Dopaminergic receptor-mediated effects in the mesenteric vasculature and renal vasculature of the chronically instrumented newborn piglet

Dose-dependent hemodynamic and metabolic effects of vasoactive medications in normotensive, anesthetized neonatal piglets

The developmentally regulated hemodynamic effects of vasoactive medications have not been well characterized. We used traditional and near-infrared spectroscopy monitoring technologies and investigated the changes in heart rate, blood pressure, common carotid artery (CCA) blood flow (BF), cerebral, renal, intestinal, and muscle regional tissue O2 saturation, and acid-base and electrolyte status in response to escalating doses of vasoactive medications in normotensive anesthetized neonatal piglets. We used regional tissue O2 saturation and CCA BF as surrogates of organ and systemic BF, respectively, and controlled minute ventilation and oxygenation. Low to medium doses of dopamine, epinephrine, dobutamine, and norepinephrine increased blood pressure and systemic and regional BF in a drug-specific manner, whereas milrinone exerted minimal effects. At higher doses, dopamine, epinephrine, and norepinephrine but not dobutamine decreased systemic, renal, intestinal, and muscle BF, while cerebral BF remained unchanged. Epinephrine induced significant increases in muscle BF and serum glucose and lactate concentrations. The findings reveal novel drug- and dose-specific differences in the hemodynamic response to escalating doses of vasoactive medications in the neonatal cardiovascular system and provide information for future clinical studies investigating the use of vasoactive medications for the treatment of neonatal cardiovascular compromise.

Preliminary pharmacokinetics and cardiovascular effects of fenoldopam continuous rate infusion in six healthy dogs

Fenoldopam is a selective dopamine-1 receptor agonist that causes peripheral arterial vasodilation, increased renal blood flow, and diuresis. Enthusiasm exists for the use of fenoldopam in nonpolyuric kidney injury in dogs, although pharmacokinetic data are lacking. The purpose of this study was to collect basic pharmacokinetic and hemodynamic effect data for fenoldopam when administered to healthy awake dogs. Six healthy, awake beagles were given a 180-min fenoldopam constant rate infusion at 0.8 μg/kg per minute followed by a 120-min washout period. Citrated blood was collected during and after infusion for the measurement of plasma fenoldopam concentration by HPLC with mass spectrometry. Heart rate and indirect systolic blood pressure were concurrently measured. Mean ± SD, steady-state plasma fenoldopam concentrations of 20 ± 17 ng/mL were achieved within 10 min of starting the infusion. Area under the plasma concentration-time curve was 3678 ± 3030 ng/mL · min, and plasma clearance was 66 ± 43 mL/min per kg. Elimination was rapidly achieved in all dogs. Heart rate and systolic blood pressure were unaffected by the fenoldopam infusion. Based on the results of this study, further evaluation of the effects of fenoldopam in dogs at differing doses and in dogs with clinical conditions such as acute nonpolyuric kidney injury is warranted.

Epinephrine versus dopamine to treat shock in hypoxic newborn pigs resuscitated with 100% oxygen

Shock and tissue hypoperfusion are common after asphyxia. We compared systemic and regional hemodynamic effects of epinephrine and dopamine in the treatment of shock and hypotension in asphyxiated newborn piglets resuscitated with 100% oxygen. Twenty-four piglets (1-3 days old; weight, 1.4-2.6 kg) were acutely instrumented to measure cardiac index (CI), carotid, mesenteric and renal arterial blood flows, and mean systemic (SAPs) and pulmonary arterial pressures (PAPs). Piglets had normocapnic alveolar hypoxia (F(IO2)=0.08-0.10) for 50 min and reoxygenated with F(IO2)=1.0 for 1 h then F(IO2)=0.21 for 3.5 h. After 2 h reoxygenation, either dopamine (2 microg kg(-1) min(-1)) or epinephrine (0.2 microg kg(-1) min(-1)) was given for 30 min in a blinded randomized manner, which was then increased to maintain SAP (within 10% of baseline, pressure-driven dose) for 2 h. Hypoxia caused hypotension (SAP, 44%+/-3% of baseline), cardiogenic shock (CI, 41%+/-4%), and metabolic acidosis (mean pH, 7.04-7.09). Upon reoxygenation, hemodynamic parameters immediately recovered but gradually deteriorated during 2 h with SAP at 45+/-1 mmHg, CI at 74+/-9% of baseline, and pH 7.32+/-0.03. Low doses of either drug had no significant systemic and renal hemodynamic response. Epinephrine (0.3-1.5 microg kg(-1) min(-1)) for 2 h increased SAP and CI (with higher stroke volume) and decreased pulmonary vascular resistance (with reduced PAP-SAP ratio), whereas the responses with dopamine (10-25 microg kg(-1) min(-1)) were modest. Low-dose epinephrine improved mesenteric and carotid arterial flows, whereas the pressure-driven doses of epinephrine and dopamine increased carotid and mesenteric arterial flows, respectively. To treat shock in asphyxiated newborn piglets resuscitated with 100% oxygen, epinephrine exhibits an inotropic action compared with dopamine, whereas both catecholamines can increase carotid and mesenteric perfusion.

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.

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.

Increasing Renal Blood Flow

BACKGROUND AND OBJECTIVES

Many clinicians believe that low-dose dopamine (LDD) [2 micro g/kg/min] increases renal blood flow (RBF) and medium-dose norepinephrine (MD-NE) [0.4 micro g/kg/min] decreases RBF. They also believe that MD-NE might induce mesenteric and/or coronary ischemia. In fact, the effects of these drugs on renal and vital organ blood flow are poorly understood. The aim of this study was to compare the effects of 6 h of IV LDD and MD-NE infusion on mammalian renal, coronary, mesenteric, and sagittal blood flow.

DESIGN

Randomized, controlled, experimental animal study.

SETTING

Animal laboratory of tertiary physiology institute.

SUBJECTS

Seven Merino cross sheep were studied.

MEASUREMENTS AND RESULTS

We performed a staged insertion of transit-time flow probes around ascending aorta, sagittal sinus and circumflex coronary, superior mesenteric, and left renal arteries. We then randomized these animal with long-term embedded flow probes to either 6 h of placebo (saline solution) or drugs (MD-NE at 0.4 micro g/kg/min or LDD at 2 micro g/kg/min), and performed continuous measurement of systemic pressures, cardiac output (CO), and flow to vital organs. We also sampled blood and urine for the measurement of lactate, creatinine, and creatinine clearances at preset intervals.

RESULTS

Compared to placebo, LDD did not affect systemic hemodynamics. However, it increased mean RBF by 20% (267.3 +/- 87.6 mL/min vs 222.0 +/- 74.4 mL/min, p = 0.028) without a detectable effect on other vital regional circulations. MD-NE, however, increased mean arterial pressure (101.0 +/- 8.3 mL/min vs 84.2 +/- 5.2 mL/min, p = 0.018) [mean +/- SD] and CO (4.93 +/- 1.45 L/min vs 3.81 +/- 0.57 L/min, p = 0.028). It also increased coronary blood flow (36.0 +/- 15.7 mL/min vs 23.0 +/- 10.7 mL/min, p = 0.018) and RBF (286.5 +/- 79.0 mL/min vs 222.0 +/- 74.4 mL/min, p = 0.018). MD-NE had no detectable effect on mesenteric or sagittal sinus flow. LDD infusion increased urine output, but did not change creatinine clearance. MD-NE infusion increased urine output significantly more than LDD but not creatinine clearance.

CONCLUSIONS

Both LDD (2 micro g/kg/min) and MD-NE (0.4 micro g/kg/min) increased RBF and urine output. However, the effect of MD-NE was more pronounced. LDD did not affect other vital organ flows, but MD-NE increased coronary blood flow without any changes in mesenteric and sagittal sinus blood flow.

Neonatal blood pressure regulation

Hypertension is often viewed solely as a disease of the adult. However, early indicators of hypertension are frequently observed in young children and neonates. Having an adequate appreciation of the normal range of infant blood pressure is critical for the appropriate management of the conditions associated with elevated or abnormally low blood pressure. In healthy neonates, systolic blood pressure increases rapidly during the first 6 weeks of life with the most rapid rise observed during the first 5 days. A similar pattern is observed for diastolic pressures. The observed increases in blood pressure are positively correlated with birth weight and both gestational and postnatal age. The incidence of hypertension in the neonate has been reported to range from 0.2% to 2.6% and is frequently an indicator of other renal or cardiovascular abnormalities. Systemic hypotension is reported in 24% to 45% of very low birth weight infants and is frequently caused by hypovolemia. The regulation of blood pressure is complex and the mechanisms involved remain to be fully elucidated. The results of several investigations into the molecular mechanism(s) of hypertension are considered.

The effects of dopamine and epinephrine on hemodynamics and oxygen metabolism in hypoxic anesthetized piglets

Background:

The most appropriate inotropic agent for use in the newborn is uncertain. Dopamine and epinephrine are commonly used, but have unknown effects during hypoxia and pulmonary hypertension; the effects on the splanchnic circulation, in particular, are unclear.

Methods:

The effects on the systemic, pulmonary, hepatic, and mesenteric circulations of infusions of dopamine and epinephrine (adrenaline) were compared in 17 newborn piglets. Three groups [control (n = 5), dopamine (n = 6) and epinephrine (n = 6)] of fentanyl anesthetized newborn piglets were instrumented to measure cardiac index (CI), hepatic arterial and portal venous blood flow, mean systemic arterial pressure (SAP), mean pulmonary arterial pressure (PAP), and arterial, portal and mixed venous oxygen saturations. Systemic, pulmonary, and mesenteric vascular resistance indices [systemic vascular resistance index (SVRI), pulmonary vascular resistance index (PVRI), mesenteric vascular resistance index (MVRI)], and systemic and splanchnic oxygen extraction and consumption were calculated. Alveolar hypoxia was induced, with arterial oxygen saturation being maintained at 55-65%. After 1 h of stabilization during hypoxia, each animal received either dopamine or epinephrine; randomly administered doses of 2, 10, and 32 μg kg^-1 min^-1 and 0.2, 1.0, and 3.2 μg kg^-1 min^-1 respectively were infused for 1 h at each dose. Results were compared with the 1 h hypoxia values by two-way analysis of variance.

Results:

Epinephrine increased CI at all doses, with no significant effects on SAP and SVRI. Although epinephrine increased PAP at 3.2 μg kg^-1min^-1, it had no effect on PVRI. Dopamine had no effect on CI, SAP, and SVRI, but increased PAP at all doses and PVRI at 32 μg kg^-1min^-1. The SAP/PAP ratio was decreased with 32 μg kg^-1min^-1 dopamine, whereas epinephrine did not affect the ratio. In the mesenteric circulation, dopamine at 32 μg kg^-1 min^-1 increased portal venous flow and total hepatic blood flow and oxygen delivery, and decreased MVRI; epinephrine had no effect on these variables. Epinephrine increased hepatic arterial flow at 0.2 μg kg^-1 min^-1; dopamine had no effect on hepatic arterial flow at any dose. Despite these hemodynamic changes, there were no differences in systemic or splanchnic oxygen extraction or consumption at any dose of dopamine or epinephrine.

Conclusions:

Epinephrine is more effective than dopamine at increasing cardiac output during hypoxia in this model. Although epinephrine preserves the SAP/PAP ratio, dopamine shows preferential pulmonary vasoconstriction, which might be detrimental if it also occurs during the management of infants with persistent fetal circulation. Dopamine, but not epinephrine, increases portal flow and total hepatic flow during hypoxia.