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Coelioscopy of the green iguana
For the purposes of this course, the green iguana will serve as a model for reptile endoscopy (Divers, 1999). A left paralumbar approach is generally preferred, unless physical examination and other diagnostic tests indicate a right-sided problem.
The iguana is positioned in right lateral recumbency, with the left hindlimb taped caudally against the tail base. The entry area is bordered by the ribs, spine and hindlimb and should be aseptically prepared and draped.
The author prefers the use of adhesive clear plastic drapes to permit better visualization of the lizard during anesthesia, insufflation, and endoscopy. Taking aseptic precautions, a small skin incision is made in the center of the defined area.
The skin and underlying muscle is grasped and elevated away from the coelomic viscera and a small pair of hemostats are gently forced into the coelomic cavity.
It is wise to reduce the force of artificial ventilation or temporarily cease ventilating until the scope has been introduced into the coelom, thereby reducing the possibility of damage to the inflated lung.
The hemostats are removed and replaced by the sheath and obturator (with air line attached). By making a small skin and muscle hole, the sheath will be tight fitting and insufflation gas leakage will be minimal.
Once in place the obturator is removed and replaced with the telescope. The coelom is inflated to permit visualization of the internal organs. Inflation is essential for improving exposure but thought must be given to the adverse effects on lung ventilation and respiration.
Various gases can be used for insufflation, but carbon dioxide is preferred. A variety of specialized gas supplies, filtration units and insufflation devices are available, and a dedicated endoflator is preferred (26012 C).
However, an inexpensive aquarium air pump with controllable air output can be used to good effect in many small reptiles and mammals. Air line tubing is used to connect the insufflation gas supply to one of the ports on the sheath.
Gas flow (0.5-1 L/min) and patient insufflation pressure (3-6 mmHg) are accurately controlled and maintained when using an endoflator. When using an aquarium air pump the second sheath port is left open to avoid over-inflation (i.e. allows air to continuously escape from the sheath-scope-animal.
Occluding this open port with a finger increases insufflation, while lifting the finger off the port decreases insufflation. By careful finger control, insufflation can be crudely controlled.
Once the endoscope has been inserted, it is often necessary to gently touch the tip of the scope against a coelomic membrane to clean the terminal lens of condensation or tissue fluid. If there is fat or blood on the lens it is usually more effective to remove the telescope from the sheath, clean with damp gauze and then replace. It is important not to persist with a dirty lens. Poor vision is your enemy that will reduce your endoscopic ability and increase procedural time. Always keep your lens clean.
Upon entry into the iguana, the first organ to note is the large brown liver lying in the mid-ventral coelom. Advancing the scope cranially will reveal the heart at the cranioventral aspect of the coelom, close to the thoracic inlet.
Note that there are no diaphragmatic, post-pulmonary, or longitudinal membranes in the iguana. These membranes do exist to a greater or lesser extent in tegus, monitors, crocodilians, and some chelonians.
Minor perforation of these membranes by the telescope will not cause any harm as long as the lumen of the lung or intestinal tract is not penetrated.
Dorsal to the heart and extending from thoracic inlet to mid-coelom are the paired lungs. Lung ventilation will be substantially reduced during insufflation and careful communication with the anesthetist is required to balance inspiration pressure and insufflation pressure.
Caudal to the lungs, the stomach resides in the mid-coelom, and just dorsocaudal to the stomach, is the spleen – an elongated dark red structure in the iguana. Careful examination between the stomach and spleen, particularly below the spleen, will reveal the pancreas.
The gonads are located just caudal to the spleen close to the dorsal midline. Gender can be determined at a very early age. Dorsal to the gonads are the adrenal glands lying adjacent to the renal veins.
The vas deferens of males and oviducts of females are also visible and can be followed caudally to the pelvic inlet. It is more difficult to examine the normal kidneys of healthy iguanas because they reside largely within the pelvic canal.
However, it is always possible to examine part of the kidney(s) with the endoscope. [Because the kidneys are located caudal to the skin incision and endoscope entry site, it is necessary for the right hand supporting the camera-sheath-scope to cross over the left hand supporting the end of the sheath-scope.
Therefore, if performing a primarily kidney examination and biopsy, the iguana can be rotated 180 degrees so that the dorsum is facing the endoscopist. In this orientation, the right-handed endoscopist, can examine and biopsy the kidney without crossing the hands.]
Moving ventrally from the pelvic inlet the endoscopist will encounter the bladder and fat body. On the left side, the small and large intestines are apparent. On the right side, the gall bladder and large colon are usually obvious.
In addition, the pancreas is easier to locate on the right side, residing close to the mid-ventral region, just caudal to the liver and gall bladder, between the duodenal loops.
Enlarged liver in a green iguana with hepatitis.
Correct handling of the 2.7 mm telescope system. (A) Two-handed technique illustrating control of the tip using the inferior hand, while supporting the sheathed telescope and camera with the superior hand. This technique maximizes fine control and reduces fatigue; (B) one-handed technique with the inferior hand supporting the shaft of the sheath and the weight of the camera, while the superior hand manipulates the instrument. This technique is only safe if the telescope is correctly housed within the sheath.
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