Systemic, pulmonary and mesenteric perfusion and oxygenation effects of dopamine and epinephrine

Comparison of various vasopressin doses to epinephrine during cardiopulmonary resuscitation in asphyxiated neonatal piglets

BACKGROUND

Current neonatal resuscitation guidelines recommend epinephrine for cardiac arrest. Vasopressin might be an alternative during asphyxial cardiac arrest. We aimed to compare vasopressin and epinephrine on incidence and time to return of spontaneous circulation (ROSC) in asphyxiated newborn piglets.

DESIGN/METHODS

Newborn piglets (n = 8/group) were anesthetized, intubated, instrumented, and exposed to 30 min of normocapnic hypoxia, followed by asphyxia and asystolic cardiac arrest. Piglets were randomized to 0.2, 0.4, or 0.8IU/kg vasopressin, or 0.02 mg/kg epinephrine. Hemodynamic parameters were continuously measured.

RESULTS

Median (IQR) time to ROSC was 172(103-418)s, 157(100-413)s, 122(93-289)s, and 276(117-480)s for 0.2, 0.4, 0.8IU/kg vasopressin, and 0.02 mg/kg epinephrine groups, respectively (p = 0.59). The number of piglets that achieved ROSC was 6(75%), 6(75%), 7(88%), and 5(63%) for 0.2, 0.4, 0.8IU/kg vasopressin, and 0.02 mg/kg epinephrine, respectively (p = 0.94). The epinephrine group had a 60% (3/5) rate of post-ROSC survival compared to 83% (5/6), 83% (5/6), and 57% (4/7) in the 0.2, 0.4, and 0.8IU/kg vasopressin groups, respectively (p = 0.61).

CONCLUSION

Time to and incidence of ROSC were not different between all vasopressin dosages and epinephrine. However, non-significantly lower time to ROSC and higher post-ROSC survival in vasopressin groups warrant further investigation.

IMPACT

Time to and incidence of ROSC were not statistically different between all vasopressin dosages and epinephrine. Non-significantly lower time to ROSC and higher post-ROSC survival in vasopressin-treated piglets. Overall poorer hemodynamic recovery following ROSC in epinephrine piglets compared to vasopressin groups. Human neonatal clinical trials examining the efficacy of vasopressin during asphyxial cardiac arrest will begin recruitment soon.

Targeted Neonatal Echocardiography in the Management of Neonatal Pulmonary Hypertension

Pulmonary hypertension (PH) in neonates, originating from a range of disease states with heterogeneous underlying pathophysiology, is associated with significant morbidity and mortality. Although the final common pathway is a state of high right ventricular afterload leading to compromised cardiac output, multiple hemodynamic phenotypes exist in acute and chronic PH, for which cardiorespiratory treatment strategies differ. Comprehensive appraisal of pulmonary pressure, pulmonary vascular resistance, cardiac function, pulmonary and systemic blood flow, and extrapulmonary shunts facilitates delivery of individualized cardiovascular therapies in affected newborns.

Evidence-Based Guidelines for Acute Stabilization and Management of Neonates with Persistent Pulmonary Hypertension of the Newborn

Persistent pulmonary hypertension of the newborn, or PPHN, represents a challenging condition associated with high morbidity and mortality. Management is complicated by complex pathophysiology and limited neonatal specific evidence-based literature, leading to a lack of universal contemporary clinical guidelines for the care of these patients. To address this need and to provide consistent high-quality clinical care for this challenging population in our neonatal intensive care unit, we sought to develop a comprehensive clinical guideline for the acute stabilization and management of neonates with PPHN. Utilizing cross-disciplinary expertise and incorporating an extensive literature search to guide best practice, we present an approachable, pragmatic, and clinically relevant guide for the bedside management of acute PPHN. KEY POINTS: · PPHN is associated with several unique diagnoses; the associated pathophysiology is different for each unique diagnosis.. · PPHN is a challenging, dynamic, and labile process for which optimal care requires frequent reassessment.. · Key management goals are adequate tissue oxygen delivery, avoiding harm..

How to diagnose and treat acute pulmonary hypertension when you have no cardiology support

Acute pulmonary hypertension (aPH) is a complex, physiology-driven disorder that causes critical illness in newborns, the hallmark of which is elevated pressure in the pulmonary vascular bed. Several underlying hemodynamic phenotypes exist, including classic arterial aPH with resistance-driven elevations in pulmonary arterial pressure (PAP), alongside flow-driven aPH from left-to-right shunt lesions, and primary left ventricular dysfunction with pulmonary venous hypertension and elevated left atrial pressure. Targeted neonatal echocardiography (TnECHO) is an important tool for evaluation of hemodynamics in aPH and is highly useful for evaluating modulators of disease and targeting cardiovascular therapy. The diagnostic approach to aPH includes confirmation of elevation of PAP, evaluation of the cause and exclusion of structural cardiac disease, assessment of the response of the myocardium to adverse loading conditions, and appraisal of the adequacy of systemic blood flow. Therapeutic goals include support of right ventricular (RV) function, RV afterload reduction, and selection of cardiotropic agents that support underlying pathophysiology without adverse effects on heart rate or pulmonary vascular resistance in addition to routine supportive intensive care. Training programs for TnECHO exist across multiple jurisdictions and strong correlation with pediatric cardiology assessment has been demonstrated. Future directions include adapting TnECHO training with a greater focus on achieving competency, and further research into the role of the modality in providing individualized cardiovascular care for patients with heterogenous underlying physiology, and its effect on key neonatal outcomes.

Copeptin Release in Arterial Hypotension and Its Association with Severity of Disease in Critically Ill Children

Low copeptin levels may indicate inadequate arginine-vasopressin release promoting arterial hypotension, whereas high copeptin concentrations may reflect disease severity. This single-center prospective non-randomized clinical trial analyzed the course of blood copeptin in critically ill normo- and hypotensive children and its association with disease severity. In 164 patients (median age 0.5 years (interquartile range 0.1, 2.9)), the mean copeptin concentration at baseline was 43.5 pmol/L. Though not significantly different after 61 h (primary outcome, mean individual change: −12%, p = 0.36, paired t-test), we detected 1.47-fold higher copeptin concentrations during arterial hypotension when compared to normotension (mixed-effect ANOVA, p = 0.01). In total, 8 out of 34 patients (23.5%) with low copeptin concentrations <10 pmol/L were hypotensive. Copeptin was highest in the adjusted mixed-effect regression analysis within the first day (+20% at 14 h) and decreased significantly at 108 h (−27%) compared to baseline (p = 0.002). Moreover, we found a significant association with vasopressor-inotrope treatment intensity, infancy (1−12 months) and cardiopulmonary bypass (all p ≤ 0.001). In conclusion, high copeptin values were associated with arterial hypotension and severity of disease in critically ill children. This study does not support the hypothesis that low copeptin values might be indicative of arginine-vasopressin deficiency.

Cardiovascular management following hypoxic-ischemic encephalopathy in North America: need for physiologic consideration

BACKGROUND

Hypotension and hypoxemic respiratory failure are common among neonates with hypoxic-ischemic encephalopathy (HIE) undergoing therapeutic hypothermia (TH). Right ventricular (RV) dysfunction is associated with adverse neurodevelopment. Individualized management utilizing targeted neonatal echocardiography (TnECHO) may enhance care.

METHODS

We evaluated the influence of TnECHO programs on cardiovascular practices in HIE/TH patients utilizing a 77-item REDCap survey. Nominated representatives of TnECHO (n = 19) or non-TnECHO (n = 96) sites were approached.

RESULTS

Seventy-one (62%) sites responded. Baseline neonatal intensive care unit characteristics and HIE volume were comparable between groups. Most centers monitor invasive blood pressure; however, we identified 17 unique definitions of hypotension. TnECHO centers were likelier to trend systolic/diastolic blood pressure and request earlier echocardiography. TnECHO responders were less likely to use fluid boluses; TnECHO responders more commonly chose an inotrope first-line, while non-TnECHO centers used a vasopressor. For HRF, TnECHO centers chose vasopressors with a favorable pulmonary vascular profile. Non-TnECHO centers used more dopamine and more extracorporeal membrane oxygen for patients with HRF.

CONCLUSIONS

Cardiovascular practices in neonates with HIE differ between centers with and without TnECHO. Consensus regarding the definition of hypotension is lacking and dopamine use is common. The merits of these practices among these patients, who frequently have comorbid pulmonary hypertension and RV dysfunction, need prospective evaluation.

IMPACT

Cardiovascular care following HIE while undergoing therapeutic hypothermia varies between centers with access to trained hemodynamics specialists and those without. Because cardiovascular dysfunction is associated with brain injury, precision medicine-based care may be an avenue to improving outcomes. Therapeutic hypothermia has introduced new physiological considerations and enhanced survival. It is essential that hemodynamic strategies evolve to keep pace; however, little literature exists. Lack of consensus regarding fundamental definitions (e.g., hypotension) highlights the importance of collaboration among the scientific community to advance the field. The value of enhanced cardiovascular care guided by hemodynamic specialists requires prospective evaluation.

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.

Current Challenges in Neonatal Resuscitation: What is the Role of Adrenaline?

Adrenaline, also known as epinephrine, is a hormone, neurotransmitter, and medication. It is the best established drug in neonatal resuscitation, but only weak evidence supports current recommendations for its use. Furthermore, the available evidence is partly based on extrapolations from adult studies, and this introduces further uncertainty, especially when considering the unique physiological characteristics of newly born infants. The timing, dose, and route of administration of adrenaline are still debated, even though this medication has been used in neonatal resuscitation for a long time. According to the most recent Neonatal Resuscitation Guidelines from the American Heart Association, adrenaline use is indicated when the heart rate remains < 60 beats per minute despite the establishment of adequate ventilation with 100% oxygen and chest compressions. The aforementioned guidelines recommend intravenous administration (via an umbilical venous catheter) of adrenaline at a dose of 0.01-0.03 mg/kg (1:10,000 concentration). Endotracheal administration of a higher dose (0.05-0.1 mg/kg) may be considered while venous access is being obtained, even if supportive data for endotracheal adrenaline are lacking. The safety and efficacy of intraosseous administration of adrenaline remain to be investigated. This article reviews the evidence on the circulatory effects and tolerability of adrenaline in the newborn, discusses literature data on adrenaline use in neonatal cardiopulmonary resuscitation, and describes international recommendations and outcome data regarding the use of this medication during neonatal resuscitation.

Hypoxia inhibits adenylyl cyclase catalytic activity in a porcine model of persistent pulmonary hypertension of the newborn

Persistent pulmonary hypertension of the newborn (PPHN) features hypoxemia, pulmonary vasoconstriction, and impaired cardiac inotropy. We previously reported low basal and stimulated cAMP in hypoxic pulmonary artery smooth muscle cells (PASMCs). We now examine pulmonary arterial adenylyl cyclase (AC) activity and regulation in hypoxic PPHN. PPHN was induced in newborn swine by normobaric hypoxia (fraction of inspired oxygen 0.10) for 72 h and compared with age-matched normoxic controls. We studied relaxation of pulmonary arterial (PA) rings to AC activator forskolin and cGMP activator sodium nitroprusside (SNP) by isometric myography, ATP content, phosphodiesterase activity, AC content, isoform expression, and catalytic activity in presence or absence of Gαs-coupled receptor agonists, forskolin, or transnitrosylating agents in human and neonatal porcine PASMCs and HEK293T stably expressing AC isoform 6, after 72 h hypoxia (10% O₂) or normoxia (21% O₂). Relaxation to forskolin and SNP were equally impaired in PPHN PA. AC-specific activity decreased in hypoxia. PASMC from PPHN swine had reduced AC activity despite exposure to normoxia in culture; transient hypoxia in vitro further decreased AC activity. Prostacyclin receptor ligand affinity decreased, but its association with Gαs increased in hypoxia. Total AC content was unchanged by hypoxia, but AC6 increased in hypoxic cells and PPHN pulmonary arteries. Impairment of AC6 activity in hypoxia was associated with nitrosylation. PPHN PA relaxation is impaired because of loss of AC activity. Hypoxic AC is inhibited because of S-nitrosylation; inhibition persists after removal from hypoxia. Downregulation of AC-mediated relaxation in hypoxic PA has implications for utility of Gαs-coupled receptor agonists in PPHN treatment.

Controversies in the identification and management of acute pulmonary hypertension in preterm neonates

It is increasingly recognized that the abnormal physiologic consequences of pulmonary hypertension (PH) may contribute to poor cardiopulmonary health in premature babies. Conflicting literature has led to clinical uncertainty, pathological misinterpretation, and variability in treatment approaches among practitioners. There are several disorders with overlapping and interrelated presentations, and other disorders with a similar clinical phenotype but diverse pathophysiological contributors. In this review, we provide a diagnostic approach for acute hypoxemic respiratory failure in the preterm neonate, outline the pathophysiological conditions that may present as acute PH, and discuss the implications of high pulmonary vascular resistance (PVR) on the cardiovascular system. Although PVR and respiratory management are highly interrelated, there may be a population of preterm neonates in whom inhaled nitric oxide may improve illness severity and may relate to outcomes. A management approach based on physiology that considers common clinical conundrums is provided. A more comprehensive understanding of the physiology may help in informed decision-making in clinical situations where conclusive scientific evidence is lacking. Regardless, high-quality research is required, and appropriate definition of the target population is paramount. A thoughtful approach to cardiovascular therapy may also provide an avenue to improve neurodevelopmental outcomes while awaiting more clear answers.

Management of Shock in Neonates

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

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.

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.

What is the optimal dose of epinephrine during cardiopulmonary resuscitation in a rat model?

OBJECTIVE

Because different species may require different doses of drug to produce the same physiologic response, we were provoked to evaluate the dose-response of epinephrine during cardiopulmonary resuscitation (CPR) and identify what is the optimal dose of epinephrine in a rat cardiac arrest model.

METHODS

Rat cardiac arrest was induced via asphyxia, and then the effects of different doses of epinephrine (0.04, 0.2, and 0.4 mg/kg IV, respectively) and saline on the outcome of CPR were compared (n = 10/each group). The primary outcome measure was restoration of spontaneous circulation (ROSC), and the secondary was the change of spontaneous respiration and hemodynamics after ROSC.

RESULTS

Rates of ROSC were 9 of 10, 8 of 10, 7 of 10, and 1 of 10 in the low-dose, medium-dose, and high-dose epinephrine groups and saline group, respectively. The rates of withdrawal from the ventilator within 60 minutes in the low-dose (7 of 9) and medium-dose epinephrine groups (7 of 8) were higher than in the high-dose epinephrine group (1 of 7, P < .05). Mean arterial pressures were comparable, but the heart rate in the high-dose epinephrine group was the lowest among epinephrine groups after ROSC. These differences in part of time points reached statistical significance (P < .05).

CONCLUSION

Different doses of epinephrine produced the similar rate of ROSC, but high-dose epinephrine inhibited the recovery of spontaneous ventilation and caused relative bradycardia after CPR in an asphyxial rat model. Therefore, low and medium doses of epinephrine were more optimal for CPR in a rat asphyxial cardiac arrest model.

Arginine vasopressin to manage hypoxemic infants after stage I palliation of single ventricle lesions

OBJECTIVE

Management of patients with single ventricle physiology following stage I palliation procedures is often challenging, with optimization of the ratio of pulmonary-to-systemic blood flow as an important goal. Persistent hypoxemia may be a manifestation of elevated pulmonary vascular resistance and therefore decreased blood flow to the lungs. In such situations, the use of arginine vasopressin to increase systemic vascular resistance may be an effective strategy to improve pulmonary blood flow and maintain adequate pulmonary-to-systemic blood flow ratio. We describe three infants in whom persistent hypoxemia improved after institution of arginine vasopressin.

DESIGN

Retrospective chart review.

SETTING

Twenty-four bed medical-surgical pediatric intensive care unit at a large tertiary care academic hospital.

PATIENTS

Three neonates with single ventricle physiology who received arginine vasopressin in the setting of hypoxemia following stage I palliation.

RESULTS

Arginine vasopressin was initiated in all three patients for hypoxemia with a goal to increase systemic vascular resistance and generate a higher driving pressure for pulmonary blood flow. Twelve hours after arginine vasopressin initiation, systemic arterial saturation as determined by pulse oximetry and blood pressure increased, whereas heart rate, inotrope score, and Fio2 decreased in all three patients. Urine output was maintained and arterial lactate decreased during this time. Pulmonary-to-systemic flow ratio increased in one patient in whom it could be determined.

CONCLUSION

In patients with single ventricle physiology and persistent hypoxemia following stage I palliation, administration of arginine vasopressin could improve oxygenation possibly by increasing systemic vascular resistance and therefore the pulmonary blood flow.

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.

Systemic and regional hemodynamic effects of high-dose epinephrine infusion in hypoxic piglets resuscitated with 100% oxygen

Shock and poor regional perfusion are common in asphyxiated neonates. We compared the systemic and regional hemodynamic effects of high-dose epinephrine (E) with those of dopamine combined with low-dose epinephrine (DE) infusions in a neonatal model of hypoxia-reoxygenation. Neonatal piglets (1-3 days, 1.5-2.5 kg) were acutely instrumented to continuously monitor systemic arterial pressure (SAP), pulmonary artery pressure, cardiac index (CI), and blood flows at the left common carotid, superior mesenteric, and renal arteries. Either epinephrine (1 microg.kg(-1).min(-1)) or dopamine (10 microg.kg(-1).min(-1)) and epinephrine (0.2 microg.kg(-1).min(-1)) were given for 2 h in hypoxic piglets resuscitated with 100% oxygen (n = 8 per group) in a randomized blinded fashion. Control piglets received hypoxia and reoxygenation but no catecholamine infusion (n = 7). Alveolar hypoxia (PaO2, 33-37 mmHg) caused reduced CI (89-92 vs. 171-186 mL.kg(-1).min(-1) of baseline, P < 0.05), hypotension (SAP, 28-32 mmHg) with pH 7.05 to 7.10, and decreased regional flows. Upon reoxygenation, CI and SAP improved but gradually deteriorated to 131 to 136 mL.kg(-1).min(-1) and 41 to 49 mmHg at 2 h of reoxygenation, respectively. E and DE administration similarly improved CI (167 +/- 60 and 166 +/- 55 vs. 121 +/- 35 mL.kg(-1).min(-1) of controls) and SAP (53 +/- 7 and 56 +/- 10 vs. 39 +/- 8 mmHg of controls), respectively, and the pulmonary vascular resistance (vs. controls, all P < 0.05). Heart rate and pulmonary artery pressure were not different between groups. Systemic oxygen delivery and consumption were increased in E- and DE-treated groups with no difference in extraction ratio between groups. There were no differences in regional blood flows and oxygen delivery between groups. After hyperlactatemia with hypoxia, plasma lactate levels decreased with no difference between groups. Epinephrine given as the sole agent is as effective as dopamine and low-dose epinephrine combined in treating shock and hypotension that follow the resuscitation of hypoxic neonatal piglets, with no reduction in regional perfusion.

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.

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.

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.

EFFECTS OF DOPAMINE AND NOREPINEPHRINE ON SYSTEMIC AND HEPATOSPLANCHNIC HEMODYNAMICS, OXYGEN EXCHANGE, AND ENERGY BALANCE IN VASOPLEGIC SEPTIC PATIENTS

Dopamine is widely used to improve systemic and hepatosplanchnic hemodynamics and oxygenation during sepsis. However, some studies have suggest that norepinephrine may have beneficial effects on regional blood flow and metabolism, whereas dopamine might have deleterious effects related to redistribution of blood flow away from the intestinal mucosa or by decreasing directly the cell redox state. In 12 vasoplegic septic patients, we compared the effects of norepinephrine and dopamine on systemic and hepatosplanchnic hemodynamics, oxygenation, and energy metabolism. Catecholamines were administered in a crossover randomized order to maintain mean arterial pressure (MAP) at 80 mmHg. Hepatosplanchnic blood flow (Qspl) was determined using a continuous infusion of indocyanine green dye. Despite a similar MAP, the cardiac index was higher with dopamine than with norepinephrine (6.3 [5.3-7.3] vs. 4.3 [3.8-4.9] L.min.m) (P <0.001). Qspl was similar with both catecholamines, but the ratio of Qspl to cardiac output was significantly lower with dopamine (23.9% [17.5-33.5]) than with norepinephrine (33.5% [25.8-37]) (P <0.05). Although global O2 delivery and O2 consumption were higher with dopamine (782 [707-859] vs. 553 [512-629] mL.min.m, P <0.001 and 164 [134-192] vs. 128 [111-149] mL.min.m, P <0.001, respectively), hepatosplanchnic O2 delivery and consumption were not different. Hepatic lactate uptake was lower (0.47 [0.3-0.89] vs. 1.01 [0.69-1.34] mmol.min) (P <0.01), and hepatic venous lactate-to-pyruvate ratio was higher (15.3 [7.6-21.1] vs. 11.2 [6.6-15.1], P <0.05) with dopamine than with norepinephrine. In vasoplegic septic patients, maintaining mean arterial pressure, hepatosplanchnic hemodynamics, and oxygen exchange with dopamine requires a consequent increased cardiac output, which is responsible for an increased global oxygen demand when compared with norepinephrine. In addition, dopamine impairs the hepatic energy balance. Its position as a preferential treatment compared with norepinephrine in this context may therefore be questionable.

Dopamine under α1-blockade, but not dopamine alone or fenoldopam, increases depressed gastric mucosal oxygenation*

OBJECTIVE

To compare the effects of dopamine, both in the presence and absence of alpha1-blockade, and fenoldopam on microvascular gastric mucosal oxygenation and systemic oxygen transport under compromised circulatory conditions, both without and with fluid resuscitation.

DESIGN

Randomized controlled animal study.

SETTING

University department of anesthesiology.

SUBJECTS

Eight anesthetized dogs with chronically implanted ultrasound flow probes around the pulmonary artery for continuous measurement of cardiac output.

INTERVENTIONS

On different days, the dogs received in random order either dopamine (2.5 and 5.0 microg.kg(-1).min(-1), with or without alpha1-blocker pretreatment), the selective DA1-agonist fenoldopam (0.1 and 1.0 microg.kg(-1).min(-1), with and without DA1-blocker pretreatment), or saline (control). These interventions were performed under compromised cardiocirculatory conditions (induced by ventilation with positive end-expiratory pressure [PEEP] of 10 cm H2O), both without and with fluid resuscitation.

MEASUREMENTS AND MAIN RESULTS

We continuously measured regional microvascular hemoglobin saturation (microHbO2) in gastric mucosa by reflectance spectrophotometry and systemic oxygen transport ([U1E0A]O2). Ventilation with PEEP significantly decreased [U1E0A]O2 (from 19 +/- 2 to 9 +/- 1 mL.kg(-1).min(-1), mean +/- sem) and gastric mucosal microHbO2 (from 57 +/- 2% to 37 +/- 3%). Fluid resuscitation restored [U1E0A]O2 back to baseline (from 9 +/- 1 to 19 +/- 2 mL.kg(-1).min(-1)) but only partially restored microHbO2 (from 37 +/- 3% to 50 +/- 4%). Under both conditions, dopamine with and without alpha1-blockade significantly increased [U1E0A]O2 (by about 5 mL.kg-1.min-1 in the nonresuscitated state and 10 mL.kg-1.min-1 in the fluid resuscitated state, respectively), but only dopamine in the presence of alpha1-blockade also significantly increased gastric mucosal microHbO2 (by 5 +/- 1% and 7 +/- 2% in the nonresuscitated and fluid resuscitated states, respectively). Fenoldopam under all study conditions did not significantly affect [U1E0A]O2 or microHbO2, either in the presence or absence of DA1-blockade.

CONCLUSIONS

During compromised cardiocirculatory conditions, alpha1-receptor activation during dopamine infusion prevented an increase in gastric mucosal oxygenation. Furthermore, selective DA1-stimulation (by fenoldopam) was insufficient to overcome the PEEP-induced depression of microHbO2. The responses of gastric mucosal oxygenation did not parallel changes in systemic oxygen transport. These findings were independent of fluid resuscitation.

Adrenaline for prevention of morbidity and mortality in preterm infants with cardiovascular compromise

BACKGROUND

Inotropes are widely used in preterm infants to treat cardiovascular compromise, which may result from early adaptive problems of the transitional circulation, perinatal asphyxia or sepsis. Sustained hypotension and poor organ blood flow are associated with brain injury including peri/intraventricular haemorrhage and subsequent poor neurodevelopmental outcomes. Adrenaline (epinephrine) infusions are used in preterm infants with clinical cardiovascular compromise.

OBJECTIVES

To determine the effectiveness and safety of adrenaline compared to no treatment or other inotropes in reducing mortality and morbidity in preterm infants with cardiovascular compromise.

SEARCH STRATEGY

Randomised controlled trials were identified by searching MEDLINE (1966-August 2003), The Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 3, 2003) and EMBASE (1980 - 2003), supplemented with searches of reference lists of published trials and abstracts of conference proceedings.

SELECTION CRITERIA

Randomised controlled trials of preterm newborn infants that compared adrenaline to no treatment or other inotropic agents (including dopamine, dobutamine, noradrenaline or isoprenaline).

DATA COLLECTION AND ANALYSIS

Data were extracted and analysed independently by two reviewers. Treatment effects on the following outcomes were to be determined: mortality in the newborn period, long term neurodevelopmental outcomes, radiological evidence of brain injury, short term haemodynamic changes, adverse drug effects and short term neonatal outcomes. Study authors were contacted for additional information. Studies were analysed for methodological quality using the criteria of the Cochrane Neonatal Review Group.

MAIN RESULTS

One ongoing study (Pellicer 2003) was identified. One study comparing adrenaline with dopamine infusion was included but was published in abstract form only (Phillipos 1996). It enrolled hypotensive, predominantly preterm infants in the first 24 hours. Only infants >1750g are included in this review (report for infants <=1750g appears incomplete). The study was reported as being randomised and double blinded, but methods were not reported. Both adrenaline and dopamine significantly increased heart rate and mean BP, with no statistically significant effect on left or right ventricular outputs. No other clinical outcomes were reported. No studies were identified that compared adrenaline to other inotropes, placebo or no treatment.

REVIEWER'S CONCLUSIONS

There are insufficient data on the use of adrenaline infusions in preterm infants with cardiovascular compromise to make recommendations for practice. There is a need for larger trials to determine whether adrenaline is effective in reducing morbidity and mortality in preterm infants with cardiovascular compromise.

Fenoldopam--but not dopamine--selectively increases gastric mucosal oxygenation in dogs

OBJECTIVE

To compare the effects of fenoldopam and dopamine on gastric mucosal and systemic oxygenation, and to identify the receptors involved.

DESIGN

Randomized controlled animal study.

SETTING

University research department of experimental anesthesiology. SUBJECTS Seven anesthetized dogs with chronically implanted ultrasound flow probes around the pulmonary artery for continuous measurement of cardiac output.

INTERVENTIONS

On different days, the dogs received in random order either the selective DA(1)-agonist fenoldopam (0.1 and 1.0 microg x kg-1.= x min-1, with or without DA(1)-blocker pretreatment), dopamine (2.5 and 5.0 microg.kg-1 x min-1, with or without alpha(1)-blocker pretreatment), or saline (control).

MEASUREMENTS AND MAIN RESULTS

We continuously measured regional microvascular hemoglobin oxygen saturation (muHbO(2)) in gastric mucosa by reflectance spectrophotometry, and systemic oxygen delivery. Fenoldopam increased gastric mucosal muHbO(2) by approximately 20%, and this effect was prevented by selective DA(1)-receptor blockade. In contrast, dopamine neither alone nor during alpha(1)-blockade altered muHbO(2). With respect to systemic measures of oxygen transport, fenoldopam had negligible effects, whereas dopamine (with and without alpha(1)-blocker pretreatment) dose-dependently increased cardiac output and systemic oxygen delivery by approximately 30%.

CONCLUSIONS

Fenoldopam dose-dependently increased microvascular oxygenation of the gastric mucosa without changing systemic oxygen transport, i.e., this drug acted selectively on the splanchnic mucosa. The increase in gastric mucosal oxygenation was mediated by DA(1)-receptors. In contrast, dopamine markedly increased systemic oxygen transport, but did not affect microvascular oxygenation of gastric mucosa. This lacking effect on gastric mucosal oxygenation was not caused by alpha(1)-mediated vasoconstriction. The regional effects of both catecholamines could not be deduced from systemic hemodynamics and oxygenation.

Effects of dopamine on systemic and regional blood flow and metabolism in septic and cardiac surgery patients

Dopamine is used in the clinical setting to support cardiac output and blood pressure and to improve diuresis. Experimental studies suggest that dopamine may reduce splanchnic perfusion and redistribute blood flow locally. To assess the effects of dopamine on splanchnic perfusion, we used dopamine to increase cardiac output by 25% in nine septic patients and 11 patients after cardiac surgery. Systemic (pulmonary artery catheter) and splanchnic (hepatic vein catheter and dye dilution) hemodynamics and oxygen transport were measured at baseline and 90 min after increasing the cardiac output. Dopamine infusion [in cardiac surgery patients 4.2 (1.4-8.5) microg x kg(-1) x min(-1) (median, range) and in septic patients 4.0 (2.1-9.0) microg x kg(-1) x min(-1)] increased splanchnic blood flow in cardiac surgery patients from 0.61 (0.13) L x min(-1) x m(-2) to 0.82 (0.13) L x min(-1) x m(-2) [mean (standard deviation; SD); P = 0.018] and in septic patients from 0.91 (0.32) L x min(-1) x m(-2) to 1.12 (0.40) L x min(-1) x m(-2) (P = 0.038). Splanchnic oxygen consumption increased in cardiac surgery patients from 39 (5) mL x min(-1) x m(-2) to 46 (6) mL x min(-1) x m(-2) (P = 0.003) but decreased in septic patients from 61 (19) mL x min(-1) x m(-2) to 51 (17) L x min(-1) x m(-2) (p = 0.021). Because of the unexpected results, we compared these data post hoc with data obtained from another group of 15 septic patients with acute lung injury, where dobutamine was used to increase cardiac output in a similar design. Dobutamine in these patients [6.4 (4.2-9.5) microg x kg(-1) x min(-1)] increased splanchnic blood flow from 1.20 (0.44) L x min(-1) x m(-2) to 1.43 (0.57) L x min(-1) x m(-2) (P = 0.008), while splanchnic oxygen consumption did not change 72 (25) mL x min(-1) x m(-2) vs. 76 (22) mL x min(-1) x m(-2) (not significant)]. The reduction of splanchnic oxygen consumption by dopamine in sepsis suggests an impairment of hepatosplanchnic metabolism despite an increase in regional perfusion. The safety and indications of dopamine use in sepsis should be re-evaluated.

Dopexamine but not dopamine increases gastric mucosal oxygenation during mechanical ventilation in dogs

OBJECTIVE

To compare the effects of dopamine and dopexamine on gastric mucosal oxygenation during mechanical ventilation without and with positive end-expiratory airway pressure (PEEP) and after compensation of the PEEP-induced hemodynamic suppression.

DESIGN

Randomized controlled animal study.

SETTING

University research department of experimental anesthesiology.

SUBJECTS

Ten anesthetized dogs with chronically implanted ultrasound flow probes around the pulmonary artery for continuous measurement of cardiac output.

INTERVENTIONS

On different days, the dogs randomly received dopamine (2.5 and 5.0 microg x kg(-1) x min(-1), n = 10), dopexamine (0.5 and 1.0 microg x kg(-1) x min(-1)) without (n = 8) or with pretreatment with a selective beta2-adrenoceptor antagonist (ICI 118,551, n = 7), or saline (control, n = 7). To simulate common clinical situations, these interventions were performed during different ventilation modes: during mechanical ventilation without and with high levels of PEEP, and after compensation of the PEEP-induced systemic hemodynamic suppression by titrated volume resuscitation with hydroxyethyl starch.

MEASUREMENTS AND MAIN RESULTS

We continuously measured microvascular hemoglobin saturation (mu-Hbo2) by light-guide spectrophotometry in the gastric mucosa. Dopexamine, but not dopamine, significantly increased gastric mucosal mu-Hbo2 by about 20%, regardless of the dose and the ventilation mode. Both catecholamines dose-dependently increased cardiac output and oxygen delivery by up to 75% without effects on systemic oxygen saturation. The effects of dopexamine on mu-Hbo2 as well as on cardiac output and oxygen delivery were prevented by selective beta2-adrenoceptor-blockade.

CONCLUSIONS

Dopexamine but not dopamine improved gastric mucosal oxygenation in dogs. This effect was independent of the dosage and the ventilation mode. Thus, dopexamine may reverse a decrease in splanchnic oxygenation induced by ventilation with PEEP. The dopexamine-induced increase in gastric mucosal oxygenation was mediated by beta2-adrenoceptors, which explains the superior effects of dopexamine to dopamine on mu-Hbo2. The regional effects of both catecholamines were not mirrored by systemic hemodynamics.

Effects of catecholamines on the pulmonary circulation in the ovine fetus

High levels of circulating catecholamines are found in the fetus, and fetal stress and birth induce a marked surge in catecholamine secretion. Little is known about the role of catecholamines on the fetal pulmonary circulation. To determine the effects of catecholamines on the pulmonary vascular tone, we tested the hemodynamic response to norepinephrine and dopamine infusion in chronically prepared late-gestation fetal lambs. We found that norepinephrine infusion (0.5 microg. kg(-1). min(-1)) increased pulmonary artery pressure (PAP) by 10 +/- 1% (P < 0.01), left pulmonary artery blood flow by 73 +/- 14% (P < 0.01), and decreased pulmonary vascular resistance (PVR) by 33 +/- 6% (P < 0.01). The pulmonary vasodilator effect of norepinephrine was abolished after nitric oxide synthase inhibition. Dopamine infusion at 5 microg. kg(-1). min(-1) did not significantly change PVR. Conversely, dopamine infusion at 10 microg. kg(-1). min(-1) increased PAP (P < 0.01) and progressively increased PVR by 30 +/- 14% (P < 0.01). These results indicate that catecholamines may modulate basal pulmonary vascular tone in the ovine fetus. We speculate that catecholamines may play a significant role in the maintenance of the fetal pulmonary circulation and in mediating changes in the transitional pulmonary circulation.

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.

Age-dependent metabolic effects of repeated hypoxemia in piglets

The aim of this study was to determine whether repeated exposure to hypoxemia would modify the response to hypoxemia during maturation. We exposed piglets to three 1-h cycles of hypoxemia (PaO2 = 30 to 35 mmHg; 1 mmHg = 133.3 Pa) at 1 week (n = 9), 2-3 weeks (n = 10), and 4-5 weeks of age (n = 10). O2 consumption (VO2) and CO2 production (VCO2) were measured, and alveolar ventilation (VA) was derived from VCO2 and PaCO2. Levels of lactic acid (lactate) and serum catecholamines were also measured. With hypoxemia, time had a significant effect on VO2 and body temperature in an age-dependent fashion: that is, whereas the 1 week group and the 4-5 week group showed both variables decreasing over time, the 2-3 week group showed no drop in VO2 and a small increase in body temperature over time. Lactate levels increased with hypoxemia in all animals during the first exposure. However, with repeated exposures to hypoxemia, only the 2-3 week group continued to increase its lactate levels. Furthermore, the changes in lactate levels paralleled the changes in epinephrine levels with hypoxemia. We found, too, that although VA increased significantly with hypoxemia in all animals, this change was not modified by age or repeated exposures. No significant effects of age or repeated exposures were found in the cardiovascular response to hypoxemia. We concluded that, from a metabolic viewpoint, after repeated exposures to hypoxemia the 2-3 week animals responded differently.Key words: metabolic rate, lactic acid, maturation, catecholamines.

Tonometry to estimate intestinal perfusion in newborn piglets

AIM

To determine the correlation between gastric intramucosal pH and superior mesenteric artery (SMA) flow in newborn piglets.

METHODS

Fourteen newborn piglets were randomly assigned to either a control or to an epinephrine group which received 0,1,2,4,0 microg/kg/min of epinephrine for 60 minutes, each dose. Gastric tonometry was performed, SMA flow was measured, and intramucosal pH and the ratio of tonometer pCO(2) over arterial pCO(2) (rCO(2)) were calculated.

RESULTS

Intramucosal pH decreased over time in both groups, but tended to be lower in the epinephrine group. With increasing dose of epinephrine, SMA flow decreased; this in turn increased rCO(2) (p = 0.04) with a tendency to decrease intramucosal pH (p = 0.06).

CONCLUSIONS

Gastric tonometry may be useful in human neonates to evaluate gut ischaemia.

Regional hemodynamic effects of dopamine in the sick preterm neonate

OBJECTIVE

To study the effects of dopamine on renal, mesenteric, and cerebral blood flow in sick preterm neonates.

STUDY DESIGN

The pulsatility index was used to assess the dopamine-induced changes in renal, mesenteric, and cerebral blood flow by means of color Doppler ultrasonography in 23 nonhypotensive preterm neonates (birth weight: 981 +/- 314 g; postnatal age: <2 days). Dopamine was given at a dose of 6.1 +/- 3.0 microgram/kg per minute to combat oliguria, impaired peripheral perfusion, or both. Blood flow velocity measurements were made before and during dopamine administration, with each patient serving as his or her own control subject.

RESULTS

Dopamine significantly increased blood pressure and urine output. Dopamine decreased the pulsatility index in the renal artery (2.98 +/- 1.18 vs 1.68 +/- 0.45; P <.05) while the pulsatility index in the superior mesenteric and medial cerebral artery was not affected. Thus renal blood flow increased while mesenteric and cerebral blood flow remained unchanged during dopamine treatment. The increase in renal blood flow was independent of the blood pressure changes.

CONCLUSIONS

These findings suggest a functionally mature renal, but not mesenteric, vasodilatory dopaminergic response in the preterm neonate. The observations also indicate the lack of an effect of low- to medium-dose dopamine on cerebral hemodynamics in the nonhypotensive preterm neonate.

Effects of vasoactive drugs on gastric intramucosal pH

OBJECTIVE

To review current knowledge about the effects of vasoactive agents on gastric intramucosal pH (pHi).

DATA SOURCES

All studies involving pHi and vasoactive agents were retrieved from a computerized MEDLINE search from 1980 to 1997. We also reviewed the reference lists of all available review articles and primary studies to identify references not found in the computerized searches.

STUDY SELECTION

Clinical and experimental studies using dopamine, dopexamine, dobutamine, norepinephrine, epinephrine, nitric oxide, N-acetylcysteine, prostaglandins, or pentoxifylline were considered if splanchnic perfusion and/or pHi measurements were utilized.

DATA EXTRACTION

From the selected studies, information was obtained regarding patient population, dosing regimen, duration of study, and effects on splanchnic blood flow (SBF), splanchnic oxygenation, and pHi.

DATA SYNTHESIS

Although dopaminergic effects increase SBF, dopamine does not generally increase pHi. Data on the effects of dopexamine on pHi are scarce and inconsistent. Dobutamine can significantly increase SBF and usually increases pHi. In septic patients, norepinephrine seems to increase pHi. Epinephrine may have detrimental effects on gastric perfusion. Prostacyclin seems to increase pHi but data are limited. Insufficient evidence exists to support the beneficial effects of nitric oxide donors or blockers, pentoxifylline, or N-acetylcysteine on pHi.

CONCLUSIONS

Overall, the effects of vasoactive agents on pHi are unpredictable. Among the catecholamines, dopamine is the least likely, and dobutamine the most likely, to increase pHi.

Perioperative management of patients with impaired left ventricular function

The development of acute perioperative left ventricular failure leading to haemodynamic catastrophe has several reasons. The management of left ventricular dysfunction requires a step-by-step therapeutic approach. Extensive haemodynamic monitoring is fundamental to distinguish between the need for positive inotropes, lowering pre- or afterload or increasing perfusion pressure by vasopressors. Catecholamines are still the cornerstone for treating acute left ventricular dysfunction. Whether synthetic, costly catecholamines offer any advantage over 'natural', low-priced catecholamines has not yet been definitely determined. Optimizing ventricular loading by vasoactive substances will help to improve overall myocardial performance. Knowledge of pre-existing cardiac disease and of haemodynamic principles are prerequisites for selecting an appropriate therapeutic regime. This appears to be more important for successfully treating acute perioperative myocardial failure than waiting for a new 'magic' substance.