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General Principles, Instruments, and Equipment

R. Avery Bennett

Introduction

Many surgeries in exotic animal are analogous to those performed in other species. The size of some patients makes surgery more challenging. Appropriate preoperative work up, patient preparation, surgeon preparation, perioperative antibiotic therapy, thermal support, and hemostasis are essential for a successful outcome. Preemptive, multimodal analgesia has long been known to improve recovery from surgery and is especially important with wildlife and exotic prey species. Additionally, in recent years, patients' anxiety has become an important consideration when these patients have to be hospitalized. Use medications evaluated for the species having surgery to develop a preemptive analgesic and antianxiety treatment plan. When prey species experience anxiety, stress, fear, and pain, they often die for no apparent reason. Alternatively, they may recover from the surgical event only to die a day or two later, likely from these stresses. In pet species, it appears that if they are accustomed to being handled by humans they are more likely to survive the perioperative period. If multiple procedures need to be accomplished, as a general rule, it is better to perform multiple short anesthetic events and surgeries than to try to do everything under one long anesthetic event. This is especially true when imaging is needed for surgical planning. It is best to anesthetize the patient for imaging, then recover it and evaluate the study. Once a diagnosis is made and a plan developed, anesthetize the patient the next day for the surgical procedure.

It is important that patients resume eating for nutritional support as soon as possible after surgery. Many small patients are not able to undergo long periods of anorexia because they do not have the energy stores to support themselves because in their natural environment they are constantly eating. The nutritional needs of the patient must be addressed and supplemented as needed either per os, using a feeding tube, or intravenously.

Presurgical Considerations

Prior to performing surgery, it is vital to evaluate the patient and address any abnormalities. In many situations, fasting is recommended; however, sometimes it is not necessary. Hemodynamic support is important for all but the shortest surgical procedures. Patient and surgeon aseptic techniques should be followed for all surgeries regardless of size and species. Perioperative or therapeutic antibiotic therapy needs to be considered. Because small patients become hypothermic quickly, thermal support is essential even for diagnostic procedures done under anesthesia.

Patient Support

Small exotic animals are especially prone to developing perioperative complications such as hypovolemia from blood loss, hypothermia, and renal and respiratory compromise. It is important to evaluate the patient systemically prior to anesthesia and surgery and to address any abnormalities preoperatively. During anesthesia and surgery, provide fluid therapy to support the cardiovascular system. Monitor body temperature and take measures to minimize hypothermia. Take appropriate steps to minimize blood loss and take precautions to minimize the risk of surgical site infections.

Data Base

The ideal preoperative data base includes a complete blood count, serum or plasma biochemistry panel, and a urinalysis. Additional diagnostics may be indicated based on the species and the medical problem being addressed. For example, mice and rats are prone to mycoplasmosis pneumonia, and preoperative chest radiographs are indicated prior to anesthesia in these species. While it may be difficult to obtain a urine sample from a small rodent, they are prone to developing renal insufficiency later in life, so it is important to evaluate urine specific gravity and a dipstick for proteinuria. These can be done with two drops of urine that can be obtained by placing the patient in a plastic or glass container for several minutes. In ferrets, it is important to determine the blood glucose level prior to anesthesia because they are prone to forming insulinomas. In very small patients, it may not be feasible to take enough blood for all of the abovementioned diagnostics. At a minimum determine a hematocrit, total protein, blood urea nitrogen (azotemia test strip), glucose, and urine specific gravity.

Preoperative Fasting

Various species such as equids, rabbits, and rodents are not able to vomit for physiologic reason, so fasting to prevent aspiration pneumonia is not necessary. Additionally, if attempting to decrease gastrointestinal contents for a surgery, it can take days to make a difference because the majority of ingesta is within the hindgut. A short fast is recommended to allow these species to swallow any food material to reduce the risk of food entering the trachea during intubation. A prolonged fast in small mammals can result in a negative energy balance which increases their risk for developing complications after surgery (Jenkins 2000). Many small patients have low hepatic glycogen stores and may develop hypoglycemia during a prolonged fast (Harkness 1993; Redrobe 2002). Administer fluids containing dextrose subcutaneously (SC), intravenously (IV), or intraosseously (IOs) in patients prone to developing hypoglycemia. The gastrointestinal transit time in ferrets is rapid, and a prolonged fast is not recommended. An hour fast in ferrets is long enough for the stomach to empty minimizing the risk of developing aspiration pneumonia. On the other end of the spectrum, some reptiles may only eat once a week or even less often so there is no need for a fast.

Hemodynamic Support

Small patients have a small total blood volume and what may appear to be minimal hemorrhage can be life-threatening. If the patient is anemic and surgery can be postponed, it should be postponed until the hematocrit is into the normal range. It would be a rare event that surgery made a hematocrit increase, typically the opposite is the norm. Consider a blood transfusion from a conspecific, if more than minimal hemorrhage is anticipated or if the patient is anemic preoperatively. Strict attention to intraoperative hemostasis is essential when performing surgery on any small patient.

In patients experiencing serious blood loss during surgery, crystalloid or colloid fluid therapy should be administered as quickly as possible for cardiovascular support. More ideal, blood from a conspecific should be used, but often this is not available. Preplanning by having a conspecific blood donor available can be life-saving. In ferrets, there are no blood types and no reports of transfusion reactions. It is safe to use any ferret as a blood donor. In many species, blood typing may not be known. If it is unknown whether a species has blood types, a crossmatch should be performed prior to administering a blood transfusion.

Anesthesia results in loss of fluids because of dry gases making parenteral fluid administration vital for most surgical procedures. It can be difficult to achieve vascular access in small patients. Vascular access provides a route for the administration of fluids during anesthesia at the standard rate of 10?ml/kg/hr and, maybe more importantly, provides a route for administration of emergency drugs in the event of a crisis. An IOs catheter can be placed relatively easily in most species even in small patients. SC administration of fluids is much less effective than IV or IOs and is an ineffective route for administration of emergency drugs. A single dose of 10?ml/kg SC of 4% dextrose has been recommended for short procedures in healthy small exotic mammals (Redrobe 2002). Fluids administered subcutaneously or intraperitoneally are slowly absorbed and not appropriate for treatment of severely ill, dehydrated, or shocky patients.

Maintain vascular access in the postoperative period if at all possible. Continue to administer fluid at least at a maintenance rate until the patient has completely recovered and is eating and drinking well.

Perioperative Antibiotic Therapy

The aim in administering perioperative antibiotics is that the blood level of antibiotic will be effective in preventing incision site infection from target organisms. In most cases, the target organisms are normal skin flora that cannot be completely eliminated during patient skin preparation. The antibiotic should be administered prior to making an incision, which is when the first exposure occurs and should continue until the surgery is complete so any blood clots that form will have therapeutic levels of antibiotic. If the patient is already receiving antibiotics for treatment of an infection and has therapeutic circulating levels of antibiotics effective against the target organisms, additional IV perioperative antibiotic is not needed. If the therapeutic antibiotic is not expected to be effective against the surgical target organisms, perioperative antibiotic administration of an antibiotic expected to be effective against the surgical target organisms should be administered perioperatively. For example, if a patient is receiving cephalexin for a skin infection, but the surgery is in the perineal area where fecal contamination is a concern, adding a perioperative antibiotic against which fecal flora are likely to be sensitive is appropriate. There is no evidence that continuing to administer a perioperative antibiotic for a...