Description of a Swine Infant Model of Volume-Controlled Hemorrhagic Shock

Hemorrhagic shock is the main cause of death in children in the developed world. This study provides the opportunity to compare the response to different therapies for hemorrhagic shock. This is a simple and highly reproducible model that allows activation of mechanisms in response to severe hemorrhages in an immature subject.

In this protocol, the translation of results is high, and with help to identify better the choice of fluids and rest for resuscitation in terms of lower adverse effect. This model allows to study the effect of different resuscitation fluids and vasoactive drugs in various systems such as micros circulation, coagulation, endothelial, and glycocalyx. Begin by placing the anesthetized animal on a surgical table with a warming blanket.

Then measure the peripheral oxygen saturation with a sensor clipped to the pig's ear. Initiate continuous three lead electrocardiographic monitoring. Insert a peripheral vein catheter into the ear vein, disinfecting the skin with at least three alternating rounds povidone iodine or chlorhexidine scrub and alcohol beforehand.

Next, place the animal in the dorsal recumbency position and immediately initiate handbag mask ventilation with a dog mask. To begin the endotracheal intubation procedure, ensure that the necessary equipment and surgical tools are sterilized and ready to use. Pull out the tongue slightly and hold the jaw open using tie gauze placed behind the upper and lower canine teeth.

Insert the laryngoscope. And once the epiglottis is visible, press it upwards towards the tongue using the laryngoscope's tip. Once the vocal cords are visualized, gently advance the tube with slight rotation into the trachea.

Remove the stylet and use a five milliliter syringe to inflate the cuff. To ensure the proper placement of the endotracheal tube, observe the symmetrical chest rise, adequate oxygen saturation between 95 and 100%and a proper waveform and end-tidal carbon dioxide reading. Once intubation is confirmed, initiate mechanical ventilation with a respiratory rate of 20 breaths per minute.

Title volume of eight milliliters per kilogram, fraction of inspired oxygen of 40%and positive end expiratory pressure of four centimeters of water. Adjust ventilation to achieve a partial pressure of carbon dioxide between 35 and 45 millimeters of mercury. Maintain deep anesthesia throughout the experiment via continuous infusion of fentanyl, propofol, and atracurium.

To prepare the femoral area for vessel catheterization, disinfect the inguinal area with at least three alternating rounds of povidone iodine or chlorhexidine scrub, and alcohol. Next, assess the femoral vessels with ultrasound and use the Doppler technique to distinguish between the artery and the vein. Under continuous ultrasound view and using the Seldinger technique, insert a 5.5 to 7.5 French central venous catheter needle in one of the femoral veins.

Then puncture the vein and obtain the blood. Withdraw the syringe and introduce the guide wire in the needle. When the guide wire is in its place in the vein, remove the guide wire and introduce the catheter until reaching the vein.

Immediately after catheter placement, connect to transducer system to measure the central venous pressure. Next, ensure that an electrolyte with a glucose infusion rate of 20 milliliters per hour is connected to one of the central line ports. And then maintenance saline is infused via the remaining port to prevent the occlusion of the catheter.

Next, insert a 4-French arterial catheter needle into the femoral artery. Then insert the guide wire under ultrasound guidance, and then insert the catheter. Once the arterial catheter is inserted, connect the arterial wire of the cardiac output monitor system and the arterial transducer directly to the monitor port.

At the same time, connect the venous measuring unit of the monitor to the central venous transducer. Next, disinfect the neck area with at least three alternating rounds of povidone iodine or chlorhexidine scrub, and alcohol. Make a 10 centimeter left paratracheal incision bisecting a line between the manubrium and the angle of the jaw.

To expose the external jugular vein, dissect the lateral tissue to the sternocleidomastoid muscle, and isolate the vein from the surrounding fascia. Next, use two non-absorbable silk sutures looped around the vein to fixate the vessel prior to the puncture. Incise the vein with an 18-gauge venflon needle.

Once inside the vein, retract the needle and insert the guide wire through the venflon tube. Remove the venflon tube and insert the sheath with the 5-French introducer over the wire. Once the sheath is inserted, remove both the introducer and the wire.

Immediately after insertion, rinse the sheaths with 0.9%sodium chloride to prevent thrombus formation. Next, tie up the proximal silk suture around the sheath to secure it in place. Then attach the handle of the sheath to the sternocleidomastoid muscle, and close the skin with staples.

To obtain cardiac index values, infuse five milliliter boluses of 0.9%normal saline through the central venous catheter. Finally, record the average of two consecutive measures. Once a steady state is achieved after instrumentation and baseline data collection, induce hypovolemic shock by withdrawing 30 milliliters per kilogram of blood from the jugular vein over 30 minutes.

Allow 30 minutes for stabilization and do not make any resuscitation efforts during this period to emulate the delay in the arrival of emergency medical teams. This model showed that a controlled hemorrhage produced noticeable changes in hemodynamic parameters as well as in cerebral and tissue perfusion. Following volume withdrawal, significant tachycardia and a decrease in mean arterial blood pressure cardiac index, stroke volume index, blood volume parameters, and carotid arterial blood flow was observed while the systemic vascular resistance index increased.

The infusion of albumin plus hypertonic saline produced a greater and longer volume expansion than normal or hypertonic saline alone with significant differences in heart rate, stroke volume index, and pressure pulse variation. The fluid infusion also depicted the absence of a progressive fall after volume expansion in blood pressure and global end diastolic volume index. The systemic perfusion parameters demonstrated an increase in the lactate concentration, whereas central venous saturation, cutaneous and cerebral tissue oxygenation index decreased.

The hypertonic albumin improved the perfusion parameters with an increase in carotid blood flow and brain tissue oxygenation index, and a significant decrease in lactate levels. Maintain deep anesthesia throughout the experiment to achieve a steady state before shock induction, including body temperature and to keep a constant rhythm during blood withdrawal. The recording and further analysis of the sublingual micro circulation is very interesting to study the difference between macro and micro circulation.

On the other hand, this scholastic testing to assess coagulation is useful to analyze the impairment induced by hemodilution after volume expansion.