Medicine
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Complete and Partial Aortic Occlusion for the Treatment of Hemorrhagic Shock in Swine
Chapters
Summary August 24th, 2018
Here, we present a protocol demonstrating a hemorrhagic shock model in swine that uses aortic occlusion as a bridge to definitive care in trauma. This model has application in testing a wide range of surgical and pharmacological therapeutic strategies.
Transcript
This method can help answer key questions in the field of trauma care, including strategies to treat non-compressible torso hemorrhage. The main advantage of this technique is that it can help test relevant endovascular resuscitative strategies in a clinically realistic large animal model with the physiology that mimics that of humans. The implications of this technique extend towards the treatment of hemorrhagic shock, which is a leading cause of preventable death in trauma.
Generally, people new to this method will struggle, because it requires surgical expertise and knowledge of critical care physiology. After confirming an appropriate level of sedation using a hind limb pinch, use a conventional laryngoscope fitted with a 12 inch lighted Miller blade to pass the tip of the blade through the oropharynx of the anesthetized pig. Taking care not to damage the oral mucosa or the teeth, slowly advance the blade tip to the epiglottis, lifting the epiglottis with the blade, and continuing past the laryngeal inlet until a clear view of the larynx is obtained.
Place a 6.5 or 7 French endotracheal tube with a stylet between the vocal folds, into the trachea, and inflate the balloon cuff with 10 to 15 cubic centimeters of air to prevent leaking around the cuff or aspiration of the gastric contents. Then, connect the endotracheal tube to the mechanical ventilator through a breathing filter, and secure the tube around the maxilla with cotton tape. For a femoral artery and vein cannulation, scrub the operative sites with a copious volume of povidone iodine for five minutes, and place the sterile surgical towels around the operative sites to preserve the sterility of the surgical fields.
Using a scalpel fitted with a number 10 sterile surgical blade, identify the inguinal crease and make a vertical eight centimeter incision in the right groin, four centimeters above and four centimeters below the right inguinal crease. Dissect through the subcutaneous tissue, and place two Weitlaner retractors into the incision. Using Mixter right angle forceps and an electrocautery, dissect through the connective tissues and muscle until the neurovascular bundle is clearly exposed, and cautiously dissect the artery, taking care to preserve the lateral nerve.
Use a 20 gauge angled introducer needle to puncture the artery, and advance a round-tipped, 0.35 inch guide wire through the lumen of the angled needle. When the guide wire is in place, withdraw the needle over the guide wire, holding slight pressure over the arteriotomy to prevent bleeding, and insert a 14 French insertion sheath over the guide wire. Then, cannulate the left femoral artery and vein as just demonstrated.
For carotid artery and external jugular vein cannulation, use a number 10 blade scalpel to make a six centimeter vertical incision about two centimeters lateral to the midline on the left side of the neck. Use electrocautery to dissect through the subcutaneous tissue until the sternocleidomastoid muscle is exposed, and dissect along the lateral border of the muscle to expose the left external jugular vein. Then, cannulate the vessel with an 8 French catheter as just demonstrated.
For left common carotid artery exposure, dissect the medial edge of the sternocleidomastoid muscle, until the carotid triangle, which contains the carotid artery, the vagus nerve, and the internal jugular vein, is observed. Cannulate the carotid artery as previously demonstrated, with a 5 French catheter. For the contralateral dissection, isolate the right external jugular vein and right common carotid artery, as demonstrated for their lateral counterparts.
Then, use a 9 French introducer sheath to cannulate the right external jugular vein, and place a four millimeter carotid artery flow probe around the right common carotid artery. Next, insert the pulmonary artery catheter through the 9 French insertion sheath 15 to 18 centimeters into the right external jugular vein. Once the catheter is in place, inflate the balloon with no more than 1.5 cubic centimeters of air.
Advance the catheter and observe the monitor to evaluate the transition of the pressure from the right atrium to the right ventricle, to the pulmonary artery, to the pulmonary artery wedge pressure. Then, deflate the balloon and confirm that a pulmonary artery trace returns to the monitor. For cystostomy tube placement, use a number 10 blade scalpel to make a midline five centimeter lower abdominal incision, and extracorporealize the urinary bladder.
Using electrocautery, make a small opening in the bladder and suction out the urine, and use a 4-0 polypropylene suture to perform a temporary purse string closure of the bladder. Place an 18 French foley catheter inside the bladder lumen, and use a 10 cubic centimeter syringe to inflate the balloon. Then, tie the suture to secure the catheter within the bladder lumen.
For aortic balloon catheter insertion, insert a 0.035 inch, 260 centimeter Amplatz stiff guide wire through the 14 French insertion sheath. Confirm its location in the supraceliac aorta using ultra sonography. Then, insert the balloon occlusion catheter over the guide wire, into the supraceliac aorta.
After calculating the total blood volume, use an automated pump to hemorrhage 35%of the total blood volume over 20 minutes, into standard blood collection bags for storage at four degrees Celsius. When all the blood has been stored, inflate the aortic balloon occlusion catheter with 9 to 12 cubic centimeters of air, or until no further decrease in the distal mean arterial pressure following an additional balloon inflation is noted. After 40 minutes of occlusion, use the automated pump to resuscitate the animal, with whole blood equal in volume to 20%of the total blood volume via the left femoral vein catheter over 20 minutes.
Then, deflate the balloon incrementally over five minutes. During the balloon inflation phase, animals in the complete occlusion group experience a higher proximal mean arterial pressure, compared to animals in the partial occlusion group, while the average distal mean arterial pressure during the balloon inflation is higher in the partial occlusion group compared to complete occlusion group, reflecting the partial distal aortic flow. Following resuscitation, the proximal and distal mean arterial pressure increases in both groups, and returns to baseline following the balloon deflation for the remainder of the critical care phase.
All animals experience reflex tachycardia immediately following the hemorrhage that undergoes an incremental increase during the balloon inflation phase in both groups. Following hemorrhage, the central venous pressure decreases in both groups, undergoing an increase following balloon deflation, and returning to baseline after resuscitation. Similarly, the cardiac output decreases following hemorrhage, increases during balloon inflation, and returns to baseline following balloon deflation in resuscitation in both groups.
The carotid flow decreases in both groups immediately following hemorrhage, with the complete occlusion group demonstrating a higher carotid flow rate compared to the partial occlusion group. Following resuscitation and balloon deflation, the carotid flow rate recovers towards baseline in both groups, but at a lower level in the complete occlusion group. After watching this video, you should have a much better understanding of how to use large animal models to test aortic occlusion using endovascular strategies.
Also, just like any other surgical operation, you have to be careful in handling the instruments to be able to do it safely.
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