Medicine
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Oleic Acid-Injection in Pigs As a Model for Acute Respiratory Distress Syndrome
Chapters
Summary October 26th, 2018
In this article, we present a protocol to induce acute lung injury in pigs by central-venous injection of oleic acid. This is an established animal model for studying the acute respiratory distress syndrome (ARDS).
Transcript
This method can help answer key questions about the pathophysiologic changes that occur during ARDS for the development and evaluation of new treatment options for this disease. The main advantage of this technique is that it reproduces the basic pathologic changes observed in human ARDS. For ultrasound guided instrumentation, place an ultrasound probe on the right inguinal ligament of the experimental pig and scan for femoral vessels.
Turn the probe 90 degrees to fully visualize the femoral artery in the long axis and use a Seldinger's needle to cannulate the right femoral artery under in-line ultrasound visualization. When pulsating bright blood flows out, introduce the guidance wire and retract the needle. Check to make sure that the positioning of the Seldinger's wire is correct by visualizing it with ultrasound.
Visualize the femoral vein and cannulate the vein under in-line ultrasonography in continuous aspiration with the needle. When venous blood is able to be aspirated, insert Seldinger's wire and retract the needle. Use Seldinger's technique to insert a 5-French arterial introducer sheath and essential venous catheter and turn the corresponding three-way stopcocks back.
Before inserting the pulmonary artery catheter, check that it is working properly and insert it through the left venous introducer sheath. When the pulmonary artery catheter has passed through the introducer sheath, inflate the balloon with one milliliter of air and advance the pulmonary artery catheter while monitoring the typical waveforms. Then deflate the balloon and check if blood can be aspirated through all of the ports of the pulmonary artery catheter.
Then insert the probe for ultrafast measurement of the partial oxygen pressure through the right arterial introducer sheath. To induce lung injury, load one 20 milliliter syringe with 0.1 milliliters per kilogram of oleic acid and a second 20 milliliter syringe with two milliliters of freshly drawn blood. Add saline to the syringe with blood, to a total volume of 20 milliliters in both syringes and connect both syringes to a three-way stopcock.
Connect a norepinephrine syringe pump to one port of the central venous catheter and begin an ultrafast partial oxygen pressure measurement. Record the baseline values of all of the relevant parameters and set the fraction of inspired oxygen to 1.0. Conduct a lung recruitment maneuver and connect the three-way stopcock to the proximal port of the pulmonary artery catheter.
Then inject the oleic and blood saline mixtures, repeatedly from one syringe into the other, via the three-way stopcock, to thoroughly mix the solutions. When a homogeneous emulsion has been achieved, inject two milliliters of the emulsion into the central venous catheter and continue mixing. Closely monitor the hemodynamics after the injection, giving norepinephrine as 10 to 100 microgram bolus injection as necessary to keep the mean arterial pressure above 60 millimeters of mercury.
Repeat the two milliliters oleic acid solution injection every three minutes, until the arterial partial pressure of oxygen fraction of inspired ratio is below 200 millimeters of mercury. Wait 30 minutes and reevaluate the partial pressure of oxygen fraction of inspired ratio. If the ratio is still over 200 millimeters of mercury, repeat the injections until the partial pressure of oxygen fraction of inspired ratio falls below 200 millimeters of mercury.
Then set the ventilation according to the suggestions from the Acute Respiratory Distress Syndrome network. The partial oxygen pressure fraction of inspired oxygen ratio decreased after the fractionated application of oleic acid. Despite a typical impairment of oxygenation after the induction of lung injury, frequent variations in oxygen impairment are observed between animals across the impairment timecourse.
Necessitating a close monitoring of the partial oxygen pressure fraction of inspired oxygen ratio while delivering the oleic acid. The decrease in partial oxygen pressure fraction of inspired oxygen ratio is paralleled by an increase in pulmonary arterial pressure which typically remains elevated for the rest of the experiment, with some fluctuation also observed between animals. Lung injury is visually detectable in lungs harvested six hours after lung injury induction, and histological analysis reveals alveolar edema and hemorrhage.
After watching this video, you should have a good understanding of how to induce an acute lung injury in pigs by essential venous injection of oleic acid. Don't forget that working with oleic acid can be extremely hazardous and take precautions such as wearing gloves, and safety classes should always be taken while performing this procedure.
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