Begin by intubating the anesthetized mouse with a 22-gauge IV catheter. Perform the intubation under visual guidance using a surgical microscope and an intubation stand, allowing proper alignment for visualization of the vocal cords. Ensure continuous delivery of inhalant anesthetics on a nasal tube until the endotracheal tube has been connected.
Ventilate the mouse at 175 strokes per minute and a tidal volume of 300 microliter per stroke. Before beginning the surgery, subcutaneously administer analgesics for peri and postoperative analgesia and saline to compensate for perioperative fluid loss. Confirm proper placement of the endotracheal tube by observing symmetrical movement of the chest.
To perform the surgery, use a scalpel to make a 10-millimeter incision in the skin above the second intercostal space from the sternal angle to the left anterior axillary line. Then, using forceps, bluntly dissect the major and minor pectoral muscles and identify the second and third costae. Place the custom-made thoracic retractor under the pectoral muscles.
Cut the intercostal muscles in the second intercostal space. Reposition the thoracic retractor to the intercostal space to keep the operating field accessible. Rotate the mouse's lower body to improve the exposure of the pulmonary trunk.
Bluntly dissect the thymus to expose the heart, pulmonary trunk, and aorta Using microscopic forceps, carefully remove the connective tissue between the vessels to separate the pulmonary trunk from the ascending aorta. Pass the guidance cannula through the transverse pericardial sinus posteriorly of the pulmonary trunk. Use forceps to grasp the knot on the tip of the guidance cannula and pull the suture through the cannula.
Carefully remove the guidance cannula while the suture stays in place around the pulmonary trunk. Load the ligating clip applier. Use the suture to guide the pulmonary trunk into the jaws of the ligating clip and compress the clip.
Release the suture immediately after placing the clip and observe the filling of the pulmonary trunk. Ensure that the clip is correctly placed. Place a 6-0 monofilament absorbable suture around the second and third costae and close the intercostal space.
Evacuate as much air as possible from the thoracic cavity by applying gentle pressure to the chest while tightening the suture. Lastly, suture the pectoral muscles and skin with a 6-0 monofilament absorbable suture. To ensure adequate postoperative analgesia, add analgesic to the drinking water as well as administer it by subcutaneous injections for the first three days after surgery.
