Noninvasive and Invasive Renal Hypoxia Monitoring in a Porcine Model of Hemorrhagic Shock
October 28th, 2022
Presented here is a protocol to measure renal oxygenation in the medulla and noninvasive urine oxygen partial pressure in a hemorrhagic shock porcine model to establish urine oxygen partial pressure as an early indicator of acute kidney injury (AKI) and a novel resuscitative endpoint.
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.
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Overview
This protocol outlines a method to measure renal oxygenation in the medulla and noninvasive urine oxygen partial pressure in a porcine model of hemorrhagic shock. It aims to establish urine oxygen partial pressure as an early indicator of acute kidney injury (AKI) and a novel resuscitative endpoint.
Key Study Components
Area of Science
- Neuroscience
- Renal physiology
- Trauma medicine
Background
- Acute kidney injury (AKI) is a critical condition often arising from traumatic hemorrhagic shock.
- Current methods for assessing kidney function may not provide timely indicators of AKI.
- Urine oxygen partial pressure could serve as a noninvasive marker for early detection.
- This study utilizes a porcine model, which is relevant for human applications.
Purpose of Study
- To establish urine oxygen partial pressure as an early indicator of AKI.
- To potentially reduce the incidence of AKI in patients with traumatic hemorrhagic shock.
- To develop a novel resuscitative endpoint based on renal oxygenation.
Methods Used
- Preparation of puncture sites on Yorkshire swine using chlorhexidine and alcohol.
- Measurement of oxygen concentration directly in the renal medulla.
- Application of sterile draping techniques for surgical procedures.
- Utilization of a porcine model for translational research.
Main Results
- Urine oxygen partial pressure was successfully measured in the porcine model.
- The technique demonstrated potential for early detection of AKI.
- Results indicate a correlation between renal oxygenation and urine oxygen levels.
- This method may improve clinical outcomes in trauma patients.
Conclusions
- Urine oxygen partial pressure can serve as a reliable early indicator of AKI.
- The findings support the use of this method in clinical settings for trauma patients.
- Further research is needed to validate these results in human subjects.
Frequently Asked Questions
Executive Industry Relevance
Early detection of acute kidney injury (AKI) remains a critical challenge in trauma and critical care, with current diagnostics lacking predictive value during resuscitation. This porcine model demonstrates the translational potential of noninvasive urinary partial pressure of oxygen (PuO2) monitoring as an early, organ-specific biomarker for renal hypoxia and AKI risk. Integrating such quantitative, real-time readouts could enable more informed intervention strategies and risk-adjusted portfolio decisions in renal and trauma drug development.
Strategic Applications in Biopharma R&D
Early Discovery & Target Validation
- Enables interrogation of renal hypoxia as a mechanistic driver of AKI in trauma models.
- Supports functional validation of PuO2 as a translational biomarker for early kidney injury.
- Facilitates biological de-risking by providing direct, quantitative hypoxia measurements.
Screening & Assay Development
- Establishes a validated, quantitative system for monitoring renal oxygenation in preclinical models.
- Enables reproducible, noninvasive measurement of PuO2 for assay standardization.
- Supports downstream screening of interventions targeting renal perfusion and hypoxia mitigation.
Translational & Preclinical Research
- Aligns preclinical endpoints with clinically relevant, organ-specific hypoxia markers.
- Provides continuity from mechanistic discovery to translational biomarker validation in AKI.
- Enables risk-adjusted advancement of renal therapeutics based on early, predictive readouts.
Pipeline & Workflow Integration
This model positions noninvasive PuO2 monitoring as a bridge from early discovery through preclinical validation in renal and trauma research pipelines.
- Discovery Biology: Quantitative PuO2 readouts clarify the relationship between renal hypoxia and AKI onset.
- Screening: Standardized PuO2 measurements enable reproducible evaluation of candidate interventions.
- Analytics: Real-time PuO2 and flow data support robust statistical comparison across experimental arms.
- Translational Research: Noninvasive monitoring aligns preclinical and clinical endpoints for biomarker-driven studies.
- Enterprise Reuse: The model and device can be adapted for broader renal and critical care research applications.
Operational & Enterprise Impact
- Scientific Value: Increases predictive confidence in AKI risk assessment and target validation.
- Operational Value: Delivers standardized, scalable, and reproducible renal hypoxia monitoring.
- Strategic Value: Enables earlier go/no-go decisions and reduces late-stage biological risk in renal portfolios.
- Portfolio Impact: Supports risk-adjusted prioritization of renal and trauma therapeutic candidates.
Implementation Considerations
- Requires expertise in large animal surgical models and renal physiology.
- Needs access to optical oxygen sensors and real-time data acquisition systems.
- Demands cross-team standardization of measurement protocols and data interpretation.
- Adaptation to other species or clinical settings may require device and protocol modification.
- Noninvasive PuO2 monitoring is validated in preclinical models; human translation requires further study.
