**5. Porcine model of hypoxia-asphyxia**

Herein we describe an experimental animal model from our research laboratory in newborn piglets that simulates neonatal hypoxia-asphyxia. Using this animal model, we are able to examine the systemic and regional hemodynamic changes during hypoxia-asphyxia, resuscitation interventions, reoxygenation, and the recovery process. The described experimental animal model is a nonsurvival acute procedure in neonatal pigs, aged between 1 and 3 days old and weighing approximately 1.5–2 kg. The approximate duration of the procedure is between six to eight hours and can be divided into the following sections: (i) anesthesia and surgical instrumentation, (ii) monitoring and stabilization, (iii) hypoxia and asphyxia, (iv) resuscitation intervention, and (v) reoxygenation and recovery.

#### **5.1 Anesthesia and surgical instrumentation**

Surgical procedures enable the establishment of mechanical ventilation, arterial and central venous access, and placement of catheters and flow probes for continuously monitoring intravascular pressures and blood flow across the common carotid artery, respectively. Anesthesia is induced using 5% inhaled isoflurane in 100% oxygen (delivered via a nose cone), and is then maintained at 2–3% with fine adjustment by 0.5% as appropriate, depending on the condition of the piglet.

Following induction of anesthesia, an incision is made in the right groin and the right femoral artery and vein are exposed. An area of approximately 1 cm is dissected around each of the vessels, which are then isolated by threading two lengths of suture ties under each vessel. The vessel is ligated distally using a suture tie, a small cut is made in the vessel wall, and then an Argyle catheter (3.5 or 5 French, Covidien, Mansfield, MA) is inserted into the vessel. A double-lumen catheter is used for the femoral vein and is inserted to 15 cm so it is placed close to the right atrium. The venous catheter can be used for medication and maintenance fluid infusions as well as continuous central venous pressure measurement. A singlelumen catheter is used for the femoral artery and is inserted to 5 cm so it is placed at the infra-renal aorta. The single-lumen arterial catheter can be used for continuous mean arterial pressure measurement and blood sampling. The groin incision is then sutured closed. Once vascular access has been established, the inhaled anesthesia can be switched to intravenous anesthesia using morphine and propofol infusions via the venous catheter. This is done after the piglet has been connected to the ventilator machine (see below).

The piglet is then intubated via tracheostomy. A horizontal incision is made at the neck, the trachea is dissected and exposed, and two lengths of suture ties are threaded around the trachea. An endotracheal tube (3.0 or 3.5) is inserted, connected to a ventilator and pressure-controlled ventilation (Acutronic Fabian HFO; Hirzel, Switzerland) is commenced at a respiratory rate of 16–20 breaths/min and pressures of 20/5 cm H2O. Oxygen saturation is kept within 90–100% by adjusting the fraction of inspired oxygen between 21 and 30%.

The right common carotid artery is dissected and exposed, and one length of suture tie is threaded around to isolate the artery. A real-time ultrasonic flow probe (2 mm; Transonic Systems, Ithaca, New York, USA) is placed around the artery and secured, and ultrasonic gel is placed between the flow probe and artery to allow for optimal signal transduction. The flow probe provides continuous carotid blood flow (CBF) measurement. The neck incision is sutured closed. **Figure 1** shows the surgical instrumentation of the piglet.

**171**

body.

**Figure 1.**

*A Porcine Model of Neonatal Hypoxia-Asphyxia to Study Resuscitation Techniques in Newborn…*

A pulse oximeter is placed on the piglet's left hind limb for measuring percutaneous oxygen saturation. Continuous monitoring of the HR is achieved by attaching a 3-lead ECG to the piglet's skin (continuously measured and recorded with Hewlett Packard 78833B monitor, Hewlett Packard, Palo Alto, California, USA). Generally, baseline HR is between 150 and 200 bpm. Glucose level and hydration is maintained with an intravenous infusion of 5% dextrose at 10 mL/kg/hour. The piglet's body temperature is maintained at 38–40°C using an overhead warmer and a heating pad. During the experiment, anesthesia is maintained with intravenous propofol (5-10 mg/kg/hour) and morphine (0.1 mg/kg/hour). Additional doses of propofol (1–2 mg/kg) and morphine (0.05–0.1 mg/kg) are given as needed. The anesthetic state of the piglet is regularly monitored throughout the entire experiment using various criteria: neurological (body movements), behavioral (agitation), cardiovascular (tachycardia and hypertension), and respiratory (tachypnoea). The piglet is allowed to stabilize for 1 hour post surgery before the hypoxia-asphyxia protocol is commenced. **Figure 1** shows the placement of the monitoring devices on the piglet's

*Schematic of neonatal hypoxia-asphyxia porcine model (copyright https://www.playretain.com).*

*DOI: http://dx.doi.org/10.5772/intechopen.89171*

**5.2 Monitoring and stabilization**

*A Porcine Model of Neonatal Hypoxia-Asphyxia to Study Resuscitation Techniques in Newborn… DOI: http://dx.doi.org/10.5772/intechopen.89171*

**Figure 1.**

*Animal Models in Medicine and Biology*

ation and recovery.

of the piglet.

ventilator machine (see below).

surgical instrumentation of the piglet.

the fraction of inspired oxygen between 21 and 30%.

**5. Porcine model of hypoxia-asphyxia**

**5.1 Anesthesia and surgical instrumentation**

Herein we describe an experimental animal model from our research laboratory in newborn piglets that simulates neonatal hypoxia-asphyxia. Using this animal model, we are able to examine the systemic and regional hemodynamic changes during hypoxia-asphyxia, resuscitation interventions, reoxygenation, and the recovery process. The described experimental animal model is a nonsurvival acute procedure in neonatal pigs, aged between 1 and 3 days old and weighing approximately 1.5–2 kg. The approximate duration of the procedure is between six to eight hours and can be divided into the following sections: (i) anesthesia and surgical instrumentation, (ii) monitoring and stabilization, (iii) hypoxia and asphyxia, (iv) resuscitation intervention, and (v) reoxygen-

Surgical procedures enable the establishment of mechanical ventilation, arterial and central venous access, and placement of catheters and flow probes for continuously monitoring intravascular pressures and blood flow across the common carotid artery, respectively. Anesthesia is induced using 5% inhaled isoflurane in 100% oxygen (delivered via a nose cone), and is then maintained at 2–3% with fine adjustment by 0.5% as appropriate, depending on the condition

Following induction of anesthesia, an incision is made in the right groin and the right femoral artery and vein are exposed. An area of approximately 1 cm is dissected around each of the vessels, which are then isolated by threading two lengths of suture ties under each vessel. The vessel is ligated distally using a suture tie, a small cut is made in the vessel wall, and then an Argyle catheter (3.5 or 5 French, Covidien, Mansfield, MA) is inserted into the vessel. A double-lumen catheter is used for the femoral vein and is inserted to 15 cm so it is placed close to the right atrium. The venous catheter can be used for medication and maintenance fluid infusions as well as continuous central venous pressure measurement. A singlelumen catheter is used for the femoral artery and is inserted to 5 cm so it is placed at the infra-renal aorta. The single-lumen arterial catheter can be used for continuous mean arterial pressure measurement and blood sampling. The groin incision is then sutured closed. Once vascular access has been established, the inhaled anesthesia can be switched to intravenous anesthesia using morphine and propofol infusions via the venous catheter. This is done after the piglet has been connected to the

The piglet is then intubated via tracheostomy. A horizontal incision is made at the neck, the trachea is dissected and exposed, and two lengths of suture ties are threaded around the trachea. An endotracheal tube (3.0 or 3.5) is inserted, connected to a ventilator and pressure-controlled ventilation (Acutronic Fabian HFO; Hirzel, Switzerland) is commenced at a respiratory rate of 16–20 breaths/min and pressures of 20/5 cm H2O. Oxygen saturation is kept within 90–100% by adjusting

The right common carotid artery is dissected and exposed, and one length of suture tie is threaded around to isolate the artery. A real-time ultrasonic flow probe (2 mm; Transonic Systems, Ithaca, New York, USA) is placed around the artery and secured, and ultrasonic gel is placed between the flow probe and artery to allow for optimal signal transduction. The flow probe provides continuous carotid blood flow (CBF) measurement. The neck incision is sutured closed. **Figure 1** shows the

**170**

*Schematic of neonatal hypoxia-asphyxia porcine model (copyright https://www.playretain.com).*

#### **5.2 Monitoring and stabilization**

A pulse oximeter is placed on the piglet's left hind limb for measuring percutaneous oxygen saturation. Continuous monitoring of the HR is achieved by attaching a 3-lead ECG to the piglet's skin (continuously measured and recorded with Hewlett Packard 78833B monitor, Hewlett Packard, Palo Alto, California, USA). Generally, baseline HR is between 150 and 200 bpm. Glucose level and hydration is maintained with an intravenous infusion of 5% dextrose at 10 mL/kg/hour. The piglet's body temperature is maintained at 38–40°C using an overhead warmer and a heating pad. During the experiment, anesthesia is maintained with intravenous propofol (5-10 mg/kg/hour) and morphine (0.1 mg/kg/hour). Additional doses of propofol (1–2 mg/kg) and morphine (0.05–0.1 mg/kg) are given as needed. The anesthetic state of the piglet is regularly monitored throughout the entire experiment using various criteria: neurological (body movements), behavioral (agitation), cardiovascular (tachycardia and hypertension), and respiratory (tachypnoea). The piglet is allowed to stabilize for 1 hour post surgery before the hypoxia-asphyxia protocol is commenced. **Figure 1** shows the placement of the monitoring devices on the piglet's body.
