This protocol is significant as it enables the study of hemodynamic and physiological changes before, during, and after perinatal asphyxia and cardiac arrest. Because this model includes cardiac arrest, it allows us to study the factors related to neonatal cardiopulmonary resuscitation and how they affect physiology and hemodynamics. This model provides valuable information about asphyxiated neonates.
The observations shed light on the pathophysiology of cardiac arrest including pulseless electrical activity. This extends its applicability to other patient groups. This model is technically challenging and experiments should be performed in facilities experienced with large and long research, preferably big sub pellets.
The protocol must be studied in detail. Joining me in demonstrating this procedure will be Ronnaug Solberg, Anne Lee Solevag, and Sera Sebastian, an operating room nurse, from our research facilities at the University of Oslo. Before beginning the surgical intervention prepare all the necessary equipment and fill all the catheters with normal saline.
Note the time the surgery starts on the case registration form or CRF. Sterilize the skin of the anesthetized piglet with five milligrams per milliliter of colored chlorhexidine using three to five surgical sponges and cover with an adhesive aperture drape. Make a 2.5 centimeter long skin incision on the right side of the piglet's neck, and retract the skin on both sides of the incision using eyelid retractors.
Next, with the help of artery forceps, dissect and expose the internal jugular vein and place two-three-zero nylon suture threads under the jugular vein to keep it stable. Holding one of the sutures in one hand, and the central venous catheter in the other, insert the catheter and withdraw the needle. Flush with one milliliter of normal saline to confirm the correct placement of the catheter.
Now tie one of the suture threads that was used to hold the vein around the vein and the catheter in the area where the catheter is inside the vein. Close the skin with absorbable four-zero sutures and connect Fentanyl IV and a balanced carbohydrate electrolyte solution to the central venous catheter. Using a scalpel, make a 2.5 centimeter long skin incision on the left side of the piglet's neck, slightly more medial than the previous incision on the right side.
Then retract the skin on both sides of the incision using eyelid retractors. With the help of artery forceps, dissect and expose the common carotid artery medial to the sternocleidomastoid muscle. Stabilize the common carotid artery by placing a pair of nylon three-zero suture threads under it.
Holding one of the sutures in one hand and the central arterial catheter in the other, insert the central arterial catheter and withdraw the needle. Then tie one of the suture threads holding the artery around the artery and the catheter in the area where the catheter is inside the artery. After confirming the correct placement of the catheter by flushing it with one milliliter of normal saline, secure the catheter wings to the skin with absorbable four-zero sutures and close the skin.
Next, connect the piglet to the invasive arterial blood pressure monitoring system. Cover the catheter with a transparent dressing and start the data acquisition. Once the central arterial catheter is in place, note the surgery ending time on the CRF.
Note down the time of starting the asphyxia on the CRF along with the physiological measurements of the piglet. Immediately before starting the asphyxia, collect blood samples from the piglet and stop the Fentanyl IV administration. To begin the asphyxia, turn the oxygen dial on the mechanical ventilator to 100%and reduce the ventilator rate by 10 inflations per minute.
While switching the oxygen hose on the ventilator to the asphyxia gas, ensure the piglet's oxygen saturation is reduced to ascertain successful induction of asphyxia. After continuing the asphyxia for 10 minutes reduce the ventilator rate by another 10 inflations per minute. From this point onwards, after 10 minutes and thereafter every five minutes till cardiac arrest.
Track the acid-based status and note the physiological measurements of the piglet down the CRF. Continue the asphyxia until cardiac arrest. Reduce the ventilator rate by 10 inflations per minute every 10 minutes, and clamp the endotracheal tube or ETT with arterial forceps after 30 minutes of asphyxia.
When the mean arterial pressure drops below 20 millimeters of mercury, start the continuous auscultation of the heart. Auscultate the heart and inform the team when the heartbeat becomes inaudible. Then remove the ETT clamp if applicable and set the appropriate fraction of inspired oxygen and the ventilator settings as per the protocol.
At the same time, switch back the asphyxia gas hose on the ventilator to the oxygen outlet. Finally, draw blood samples corresponding to the cardiac arrest time point while preparing for cardiopulmonary resuscitation. If following the International Liaison Committee on resuscitation recommended three to one CPR, mechanically ventilate the piglet for 30 seconds after the cardiac arrest.
Then start the chest compressions and aim for a chest compression to ventilation ratio of three to one. Use the two thumb and circling hands technique to compress the chest to a depth of one third of the thoracic and posterior diameter and allow full chest recoil. Aim to generate a systolic arterial pressure greater than 20 millimeters of mercury.
After 30 seconds of chest compressions administer adrenaline IV and repeat it after every three minutes of CPR for a maximum of four doses. Flush the catheter with one milliliter of normal saline after each adrenaline administration. Determine the return of spontaneous circulation or ROSC by observing the arterial blood pressure tracings and the ECG and confirm the same by cardiac auscultation.
Continue the resuscitation efforts until ROSC or for a maximum of 15 minutes. If resuscitation is successful, note the time of ROSC, the duration of CPR in seconds, and the number of adrenaline doses administered in the CRF. If CPR is not successful within 15 minutes stop the resuscitation efforts and record the time of death.
Finally, after ROSC, take blood samples and CRF registrations as soon as possible and continue the registrations as described in the manuscript for another 9.5 hours. The piglet's blood pressure dropped gradually since the beginning of asphyxia and became zero when cardiac arrest occurred. The BP increased once ROSC was achieved before taking some time to normalize again.
The changes in the piglet's physiology during the asphyxia were clearly indicated by the changes in the heart rate, the mean arterial pressure, the pH, the partial pressure of carbon dioxide, the base excess, and the lactate. As expected, the mean arterial pressure, pH and base excess decreased during asphyxia while the partial pressure of carbon dioxide and lactate signifying the mixed respiratory and metabolic acidosis increased. However, the values normalized toward the end of the experiment.
Maintaining good ventilation during cardiopulmonary resuscitation and correct data sampling throughout are particularly critical parts of this protocol. This newborn model has provided evidence for guideline development through research on the use of supplementary oxygen and resuscitation protocols. In addition, pathophysiology, biomarkers, and novel methods for hemodynamic monitoring have been investigated.
