The overall goal of this procedure is to intubate a mouse to allow either mechanical ventilation or the installation of liquids. This is accomplished by first assembling the cannula and light source. The second step is to hang the mouse vertically by the upper incisors.
After manipulating the head and body to allow a straight path for intubation, insert the fiber optic introducer and cannula through the vocal cords. Ultimately, the optical fiber is removed and the mouse with cannula in place is put into a supine position for ventilation or installation. Okay, today we're gonna demonstrate simple procedure to intubate a mouse lung.
The visualization is important because often the positioning of the mouse is a critical step in terms of inserting the cannula, and so with a little practice, it takes a little practice. It should be possible for anybody to do this repeatedly in a relatively short time demonstrating the procedure today is Dr.Sandy Doss, who is a junior faculty member in the division of Pulmonary Medicine and the school of medicine. The first step is to prepare.
Prepare the cannula for adult mice, a one to 1.5 inch long, 20 gauge IV catheter is used. Next, prepare the fiber optic cable by cutting a length of 0.5 millimeters optical cable to smooth the edge. After cutting, hold the fiber at the end and make small circles so that the tips touch a piece of 1000 grit emery paper.
The other end is inserted into a silicone rubber stopper sized to fit the light source opening. First, push through an 18 gauge needle. Next, insert the optical fiber through the needle bore and withdraw the needle.
The rubber stopper is then connected to a 150 watt halogen light source. Next, insert the fiber optic cable through a short piece of silicone rubber tubing. Secure the tube in place while still allowing the fiber optic cable to be adjusted.
Once in place, insert the silicone tubing snugly into the lure end of the cannula. Adjust the position of the fiber optic cable so that it extends through the cannula and about four millimeters in front of the tip. Once everything is prepared, place an anesthetized mouse on a vertical support by carefully suspending the animal by its upper incisors.
Once secured, very gently, pull out the tongue and hold it with the thumb and forefinger. Place the middle finger between the neck and plastic support traction on the tongue with the index. Finger and thumb is used to open the mouth and to straighten the intubation path.
The angle of the head is adjusted with the middle finger behind the neck as shown here. Next, visualize the vocal cords. If the cords are not visible, gently pull harder on the tongue using the middle finger as support.
Once visualized, use the fiber optic cable as both a light source and introducer and push it through the vocal cords. One indication that the cannula is in the trachea is that the mouse may gasp when the cannula is first inserted. Once inserted, advance the cannula about five millimeters Further, then being careful not to move the cannula, withdraw the fiber optic cable, lie the mouse down, and secure the cannula with a piece of tape and support the cannula hub on a piece of modeling clay.
A small dental mirror kept in the freezer can be used to confirm that the cannula is in the trachea and not the esophagus. Place the mirror in front of the lure hub of the catheter. If the catheter is in the correct position, the exhaled breath will form condensation on the mirror.
If the intubation procedure is being done only for aerosol installation of agents into the lung, this can be done while the mouse is lying supine. In this position, however, liquid installations are more efficiently done while the mouse is still suspended in the vertical position, followed by immediate removal of the cannula for measurement of lung function. The intubated anesthetized mouse is then connected to a mechanical ventilator as shown here.
The settings for the ventilator should be done prior to starting the intubation, so there will be no delay in ventilation. A record of ventilation pressure and volume is shown for this intubated mouse. We evaluated the ability of the method to obtain reproducible measurements of airway resistance over a period of five weeks.
The data in this graph shows that there is no effect of making repeated measurements since baseline resistance remains relatively constant. In each of four mice studied at weekly intervals, we evaluated the tightness of the seal between the trachea and intubation cannula by injecting air boluses into the lungs after sacrificing the mouse. Although there may be a very slow leak after the stress, relaxation recovery, the pressure leaks appear to be minimal.
While attempting this procedure, it is very important to be careful while removing the mouse from the supporting stand as it is very easy to pull out the cannula accidentally.
