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Ex Vivo Porcine Experimental Model for Studying and Teaching Lung Mechanics
Chapters
Summary April 19th, 2024
We present an ex vivo pig lung model for the demonstration of pulmonary mechanics and alveolar recruitment maneuvers for teaching purposes. The lungs can be used for more than one day (up to five days) with minimal changes in pulmonary mechanics variables.
Transcript
Mechanical ventilation is widely used in respiratory failure, partially or completely replacing spontaneous ventilation. Its management requires prior knowledge and expertise. However, some studies show that professionals feel insecure in its management.
Any claim, lack of training, or prior knowledge. The experimental models come to facilitate the concepts of mechanical ventilation and visualization of lung mechanics with visual feedback. Initially obtained the animal weight to adjust the medications and sedation necessary to the procedure.
Administer ketamine five milligrams per kilogram, and midazolam point 25 milligram per kilogram intramuscularly. Then puncture the marginal ear vein with a 20 G venous catheter and administer intravenous propofol, five milligrams per kilogram for anesthesia induction. Administer three milliliters of heparin intravenously to eight cardiopulmonary block extraction and perfusion.
After anesthesia, perform orotracheal intubation with a 6.5 millimeter cannula. The tracheal cannula must be securely fixed to prevent displacement during the procedure. After preparation, connect the NMO via cannula to mechanical ventilation, and maintain the NMO anesthesia with a 1.5%isofluorine in 50%of inspired fraction of oxygen.
And fentanyl, 10 micrograms per kilogram bolus, plus 10 micrograms per kilogram per hour continuous infusion. The assessment of the depth of sedation is performed based on the monitoring of hemodynamic parameters and the use of a gas analyzer. Adjust the mechanical ventilator for volume controlled model with a tidal volume of eight milliliters per kilogram.
The ventilation mode and other settings are selected on the mechanical ventilator screen. The respiratory rate must be adjusted to maintain end-tidal Co2 of 35 to 45 millimeters of mercury. Make a sternal incision large enough to access the thoracic cavity, two centimeters above the manubrium to two centimeters below the xifoide process of the sternum, and position the rib retractors, expanding the field of view during the procedure.
Make a tracheal incision horizontally using the scalpel. The incision must be large enough to introduce a new tracheal cannula, removing the oral tracheal tube. Inflate the cuff of the newly introduced tracheal cannula.
Attach the new tracheal cannula directly to the trachea. The tracheal cannula is not sutured, just tied, to avoid leaks and movement during the lungs placement in the ventilation box. With the scalpel dissect the tissues to remove the cardiopulmonary block from the thorax.
At the end, increase the isoflourane concentration to 5%and administer 10 milliliters of potassium chloride. After tissue dissection, clamp the orotracheal cannula with the appropriate Cali forceps during the end of inspiration, keeping the lung inflated. Disconnect the mechanical ventilator.
Section the aortic artery, and position the aspirator inside the thoracic cavity to remove extravasated blood, and maintain visualization of the cavity. The inferior pulmonary ligament should be carefully released to avoid pulmonary laceration. Remove the cardiopulmonary block from the ribcage with the orotracheal cannula clamped, and place it on a tray.
Cannulate the pulmonary artery with a large bore single lumen catheter, and connect it to the infusion set to continuously administer 2000 milliliters of code 9%saline solution until clear liquid flows from the aorta. The saline solution should be administered at a normal rate. Avoiding squeezing the IV bag.
After clearing the flow, suture the aortic artery and administer another a hundred milliliters of saline solution. The saline solution remains inside the lungs until the end of the experiment. After preparing the lungs, position them vertically inside the acrylic box and connect the tracheal cannula to the mechanical ventilator.
Make sure the tracheal cannula is firmly secured in the trachea. Adjust the mechanical ventilator for volume controlled mode with the following parameters. Tau volume, six milliliters per kilogram.
PEEP, five centimeters of water. Inspired fraction of oxygen, 21%Respiratory rate, 15. An inspiratory pause time, 10%Settings are selected on the mechanical ventilator screen.
To start recruitment increase PEEP from five to six centimeters of water, and then increase it in step-by-step increments of two centimeters of water, until reaching 14 centimeters of water. PEEP is increased using the onscreen button on the mechanical ventilator. Each PEEP value is maintained for 10 minutes while recording lung mechanics.
After reaching 14 centimeters of water, reduce PEEP step-by-step in decrements of two centimeters of water until reaching six centimeters of water, and then reduce it to five centimeters of water. During this decrease, the PEEP value is maintained for five minutes, while recording lung mechanics. At the end of the recruitment stage, gently clamp the tracheal cannula with the clamp during inspiration, keeping the lungs inflated.
Open the acrylic box. Remove the lungs from the acrylic box and carefully place them in a glass container. After placing the lungs into the glass container, make sure the clamp is tightly closed, and pour 500 milliliters of 9%saline solution.
Store the lungs in the refrigerator in a plastic wrapped glass container at a temperature of two to eight degrees Celsius for 24 hours. Repeat the process for mechanical ventilation, and the ovular recruitment maneuver for five consecutive days. After each time the process is completed, place the lungs in the glass container and store it in the refrigerator.
We analyze the lungs for five consecutive days, repeating the entire process as described in the flow chart. We were able to show how the lung variables behaved before and after recruitment, and establish the durability of the ex vivo lung model in the study period. We observed significant differences between all variables before and after recruitment maneuvers.
Peak pressure, plateau pressure, and driving pressure decreased after the maneuver, while dynamic compliance increased, demonstrating opening of the collapsed alveoli, and gain in lung area. Airway resistance also increased after recruitment. We show that the model is effective in demonstrating visual changes in lung mechanics through the Alveolar recruitment maneuver, and its effectiveness for the study and teaching of lung mechanics.
In addition, we show that the model can be used for at least five consecutive days. In the pilot study, we started with a PEEP of five centimeters of water, and increased it in five centimeters of water increments up to 25 centimeters. However, the peak and plateau pressures reach values greater than 40 and 30 centimeters of water respectively, with fistula formation.
Thus, we chose to perform a gradual increase in two centimeter increments to provide a better analyze of the behavior of pressures over time, and understand the PEEP limits in your ex-vivo logging model. There is no difference between sustained or incremental inflation in relation to mortality, but in addition to being the most used incremental inflation can facilitate the stepwise analyze of lung mechanics. There have been studies using XV over C models with positive and negative pressure with different initiatives, such as the development of a similar model of for preclinical studies, the verification of aerosol distributions, and establishment of pediatric simulations.
Despite the different objectives, such studies open possibilities for our new research, aid applications for our learning model. Although studies have demonstrated that the use of positive pressure ventilation in the XV volume model can lead to abrupt recruitment, with a greater local deformation than negative pressure ventilation. It's necessary to create positive pressure models because our patients are usually submit to positive pressure during mechanical ventilation, as limitation of we have first, knowledge of any animal anatomy so the legs can be properly removed.
Second, the model was not evaluated beyond five days. Third, this model, it fits well for just for ventilation teaching. And finally, to translate its results to all human beings, it is important to consider the limitations of animal model.
The X vivo pulmonary model is viable and reproducible, it can submitted to recruitment maneuvers with visualization of the pulmonary mechanical variables. The model provides a new view of the lung under mechanical ventilation, facilitating the teaching of these concepts through visual feedback.
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