CHAPTER 24 Surgical Considerations in the Young Patient
Surgery on immature dogs and cats is routinely performed in clinical practice and is often necessary to correct traumatic injuries or serious congenital problems. As with any other surgical patient, presurgical evaluation of the patient is paramount, and careful consideration needs to be given to differences between immature and mature patients in interpreting the findings. Physiologic differences between immature and mature patients affect many aspects of the management of the surgical patients regarding anesthesia and choice and doses of drugs for example. Specific anesthetic considerations are covered in Chapter 23. This chapter will concentrate on the issues directly related to the surgery of immature dogs and cats. Following sound principles of surgery may be even more important in immature patients because these patients are less forgiving.
Preparation of the Patient for Surgery
Immature dogs and cats have greater insensible water losses and do not have the ability to concentrate urine as much as adult animals. Therefore puppies and kittens have greater fluid requirement relative to body mass than adults. For these reasons, water restriction before surgery should not exceed 1 hour. As well, fasting should be of shorter duration, meaning 4 to 8 hours. The liver store of glycogen is minimal and rapidly declines during fasting. After hepatic glycogen stores are depleted, hepatic gluconeogenesis is responsible to maintain normal glycemia. However, there are decreased feedback mechanisms between hepatic gluconeogenesis and glycemia in puppies and kittens.
Thermoregulation is another challenge that is exacerbated in immature dogs and cats. Puppies and kittens have a larger surface area–to–body weight ratio, with high radiation and evaporative heat losses, an inability to shiver, a small amount of subcutaneous fat, and an immature thermoregulatory system. Appropriate steps can be taken to help limit the loss of heat during anesthesia and surgery. Clipping of the hair should be more conservative (but still adequate), and alcohol or alcohol-containing antiseptics should be avoided if possible. Other means of maintaining the patient’s warmth, such as warm water blankets or a Bair Hugger (Arizant Inc., Eden Prairie, MN), should be used.
The skin is very delicate and relatively thin in immature animals. Therefore clipping of the hair should be done very carefully to avoid lacerating the skin.
Tissues in general are more delicate in puppies and kittens and therefore require very gentle handling. The use of pediatric instruments is, in some instances, necessary to properly handle and manipulate the tissues.
Providing adequate hemostasis should be done more thoroughly because small volumes of blood loss in puppies and kittens can lead to clinically relevant hypovolemia and anemia. Even a small volume of blood loss can be a relatively large amount for a very young dog or cat (the total blood volume of a 1-kg kitten or dog is only 70 to 100 ml). Animals between age 2 and 8 weeks are at greater risk, as hematopoiesis does not begin until age 6 to 12 weeks in response to low levels of hemoglobin. Young animals, irrespective of species, are less able to compensate for hypovolemia. In 1-week-old pigs, a blood loss of only 5 to 10 ml/kg resulted in tachycardia and hypotension. Electrocautery should be used very discriminately because of its deleterious effects on wound healing.
On entering the abdominal cavity, kittens and puppies aged less than 16 to 20 weeks usually have a substantial amount of clear fluid in the peritoneal cavity. The surgeon should not be surprised or alarmed.
When selecting a suture material, the strength of the tissue, the rate of healing of the tissue, and the physical condition of the animal should be considered. In the healthy dog or cat, a rapid gain in wound strength is achieved at 7 to 10 days postoperatively. Most absorbable suture materials provide adequate tensile strength for this period. Soft, nonirritating suture materials, such as polyglactin 910, may be preferred. Polydioxanone, which has a prolonged rate of absorption (180 days), has been reported to cause calcinosis circumscripta in two young dogs. The true significance of this phenomenon is undetermined as it is unknown what incidence of this problem is associated with polydioxanone.
Multifilament or coated nonabsorbable suture materials are best avoided. Suture materials of the smallest possible diameter to achieve successful outcome should be used. In general, sutures of 4-0 to 5-0 are used for most tissues of very young animals, and 3-0 to 4-0 suture material is used for older animals. Obviously the tissue type and the size of the patient will also be critical factors in deciding the suture size.
When suturing skin, fine nonabsorbable suture such as 4-0 or 5-0 nylon should be placed loosely. Skin tension should be alleviated with a subcutaneous or subcuticular closure to avoid sutures pulling through the thin delicate skin.
Specific considerations apply when a fracture of a bone involves a growth plate. Ideally, fixation methods chosen will allow the physis to continue to grow if the potential remains. This topic will be covered in greater depth in Chapter 25. For some surgeries, it is best to delay the onset of the surgery until the animal is older. Specifically, correction of a cleft palate is best attempted when the patient is aged 8 to 12 weeks, and even ideally at least age 16 weeks. Even so, palatoplasty performed in a 16-week-old patient may lead to abnormal maxillofacial growth and development, leading to a narrow maxilla and occlusal problems. Also, the tissues in the older patient will be stronger and less friable, increasing the likelihood of a successful outcome. Until the patient is old enough to undergo the surgery to correct a cleft palate, some patients may need nutritional support by use of a feeding tube.