This protocol is significant because it will establish urine oxygen partial pressure as an early indicator of acute kidney injury, and potentially reduce the incidence in patients with traumatic hemorrhagic shock. As this is a porcine model, it is highly translatable to humans. This technique involves measuring oxygen concentration directly in the renal medulla which cannot be done in humans.
To begin, prepare all puncture sites by scrubbing the skin of Yorkshire swine with three alternating scrubs of chlorhexidine, followed by alcohol. After the last scrub, apply chlorhexidine and allow it to dry completely. Then, drape the surgical site in a sterile fashion.
Locally infiltrate all puncture and incision sites with 2%lidocaine for local pain relief. Using ultrasound guidance and the seldinger technique, place a nine French catheter in the right external jugular vein for medication infusion and central venous pressure monitoring. Next, to monitor pressure distal to the balloon of the resuscitative endovascular occlusion of the aorta or reboa catheter via the left femoral artery sheath.
Connect a disposable pressure transducer to the arterial catheter, distal to the reboa balloon. Perform a midline laparotomy by making an incision along the midline of the abdomen, starting at the inferior part of the sternum and ending at the pubis. To measure PuO2 at the outlet of the bladder, identify the balloon on the catheter.
Then, just below the balloon make an incision along the long axis of the catheter, ensuring not to cut the lumen that connects the balloon. After making an incision, insert a T-connector containing sensing material into the incision and secure the connector in place using tissue glue. With the abdomen open, identify the bladder and perform a cystotomy or make a small incision to insert the tip of a 20 French urinary catheter in the bladder.
Close the cystotomy with the urinary catheter in place using a purse string suture. Then, secure the catheter to the skin with sutures. Before connecting the outlet of the catheter to the urinary collection bag, insert the cone-shaped end of the non-invasive urinary partial pressure of oxygen or PuO2 monitor into the outlet of the catheter.
Place the open tubing at the end of the novel PuO2 monitor over the cone-shaped connector on the tubing connected to the urine collection bag. Next, locate the spleen and identify the hilum of the spleen or the site where the splenic artery and vein enter the spleen. Ligate each vessel using modified miller knots using 2-0 sutures.
Then, clamp and transect each vessel. Connect the fiber optic cable from the bladder data collection device to the connector that contains the sensing material. To measure medullary renal tissue oxygenation, identify the location of the kidney internally and move the bowel to have a clear line of sight and access to the entire kidney.
Under ultrasound guidance, place an 18 gauge needle and the two inch catheter into the renal medulla by inserting the needle into the kidney at a 45 degree angle relative to the surface of the kidney, such that the lure lock end of the needle is positioned towards the feet. Remove the needle while maintaining the catheter in place. Thread the tissue sensor through the catheter and connect the sensor to the catheter using the lure lock.
Secure the catheter using tissue glue and connect the tissue sensor to the data collection box. To induce hemorrhagic shock, remove 25%of the animal's estimated blood volume through the right brachial artery sheath over 30 minutes into a gently agitated citrated blood collection bag. Mark the beginning of blood removal as time zero minute.
Store the removed blood in a water bath at 37 degrees Celsius. Next, insert a seven French reboa catheter in the right femoral artery sheath. Place the balloon of the catheter immediately superior to the diaphragm, and confirm the location using fluoroscopy.
At 30 minutes, inflate the reboa balloon and completely occlude the aorta for 45 minutes. Next, infuse intravenous calcium over 10 minutes to prevent citrate induced hypocalcemia. Then initiate resuscitation and administer critical care.
At 70 minutes, transfuse pig with shed blood over 15 minutes. At 105 minutes, deflate the reboa balloon for 10 minutes. Then, resuscitate the pig until 360 minutes with norepinephrine and fluids to maintain a mean arterial pressure, or MAP, higher than 65 millimeters of mercury.
A plot of MAP and non-invasive PuO2 measurements during the described hemorrhagic shock porcine model is shown here. At the start of the experiment, as hemorrhage was initiated, there was a drop in MAP and PuO2. Following the initial decline in PuO2, it gradually increased until after the reboa balloon was deflated.
During the critical care phase, there was a significant drop off in PuO2. The MAP appears to remain constant during the critical care period, and PuO2 reaches a maximum at around 180 minutes followed by a decrease until 240 minutes, which is followed by a gradual increase until the end of the experiment. Based on this study, urine oxygen partial pressure monitoring may lead to earlier detection of acute kidney injury and guide future potential interventions to improve outcomes in patients with trauma.
