This model can help to improve our understanding of the mechanism involved in lung injury and to test halogenated agent as potential novel therapy for acute respiratory distress syndrome. The main advantage of this technique is that inhaled anesthetics are delivered through an aesthetic conserving device, such as those used for ICU patients. Our technique uses a clinically relevant device to deliver inhaled ICU sedation, facilitating translational opportunities for the study of the effects of halogenated agents in acute respiratory distress syndrome.
After confirming a lack of response to pedal reflex in a two to four month old, 10 to 15 kilogram, white male land-raised piglet, use surgical exposure of the right internal jugular vein and the Seldinger method to insert a three lumen catheter into the vessel for central venous access. Make a cutaneous midline incision on the ventral aspect of the neck, two centimeters lateral from the trachea. And use surgical forceps to dissect the tissues.
After using an 18 gauge needle to make a puncture in the internal jugular vein in a cranial-caudal direction, insert a 60 centimeter piece of 0.81 millimeter diameter J guidewire through the needle, and quickly but carefully replace the needle with a venous catheter with three lines along the guidewire. Then remove the guidewire while keeping the catheter in place. With the right forelimb of the piglet in extension, make a cutaneous incision on the right groin area of the piglet and use surgical forceps to dissect the subcutaneous and muscular tissues.
Then use surgical exposure of the right femoral artery and the Seldinger method to insert a 20 centimeter, 35 French thermodilution catheter as an arterial line. For acid-induced acute lung injury, using an anatomical landmark of the last segment of the sternum, measure the distance between the tip of the endotracheal tube and the carina of the piglet. Use a black pen to mark this distance on a size 14 suction catheter, and insert the catheter through the endotracheal tube up to the landmark.
Then gently instill four milligrams per kilogram of 0.05 molar hydrogen chloric acid through the suction catheter for a period of three minutes before removing the catheter. After removing the catheter, set an intensive care ventilator to deliver volume controlled ventilation at a tidal volume of six milligrams per kilogram, a positive end expiratory pressure of five centimeters of water, and an inspired oxygen fraction of 40%Next, attach the appropriate filling adapter to a 250 milliliter bottle of the halogenated agent of interest. And attach a 60 milliliter syringe to the adapter.
Turn the bottle upside down and retract the plunger to fill the syringe with the agent. Turn the bottle upright and remove the syringe. Place a charcoal filter close to the ventilator.
Remove the protective cap from the charcoal filter and use a flex tube to connect the filter to the expiratory valve of the ventilator. Connect an ionomer membrane dryer line to the gas sampling port of an anesthetic conserving device. Connect the other side of the gas sampling line to the gas analyzer, and insert the anesthetic conserving device between the Y piece of the respiratory circuit and the endotracheal tube.
Ensure that the anesthetic conserving device is black side up and sloped toward the piglet, and deliver inhaled sedation through the anesthetic conserving device. Place the syringe in the syringe pump and connect the anesthetic agent line to the syringe. Prime the agent line with a 1.5 milliliter bolus of the halogenated agent.
And set the pump to the appropriate initial pump rate, to three milliliters per hour of isoflurane or five milliliters per hour of sevoflurane. Confirm that the gas analyzer displays an expired halogenated agent fraction or equivalent minimal alveolar concentration value greater than zero, giving an additional 300 microliter bolus of halogenated agent as necessary. Then adjust the syringe pump as necessary to reach the appropriate concentration depending on the minute volume and targeted concentration, continuing to administer the appropriate anesthetic fractions throughout the experiment.
Use the external monitor to collect heart rate, blood pressure, and peripheral oxygen saturation measurements, and record the tidal volume, respiratory rate, set and auto positive end expiratory pressure, compliance of the respiratory system, airway resistance, inspiratory plateau pressure, peak inspiratory pressure, and driving pressure as measured by the ventilator. Use the nitrogen wash in, wash out method to calculate the lung functional residual capacity. And use the thermal indicator to measure the extravascular water volume of the lungs, cardiac index, and systemic vascular resistance.
To measure the net alveolar fluid clearance rate, insert a soft 14 French suction catheter through the endotracheal tube into a wedged position in the distal bronchus and apply gentle suction to collect an undisputed pulmonary edema fluid sample. For many bronchoalveolar lavage sampling, instill 50 milliliters of a 0.9%sodium chloride solution into the suction catheter. And collect the resulting volume of lavage.
For blood gas analysis, collect arterial blood gases through the arterial line in a three milliliter preset syringe with a Leur-lock tip at the baseline. And use a point of care blood gas analyzer to immediately measure the acute respiratory distress syndrome partial pressure of arterial oxygen ratio, partial pressure of carbon dioxide, pH, serum lactate, and serum creatinine levels. At the end of the experiment, harvest the whole lung tissue into alcohol acetified formalin for macro and histologic tissue analysis.
In this representative experiment, a two way repeated measure analysis of variance indicated a significant time by group interaction with a detrimental effect of hydrogen chloride induced ARDS on the acute respiratory distress syndrome partial pressure of arterial oxygen ratio compared to sham animals without ARDS. A significant between group difference was noted in the undiluted pulmonary edema fluid levels of the total protein four hours after mechanical ventilation with an association observed between hydrogen chloride induced ARDS and increased bronchoalveolar protein levels compared to that observed in sham animals. Two-way repeated measures analysis of variance also revealed a significant time by group interaction between hydrogen chloride induced ARDS and increased extravascular lung water compared to sham animals.
Cardiac output demonstrated an increased trend in acid injured animals while systemic vascular resistance values were slightly lower in the hydrogen chloride induced ARDS group. Four hours after injury, macroscopic lung damage, including visible hemorrhage and congestion, can be observed within the red regions of lungs harvested from hydrogen chloride induced ARDS animals that is absent in untreated piglet lung tissue. Histologic analysis reveals a greater cellularity within acid injured lung tissue slices with more areas of atelectasis and increased alveolar disruption, hyaline membranes, protein debris, hemorrhage, and alveolar wall thickening.
These disruptions are absent in sham samples. In addition to administrate halogenated volatiles, this model of acid induced ARDS could be useful for studying specific pathways of interest such as those involved in lung epithelial injury and repair.
