Animal models in neonatal resuscitation research: What can they teach us?

Impact of cord clamping on haemodynamic transition in term newborn infants

OBJECTIVE

To assess the haemodynamic consequences of cord clamping (CC) in healthy term infants.

DESIGN

Cohort study.

SETTING

Tertiary maternity hospital.

PATIENTS

46 full-term vigorous infants born by caesarean section.

INTERVENTIONS

Echocardiography was performed before CC, immediately after CC and at 5 min after birth.

MAIN OUTCOME MEASURES

Pulsed wave Doppler-derived cardiac output and the pulmonary artery acceleration time indexed to the right ventricle ejection time were obtained. As markers of loading fluctuations, the myocardial performance indexes and the velocities of the tricuspid and mitral valve annuli were determined with tissue Doppler imaging. Heart rate was derived from Doppler imaging throughout the assessments.

RESULTS

Left ventricular output increased throughout the first minutes after birth (mean (SD) 222.4 (32.5) mL/kg/min before CC vs 239.7 (33.6) mL/kg/min at 5 min, p=0.01), while right ventricular output decreased (306.5 (48.2) mL/kg/min before vs 272.8 (55.5) mL/kg/min immediately after CC, p=0.001). The loading conditions of both ventricles were transiently impaired by CC, recovering at 5 min. Heart rate progressively decreased after birth, following a linear trend temporarily increased by CC. The variation in left ventricular output across the CC was directly correlated to the fluctuation of left ventricular preload over the same period (p=0.03).

CONCLUSIONS

This study illustrates the cardiovascular consequences of CC in term vigorous infants and offers insight into the haemodynamic transition from fetal to neonatal circulation in spontaneously breathing newborns. Strategies that aim to enhance left ventricular preload before CC may prevent complications of perinatal cardiovascular imbalance.

Chest compressions superimposed with sustained inflation during neonatal cardiopulmonary resuscitation: are we ready for a clinical trial?

Neonates requiring cardiopulmonary resuscitation (CPR) are at risk of mortality and neurodevelopmental injury. Poor outcomes following the need for chest compressions (CCs) in the delivery room prompt the critical need for improvements in resuscitation strategies. This article explores a technique of CPR which involves CCs with sustained inflation (CC+SI). Unique features of CC+SI include (1) improved tidal volume delivery, (2) passive ventilation during compressions, (3) uninterrupted compressions and (4) improved stability of cerebral blood flow during resuscitation. CC+SI has been shown in animal studies to have improved time to return of spontaneous circulation and reduced mortality without significant increase in markers of inflammation and injury in the lung and brain, compared with standard CPR. The mechanics of CCs, rate of compressions, ventilation strategies and compression-to-ventilation ratios are detailed here. A large randomised controlled trial comparing CC+SI versus the current 3:1 compression-to-ventilation ratio is needed, given the growing evidence of its potential benefits.

Intact cord resuscitation in newborns with congenital diaphragmatic hernia: insights from a lamb model

Introduction

Congenital diaphragmatic hernia (CDH) is a rare condition characterized by pulmonary hypoplasia, vascular dystrophy, and pulmonary hypertension at birth. Validation of the lamb model as an accurate representation of human CDH is essential to translating research findings into clinical practice and understanding disease mechanisms. This article emphasizes the importance of validating the lamb model to study CDH pathogenesis and develop innovative therapeutics.

Material and methods

At 78 days of gestation, the fetal lamb's left forelimb was exposed through a midline laparotomy and hysterotomy, and a supra diaphragmatic thoracotomy was performed to allow the digestive organs to ascend into the thoracic cavity. At 138 ± 3 days of gestation, lambs were delivered via a cesarean section; then, with umbilical cord intact during 1 hour, the lambs were mechanically ventilated with gentle ventilation in a pressure-controlled mode for 2 h.

Results

CDH lambs exhibited a lower left lung-to-body weight ratio of 5.3 (2.03), p < 0.05, and right lung-to-body weight ratio of 8.2 (3.1), p < 0.05. They reached lower Vt/kg (tidal volume per kg) during the course of the resuscitation period with 1.2 (0.7) ml/kg at 10 min and 3 (1.65) ml/kg at 60 min (p < 0.05). Compliance of the respiratory system was lower in CDH lambs with 0.5 (0.3) ml/cmH2O at 60 min (p < 0.05) and 0.9 (0.26) ml/cmH2O at 120 min (p < 0.05). Differences between pre- and postductal SpO2 were higher with 15.1% (21.4%) at 20 min and 6.7% (14.5%) at 80 min (p < 0.05). CDH lambs had lower differences between inspired and expired oxygen fractions with 4.55% (6.84%) at 20 min and 6.72% (8.57%) at 60 min (p < 0.05). CDH lamb had lower left ventricle [2.73 (0.5) g/kg, p < 0.05] and lower right ventricle [0.69 (0.8), p < 0.05] to left ventricle ratio.

Discussion

CDH lambs had significantly lower tidal volume than control lambs due to lower compliance of the respiratory system and higher airway resistance. These respiratory changes are characteristic of CDH infants and are associated with higher mortality rates. CDH lambs also exhibited pulmonary hypertension, pulmonary hypoplasia, and left ventricle hypoplasia, consistent with observations in human newborns. To conclude, our lamb model successfully provides a reliable representation of CDH and can be used to study its pathophysiology and potential interventions.

Vasopressin versus epinephrine during neonatal cardiopulmonary resuscitation of asphyxiated post-transitional piglets

Background

Epinephrine is currently the only recommended cardio-resuscitative medication for use in neonatal cardiopulmonary resuscitation (CPR), as per the consensus of science and treatment recommendations. An alternative medication, vasopressin, might be beneficial in neonatal CPR due to its combined pulmonary vasodilation and systemic vasoconstriction properties.

Aim

We aimed to compare the time to return of spontaneous circulation (ROSC) with administration of vasopressin or epinephrine during CPR of asphyxiated post-transitional piglets.

Methods

Newborn piglets (n = 8/group) were anesthetized, tracheotomized and intubated, instrumented, and exposed to 50 min normocapnic hypoxia followed by asphyxia and cardiac arrest. Piglets were randomly allocated to receive vasopressin (Vaso, 0.4 U/kg) or epinephrine (Epi, 0.02 mg/kg) during CPR. Piglets were resuscitated with chest compressions superimposed with sustained inflations, and were administered either Vaso or Epi intravenously every 3 min until ROSC (max. 3 doses). Hemodynamic and cardiac function parameters were collected.

Main Results

The median (IQR) time to ROSC was 106 (93-140) s with Vaso and 128 (100-198) s with Epi (p = 0.28). The number of piglets that achieved ROSC was 8 (100%) with Vaso and 7 (88%) with Epi (p = 1.00). Vaso-treated piglets had a significantly longer post-resuscitation survival time (240 (240-240) min) than Epi-treated piglets (65 (30-240) min, p = 0.02). Vaso-treated piglets had significantly improved carotid blood flow immediately after ROSC (p < 0.05), had longer duration of post-resuscitation hypertension (p = 0.05), and had significantly improved heart rate, arterial pressure, and cerebral blood oxygen saturation 4 h after ROSC (p < 0.05).

Conclusions

Vasopressin improved post-resuscitation survival and hemodynamics, and might be an alternative cardio-resuscitative medication during neonatal CPR, but further studies are warranted.

Four Different Finger Positions and Their Effects on Hemodynamic Changes during Chest Compression in Asphyxiated Neonatal Piglets

Background: The Neonatal Life Support Consensus on Science With Treatment Recommendations states that chest compressions (CC) be performed preferably with the 2-thumb encircling technique. The aim of this study was to compare the hemodynamic effects of four different finger positions during CC in a piglet model of neonatal asphyxia. Methods: Seven asphyxiated post-transitional piglets were randomized to CC with 2-thumb-, 2-finger-, knocking-fingers-, and over-the-head 2-thumb-techniques for one minute at each technique. CC superimposed with sustained inflations were performed manually. Results: Seven newborn piglets (age 0-4 days, weight 2.0-2.1 kg) were included in the study. The mean (SD) slope rise of carotid blood flow was significantly higher with the 2-thumb-technique and over-the-head 2-thumb-technique (118 (45) mL/min/s and 121 (46) mL/min/s, respectively) compared to the 2-finger-technique and knocking-finger-technique (75 (48) mL/min/s and 71 (67) mL/min/s, respectively) (p < 0.001). The mean (SD) dp/dt_min (as an expression of left ventricular function) was significantly lower with the 2-thumb-technique, with -1052 (369) mmHg/s, compared to -568 (229) mmHg/s and -578(180) mmHg/s (both p = 0.012) with the 2-finger-technique and knocking-finger-technique, respectively. Conclusion: The 2-thumb-technique and the over-the-head 2-thumb-technique resulted in improved slope rises of carotid blood flow and dp/dtmin during chest compression.

Optimizing initial neonatal resuscitation to reduce neonatal encephalopathy around the world

One million two hundred thousand neonatal lives are lost each year due to intrapartum-related events; 99% of these deaths occur in low- and lower middle-income countries. Neonates exposed to intrapartum-related events present with failure to breathe at birth. Quick and effective delivery room management of these neonates is critical in the prevention of brain injury. Given the prominent role of lung aeration in the cardiopulmonary transition at birth, the mainstay of neonatal resuscitation is effective ventilation. Basic neonatal resuscitation focuses on simple stimulation, airway positioning and clearing, and bag-mask ventilation. Although principles for basic neonatal resuscitation remain the same for high- and low-resource settings, guidelines may differ based on available human and material resources. Formal training in basic resuscitation reduces intrapartum-related neonatal mortality in low-resource settings. However, there remain opportunities to improve provider performance for increased impact with other strategies such as regular practice and continuous quality improvement.

Future Perspective of Diabetic Animal Models

Objective

The need of today’s research is to develop successful and reliable diabetic animal models for understanding the disease susceptibility and pathogenesis. Enormous success of animal models had already been acclaimed for identifying key genetic and environmental factors like Idd loci and effects of microorganisms including the gut microbiota. Furthermore, animal models had also helped in identifying many therapeutic targets and strategies for immune-intervention. In spite of a quite success, we have acknowledged that many of the discovered immunotherapies are working on animals and did not have a significant impact on human. Number of animal models were developed in the past to accelerate drug discovery pipeline. However, due to poor initial screening and assessment on inequivalent animal models, the percentage of drug candidates who succeeded during clinical trials was very low. Therefore, it is essential to bridge this gap between pre-clinical research and clinical trial by validating the existing animal models for consistency.

Results and Conclusion

In this review, we have discussed and evaluated the significance of animal models on behalf of published data on PUBMED. Amongst the most popular diabetic animal models, we have selected six animal models (e.g. BioBreeding rat, “LEW IDDM rat”, “Nonobese Diabetic (NOD) mouse”, “STZ RAT”, “LEPR Mouse” and “Zucker Diabetic Fatty (ZDF) rat” and ranked them as per their published literature on PUBMED. Moreover, the vision and brief imagination for developing an advanced and robust diabetic model of 21^st century was discussed with the theme of one mice-one human concept including organs-on-chips.

Physiological-based cord clamping in preterm infants using a new purpose-built resuscitation table: a feasibility study

OBJECTIVE

Physiological-based cord clamping (PBCC) led to a more stable cardiovascular adaptation and better oxygenation in preterm lambs, but in preterm infants, this approach has been challenging. Our aim was to assess the feasibility of PBCC, including patterns of oxygen saturation (SpO₂) and heart rate (HR) during stabilisation in preterm infants using a new purpose-built resuscitation table.

DESIGN

Observational study.

SETTING

Tertiary referral centre, Leiden University Medical Centre, The Netherlands.

PATIENTS

Infants born below 35 weeks' gestational age.

INTERVENTIONS

Infants were stabilised on a new purpose-built resuscitation table (Concord), provided with standard equipment needed for stabilisation. Cord clamping was performed when the infant was stable (HR >100 bpm, spontaneous breathing on continuous positive airway pressure with tidal volumes >4 mL/kg, SpO₂ ≥25th percentile and fraction of inspired oxygen (FiO₂) <0.4).

RESULTS

Thirty-seven preterm infants were included; mean (SD) gestational age of 30.9 (2.4) weeks, birth weight 1580 (519) g. PBCC was successful in 33 infants (89.2%) and resulted in median (IQR) cord clamping time of 4:23 (3:00-5:11) min after birth. There were no maternal or neonatal adverse events. In 26/37 infants, measurements were adequate for analysis. HR was 113 (81-143) and 144 (129-155) bpm at 1 min and 5 min after birth. SpO₂ levels were 58%(49%-60%) and 91%(80%-96%)%), while median FiO₂ given was 0.30 (0.30-0.31) and 0.31 (0.25-0.97), respectively.

CONCLUSION

PBCC in preterm infants using the Concord is feasible. HR remained stable, and SpO₂ quickly increased with low levels of oxygen supply.

TRIAL REGISTRATION NUMBER

NTR6095, results.

Chest Compressions in the Delivery Room

Annually, an estimated 13–26 million newborns need respiratory support and 2–3 million newborns need extensive resuscitation, defined as chest compression and 100% oxygen with or without epinephrine in the delivery room. Despite such care, there is a high incidence of mortality and neurologic morbidity. The poor prognosis associated with receiving chest compression alone or with medications in the delivery room raises questions as to whether improved cardiopulmonary resuscitation methods specifically tailored to the newborn could improve outcomes. This review discusses the current recommendations, mode of action, different compression to ventilation ratios, continuous chest compression with asynchronous ventilations, chest compression and sustained inflation optimal depth, and oxygen concentration during cardiopulmonary resuscitation.

The Changing Landscape in Supporting Preterm Infants at Birth

Noninvasive ventilation for preterm infants at birth has been recommended and universally adopted. The umbilical cord is often clamped immediately in order to provide the support the infant needs for stabilization. However, recent scientific data from experimental studies that involve animals in transition and human studies using physiological measurements at birth have increased awareness as to how little we know about how these interventions interact and integrate with the infant's changing physiology. It has become clear that in apneic infants the larynx is closed immediately after birth, which can completely negate the effect of noninvasive ventilation of the lung. For this reason, stimulating and supporting spontaneous breathing could enhance the success of noninvasive ventilation. Animal data also demonstrated that the large swings in blood pressure, blood flow, and oxygenation caused by immediate cord clamping can be avoided by postponing cord clamping until lung aeration has been established. In this review we will focus on these "game changers" that have the potential to completely change the approach used in stabilizing preterm infants at birth.