**7. Advantages and limitations of the porcine model of neonatal hypoxia-asphyxia**

Owing to its many advantages, the clinically relevant porcine model of neonatal hypoxia-asphyxia has provided a platform to extensively investigate neonatal resuscitation. The newborn piglet is equivalent to a human infant at 36–38 weeks of gestational age, and has a comparable size and weight (1.5–2 kg body weight). This allows for relatively easy instrumentation to invasively monitor hemodynamic and physiological measurements, such as blood pressure and blood gases, as well as the ability to monitor the degree of hypoxia-asphyxia and reoxygenation in the recovery phase. The large size of this animal model (compared to smaller rodent models) allows the repeated collection of biological samples (plasma, whole blood) during the experimental period for biochemical assays. The piglet's cerebral metabolic data and many of the body systems, including cerebrovascular and cardiovascular systems, are also comparable to the human counterparts. This allows for better interpretation of the findings and makes it an exceptional animal model to study resuscitation interventions. The porcine model of neonatal hypoxia-asphyxia closely simulates delivery room events, with the gradual onset of severe hypoxia-asphyxia leading to cardiac arrest. Bradycardia or asystole (cardiac arrest) in newborn infants is usually caused by hypoxia/asphyxia, rather than

*Animal Models in Medicine and Biology*

The piglet is exposed to severe hypoxemia, which is induced via 30–60 min of normocapnic alveolar hypoxia. The piglet is ventilated with low inspired oxygen concentration delivered by increasing the inhaled concentration of nitrogen gas to induce hypoxemia. The inspired oxygen concentration is adjusted between 10 and 15% to obtain arterial oxygen saturations (SaO2) of 30–40% and partial pressure of oxygen (PaO2) of 20–40 mmHg. Arterial blood sampling is conducted to assess the partial pressure of carbon dioxide (PaCO2) and the ventilator rate is then adjusted

Hypoxia is followed by asphyxia, which is achieved by disconnecting the ventilator and clamping the endotracheal tube. Asphyxia can be conducted until either bradycardia, asystole or PEA (cardiac arrest). In this experimental animal model, bradycardia is defined as 25% of baseline heart rate, and asystole or PEA is defined as zero CBF and confirmed by auscultation of no HR. Following hypoxia-asphyxia,

The primary goal of this experimental animal model is to provide a platform to investigate various resuscitation interventions in a pre-clinical scenario. Although the exact details of resuscitation interventions vary, they are predominantly comprised of the following elements: PPV (performed with a Neopuff T-Piece, Fisher and Paykel, Auckland, New Zealand), CC, ventilations, oxygen, and epinephrine administration. The ultimate outcome of the resuscitation intervention is to achieve return of spontaneous circulation (ROSC) in a timely manner, defined as an unassisted HR ≥100 bpm for at least 15 s. Section 8 summarizes the various resuscitation interventions pub-

Following the resuscitation intervention and ROSC, the piglet is then reconnected to the ventilator with 100% oxygen briefly, and weaned down to 21% oxygen for the 4-hour post-resuscitation recovery period. At the end of the recovery period, the piglet is euthanized with an intravenous overdose of sodium pentobarbital

Using our porcine model of neonatal hypoxia-asphyxia, we are able to describe an increasingly important clinical situation in the laboratory setting. Recent studies from our group have identified the presence of PEA rhythms in nearly half of neonatal pigs that were subjected to hypoxia-asphyxia in animal models of neonatal resuscitation [19–21]. In the study by Patel et al., 43% of piglets (23/54) had no CBF or HR on auscultation but had a HR of 15–80 bpm displayed on ECG, indicating PEA rhythm [20]. Luong et al. reported that 49% of piglets (22/45) presented with PEA rhythms, as indicated by no CBF or HR on auscultation but a HR of 17–75 bpm was displayed on ECG [19]. Solevag et al. also reported that 43% of piglets (9/21) presented with PEA rhythm on ECG, as confirmed by zero CBF and no audible HR/ pulse; however, only 56% of piglets with PEA rhythms achieved ROSC compared to 100% of piglets with non-PEA rhythms (p = 0.02) [21]. Furthermore, survival

lished from our research group using this experimental animal model.

**6. Pulseless electrical activity in the porcine model of neonatal** 

the resuscitation intervention protocol is commenced.

(120 mg/kg). Tissue samples are collected as required.

**5.3 Hypoxia and asphyxia**

**5.4 Resuscitation intervention**

**5.5 Reoxygenation and recovery**

**hypoxia-asphyxia**

accordingly.

**172**

primary cardiac compromise/ventricular fibrillation observed in adult patients. Furthermore, using our newborn piglet model, we are able to describe an increasingly important clinical situation in the laboratory setting – PEA, which is not well described in newborns in the delivery room. However, the asphyxia model uses piglets that have already undergone the transition from fetal to neonatal circulation and have cleared their lung fluid, which may present as a limitation. Furthermore, our model requires piglets to be intubated with a tightly sealed endotracheal tube to prevent any endotracheal tube leak. This may not occur in the delivery room where infants are either intubated (larynx bypassed, leak present) or receive respiratory support via a facemask, resulting in the possibility of airway obstruction or mask leaks. Nevertheless, many of its advantages make up for the few limitations of the model.
