The authors would like to thank Dr. Jos&#233; A. Diaz, Jamie Adcock, and Mary Susan Fultz and the S.R. Light Laboratory at Vanderbilt University Medical Center for assistance and support. Another special thanks to John Poland and the rest of the Vanderbilt University Medical Center perfusionists and their students for their help with this study. This work was supported by a grant from the National Heart, Lung, and Blood Institute of the National Institutes of Health (BA; R01HL148244). The content is the sole responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

The study protocol was approved by the Vanderbilt University Institutional Animal Care and Use Committee (protocol M1800176-00) and strictly adhered to the National Institute of Health Guidelines for the Care and Use of Laboratory Animals. Male and Female Yorkshire pigs and piglets weighing approximately 40-45 kg and 4-10 kg are used in this experiment. The present approach does not encompass a screening for preexisting medical conditions in the ordered swine. Acknowledging that this practice could potentially influence ...

Investigating Physiological Responses to Acute Volume Overload in Porcine Models

<ol>
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There are two critical steps in this protocol. First, it is imperative that time is taken to obtain appropriate cannulation and ensure the positioning of hemodynamic/volume monitoring. In both adult and piglet models, surgical cutdown is necessary to cannulate the required vessel appropriately and introduce the required catheter. Percutaneous, ultrasound guided approaches have proven challenging and traumatic around the small caliber vessels seen in pigs and piglets. Two catheters that can present a challenge are the PAC...

Acute volume overload, a condition characterized by an abrupt and excessive increase in body fluid volume, is a critical medical concern that warrants comprehensive study1. It is often associated with aggressive and/or inappropriate fluid resuscitation, blood transfusion, and comorbidities such as heart failure and renal failure. It can lead to severe morbidity and an increased likelihood of mortality1,2,3. Despite its clinical significance, the pathophysiology of acute volume overload remains poorly understood3,4. Furthermore, the lack of specific diagnostic criteria and effective monitoring strategies further underscores the need for rigorous scientific investigation. Studying acute volume overload is not only crucial for improving patient outcomes but also for advancing our understanding of human physiology. It provides a unique opportunity to explore the body&#39;s fluid homeostasis mechanisms and their responses to extreme stress1. Studies investigating goal-directed fluid therapy (GDFT) to prevent liberal fluid resuscitation and promote a more goal-directed resuscitation approach have demonstrated improved morbidity and mortality in perioperative settings and in sepsis1,3,4. These studies used a variety of devices to monitor the volume state, including central venous catheters with central venous pressure measurements, ScVO2, arterial line lactate measurements, stroke volume/cardiac output measurements through transesophageal Doppler, lithium dilution cardiac output, arterial pulse contour analysis, thoracic electrical bioimpedance, and transpulmonary thermodilution1,3,4,5. The multiple approaches utilized to assess volume status, each with limitations in accuracy and usability, suggest that there is room for significant improvement in GDFT by enhancing intravascular volume assessment3,4.
Porcine models have emerged as particularly valuable tools in the study of human cardiovascular physiology6. The anatomical and physiological similarities between porcine and human cardiovascular systems, such as heart size, coronary anatomy, and hemodynamic parameters, make pigs ideal models for translational research6. Furthermore, pigs exhibit a comparable response to volume overload as humans, making them excellent models for studying the pathophysiology of acute volume overload and the effectiveness of various therapeutic interventions7,8. The use of porcine models also allows for the collection of high-quality, detailed data points, such as real-time hemodynamic measurements and tissue samples, which are often unattainable in human studies7. This superiority of data points provides a more comprehensive understanding of acute volume overload, which could ultimately contribute to the development of more effective monitoring and prevention strategies.
The use of piglet models in studying acute volume overload is of paramount importance, particularly given the scarcity of pediatric research in this field. Piglets, with their physiological and developmental similarities to human infants, provide an invaluable model, like their adult counterparts, for understanding the pediatric population9,10,11. Despite the high incidence of volume overload conditions in pediatric patients, such as those related to congenital heart diseases or intensive care interventions, research in this area has been markedly limited, especially when it comes to animal models that accurately represent human infants5,12,13. Utilizing piglet models can help bridge this gap, offering insight into the pediatric-specific pathophysiology of acute volume overload and the efficacy of potential therapeutic strategies7,11.
This manuscript describes a method of using a continuous infusion of crystalloid solution directly into the external jugular vein of both adult and pediatric pigs to induce acute volume overload and to study the hemodynamic effects of such volume changes on common peripheral and central data points used in volume status monitoring. This outlined method should serve as a valuable tool to help future scientists investigate the underlying pathophysiological mechanisms of acute volume overload and evaluate potential superior monitoring modalities and innovations.

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	<tbody>
		<tr>
			<td>1% Isoflurane</td>
			<td>Primal, Boston, MA, USA</td>
			<td>26675-46-7</td>
			<td>https://www.sigmaaldrich.com/US/en/product/aldrich/792632?gclid=Cj0KCQjw9fqnBhDSARIsAHl 
			cQYS_W-q6tS2s6LQw2Qn7Roa3TGIpTLPf5 
			2351vrhgp44foEcRozPqtYaAtvfEAL 
			w_wcB</td>
		</tr>
		<tr>
			<td>Arterial Catheter</td>
			<td>Merit Medical, South Jordan, UT, USA</td>
			<td>MAK401</td>
			<td>MAK Mini Access Kit 4F</td>
		</tr>
		<tr>
			<td>Arterial Catheter</td>
			<td>Cook Medical, Bloomington, IN, USA</td>
			<td>C-PMS-300-RA/G01908</td>
			<td>Radial Artery Catheter Set 3.0Fr./5cm</td>
		</tr>
		<tr>
			<td>Blood Pressure Amp</td>
			<td>AD Instruments, Colorado Springs, CO, USA</td>
			<td>FE117</td>
			<td>https://www.adinstruments.com/products/bp-blood-pressure-amp</td>
		</tr>
		<tr>
			<td>Central Venous Catheter Introducer</td>
			<td>Arrow International Inc, Reading, PA, USA</td>
			<td>AK-09800</td>
			<td>8.5 Fr. x 4&#34; (10 cm) Arrow-Flex</td>
		</tr>
		<tr>
			<td>Central Venous Catheter-Introducer</td>
			<td>Arrow International</td>
			<td>CP-07611-P</td>
			<td>Super Arrow-Flex Percutaneous Sheath Introducer Kit 6Fr./7.5cm</td>
		</tr>
		<tr>
			<td>Disposable BP Transducers</td>
			<td>AD Instruments, Colorado Springs, CO, USA</td>
			<td>MLT0670</td>
			<td>https://www.adinstruments.com/products/disposable-bp-transducers</td>
		</tr>
		<tr>
			<td>Kendall 930 FoamElectrodes</td>
			<td>Covidien, Mansfield, MA, USA</td>
			<td>22935</td>
			<td>https://www.cardinalhealth.com/en/product-solutions/medical/patient-monitoring/electrocardiography/monitoring-ecg-electrodes/radiolucent-electrodes/kendall-930-series-radiolucent-foam-electrodes.html</td>
		</tr>
		<tr>
			<td>LabChart 8 software</td>
			<td>AD Instruments, Colorado Springs, CO, USA</td>
			<td>N/A</td>
			<td>https://www.adinstruments.com/products/labchart</td>
		</tr>
		<tr>
			<td>Peripheral IV Catheter Angiocath 18-24 Gauge 1.16 inch</td>
			<td>McKesson, Irving, TX, USA</td>
			<td>329830</td>
			<td>https://mms.mckesson.com/product/329830/Becton-Dickinson-381144</td>
		</tr>
		<tr>
			<td>PlamaLyte Crystilloid Solution</td>
			<td>Baxter International, Deerfield, IL USA</td>
			<td>2B2544X</td>
			<td>https://www.ciamedical.com/baxter-2b2544x-each-solution-plasma-lyte-a-inj-ph-7-4-1000ml</td>
		</tr>
		<tr>
			<td>PowerLab</td>
			<td>ADInstruments, Colorado Springs, CO, USA</td>
			<td>N/A</td>
			<td>https://www.adinstruments.com/products/powerlab/c?creative=532995768429&#38;keyword= 
			powerlab&#38;matchtype=e&#38;network= 
			g&#38;device=c&#38;gclid=CjwKCAjwysipB 
			hBXEiwApJOcu-ulfO0bfCc-j6B7PpO 
			kOAGur8IZ4SWNkhNZ7mORGstO 
			vKON6plWLxoCigsQAvD_BwE</td>
		</tr>
		<tr>
			<td>Pulmonary Artery Catheter</td>
			<td>Edwards Life Sciences, Irvine, CA, USA</td>
			<td>TS105F5</td>
			<td>True Size Thermodilution Catheter 24cm Proximal Port- Swan Ganz&#160;</td>
		</tr>
		<tr>
			<td>Pulmonary Artery Catheter (7F)</td>
			<td>Edwards Life Sciences, Irvine, CA, USA</td>
			<td>131F7</td>
			<td>Swan Ganz 7F x 110cm&#160;</td>
		</tr>
		<tr>
			<td>Telazol (Tiletamine HCl and Zolazepam HCl), Injectable Solution, 5 mL</td>
			<td>Patterson Veterinary, Loveland, CO 80538</td>
			<td>07-801-4969</td>
			<td>https://www.pattersonvet.com/ProductItem/078014969?omni=telazol</td>
		</tr>
		<tr>
			<td>Terumo Sarns 8000 Roller Pump</td>
			<td>Terumo Cardiovascular, Ann Arbor, MI, USA</td>
			<td>16402</td>
			<td>https://aamedicalstore.com/products/terumo-sarns%E2%84%A2-8000-roller-pump</td>
		</tr>
		<tr>
			<td>Xylazine HCl 100 mg/mL, Injectable Solution, 50 mL</td>
			<td>Patterson Veterinary, Loveland, CO 80538</td>
			<td>07-894-5244</td>
			<td>https://www.pattersonvet.com/ProductItem/078945244</td>
		</tr>
		<tr>
			<td>Yorkshire Adult Pigs</td>
			<td>Oak Hill Genetics, Ewing, IL, USA</td>
			<td>N/A</td>
			<td>Yorkshire/Landrace 81-100lbs</td>
		</tr>
		<tr>
			<td>Yorkshire Piglets</td>
			<td>Oak Hill Genetics&#160;</td>
			<td>N/A</td>
			<td>Female &#34;piglet&#34;, specify age 5 weeks with a correlating healthy weight range (approximately 10-20lbs.)</td>
		</tr>
	</tbody>
</table>

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

Adult and Pediatric Porcine Model of Acute Volume Overload

Our team's translational research is in how vascular waveforms, specifically the low-frequency venous waveform, change in various volume and respiratory states. We are trying to understand better and improve volume status monitoring. Our research has revealed that the proper analysis of the fundamental frequency and harmonics of the pulse rate, we can sensibly monitor volume status.This novel discovery brings excitement that we may be able to achieve better volume status monitoring in a non-invasive way. Given the novel nature of our research, obtaining venous waveforms in extreme human conditions can be a big challenge. That is why porcine models such as this one are so important to what we do and what we hope to achieve.The significant finding of our research is that waveforms from the venous side, a traditionally ignored field, hold a vast amount of information, specifically the low-frequency spectrum, which is very sensitive to volume status changes. This discovery has given hope that volume monitoring in humans can be improved upon in a non-invasive way. Volume overload is a massive problem in medicine.Little research is being done on how to properly monitor against it. This protocol establishes a reproducible porcine model that can aid future scientists work to tackle this problem.

The preliminary representative pilot data after linear regression analysis for the adult pig model demonstrated linearity to volume administration in the first eight pigs (Figure 2). While many other data points, and volume beyond 2.5 L, were measured during this experiment, these data represent the analysis to date. The two vital signs most used for volume assessment, HR (R2=0.15) and MAP (R2=0.79), both demonstrated a linear relationship during forced hypervolemia, bu...

Watch this Scientific Journal Video about Author Spotlight: Exploring Venous Waveforms in Porcine Models to Tackle Volume Overload in Medicine at JoVE.com

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.