This study was supported by the National Institutes of Health grants R01 DK120595 and R01 DK127625 awarded to Dr. Adebiyi. The content of this paper is solely the authors&#39; responsibility and does not necessarily represent the official views of the National Institutes of Health. Thanks to Dr. Daniel Schock-Kusch, site Director at MediBeacon GmbH, for his advice.

The procedures are written according to national standards for the care and use of laboratory animals and were approved by the Institutional Animal Care and Use Committee (IACUC) of the University of Tennessee Health Science Center (UTHSC).
NOTE: Piglets in the experimental group are subjected to cecal ligation and puncture, while the sham group only undergoes opening of the abdomen without cecal ligation or puncture. Piglets in both groups are kept under anesthesia for 12 h post-procedure to allow enough time for sepsis and acute kidney injury (AKI) to ensue in the experimental group. Transdermal GFR measurement will ensue at 8 h post-procedure for a total of 12 h.
1. Piglet supply and housing
<ol>
	<li>Identify a local hog farm that can provide neonatal piglets aged 3-5 days. Schedule the delivery early in the week to complete the experimentation before any piglets are older than 7 days. 
	NOTE: The supplier provided three to five piglets on Mondays for this experiment; by Friday, the piglets would have undergone the experiment. Using the same sex and near similar age is essential to avoid confounding factors.</li>
	<li>Upon the piglet&#39;s arrival, ensure they have an individual identification (e.g., an ear tag and a record that includes weight and age).</li>
	<li>House the piglets in a lab animal care unit (LACU) under the care of a licensed veterinarian. The animals are housed as a group in a spacious pen with a solid concrete floor that is easily washed with water to maintain good sanitation.</li>
	<li>Add a piece of furniture such as a heavy ball to allow for environmental enrichment and stimulation.</li>
	<li>Ensure that the LACU provides optimal environmental conditions, including the following key elements: sanitation, nutrition, temperature control, ventilation, and day-night cycle by controlling illumination.</li>
	<li>Have the veterinarian check on the piglet daily, including weight measurement, to inform the investigator if any piglet appears sick, which may necessitate exclusion from the experiment.</li>
	<li>Leave the piglets for at least 1 day to acclimatize to the environment, which helps minimize the stress.</li>
</ol>
2. Pre-operative preparation
<ol>
	<li>Prepare the surgical station before initiating the experiment. This includes a heating pad, catheters, a ventilator, an endotracheal tube, heparinized saline, and a bag of ringer lactate fluid. 
	NOTE: Piglets have poor thermoregulatory capacitance and are prone to hypothermia which alters hemodynamics22,23. Therefore, allowing enough time for the heating pad to warm up is essential.</li>
	<li>Prepare 10 mg/mL of &#945;-chloralose by mixing it with saline at 60 &#730;C until the mixture is clear. Do not overheat the solution to avoid crystallizing of the medication upon cooling. Filter with a syringe filter (size 0.22 &#181;m) before administering to the piglets.</li>
	<li>Draw up anesthetic medication based on animal weight-Ketamine: 20 mg/kg and Xylazine: 2.2 mg/kg. Use &#945; -chloralose (5 mL/kg) to maintain anesthesia. 
	NOTE:&#160;&#945; -chloralose is used due&#160;to the ease of IV administration when compared to inhaled&#160; 
	anesthetics, as the latter require an anesthetic machine and an appropriate scavenging system to be delivered via an endotracheal tube.</li>
</ol>
3. Anesthesia
<ol>
	<li>Perform induction of anesthesia in the pig pen, an environment familiar for piglets, to avoid undue stress.</li>
	<li>Gently pick the piglet by the back legs and administer Ketamine: 20 mg/kg and Xylazine: 2.2 mg/kg into the rear leg at the semimembranosus/semitendinosus muscle, using a 23 G &#190; needle.</li>
	<li>Allow a few minutes for the medications to take effect. Check for the adequate anesthesia level by ensuring that the animal is relaxed enough to be immobile, with loss of palpebral reflex and jaw tone to allow ease and safe transportation to the surgical station. Assess the palpebral reflex by touching the inner corner of the eye; absence of blinking indicates adequate anesthesia.</li>
</ol>
4. Tracheostomy
NOTE: This experiment is non-survival, so a tracheotomy is performed to establish an airway for mechanical ventilation. Tracheostomy is a quick and easy procedure, as opposed to endotracheal intubation, which is challenging in piglets given their head and upper airway anatomy24,25. Additionally, laryngospasm is commonly reported during intubation, resulting in a prolonged period of hypoxia and hypercarbia that may compromise results26.
<ol>
	<li>Position the piglet in dorsal recumbency. Identify the cricothyroid cartilage by palpating the prominence of the thyroid cartilage which feels firm. Sterilize the area using povidone-iodine and 70% ethanol before applying a sterile drape.</li>
	<li>Using a a surgical blade, make a 2-3 cm ventral midline incision inferior to the caudal end of the thyroid cartilage.</li>
	<li>Using a curved mosquito hemostat, bluntly dissect the overlying subcutaneous tissues and muscles (sternohyoideus and cutaneous coli) until the cricothyroid membrane and the first few tracheal rings are visualized. When dissecting, be cautious to avoid injuring any blood vessels.</li>
	<li>Obtain a clear view of the cricothyroid membrane and tracheal rings24, then use a pair of long mixter right angle forceps to elevate the structures.
	<ol>
		<li>With a pair of small scissors, make a small cut at the cricothyroid membrane or the first tracheal ring. Extend the cut horizontally to ~0.5 cm to pass a 3.0 mm endotracheal tube.</li>
		<li>Insert the tube to the 5 cm mark. Ensure bilateral chest expansion and breath sounds prior to securing the tube.</li>
	</ol>
	</li>
	<li>Pass umbilical tape around the trachea to secure it in place. Additional tape is used to secure the tube to the base of the jaw.</li>
	<li>Switch on the ventilator, connect the endotracheal tube, and roll the specific knobs (eg. SIMV knobs, PEEP knobs, etc) to select the following baseline settings. Pressure Control Mode: synchronized intermittent mechanical ventilation (SIMV); peak inspiratory pressure (PIP) - 15; positive end-expiratory pressure (PEEP) - 5; Rate- 20; I-time - 0.6. Following the first blood gas analysis, adjust the ventilator settings according to the blood gas results, with the goal of maintaining adequate oxygenation and ventilation.</li>
</ol>
5. Femoral vessel cannulation
<ol>
	<li>Establish the airway and ventilation, before switching attention to the femoral vessels for venous access and invasive blood pressure monitoring. The femoral artery is identified by feeling a pulse at the groove between the sartorius and gracilis muscles, and the vein can be found just medial to the artery.</li>
	<li>While the piglet is lying in a dorsal recumbent position, sterilize the groin area using povidone-iodine and ethanol, and apply an appropriately sized drape.</li>
	<li>Use a surgical blade to create a 3-4 cm longitudinal incision, starting cranially at the inguinal crease and extending distally along the femoral canal.</li>
	<li>Apply blunt and sharp dissection, using mosquito curved forceps and scissors, respectively, to dissect down to the level of the femoral neurovascular bundle. The bundle can be found deep in the body of the gracillis muscle27. Circumferentially dissect the femoral artery and vein over the course of 2-3 cm to allow for cannulation. Ligate small side branches if necessary.</li>
	<li>Apply a 3.0 silk tie at both the artery and vein&#39;s proximal and distal ends to apply traction. Tie the distal silk suture on both the vein and artery, ligating the vessels.</li>
	<li>Beginning with the femoral vein, maintain distal and proximal traction on the silk ties and then use a pair of micro scissors to create a venotomy.</li>
	<li>Next, use a vein pick catheter introducer to open the vessel while inserting a pre-measured polyurethane catheter with an internal diameter x outer diameter of 0.86 mm x 1.32 mm. Once inserted, tie the proximal 3.0 silk suture to fixate the catheter. Flush the catheter with 3 mL of heparinized saline solution (1 U/mL). This solution can be made by adding 0.5 mL of heparin to 50 mL of normal saline.</li>
	<li>Insert an invasive blood pressure catheter using the same approach above to create an arteriotomy and pass the catheter. 
	NOTE: Maintaining distal and proximal traction is essential to minimize blood loss when accessing the artery.</li>
	<li>Once the catheters are secured, cover the site with saline-soaked gauze, and if necessary, the skin may be sutured using a 3.0 silk suture to prevent infection.</li>
</ol>
6. Maintenance of anesthesia, fluid and blood gas
<ol>
	<li>Monitor the depth of anesthesia throughout the experiment, using jaw tone and palpebral reflex, and administer&#160; &#945;-chloralose, intravenously, as needed to maintain the animal under deep anesthesia. Use an&#160;initial loading dose of 50 mg/kg, and&#160;20 mg/kg for further boluses.</li>
	<li>Infuse ringer lactate at a rate of 4 mL/kg/h throughout the experiment as maintenance fluid. For example, if the piglet weight is 3 kg, then the fluid infusion rate is 12 mL/h.</li>
	<li>For bedside gas analysis, draw an arterial blood sample in a heparinized blood gas syringe and present the sample to the analyzer machine. Select the option arterial blood gas, and wait for ~2-3 s for the the analyzer to present the blood-draw needle.
	<ol>
		<li>Carefully insert the needle into the end of the syringe containing the blood sample. Wait for the analyzer to aspirate the required sample and withdraw the syringe. Allow the machine to analyze the blood gas and present the results.</li>
		<li>Based on the results, adjust the ventilator to maintain the pH between 7.35--7.45, partial pressure of carbon dioxide (PCO2) between 35-45 mmHg, and partial pressure of oxygen (PaO2) between 80-150 mmHg. The settings differ based on the ventilator type, but largely involves increasing or reducing the respiratory rate using appropriate knobs to compensate for hypoxia and/or hypercapnia.</li>
	</ol>
	</li>
	<li>Draw 3 mL of blood into a light green tube (Lithium Heparin). Centrifuge the sample at 2000 xg for 15 min, maintained at 4 &#730;C to extract plasma. Once completed, the plasma can be analysed immediately for serum creatinine level with the bedside chemistry analyzer or stored at -80 &#730;C for later analysis.</li>
	<li>Monitor the temperature continuously&#160;using a rectal probe thermometer and adjust the heating pad temperature to maintain piglet temperature between 101 to 103 &#730;F.</li>
</ol>
7. Experiment group; cecal ligation and perforation (CLP) 25,28,29
NOTE: For piglets in the experiment group, perform CLP to induce polymicrobial sepsis28 and monitor the animal for 12 h post-surgery to allow enough time for severe sepsis to ensue. Transdermal GFR recording starts at 8 h post-cecal ligation to allow for 4 h of recording.
<ol>
	<li>Use a surgical blade to create a 5-6 cm left paramedian vertical incision, as the cecum in pigs lies in the left paralumbar fossa30. Dissect down the abdominal wall layers, avoiding injury to the superficial epigastric vessels.</li>
	<li>Once the peritoneal layer is incised, use a retractor to improve access to intrabdominal structures.</li>
	<li>Identify the spiral colon in the upper left quadrant of the abdomen. Trace the spiral colon, caudally and dorsally, to locate the cecum. The ileum is seen joining the spiral colon at the base of the cecum.</li>
	<li>Ligate the cecum just distal to the ileocecal junction (Figure 1).</li>
	<li>Using a 18 G needle, make seven punctures in the cecum and extrude feces into the peritoneal area.</li>
	<li>Close the abdomen in 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.</li>
</ol>
8. Sham group
<ol>
	<li>Follow the steps 7.2-7.4 as above. After identifying the cecum, place it back untouched and close the abdominal wall similarly.</li>
	<li>Monitor piglets in the sham group for 12 h to eliminate any confounding bias attributed to prolonged exposure to anesthesia.</li>
</ol>
9. Transdermal GFR device setup
<ol>
	<li>After 8 h of cecal ligation, get ready to initiate transdermal measurement of GFR.</li>
	<li>Use the MB service software version 3.0 to adjust the sampling rate on the GFR device. Briefly, connect the transdermal GFR device to the computer software using the USB connector. Open the software, click connect, and adjust the timing to 4000 ms. Click write to save the settings. 
	NOTE: This gives up to 6 h of total sampling time. In the pigs, transdermal GFR is completed in 4 h. For experiments that require sampling up to 12 h, choose the 8000 ms option.</li>
	<li>Attach the dual-sided adhesive patches with a clear window to the device. Attach the device to one side, ensuring the light-emitting diode overlies the clear window to allow tracer detection.</li>
	<li>Shave the area overlying the lateral thoracic wall. Attach the battery to the device and immediately stick the adhesive patch with the device in place and make sure it is well secured (Figure 2). Since the piglets are deeply anesthetized, tape might be unnecessary to hold the device in place. 
	NOTE: The adhesive patch alone is enough to secure. However, in procedures where the animal would be manipulated, become active, or where anesthesia might be disrupted, it might be important to apply a tape. A bandage might also be an alternative approach31.</li>
	<li>A baseline recording of 3-5 min is required before administering FITC-sinistrin.</li>
</ol>
10. FITC-sinistrin preparation and injection
<ol>
	<li>Prepare a mixture of FITC-sinistrin with saline solution to a final concentration of 50 mg/mL. The dose administered to the piglet is 20 mg/kg. FITC-sinistrin is supplied in powder form. 
	NOTE: The FITC-sinistrin may also be administered through a peripheral venous catheter inserted in the auricular vein. It is essential to achieve a high peak level by administering FITC-sinistrin as a push bolus through the femoral vein venous catheter.</li>
	<li>Attach the syringe with medication to one side of a three-way stop cock and a saline flush on the other side of the stop cock. Push the FITC-sinistrin and immediately follow with a 5 mL saline bolus before closing the three-way stop cock to the piglet vein.</li>
</ol>
11. Transdermal GFR recording
<ol>
	<li>Keep the device attached to the piglet for 4 h. During this time, keep the piglet under anesthesia using intermittent doses of &#945;-chloralose at a concentration of 20 mg/kg to avoid any motion artifact.</li>
	<li>At the end of the 4 h, remove the device and immediately disconnect the battery.</li>
</ol>
12. GFR measurement
<ol>
	<li>Connect the transdermal GFR device to the computer using the USB connector provided by the supplier.</li>
	<li>Open the reading software to retrieve data from the device. Save the raw data by clicking the sequence: connect, read, re-name, and save. As instructed in the manual, process and evaluate the saved data in the analysis software.</li>
	<li>Briefly, open the software ver. 3.0 and import the data. Adjust the offset, start, and end positions using the automated markers. Remove artifacts if necessary, and click fit. This gives a readout that shows FITC-sinistrin clearance in minutes (t1/2). The t1/2 is subsequently used to calculate the tGFR32,33 as below: 
	<img alt="Equation 1" src="/files/ftp_upload/64413/64413eq01.jpg" style="margin: auto;" /> 
	NOTE: In consultation with the manufacturer, the conversion factor used for pigs is 20 (indicating that 20% of the body weight is extracellular space), as opposed to 21.33 in rats (tGFR in mL/min) and 14,616.8 in mice (tGFR in &#181;L/min). This is because GFR is accurately measured as a function of extracellular fluid34,35, which in turn is dependent on body weight36.</li>
</ol>
13. Piglet euthanasia
<ol>
	<li>Collect 3 mL of blood after 12 h of CLP for further biochemical analysis.</li>
	<li>Euthanize the piglet by administering 0.2 mL/kg of pre-mixed mixture of 20% sodium pentobarbital and Phenytoin Sodium intravenously.</li>
	<li>Harvest the right kidney for histopathologic study before taking the piglet to the morgue.</li>
</ol>

This paper describes practical steps to determining kidney function in pigs using the miniaturized transdermal GFR monitors and FITC-sinistrin in a mechanically ventilated, anesthetized neonatal pig model. Previous papers have established experimental transdermal GFR protocols in rodents11,12,14, but no protocols exist in pigs.
Recently, there has been a drive to explore alternative animal models to s...

A practical and quantitative evaluation of renal function is the glomerular filtration rate (GFR) measurement, which tells how well the kidneys filter blood based on the clearance principle1. An earlier method of measuring GFR entails the intravenous injection of exogenous compounds such as inulin or sinistrin, conducting serial measurements of plasma/urinary levels to detect their clearance2,3. This method is cumbersome, requiring the serial collection of plasma and urine samples4. An alternative is the measurement of endogenous metabolic end-products such as creatinine. However, this is time-consuming and, at times, inaccurate, as it is not only filtered by the glomerulus but also secreted by the tubules5,6. Furthermore, creatinine level is influenced by gender, age, diet, and muscle mass7,8,9.
A more precise, minimally invasive, and widely used measure of GFR is the use of transdermal GFR monitors, which measure real-time GFR in animals4,10. Sinistrin, a highly soluble and freely filtered exogenous renal marker, is labeled with fluorescein-isothiocyanate (FITC). This conjugated compound is injected intravenously, and real-time kidney function can be assessed without collecting blood and urine samples11. The use of transdermal GFR measurement has been validated in rodents12, dogs13, and cats14, but not in swine.
Porcine species share several anatomical and physiological characteristics with humans, making them ideal animals for studying various human diseases15. The use of pigs in translational biomedical research has become increasingly popular and preferred over rodent models because it mimics human physiology and pathophysiology16. Neonatal pigs are of interest in understanding the mechanisms of diseases unique to pediatric patients17. Moreover, the recent advancement in pig to human organ transplantation puts an urge to expand the diagnostic tools for preclinical and clinical trials18,19,20,21. This paper, for the first time, provides a guide for the use of the transdermal device in measuring GFR in neonatal pigs.

<table><tbody><tr><td>Alpha - Chloralose</td><td>Sigma-Aldrich</td><td>C0128-25G</td><td>Used for maintanining anesthesia</td></tr><tr><td>Black braided silk&amp;nbsp; 3-0</td><td>Surgical Specialties</td><td>SP117</td><td>Silk tie for blood vessel traction and ligation</td></tr><tr><td>Centrifugation machine AccuSpin 8C</td><td>Fischer Scientific</td><td>75-008-821</td><td>Used to extract plasma from whole blood sample</td></tr><tr><td>Endotracheal Tube 3.0 uncuffed</td><td>Progressive Medical International</td><td>1109021995</td><td>Inserted through tracheostomy</td></tr><tr><td>FITC-Sinistrin 1.0 g</td><td>MediBeacon Inc.</td><td>FTCF S001</td><td>Store at room temp and protect from light</td></tr><tr><td>GEM Premier 3000 Blood gas analyzer</td><td>Instrumentation Laboratory</td><td>5700</td><td>For bedside blood gas analysis</td></tr><tr><td>Heating Pad medium size 20 in x 29 in</td><td>Adroit Medical Systems</td><td>V029</td><td>Connects to heat therapy pump</td></tr><tr><td>HTP-Heat Therapy Pump</td><td>Adroit Medical Systems</td><td>HTP</td><td>Allows you to set temperature as needed.</td></tr><tr><td>IDEXX Catalyst One</td><td>IDEXX Laboratories</td><td>89-92525-00</td><td>Plasma creatinine analysis</td></tr><tr><td>Invasive blood pressure catheter 3.5Fr</td><td>Millar</td><td>SPR-524</td><td>Inserted in femoral artery</td></tr><tr><td>IV adminstration set with flow regulator</td><td>True Care</td><td>TCRTCBINF033G</td><td>Used to connect IV fluid bag to vein catheter</td></tr><tr><td>Ketamine</td><td>Covetrus</td><td>68317</td><td>Used for induction of Anesthesia</td></tr><tr><td>MediBeacon analysis software version 3.0</td><td>MediBeacon Inc.</td><td>N/A</td><td>Software program used for analysing data to obtain sinistrin clearance half life and curve</td></tr><tr><td>Millex-GV Syringe Filter Unit 0.22 &amp;micro;m</td><td>Millipore Sigma</td><td>SLGVR33RS</td><td>Syringe filter for chloralose injection</td></tr><tr><td>Neonate/Infant Ventilator</td><td>Sechrist Millennium</td><td>20409</td><td>Connected to air supply to provide ventilation through endotracheal tube</td></tr><tr><td>Phenobarbital Sodium + Phenytoin Sodium (Euthasol)</td><td>Covetrus</td><td>72934</td><td>Used for euthanasia</td></tr><tr><td>Ringer Lactate 500 mL bag</td><td>Baxter</td><td>2B2323Q</td><td>Maintanence fluid infusion</td></tr><tr><td>Sterile Gloves</td><td>Henry Schein</td><td>104-5920</td><td>Used by operator during surgery</td></tr><tr><td>Sterile Gown</td><td>Halyard Health</td><td>95021</td><td>Used by operator during surgery</td></tr><tr><td>Steril Towel</td><td>Medline</td><td>42131704</td><td>Used as drape to maintaine sterile field when operating</td></tr><tr><td>Suture 3-0 silk reverse cutting needle</td><td>Ethicon</td><td>NC1842168</td><td>Used for suturing abdominal wall layers</td></tr><tr><td>Transdermal Mini GFR Monitor</td><td>MediBeacon Inc.</td><td>TDM004</td><td>Battery and USB connector included in package</td></tr><tr><td>Transdermal monitor adhesive patch</td><td>MediBeacon Inc.</td><td>PTC-SM001</td><td>Doubl sided adhesive patch for GFR probe</td></tr><tr><td>Umbilical Tape 1/8 in x 20 yds</td><td>Fisher Scientific</td><td>NC9303017</td><td>To secure endotracheal tube</td></tr><tr><td>Venous Catheter size PE/5</td><td>Micro medical tubing</td><td>BB31695</td><td>For femoral vein cannulation</td></tr><tr><td>Xylazine</td><td>Covetrus</td><td>61035</td><td>Used for induction of anesthesia</td></tr></tbody></table>

transdermal measurement of glomerular filtration rate in mechanically ventilated piglets

Transdermal measurement of glomerular filtration rate (GFR) has been used to evaluate kidney function in conscious animals. This technique is well established in rodents to study acute kidney injury and chronic kidney disease. However, GFR measurement using the transdermal system has not been validated in pigs, a species with a similar renal system to humans. Hence, we investigated the effect of sepsis on transdermal GFR in anesthetized and mechanically ventilated neonatal pigs. Polymicrobial sepsis was induced by cecal ligation and puncture (CLP). The transdermal GFR measurement system consisting of a miniaturized fluorescence sensor was attached to the pig's shaved skin to determine the clearance of fluorescein-isothiocyanate (FITC) conjugated sinistrin, an intravenously injected GFR tracer. Our results show that at 12 h post-CLP, serum creatinine increased with a decrease in GFR. This study demonstrates, for the first time, the utility of the transdermal GFR approach in determining renal function in mechanically ventilated, neonatal pigs.

In this section, we present for the first time, the representative data from the use of transdermal GFR in neonatal pigs. We used a cecal ligation and puncture model which has previously been shown to decrease kidney function28. Accordingly, we hypothesized that in our CLP pigs, there should be an acute drop in GFR corresponding to AKI, and this should be detected on the transdermal GFR device as increased clearance time (t1/2), thereby validating its use in pigs. Seven male piglets wer...

Watch this Scientific Journal Video about Transdermal Measurement of Glomerular Filtration Rate in Mechanically Ventilated Piglets at JoVE.com

Transdermal Measurement of Glomerular Filtration Rate in Mechanically Ventilated Piglets

Glomerular filtration rate (GFR) is the ideal marker for assessing kidney function. However, the standard measurement method using inulin injection with serial blood and urine analysis is impractical. This article delineates a practical method to measure GFR transdermally in piglets.

Transdermal measurement of glomerular filtration rate (GFR) has been used to evaluate kidney function in conscious animals. This technique is well ...

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2.2K Views.  College of Medicine University of Tennessee Health Science Center. Glomerular filtration rate (GFR) is the ideal marker for assessing kidney function. However, the standard measurement method using inulin injection with serial blood and urine analysis is impractical. This article delineates a practical method to measure GFR transdermally in piglets.

Video: Transdermal Measurement of Glomerular Filtration Rate in Mechanically Ventilated Piglets

Increasing Pulmonary Artery Pulsatile Flow Improves Hypoxic Pulmonary Hypertension in Piglets

Pulmonary arterial hypertension (PAH) is a disease affecting distal pulmonary arteries (PA). These arteries are deformed, leading to right ventricular failure. Current treatments are limited. Physiologically, pulsatile blood flow is detrimental to the vasculature. In response to sustained pulsatile stress, vessels release nitric oxide (NO) to induce vasodilation for self-protection. Based on this observation, this study developed a protocol to assess whether an artificial pulmonary pulsatile blood flow could induce an NO-dependent decrease in pulmonary artery pressure. One group of piglets was exposed to chronic hypoxia for 3 weeks and compared to a control group of piglets. Once a week, the piglets underwent echocardiography to assess PAH severity. At the end of hypoxia exposure, the piglets were subjected to a pulsatile protocol using a pulsatile catheter. After being anesthetized and prepared for surgery, the jugular vein of the piglet was isolated and the catheter was introduced through the right atrium, the right ventricle and the pulmonary artery, under radioscopic control. Pulmonary artery pressure (PAP) was measured before (T0), immediately after (T1) and 30 min after (T2) the pulsatile protocol. It was demonstrated that this pulsatile protocol is a safe and efficient method of inducing a significant reduction in mean PAP via an NO-dependent mechanism. These data open up new avenues for the clinical management of PAH.

Pulmonary hypertension is associated with a significant reduction in pulmonary artery pulsatility, contractility and elasticity, contributing to an increase in pulmonary artery pressure and pulmonary resistance. Using a hypoxic piglet model, this study demonstrated that improving pulmonary artery plasticity using a newly developed pulsatile catheter improves hypoxic pulmonary hypertension.

Pulmonary arterial hypertension (PAH) is a disease affecting distal pulmonary arteries (PA). These arteries are deformed, leading to right ventricular ...

Chronic Thromboembolic Pulmonary Hypertension and Assessment of Right Ventricular Function in the Piglet

An original piglet model of Chronic Thromboembolic Pulmonary Hypertension (CTEPH) associated with chronic Right Ventricular (RV) dysfunction is described. Pulmonary Hypertension (PH) was induced in 3-week-old piglets by a progressive obstruction of the pulmonary vascular bed. A ligation of the left Pulmonary Artery (PA) was performed first through a mini-thoracotomy. Second, weekly embolizations of the right lower pulmonary lobe were done under fluoroscopic guidance with n-butyl-2-cyanoacrylate during 5 weeks. Mean Pulmonary Arterial Pressure (mPAP) measured by ritght heart catheterism, increased progressively, as well as Right Atrial pressure and Pulmonary Vascular Resistances (PVR) after 5 weeks compared to sham animals. Right Ventricular (RV) structural and functional remodeling were assessed by transthoracic echocardiography (RV diameters, RV wall thickness, RV systolic function). RV elastance and RV-pulmonary coupling were assessed by Pressure-Volume Loops (PVL) analysis with conductance method. Histologic study of the lung and the right ventricle were also performed. Molecular analyses on RV fresh tissues could be performed through repeated transcutaneous endomyocardial biopsies. Pulmonary microvascular disease in obstructed and unobstructed territories was studied from lung biopsies using molecular analyses and pathology. Furthermore, the reliability and the reproducibility was associated with a range of PH severity in animals. Most aspects of the human CTEPH disease were reproduced in this model, which allows new perspectives for the understanding of the underlying mechanisms (mitochondria, inflammation) and new therapeutic approaches (targeted, cellular or gene therapies) of the overloaded right ventricle but also pulmonary microvascular disease.

Chronic Thromboembolic Pulmonary Hypertension (CTEPH) and Right Ventricular (RV) dysfunction were induced in piglets by progressive obstruction of the pulmonary arteries. Consequences were remarkably similar to those observed in CTEPH patients. This animal model would be a very useful tool for pathophysiology and therapeutic experiments on CTEPH and RV failure.

An original piglet model of Chronic Thromboembolic Pulmonary Hypertension (CTEPH) associated with chronic Right Ventricular (RV) dysfunction is described. ...

Transcutaneous Assessment of Renal Function in Conscious Rodents

Glomerular filtration rate (GFR) is the gold standard to assess overall kidney function. However, traditional methods to evaluate GFR are cumbersome and time-consuming. In addition, serial blood or urine samples are required, with the associated stress for the experimental animals. A recent technique significantly reduces the investment in time and resources, minimizing the invasiveness and the animal stress, but being equally valid as the traditional approaches. The method measures transcutaneously renal function. Using an optical device and the exogenous renal marker fluorescein isothiocyanate (FITC)-sinistrin, this technique is capable of measuring the elimination kinetics of the marker through the skin. With neither blood nor urine samples nor the associated laboratory assays needed, the results of the transcutaneous measurement are almost instantaneously available. The method has been already validated in different species and successfully applied in several models of renal pathology. Moreover, due to its minimally invasive characteristics, it is suitable for sequential measurements within the same animal. Here is provided a detailed protocol to carry out the transcutaneous assessment of renal function in rodents.

Determination of glomerular filtration rate (GFR) is the gold standard to assess overall kidney function. However, traditional procedures to measure this parameter are cumbersome and require a large investment of time. Here we describe a faster and minimally invasive method to determinate GFR transcutaneously.

Glomerular filtration rate (GFR) is the gold standard to assess overall kidney function. However, traditional methods to evaluate GFR are cumbersome and ...

Use of a Piglet Model for the Study of Anesthetic-induced Developmental Neurotoxicity (AIDN): A Translational Neuroscience Approach

Anesthesia cannot be avoided in many cases when surgery is required, particularly in children. Recent investigations in animals have raised concerns that anesthesia exposure may lead to neuronal apoptosis, known as anesthesia-induced developmental neurotoxicity (AIDN). Furthermore, some clinical studies in children have suggested that anesthesia exposure may lead to neurodevelopmental deficits later in life. Nonetheless, an ideal animal model for preclinical study has yet to be developed. The neonatal piglet represents a valuable model for preclinical study, as they share a striking number of developmental similarities with humans.
The anatomy and physiology of piglets allow for implementation of rigorous human perioperative conditions in both survival and non-survival procedures. Femoral artery catheterization allows for close monitoring, thus enabling prompt correction of any deviation of the piglet's vital signs and chemistries. In addition, there are multiple developmental similarities between piglets and human neonates. The techniques required to use piglets for experimentation will require experience to master. A pediatric anesthesiologist is a critical member of the investigative team. We describe, in a general sense, the appropriate use of a piglet model for neurodevelopmental study.

Use of a Piglet Model for the Study of Anesthetic-induced Developmental Neurotoxicity AIDN: A Translational Neuroscience Approach

Anesthesia-induced developmental neurotoxicity (AIDN) research has focused on rodents, which are not broadly applicable to humans. Non-human primate models are more relevant, but are cost-prohibitive and difficult to use for experimentation. The piglet, in contrast, is a clinically relevant, practical animal model ideal for the study of anesthetic neurotoxicity.

Anesthesia cannot be avoided in many cases when surgery is required, particularly in children.  Recent investigations in animals have raised concerns that ...

A High-throughput Method for Measurement of Glomerular Filtration Rate in Conscious Mice

The measurement of glomerular filtration rate (GFR) is the gold standard in kidney function assessment. Currently, investigators determine GFR by measuring the level of the endogenous biomarker creatinine or exogenously applied radioactive labeled inulin (3H or 14C). Creatinine has the substantial drawback that proximal tubular secretion accounts for ~50% of total renal creatinine excretion and therefore creatinine is not a reliable GFR marker. Depending on the experiment performed, inulin clearance can be determined by an intravenous single bolus injection or continuous infusion (intravenous or osmotic minipump). Both approaches require the collection of plasma or plasma and urine, respectively. Other drawbacks of radioactive labeled inulin include usage of isotopes, time consuming surgical preparation of the animals, and the requirement of a terminal experiment. Here we describe a method which uses a single bolus injection of fluorescein isothiocyanate-(FITC) labeled inulin and the measurement of its fluorescence in 1-2 &mu;l of diluted plasma. By applying a two-compartment model, with 8 blood collections per mouse, it is possible to measure GFR in up to 24 mice per day using a special work-flow protocol. This method only requires brief isoflurane anesthesia with all the blood samples being collected in a non-restrained and awake mouse. Another advantage is that it is possible to follow mice over a period of several months and treatments (i.e. doing paired experiments with dietary changes or drug applications). We hope that this technique of measuring GFR is useful to other investigators studying mouse kidney function and will replace less accurate methods of estimating kidney function, such as plasma creatinine and blood urea nitrogen.

Measurement of glomerular filtration rate (GFR) is the gold standard for kidney function assessment. Here we describe a high-throughput method which allows the determination of GFR in conscious mice by using a single bolus injection, determination of fluorescein isothiocyanate (FITC)-inulin in plasma and calculation of GFR by a two-phase exponential decay model.

The measurement of  glomerular filtration rate (GFR) is the gold standard in kidney function  assessment. Currently, investigators determine GFR by ...

Biology

Transdermal Measurement of Glomerular Filtration Rate in Mice

Transdermal analysis of glomerular filtration rate (GFR) is an established technique that is used to assess renal function in mouse and rat models of acute kidney injury and chronic kidney disease. The measurement system consists of a miniaturized fluorescence detector that is directly attached to the skin on the back of conscious, freely moving animals, and measures the excretion kinetics of the exogenous GFR tracer, fluorescein-isothiocyanate (FITC) conjugated sinistrin (an inulin analog). This system has been described in detail in rats. However, because of their smaller size, measurement of transcutaneous GFR in mice presents additional technical challenges. In this paper we therefore provide the first detailed practical guide to the use of transdermal GFR monitors in mice based on the combined experience of three different investigators who have been performing this assay in mice over a number of years.

Here we describe a protocol to measure glomerular filtration rate (GFR) in conscious, freely moving mice using a transdermal GFR monitor.

Transdermal analysis of glomerular filtration rate (GFR) is an established technique that is used to assess renal function in mouse and rat models of ...

Physiology Lab Demonstration: Glomerular Filtration Rate in a Rat

Measurements of glomerular filtration rate (GFR), and the fractional excretion of sodium (Na) and potassium (K) are critical in assessing renal function in health and disease. GFR is measured as the steady state renal clearance of inulin which is filtered at the glomerulus, but not secreted or reabsorbed along the nephron. The fractional excretion of Na and K can be determined from the concentration of Na and K in plasma and urine. The renal clearance of inulin can be demonstrated in an anesthetized animal which has catheters in the femoral artery, femoral vein and bladder. The equipment and supplies used for this procedure are those commonly available in a research core facility, and thus makes this procedure a practical means for measuring renal function. The purpose of this video is to demonstrate the procedures required to perform a lab demonstration in which renal function is assessed before and after a diuretic drug. The presented technique can be utilized to assess renal function in rat models of renal disease.

The purpose of this protocol is to demonstrate the principles and techniques for measuring and calculating glomerular filtration rate, urine flow rate, and excretion of sodium and potassium in a rat. This demonstration can be used to provide students with an overall conceptual understanding of how to measure renal function.

Measurements of glomerular filtration rate (GFR), and the fractional excretion of sodium (Na) and potassium (K) are critical in assessing renal function ...

A Piglet Perinatal Asphyxia Model to Study Cardiac Injury and Hemodynamics after Cardiac Arrest, Resuscitation, and the Return of Spontaneous Circulation

Neonatal piglets have been extensively used as translational models for perinatal asphyxia. In 2007, we adapted a well-established piglet asphyxia model by introducing cardiac arrest. This enabled us to study the impact of severe asphyxia on key outcomes, including the time taken for the return of spontaneous circulation (ROSC), as well as the effect of chest compressions according to alternative protocols for cardiopulmonary resuscitation. Due to the anatomical and physiological similarities between piglets and human neonates, piglets serve as good models in studies of cardiopulmonary resuscitation and hemodynamic monitoring. In fact, this cardiac arrest model has provided evidence for guideline development through research on resuscitation protocols, pathophysiology, biomarkers, and novel methods for hemodynamic monitoring. Notably, the incidental finding that a substantial fraction of piglets have pulseless electrical activity (PEA) during cardiac arrest may increase the applicability of the model (i.e., it may be used to study pathophysiology extending beyond the perinatal period). However, the model generation is technically challenging and requires various skill sets, dedicated personnel, and a fine balance of the measures, including the surgical protocols and the use of sedatives/analgesics, to ensure a reasonable rate of survival. In this paper, the protocol is described in detail, as well as experiences with adaptations to the protocol over the years.

This piglet model involves surgical instrumentation, asphyxiation until the cardiac arrest, resuscitation, and post-resuscitation observation. The model allows for multiple sampling per animal, and by using continuous invasive arterial blood pressure, ECG, and non-invasive cardiac output monitoring, it provides knowledge about hemodynamics and cardiac pathophysiology in perinatal asphyxia and neonatal cardiopulmonary resuscitation.

Neonatal piglets have been extensively used as translational models for perinatal asphyxia. In 2007, we adapted a well-established piglet asphyxia model ...

Investigating Physiological Responses to Acute Volume Overload in Porcine Models

Adult and Pediatric Porcine Model of Acute Volume Overload

This protocol describes an acute volume overload porcine model for adult Yorkshire pigs and piglets. Both swine ages undergo general anesthesia, endotracheal intubation, and mechanical ventilation. A central venous catheter and an arterial catheter are placed via surgical cutdown in the external jugular vein and carotid artery, respectively. A pulmonary artery catheter is placed through an introducer sheath of the central venous catheter. PlasmaLyte crystalloid solution is then administered at a rate of 100 mL/min in adult pigs and at 20 mL/kg boluses over 10 min in piglets. Hypervolemia is achieved either at 15% decrease in cardiac output or at 5 L in adult pigs and at 500 mL in piglets. Hemodynamic data, such as heart rate, respiratory rate, end-tidal carbon dioxide, fraction of oxygen-saturated hemoglobin, arterial blood pressure, central venous pressure, pulmonary artery pressure, pulmonary capillary wedge pressure, partial arterial oxygen pressure, lactate, pH, base excess, and pulmonary artery fraction of oxygen-saturated hemoglobin, are monitored during experimentation. Preliminary data observed with this model has demonstrated statistically significant changes and strong linear regressions between central hemodynamic parameters and acute volume overload in adult pigs. Only pulmonary capillary wedge pressure demonstrated both a linear regression and a statistical significance to acute volume overload in piglets. These models can aid scientists in the discovery of age-appropriate therapeutic and monitoring strategies to understand and prevent acute volume overload.

Author Spotlight: Exploring Venous Waveforms in Porcine Models to Tackle Volume Overload in Medicine

The protocol here shows how continuous administration of crystalloids into the central veins of a euvolemic pig/piglet allows for the appropriate investigation of the physiological effects of acute volume overload.

This protocol describes an acute volume overload porcine model for adult Yorkshire pigs and piglets. Both swine ages undergo general anesthesia, ...

Surgical Technique for Jugular Vein Thermodilution Catheter Placement in Pigs

Determination of Cardiac Output in a Porcine Model for Ex Vivo Pulmonary Perfusion

Due to their physiological similarities to humans, pigs are used as experimental models for ex vivo lung perfusion (EVLP). EVLP is a technique that perfuses lungs that are not suitable for transplantation via an extracorporeal circulation pump to improve their function and increase their viability. Existing EVLP protocols are differentiated by the type of perfusion solution and perfusion flow, which varies from 40%-100% of the estimated cardiac output (CO) according to the body surface area (BSA). Devices for measuring CO use simple physical principles and other mathematical models. Thermodilution in animal models continues to be the reference standard for estimating CO because of its simplicity and ease of reproduction. Therefore, the objective of this study was to reproduce the measurement of CO by thermodilution in pigs and compare its precision and accuracy with those obtained by the BSA, weight, and Fick's method, to establish perfusion flow during EVLP. In 23 pigs, a thermodilution catheter was placed in the right jugular vein, and the carotid artery on the same side was cannulated. Blood samples were obtained for gasometry, and CO was estimated by thermodilution, adjusted body surface area, Fick's principle, and per body weight. The CO obtained by the BSA was greater (p = 0.0001, ANOVA, Tukey) than that obtained by the other methods. We conclude that although the methods used in this study to estimate CO are reliable, there are significant differences between them; therefore, each method must be evaluated by the investigator to determine which meets the needs of the protocol.

Author Spotlight: Assessment of Cardiac Output Calculation by Thermodilution in Pigs for Effective Perfusion Flow During EVLP

This protocol describes the surgical technique used for the placement of a thermodilution catheter through the jugular vein in pigs to estimate cardiac output and ensure adequate lung perfusion during ex vivo lung perfusion (EVLP).

Due to their physiological similarities to humans, pigs are used as experimental models for ex vivo lung perfusion (EVLP). EVLP is a technique that ...