The authors would like to thank Beatrice Beck-Schimmer (MD) and Erik Schadde (MD) for their critical examination and their valuable contribution for this manuscript.

All experiments presented in this protocol were approved by the Veterinary Authorities of the Canton Zurich, Switzerland (approval numbers 134/2014 and ZH088/19). Moreover, all steps performed in this experiment were in accordance with the Guidelines on Experiments with Animals by the Swiss Academy of Medial Sciences (SAMS) and Guidelines of the Federation of European Laboratory Animal Science Associations (FELASA).
1. Anesthesia induction and animal monitoring
<ol>
	<li>Keep male Wistar rat...

<ol>
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L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+the+worldwide+burden+of+critical+illness:+the+intensive+care+over+nations+(ICON)+audit.">Assessment of the worldwide burden of critical illness: the intensive care over nations (ICON) audit.</a> Lancet Respiratory Medicine. 2 (5), 380-386 (2014).</li><li>Fleischmann, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Assessment+of+Global+Incidence+and+Mortality+of+Hospital-treated+Sepsis.+Current+Estimates+and+Limitations.">Assessment of Global Incidence and Mortality of Hospital-treated Sepsis. Current Estimates and Limitations.</a> American Journal of Respiratory and Critical Care Medicine. 193 (3), 259-272 (2016).</li><li>Kumar, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Duration+of+hypotension+before+initiation+of+effective+antimicrobial+therapy+is+the+critical+determinant+of+survival+in+human+septic+shock.">Duration of hypotension before initiation of effective antimicrobial therapy is the critical determinant of survival in human septic shock.</a> Critical Care Medicine. 34 (6), 1589-1596 (2006).</li><li>Gotts, J. E., Matthay, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sepsis:+pathophysiology+and+clinical+management.">Sepsis: pathophysiology and clinical management.</a> British Medical Journal. 353, (2016).</li><li>Akira, S., Takeda, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toll-like+receptor+signalling.">Toll-like receptor signalling.</a> Nature Reviews Immunology. 4 (7), 499-511 (2004).</li><li>Urner, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Insight+into+the+beneficial+immunomodulatory+mechanism+of+the+sevoflurane+metabolite+hexafluoro-2-propanol+in+a+rat+model+of+endotoxaemia.">Insight into the beneficial immunomodulatory mechanism of the sevoflurane metabolite hexafluoro-2-propanol in a rat model of endotoxaemia.</a> Clinical and Experimental Immunology. 181 (3), 468-479 (2015).</li><li>Beck-Schimmer, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Which+Anesthesia+Regimen+Is+Best+to+Reduce+Morbidity+and+Mortality+in+Lung+Surgery?:+A+Multicenter+Randomized+Controlled+Trial.">Which Anesthesia Regimen Is Best to Reduce Morbidity and Mortality in Lung Surgery?: A Multicenter Randomized Controlled Trial.</a> Anesthesiology. 125 (2), 313-321 (2016).</li><li>Deitch, E. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Animal+models+of+sepsis+and+shock:+a+review+and+lessons+learned.">Animal models of sepsis and shock: a review and lessons learned.</a> Shock. 9 (1), 1-11 (1998).</li><li>Buras, J. A., Holzmann, B., Sitkovsky, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Animal+models+of+sepsis:+setting+the+stage.">Animal models of sepsis: setting the stage.</a> Nature Reviews Drug Discovery. 4 (10), 854-865 (2005).</li><li>Perretti, M., Duncan, G. S., Flower, R. J., Peers, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Serum+corticosterone,+interleukin-1+and+tumour+necrosis+factor+in+rat+experimental+endotoxaemia:+comparison+between+Lewis+and+Wistar+strains.">Serum corticosterone, interleukin-1 and tumour necrosis factor in rat experimental endotoxaemia: comparison between Lewis and Wistar strains.</a> British Journal of Pharmacology. 110 (2), 868-874 (1993).</li><li>Marechal, X., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Endothelial+glycocalyx+damage+during+endotoxemia+coincides+with+microcirculatory+dysfunction+and+vascular+oxidative+stress.">Endothelial glycocalyx damage during endotoxemia coincides with microcirculatory dysfunction and vascular oxidative stress.</a> Shock. 29 (5), 572-576 (2008).</li><li>Thiemermann, C., Ruetten, H., Wu, C. C., Vane, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+multiple+organ+dysfunction+syndrome+caused+by+endotoxin+in+the+rat:+attenuation+of+liver+dysfunction+by+inhibitors+of+nitric+oxide+synthase.">The multiple organ dysfunction syndrome caused by endotoxin in the rat: attenuation of liver dysfunction by inhibitors of nitric oxide synthase.</a> British Journal of Pharmacology. 116 (7), 2845-2851 (1995).</li><li>Osuchowski, M. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Minimum+quality+threshold+in+pre-clinical+sepsis+studies+(MQTiPSS):+an+international+expert+consensus+initiative+for+improvement+of+animal+modeling+in+sepsis.">Minimum quality threshold in pre-clinical sepsis studies (MQTiPSS): an international expert consensus initiative for improvement of animal modeling in sepsis.</a> Intensive Care Medicine Experimental. 6 (1), 26 (2018).</li><li>Fink, M. P., Heard, S. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Laboratory+models+of+sepsis+and+septic+shock.">Laboratory models of sepsis and septic shock.</a> Journal of Surgical Research. 49 (2), 186-196 (1990).</li><li>Buras, J. 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The protocol described here allows for a highly reproducible, yet simple to learn sepsis model, which can be adapted according the research question. Essential in vivo data referring to organ function such as heart rate, blood pressure, and peripheral arterial oxygen saturation may be collected continuously, and blood sampling may be performed repetitively throughout the experiment. In addition, modifications with regard to fluid replacement protocols and vasopressor support can be installed. Given the hemodynamic stabil...

Sepsis and its more severe form, septic shock, are syndromes on the ground of an infection, resulting in an overshooting inflammatory reaction with the release of cytokines, leading to physiological and biochemical changes with a suppressed immune defense and fatal results1,2. This unbalanced inflammatory reaction results in organ dysfunction and organ failure in various vital organs such as lung, kidney, and liver. With 37%3, sepsis is one of the most common reasons for a patient to be admitted to an intensive care unit (ICU). Mortality of sepsis currently ranges around 20-30%4. Early and effective antibiotic treatment is of utmost importance5. Fluid and vasopressor resuscitation need to be installed early, other than that, treatment is purely supportive6.
Sepsis is defined as a proven or suspected infection with bacteria, fungi, viruses, or parasites, which is accompanied by organ dysfunction. Septic shock criteria are met when a further cardiovascular collapse irresponsive to fluid treatment alone, and a lactate level of more than 2 millimole/liter is present2. Sepsis related organ failure may occur in any organ, but is very common in the cardiovascular system, the brain, the kidney, the liver, and the lung. Most patients suffering from sepsis require endotracheal intubation to secure the patient&#39;s airway, to protect from aspiration, and to apply positive end expiratory ventilation with a high fraction of inspired oxygen to prevent or overcome hypoxia. In order to tolerate a tracheal tube and mechanical ventilation, patients usually require sedation.
Endotoxins, such as lipopolysaccharides (LPS) as a component of the membrane of gram negative bacteria induce a strong inflammatory reaction via the toll-like receptor (TLR) 47. Activation of a defined pathway ensures a stable inflammatory reaction. Cytokines like cytokine induced neutrophil chemoattractant protein 1 (CINC-1), monocyte chemoattractant protein 1 (MCP-1), and interleukin 6 (IL-6) are known as prognostic factors for severity and outcome in this model8. Intravenous LPS application has been successfully used to study various aspects of sepsis in rats8,9.
Treatment of sepsis is still a challenge, particularly due to the lack of predictive animal models. If endotoxemia with activation of systemic inflammation is an adequate model for the development of pharmacological therapies is debatable. However, with the well-known LPS-induced TLR 4 pathway important knowledge can be gained.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>2-0 silk sutures</td>
			<td>Ethicon, Sommerville, NJ</td>
			<td>K833</td>
			<td>Standard surgical</td>
		</tr>
		<tr>
			<td>26 intravenous catheter</td>
			<td>Becton Dickinson, Franklin Lakes, NJ</td>
			<td>391349</td>
			<td>Standard anesthesia equipment</td>
		</tr>
		<tr>
			<td>6-0 LOOK black braided silk</td>
			<td>Surgical Specalities Corporation, Wyomissing, PA</td>
			<td>SP114</td>
			<td>Standard surgical</td>
		</tr>
		<tr>
			<td>Alaris Syringe Pump</td>
			<td>Bencton Dickinson</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Betadine</td>
			<td>Mundipharma, Basel, Switzerland</td>
			<td>7.68034E+12</td>
			<td>GTIN-number</td>
		</tr>
		<tr>
			<td>Curved fine tips microforceps</td>
			<td>World precision instruments (WPI), Sarasota, FL</td>
			<td>504513</td>
			<td>Facilitates vascular preparation</td>
		</tr>
		<tr>
			<td>Fine tips microforceps</td>
			<td>World precision instruments (WPI), Sarasota, FL</td>
			<td>501976</td>
			<td>Tips need to be polished regularly</td>
		</tr>
		<tr>
			<td>Infinity Delta XL Anesthesia monitoring</td>
			<td>Draeger, L&#252;beck, Germany</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Isoflurane, 250 mL bottles</td>
			<td>Attane, Piramal, Mumbai, India</td>
			<td>LDNI 22098</td>
			<td>Standard vet. equipment</td>
		</tr>
		<tr>
			<td>Ketamine (Ketalar)</td>
			<td>Pfitzer, New York, NY</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Lipopolysaccharide (LPS) from Escherichia coli, serotype 055:B5</td>
			<td>Sigma, Buchs, Switzerland</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Q-tips small</td>
			<td>Carl Roth GmbH, Karlsruhe, Germany</td>
			<td>EH11.1</td>
			<td>Standard surgical</td>
		</tr>
		<tr>
			<td>Ringerfundin</td>
			<td>Bbraun, Melsungen, Germany</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Tec-3 Isofluorane Vaporizer</td>
			<td>Ohmeda, GE-Healthcare, Chicago, IL</td>
			<td>not available anymore</td>
			<td>Standard vet. equipment</td>
		</tr>
		<tr>
			<td>Xylazine (Xylazin Streuli)</td>
			<td>Streuli AG, Uznach, Switzerland</td>
			<td></td>
			<td></td>
		</tr>
	</tbody>
</table>

a reproducible intensive care unit-oriented endotoxin model in rats

Sepsis and septic shock remain the leading cause of death in intensive care units. Despite significant improvements in sepsis management, mortality still ranges between 20 and 30%. Novel treatment approaches in order to reduce sepsis-related multiorgan failure and death are urgently needed. Robust animal models allow for one or multiple treatment approaches as well as for testing their effect on physiological and molecular parameters. In this article, a simple animal model is presented.
First, general anesthesia is induced in animals either with the use of volatile or by intraperitoneal anesthesia. After placement of an intravenous catheter (tail vein), tracheostomy, and insertion of an intraarterial catheter (tail artery), mechanical ventilation is started. Baseline values of mean arterial blood pressure, arterial blood oxygen saturation, and heart rate are recorded.
The injection of lipopolysaccharides (1 milligram/kilogram body weight) dissolved in phosphate-buffered saline induces a strong and reproducible inflammatory response via the toll-like receptor 4. Fluid corrections as well as the application of norepinephrine are performed based on well-established protocols.
The animal model presented in this article is easy to learn and strongly oriented towards clinical sepsis treatment in an intensive care unit with sedation, mechanical ventilation, continuous blood pressure monitoring, and repetitive blood sampling. Also, the model is reliable, allowing for reproducible data with a limited number of animals in accordance with the 3R (reduce, replace, refine) principles of animal research. While animal experiments in sepsis research cannot easily replaced, repetitive measurements allow for a reduction of animals and keeping septic animals anesthetized diminishes suffering.

The system presented allows for endotoxemia with hemodynamically stable animals as reported previously9. While the mean arterial pressure remains stable in animals with, and without LPS stimulation LPS treated animal develop characteristics of sepsis such as a negative base excess and a strong inflammatory reaction measured by plasma cytokines (6 hours after application) such as CINC-1 (867 ng/mL), MCP-1 (5027 ng/mL), and IL-6 (867 ng/mL)8, Figure 5</st...

Watch this Scientific Journal Video about A Reproducible Intensive Care Unit-Oriented Endotoxin Model in Rats at JoVE.com

A Reproducible Intensive Care Unit-Oriented Endotoxin Model in Rats

Here, we present a reproducible intensive care unit-oriented endotoxin model in rats.

Sepsis and septic shock remain the leading cause of death in intensive care units. Despite significant improvements in sepsis management, mortality still ...

This protocol is robust and reproducible model of endotoxemia in which physiological and molecular parameters can be assessed repeatedly. This approach may help to answer questions in sepsis research. While our model does not replace animal experiments, it refines sepsis models through continuous sedation and reduces the number of animals through repeated sampling.Beginners might struggle with the insertion of arterial and venous catheters, but only limited training is required to master these techniques. Visualization of the entire experimental setup facilitates researchers to set up, or adapt, their models to mimic more closely a situation on ICU. Begin by transferring the anesthetized animal to a heating mat.Keeping the body temperature between 36.5 and 37 degrees Celsius. Make sure that the animal is spontaneously breathing by providing oxygen with a nose cone. Confirm the level of anesthesia by the absence of the toe pinch reflex prior to the installation of tracheostomy and arterial and venous catheters.Use an ointment to protect the eyes. Prepare sterile surgical instruments and catheters along with pressure and oxygen saturation monitoring for sufficient oxygenation. Apply a tourniquet at the rat's proximal tail to facilitate venous access and disinfect the tail three times with alcohol.Introduce a 26-gauge intravenous catheter into one of the two lateral tail veins avoiding air injection. Untie the tourniquet after placing the intravenous catheter and fix the intravenous catheter in place with adhesive tape. Connect syringe pumps with three-way stopcocks to the intravenous access for continuous fluid and drug application.Begin the tracheostomy by shaving the animal's anterior neck area, and then disinfect the shaved skin three times with povidone iodine solution. Perform a two centimeter longitudinal incision using a scalpel blade number 10. Retract the skin with 2-0 silk sutures.Then bluntly prepared the larynx and the trachea to be opened with surgical scissors. Insert a sterile tracheal cannula into the trachea, being careful not to penetrate too deeply in order to avoid unilateral ventilation. Fix the cannula in place by using a 2-O silk suture and then connect the cannula to a ventilator for pressure or volume-controlled ventilation.Define fluid replacement protocols, vasoconstrictor application protocols, and abortion criteria before setting up the experiment. Disinfect the rat tail three times with povidone iodine solution and then cut the skin circle one centimeter longitudinally at the ventral side using a scalpel, taking care not to cut too deeply to avoid an injury of the tail artery. Use a surgical microscope to expose the artery carefully.Cut the fascia surrounding the artery with surgical micro scissors. Then ligate the distal part of the artery by performing proximal 6-0 silk suture, but do not tighten the silk. Introduce a 26-gauge catheter into the artery between the distal and proximal silk suture, and then tighten the proximal silk suture to fix the catheter in place.Connect the catheter to a pressure transducer to provide continuous arterial pressure measurement. Additionally, place a three-way stopcock between the catheter connected to the pressure transducer and the 26-gauge catheter for arterial blood sampling. After the animal has reached a steady state, induced sepsis by injecting LPS and collect blood samples.Replace fluid loss from the blood samples by Ringer's solution at a ratio of one to four, avoiding air injection at all times in order to prevent air embolism. The mean arterial pressure remains stable in animals with and without LPS stimulation. LPS-treated animals develop characteristics of sepsis, such as negative base excess.LPS-treated animals also developed a strong inflammatory reaction, which was measured by plasma cytokines, such as chemoattractant protein-1, monocyte chemoattractant protein-1, and interleukin-6. When attempting this protocol, remember to predefine fluid and vasopressor regimens as well as to define termination criteria in order to obtain solid and reproducible research data. This protocol can be adapted to other sepsis models.So a research question is answered with the most suitable approach and in accordance with the principles of reduce, refine, replace of animal welfare.

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1.9K Views.  University of Zurich. This protocol is robust and reproducible model of endotoxemia in which physiological and molecular parameters can be assessed repeatedly. This approach may help to answer questions in sepsis research. While our model does not replace animal experiments, it refines sepsis models through continuous sedation and reduces the number of animals through repeated sampling.Beginners might struggle with the insertion of arterial and venous catheters, but only limited training is required to mast...