Normocapnic Alveolar Hypoxia Research Articles

Electrocardiography vs. Auscultation to Assess Heart Rate During Cardiac Arrest With Pulseless Electrical Activity in Newborn Infants.

Background: In 2015, the neonatal resuscitation guidelines incorporated the use of electrocardiography (ECG) to monitor heart rate of newborns. However, previous studies have indicated that cardiac arrest with pulseless electrical activity rhythm (PEA) may occur in the delivery room, rendering this method problematic.Objective: To evaluate the accuracy of ECG and auscultation to assess heart rate during PEA.Methods: A total of 45 piglets (age 1–3 days, weight 1.7–2.3 kg) were exposed to 30 min normocapnic alveolar hypoxia followed by asphyxia until asystole, achieved by disconnecting the ventilator and clamping the endotracheal tube. During asphyxia, heart rate (HR) was assess using auscultation, ECG, and carotid blood flow (CBF). At the time of asystole (defined as zero CBF) HR auscultated using a neonatal/infant stethoscope was compared to ECG traces.Results: The median (IQR) duration of asphyxia was 325 (200–491) s. In 8 (18%) piglets, CBF, ECG, and auscultation identified asystole. In 22 (49%) piglets no CBF and no audible heart sounds, were observed, while ECG displayed a HR ranging from 17 to 75/min. Fifteen (33%) piglets remained bradycardic (defined as HR of < 100/min) after 10 min of asphyxia, which was identified by CBF, ECG, and auscultation. The overall accuracy of ECG and auscultation in the detection of HR were 51 and 80%, respectively (p = 0.004).Conclusion: In cases with PEA ECG is not superior in correctly identifying HR in newborn piglets.

Pulseless electrical activity: a misdiagnosed entity during asphyxia in newborn infants?

BackgroundThe 2015 neonatal resuscitation guidelines added ECG as a recommended method of assessment of an infant’s heart rate (HR) when determining the need for resuscitation at birth. However, a recent...

Postresuscitation Administration of Doxycycline Preserves Cardiac Contractile Function in Hypoxia-Reoxygenation Injury of Newborn Piglets*

Cardiac injury is common in asphyxiated neonates and is associated with matrix metalloproteinase-2 activation. Although studies have demonstrated the cardioprotective effects of matrix metalloproteinase inhibition, this has not been tested in clinically translatable models of hypoxia-reoxygenation injury. We aimed to elucidate the effect of doxycycline, a matrix metalloproteinase inhibitor, on cardiac injury and functional recovery in a swine model of neonatal hypoxia-reoxygenation. Thirty-three newborn piglets were acutely instrumented for continuous monitoring of cardiac output and systemic arterial pressure. After stabilization, normocapnic alveolar hypoxia (10-15% oxygen) was instituted for 2 hours followed by 4 hours of normoxic reoxygenation. Piglets were blindly, block randomized to receive IV boluses of normal saline (control) and doxycycline at 5 minutes of reoxygenation (n = 7/group). Sham-operated piglets (n = 5) received no hypoxia-reoxygenation. Markers of myocardial injury (plasma and myocardial tissue troponin I; myocardial lactate) and oxidative stress (lipid hydroperoxides) were measured by enzyme-linked immunosorbent assay and Western blot. Myocardial matrix metalloproteinase-2 activity was quantified by gelatin zymography and immunoprecipitation. University animal laboratory. Piglets (1-4 d old, weighing 1.4-2.5 kg). IV doxycycline (3, 10, or 30 mg/kg) given during resuscitation. Hypoxic piglets had cardiogenic shock (cardiac output 58% ± 1% of baseline), hypotension (systemic arterial pressure 31 ± 1 mm Hg), and acidosis (pH 7.02 ± 0.02). Doxycycline improved cardiac and stroke volume index with no chronotropic effect in doxycycline-treated piglets compared with controls. Systemic arterial pressure was higher and the pulmonary artery pressure/systemic arterial pressure ratio was lower in doxycycline groups, with reduced levels of markers of myocardial injury and oxidative stress in doxycycline-treated piglets compared with controls. Negative correlations were found between markers of myocardial injury (plasma troponin I, myocardial lactate) and functional recovery and between myocardial tissue and plasma troponin I. Doxycycline-treated piglets had lower myocardial matrix metalloproteinase-2 activity compared with controls. Postresuscitation administration of doxycycline attenuates cardiac injury and improves functional recovery in newborn piglets with hypoxia-reoxygenation.

Effects of post-resuscitation administration with sodium hydrosulfide on cardiac recovery in hypoxia-reoxygenated newborn piglets

Hydrogen sulfide may protect multiple organ systems against ischemic–reperfusion injuries. It is unknown if treatment with sodium hydrosulfide (NaHS, a hydrogen sulfide donor) will improve myocardial function and minimize oxidative stress in hypoxic-reoxygenated newborn piglets. Mixed breed piglets (1–5 day, 1.5–2.5kg) were anesthetized and acutely instrumented for the measurement of systemic, pulmonary and regional (carotid, superior mesenteric and renal) hemodynamics and blood gas parameters. The piglets were induced with normocapnic alveolar hypoxia (10–15% oxygen, 2h) followed by reoxygenation with 100% (1h) then 21% oxygen (3h). At 10min of reoxygenation, either NaHS (10mg/kg, 5ml) or saline (5ml) was administered intravenously for 30min (5min bolus followed by 25min of continuous infusion) in a blinded, block-randomized fashion (n=7/group). Plasma lactate and troponin I levels and tissue markers of myocardial oxidative stress were also determined. Two hours hypoxia caused cardiogenic shock (45±3% of respective normoxic baseline), reduced regional perfusion with metabolic acidosis (pH 6.94±0.02). NaHS infusion significantly improved recovery of cardiac index (84±3% vs. 72±5% in controls), systemic oxygen delivery (84±3% vs. 72±5% in controls) and systemic oxygen consumption (102±5% vs. 84±6% in controls) at 4h of reoxygenation. NaHS had no significant effect on systemic and pulmonary blood pressures, regional blood flows, plasma lactate and troponin I levels. The myocardial glutathionine ratio was reduced in piglets treated with NaHS (vs. controls, P<0.05). Post-resuscitation administration of NaHS improves cardiac function and systemic perfusion and attenuates myocardial oxidative stress in newborn piglets following hypoxia-reoxygenation.

Postresuscitation Cyclosporine Treatment Attenuates Myocardial and Cardiac Mitochondrial Injury in Newborn Piglets with Asphyxia-Reoxygenation*

Cardiovascular dysfunction occurs in the majority of asphyxiated neonates and has been suggested to be a major cause of neonatal morbidity and mortality. We previously demonstrated that cyclosporine A treatment during resuscitation can significantly improve cardiovascular performance in asphyxiated newborn piglets. However, the mechanisms through which cyclosporine elicits its protective effect in neonates have not yet been fully characterized. We hypothesized that cyclosporine A treatment would attenuate myocardial and cardiac mitochondrial injury during the resuscitation of asphyxiated newborn piglets. After acute instrumentation, piglets received normocapnic alveolar hypoxia (10% to 15% oxygen) for 2 hours followed by reoxygenation with 100% oxygen (0.5 hr) and then 21% oxygen (3.5 hr). At 4 hours of reoxygenation, plasma troponin level, left ventricle myocardial levels of lipid hydroperoxides, cytochrome-c, and mitochondrial aconitase activity were determined. Neonatal asphyxia and reoxygenation. Twenty-four newborn (1-4 days old) piglets. Piglets were randomized to receive an IV bolus of cyclosporine A (10 mg/kg) or normal saline (placebo, control) at 5 minutes of reoxygenation (n=8/group). Sham-operated piglets (n=8) underwent no asphyxia-reoxygenation. Asphyxiated piglets treated with cyclosporine had lower plasma troponin and myocardial lipid hydroperoxides levels (vs. controls, both p<0.05, analysis of variance). Cyclosporine treatment also improved mitochondrial aconitase activity and attenuated the rise in cytosol cytochrome-c level (vs. controls, all p<0.05). The improved mitochondrial function significantly correlated with cardiac output (p<0.05, Spearman rank-correlation test). We demonstrate that the postresuscitation administration of cyclosporine attenuates myocardial and cardiac mitochondrial injury in asphyxiated newborn piglets following resuscitation.

Pharmacokinetic Characterization of Intravenous Cyclosporine Treatment for Cardioprotection During Resuscitation of Asphyxiated Newborn Piglets

Cyclosporine treatment, as a single intravenous bolus, during resuscitation has been shown to attenuate myocardial injury in asphyxiated newborn piglets. However, the pharmacokinetics of cyclosporine treatment for cardioprotection in newborns has not been studied. We aimed to assess the pharmacokinetics of a single intravenous cyclosporine treatment during resuscitation of asphyxiated newborn piglets and compare these parameters with healthy newborn piglets. Newborn piglets were acutely instrumented and normocapnic alveolar hypoxia was induced for 2 hours followed by 4 hours of reoxygenation. Piglets were block-randomized to receive a single intravenous bolus of cyclosporine (2.5-25 mg/kg) (n = 8 per group). Eight piglets underwent no hypoxia-reoxygenation and received 10 mg/kg cyclosporine at the corresponding time point. Plasma cyclosporine and troponin concentrations during reoxygenation period were determined by high-pressure liquid chromatography and enzyme-linked immunosorbent assay, respectively. Noncompartmental methods were used to calculate the pharmacokinetic parameters. Cyclosporine concentrations and pharmacokinetic parameters were analyzed by one-way analysis of variance. University animal laboratory. Piglets (1-4 days old, weighing 1.4-2.5 kg). Intravenous cyclosporine (2.5, 10, or 25 mg/kg) given during resuscitation. In the hypoxic-reoxygenated piglets, the plasma AUC(0-4 hrs) and C(max) of cyclosporine at reoxygenation were in the following rank order: 25 > 10 > 2.5 mg/kg treatment (p < 0.001 between groups, analysis of variance). Plasma AUC(0-4 hrs) and C(max) in piglets treated with cyclosporine at 25 mg/kg was associated with increased plasma troponin levels, a marker of myocardial injury, relative to piglets treated with 2.5 and 10 mg/kg. Asphyxiated newborn piglets had higher clearance and lower AUC(0-∞), but similar AUC(0-4 hrs), steady-state volume of distribution, and mean residence time compared with those of healthy newborn piglets. This is the first study to demonstrate the pharmacokinetics of intravenous cyclosporine treatment during resuscitation of asphyxiated newborn piglets, which did not appear to different from that of healthy piglets.

316 Early Versus Delayed Cyclosporine Treatment in Cardiac Recovery and Intestinal Injury During Resuscitation of Asphyxiated Newborn Piglets

BackgroundRecently, we have demonstrated that treating asphyxiated newborn piglets with intravenous cyclosporine immediately following resuscitation can improve cardiac function. However, immediate treatment may not be feasible for a large portion...

317 The Cardio-Protective Effects of Doxycycline in a Swine Model of Neonatal Asphyxia

BackgroundMyocardial reoxygenation injury following asphyxia in neonates is common. Matrix metalloproteinase-2 activation is associated with myocardial ischemic-reperfusion injury and stunning. Previous in vitro, ex vivo, and small animal studies have...

320 The Regional Hemodynamic Effects of Doxycycline in Newborn Piglets with Asphyxia-Reoxygenation

BackgroundNeonatal asphyxia has significant morbidities including hypoxic-ischemic encephalopathy, necrotizing enterocolitis and acute renal failure. These complications are associated with regional perfusion deficits. During reoxygenation, oxygen free radicals are produced and...

Infusing Sodium Bicarbonate Suppresses Hydrogen Peroxide Accumulation and Superoxide Dismutase Activity in Hypoxic-Reoxygenated Newborn Piglets

BackgroundThe effectiveness of sodium bicarbonate (SB) has recently been questioned although it is often used to correct metabolic acidosis of neonates. The aim of the present study was to examine its effect on hemodynamic changes and hydrogen peroxide (H2O2) generation in the resuscitation of hypoxic newborn animals with severe acidosis.MethodsNewborn piglets were block-randomized into a sham-operated control group without hypoxia (n = 6) and two hypoxia-reoxygenation groups (2 h normocapnic alveolar hypoxia followed by 4 h room-air reoxygenation, n = 8/group). At 10 min after reoxygenation, piglets were given either i.v. SB (2 mEq/kg), or saline (hypoxia-reoxygenation controls) in a blinded, randomized fashion. Hemodynamic data and blood gas were collected at specific time points and cerebral cortical H2O2 production was continuously monitored throughout experimental period. Plasma superoxide dismutase and catalase and brain tissue glutathione, superoxide dismutase, catalase, nitrotyrosine and lactate levels were assayed.ResultsTwo hours of normocapnic alveolar hypoxia caused cardiogenic shock with metabolic acidosis (pH: 6.99±0.07, HCO3 −: 8.5±1.6 mmol/L). Upon resuscitation, systemic hemodynamics immediately recovered and then gradually deteriorated with normalization of acid-base imbalance over 4 h of reoxygenation. SB administration significantly enhanced the recovery of both pH and HCO3− recovery within the first hour of reoxygenation but did not cause any significant effect in the acid-base at 4 h of reoxygenation and the temporal hemodynamic changes. SB administration significantly suppressed the increase in H2O2 accumulation in the brain with inhibition of superoxide dismutase, but not catalase, activity during hypoxia-reoxygenation as compared to those of saline-treated controls.ConclusionsDespite enhancing the normalization of acid-base imbalance, SB administration during resuscitation did not provide any beneficial effects on hemodynamic recovery in asphyxiated newborn piglets. SB treatment also reduced the H2O2 accumulation in the cerebral cortex without significant effects on oxidative stress markers presumably by suppressing superoxide dismutase but not catalase activity.

Early versus delayed cyclosporine treatment in cardiac recovery and intestinal injury during resuscitation of asphyxiated newborn piglets

We previously demonstrated that treating asphyxiated newborn piglets with cyclosporine immediately following resuscitation can improve cardiac and intestinal recovery. However, immediate treatment may not be feasible for a large portion of neonates delivered in peripheral or rural hospitals. Therefore, our objective was to determine if delayed cyclosporine treatment remained effective in treating neonatal asphyxia. We hypothesized that early and delayed cyclosporine treatment would improve cardiac and intestinal recovery during resuscitation of asphyxiated newborn piglets. Thirty piglets (1-4 days old) were instrumented for continuous monitoring of cardiac output and mesenteric hemodynamics. After stabilization, normocapnic alveolar hypoxia (10-15 % oxygen) was instituted for 2 h followed by reoxygenation with 100 % oxygen for 0.5 h, then 21 % for 5.5 h. Piglets were block-randomized to receive either intravenous bolus of cyclosporine A (10 mg/kg) or normal saline (control) at 5 or 120 min of reoxygenation (early or delayed, respectively; n = 8/group). Myocardial and intestinal lactate concentrations as well as histological examinations were determined. Hypoxic piglets had cardiogenic shock (cardiac output 52 ± 1 % of baseline, mean arterial pressure 32 ± 1 mmHg) and acidosis (pH 6.98 ± 0.1). Although both cyclosporine treatments improved cardiac output (p < 0.05 vs. controls), only early cyclosporine treatment improved stroke volume and systemic oxygen delivery (p < 0.05 vs. controls). Left ventricle and intestinal lactate were lowered in both cyclosporine-treated groups (p < 0.05 vs. controls). Early, but not delayed, cyclosporine treatment also attenuated intestinal injury (p < 0.05 vs. controls). This study demonstrates that treating asphyxiated newborn piglets with cyclosporine within 2 h of resuscitation is effective with superior cardioprotection and intestinal injury attenuation with early treatment.

Cyclosporine treatment improves cardiac function and systemic hemodynamics during resuscitation in a newborn piglet model of asphyxia

Asphyxiated neonates often have myocardial depression, which is a significant cause of morbidity and mortality. Cardioprotective effects of cyclosporine have been observed in adult patients and animals with myocardial infarction. However, the cardioprotective effect of cyclosporine in neonates has not yet been studied. We hypothesize that cyclosporine will improve cardiac function and reduce myocardial injury in asphyxiated newborn piglets. Thirty-six piglets (1-4 days old, weighing 1.4-2.5 kg) were acutely instrumented for continuous monitoring of cardiac output and systemic arterial pressure. After stabilization, normocapnic alveolar hypoxia (10% to 15% oxygen) was instituted for 2 hrs followed by reoxygenation with 100% oxygen for 0.5 hrs and then 21% for 3.5 hrs. A nonasphyxiated, sham-operated group was included (n = 4) to control for effects of the surgical model. Plasma troponin and myocardial lactate concentrations were determined as well as morphologic examinations. Neonatal asphyxia and reoxygenation. Newborn (1-4 days old) piglets. Piglets were block-randomized to receive intravenous boluses of cyclosporine A (2.5, 10, or 25 mg/kg) or normal saline (control) at 5 mins of reoxygenation (n = 8/group). Cardiac index, heart rate, systemic oxygenation, plasma troponin, and left ventricular lactate were measured. Hypoxic piglets had cardiogenic shock (cardiac output 40% to 48% of baseline), hypotension (mean arterial pressure 27-31 mm Hg), and acidosis (pH 7.04). Cyclosporine treatment caused bell-shaped improvements in cardiac output, stroke volume, and systemic oxygen delivery (p < .05 vs. controls). Plasma troponin and left ventricle lactate were higher in controls than that of 2.5 and 10 mg/kg cyclosporine-treated groups (p < .05). Although histologic features of myocardial injury were not different among groups, severe damage was observed in mitochondria of control piglets but attenuated in that of cyclosporine (10 mg/kg) treatment. Postresuscitation administration of cyclosporine causes preservation of cardiac function and attenuates myocardial injury in newborn piglets after asphyxia-reoxygenation.

Cyclosporine treatment improves mesenteric perfusion and attenuates necrotizing enterocolitis (NEC)-like intestinal injury in asphyxiated newborn piglets during reoxygenation

Asphyxia-related intestinal injury in neonates may present similar to necrotizing enterocolitis (NEC) and is partially associated with hypoxia-reoxygenation injury. Cyclosporine has been shown to reduce myocardial cell death following ischemia-reperfusion. We hypothesize that cyclosporine treatment may attenuate NEC-like intestinal injury in asphyxiated newborn piglets during reoxygenation. Twenty piglets (1-4 days old) were acutely anesthetized and instrumented for continuous monitoring of systemic hemodynamics and superior mesenteric arterial (SMA) flow. After stabilization, normocapnic alveolar hypoxia (10-15% oxygen) was instituted for 2 h followed by reoxygenation with 100% oxygen for 0.5 h, then 21% for 3.5 h. The piglets were blindly block-randomized to receive cyclosporine (10 mg/kg) or placebo (normal saline) boluses at 5 min of reoxygenation (n = 8/group). A sham-operated group was included (n = 4) and received no hypoxia-reoxygenation. Intestinal samples were collected for tissue lactate and histological assessment (Park's criteria). At 2 h of hypoxia, piglets had cardiogenic shock (cardiac output 45% of baseline), hypotension (mean arterial pressure 30 mmHg), acidosis (pH 7.04), and decreased superior mesenteric perfusion (all P < 0.05 vs. sham-operated group, ANOVA). Cyclosporine treatment increased SMA flow (114 ± 6 vs. 78 ± 19% of baseline of controls, respectively) with improved SMA oxygen delivery and intestinal tissue lactate (all P < 0.05). Some control piglets had NEC-like injuries including pneumatosis intestinalis, which were attenuated in cyclosporine-treated piglets (P < 0.05 vs. controls). This is the first study to demonstrate that post-resuscitation administration of cyclosporine improves mesenteric perfusion and attenuates NEC-like intestinal injury in newborn piglets following asphyxia-reoxygenation.

Differential Hemodynamic Effects of Levosimendan in a Porcine Model of Neonatal Hypoxia-Reoxygenation

Background: Neonatal asphyxia can be complicated by myocardial dysfunction with secondary alterations in pulmonary and regional hemodynamics. Levosimendan is a calcium-sensitizing inotrope that may support cardiac output, but little is known regarding its differential hemodynamic effects in asphyxiated neonates. Methods: Mixed breed piglets (1–4 days old, weight 1.6–2.3 kg) were acutely instrumented. Normocapnic alveolar hypoxia (10–15% oxygen) was induced for 2 h, followed by reoxygenation with 100% (1 h) and then 21% oxygen (3 h). At 2 h of reoxygenation, after volume loading (Ringer’s lactate 10 ml/kg), either levosimendan (0.1 or 0.2 µg/kg/min) or D₅W (placebo) was infused for 2 h in a blinded, block-randomized fashion (n = 7–8/group). The systemic, pulmonary and regional (carotid, superior mesenteric and renal) hemodynamics were compared. Results: At 0.1 and 0.2 µg/kg/min, levosimendan significantly increased cardiac output (121 and 123% of pretreatment, respectively) and heart rate, and decreased systemic vascular resistance without causing hypotension. Pulmonary arterial pressure and estimated pulmonary vascular resistance were significantly increased from pretreatment baseline in 0.1 but not 0.2 µg/kg/min levosimendan. Levosimendan infusion had no effects on regional hemodynamics. Myocardial efficiency but not oxygen consumption increased with 0.1 µg/kg/min levosimendan without significant effects on plasma troponin and myocardial lactate levels. Conclusions: In newborn piglets following hypoxia-reoxygenation injury, levosimendan improves cardiac output but has no marked effects in carotid, superior mesenteric and renal perfusion. It appears that various doses of levosimendan increase the cardiac output through different mechanisms. Further investigations are needed to examine the effectiveness of levosimendan as a cardiovascular supportive therapy either alone or in conjunction with other inotropes in asphyxiated neonates.

Vasopressin Treatment Improves Systemic Hemodynamics Without Compromising Mesenteric Perfusion During Reoxygenation of Asphyxiated Newborn Piglets: a Dose Response Study

Background: Asphyxia is associated with over 1-million newborn deaths worldwide. Asphyxiated newborns may present with myocardial dysfunction and hypotension. Vasopressin, an endogenous vasoconstrictive hormone, is commonly administered in adults with refractory shock. Anecdotal concerns regarding mesenteric vasoconstriction has limited its use in newborns. Objective: We hypothesize that vasopressin administration will improve systemic hemodynamics without compromising mesenteric perfusion during reoxygenation of severely asphyxiated newborn piglets. Methods: Thirty-three piglets (1-4 days-old) were instrumented for continuous monitoring of cardiac output, systemic arterial pressures (SAP) and superior mesenteric arterial (SMA) flow. After stabilization, normocapnic alveolar hypoxia (10-15% oxygen) was instituted for 2h followed by reoxygenation with 100% (0.5h) and 21% (3.5h) oxygen. Piglets were block-randomized to receive vasopressin-infusion following 2h of reoxygenation, at one of three doses (0.005, 0.01, 0.02 mg/kg/h) or placebo (normal saline, control) for an additional 2h. Blood samples and intestinal tissue were collected for analysis. Statistical analysis was performed with ANOVA. Results: All piglets demonstrated hypotension (SAP 27-31 mmHg) and decreased SMA flow (42-62 % of baseline) at the end of hypoxia. Following 2h of reoxygenation, vasopressin infusion at 0.02 mg/kg/h caused significant improvement of SAP versus controls (P< 0.05) with no significant effects on cardiac function. Left ventricular lactate was significantly decreased in all vasopressin treated piglets compared to controls (P< 0.05). Mesenteric oxygen delivery, vascular resistance and intestinal lactate levels were similar among groups. Conclusion: We are first to demonstrate that post-resuscitation vasopressin infusion improves systemic hemodynamics without compromising mesenteric perfusion in asphyxiated newborn piglets following reoxygenation.

Cyclosporine Treatment Improves Cardiac Function and Attenuates Mitochondrial Injury in Asphyxiated Newborn Piglets During Reoxygenation

Background: Asphyxiated neonates often have myocardial depression which is a significant cause of morbidity and mortality. Cardioprotective effects of cyclosporine have been observed in adult patients and animals with myocardial infarction. However, the cardioprotective effect of cyclosporine in neonates has not yet been studied.Objectives: We hypothesize that cyclosporine will improve cardiac function and reduce myocardial injury in asphyxiated newborn piglets.Methods: Thirty-six piglets (1-4 days-old) were acutely instrumented for continuous monitoring of cardiac output and systemic arterial pressure. After stabilization, normocapnic alveolar hypoxia (10-15% oxygen) was instituted for 2h followed by reoxygenation with 100% (0.5h), then 21% (3.5h) oxygen. Piglets were block-randomized to receive intravenous boluses of cyclosporine A (2.5, 10 or 25 mg/kg) or normal saline (control) at 5 min of reoxygenation (n=8/group). Cardiomyocyte mitochondria were assessed for morphology and markers of injury.Results: Hypoxic piglets had cardiogenic shock (cardiac output 40-48% of baseline), hypotension (mean arterial pressure 30mmHg) and acidosis (pH 7.04). Cyclosporine-treatment caused bell-shaped improvements in cardiac output and systemic oxygen delivery (p< 0.05 vs. controls). Although histological features of myocardial injury were not different among groups, severe damage was observed in mitochondria of control piglets but attenuated in that of cyclosporine (10 mg/kg) treatment. Markers of mitochondrial injury including cytosol cytochrome-c and lipid hydroperoxides were significantly decreased and mitochondrial aconitase activity was preserved in cyclosporine-treated piglets compared to controls (all P< 0.05).Conclusions: Post-resuscitation administration of cyclosporine causes preservation of cardiac function and attenuates cardiac mitochondrial injury in newborn piglets following asphyxia-reoxygenation.

A Swine Model of Neonatal Asphyxia

Annually more than 1 million neonates die worldwide as related to asphyxia. Asphyxiated neonates commonly have multi-organ failure including hypotension, perfusion deficit, hypoxic-ischemic encephalopathy, pulmonary hypertension, vasculopathic enterocolitis, renal failure and thrombo-embolic complications. Animal models are developed to help us understand the patho-physiology and pharmacology of neonatal asphyxia. In comparison to rodents and newborn lambs, the newborn piglet has been proven to be a valuable model. The newborn piglet has several advantages including similar development as that of 36-38 weeks human fetus with comparable body systems, large body size (~1.5-2 kg at birth) that allows the instrumentation and monitoring of the animal and controls the confounding variables of hypoxia and hemodynamic derangements. We here describe an experimental protocol to simulate neonatal asphyxia and allow us to examine the systemic and regional hemodynamic changes during the asphyxiating and reoxygenation process as well as the respective effects of interventions. Further, the model has the advantage of studying multi-organ failure or dysfunction simultaneously and the interaction with various body systems. The experimental model is a non-survival procedure that involves the surgical instrumentation of newborn piglets (1-3 day-old and 1.5-2.5 kg weight, mixed breed) to allow the establishment of mechanical ventilation, vascular (arterial and central venous) access and the placement of catheters and flow probes (Transonic Inc.) for the continuously monitoring of intra-vascular pressure and blood flow across different arteries including main pulmonary, common carotid, superior mesenteric and left renal arteries. Using these surgically instrumented piglets, after stabilization for 30-60 minutes as defined by Z<10% variation in hemodynamic parameters and normal blood gases, we commence an experimental protocol of severe hypoxemia which is induced via normocapnic alveolar hypoxia. The piglet is ventilated with 10-15% oxygen by increasing the inhaled concentration of nitrogen gas for 2h, aiming for arterial oxygen saturations of 30-40%. This degree of hypoxemia will produce clinical asphyxia with severe metabolic acidosis, systemic hypotension and cardiogenic shock with hypoperfusion to vital organs. The hypoxia is followed by reoxygenation with 100% oxygen for 0.5 h and then 21% oxygen for 3.5 h. Pharmacologic interventions can be introduced in due course and their effects investigated in a blinded, block-randomized fashion.

Improved Renal Recovery with Postresuscitation N-Acetylcysteine Treatment in Asphyxiated Newborn Pigs

Renal injury is one of the severe and common complications that occurs early in neonates with asphyxia, and reactive oxygen species have been implicated to play an important role on its pathogenesis. Improved renal recovery has been shown previously with N-acetyl-l-cysteine (NAC) in various acute kidney injuries. Using a subacute swine model of neonatal hypoxia-reoxygenation (H/R), we examined whether NAC can sustain its beneficial effect on renal recovery for 48 h. Newborn piglets were randomly assigned into a sham-operated group (without H/R, n = 6) and two H/R experimental groups (n = 8 each) with 2 h normocapnic alveolar hypoxia and 1 h 100% oxygen of reoxygenation followed by 21% oxygen for 47 h. Five minutes after reoxygenation, piglets received either normal saline (H/R control) or NAC (150-mg/kg bolus and 20 mg/kg per hour i.v. for 24 h) in a blinded, randomized fashion. All piglets were acidotic and in cardiogenic shock after hypoxia. Treating the piglets with NAC significantly increased both renal blood flow and oxygen delivery throughout the reoxygenation period. N-acetyl-l-cysteine treatment also improved the renal function with the attenuation of elevated urinary N-acetyl-β-d-glucosaminidase activity and plasma creatinine concentration observed in H/R controls (both P < 0.05). The tissue levels of lipid hydroperoxides and caspase 3 in the kidney of NAC-treated animals were significantly lower than those of H/R controls. Conclusively, postresuscitation administration of NAC elicits a prolonged beneficial effect in improving renal functional recovery and reducing oxidative stress in newborn piglets with H/R insults for 48 h.

Effects of Post-Resuscitation Treatment with N-acetylcysteine on Cardiac Recovery in Hypoxic Newborn Piglets

AimsAlthough N-acetylcysteine (NAC) can decrease reactive oxygen species and improve myocardial recovery after ischemia/hypoxia in various acute animal models, little is known regarding its long-term effect in neonatal subjects. We investigated whether NAC provides prolonged protective effect on hemodynamics and oxidative stress using a surviving swine model of neonatal asphyxia.Methods and ResultsNewborn piglets were anesthetized and acutely instrumented for measurement of systemic hemodynamics and oxygen transport. Animals were block-randomized into a sham-operated group (without hypoxia-reoxygenation [H–R, n = 6]) and two H-R groups (2 h normocapnic alveolar hypoxia followed by 48 h reoxygenation, n = 8/group). All piglets were acidotic and in cardiogenic shock after hypoxia. At 5 min after reoxygenation, piglets were given either saline or NAC (intravenous 150 mg/kg bolus + 20 mg/kg/h infusion) via for 24 h in a blinded, randomized fashion. Both cardiac index and stroke volume of H-R controls remained lower than the pre-hypoxic values throughout recovery. Treating the piglets with NAC significantly improved cardiac index, stroke volume and systemic oxygen delivery to levels not different from those of sham-operated piglets. Accompanied with the hemodynamic improvement, NAC-treated piglets had significantly lower plasma cardiac troponin-I, myocardial lipid hydroperoxides, activated caspase-3 and lactate levels (vs. H-R controls). The change in cardiac index after H-R correlated with myocardial lipid hydroperoxides, caspase-3 and lactate levels (all p<0.05).ConclusionsPost-resuscitation administration of NAC reduces myocardial oxidative stress and caused a prolonged improvement in cardiac function and in newborn piglets with H-R insults.

333 Cyclosporine and Regional Hemodynamics of Newborn Piglets Following Asphyxia-Reoxygenation: A Dose-Response Study

Introduction: Asphyxiated neonates commonly have multi-organ failure. Cyclosporine has recently been shown to improve systemic hemodynamics, however, its effects on the regional circulation have not yet been studied. We hypothesize that cyclosporine in asphyxiated newborn piglets will dose-dependently improve regional hemodynamics and oxygen metabolism. Methods: Piglets (1-4 days-old) were acutely instrumented for continuous monitoring of common carotid (CA), superior mesenteric (SMA) and renal (RA) arterial flows. After stabilization, normocapnic alveolar hypoxia (10-15% oxygen) was instituted for 2h followed by reoxygenation with 100% oxygen for 0.5h, then 21% for 3.5h. Piglets were blockrandomized to receive one of three cyclosporine intravenous boluses (2.5, 10 or 25 mg/kg) or placebo (normal saline, control) after 5 minutes of 100% reoxygenation (n=8/group). Blood samples were collected for co-oximetry analysis and oxygen transport calculation. Statistical analysis was performed using ANOVA. Results: All piglets had decreased regional blood flow (CA 52-64%, SMA 34-56%, RA 25-35% compared to respective baseline), hypotension (mean arterial pressure 30mmHg) and acidosis (pH 7.04) at 2h of hypoxia. Cyclosporine (2.5 and 10 mg/ kg) treatment at reoxygenation caused dose-related improvements in SMA flow and oxygen delivery. Cyclosporine (10 mg/kg) significantly increased RA flow and oxygen delivery (P< 0.05 vs. controls). While CA flows were not different among groups, cyclosporine (25 mg/kg) had significantly higher CA oxygen delivery than controls. Conclusion: In newborn piglets following asphyxiareoxygenation, post-resuscitation administration of cyclosporine caused differential and dose-related improvements of regional perfusion.