Open-Drop Isoflurane Anesthesia for Field Studies

Last Date Reviewed: November 29, 2017


Procedure

A.  Materials

1.  Isoflurane

2.  Cotton gauze pad 

3.  Tea strainer or conical tube with pre-drilled holes

4.  Bell jar or wide-mouth glass container (with known volume).  Any type of   
     container with a secure lid may be used, provided it is constructed of non
     porous material that is sanitizeable and allows for constant visualization of the
     animal. The jar should be of sufficient size to comfortably accommodate the
     animal and your hand, but not so large as to require excessive anesthetic.

B.  Mice will remain deeply anesthetized for approximately 30 seconds following  
     exposure in the induction chamber. This method can be used for retro- orbital
     blood sampling, tail biopsies and similar rapid procedures in the field.

C.  Close constant monitoring of animals is essential during induction and anesthesia
      maintenance.

D.  Procedure must be performed in an area with good ventilation. If performed in a
     temporary field station – open two sides of the wall tent for air circulation. Don
     gloves. Wet a cotton pad (e.g., nestlet, gauze) with the isoflurane 0.5 cc per 500
     cc volume of the anesthesia jar.

1.  Place the cotton pad inside a small container (metal tea strainer). The use of
     the tea strainer ensures that the animal does not contact the isoflurane-soaked
     pad, which can cause skin irritation and potential overdosing since isoflurane is
     also absorbed through the skin.

2.  Transfer animal to anesthesia jar and close lid tightly. Monitor animal closely.
     Within approximately one minute the animal will become anesthetized. Initially,
     respiratory rate will increase and then decrease. Clinical indications of a deep
     plane of anesthesia in rodents include the lack of a righting reflex (upon
     tipping jar gently) and a 50% reduction in respiratory rate compared to pre-
     anesthesia levels (i.e., to ~80- 100 breaths per minute).

3.  Allow the animal to remain at a deep anesthetic plane for ~10 seconds
     before proceeding. Quickly, yet carefully, remove the animal from the jar and
     place it on a clean work surface. Replace the lid on the jar immediately.

4.  Apply a noxious stimulus (i.e., toe pinch) to ensure adequate plane of   
     anesthesia. If no response is noted, the procedure can be initiated. If the
     animal responds to noxious stimulus, return it to the jar and monitor respiratory
     rate as in step 2.

5.  The animal will remain deeply anesthetized for approximately 30 seconds
     following exposure to the isoflurane in the induction chamber.

6.  If the animal reaches a lighter plane of anesthesia during the procedure,
     evidenced by increased respiratory rate, whisker twitch, or purposeful  
     movement, stop the procedure and transfer the animal back to the bell jar,
     until the animal again reaches a deep plane of anesthesia. Proceed with step
     #4.

7.  If anesthetizing multiple animals, proceed as described above but if the
     subsequent animal does not reach a surgical depth of anesthesia, remove
     used isoflurane/cotton pad and replace with a fresh pad.

8.  Allow the animal to recover on a piece of clean paper towel in a bedding-free
     cage. Monitor the animal closely until it is fully recovered.