Mouse and rat transgenic technology has lead to the development of complex surgical rodent models. These models are so complicated that often scientist concentrate on that particular surgical procedure while forgetting about the patient. This can lead to undesirable side effects, leading to the introduction of unnecessary variables which makes interpreting the experimental data challenging.
Organization is imperative when planning rodent surgery, since often several surgical procedures are performed within the same day. A check list should be developed which includes all of the materials required per animal for each individual procedure. These lists have been introduced in human surgical suites and reduced surgical mistakes by as much as 30%.
Anesthesia and surgical stress
Placing a rodent under anesthesia has significant effects on their physiological status, and these effects are compounded by the stress of a surgical procedure.
In the last blog, the physiological stresses that were addressed were pain and distress. In this blog we will address the stresses of hypothermia, hypovolemia, and dehydration.
Rodent physical exam
First, before any anesthetic procedure, a mouse or rat should be observed within its environment, and then a thorough physical exam should be performed. This provides a baseline for the assessment after surgery.Obtaining the weight of the mouse or rat must be part of this exam. This will allow for the provision of appropriate drug and fluid doses and allow the scientist to monitor post-surgical weight. Weight loss can indicate pain, dehydration, or the presence of a postoperative infection.
Rodent corneal desiccation
A petroleum based ocular ointment should be used to prevent desiccation of the cornea. Antibiotic ocular ointment should not serve as a replacement for petroleum ocular ointment. Rodents’ eyes should especially be monitored when a face mask is used since it can exacerbate eye desiccation and irritation due to the air flow and irritating gas anesthetic.
Rodents can become hypothermic rapidly after anesthesia induction if appropriate heat support is not provided. This is because of the rodents’ high ratio of surface area to size, high metabolic rate and high oxygen flow rate. All of these factors result in an accelerated rate of cooling in mice and rats. Addressing hypothermia in rodents has been challenging in the past. However, with the development of rodent specific instrumentation this can be accomplished more easily with more consistent results. One of our favorites is a surgical homeothermic table. This table measures rodent’s temperature rectally and provides feedback to the heating unit which then automatically adjusts the temperature in order to keep the animal at a homeothermic temperature. These units are well worth the investment especially when performing prolonged surgical procedures such as mouse or rat laparoscopies.
Mice and rats should receive a subcutaneous bolus of Lactated Ringers Solution prior to surgery. This solution should be warm since injecting cold or room temperature solutions will immediately make the rodent hypothermic. Mice and rats should also receive subcutaneous fluids during prolonged surgical procedures as well as post surgically, since in most cases rodents will not return to normal drinking patterns quickly post surgically.
Hemostasis is important in all surgical procedures. In mice and rats it is especially important because a loss of a ‘few drops’ can lead to severe hypovolemia and result in mortality. Hemorrhage can be controlled with electrocautery, pressure (gauze or instruments) and suture ties. When utilizing electorcautery it is important not to induce thermal damage to the tissue, and when utilizing gauze, pressure should be applied without dragging the gauze on the tissue which can lead to the dislodgment of formed clots.
Paying attention to the animal and being organized while performing rodent surgery will lead to an increase in the surgical success rate, improve animal welfare and improve experimental data.
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