Femoral Occlusion during Neonatal Cardiopulmonary Resuscitation Improves Outcomes in an Ovine Model of Perinatal Cardiac Arrest.

BACKGROUND: The goal of chest compressions during neonatal resuscitation is to increase cerebral and coronary blood flow leading to the return of spontaneous circulation (ROSC). During chest compressions, bilateral femoral occlusion may increase afterload and promote carotid and coronary flow, an effect similar to epinephrine. Our objectives were to determine the impact of bilateral femoral occlusion during chest compressions on the incidence and timing of ROSC and hemodynamics. METHODOLOGY: In this randomized study, 19 term fetal lambs in cardiac arrest were resuscitated based on the Neonatal Resuscitation Program guidelines and randomized into two groups: femoral occlusion or controls. Bilateral femoral arteries were occluded by applying pressure using two fingers during chest compressions. RESULTS: Seventy percent (7/10) of the lambs in the femoral occlusion group achieved ROSC in 5 ± 2 min and three lambs (30%) did not receive epinephrine. ROSC was achieved in 44% (4/9) of the controls in 13 ± 6 min and all lambs received epinephrine. The femoral occlusion group had higher diastolic blood pressures, carotid and coronary blood flow. CONCLUSION: Femoral occlusion resulted in faster and higher incidence of ROSC, most likely due to attaining increased diastolic pressures, coronary and carotid flow. This is a low-tech intervention that can be easily adapted in resource limited settings, with the potential to improve survival and neurodevelopmental outcomes.

Viral Infections and Neonatal Necrotizing Enterocolitis: A Meta-analysis.

CONTEXT: Necrotizing enterocolitis (NEC) is a devastating intestinal disease affecting preterm infants. Studies implicate viral infections in etiopathogenesis. OBJECTIVE: To summarize the association of viral infections with NEC by systematic review and meta-analysis. DATA SOURCES: We searched Ovid-Medline, Embase, Web of Science, and Cochrane databases in November 2022. STUDY SELECTION: We included observational studies that examined the association between viral infections and NEC in newborn infants. DATA EXTRACTION: We extracted data regarding the methodology, participant characteristics, and outcome measures. RESULTS: We included 29 and 24 studies in the qualitative review and meta-analysis, respectively. The meta-analysis demonstrated a significant association between viral infections and NEC (odds ratio [OR], 3.81, 95% confidence interval: 1.99-7.30, 24 studies). The association remained significant after excluding the outliers (OR, 2.89 [1.56-5.36], 22 studies) and studies with poor methodology (OR, 3.33 [1.73-6.43], 22 studies). In subgroup analysis based on participants' birth weight, studies including very low birth weight infants only (OR, 3.62 [1.63-8.03], 8 studies) and non-very low birth weight infants only (OR, 5.28 [1.69-16.54], 6 studies) showed a significant association. In subgroup analysis based on specific viruses, infection with rotavirus (OR, 3.96 [1.12-13.95], 10 studies), cytomegalovirus (OR, 3.50 [1.60-7.65], 5 studies), norovirus (OR, 11.95 [2.05-69.84], 2 studies), and astrovirus (OR, 6.32 [2.49-16.02], 2 studies) was significantly associated with NEC. LIMITATIONS: Heterogeneity of the included studies. CONCLUSIONS: Viral infection is associated with an increased risk of NEC in newborn infants. We need methodologically sound prospective studies to assess the effect of preventing or treating viral infections on NEC incidence.

Masked Randomized Trial of Epinephrine versus Vasopressin in an Ovine Model of Perinatal Cardiac Arrest.

BACKGROUND: Current neonatal resuscitation guidelines recommend the use of epinephrine for bradycardia/arrest not responding to ventilation and chest compressions. Vasopressin is a systemic vasoconstrictor and is more effective than epinephrine in postnatal piglets with cardiac arrest. There are no studies comparing vasopressin with epinephrine in newly born animal models with cardiac arrest induced by umbilical cord occlusion. Objective: To compare the effect of epinephrine and vasopressin on the incidence and time to return of spontaneous circulation (ROSC), hemodynamics, plasma drug levels, and vasoreactivity in perinatal cardiac arrest. Design/Methods: Twenty-seven term fetal lambs in cardiac arrest induced by cord occlusion were instrumented and resuscitated following randomization to epinephrine or vasopressin through a low umbilical venous catheter. Results: Eight lambs achieved ROSC prior to medication. Epinephrine achieved ROSC in 7/10 lambs by 8 ± 2 min. Vasopressin achieved ROSC in 3/9 lambs by 13 ± 6 min. Plasma vasopressin levels in nonresponders were much lower than responders after the first dose. Vasopressin caused in vivo increased pulmonary blood flow and in vitro coronary vasoconstriction. Conclusions: Vasopressin resulted in lower incidence and longer time to ROSC compared to epinephrine in a perinatal model of cardiac arrest supporting the current recommendations for exclusive use of epinephrine in neonatal resuscitation.

Initial Use of 100% but Not 60% or 30% Oxygen Achieved a Target Heart Rate of 100 bpm and Preductal Saturations of 80% Faster in a Bradycardic Preterm Model.

Background: Currently, 21−30% supplemental oxygen is recommended during resuscitation of preterm neonates. Recent studies have shown that 58% of infants < 32 week gestation age are born with a heart rate (HR) < 100 bpm. Prolonged bradycardia with the inability to achieve a preductal saturation (SpO2) of 80% by 5 min is associated with mortality and morbidity in preterm infants. The optimal oxygen concentration that enables the achievement of a HR ≥ 100 bpm and SpO2 of ≥80% by 5 min in preterm lambs is not known. Methods: Preterm ovine model (125−127 d, gestation equivalent to human neonates < 28 weeks) was instrumented, and asphyxia was induced by umbilical cord occlusion until bradycardia. Ventilation was initiated with 30% (OX30), 60% (OX60), and 100% (OX100) for the first 2 min and titrated proportionately to the difference from the recommended preductal SpO2. Our primary outcome was the incidence of the composite of HR ≥ 100 bpm and SpO2 ≥ 80%, by 5 min. Secondary outcomes were to evaluate the time taken to achieve the primary outcome, gas exchange, pulmonary/systemic hemodynamics, and the oxidative injury. Results: Eighteen lambs (OX30-6, OX60-5. OX100-7) had an average HR < 91 bpm with a pH of <6.92 before resuscitation. Sixty seven percent achieved the primary outcome in OX100, 40% in OX60, and none in OX30. The time taken to achieve the primary outcome was significantly shorter with OX100 (6 ± 2 min) than with OX30 (10 ± 3 min) (* p = 0.04). The preductal SpO2 was highest with OX100, while the peak pulmonary blood flow was lowest with OX30, with no difference in O2 delivery to the brain or oxidative injury by 10 min. Conclusions: The use of 30%, 60%, and 100% supplemental O2 in a bradycardic preterm ovine model did not demonstrate a significant difference in the composite primary outcome. The current recommendation to use 30% oxygen did not achieve a preductal SpO2 of 80% by 5 min in any preterm lambs. Clinical studies to optimize supplemental O2 in depressed preterm neonates not requiring chest compressions are warranted.

Alloimmune Neutropenia in a Neonate: Case Report and Review of Literature.

Neonatal alloimmune neutropenia, variably referred to in the literature as NAIN, FNAIN or NIN, is a disorder of neutrophil destruction in newborns similar to better-known conditions such as hemolytic disease of the newborn and neonatal alloimmune thrombocytopenia (FNAIT). Infants affected by this self-limiting condition can present asymptomatically or have a wide range of symptoms, from skin manifestations and mucositis to severe infections such as sepsis and pneumonia. In our case, we report an otherwise asymptomatic term infant born with severe neutropenia to a mother affected by COVID-19 in the 3rd trimester. However, it is unclear if COVID-19 contributed to our patients' neutropenia. Diagnostic testing eventually revealed the presence of anti-neutrophil antibodies, confirming the diagnosis of alloimmune neutropenia. The infant was conservatively managed with early discharge prior to resolution of neutropenia and close post-discharge follow up.

Placental transfusion during neonatal resuscitation in an asphyxiated preterm model.

BACKGROUND: Neonatal Resuscitation Program does not recommend placental transfusion in depressed preterm neonates. METHODS: Our objectives were to study the effect of delayed cord clamping (DCC) with ventilation for 5 min (DCCV, n-5), umbilical cord milking (UCM) without ventilation (n-6), UCM with ventilation (UCMV, n-6), early cord clamping followed by ventilation (ECCV, n-6) on red cell volume (RCV), and hemodynamic changes in asphyxiated preterm lambs. Twenty-three preterm lambs at 127-128 days gestation were randomized to DCCV, UCM, UCMV, and ECCV. We defined asphyxia as heart rate <100/min. RESULTS: The UCMV had the highest neonatal RCV as a percentage of fetoplacental volume compared to the other groups (UCMV 85.5 ± 10%, UCM 72 ± 10%, ECCV 65 ± 14%, DCCV 61 ± 10%, p < 0.01). The DCCV led to better ventilation (66 ± 1 mmHg) and higher pulmonary blood flow (75 ± 24 ml/kg/min). The carotid flow was significantly higher in UCM without ventilation. The fluctuations in carotid flow with milking were 25 ± 6% higher from baseline during UCM, compared to 6 ± 3% in UCMV (p < 0.01). CONCLUSIONS: Cord milking with ventilation led to higher RCV than other interventions. Ventilation during cord milking reduced fluctuation in carotid flow compared to UCM alone. DCCV led to better ventilation and pulmonary blood flow but did not increase RCV. IMPACT: The best practice of placental transfusion in a depressed preterm neonate remains unknown. Ventilation with an intact cord improves gas exchange and hemodynamics in an asphyxiated preterm model. Cord milking without ventilation led to lower red cell volume but higher carotid blood flow fluctuations compared to milking with ventilation. Our data can be translated to bedside and could impact preterm resuscitation.

Inadequate Bioavailability of Intramuscular Epinephrine in a Neonatal Asphyxia Model.

Background: Over half a million newborn deaths are attributed to intrapartum related events annually, the majority of which occur in low resource settings. While progress has been made in reducing the burden of asphyxia, novel approaches may need to be considered to further decrease rates of newborn mortality. Administration of intravenous, intraosseous or endotracheal epinephrine is recommended by the Newborn Resuscitation Program (NRP) with sustained bradycardia at birth. However, delivery by these routes requires both advanced skills and specialized equipment. Intramuscular (IM) epinephrine may represent a simple, low cost and highly accessible alternative for consideration in the care of infants compromised at birth. At present, the bioavailability of IM epinephrine in asphyxia remains unclear. Methods: Four term fetal lambs were delivered by cesarean section and asphyxiated by umbilical cord occlusion with resuscitation after 5 min of asystole. IM epinephrine (0.1 mg/kg) was administered intradeltoid after 1 min of positive pressure ventilation with 30 s of chest compressions. Serial blood samples were obtained for determination of plasma epinephrine concentrations by ELISA. Results: Epinephrine concentrations failed to increase following administration via IM injection. Delayed absorption was observed after return of spontaneous circulation (ROSC) in half of the studies. Conclusions: Inadequate absorption of epinephrine occurs with IM administration during asphyxial cardiac arrest, implying this route would be ineffective in infants who are severely compromised at birth. Late absorption following ROSC raises concerns for risks of side effects. However, the bioavailability and efficacy of intramuscular epinephrine in less profound asphyxia may warrant further evaluation.

Gestational Age Alters Assessment of Neonatal Abstinence Syndrome.

Neonatal abstinence syndrome (NAS) due to maternal opioid use affects both term and preterm infants; however, the relationship between gestational age and clinical symptomatology is still poorly understood. In this study, we compared the clinical features and outcomes of NAS in infants admitted to a neonatal intensive care unit (NICU) based on gestational age groups: preterm (32-36 6/7 weeks) and term (37 weeks or older). A retrospective data analysis was conducted using the medical records of infants with a diagnosis of NAS admitted to a regional perinatal center between 2014 and 2020. A modified Finnegan scoring system was used based on three different symptom categories, including Central Nervous System (CNS), Gastrointestinal (GI) and Other. In total, 166 infants with a diagnosis of NAS were included, with 52 (31%) who were preterm and 114 (69%) who were term. The highest NAS score was significantly lower for the preterm group than for the term group. Preterm infants were less likely to require first-line pharmacotherapy with morphine (52% versus 75%) and to experience GI symptoms during their hospitalization. Newer NAS assessment modalities, such as eat, sleep, console (ESC), may overcome the existing challenges of traditional scoring systems, but will require validation in preterm infants.

Essentials of Neonatal-Perinatal Medicine fellowship: part 2 - clinical education and experience.

This is the second article in a seven-part series in the Journal of Perinatology that aims to critically examine the current state of Neonatal-Perinatal Medicine (NPM) fellowship training from the structure and administration of a program, to the clinical and scholarly requirements, and finally to the innovations and future careers awaiting successful graduates. This article focuses on the current clinical requirements; recent changes to the clinical environment and their effect on learning; and additional challenges and opportunities in clinical education.

Laryngeal mask ventilation with chest compression during neonatal resuscitation: randomized, non-inferiority trial in lambs.

BACKGROUND: Effective positive-pressure ventilation is a critical factor in newborn resuscitation. Neonatal endotracheal intubation (ETT) needs considerable training and experience, which poses a human factor challenge. Laryngeal mask airway (LMA) ventilation can be a secure and viable alternative during the initial stages of newborn resuscitation. However, there is limited evidence for its use during chest compression (CC). METHODS: Seventeen lambs were randomized into LMA or ETT ventilation post cord occlusion induced cardiac arrest. After 5 min of cardiac arrest, resuscitation was initiated as per NRP recommendations. Ventilation, oxygenation, systemic and pulmonary hemodynamic parameters were recorded till the return of spontaneous circulation (ROSC) or 20 min. RESULTS: Baseline characteristics were similar between the groups. The incidence of ROSC was 75% (6/8) in the LMA group and 56% (5/9) in the ETT group (p = 0.74). The median (IQR) time to achieve ROSC was 6.85 min (6 min-9.1 min) in the LMA group and 7.50 min (5.33 min-18 min) in the ETT group (p = 0.65). CONCLUSION: LMA ventilation during CC is feasible and non-inferior to ETT in this model. IMPACT: Laryngeal mask airway (LMA) ventilation with chest compression is feasible and non-inferior to endotracheal tube ventilation in this experimental near-term lamb model of asphyxial cardiac arrest. First translational study to evaluate the use of LMA as an airway device with chest compression. Evidence primer for clinical studies to evaluate and confirm the feasibility and efficacy of LMA ventilation with chest compression are necessary before randomized clinical trials in neonates. LMA use in neonatal cardiopulmonary resusciation (CPR) could have the potential to optimize advanced resuscitation, especially in resource-limited healthcare settings.

Non-coding RNAs in Necrotizing Enterocolitis- A New Frontier?

With the recognition that only 2% of the human genome encodes for a protein, a large part of the "non-coding" portion is now being evaluated for a regulatory role in cellular processes. These non-coding RNAs (ncRNAs) are subdivided based on the size of the nucleotide transcript into microRNAs (miRNAs) and long non-coding RNAs (lncRNAs), but most of our attention has been focused on the role of microRNAs (miRNAs) in human health and disease. Necrotizing enterocolitis (NEC), an inflammatory bowel necrosis affecting preterm infants, has a multifactorial, unclear etiopathogenesis, and we have no specific biomarkers for diagnosis or the impact of directed therapies. The information on ncRNAs, in general, and particularly in NEC, is limited. Increasing information from other inflammatory bowel disorders suggests that these transcripts may play an important role in intestinal inflammation. Here, we review ncRNAs for definitions, classifications, and possible roles in prematurity and NEC using some preliminary information from our studies and from an extensive literature search in multiple databases including PubMed, EMBASE, and Science Direct. miRNAs will be described in another manuscript in this series, hence in this manuscript we mainly focus on lncRNAs.

Antenatal Bartter syndrome: a new compound heterozygous mutation in exon 2 of KCNJ1 gene.

A 30+6/7-week infant was born by vaginal delivery to a 21-year-old primigravida with pregnancy complicated by polyhydramnios. The infant developed polyuria and significant weight loss in the first 2 weeks of life despite appropriate fluid management. He developed hyponatraemia, hypochloraemia, transient hyperkalaemia and prerenal azotaemia with metabolic acidosis. On further evaluation, he had elevated plasma renin and aldosterone levels. Bartter syndrome was considered in the differential diagnosis. Bartter syndrome gene panel revealed a rare compound heterozygous mutation in exon 2 of the KCNJ1 gene (Lys186Glu/Thr71Met), suggesting antenatal Bartter syndrome (type 2). The infant developed late-onset hypokalaemia and metabolic alkalosis by week 4 of life. He regained birth weight by week 3 of life but failed to thrive (10-20 g/kg/day) despite high caloric intake (140 kcal/kg/day). His electrolyte abnormalities gradually improved, and he was discharged home without the need for electrolyte supplements or medications.

Effect of a Larger Flush Volume on Bioavailability and Efficacy of Umbilical Venous Epinephrine during Neonatal Resuscitation in Ovine Asphyxial Arrest.

The 7th edition of the Textbook of Neonatal Resuscitation recommends administration of epinephrine via an umbilical venous catheter (UVC) inserted 2-4 cm below the skin, followed by a 0.5-mL to 1-mL flush for severe bradycardia despite effective ventilation and chest compressions (CC). This volume of flush may not be adequate to push epinephrine to the right atrium in the absence of intrinsic cardiac activity during CC. The objective of our study was to evaluate the effect of 1-mL and 2.5-mL flush volumes after UVC epinephrine administration on the incidence and time to achieve return of spontaneous circulation (ROSC) in a near-term ovine model of perinatal asphyxia induced cardiac arrest. After 5 min of asystole, lambs were resuscitated per Neonatal Resuscitation Program (NRP) guidelines. During resuscitation, lambs received epinephrine through a UVC followed by 1-mL or 2.5-mL normal saline flush. Hemodynamics and plasma epinephrine concentrations were monitored. Three out of seven (43%) and 12/15 (80%) lambs achieved ROSC after the first dose of epinephrine with 1-mL and 2.5-mL flush respectively (p = 0.08). Median time to ROSC and cumulative epinephrine dose required were not different. Plasma epinephrine concentrations at 1 min after epinephrine administration were not different. From our pilot study, higher flush volume after first dose of epinephrine may be of benefit during neonatal resuscitation. More translational and clinical trials are needed.

Inhaled Nitric Oxide at Birth Reduces Pulmonary Vascular Resistance and Improves Oxygenation in Preterm Lambs.

Resuscitation with 21% O2 may not achieve target oxygenation in preterm infants and in neonates with persistent pulmonary hypertension of the newborn (PPHN). Inhaled nitric oxide (iNO) at birth can reduce pulmonary vascular resistance (PVR) and improve PaO2. We studied the effect of iNO on oxygenation and changes in PVR in preterm lambs with and without PPHN during resuscitation and stabilization at birth. Preterm lambs with and without PPHN (induced by antenatal ductal ligation) were delivered at 134 d gestation (term is 147-150 d). Lambs without PPHN were ventilated with 21% O2, titrated O2 to maintain target oxygenation or 21% O2 + iNO (20 ppm) at birth for 30 min. Preterm lambs with PPHN were ventilated with 50% O2, titrated O2 or 50% O2 + iNO. Resuscitation with 21% O2 in preterm lambs and 50%O2 in PPHN lambs did not achieve target oxygenation. Inhaled NO significantly decreased PVR in all lambs and increased PaO2 in preterm lambs ventilated with 21% O2 similar to that achieved by titrated O2 (41 ± 9% at 30 min). Inhaled NO increased PaO2 to 45 ± 13, 45 ± 20 and 76 ± 11 mmHg with 50% O2, titrated O2 up to 100% and 50% O2 + iNO, respectively, in PPHN lambs. We concluded that iNO at birth reduces PVR and FiO2 required to achieve target PaO2.

Sustained Inflation Reduces Pulmonary Blood Flow during Resuscitation with an Intact Cord.

The optimal timing of cord clamping in asphyxia is not known. Our aims were to determine the effect of ventilation (sustained inflation-SI vs. positive pressure ventilation-V) with early (ECC) or delayed cord clamping (DCC) in asphyxiated near-term lambs. We hypothesized that SI with DCC improves gas exchange and hemodynamics in near-term lambs with asphyxial bradycardia. A total of 28 lambs were asphyxiated to a mean blood pressure of 22 mmHg. Lambs were randomized based on the timing of cord clamping (ECC-immediate, DCC-60 s) and mode of initial ventilation into five groups: ECC + V, ECC + SI, DCC, DCC + V and DCC + SI. The magnitude of placental transfusion was assessed using biotinylated RBC. Though an asphyxial bradycardia model, 2-3 lambs in each group were arrested. There was no difference in primary outcomes, the time to reach baseline carotid blood flow (CBF), HR ≥ 100 bpm or MBP ≥ 40 mmHg. SI reduced pulmonary (PBF) and umbilical venous (UV) blood flow without affecting CBF or umbilical arterial blood flow. A significant reduction in PBF with SI persisted for a few minutes after birth. In our model of perinatal asphyxia, an initial SI breath increased airway pressure, and reduced PBF and UV return with an intact cord. Further clinical studies evaluating the timing of cord clamping and ventilation strategy in asphyxiated infants are warranted.

Resuscitation with an Intact Cord Enhances Pulmonary Vasodilation and Ventilation with Reduction in Systemic Oxygen Exposure and Oxygen Load in an Asphyxiated Preterm Ovine Model.

(1) Background: Optimal initial oxygen (O2) concentration in preterm neonates is controversial. Our objectives were to compare the effect of delayed cord clamping with ventilation (DCCV) to early cord clamping followed by ventilation (ECCV) on O2 exposure, gas exchange, and hemodynamics in an asphyxiated preterm ovine model. (2) Methods: Asphyxiated preterm lambs (127-128 d) with heart rate <90 bpm were randomly assigned to DCCV or ECCV. In DCCV, positive pressure ventilation (PPV) was initiated with 30-60% O2 and titrated based on preductal saturations (SpO2) with an intact cord for 5 min, followed by clamping. In ECCV, the cord was clamped, and PPV was initiated. (3) Results: Fifteen asphyxiated preterm lambs were randomized to DCCV (N = 7) or ECCV (N = 8). The inspired O2 (40 ± 20% vs. 60 ± 20%, p < 0.05) and oxygen load (520 (IQR 414-530) vs. 775 (IQR 623-868), p-0.03) in the DCCV group were significantly lower than ECCV. Arterial oxygenation and carbon dioxide (PaCO2) levels were significantly lower and peak pulmonary blood flow was higher with DCCV. (4) Conclusion: In asphyxiated preterm lambs, resuscitation with an intact cord decreased O2 exposure load improved ventilation with an increase in peak pulmonary blood flow in the first 5 min.

Epigenetics in Necrotizing Enterocolitis.

Epigenetic alterations in our genetic material can lead to heritable changes in the risk, clinical manifestations, course, and outcomes of many diseases. Understanding these epigenetic mechanisms can help in identifying potential therapeutic targets. This is especially important in necrotizing enterocolitis (NEC), where prenatal as well as postnatal factors impact susceptibility to this devastating condition, but our therapeutic options are limited. Developmental factors affecting intestinal structure and function, our immune system, gut microbiome, and postnatal enteral nutrition are all thought to play a prominent role in this disease. In this manuscript, we have reviewed the epigenetic mechanisms involved in NEC. These include key developmental changes in DNA methylation in the immature intestine, the role of long non-coding RNA (lncRNA) in maintaining intestinal barrier function, epigenetic influences of prenatal inflammation on immunological pathways in NEC pathogenesis such as Toll-Like Receptor 4 (TLR4) and epigenetic changes associated with enteral feeding causing upregulation of pro-inflammatory genes. We have assimilated research findings from our own laboratory with an extensive review of the literature utilizing key terms in multiple databases, including PubMed, EMBASE, and Science Direct.

Randomised trial of epinephrine dose and flush volume in term newborn lambs.

OBJECTIVES: Neonatal resuscitation guidelines recommend 0.5-1 mL saline flush following 0.01-0.03 mg/kg of epinephrine via low umbilical venous catheter for persistent bradycardia despite effective positive pressure ventilation (PPV) and chest compressions (CC). We evaluated the effects of 1 mL vs 3 mL/kg flush volumes and 0.01 vs 0.03 mg/kg doses on return of spontaneous circulation (ROSC) and epinephrine pharmacokinetics in lambs with cardiac arrest. DESIGN: Forty term lambs in cardiac arrest were randomised to receive 0.01 or 0.03 mg/kg epinephrine followed by 1 mL or 3 mL/kg flush after effective PPV and CC. Epinephrine (with 1 mL flush) was repeated every 3 min until ROSC or until 20 min. Haemodynamics, blood gases and plasma epinephrine concentrations were monitored. RESULTS: Ten lambs had ROSC before epinephrine administration and 2 died during instrumentation. Among 28 lambs that received epinephrine, 2/6 in 0.01 mg/kg-1 mL flush, 3/6 in 0.01 mg/kg-3 mL/kg flush, 5/7 in 0.03 mg/kg-1 mL flush and 9/9 in 0.03 mg/kg-3 mL/kg flush achieved ROSC (p=0.02). ROSC was five times faster with 0.03 mg/kg epinephrine compared with 0.01 mg/kg (adjusted HR (95% CI) 5.08 (1.7 to 15.25)) and three times faster with 3 mL/kg flush compared with 1 mL flush (3.5 (1.27 to 9.71)). Plasma epinephrine concentrations were higher with 0.01 mg/kg-3 mL/kg flush (adjusted geometric mean ratio 6.0 (1.4 to 25.7)), 0.03 mg/kg-1 mL flush (11.3 (2.1 to 60.3)) and 0.03 mg/kg-3 mL/kg flush (11.0 (2.2 to 55.3)) compared with 0.01 mg/kg-1 mL flush. CONCLUSIONS: 0.03 mg/kg epinephrine dose with 3 mL/kg flush volume is associated with the highest ROSC rate, increases peak plasma epinephrine concentrations and hastens time to ROSC. Clinical trials evaluating optimal epinephrine dose and flush volume are warranted.