediatric and adult critical care. This review explores the known key clinical aspects of fluid bolus therapy and fluid balance in the first 7 days of life and provides suggestions for further work in this area. It draws on the pediatric and adult critical care literature to provide thought-provoking data around the potential harms of excessive intravenous fluids, which may prove relevant to neonatology. Current data suggest that fluid bolus therapy and early-life positive fluid balance in neonates may be associated with harm.

Clinical Trials in Hemodynamic Support: Past, Present, and Future

Managing low blood flow states in the preterm population remains a challenge in neonatal clinical care. The heterogeneity of the trials to date and the relatively low number of infants enrolled, in addition to a desire to oversimplify the underlying pathophysiology, have contributed to an inability to draw meaningful conclusions to direct clinical care. This article reviews the current literature on this topic in the preterm population and outlines the challenges that have been encountered in performing such trials. Alternative studies are proposed, based on the lessons learned over the past number of years.

Intervention and Outcome for Neonatal Hypotension

Many observational studies have shown that infants with blood pressures (BPs) that are in the lower range for their gestational age tend to have increased complications such as an increased rate of significant intraventricular hemorrhage and adverse long-term outcome. This relationship does not prove causation nor should it create an indication for treatment. However, many continue to intervene with medication for low BP on the assumption that an increase in BP will result in improved outcome. Only adequately powered prospective randomized controlled trials can answer the question of whether individual treatments of low BP are beneficial.

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.

International, multicentre, observational study of fluid bolus therapy in neonates

AIM

To assess the prevalence, types and indications for fluid bolus therapy in neonates with haemodynamic compromise.

METHODS

This was a pragmatic, international, multicentre observational study in neonatal units across Australasia, Europe and North America with a predefined study period of 10-15 study days per participating neonatal unit between December 2015 and March 2017. Infants ≤28 days of age who received a fluid bolus for the management of haemodynamic compromise (≥10 mL/kg given at ≤6 h) were included.

RESULTS

A total of 163 neonates received a bolus over 8479 eligible patient days in 41 neonatal units. Prevalence of fluid bolus therapy varied between centres from 0 to 28.6% of admitted neonates per day, with a pooled prevalence rate of 1.5% (95% confidence interval 1.1-1.9%). The most common fluid used was 0.9% sodium chloride (129/163; 79%), and the volume of fluid administered was most commonly 10 mL/kg (115/163; 71%) over a median of 30 min (interquartile range 20-60). The most frequent indications were hypotension (n = 56; 34%), poor perfusion (n = 20; 12%) and metabolic acidosis (n = 20; 12%). Minimal or no clinical improvement was reported by clinicians in 66 of 163 cases (40%).

CONCLUSIONS

Wide international variations in types, indications and effects of fluid bolus administration in haemodynamically compromised neonates suggest uncertainty in the risk-benefit profile. This is likely to reflect the lack of robust evidence to support the efficacy of different fluid types, doses and appropriate indications. Together, these highlight a need for further clinically relevant studies.

Inotropes for Preterm Infants: 50 Years on Are We Any Wiser?

For almost half a century, inotropes have been administered to preterm infants with the ultimate goal of increasing their blood pressure. A number of trials, the majority of which focused on dopamine administration, have demonstrated increased blood pressure following inotrope administration in preterm infants and have led to continued use of inotropes in our neonatal units. We have also seen an increase in the number of potential agents available to the clinician. However, we now know that hypotension is a much broader concept than blood pressure alone, and our aim should instead be focused on improving end organ perfusion, specifically cerebral perfusion. Only a limited number of studies have incorporated the organ-relevant hemodynamic changes and long-term outcomes when assessing inotropic effects in neonates, the majority of which are observational studies or have a small sample size. In addition, important considerations, including the developing/maturing adrenergic receptors, polymorphisms of these receptors, and other differences in the pharmacokinetics and pharmacodynamics of preterm infants, are only recently being recognized. Certainly, there remains huge variation in practice. The lack of well-conducted randomized controlled trials addressing these relevant outcomes, along with the difficulty executing such RCTs, leaves us with more questions than answers. This review provides an overview of the various inotropic agents currently being used in the care of preterm infants, with a particular focus on their organ/cerebral hemodynamic effects both during and after transition.

Uses and misuses of albumin during resuscitation and in the neonatal intensive care unit

Albumin is one of the most abundant proteins in plasma and serves many vital functions. Neonatal concentrations vary greatly with gestational and postnatal age. In critically ill neonates, hypoalbuminemia occurs due to decreased synthesis, increased losses or redistribution of albumin into the extravascular space, and has been associated with increased morbidities and mortality. For that reason, infusion of exogenous albumin as a volume expander has been proposed for various clinical settings including hypotension, delivery room resuscitation, sepsis and postoperative fluid management. Albumin is often prescribed in infants with hypoalbuminemia, hyperbilirubinemia, and protein-losing conditions. However, the evidence of these practices has not been reviewed or validated. Albumin infusion may initiate highly complex processes that vary according to the individual and disease pathophysiology. Indeed, it may be associated with harms when misused. In this review, we critically appraise the scientific evidence for administering albumin in most conditions encountered in the neonatal intensive care unit, while emphasizing the benefits and risks associated with their use.

Propofol Dose-Finding to Reach Optimal Effect for (Semi-)Elective Intubation in Neonates

OBJECTIVE

To define the effective dose for 50% of patients (ED₅₀) of propofol for successful intubation and to determine the rate of successful extubation in those patients with planned intubation, surfactant administration, and immediate extubation (INSURE procedure). In addition, pharmacodynamic effects were assessed.

STUDY DESIGN

Neonates (n = 50) treated with propofol for (semi-)elective endotracheal intubation were stratified in 8 strata by postmenstrual and postnatal age. The first patient in each stratum received an intravenous bolus of 1 mg/kg propofol. Dosing for the next patient was determined using the up-and-down method. A propofol ED₅₀ dose was calculated in each stratum with an effective sample size of at least 6, via the Dixon-Masey method, with simultaneous assessment of clinical scores and continuous vital sign monitoring.

RESULTS

Propofol ED₅₀ values for preterm neonates <10 days of age varied between 0.713 and 1.350 mg/kg. Clinical recovery was not attained at the end of the 21-minute scoring period. Mean arterial blood pressure showed a median decrease between 28.5% and 39.1% from baseline with a brief decrease in peripheral and regional cerebral oxygen saturation. Variability in mean arterial blood pressure area under the curve could not be explained by weight or age.

CONCLUSIONS

Low propofol doses were sufficient to sedate neonates for intubation. Clinical recovery was accompanied by permissive hypotension (no clinical shock and no treatment). The propofol ED₅₀ doses can be administered at induction, with subsequent up-titration if needed, while monitoring blood pressure. They can be used for further dosing optimalization and validation studies.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01621373; EudraCT: 2012-002648-26.

Blood pressure and aEEG in the 96h after birth and correlations with neurodevelopmental outcome in extremely preterm infants

BACKGROUND

The management of hypotension immediately after the birth of preterm infants is controversial.

AIM

To investigate the relationship between blood pressure (BP), amplitude-integrated electroencephalography (aEEG), and neurodevelopmental outcome in extremely preterm infants.

METHODS

BP and aEEG were monitored for 96h after birth in 36 infants born at <27weeks gestation. aEEG data were analyzed with Burdjalov scores. Correlations of aEEG findings with BP and several clinical characteristics, including the Score for Neonatal Acute Physiology, Perinatal Extension-II (SNAPPE-II) were explored. A subgroup analysis of BP, aEEG activity, and neurodevelopmental outcome at 18-22months corrected age was also performed. Poor outcome was defined as death or a developmental quotient <70.

RESULTS

Multiple regression analyses revealed no association between BP during the first 48h after birth and aEEG activity. However, BP 48-96h after birth was significantly associated with simultaneous aEEG activity (p<0.001). Within 48h after birth, SNAPPE-II was significantly associated with aEEG activity. Outcome was assessed in 32 infants; 24 and 8 of whom had good and poor outcomes, respectively. aEEG activity was significantly lower in neonates with a poor outcome than those with a good outcome (<0.001). No significant differences in outcome were observed for BP.

CONCLUSION

The activity of aEEG was associated with illness severity during the first 48h after birth. After 48h, there was no effect of illness severity but there was an association with BP. We do not know if hypotension results in a poor outcome. However, aEEG activity was associated with neurodevelopmental outcome.

Response to dopamine in prematurity: a biomarker for brain injury?

OBJECTIVE

To identify factors associated with responsiveness to dopamine therapy for hypotension and the relationship to brain injury in a cohort of preterm infants.

STUDY DESIGN

The pharmacy database at St Louis Children's Hospital was retrospectively queried to identify infants who (a) were born <28 weeks gestation between 2012 and 2014, (b) received dopamine and (c) had blood pressure measurements from an umbilical arterial catheter. A control group was constructed from contemporaneous infants who did not receive dopamine. Mean arterial blood pressure (MABP) at baseline, 1 h and 3 h after initiating dopamine were obtained for each dopamine-exposed infant. MABP measurements at matched time points were obtained in the control group.

RESULT

Sixty-nine dopamine-treated and 45 control infants were included. Mean ΔMABP at 3 h was 4.5±6.3 mm of Hg for treated infants vs 1±2.9 for the control. Median dopamine starting dose was 2.5 μg kg(-1) min(-1). Dopamine-treated infants were less mature and of lower birth weight while also more likely to be intubated at 72 h, diagnosed with intraventricular hemorrhage (IVH) and to die. Failure to respond to dopamine was associated with greater likelihood of developing IVH (odds ratio (OR) 5.8, 95% confidence interval (CI) 1.1-42.3), while a strong response (ΔMABP>10 mm Hg) was associated with a reduction in risk of IVH (OR 0.1, 95% CI 0.01-0.8).

CONCLUSION

Low-moderate dose dopamine administration results in modest blood pressure improvements. A lack of response to dopamine is associated with a greater risk of IVH, whereas a strong response is associated with a decreased risk. Further research into underlying mechanisms and management strategies is needed.

Early blood pressure, antihypotensive therapy and outcomes at 18-22 months' corrected age in extremely preterm infants

OBJECTIVE

To investigate the relationships between early blood pressure (BP) changes, receipt of antihypotensive therapy and 18-22 months' corrected age (CA) outcomes for extremely preterm infants.

DESIGN

Prospective observational study of infants 23(0/7)-26(6/7) weeks' gestational age (GA). Hourly BP values and antihypotensive therapy exposure in the first 24 h were recorded. Four groups were defined: infants who did or did not receive antihypotensive therapy in whom BP did or did not rise at the expected rate (defined as an increase in the mean arterial BP of ≥5 mm Hg/day). Random-intercept logistic modelling controlling for centre clustering, GA and illness severity was used to investigate the relationship between BP, antihypotensive therapies and infant outcomes.

SETTING

Sixteen academic centres of the Eunice Kennedy Shriver National Institute of Child Health and Human Development Neonatal Research Network.

MAIN OUTCOME MEASURES

Death or neurodevelopmental impairment/developmental delay (NIDD) at 18-22 months' CA.

RESULTS

Of 367 infants, 203 (55%) received an antihypotensive therapy, 272 (74%) survived to discharge and 331 (90%) had a known outcome at 18-22 months' CA. With logistic regression, there was an increased risk of death/NIDD with antihypotensive therapy versus no treatment (OR 1.836, 95% CI 1.092 to 3.086), but not NIDD alone (OR 1.53, 95% CI 0.708 to 3.307).

CONCLUSIONS

Independent of early BP changes, antihypotensive therapy exposure was associated with an increased risk of death/NIDD at 18-22 months' CA when controlling for risk factors known to affect survival and neurodevelopment.

CLINICAL TRIAL REGISTRATION NUMBER

clinicaltrials.gov #NCT00874393.

Assessing cerebrovascular autoregulation in infants with necrotizing enterocolitis using near-infrared spectroscopy

BACKGROUND

We assessed cerebrovascular autoregulation (CAR) in preterm infants with definite necrotizing enterocolitis (NEC), Bell's stage 2 or 3, and infants without NEC, using near-infrared spectroscopy. We hypothesized that CAR would be more often impaired in infants with NEC compared with infants without NEC.

METHODS

We measured cerebral regional tissue oxygen saturation, arterial oxygen saturation, and mean arterial blood pressure (MABP) during 48 h. We calculated the correlation between cerebral fractional tissue oxygen extraction and MABP for each patient. A statistically significant negative correlation reflected impaired CAR.

RESULTS

We included 15 infants with definite NEC (median (range) gestational age 27.4 (25.6-34.7) wk; birth weight 1,070 (670-2,400) g) and 13 infants without NEC (gestational age 27.9 (26.3-34.7) wk; birth weight 980 (640-2,640) g). Fourteen infants had a statistically significant negative correlation (ρ -0.468 to-0.104), of whom five were infants without NEC (5/13; 38%) and nine with definite NEC (9/15; 60%). The difference in prevalence of impaired CAR was not statistically significant.

CONCLUSION

Impaired CAR is present in a substantial proportion of infants with definite NEC, which may predispose them to NEC-associated neurological damage.

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.

Dopamine therapy is associated with impaired cerebral autoregulation in preterm infants

AIM

Hypotension is a common problem in newborn infants and is associated with increased mortality and morbidity. Dopamine is the most commonly used antihypotensive drug therapy, but has never been shown to improve neurological outcomes. This study tested our hypothesis that dopamine affects cerebral autoregulation (CA).

METHODS

Near-infrared spectroscopy was used to measure the cerebral oxygenation index in 60 very preterm infants, and mean arterial blood pressure was monitored towards the end of their first day of life. Measurements were performed continuously for two to three hour periods. CA was quantified as the cerebral oximetry index (COx).

RESULTS

We treated 13 of the 60 infants (22%) with dopamine during the measurements. COx was higher in the dopamine group than the untreated group (0.41 ± 0.25 vs. 0.08 ± 0.25, p < 0.001). Blood pressure tended to be lower in the dopamine group, but the anticipated difference in cerebral oxygenation was not detected. The need for mechanical ventilation in the first day of life and incidences of mortality was higher in the dopamine group.

CONCLUSION

Dopamine therapy was associated with decreased CA in preterm infants. We were unable to determine whether dopamine directly impaired CA or was merely an indicator of illness.

Diagnosis and management of hypotension in neonates

The diagnosis and management of hypotension in neonates is a frequently encountered issue in the intensive care setting. There is an ongoing debate as to the appropriateness of blood pressure monitoring as an indicator of organ perfusion and tissue hypoxia. These ultimately determine morbidity and mortality in the sick newborn. This article explores the methods available for the assessment of organ perfusion and speculates on other means that may become available in the future. Different modalities of treatment currently in use are discussed, with the aim of using information gained from perfusion monitoring techniques to determine the optimal choice of therapy.

Evolving blood pressure dynamics for extremely preterm infants

OBJECTIVE

To examine changes in arterial blood pressure (ABP) after birth in extremely preterm infants.

STUDY DESIGN

Prospective observational study of infants 23(0/7) to 26(6/7) weeks gestational age (GA). Antihypotensive therapy use and ABP measurements were recorded for the first 24 h.

RESULT

A cohort of 367 infants had 18 709 ABP measurements recorded. ABP decreased for the first 3 h, reached a nadir at 4 to 5 h and then increased at an average rate of 0.2 mm Hg h(-1). The rise in ABP from hour 4 to 24 was similar for untreated infants (n=164) and infants given any antihypotensive therapy (n=203), a fluid bolus (n=135) or dopamine (n=92). GA-specific trends were similar. ABP tended to be lower as GA decreased, but varied widely at each GA.

CONCLUSION

ABP increased spontaneously over the first 24 postnatal hours for extremely preterm infants. The rate of rise in ABP did not change with antihypotensive therapy.

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.

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.

Relationship between systemic blood flow, blood pressure, inotropes, and aEEG in the first 48 h of life in extremely preterm infants

BACKGROUND

Significant hemodynamic changes occur immediately after birth in preterm infants. Amplitude-integrated electroencephalography (aEEG) provides a method of assessing brain activity in sick neonates; however, the relationship among systemic blood flow, blood pressure (BP), and aEEG is not clear.

METHODS

Quantitative measures of aEEG continuity and amplitude were correlated with superior vena cava (SVC) flow, right-ventricular output (RVO), and BP at 12, 24, and 48 h in 92 infants born at <29 wk gestation.

RESULTS

SVC flow, RVO, BP, aEEG amplitude, and EEG continuity all increased from 12 to 48 h. SVC flow at 12 h, but not 24 or 48 h, was significantly associated with aEEG amplitude after adjustment for gestational age (GA) and severity of illness markers (r(2) = 0.21, P = 0.004). RVO and BP showed less consistent associations with aEEG parameters. Infants receiving inotropes at 12 h, including those in whom cardiovascular parameters had normalized, had significantly lower aEEG amplitude (P < 0.01) and EEG continuity at the 10, 25, and 50 μV levels (P < 0.01) at 12, 24, and 48 h than neonates who were not receiving inotropes.

CONCLUSION

aEEG measurements in the first 48 h of life are related to SVC flow and treatment with inotropes at 12 h of life in extremely preterm infants.

Cerebral effects of commonly used vasopressor-inotropes: a study in newborn piglets

Background

Despite widespread use in sick infants, it is still debated whether vasopressor-inotropes have direct cerebral effects that might affect neurological outcome. We aimed to test direct cerebrovascular effects of three commonly used vasopressor-inotropes (adrenaline, dopamine and noradrenaline) by comparing the responses to those of nonpharmacologically induced increases in blood pressure. We also searched for reasons for a mismatch between the response in perfusion and oxygenation.

Methods

Twenty-four piglets had long and short infusions of the three vasopressor-inotropes titrated to raise mean arterial blood pressure (MAP) 10 mmHg in random order. Nonpharmacological increases in MAP were induced by inflation of a balloon in the descending aorta. We measured cerebral oxygenation (near-infrared spectroscopy), perfusion (laser-Doppler), oxygen consumption (co-oximetry of arterial and superior sagittal sinus blood), and microvascular heterogeneity (side stream dark field video microscopy).

Results

Vasopressor-inotropes increased cerebral oxygenation significantly less (p≤0.01) compared to non-pharmacological MAP increases, whereas perfusion was similar. Furthermore, cerebral total hemoglobin concentration increased significantly less during vasopressor-inotrope infusions (p = 0.001). These physiologic responses were identical between the three vasopressor-inotropes (p>0.05). Furthermore, they induced a mild, although insignificant increase in cerebral metabolism and microvascular heterogeneity (p>0.05). Removal of the scalp tissue did not influence the mismatch (p>0.05).

Conclusion

We demonstrated a moderate vasopressor-inotrope induced mismatch between cerebral perfusion and oxygenation. Scalp removal did not affect this mismatch, why vasopressor-inotropes appear to have direct cerebral actions. The statistically nonsignificant increases in cerebral metabolism and/or microvascular heterogeneity may explain the mismatch. Alternatively, it may simply reflect a vasopressor-inotrope-induced decrease in the arterial-to-venous volume ratio as detected by near-infrared spectroscopy.

Volume expansion does not alter cerebral tissue oxygen extraction in preterm infants with clinical signs of poor perfusion

BACKGROUND

Preterm infants with signs of poor perfusion are often treated with volume expansion, although evidence regarding its effect on cerebral perfusion is lacking. Moreover, the effect is questionable in preterm infants with an adequate cerebrovascular autoregulation (CAR). A useful measure to assess perfusion is cerebral fractional tissue oxygen extraction (cFTOE).

OBJECTIVES

To assess the effect of volume expansion on cFTOE in preterm infants with signs of poor perfusion.

METHODS

In this observational study, we assessed cFTOE using near-infrared spectroscopy in preterm infants with signs of poor perfusion before, during and 1 h after volume expansion treatment. Simultaneously, we measured mean arterial blood pressure (MABP). We tested the effect of volume expansion on both cFTOE and MABP, using multi-level analyses. We intended to define a subgroup that responded to volume expansion with an increase in blood pressure and a decrease in cFTOE, suggesting absent CAR.

RESULTS

In 14 preterm infants, with a median gestational age of 26.7 weeks (25.0-28.7 weeks) and a median birth weight of 836 g (615-1,290 g), we found a small increase in MABP during (1.4 ± 1.4 mm Hg, p = 0.003) and after (1.8 ± 1.7 mm Hg, p = 0.001) volume expansion, but no change in cFTOE during (-0.19 ± 0.1% p = 0.44) or after (-0.53 ± 0.1% p = 0.34) volume expansion. We were unable to define a subgroup lacking CAR.

CONCLUSIONS

Cerebral perfusion, as assessed by cFTOE, does not improve in preterm infants with signs of poor perfusion following volume expansion. In these infants, either CAR is present or volume expansion is inadequate to affect cFTOE.

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.

Challenges in understanding the impact of blood pressure management on cerebral oxygenation in the preterm brain

Systemic hypotension in preterm infants has been related to increased mortality, cerebrovascular lesions, and neurodevelopmental morbidity. Treatment of hypotension with inotropic medications aims at preservation of end organ perfusion and oxygen delivery, especially the brain. The common inotropic medications in preterm infants include dopamine, dobutamine, adrenaline, with adjunctive use of corticosteroids in cases of refractory hypotension. Whether maintenance of mean arterial blood pressure (MAP) by use of inotropic medication is neuroprotective or not remains unclear. This review explores the different inotropic agents and their effects on perfusion and oxygenation in the preterm brain, in clinical studies as well as in animal models. Dopamine and adrenalin, because of their α-adrenergic vasoconstrictor actions, have raised concerns of reduction in cerebral blood flow (CBF). Several studies in hypotensive preterm infants have shown that dopamine elevates CBF together with increased MAP, in keeping with limited cerebro-autoregulation. Adrenaline is also effective in raising cerebral perfusion together with MAP in preterm infants. Experimental studies in immature animals show no cerebro-vasoconstrictive effects of dopamine or adrenaline, but demonstrate the consistent findings of increased cerebral perfusion and oxygenation with the use of dopamine, dobutamine, and adrenaline, alongside with raised MAP. Both clinical and animal studies report the transitory effects of adrenaline in increasing plasma lactate, and blood glucose, which might render its use as a 2nd line therapy. To investigate the cerebral effects of inotropic agents in long-term outcome in hypotensive preterm infants, carefully designed prospective research possibly including preterm infants with permissive hypotension is required. Preterm animal models would be useful in investigating the relationship between the physiological effects of inotropes and histopathology outcomes in the developing brain.

Cerebral vascular effects of hypovolemia and dopamine infusions: a study in newborn piglets

AIM

Despite widespread use, effects of volume boluses and dopamine in hypotensive newborn infants remain controversial. We aimed to elucidate if hypovolemia alone impairs cerebral autoregulation (CA) and if dopamine affects cerebral vasculature.

METHODS

In 12 piglets, cerebral perfusion (laser-Doppler flux) and oxygenation [near-infrared spectroscopy (NIRS)] were examined during dopamine (20-50 μg/kg per minute) and nonpharmacologically induced blood pressure (ABP) changes. Effect on cerebral perfusion and oxygenation was quantified as frequency gain between ABP and laser-Doppler flux (gain-LDF) and NIRS [gain-oxygenation index (OI)], respectively. Gain quantifies change in perfusion or oxygenation per ABP-change. CA was estimated as gain-LDF during nonpharmacologically induced ABP changes, that is, as degree of impairment. Dopamine's cerebrovascular effect was estimated by contrasting gain during dopamine- and nonpharmacologically induced ABP changes. Measurements were conducted during both normovolemia- and haemorrhage-induced hypovolemia.

RESULTS

Hypovolemia elicited hypotension (p = 0.02) as well as increasing impairment of CA (p = 0.01). However, hypovolemia without hypotension did not affect CA significantly. Dopamine increased perfusion significantly compared to nonpharmacological challenges (mean difference: 1.5%/mmHg, 95% CI: 0.5-2.6, p = 0.007). Oxygenation was, however, similar (mean difference: 0.01 μmol/L per mmHg, 95% CI: -0.03 to 0.05, p = 0.7).

CONCLUSION

Our findings do not support that hypovolemia alone impairs CA. Furthermore, dopamine seems to increase cerebral perfusion but not oxygenation.

Feasibility study of early blood pressure management in extremely preterm infants

OBJECTIVE

To assess the feasibility of a randomized placebo controlled trial (RCT) of blood pressure (BP) management for extremely preterm infants.

STUDY DESIGN

This was a prospective pilot RCT of infants 23-0/7 to 26-6/7 weeks gestation who had protocol-defined low BP in the first 24 postnatal hours. Enrolled infants were administered a study infusion (dopamine or placebo) and a study syringe medication (hydrocortisone or placebo).

RESULTS

Of the 366 infants screened, 119 (33%) had low BP, 58 (16%) met all entry criteria, and 10 (3%) were enrolled. A total of 161 infants (44%) were ineligible because they received early indomethacin. Only 17% of eligible infants were enrolled. Problems with consent included insufficient time, parent unavailability, and physician unwillingness to enroll critically ill infants. Two infants were withdrawn from the study because of the potential risk of intestinal perforation with simultaneous administration of hydrocortisone and indomethacin.

CONCLUSIONS

This pilot RCT was not feasible because of low eligibility and consent rates. An RCT of BP management for extremely preterm infants may require a waiver of consent for research in emergency care. The frequent use of early indomethacin and the associated risk of intestinal perforation when used with hydrocortisone may limit future investigations to only inotropic medications.

Effect of dopamine on peripheral perfusion in very-low-birth-weight infants during the transitional period

INTRODUCTION

Dopamine is one of the most frequently used inotropic drugs in neonatal intensive care units (NICUs); however, it does not seem to improve outcomes in premature infants. Given that the ultimate aim of cardiovascular management is to stabilize and maintain organ perfusion, an understanding of dopamine's effects on organ blood flow will help in judging when to use dopamine and how to titrate the dosage. Such an approach can lead to improved outcomes. This study aimed to evaluate the effects of dopamine on peripheral perfusion in very-low-birth-weight (VLBW) infants within 72 h of birth.

METHODS

This prospective observational study identified and sampled 44 instances of initiation of dopamine treatment or increase in dopamine dose in 29 VLBW infants. Blood pressure, heart rate, and skin and subcutaneous blood flow were measured and compared before and after each instance.

RESULTS

Blood pressure and skin and subcutaneous blood flow in the lower limbs increased after initiation of dopamine treatment or after dose increase.

DISCUSSION

Dopamine increases blood pressure as well as skin and subcutaneous blood flow in VLBW infants despite its supposed vasoconstrictive action, indicating that it increases both perfusion pressure and blood flow and is devoid of overwhelming peripheral vasoconstrictive effects.

Neonatal blood pressure support: the use of inotropes, lusitropes, and other vasopressor agents

A solid understanding of the mechanisms of action of cardiovascular medications used in clinical practice along with efforts to develop comprehensive hemodynamic monitoring systems to improve the ability to accurately identify the underlying pathophysiology of cardiovascular compromise are essential in the management of neonates with shock. This article reviews the mechanisms of action of the most frequently used cardiovascular medications in neonates. Because of paucity of data from controlled clinical trials, evidence-based recommendations for the clinical use of these medications could not be made. Careful titration of the given medication with close monitoring of the cardiovascular response might improve the effectiveness and decrease the risks associated with administration of these medications.

The methodology of Doppler-derived central blood flow measurements in newborn infants

Central blood flow (CBF) measurements are measurements in and around the heart. It incorporates cardiac output, but also measurements of cardiac input and assessment of intra- and extracardiac shunts. CBF can be measured in the central circulation as right or left ventricular output (RVO or LVO) and/or as cardiac input measured at the superior vena cava (SVC flow). Assessment of shunts incorporates evaluation of the ductus arteriosus and the foramen ovale. This paper describes the methodology of CBF measurements in newborn infants. It provides a brief overview of the evolution of Doppler ultrasound blood flow measurements, basic principles of Doppler ultrasound, and an overview of all used methodology in the literature. A general guide for interpretation and normal values with suggested cutoffs of CBFs are provided for clinical use.

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.

A meta-analysis of dopamine use in hypotensive preterm infants: blood pressure and cerebral hemodynamics

OBJECTIVE

Dopamine administration results in variable effects on blood pressure in hypotensive preterm infants. The clinical benefits of dopamine administration in increasing cerebral blood flow (CBF) and reducing adverse neurological outcomes in hypotensive preterm neonates are unclear. The objective of this study was to examine the efficacy of dopamine for treatment of hypotension and investigate the changes in cerebral hemodynamics and central nervous system injury in hypotensive preterm infants following dopamine administration.

STUDY DESIGN

Standard meta-analytic techniques, including random and fixed effects models, were used to calculate combined effect size correlations and significance levels.

RESULT

Random effects meta-analysis found that dopamine increases mean arterial blood pressure (12 studies; N=163; r=0.88, 95% confidence interval (CI)=0.76 to 0.94) and systolic blood pressure (8 studies; N=142; r=0.81, 95% CI=0.42 to 0.94). For the increase in blood pressure, dopamine administration was associated with a significantly greater overall efficacy than dobutamine (seven studies; N=251; r=0.26; 95% CI=0.20 to 0.32), colloid (two studies; N=67; r=0.60; 95% CI=0.41 to 0.74) and hydrocortisone (one study; N=28; r=0.40; 95% CI=0.034 to 0.67). CBF increased following dopamine administration (five studies; N=75; r=0.36; 95% CI=-0.059 to 0.67) and the increase in CBF was greater in hypotensive than normotensive preterm infants (eight studies; N=153; r=0.16; 95% CI=-0.0080 to 0.32). There were no statistically significant differences in adverse neurological outcome between dopamine and dobutamine (three studies; N=118; r=-0.13; 95% CI=-0.31 to 0.059), epinephrine (two studies; N=46; r=0.06; 95% CI=-0.23 to 0.34), colloid (two studies; N=80; r=0.0070; 95% CI=-0.218 to 0.23) or hydrocortisone administration (one study; N=40; r=-0.10; 95% CI=-0.40 to 0.22).

CONCLUSION

Dopamine administration increases mean and systolic blood pressure in hypotensive preterm infants, and is more effective than dobutamine, colloid or hydrocortisone alone. Dopamine administration is associated with increased CBF, with greater increases in CBF in hypotensive than in normotensive preterm infants. Dopamine is not associated with a greater incidence of adverse effects than other therapies used to treat hypotension.

Functional echocardiography; from physiology to treatment

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

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.

To autoregulate or not to autoregulate--that is no longer the question

In the late 1970s, high cerebral blood flow was perceived as a cause of intracranial hemorrhage in the preterm infant. Intracranial hemorrhage was diagnosed by computed tomography and ultrasound found to be frequent not only in babies who died. Hemorrhage was soon linked to cerebral palsy in survivors. The analogy was hypertensive hemorrhagic stroke in the adult. Cerebral hemorrhage was perceived as the major (preventable) cause of brain injury in the preterm baby. An immature cerebral autoregulation or a vulnerability of the autoregulation exposed by preceding hypoxia or ischemia therefore became a focus of neonatal brain research in the 1980s. Over the years the focus has changed, first to the pathogenesis of hypoxic-ischemic brain injury, then to the effects of pCO(2), and now 30 years later to a more comprehensive, less clearly hypothesis-driven exploration of the multitude of factors involved in cerebral blood flow and oxygenation. Meanwhile, some basic questions regarding autoregulation remain unanswered, and some concepts from the 1970s still direct clinical practice.

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.

Definition of hypotension and assessment of hemodynamics in the preterm neonate

The complexity of postnatal cardiovascular transition has only recently been better appreciated in the very low birth weight neonate. As blood pressure in itself poorly represents systemic blood flow, especially when the fetal channels are open and the developmentally regulated vital organ assignment may not have been completed, efforts to measure systemic blood flow have resulted in a novel, yet incomplete, understanding of the principles and clinical relevance of cardiovascular adaptation during postnatal transition in this patient population. This article describes the definition of hypotension based on the principles of cardiovascular physiology, and reviews the tools available to the clinician and researcher at the bedside to examine the complex relationship among blood pressure, systemic and organ blood flow, and tissue oxygen delivery and oxygen demand in vital and non-vital organs in the very low birth weight neonate. Only after gaining an insight into these complex relationships and processes will we be able to design clinical trials of selected treatment modalities targeting relevant patient sub-populations for the management of neonatal cardiovascular compromise. Only clinical trials based on a solid understanding of developmental cardiovascular physiology tailored to the appropriate patient sub-population hold the promise of being effective and practical, and can lead to improvements in both hemodynamic parameters and clinically relevant outcome measures.

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.

Hypotension and shock in the preterm infant

Between 16% and 98% of extremely preterm infants receive treatment for hypotension in the first few days of life. This enormous variation has arisen because of a lack of reliable information to create an evidence base for intervention. This review article provides the unique characteristics of the neonatal cardiovascular system, and addresses the definitions of hypotension and shock in the preterm infant, the indications for treatment and appropriate therapies in individual cases. The treatment of shock and hypotension in the preterm infant may be the area of neonatology where there is the greatest 'intervention/data imbalance'; more babies receive more treatments with less supportive evidence than in virtually any other domain. Treatment of hypotension in infants with good perfusion is probably unnecessary and may be harmful, but the assessment of adequate perfusion remains problematic. Infants with inadequate oxygen delivery to the tissues may benefit from treatment, but which treatments are effective are unknown. It is essential that better evidence be available to create a rational basis for intervention.

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.

The effect of inotropes on morbidity and mortality in preterm infants with low systemic or organ blood flow

BACKGROUND

Low systemic blood flow (SBF) is common in extremely premature infants in the first day after birth and has been associated with peri / intraventricular haemorrhage (PIVH), necrotising enterocolitis (NEC), mortality and developmental impairment.

OBJECTIVES

To determine the effect of specific inotropes on morbidity and mortality in preterm infants with low systemic blood flow

SEARCH STRATEGY

Searches were made of The Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 1, 2006 ), MEDLINE (1966 - April 2006), EMBASE (1980 - April 2006) and CINAHL (1982 - April 2006), supplemented by searches of abstracts of conference proceedings, citations of reviews and expert informants.

SELECTION CRITERIA

Random and quasi-random controlled trials of inotropes enrolling preterm infants with low systemic or organ blood flow in the neonatal period.

DATA COLLECTION AND ANALYSIS

Independent assessment of trial eligibility, quality and data extraction by each review author. Synthesis of data using relative risk (RR) and weighted mean difference (WMD) using standard methods of the Cochrane Collaboration.

MAIN RESULTS

No studies that compared an inotrope to no treatment in preterm infants with low SBF were found. One study (Osborn 2002a) was found that compared dobutamine versus dopamine. The study was of adequate methodology. It enrolled 42 infants < 30 weeks gestation and < 12 hours after birth with low SVC flow. The trial compared the effect of dobutamine versus dopamine titrated 10 to 20 mug/kg/min with the goal of increasing and maintaining SVC flow > 40 ml/kg/min. No significant difference was reported in mortality to discharge (RR 1.41, 95% CI 0.79, 2.52), PIVH (RR 1.01, 95% 0.52, 1.97), grade 3 or 4 PIVH (RR 0.39, 95% CI 0.12, 1.31) or NEC. At three years, there was no significant difference in cerebral palsy, deafness, Developmental quotient > 2 sd below norm or combined disability (RR 0.10, 95% CI 0.01, 1.56). Surviving infants treated with dobutamine had a significantly higher development quotient (MD 35.00, 95% CI 17.68, 52.32). There was no significant difference in death or disability at the latest time reported (RR 0.95, 95% CI 0.66, 1.38). For secondary outcomes, there was no significant difference in periventricular leucomalacia, renal impairment, pulmonary haemorrhage, retinopathy of prematurity or CLD at 36 weeks. There was no significant difference in treatment failure. Dobutamine produced a significantly greater increase in SVC flow at the highest dose reached (MD 13.10, 95% CI 2.87, 23.33), whereas dopamine produced a significantly greater increase in mean BP at 10 and 20 mug/kg/min and at the highest dose reached (MD -7.20, 95% CI -11.41, -2.99).

AUTHORS' CONCLUSIONS

In preterm infants with low systemic blood flow, there is some evidence that dobutamine is better than dopamine at increasing and maintaining systemic blood flow. The only eligible trial did not demonstrate any consistent differences in clinical outcomes. However, this study was not sufficiently powered to prove or disprove effects on clinical outcomes. It is unclear what is the most effective strategy for improving the cardiovascular status of immature infants in the first day. Further trials are needed to determine effective strategies for preventing and improving low systemic and organ blood flow.

Dopamine does not limit fetal cerebrovascular responses to hypoxia

Dopamine is used clinically to stabilize mean arterial blood pressure (MAP) in sick infants. One goal of this therapeutic intervention is to maintain adequate cerebral blood flow (CBF) and perfusion pressure. High-dose intravenous dopamine has been previously demonstrated to increase cerebrovascular resistance (CVR) in near-term fetal sheep. We hypothesized that this vascular response might limit cerebral vasodilatation during acute isocapnic hypoxia. We studied nine near-term chronically catheterized unanesthetized fetal sheep. Using radiolabeled microspheres to measure fetal CBF, we calculated CVR at baseline, during fetal hypoxia, and then with the addition of an intravenous dopamine infusion at 2.5, 7.5, and 25 μg·kg−1·min−1 while hypoxia continued. During acute isocapnic fetal hypoxia, CBF increased 73.0 ± 14.1% and CVR decreased 38.9 ± 4.9% from baseline. Dopamine infusion at 2.5 and 7.5 μg·kg−1·min−1, begun during hypoxia, did not alter CVR or MAP, but MAP increased when dopamine infusion was increased to 25 μg·kg−1·min−1. Dopamine did not alter CBF or affect the CBF response to hypoxia at any dose. However, CVR increased at a dopamine infusion rate of 25 μg·kg−1·min−1. This increase in CVR at the highest dopamine infusion rate is likely an autoregulatory response to the increase in MAP, similar to our previous findings. Therefore, in chronically catheterized unanesthetized near-term fetal sheep, dopamine does not alter the expected cerebrovascular responses to hypoxia.

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.

The relationship between cardiac output, cerebral electrical activity, cerebral fractional oxygen extraction and peripheral blood flow in premature newborn infants

Cardiac output is a determinant of systemic blood flow and its measurement may therefore be a useful indicator of abnormal hemodynamics and tissue oxygen delivery. The purpose of this study was to investigate in very premature newborn infants the relationships between cardiac output (left and right ventricular outputs), systemic blood pressure, peripheral blood flow (PBF) and two indicators of cerebral oxygen delivery (cerebral electrical activity and cerebral fractional oxygen extraction (CFOE)). This was a prospective observational study performed on 40 infants of less than 30 wk gestation. Digital electroencephalograms (EEGs) were recorded for one hour every day during the first four days after birth and subjected to qualitative and quantitative analysis. Left and right ventricular outputs, mean blood pressure (MBP), CFOE, PBF and arterial blood gases were measured at the same time. Within the ranges studied, there was no apparent relationship between left or right ventricular output (RVO), PBF and indicators of cerebral perfusion (cerebral electrical activity and CFOE). The EEG was normal in infants with low left and right ventricular outputs (<150 mL/kg/min) and MBP > 30 mm Hg. Infants with low cardiac output and normal MBP seem able to maintain cerebral perfusion, possibly through vasodilatation of the cerebral microvasculature.

Cardiovascular support in preterm infants

BACKGROUND

Despite increasing investigation in the area of cardiovascular instability in preterm infants, huge gaps in knowledge remain. None of the current treatments for hypotension, including the use of inotropic agents, have been well studied in the preterm population, and data regarding safety and efficacy are lacking. Thus, the labeling information regarding the use of inotropes as therapeutic agents in this population is inadequate.

OBJECTIVE

This article reviews the current deficiencies in knowledge with respect to measuring and achieving normal organ perfusion; summarizes the clinical, methodological, and ethical issues to consider when designing trials to evaluate medications for hemodynamic instability in the preterm neonate; and proposes 2 possible trial designs. Unanswered questions and potential obstacles for the systematic study of drugs to treat cardiovascular instability in preterm neonates are discussed.

METHODS

The neonatal Cardiology Group was established in 2003 by the US Food and Drug Administration (FDA) and the National Institute of Child Health and Human Development (NICHD) as part of the Newborn Drug Development Initiative. The Cardiology Group conducted a number of teleconferences and one meeting to develop a document addressing gaps in knowledge regarding cardiovascular drugs commonly used in low-birth-weight neonates and possible approaches to investigate these drugs. This work was presented at a workshop cosponsored by the NICHD and the FDA held in March 2004 in Baltimore, Maryland. Information for this article was gathered during this initiative.

RESULTS

To develop rational, evidence-based guidelines corroborated by robust scientific data for cardiovascular support in newborns, well-designed and adequately powered pharmacologic studies and clinical trials are needed to evaluate the safety and efficacy of inotropic agents and to determine the short- and long-term effects of these drugs. Trials investigating the currently available and novel therapies for cardiovascular instability in neonates will provide information that can be incorporated into product labeling and a scientific framework for cardiovascular management in critically ill neonates. The Cardiology Group identified and prioritized 2 conditions for investigation of therapeutic options for the management of neonatal cardiovascular instability: (1) cardiovascular instability in preterm neonates; and (2) cardiac dysfunction in neonates after cardiopulmonary bypass surgery. Key research questions in the area of cardiovascular instability in the preterm infant include determining optimal blood pressure (BP) in preterm infants; identifying better measures than BP to determine organ perfusion; optimizing hemodynamic treatments; and clarifying any associations between BP or therapy for low BP and mortality, intraventricular hemorrhage, periventricular leukomalacia, necrotizing enterocolitis, retinopathy of prematurity, and neurodevelopmental outcome. The Cardiology Group concluded that the study of inotropic agents in neonates using outcomes of importance to patients will require a complicated trial design to address the elements discussed. The group proposed 2 clinical trial designs: (1) a placebo-controlled trial with rescue therapy for symptomatic infants; and (2) a targeted BP trial.

CONCLUSION

This summary is intended to stimulate and assist future research in the area of cardiovascular support for preterm infants.

Systemic and Pulmonary Effects of Vasopressors and Inotropes in the Neonate

This paper briefly reviews the systemic and pulmonary hemodynamic actions of the most frequently used vasopressor-inotropes and inotropes in the preterm and term neonate. It is important to note that very little is known about the medium- and long-term cardiovascular and neurodevelopmental benefits of the use of these medications in the neonate.

Dopamine versus epinephrine for cardiovascular support in low birth weight infants: analysis of systemic effects and neonatal clinical outcomes

BACKGROUND

Early postnatal adaptation to transitional circulation in low birth weight infants frequently is associated with low blood pressure and decreased blood flow to organs. Catecholamines have been used widely as treatment, despite remarkably little empirical evidence on the effects of vasopressor/inotropic support on circulation and on clinically important outcomes in sick newborn infants.

AIMS

To explore the effectiveness of low/moderate-dose dopamine and epinephrine in the treatment of early systemic hypotension in low birth weight infants, evaluate the frequency of adverse drug effects, and examine neonatal clinical outcomes of patients in relation to treatment.

DESIGN/METHODS

Newborns of <1501-g birth weight or <32 weeks of gestational age, with a mean blood pressure lower than gestational age in the first 24 hours of life, were assigned randomly to receive dopamine (2.5, 5, 7.5, and 10 microg/kg per minute; n = 28) or epinephrine (0.125, 0.250, 0.375, and 0.5 microg/kg per minute; n = 32) at doses that were increased stepwise every 20 minutes until optimal mean blood pressure was attained and maintained (responders). If this treatment was unsuccessful (nonresponders), sequential rescue therapy was started, consisting first of the addition of the second study drug and then hydrocortisone.

OUTCOME MEASURES

These included: (1) short-term changes (first 96 hours, only responders) in heart rate, mean blood pressure, acid-base status, lactate, glycemia, urine output, and fluid-carbohydrate debit; and (2) medium-term morbidity, enteral nutrition tolerance, gastrointestinal complications, severity of lung disease, patent ductus arteriosus, cerebral ultrasound diagnoses, retinopathy of prematurity, and mortality.

RESULTS

Patients enrolled in this trial did not differ in birth weight or gestational age (1008 +/- 286 g and 28.3 +/- 2.3 weeks in the dopamine group; 944 +/- 281 g and 27.7 +/- 2.4 weeks in the epinephrine group). Other main antenatal variables were also comparable. However, responders and nonresponders differed significantly with respect to the need for cardiorespiratory resuscitation at birth (3% vs 23%), Critical Risk Index for Babies score (3.8 +/- 3 vs 7 +/- 5), and premature rupture of membranes >24 hours (39.5% vs 13.6%), respectively. No differences were found in the rate of treatment failure (dopamine: 36%; epinephrine: 37%) or need for rescue therapy according to treatment allocation. Groups did not differ in age at initiation of therapy (dopamine: 5.3 +/- 3.9 hours; epinephrine: 5.2 +/- 3.3 hours), but withdrawal was significantly later in the dopamine group. For short-term changes, mean blood pressure showed a significant increase from baseline throughout the first 96 hours with no differences between groups. However, epinephrine produced a greater increase in heart rate than dopamine. After treatment began, epinephrine patients showed higher plasma lactate (first 36 hours) and lower bicarbonate and base excess (first 6 hours) and received more bicarbonate. Patients in the epinephrine group also had higher glycemia (first 24 hours) and needed insulin therapy more often. Groups did not differ in urine output or fluid-carbohydrate supply during the first 96 hours. For medium-term morbidity, there were no differences in neonatal clinical outcomes in responders. However, significant differences were found in the incidence of patent ductus arteriosus, bronchopulmonary dysplasia, need for high-frequency ventilation, occurrence of necrotizing enterocolitis, and death between responders and nonresponders.

CONCLUSIONS

Low/moderate-dose epinephrine is as effective as low/moderate-dose dopamine for the treatment of hypotension in low birth weight infants, although it is associated with more transitory adverse effects.