Transdermal Measurement of Glomerular Filtration Rate in Mechanically Ventilated Piglets

TGFR offers a real-time assessment of kidney functions. Compared to traditional markers, TGFR can monitor changes in kidney function in the same animals multiple times. Additionally, the technique does not require any blood or urine collection.

With recent advances in xenotransplantation, more research will be conducted using the swine model. So we believe this tool will be essential for translational research, and it's more likely to be utilized clinically in the coming years. The experiment is conducted on three to seven-days-old piglets.

The animals are prone to hypothermia, hypovolemia, and other complications arising from surgery. Hence, close monitoring is required throughout the procedure. Also, the methodology requires practice as it involves tracheostomy and vessel cannulations.

After preparing the animal for the procedure, use a surgical blade to create a five to six-centimeter left paramedian vertical incision, as the cecum in pigs lies in the left paralumbar fossa. Dissect the abdominal wall layers, avoiding injury to the superficial epigastric vessels. Once the peritoneal layer is incised, use a retractor to improve access to the intraabdominal structures and identify the spiral colon in the upper left quadrant of the abdomen.

To locate the cecum, trace the spiral colon caudally and dorsally. The spiral colon at the base of the cecum is joined to the ilium. Ligate the cecum just distal to the ileocecal junction.

Using an 18-gauge needle, make seven punctures in the cecum and extrude feces into the peritoneal area. Close the abdominal layers with a 3/0 silk suture, using either simple interrupted or continuous stitches. A stapler may also be used to close the skin layer if available.

After eight hours of cecal ligation, initiate transdermal GFR measurement. Use the MB Service software version 3.0 to adjust the sampling rate on the GFR device. Using the USB connector, connect the transdermal GFR device to the computer.

Open the MB Service software. Click connect and adjust the timing to 4, 000 milliseconds. Click write to save the settings and then, click disconnect.

Attach the dual-sided adhesive patches with a clear window to one side of the device. Connect the battery to the device, ensuring the light-emitting diode overlies the transparent window to allow tracer detection. Once the battery is attached, immediately stick the adhesive patch with the device in place.

Make sure it is well secured. Since the piglets are deeply anesthetized, the tape might be unnecessary to hold the device in place. Prepare 50 milligrams per milliliter of FITC-sinistrin solution with saline and draw appropriate dosage into a syringe.

Attach the syringe with medication to one side of a three-way stopcock, and a saline flush on the other side of the stopcock. Push the FITC-sinistrin, immediately followed by five milliliters saline bolus before closing the three-way stopcock to the piglet vein. Keep the device attached to the piglet for four hours.

To avoid motion artifacts during this time, keep the piglet under anesthesia as described in the manuscript. At the end of the four hours, remove the device and immediately disconnect the battery. Connect the transdermal GFR device to the computer using the USB connector provided by the supplier.

Open the MB lab software to retrieve data from the device. To save the raw data, click connect and select read. Then, wait for the device to finish reading.

Click rename and finally, click save. Process and evaluate the saved data in the analysis software according to the manual's instructions. Briefly, open the MB studio and click load to import the saved data.

Adjust the offset, start and stop positions using the automated markers. Remove artifacts if necessary. Select the three-compartment model and click fit to get a readout showing FITC-sinistrin clearance in minutes and calculate the TGFR using this equation.

Both the sham and sepsis animals had comparable weights. After 12 hours of sepsis, increased serum levels of C-reactive protein, a marker for sepsis, were observed in the sepsis group. FITC-sinistrin clearance curves were shown for sham and septic piglets 12 hours post-surgery.

Septic pigs with impaired renal function demonstrated an increased area under the curve. The piglets with sepsis showed impaired clearance of FITC-sinistrin, indicating acute kidney injury. The average half-life for FITC-sinistrin in the sham and sepsis groups were 114 and 537 minutes respectively.

The average GFR in the sham group was significantly higher than in the sepsis group. The serum creatinine level at zero and 12 hours was similar in the sham group. However, a significant increase was observed in the creatinine level in the septic pigs after 12 hours.

Ensure the battery is connected properly to the piglets. If the batteries get dislodged, the device will not work. Try and inject the FITC-sinistrin in one fluid bolus to prevent multiple peaks.

Also, ensure the device is connected properly to the piglets to prevent motion artifacts. With a real-time measurement of GFR, we can properly evaluate renal function to detect early stage AKI and possibly evaluate therapeutic agents under investigation.