The hemodynamic effects of dobutamine infusion in the chronically instrumented newborn piglet

Cardiovascular Supportive Therapies for Neonates With Asphyxia - A Literature Review of Pre-clinical and Clinical Studies

Asphyxiated neonates often have hypotension, shock, and poor tissue perfusion. Various "inotropic" medications are used to provide cardiovascular support to improve the blood pressure and to treat shock. However, there is incomplete literature on the examination of hemodynamic effects of these medications in asphyxiated neonates, especially in the realm of clinical studies (mostly in late preterm or term populations). Although the extrapolation of findings from animal studies and other clinical populations such as children and adults require caution, it seems appropriate that findings from carefully conducted pre-clinical studies are important in answering some of the fundamental knowledge gaps. Based on a literature search, this review discusses the current available information, from both clinical studies and animal models of neonatal asphyxia, on common medications used to provide hemodynamic support including dopamine, dobutamine, epinephrine, milrinone, norepinephrine, vasopressin, levosimendan, and hydrocortisone.

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.

Effects of meloxicam and phenylbutazone on renal responses to furosemide, dobutamine, and exercise in horses

OBJECTIVE

To compare the effects of 2 NSAIDs (phenylbutazone and meloxicam) on renal function in horses.

ANIMALS

9 Thoroughbred or Standardbred mares (mean ± SD age, 5.22 ± 1.09 years [range, 2 to 12 years]; mean body weight, 470 ± 25 kg [range, 442 to 510 kg]).

PROCEDURES

A randomized blinded placebo-controlled crossover study was conducted to examine the effects of treatment with phenylbutazone, meloxicam, or a placebo (control solution) on renal responses to the administration of furosemide, dobutamine, and exercise (15 minutes at 60% of maximum heart rate). Renal function was assessed by use of bilateral ureteral catheterization for simultaneous determination of creatinine clearance, sodium excretion, and urine flow rate.

RESULTS

Both phenylbutazone and meloxicam attenuated diuresis and natriuresis and reduced glomerular filtration rate, compared with results for the control solution, when horses were treated with furosemide. Mean arterial blood pressure, urine flow rate, and glomerular filtration rate were increased during or after (or both) dobutamine infusion. Both NSAIDs reduced urine flow rate and sodium excretion associated with dobutamine infusion and exercise but had no effect on glomerular filtration rate.

CONCLUSIONS AND CLINICAL RELEVANCE

Responses to meloxicam, a cyclooxygenase (COX)-2 preferential agent, appeared comparable to those detected after phenylbutazone treatment, which suggested that COX-2 was the mediator of prostanoid-induced changes to renal function in horses and indicated that COX-2-preferential agents would be likely to have adverse renal effects similar to those for nonselective COX inhibitors in volume-depleted horses.

Dobutamine in paediatric population: a systematic review in juvenile animal models

OBJECTIVE

Although dobutamine is widely used in neonatal clinical practice, the evidence for its use in this specific population is not clear. We conducted a systematic review of the use of dobutamine in juvenile animals to determine whether the evidence from juvenile animal experiments with dobutamine supported the design of clinical trials in neonatal/paediatric population.

METHODS

Studies were identified by searching MEDLINE (1946-2012) and EMBASE (1974-2012). Articles retrieved were independently reviewed by three authors and only those concerning efficacy and safety of the drug in juvenile animals were included. Only original articles published in English and Spanish were included.

RESULTS

Following our literature search, 265 articles were retrieved and 24 studies were included in the review: 17 focused on neonatal models and 7 on young animal models. Although the aims and design of these studies, as well as the doses and ages analysed, were quite heterogeneous, the majority of authors agree that dobutamine infusion improves cardiac output in a dose dependent manner. Moreover, the cardiovascular effects of dobutamine are influenced by postnatal age, as well as by the dose used and the duration of the therapy. There is inadequate information about the effects of dobutamine on cerebral perfusion to draw conclusions.

CONCLUSION

There is enough preclinical evidence to ensure that dobutamine improves cardiac output, however to better understand its effects in peripheral organs, such as the brain, more specific and well designed studies are required to provide additional data to support the design of clinical trials in a paediatric population.

While waiting: early recognition and initial management of neonatal hypoxic-ischemic encephalopathy

Hypoxic-ischemic encephalopathy (HIE) occurring during the perinatal period is one of the primary causes of severe, long-term neurological deficits in children. Initial systemic supportive therapy remains a critical aspect of HIE management. In addition to support therapy, the widespread use of hypothermia has demonstrated a reduction in death and neurodevelopmental disability in infants with moderate to severe HIE. Neonates with HIE born outside of tertiary care centers must be rapidly identified as hypothermia candidates and have emergent transport arranged. While waiting for the transport team to arrive, these neonates often require intensive stabilization, including meticulous temperature management. This article examines the need for HIE outreach teaching programs, assists in the identification of a neonate for hypothermia therapy, and supplies evidence-based recommendations for the initial stabilization and care of neonates delivered at nontertiary care facilities. The guidelines and materials supplied represent the outreach model used by our regional hypothermia center and disseminated to the surrounding referral hospitals.

Pulmonary hypertension and the asphyxiated newborn

Persistent pulmonary hypertension of the newborn may occur with perinatal asphyxia, either because of direct effects of hypoxia/ischemia on pulmonary arterial function or indirectly because both are associated with meconium aspiration syndrome or perinatal sepsis/pneumonia. Therapies for persistent pulmonary hypertension of the newborn have the potential to affect cerebral function and cerebral perfusion in infants with hypoxic ischemic encephalopathy. Our literature review concludes that hyperventilation should be avoided, bicarbonate therapy is unproven, and hypoxia and hyperoxia should both be avoided. Nitric oxide improves pulmonary artery pressure and systemic perfusion. The effects of inotropic agents on cerebral perfusion or outcomes are uncertain.

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.

The hemodynamic effects of dobutamine during reoxygenation after hypoxia: a dose-response study in newborn pigs

Asphyxiated neonates usually have myocardial stunning and hypotension and require inotropic support. A randomized controlled study was designed to examine the dose-response effect of dobutamine (5-20 microg x kg(-1) x min(-1)) on systemic and regional circulations and oxygen metabolism in a neonatal swine model of hypoxia/reoxygenation. Thirty-eight anesthetized newborn piglets were acutely instrumented for continuous monitoring of heart rate, systemic and pulmonary arterial pressures, and pulmonary (surrogate for cardiac index), right common carotid, and superior mesenteric and left renal arterial flows. After stabilization, they were exposed to normocapnic alveolar hypoxia (10%-15% oxygen) for 2 h followed by reoxygenation with 100% oxygen for 1 h, then 21% for 3 h. Piglets were block randomized to receive dobutamine infusion (5, 10, or 20 microg x kg(-1) x min(-1)) or saline (control) at 2 to 4 h of reoxygenation (n = 8 each). A nonasphyxiated, sham-operated group was included (n = 6). Blood samples were collected for blood gas analysis, arterial and venous co-oximetry, and plasma lactate concentration determination. At 2-h reoxygenation after hypoxia, there was hypotension (systemic arterial pressure, 27 to 36 mmHg) and myocardial dysfunction (cardiac index from 178-209 to 134-156 mL x kg(-1) x min(-1)). Cardiac index improved significantly with 20 microg x kg(-1) x min(-1) of dobutamine (P < 0.05) and modestly in the treatment groups of 5 and 10 microg x kg(-1) x min(-1) (P < 0.1) (at 120 min, 172 +/- 35, 160 +/- 30, and 158 +/- 56 mL x kg(-1) x min(-1) vs. 119 +/- 33 mL x kg(-1) x min(-1) of controls, respectively), with corresponding increases in stroke volume. Pulmonary vascular resistance was lower in all dobutamine-treated groups (vs. controls, P < 0.05) There were no differences in heart rate, systemic and pulmonary arterial pressures, systemic vascular resistance, and regional flows between groups. The group of 20 mug.kg.min of dobutamine also had higher systemic oxygen delivery (at 120 min, 18 +/- 5 vs. 11 +/- 3 O(2) mL x kg(-1) x min(-1) of controls, P < 0.05) with no significant differences in systemic oxygen consumption and regional oxygen delivery between groups. After the reoxygenation of newborn piglets with severe hypoxia, high dose of dobutamine is effective to treat myocardial stunning and low cardiac output with no significant effect on blood pressure or regional circulation. Further clinical studies are needed to confirm these findings in the human neonate.

Pulmonary vasodilator effects of norepinephrine during the development of chronic pulmonary hypertension in neonatal lambs

BACKGROUND

This experimental study was performed to determine the effects of norepinephrine on: (i) the pulmonary vascular tone during the development of pulmonary hypertension (PH) in the fetus and (ii) the circulatory adaptation at birth after chronic intrauterine PH.

METHODS

Chronically instrumented fetal lambs were randomized into two groups: (i) a group with PH obtained by antenatal partial ligation of the ductus arteriosus (DA) (n=9) and (ii) a control group without DA ligation (n=6). Pulmonary vascular responses to norepinephrine (1.5 microg min(-1)) were measured in utero 7 days after surgery. At day 8 post-surgery, after delivery, animals were ventilated for 3 h with oxygen 100%. The group with PH was randomly assigned to receive norepinephrine or saline.

RESULTS

Mean pulmonary artery pressure (PAP) and pulmonary vascular resistance (PVR) were higher in the PH group (P<0.01). Norepinephrine-induced decrease in PVR was more pronounced in the PH group than in the control group (63 vs 35%, respectively; P<0.01). In the PH group, the decrease in PVR during mechanical ventilation was greater in the animals receiving norepinephrine than in the animal receiving saline (from 1.05 (0.12) to 0.1 (0.02) vs from 1.04 (0.1) to 0.2 (0.04) mm Hg ml(-1) min(-1), respectively; P<0.01). After 3 h of ventilation, mean PVR in the PH lambs treated by norepinephrine was similar to those measured in the control lambs. Aortic pressure was higher in the group treated with norepinephrine.

CONCLUSION

The data suggest that norepinephrine may improve post-natal pulmonary adaptation in the newborn with persistent PH both by increasing systemic vascular pressure and by increasing pulmonary blood flow.

Dobutamine alters carnitine metabolism in the neonatal piglet heart

The use of inotropic agents to support the neonatal heart after sepsis or hypoxia increases cardiac energy demand. Carnitine plays a vital role in energy, fuel metabolism. To test the hypothesis that inotropic agents affect carnitine metabolism, hearts from sow-fed piglets were isolated and perfused with an oxygenated buffer containing glucose and palmitate. Increasing dosages of dobutamine (DOB 2.5–15 µg/Kg body wt per min, 0.007–0.044 µmol/kg per min) or saline vehicle (SAL) were administered. Heart rate (HR), left ventricular systolic (LVSP) and end diastolic pressures (LVEDP) were measured. Left ventricular developed pressure (LVDP = LVSP - LVEDP) and pressure-rate product (LVDP × HR) were calculated. Coronary effluent was collected to measure flow and metabolites. Heart tissue samples were collected for metabolite analysis. Results: DOB increased HR, LVEDP and the pressure-rate product [LVDP × HR]. Mean lactate production increased in DOB, but not in SAL control hearts, and was correlated with heart acylcarnitine, but not with coronary flow. Tissue acylcarnitine levels were higher in the DOB than in the SAL group. Plasma total carnitine was correlated with [LVDP × HR] and LVDP, but not with HR. The findings demonstrate that DOB alters myocardial carnitine metabolism and suggest that carnitine status may affect cardiac response to inotropic agents.Key words: carnitine, dobutamine, neonate, swine, isolated perfused heart.

Randomized trial of dobutamine versus dopamine in preterm infants with low systemic blood flow

OBJECTIVE

Our purpose was to determine if dobutamine or dopamine results in greater improvements in systemic blood flow in very preterm infants with low flow during the first 24 hours of life.

STUDY DESIGN

A 2-center, randomized, double-blind study. Infants (n = 42) with low superior vena cava (SVC) flow (<41 mL/kg/min) in the first 12 hours were randomly assigned to receive 10 mL/kg normal saline solution, followed by 10 microg/kg/minute of dobutamine or dopamine. If low flow persisted or recurred, the inotrope was increased to 20 microg/kg/minute, with crossover to the other inotrope if treatment failed to maintain flow.

RESULTS

Volume produced a more significant increase in SVC flow than dopamine (+43%). At the highest dose, dobutamine resulted in a significantly greater increase in SVC flow than dopamine (mean, +9.9 vs -3.2 mL/kg/min, P =.02). Dopamine resulted in a significantly greater increase in blood pressure. Infants receiving dobutamine only at 24 hours had a greater right ventricular output than infants receiving dopamine (mean, 295 vs 167 mL/kg/min, P <.001). Forty percent failed to increase or maintain SVC flow in response to either inotrope. No significant differences in mortality or morbidity were found.

CONCLUSIONS

Dobutamine produced a greater increase in blood flow than dopamine.