Ovariohysterectotny

Methods for prepubertal ovariohysterectomy are similar to those routinely used in more mature animals and have been described in detail (Salmeri et al., 1991; Aronsohn and Faggella, 1993; Theran. 1993). Because of the small amount of abdominal fat present in young animals, visualization of the ovarian pedicle is excellent. This, coupled with the small vessel size, allows for precise hemostasis and shortens operative time. Fine (3-0 or 4-0) absorbable suture material such as chromic gut (chromic gut, Ethicon), polyglyconate (Maxon, Davis and Geck) or stainless steel hemostatic clips may be used for ligation of the ovarian pedicles and uterine body. The linea alba can be closed using either fine (3-0 or 4-0) absorbable or nonabsorbable suture material in an interrupted or continuous pattern. Closure of the subcutaneous layer is optional if skin sutures are to be used. The use of subcuticular sutures without skin sutures has been suggested (Aronsohn and Faggella, 1993) to decrease the patient"s interest in the incision.

Orchidectomy

In dogs and cats, the testicles are usually descended at birth and are easily palpable in the immature scrotum by 6 to 8 weeks of age. Orchidectomy in the kitten is similar to the procedure performed in adult cats. The spermatic cord may be ligated in a closed or open fashion with fine absorbable suture material, stainless steel hemostatic clips, or by tying the cord upon itself using a hemostat. The scrotal incisions are left to heal by second intention. A scrotal (rather than prescrotal) approach to the testicles is also used in 6- to 8-week old puppies. The procedure can be performed in an open or closed fashion, using absorbable suture material or hemostatic clips for ligatures. Fine subcuticular sutures can be used to close the scrotal incisions or they can be left to heal by second intention.

Pediatric Considerations

The potential for hypothermia and hypoglycemia, a relatively small blood volume, and delicate tissues are factors that must be considered when performing surgery on pediatric patients.

Hypothermia can be minimized by placing patients on recirculating warm water blankets during surgery and by administering warm balanced electrolyte solutions intravenously (ovariohystereetomy). The animal should also be kept from getting excessively wet during preparation of the surgical site. Neonates are also more susceptible to hypoglycemia than adults; therefore, food should be withheld no longer than 8 hr prior to surgery, with 3 to 4 hr being optimal in the youngest patients. If necessary, oral or intravenous 50% dextrose or oral corn syrup can be administered perioperatively and animals should he fed within a few hours of recovery. If not yet weaned, neonates should be returned to their dam and littermates as soon as they have recovered sufficiently from anesthesia. Handling of the animals should be minimized and they should be housed in a quiet environment preoperatively and postoperativeiy. Friable pediatric tissues necessitate gentle handling, with special attention given to careful hemostasis in light of the relatively small blood volume of these patients.

ANESTHETIC TECHNIQUES

Although concerns are often expressed regarding the risks and feasibility of pediatric anesthesia, it can be performed safely using a number of different techniques. Special considerations in the pediatric patient include differences in drug uptake, distribution, and action as compared to adults as well as immature hepatorenal, respiratory, and cardiovascular system function (Grandy and Dunlop, 1991; Theran, 1993).

Neonates have a larger percentage of total body water, lower albumin concentration and body fat levels, and relatively high cardiac output to vessel-rich organs. All of these factors affect drug pharmacoldnetics. A heightened sensitivity to protein-bound drugs may be seen and, in general, dosages of parenterally administered anesthetic agents should be reduced (Grandy and Dunlop, 1991). Pediatric patients have immature hepatic enzyme systems responsible for drug metabolism; therefore, anesthetics metabolized in this manner may have a longer duration of action. Glomerular filtration and tubular function are also incompletely developed, delaying renal excretion of certain drugs.

The high rate of oxygen consumption in neonates necessitates a greater respiratory rate; therefore, anesthetic-induced respiratory depression and subsequent hypoventilation should-be avoided by careful monitoring. Because of differences in respiratory dynamics, atelectasis is also of concern (Grandy and Dunlop, 1991). Cardiac output in young animals is mainly rate dependent and baroresponses are immature; therefore, bradycardia and hypotension should be avoided.

Various anesthetic combinations have been used successfully in pediatric patients. The preanesthetic administration of anticholinergics (atropine or glycopyrrolate) has been advocated by some authors to stabilize heart rate and thus cardiac output, and to decrease respiratory secretions (Grandy and Dunlop, 1991). We have not found this to be necessary however.

General anesthesia can be rapidly induced and maintained with isoflurane (AErrane, Anaquest) or halothane (Halocarbon Labs) administered by mask or tank infusion. Most young animals (6 to 14 weeks) will tolerate the required restraint with minimal excitement or struggling, A tight-fitting mask will serve well through out the short duration of an orchidectomv procedure. Endotracheal intubatian should be performed in animals undergoing ovariohysterectomy. A 2.0- to 3.5-mm Cole or Magill endotracheat tube is recommended in kittens (Aronsohn and Faggella, 1993). Intubation should be gentle to avoid airway trauma and edema and the tube should be suctioned at 30-min intervals to prevent obstruction by respiratory secretions, a potential problem with tubes o£ such small diameter (Grandy and Dunlop, 1991). It is also vitally important to select a tube of proper length to minimize dead space and

avoid endobronchial intubation. Isoflurane is probably the preferred inhalant agent in young animals due to its rapid induction and recovery characteristics (low solubility), decreased need for metabolism, and diminished cardiovascular depression as compared with halothane (Grandy and Dunlop, 1991). A nonrebreathing anesthetic circuit should be used for neonatal patients weighing less than 5 kg (Ayres T -piece, Bain circuit, Norman elbow). Fresh gas flow rates x£200 ml/kg/minare recommended.

Several injectable anesthetics ale suitable for premedication or anesthetic induction for longer procedures (ovariohysterectamy) or as sole agents for a shorter procedure (orchidectomy). In kittens, benzodiazepine/dissociative combinations such as tiletamine/ zoIazepam (Telazol, AH Robins) and midazolam (Versed, Hoffman-LaRoche)! ketamine (Ketaset, Fort Dodge Laboratories) are very safe and effective. Tiletamine/zolazepam at 11 mg/kg IM (2 to 4 mg/kg IV) has been recommended for orchidectomy in young kittens (Faggella and Aronsohn, 1993, Theran, 1993). If necessary, supplemental inhalational anesthetic can be provided by mask. This combination can also be used in puppies.

Midazolam (0.22 mg/kg IM)/ketamine (11 mg/kg IM) followed by intubation and administration of an inhalant agent is recommended for feline ovariohystereetomy (Faggella and Aronsohn, 1993; Theran, 1993). The authors have successfully used an intravenous combination o£ 0.2 mg/kg diazepam (Valium, HoffmanLaRoche) and 5 to 7 mg/kg ketamine for anesthetic induction. Xylazine (Rompun, Miles) and phenothiazine tranquilizers (such as acepromazine) should be avoided in animals less than 3 months old because of their potential to cause bradycardia (decreased cardiac output) and hypotension, respectively. The use of barbiturates in animals less than 3 months of age is also discouraged.

Ogioitis provide analgesia and sedation as premedicants but should be administered with anticholinergics to prevent bradycardia. An advantage to their use is the potential for reversal with antagonists or agonist/antagonist agents.

Another option for intravenous anesthetic induction is propofol (Dipnvan, Stuart Pharmaceuticals). This drug produces a rapid, smooth induction and recovery. It is given at a dose of 4 to 6 mg/kg following premedications and 8 to 12 mg/kg as a sale agent. It has been used successfully for early neutering in pups (Theran, 1993).

Monitoring during anesthesia is similar to that performed in adults, with care being taken to prevent bradycardia, hypotension, and hypothermia. A Doppler ultrasound device (Ultrasonic Doppler Flow Detector Model 811-AL, Parks Medical Electronics) is useful to monitor blood pressure.

SUMMARY

Early neutering in dogs and cats is a safe and effective means of pet population control. The risks associated with surgery and anesthesia of pediatric patients are minimal, with the advantages being a shorter operative time, better visualization, rapid recovery, and decreased morbidity. The effects of prepubertal gonadectomy on skeletal, physical, and behavioral development are similar to those seen in animals that are neutered at a more traditional age.