Comparative hemodynamic effects of isoproterenol, dopamine, and dobutamine in the newborn dog

To compare the hemodynamic effects of isoproterenol, dopamine, and dobutamine in the immature animal, each drug was infused into anesthetized open chest puppies and cardiac output was measured, as were systemic arterial blood pressure, heart rate, and renal artery blood flow. Cardiac output was increased by dopamine and dobutamine. Isoproterenol caused a significantly greater increment of heart rate than either of the other agents to achieve a similar change of cardiac output. Systemic arterial mean blood pressure was increased by dopamine and dobutamine, but decreased by isoproterenol. Dopamine produced a significant increase of renal artery blood flow while renal artery blood flow was unchanged by dobutamine and decreased by isoproterenol.     

Supranormal Cardiac Output in the Dopamine- and Dobutamine-Dependent Preterm Infant

To evaluate the incidence of low cardiac output in preterm infants with respiratory distress syndrome (RDS), we measured cardiac output, stroke volume, heart rate, mean arterial blood pressure, and systemic vascular resistance at 8–48 hours of age in 30 preterm infants with RDS who were dependent on inotropic support. We then compared them to 23 normotensive preterm infants with RDS and 27 preterm infants without RDS. RDS infants had a higher cardiac output and lower systemic vascular resistance and blood pressure than infants without RDS. Infants treated with dopamine and dobutamine had a higher cardiac output and heart rate than infants on dopamine alone or the normotensive controls but a lower blood pressure and systemic vascular resistance than the normotensive controls. Supranormal cardiac output (>400 ml/min/kg) was detected in 57% of the infants in the dopamine + dobutamine subgroup (p= 0.009) versus 17% in the normotensive RDS subgroup and 12% in the dopamine subgroup. These data show that high cardiac output is relatively common in infants with RDS dependent on dopamine and dobutamine but is not reflected in the blood pressure.     

Effects of dopamine and dobutamine on the myocardial and systemic circulation during and following cardiopulmonary bypass in dogs

Summary The effect of dopamine (Dp) and dobutamine (Db) on myocardial and systemic blood flow (BF) distribution was compared in dogs being weaned from cardiopulmonary bypass (CPB) after 20 min of normothermic global myocardial ischemia. Drug infusions (10 mcg/kg/min) were begun and BF was measured (radiolabeled microspheres) prior to weaning and 60 min off CPB.On CPB: Pump flows, by design, were similar (100 ml/kg/min) in Dp, Db, and saline control (NS) dogs. Dp and Db significantly (p<0.05) increased myocardial BF. Dp did not alter renal, visceral, and skeletal muscle BF and only increased BF to the cervical spinal cord and medulla. Db, however, significantly reduced renal (–49%), splenci (–58%), pancreatic (–27%), and colonic (–47%) BF but increased perfusion in essentially all of the central nervous system.Off CPB: Cardiac output during Dp and Db infusions was significantly greater than NS dogs (107±7 vs 152±12 vs 82±10 ml/kg/min resp.); the greater increase for Db resulting from a larger stroke volume. Dp and Db significantly increased myocardial BF. Dp increased splenic (+77%), gastric (+139%), and gallbladder (+125%) BF but had no effect on renal, hepatic, skeletal muscle, and intestinal BF. Db infusion maintained renal BF similar to NS and elevated BF to most visceral organs. The results of this study show that the myocardium responded to inotropic stimulation despite the previous ischemic insult but the BF changes varied among regional vascular beds with Dp and Db infusions during and following CPB. Of the 2 drugs, Db showed the greater inotropic response off CPB, a similar increase in myocardial perfusion and greater visceral organ bloodflow.Supported in part by Grants HL26640, HL 18204 and HL06185 from the National Institutes of Health and by a Grant-in-Aid from the American Heart Association Minnesota AffiliateThis paper was part of the Ray C. Anderson Symposium.     

Effects of vasoactive drugs on thromboxane A2 mimetic-induced pulmonary hypertension in newborn lambs

Isoproterenol, dobutamine, dopamine, and nitroprusside are four vasoactive drugs used to decrease pulmonary arterial pressure and increase cardiac output in newborns, infants, and children with sepsis. Thromboxane A2 likely produces some of the hemodynamic changes in sepsis, and U46619, a thromboxane A2 mimetic, produces similar changes in lambs. We studied the hemodynamic effects of these four vasoactive drugs in 10 spontaneously breathing newborn lambs during an infusion of U46619. After baseline hemodynamic measurements, U46619 (1-2 micrograms/kg/min) was infused to increase pulmonary arterial pressure and to decrease cardiac output. Then, either isoproterenol (0.05-1.0 micrograms/kg/min), dobutamine (5-20 micrograms/kg/min), dopamine (3-30 micrograms/kg/min), or nitroprusside (0.5-10.0 micrograms/kg/min) was infused. Every 10 min, measurements were repeated and the dose increased. U46619 significantly increased pulmonary arterial pressure by 182% and decreased cardiac output by 25% (p less than 0.05). Isoproterenol decreased pulmonary arterial pressure by 30% (p less than 0.05) and increased cardiac output by 25% (p less than 0.05) at low doses, and increased cardiac output by 115% at the maximum dose (p less than 0.05). Dobutamine decreased pulmonary arterial pressure by 11% (p less than 0.05) at low doses, and increased cardiac output by 28% (p less than 0.05) at low doses, and increased cardiac output by 71% at the maximum dose (p less than 0.05). Dopamine did not decrease pulmonary arterial pressure or increase cardiac output. Nitroprusside decreased pulmonary arterial pressure by 11% at the maximum dose (p less than 0.05). Isoproterenol and dobutamine may be more useful than dopamine and nitroprusside in the management of pulmonary hypertension and decreased cardiac output during sepsis.     

Hemodynamic effects of dobutamine in children with cardiovascular failure

The effect of dobutamine, a synthetic catecholamine, was studied in 12 patients aged one day to 14 years with low cardiac output syndromes.After initial stabilization of the patients dobutamine was administered by continuous infusion in a dosage of 7.5 or 10 g/kg/min.Heart rate, cardiac output (using thermodilution technique and/or pulse contour method), mean systemic and mean pulmonary artery pressures were determined before and after the dobutamine infusion. Systemic and pulmonary vascular resistances, cardiac index and stroke volume index were calculated.Cardiac output and cardiac index increased significantly in every patient, whereas the heart rate changed only slightly, suggesting that the increase in cardiac output was mainly due to the alteration of stroke volume. The mean arterial pressure increased significantly, but the mean pulmonary artery pressure was unchanged. No side effects were observed during the dobutamine infusion. Dobutamine is a potent inotropic drug with limited chronotropic and peripheral vascular effects in newborns, infants and chidren.     

In vivo demonstration of maturational changes of the chronotropic response to alpha-adrenergic stimulation

In vitro studies suggest that neonates and adults may have different cardiac chronotropic responses to alpha-adrenergic stimulation. To investigate these differences in vivo, three groups of dogs were studied. Group I = 12 puppies, ages 3-7 days; group II = 12 puppies ages 8-15 days, and group III = seven adult dogs. Heart rate and blood pressure determinations were made in the control setting and then after combined beta-adrenergic and parasympathetic blockade (propranolol 0.6 mg/kg and bilateral vagotomies). Alpha-stimulation was then achieved with phenylephrine given in doses of 0.5, 1.0, and 10.0 micrograms/kg/min. A second, high dose of propranolol (1.0 mg/kg intravenously) was administered after the highest phenylephrine infusion dosage to assure complete beta-blockade. Finally, alpha-blockade was achieved with phentolamine (groups I and II: 0.5 mg intravenously; group III: 5.0 mg intravenously). An alpha-mediated positive chronotropic effect was observed in 42 and 100% of subjects in groups I and II, respectively, but never observed in the adults. Whereas alpha-blockade with phentolamine resulted in a large decrease in heart rate of all puppies (groups I and II), it had no effect on adults. Blood pressure responses were similar in all three groups. Thus, there are important maturational changes in the chronotropic response to alpha-adrenergic stimulation and blockade demonstrable in the intact neonatal canine.     

Augmentation of cardiac output with intravenous catecholamines in unanesthetized hypoxemic newborn lambs

We compared the effects of three different sympathetic-type agonist drugs upon cardiac output (pump function) and its determinants during hypoxemia, a condition of increased endogenous catecholamines. At 1-3 days after birth, 15 lambs were instrumented with catheters in the aorta, the left atrium, and a vein, and thermistors were placed in the abdominal aorta for cardiac output sampling. In eight animals, a pressure transducer was placed in the left ventricle. After a 2- to 3-day recovery, sequential measurements were made of blood gases, cardiac output, aortic and left atrial pressure and left ventricular maximal first derivative of pressure with respect to time (LV dP/dtmax) in room air and in hypoxemia (FiO2 = 0.08-0.10). Measurements were repeated during continued hypoxemia with increasing doses of isoproterenol (0.1, 0.4, 0.7, and 1.0 microgram/kg/min) and dopamine and dobutamine (10, 20, 40, and 80 micrograms/kg/min). Hypoxemia alone was associated with no significant change in cardiac output, but cardiac output rose significantly during continued hypoxemia with each drug (maximum increases-dobutamine 58%, isoproterenol 51%, dopamine 31% all p less than 0.05). Studies with continued hypoxemia alone showed no rise in cardiac output over time. Augmentation of contractility, demonstrated by a doubling of LV dP/dtmax by each of the drugs, contributed to the increases in cardiac output. Differences in cardiac output responses could not be explained by contractile effects of the drugs alone, since LV dP/dtmax increased in similar fashion for all three. The relatively limited cardiac output response and downward trend at the highest dosage of dopamine occurred with a reduction in heart rate and an increase in systemic vascular resistance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inotropic response of the neonatal canine myocardium to dopamine

The inotropic responsiveness of the developing myocardium to dopamine and isoproterenol was evaluated using isolated, perfused ventricles and atrial strips from puppies ages 15 hr to 33 days. Responses were compared to those in adult animals. The maximum percentage of increase of left ventricular dF/dt increased from 12 +/- 5 (mean +/- SEM) at 0-7 days (n = 6) to 100 +/- 40 at 21-33 days (n = 3) of postnatal age. At 7-14 days (n = 4) and 15-20 days (n = 5) of age the maximum percentage of increase of left ventricular dF/dt was 28 +/- 10 and 39 +/- 17, respectively. Puppy ventricle responded to isoproterenol at all ages equally (maximum percentage increase of left ventricular dF/dt = 46 +/- 13). Atrial muscle strips from puppies, ages 15 hr to 35 days (n = 22), and adult dogs (n = 19) demonstrated equal responsiveness to dopamine as well as to isoproterenol. The maximum percentage of increase of dF/dt was 117 +/- 18 with dopamine. Maximum percentage of increase of dF/dt with dopamine after propranolol (10(-7) M) was 52 +/- 18. Haloperidol (1.10(-7)-2.10(-6) M) did not alter responsiveness of atria to dopamine.     

Left ventricular function in dogs 1 year after coarctectomy

Summary Juxtaductal aortic coarctation was surgically created in beagle puppies at the age of 2 months and resected at the age of 10 months, after the development of good collateral circulation. Control dogs undergoing sham operations on each occasion were studied in the same environment. Cardiac catheterization was performed 1 year after the coarctectomy to evaluate the recovery of the heart.Cardiac output, heart rate, end-diastolic pressure, andV _max were similar in both groups of seven dogs, but the systolic pressure gradient (SPG) over the operated area during isoproterenol infusion was significantly higher in the coarctectomized group, with a mean of 8.9±6.3 (SD) vs. 0.1±0.3 mmHg (p<0.05). The preejection period [PEP, 58±8 vs. 47±5 ms (p<0.01)], electromechanical delay [EMD, 18±3 vs. 13±3 ms (p<0.05)], and isometric contraction time [ICT, 39±7 vs. 32±4 ms (p<0.05)], were all significantly longer in the coarctation group after isoproterenol infusion.The results demonstrate that, even though cardiac output increased adequately during loading and mechanical pumping efficiency was preserved, excitation-contraction coupling was still prolonged. Thus, an anatomical successful coarctectomy, even at the age of 10 months, does not fully restore left ventricular function in dogs after chronic experimental coarctation.     

Noradrenaline for management of septic shock refractory to fluid loading and dopamine or dobutamine in full-term newborn infants

AIM: To determine the effects of noradrenaline in full-term newborns with refractory septic shock. METHODS: Newborns of >35 weeks' gestation with persistent septic shock, despite adequate fluid resuscitation and high dose of dopamine/dobutamine were eligible. In this prospective observational study, we recorded respiratory and hemodynamic parameters prior to and 3 h after starting noradrenaline infusion. RESULTS: Twenty-two newborns were included (gestational age [GA] 39 +/- 1.7 weeks, birth weight (BW) 3110 +/- 780 g). Before starting noradrenaline, the infants received a mean volume expansion of 31 +/- 15 mL/kg and a mean infusion rate of dopamine of 14 +/- 5 microg/kg/min or dobutamine of 12 +/- 6 microg/kg/min. Three hours after starting noradrenaline (rate 0.5 +/- 0.4 microg/kg/min), the mean arterial blood pressure rose from 36 +/- 5 to 51 +/- 7 mmHg (p < 0.001). Urine output increased from 1 +/- 0.5 to 1.7 +/- 0.4 mL/kg/h (p < 0.05). Blood lactate concentration decreased from 4.8 +/- 2.3 to 3.3 +/- 1.8 mmol/L (p < 0.01). Despite an initial correction of hypotension, four infants died later. CONCLUSION: Noradrenaline was effective in increasing systemic blood pressure. An increase in urine output and a decrease in blood lactate concentration suggest that noradrenaline may have improved cardiac function and tissue perfusion.     

Physiologic and neuropathologic aspects of hypothermic circulatory arrest in newborn dogs

A model of hypothermic circulatory arrest has been developed in the newborn dog. Ten puppies were anesthetized with halothane, paralyzed, and artificially ventilated with 70% nitrous oxide 30% oxygen to arterial oxygen pressure greater than 8.0 kPa (60 mm Hg), arterial carbon dioxide pressure of 4.4-5.6 kPa (33-42 mm Hg), and arterial pH of 7.35-7.42. Animals were surface cooled to 20 degrees C, after which cardiac arrest was produced with i.v. KCl. Dogs remained asystolic without ventilation for 1.0 (n = 4), 1.5 (n = 3), or 2.0 (n = 3) h. Resuscitation was accomplished with closed-chest compression, mechanical ventilation, i.v. epinephrine and NaHCO3, and rewarming to 37 degrees C. Postarrest recovery was maintained for 3-4 h; thereafter, the puppies underwent perfusion-fixation of their brains for pathologic analysis. Plasma glucose (control = 8.3 mmol/L) increased slightly during hypothermic cardiac arrest (+36%) but was markedly elevated at 15 min postarrest (20 mmol/L). Blood lactate (control = 1.1 mmol/L) increased almost 200% during hypothermic circulatory arrest, with a further rise to 9.0 mmol/L at 15 min postarrest. Thereafter, lactate decreased in the 1-h arrested dogs but increased progressively in the other groups. Mean arterial blood pressure returned to baseline (73 mm Hg) by 15 min postarrest, remained stable in the 1-h dogs, but fell at 3 h to 62 and 34 mm Hg in the 1.5- and 2.0-h groups, respectively. No neuropathologic alterations were seen in puppies arrested for 1 h, whereas all puppies arrested for 1.5 or 2 h had varying degrees of cerebral cortical and hippocampal damage.(ABSTRACT TRUNCATED AT 250 WORDS)     

Intraosseous infusion of dobutamine and isoproterenol

Intraosseous infusion has been advocated as an emergency route in sick infants and children when intravenous access is not readily obtainable. Dobutamine hydrochloride and isoproterenol hydrochloride are useful emergency drugs that have not been studied when administered into the bone marrow. In a swine model, we compared the physiologic responses (heart rate, arterial pressure, and cardiac output) of dobutamine and isoproterenol infusions delivered intravenously and intraosseously during 20-minute intervals. We observed statistically significant effects of both dobutamine and isoproterenol delivered by the intraosseous route. In addition, the effects resulting from intraosseous infusion were statistically similar to those resulting from intravenous administration of these drugs. We conclude that the intraosseous infusion of dobutamine and isoproterenol is an effective and useful method for emergency administration of these medications.     

Hemodynamic effects of dobutamine in asphyxiated newborn infants

The hemodynamic effects of dobutamine were studied by non invasive techniques in 6 full term neonates with severe perinatal asphyxia. At 10 micrograms/kg/min, dobutamine significantly increased the cardiac output, the heart rate and the aortic blood flow velocity. The mean arterial pressure increased but not significantly and the stroke volume remained unchanged. These changes seem to be dose dependent. The increase of cardiac output may be due to a chronotropic and inotropic effect of dobutamine. Dobutamine seems to be an effective agent for the treatment of low cardiac output in asphyxiated neonates.     

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.     

Effect of low dose dopamine on hemodynamic and renal function in children

The purpose of the study was to investigate the effect of low doses of dopamine in children. Fourteen cases were studied after open heart surgery. Cardiac output and renal parameters were determined under baseline conditions and under continuous infusion of dopamine 2.5 and 5 micrograms/kg/min. During the control period cardiac index was 2.62 +/- 0.19 L/min/m2, renal plasma flow was decreased at 269 +/- 41 mL/min/1.73 m2, GFR was 86.6 +/- 9.2 mL/min/1.73 m2, and filtration fraction was elevated at 37.1 +/- 1.9%. Plasma concentration of aldosterone correlated with the filtration fraction. At 5 micrograms/kg/min dopamine increased significantly cardiac output, renal plasma flow, and to a lesser extent GFR, thus decreasing the filtration fraction. At 2.5 micrograms/kg/min dopamine, increased renal plasma flow only in patients older than 5 y and had no effect on the other parameters. The increase of cardiac output in response to dopamine was abolished by propranolol pretreatment. By contrast, the hemodynamic renal response to dopamine was not altered by beta-blockade. These results indicate that 5 micrograms/kg/min of dopamine could prevent renal failure after open heart surgery in children by increasing renal blood flow and attenuating renal compensatory mechanisms.     

Relationship between mean airway pressure, cardiac output, and organ blood flow with normal and decreased respiratory compliance

We investigated the relation between blood flow and mean airway pressure in two groups of anesthetized newborn piglets. The first group had normal respiratory compliance; the second group had pulmonary surfactant depleted by repeated saline lavage, which decreased static respiratory compliance by 42%. In the normal group, cardiac output decreased linearly from 292 +/- 43 mL/min/kg at 5 cm H2O airway pressure to 134 +/- 37 ml/min/kg at 20 cm H2O airway pressure, a drop of 43% (r2 = 0.79). Blood flow to the heart, kidney, and intestines had a similar decline, but brain, hepatic artery, and adrenal flow were constant. Mean arterial blood pressure did not decrease significantly until the highest airway pressure was reached, whereas sagittal sinus pressure increased as mean airway pressure increased. In contrast, the surfactant-depleted group maintained cardiac output up to a mean airway pressure of 15 cm H2O. At 20 cm H2O, cardiac output fell to 40% of the original value. Blood flow to the heart and kidneys fell at a mean airway pressure of 20 cm H2O; intestinal blood flow decreased beginning at 10 cm H2O. As in the normal piglets, brain, hepatic arterial, and adrenal blood flow were not affected by increasing ventilation pressure. Our data show that positive pressure ventilation in the neonate has important cardiovascular effects that are blunted when respiratory compliance is decreased. More important, because cardiac output decreased prior to a significant decline in arterial blood pressure, these data suggest that in a clinical setting considerable cardiovascular alterations can occur before a decline in arterial blood pressure is detected.     

Effect of continuous tolazoline infusion on cardiopulmonary response to dopamine in unanesthetized newborn lambs

We evaluated the cardiopulmonary interaction of tolazoline and low-, medium-, and high-dose dopamine infusion (2.7, 27, and 270 micrograms/kg/min) in 11 normal, chronically instrumented, unsedated neonatal lambs. Concomitant tolazoline and dopamine infusions caused tachycardia at all dopamine doses and blocked alpha-adrenergic-mediated increases in systemic resistance and left atrial pressure caused by medium and high doses of dopamine. Moderate doses of dopamine alone increased cardiac output. During simultaneous tolazoline infusion, dopamine increased cardiac output at both moderate and high doses. The effect of dopamine on pulmonary artery pressure was not modified by tolazoline; pulmonary pressure increased similarly with dopamine alone and with dopamine plus tolazoline. Calculated pulmonary vascular resistance rose with dopamine alone, but not with infusion of tolazoline and dopamine, because pulmonary blood flow rose in proportion to pulmonary artery pressure.     

Effects of low-dose dobutamine on left ventricular diastolic filling in children

To investigate the effects of dobutamine on the Doppler transmitral flow pattern in children with normal left ventricular function, Doppler echocardiography was used to measure the transmitral flow in 14 healthy children before and during infusion of dobutamine (5 μg/kg per minute). Cardiac output was measured by the thermodilution method, and stroke volume was calculated as the cardiac output divided by the heart rate. Dobutamine increased the peak velocity and flow velocity–time integral of early diastolic filling without changing those of atrial contraction and normalized peak velocity of early diastolic filling, suggesting an increase in left ventricular relaxation. Dobutamine increased the stroke volume and rate-corrected mean velocity of fiber shortening with reduced end-systolic wall stress, indicating an increase in left ventricular contractility. The percentage of increase in the flow velocity–time integral of early diastolic filling during dobutamine infusion tended to correlate with the increase in stroke volume (r= 0.67, p < 0.05) and with the decrease in end-systolic wall stress (r=−0.61, p < 0.05). Our results suggest that low-dose dobutamine increases left ventricular relaxation with enhanced systolic function. The observed decreased end-systolic wall stress might have caused enhanced relaxation characteristics with dobutamine.     

Randomized trial comparing dopamine and dobutamine in preterm infants

The aim of this study was to compare the efficacy of two inotropic infusions in treating low BP in preterm neonates. Forty infants with median gestational age 27 weeks (range 23–33) were studied. At trial entry the infants, who all had a systolic BP<40 mmHg despite receiving a colloid infusion, were randomized to receive either a dopamine or dobutamine infusion. The infusions were commenced at a rate of 5 g/kg per min and, if necessary, this was increased over the 3 h study period to 15 g/kg per min. There was no significant difference in the gestational or postnatal age or baseline BP of the 20 infants who received dopamine and those 20 who received dobutamine. Three hours after commencing the infusions, although there was no difference in the rate of inotrope infusion between the two groups, the infants who received dopamine had a significantly higher systolic BP, a median of 39 mmHg (range 30–58) compared to a median of 34 mmHg (range 21–46) in the dobutamine group,P<0.05. In addition, 10 infants who received dopamine, but only 3 who received dobutamine, had a systolic BP>40 mmHg (P<0.05). We conclude that dopamine rather than dobutamine infusion is more efficacious in improving the BP of preterm neonates.     

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.