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Surgery and Its Application
CHAPTER 8
Surgery and Its Application DON R. WALDRON
The increased numbers of animals under veterinary care has seemingly increased the number of geriatric animals presented for medical and surgical care.1 Improvement in veterinary nutrition, the quality of veterinary care, and the numbers of owners seeking improved veterinary care are likely causes of this increase in geriatric patients. It has been stated repeatedly that aging is not a specific disease but rather a complex process influenced by genetics, environment, and nutrition.2 The veterinary profession has advanced over the past dozen years, allowing a distinction to be made between processes of aging as opposed to age-related disease. Nevertheless, increasing age does negatively affect an animal’s ability to respond to stress. Furthermore, the geriatric animal is more likely to have multiple organ system disease and less functional organ reserve capacity than the young patient.3,4 Surgery should not be viewed as impractical or prohibitive in the aged patient; however, complete and thorough evaluation of the animal is necessary to identify subclinical organ dysfunction that may become significant after hospitalization, anesthesia, and surgery. Similarly, there are known physiologic changes that occur in the aging animal that may affect the morbidity or mortality associated with surgical procedures. Identification of specific problems that may affect an animal requires a complete and thorough history and physical examination, and collection of data regarding both the animal’s surgical problem and any other clinical disease (Table 8-1). Focusing on the surgical problem is to be avoided initially; rather, the emphasis should
be placed on identification of covert clinical disease by means of appropriate laboratory testing and imaging techniques.5 Complete evaluation of the animal as a whole and specific evaluation of the surgical problem will allow the veterinarian to develop a rational plan of therapy that may or may not include surgery. If surgery is deemed necessary or appropriate, proper surgical planning should include consideration of the preoperative, intraoperative, and postoperative needs of the animal.
PHYSIOLOGY OF THE GERIATRIC ANIMAL AND ITS CLINICAL SIGNIFICANCE Many organ systems undergo change with aging. Organ changes have been described in geriatric humans, and it is thought these same changes occur in animals.3 In addition to physiologic changes in organ systems, aging may increase the role of other extrinsic factors that may affect the morbidity related to surgery in the aged animal. The risk of any surgical procedure is the sum of risks inherent in the animal’s physical condition and the direct risk factors associated with the specific surgical procedure. In many cases, increased risk in the geriatric patient is due to the previously described impaired ability to maintain normal homeostasis. The stress of disease, hospitalization, anesthesia, and surgery may cause a compensated geriatric animal to decompensate, thus causing overt clinical disease in addition to the primary surgical problem. 87
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TABLE 8-1. GERIATRIC SURGICAL DISEASE SYSTEM OR ORGAN Digestive System Oral cavity
Tongue Salivary gland Esophagus Stomach
PATHOLOGY
THERAPEUTIC OPTIONS
Neoplasia Inflammation or abscess Gingival hyperplasia Oronasal fistula Neoplasia Mucocele Neoplasia Neoplasia
Maxillectomy or mandibulectomy Dentistry Gingivectomy Mucoperiosteal flap Partial glossectomy Mandibular or sublingual salivary gland, excision, drain mucocele Excision of affected gland Resection and anastomosis, local excision for benign lesions (leiomyomas) Partial gastrectomy or gastroduodenostomy Decompression, permanent gastropexy Local excision or partial gastrectomy, consider underlying cause (nonsteroidal antiinflammatory drugs, mast cell tumor, gastrinoma, hepatic disease) Gastroduodenostomy, Y-U pyloroplasty if benign Resection and anastomosis if localized, chemotherapy for lymphosarcoma Typhlectomy Resection and anastomosis for malignancy, colonoscopic polyp excision Subtotal colectomy Submucosal resection, partial pull-through, Swenson’s pull-through, dorsal approach for resection and anastomosis or extramural tumor excision Herniorrhaphy with internal obturator muscle flap and castration Surgical excision and castration for adenomas, castration and delayed local aggressive resection for sebaceous adenocarcinoma, excision for large adenomas Anal sacculectomy and abdominal lymphadenectomy, chemotherapy Anal sacculectomy Partial or total lobectomy if disease is localized to one lobe Cholecystectomy Cholecystectomy Tumor excision, metastases are functional; corticosteroids, diazoxide, or streptozotocin Partial pancreatectomy if localized Partial pancreatectomy, H2 blockers, octreotide, proton pump inhibitors Drainage, lavage
Neoplasia Gastric dilation-volvulus Ulceration
Small intestine
Outlet obstruction Neoplasia
Cecum Colon
Neoplasia Neoplasia
Rectum
Idiopathic megacolon Neoplasia
Perineum
Perineal hernia Perianal neoplasia
Anal sac
Neoplasia
Liver Gall bladder Pancreas
Abscess or inflammation Neoplasia Cholelithiasis Cholecystitis Beta-cell neoplasia Adenocarcinoma Gastrinoma Abscess
Respiratory System Nasal planum Nasal cavity
Neoplasia Neoplasia
Larynx
Paralysis Collapse
Trachea
Collapse
Lung Pleural space
Neoplasia Chylothorax
Cardiovascular System Cardiac Right atrial neoplasia Atrioventricular block Pericardial effusion Urologic System Renal
Lithiasis Neoplasia Chronic renal failure or acute renal failure
Nosectomy Radiation therapy (megavoltage or cobalt), rhinotomy plus orthovoltage radiation Unilateral arytenoid lateralization Permanent tracheostomy, unilateral arytenoid lateralization, partial laryngectomy Prosthetic rings for extrathoracic collapse, intraluminal stent for intrathoracic collapse Lobectomy, lymph node biopsy Thoracic duct ligation or embolization, pleuroperitoneal shunt Excision of right atrial appendage and tumor and pericardiectomy Pacemaker implantation if second or third degree Pericardiectomy if caused by neoplasia or idiopathic Lithotripsy or nephrotomy and calculus removal if obstructive disease is present, “watchful waiting” if no infection or obstruction, nephrectomy if kidney is nonfunctional Nephrectomy if unilateral Medical management, renal transplantation
Chapter 8 Surgery and Its Application
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TABLE 8-1. GERIATRIC SURGICAL DISEASE—cont’d SYSTEM OR ORGAN
PATHOLOGY
Urologic System—cont’d Ureter Lithiasis Urinary bladder Lithiasis Neoplasia Urethra
Endocrine System Thyroid Parathyroid Adrenal Pituitary Reproductive System Testes Prostate
Mammary Uterus or ovary Vagina
Incontinence Lithiasis Neoplasia Stricture Neoplasia, canine Neoplasia, feline Neoplasia Neoplasia Neoplasia Neoplasia Hyperplasia Cyst Inflammation Abscess Neoplasia Neoplasia, canine Neoplasia, feline Pyometra Neoplasia Neoplasia
Hematopoietic System Spleen Neoplasia Hematoma Nervous System Brain Spinal Cord
Neoplasia Disk Neoplasia
Nerve
Neoplasia Cauda equina
Skeletal System Joints
Degenerative joint disease
Coxofemoral
Hip dysplasia
Stifle
Cranial cruciate rupture
Bone
Neoplasia
Special Senses Skin Ear Eye
Neoplasia Neoplasia Inflammation Hypertrophy Neoplasia Cataracts
THERAPEUTIC OPTIONS Ureterotomy, lithotripsy Cystectomy, lithotripsy, or medical management if calculi are magnesium ammonium phosphate Partial cystectomy if possible and/or chemotherapy, tube cystostomy for palliation Colposuspension if unresponsive to medical management Urohydropulsion, scrotal, perineal, or antepubic urethrostomy Vaginourethroplasty Tube cystostomy for palliation Thyroidectomy if freely movable and noninvasive, radiation I-131 therapy, thyroidectomy or medical management with methimazole Parathyroidectomy Adrenalectomy Hypophysectomy Neutering Neutering Drainage procedure, excision of cyst Omentalization of abscess Lumpectomy, regional or unilateral mastectomy, ovariohysterectomy Regional or unilateral mastectomy Ovariohysterectomy Ovariohysterectomy Excision of tumor, with or without episiotomy Splenectomy Splenectomy, partial splenectomy Excision, radiation therapy Medical treatment or laminectomy if motor impairment or chronic pain Excision by laminectomy if extradural or intradural or extramedullary Excision with or without amputation Laminectomy with or without foraminotomy Treatment of underlying cause, weight control, exercise modification, analgesics, arthrodesis, excision arthroplasty, joint replacement Weight control, exercise modification, medical management, total hip arthroplasty, femoral head ostectomy Arthrotomy, joint stabilization, tibial plateau leveling osteotomy, fibular head transposition, conservative in small dogs and cats Amputation plus chemotherapy, limb-sparing treatment plus chemotherapy Excision, laser ablation, cryosurgery Excision of tumor, vertical or total ear canal ablation Lateral ear canal resection, vertical or total ear canal ablation Lateral ear canal resection, vertical or total ear canal ablation Observation or enucleation Observation, phacoemulsification, intraocular lens implantation
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Hepatic System Altered hepatic microsomal enzyme systems may cause a decreased ability to metabolize drugs in the geriatric animal.4 Elimination of some drugs is dependent on hepatic blood flow, which decreases with aging.6 This decreased metabolic function may be present in spite of normal laboratory values. A decreased ability to metabolize or eliminate drugs has obvious implications from an anesthetic point of view but also affects administration of other drugs in the perioperative period such as antimicrobial and nonsteroidal antiinflammatory agents (NSAIDs). Severe liver disease may be responsible for hypoproteinemia, which delays wound healing. Similarly, severe disease may result in a decrease in blood clotting factors, thereby prolonging normal clotting times. Serum liver enzymes, albumin, and total protein levels and prothrombin and partial thromboplastin times may assist in assessing liver function. Fasted and postprandial serum bile acids more accurately reflect true liver function.
Renal System Decreased renal function and decreased renal reserve are of utmost concern in the geriatric animal in the perioperative period (Table 8-2).
The kidneys of the geriatric animal have decreases in glomerular numbers, tubular size and weight, and increased fibrosis.7 It should be recalled that decreases in renal function as indicated by abnormal elevations in laboratory values (blood urea nitrogen and serum creatinine) are not linearly related. At least 65% to 75% of renal function is lost before there are increases in the commonly obtained laboratory values; therefore small increases in blood urea nitrogen may indicate large decreases in glomerular filtration rate. As always, blood urea nitrogen and serum creatinine values are interpreted in conjunction with urinalysis. Chronic renal failure produces mild to moderate elevations in blood urea nitrogen and serum creatinine, an isosthenuric urine, and mild anemia in some cases. More specific testing for renal function involves the use of creatinine clearance or glomerular filtration rates as determined by nuclear scintigraphy. Even in the face of normal renal laboratory values, decreased renal blood flow as a result of less than normal cardiac output causes glomerular filtration rates of the kidneys to decrease. Glomerular filtration rates as determined by nuclear scintigraphy are not widely available in practice; however, they represent an excellent noninvasive means of evaluating the contribution of each kidney to overall renal function. This information is especially valuable when one is
TABLE 8-2. PRACTICAL GUIDE TO THE PREVENTION OF PERIOPERATIVE RENAL FAILURE IN GERIATRIC ANIMALS PRINCIPLE
METHOD OR MEASUREMENT
Assess renal function accurately
Blood urea nitrogen Serum creatinine Urine output Glomerular filtration rate measured via scintigraphy Physical examination Serial body weights Packed cell volume and total solids Central venous pressure Avoid hypotension by assuring normal volume status and surgical hemostasis Reverse severe hypotension with crystalloid fluids, blood products, and vasopressors Prompt radiographic diagnosis Catheter drainage Surgical correction Limit use of aminoglycosides or nonsteroidal antiinflammatory drugs Limit use of intravenous contrast agents Adjust drug doses Abscess drainage (local, pancreatic, prostate) Catheter care Appropriate antibiotics Crystalloid fluids in correct volume Mannitol, furosemide, dopamine Monitor urine output
Assess and monitor volume status
Control and maintain blood pressure Relieve urinary tract obstruction Avoid known nephrotoxins Prevent sepsis Consider diuresis
Modified from Monroe WE, Waldron DR: Renal failure: surgical considerations. In Bojrab MJ, ed: Disease mechanisms in small animal surgery, ed 2, Philadelphia, 1993, Lea & Febiger.
Chapter 8 Surgery and Its Application considering surgery on the kidney itself, for example, nephrotomy or nephrectomy. Animals with compensated renal disease may be anesthetized and operated on successfully; however, attention to perioperative fluid needs and urine production is critical in ensuring that the animal is not pushed into decompensated renal failure or that, conversely, overly zealous fluid administration does not cause pulmonary edema. Drugs that are potentially nephrotoxic such as NSAIDs and aminoglycoside antibiotics are used cautiously in the geriatric animal.
Cardiopulmonary Function As with other organ systems, there is a decrease in cardiac reserve in geriatric patients compared with healthy young animals.3 Although animals are not routinely diagnosed with primary vascular disease and hypertension as geriatric humans are, there is a decrease in cardiac output, baroreceptor activity, and circulation time in the geriatric animal.8,9 Although the geriatric heart has normal contractile elements, its ability to respond to catecholamines is reduced.5 The changes that occur negatively affect the animal’s ability to maintain blood pressure during stress and anesthesia.3,10 Valvular disease is extremely common in the geriatric canine, and myocardial disease may be seen in both the aging canine and feline. Valvular disease by itself, as evidenced by cardiac murmurs detected on physical examination, does not prohibit anesthesia or surgery; however, judicious use of crystalloid fluids is indicated, especially if renal function is also compromised. In addition to careful auscultation and pulse examination, thoracic radiography, electrocardiography, and ultrasonography of the heart may aid in identifying specific disease, which may affect anesthesia and surgical planning. Respiratory function decreases as the animal ages. Respiratory rate, tidal volume, lung elasticity, and partial pressure of arterial oxygen all decrease in the geriatric animal.11,12 Gas exchange is less efficient, and ventilation-perfusion mismatch is potentially more prevalent and severe than in the young animal.13 Clinically, the decreased function may result in hypoxia and hypercarbia, which may in turn negatively affect cardiac function by predisposing the animal to arrhythmias. Mild anesthetic depression of respiration in the normal young animal may be critical to the geriatric animal.3 Pulmonary function testing is not routinely performed in animals. Auscultation, thoracic
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radiography, and blood-gas analysis are available to aid in assessment of pulmonary function. Aspiration pneumonia may occur more commonly in geriatric humans and is especially common in the perioperative period in animals with laryngeal paralysis or esophageal disease.
Endocrine Disease Endocrine diseases are diagnosed more commonly in the geriatric dog and cat. Diseases of the endocrine system often have a primary affect and also may affect other organ systems important in anesthesia and surgery. For example, parathyroid adenomas cause hypercalcemia, which may cause peripheral weakness and renal disease. Hyperthyroidism in cats causes primary gastrointestinal disturbances but has profound secondary effects on cardiac function. Hyperadrenocorticism, either naturally occurring or iatrogenic, may affect wound healing or wound infection rates in surgery of any type performed in the geriatric animal. Some of the endocrine diseases diagnosed in geriatric animals are potentially surgical in nature, such as beta-cell tumors of the pancreas, hyperthyroidism in the cat, parathyroid adenomas, and functional adrenal tumors. Careful assessment of multiorgan systems before surgery is indicated in these animals. In some cases, the animal can be treated medically in the short term before surgery, and the risks associated with anesthesia and surgery are reduced. A hyperthyroid feline made euthyroid with methimazole and an animal with hyperadrenocorticism that is treated medically are examples of geriatric disease states in which the animal may be improved with medical therapy prior to definitive surgical therapy.
INFECTION AND WOUND HEALING Wound infection rates in geriatric humans with clean or clean-contaminated wounds have been reported to be higher than in the younger population. Other authors, however, have not found age to be an independent predictor of wound infection.14 Similarly, wound infection rates in animals, when assessed by univariate analysis, appear increased in the geriatric animal. However, when the same data are assessed by multivariate analysis, infection rates in the geriatric population appear the same as in younger populations; therefore, it appears that other factors including concurrent infections at distant sites or
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the presence of endocrinopathies likely influence wound infection rates.15 Wound healing is reported as delayed in geriatric humans16 and in rats.17,18 The effect of increasing age on wound healing in dogs and cats is questionable and probably not clinically significant; however, concurrent pathologic problems such as hyperadrenocorticism, diabetes mellitus, or hypoproteinemia negatively affects wound healing.5 Supplementation with vitamin A and anabolic steroids may correct the adverse effects of diabetes mellitus, corticosteroids, or radiation on healing and is commonly used in human surgical patients.19
PREOPERATIVE ASSESSMENT History and Physical Examination A thorough history and detailed physical examination are essential in assessing the geriatric animal’s surgical needs. Information acquired may affect both the anesthesia and surgical protocols. Attention to possible drug interactions or their specific effects is especially important. Prolonged administration of corticosteroids or certain antibiotics for dermatologic disease or NSAIDs for degenerative joint disease is common in geriatric animals. These agents may affect wound healing, wound infection, renal function, microbial susceptibility, and blood clotting.5,20 History or physical findings of polydipsia, polyuria, lack of exercise tolerance, persistent cough, lameness, or undiagnosed mass may indicate a serious problem that requires further attention prior to surgery. History regarding the primary clinical problem is also important. A spontaneously occurring long bone or facial fracture in a geriatric animal with minor trauma may be secondary to neoplasia, infection, dental disease, or metabolic bone disease. Acute clinical signs seemingly associated with chronic problems may, in fact, be due to secondary disease. An acute rear limb lameness in a canine with a chronically luxating patella may indicate a cranial cruciate ligament injury. Similarly, a dyspneic geriatric animal of a brachycephalic breed may have an obstructed airway from laryngeal collapse or neoplasia rather than an elongated soft palate. Physical examination includes careful thoracic auscultation and abdominal palpation. Superficial palpation of the entire body is advised to diagnose skin and mammary tumors, both of which have an increased prevalence in the geriatric animal.21,22
Preoperative Evaluation The extent of preoperative evaluation is dictated by the primary surgical problem and any problems identified historically or on physical examination. A problem list should be made to guide the veterinarian in formulating differential diagnoses and a diagnostic plan. For elective surgery, a minimum database for geriatric animals should include a complete blood count, serum chemistry panel, urinalysis, and a lead II electrocardiogram. Thoracic radiographs are taken in many animals to identify cardiac or lung pathology that may affect anesthetic administration, although the value of such screening has been questioned in asymptomatic animals.13 Three-view thoracic radiographs are considered mandatory in the animal with suspected or known cancer to identify possible metastatic disease prior to surgery. Thoracic metastatic lesions must be 3 to 5 mm in diameter before they are visible radiographically. A lead II electrocardiogram tracing is valuable as a screening tool for cardiac arrhythmias. Undiagnosed lesions or masses identified on or within an animal can be initially assessed by fine needle aspiration and cytologic examination. Aspiration of superficial masses is routine; aspiration of abdominal or thoracic masses may require ultrasound guidance. In many animals, these procedures may be performed without anesthesia; however, sedation may be required for aspiration of masses within body cavities. Similarly, tissue biopsies from a sedated animal may be obtained using ultrasound guidance, local anesthesia, and a biopsy punch or Tru-Cut needle (Travenol Laboratories, Deerfield, Ill) technique. Biopsies of the liver, spleen, prostate, and kidneys are commonly performed by this method. A diagnosis obtained from biopsy specimens can be vital to constructing a rational therapeutic plan that may or may not include surgery. Ultrasonography, magnetic resonance imaging, and computed tomography are valuable noninvasive tools for more complete evaluation of the geriatric animal. Sonographic evaluation of the abdomen by a skilled examiner is a sensitive means of screening for either primary or metastatic masses in the animal with suspected or known cancer. Advanced imaging techniques, such as magnetic resonance imaging or computed tomography, require general anesthesia but allow for more accurate assessment of normal and diseased tissue than conventional radiography and may further assist the surgeon in developing a
Chapter 8 Surgery and Its Application therapeutic plan. The increased ability to image diseased tissue accurately may allow the surgeon to avoid unnecessary surgery when successful resection of diseased tissue is not possible. Endoscopic examination of the upper and/or lower gastrointestinal tract may provide tissue for diagnosis of enteric disease. Endoscopic examination may also characterize disease as focal or more diffuse in nature, thereby contributing to accurate therapeutic planning.
Preoperative Care In the case of elective geriatric surgery, it is desirable that the animal be as “normal” as possible for anesthesia and surgery. This implies that any current therapy for preexisting defined disease be optimal. In addition to treatment of defined disease, provision of preoperative nutrition may be indicated to improve the overall health of the animal, especially if the animal has had chronic disease.5 The stress of anesthesia and surgery can increase the basal metabolic rate significantly; therefore, attention to nutritional needs preoperatively and postoperatively is important. A high-energy, high-protein diet can meet these needs. Alternatively, a nasogastric, esophagostomy, or gastrostomy tube may be placed to assure that caloric and energy needs are met in the perioperative period. The importance of maintaining adequate nutrition in the feline to prevent hepatic lipidosis is well known. Attention to fluid and electrolyte needs is important in the perioperative period. Electrolyte abnormalities should be corrected by oral or parenteral means prior to general anesthesia. During the preoperative fasting period, the wellhydrated animal is allowed free access to water until anesthesia is induced. If the animal’s hydration status is questionable or there is evidence of renal disease, preoperative fluid therapy is advisable prior to anesthesia. Effects of fluid therapy may be monitored by packed cell volume and total solids measurement, body weight, serum chemistries, and quantitative urine production. The latter requires placement of an indwelling urinary catheter that is connected to a closed collection system. The need for blood transfusion is a clinical judgment; however, existing anemia in which the packed cell volume is less than 25% is an indication for cross-matched packed cells or whole blood transfusion prior to general anesthesia and surgery.
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Surgical Planning The critical periods for the geriatric animal undergoing surgery are at anesthesia induction, intraoperatively, and in the immediate postoperative period.5 Every effort is made to minimize stress on the animal preoperatively. For elective surgery, geriatric animals may be evaluated as outpatients and then presented fasted (free-choice water) on the morning of surgery. Proper planning and preparation for both general and specific needs during surgery will allow the surgeon to minimize the animal’s time under general anesthesia. Consideration of the following guidelines may decrease anesthesia time and improve operative efficiency in the geriatric animal.5,20 • Consider the need for equipment appropriate to the specific surgery. • Have a specific operative goal or goals prior to surgery; have contingency or alternative plans should problems arise. Plan on biopsy of diseased tissue if resection is not possible. • Be familiar with the surgical procedure and know the appropriate anatomy. • Consider the need for cross-matching and possible intraoperative or postoperative blood transfusion if blood loss is likely. Consider the possibility of using colloids such as plasma or hetastarch. • If the animal is cooperative clip the surgical site immediately prior to induction of anesthesia; alternatively the clip may be performed in the premedicated animal. • Once anesthesia is induced and the animal is stabilized, complete the preoperative surgical site preparation as expeditiously as possible and move the animal to the operating room. • Consider the need for appropriate antibiotics in the intraoperative and postoperative periods. Surgical procedures that are expected to last longer than 90 minutes have a higher rate of bacterial wound contamination, and prophylactic antibiotic therapy is indicated. In addition, procedures that are clean-contaminated (entry into the gastrointestinal, respiratory, or infected urinary tract) or contaminated (entry into the colon) require the administration of antibiotics effective against suspected pathogens. Perioperative antimicrobial agents should be given in these cases in the immediate preoperative period after anesthetic induction and intraoperatively if the procedure exceeds 90 minutes; one or two doses should be given postoperatively.
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Intraoperative Monitoring and Support Close monitoring of the animal is indicated during surgery. Routine intraoperative monitoring should include electrocardiogram and pulse oximetry in addition to physical monitoring of pulse quality (Figure 8-1). End-tidal CO2 monitoring is a sensitive means of measuring the adequacy of ventilation, but the equipment is expensive. Blood pressure may be monitored noninvasively with Doppler equipment or oscillometric monitoring using a pneumatic cuff. Urine production as measured by use of an indwelling urinary catheter and closed collection system is an indirect measure of the adequacy of blood pressure and a direct measure of renal function, which is important in any animal with renal compromise or in an animal that undergoes renal surgery. Normal urine output should be at least 1 to 2 ml/kg/h. Intraoperative administration of crystalloid intravenous fluids is routinely provided at 10 to 20 ml/kg/h to provide cardiovascular and renal support. In general, a balanced electrolyte solution such as lactated Ringer’s is used, although specific disease processes may dictate the selection of other fluids. Pharmacologic management of oliguria during surgery is indicated in some cases. If the animal has been adequately volume expanded, the use of a dopamine drip (2 to 5 μg/kg/min), furosemide (2 to 4 mg/kg bolus), or mannitol 0.5 g/kg given over 15 minutes) may be considered to increase urine production. The older animal has less efficient thermoregulatory control, so attempts should be made during surgery to keep the animal warm.5 Core body temperature is usually monitored with rectal
Figure 8-1. Intraoperative monitoring of electrocardiographic tracing, heart rate, and pulse oximetry with one monitor.
or esophageal thermometers or by other intermittent manual methods. Maintenance of body temperature is especially difficult in animals weighing <5 kg when body cavities are opened. Warm water–circulating blankets (Gaymar Industries, Orchard Park, N.Y.) (Figure 8-2), circulating hot air blankets (Bair Hugger, Augustine Medical, Eden Prairie, Minn.) (Figure 8-3), and warm lavage solutions are useful in prevention and treatment of hypothermia.
SURGICAL PRINCIPLES Appropriate surgical planning, as suggested previously, will expedite the surgical procedure and reduce the need for crisis-based decisions. In addition to a surgical plan, specific techniques and equipment are available to maximize the surgeon’s efficiency. Maximizing the efficiency of
Figure 8-2. Circulating warm water blanket that is useful in preventing hypothermia.
Figure 8-3. Circulating hot air blankets also assist in preventing hypothermia and provide more uniform body coverage than water blankets.
Chapter 8 Surgery and Its Application the surgical procedure will reduce anesthesia time and stress on the geriatric animal.5 Adequate surgical exposure is extremely important for any surgical procedure. A generous incision that is appropriate for the specific procedure is made. Small incisions made in an effort to decrease operative time compromise surgical exposure and tend to increase operative time. Another technique to assist in exposure involves the use of self-retaining retractors. Balfour retractors are especially valuable to maintain exposure during abdominal procedures; Gelpi or Weitlander retractors are useful for orthopedic or neurologic cases. Direct surgical assistance from and tissue retraction by a technician are invaluable during many surgical procedures. Appropriate tissues should be excised or biopsies obtained. If neoplastic masses or organs are excised, regional lymph nodes should be excised or biopsied to stage the disease. Liver biopsies are easily obtained by the “guillotine” method using a loop of absorbable suture to attain hemostasis and cut through the edge of a liver lobe. Simple incisional biopsies are appropriate for obtaining renal, intestinal, bladder, or prostatic biopsies. Simple interrupted or mattress sutures of 3-0 or 4-0 polydioxanone (PDS II, Ethicon, N.J.) are used postbiopsy for hemostasis and to provide a leak-proof closure of hollow viscus. The use of mechanical surgical stapling equipment saves considerable time for the surgeon and results in decreased anesthesia time. Thoracoabdominal surgical instruments (TA, United States Surgical Corporation, Norwalk, Conn.) are easy to use and place two or three staggered rows of staples that provide good hemostasis and leakproof closure of soft tissues. These instruments place staple lines measuring 90, 55, or 30 mm in length and have been used for complete lung lobectomy, partial lung lobectomy, partial hepatectomy and splenectomy, closure of the stomach following partial gastrectomy, cecal removal, and prostatic and paraprostatic cyst removal.23 Ligateand-divide staplers (LDS, United States Surgical Corporation, Norwalk, Conn.) place two staples while a cutting blade cuts between them. This instrument is extremely useful for procedures such as splenectomy or in which the wellvascularized omentum must be dissected from abdominal masses. Vascular staples (Surgiclips, United States Surgical Corporation, Norwalk, Conn.) place a single vascular clip on vessels and are very convenient for use in deep cavities. The LDS stapler and Surgiclips are “user friendly” with essentially little or no learning curve for the surgeon.
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Other stapling devices such as the gastrointestinal anastomosis (GIA, United States Surgical Corporation, Norwalk, Conn.) and endto-end anastomosis (EEA, United States Surgical Corporation, Norwalk, Conn.) can save time when one performs gastrointestinal anastomoses, but efficient and safe use of these instruments requires considerable training and experience. Simple continuous suture closure of the linea alba is a safe and quick alternative to simple interrupted patterns. Monofilament absorbable suture with prolonged tensile strength such as polydioxanone or polyglyconate (Maxon, United States Surgical Corporation, Norwalk, Conn.) or nonabsorbable material such as polypropylene (Prolene, Ethicon, NJ) or nylon (Dermalon, Ethicon, N.J.) is recommended for continuous closure. General suture size guidelines for continuous closure are as follows: for animals weighing <5 kg, use 3-0 suture; for those weighing 5 to 25 kg, use 2-0 suture; for those weighing 25 to 50 kg, use 0 suture; and for animals weighing >50 kg, use size 1 suture. Skin staples are a time-saving adjunct to efficient surgery, especially when long linear incisions such as celiotomy or thoracotomy incisions are closed. Skin stapling is reported to be three to five times faster than suturing for wound closure.24 Staplers are available from several manufacturers and generally come in two widths. Wide staples are preferred for use in animals and are most easily placed after an intradermal closure of the incision, which enhances skin alignment. In recent years, minimally invasive surgical techniques have become more widely used in veterinary surgery. Arthroscopy, laparoscopy, thoracoscopy, and urethrocystoscopy have been used for diagnosis and therapy of some disease processes. Advantages include less morbidity and mortality than with open surgical techniques, and definitive tissue biopsy is possible under direct visualization. Disadvantages include the expense of the equipment, the need for training in specialized techniques, and in some cases limited visualization of complete body cavities. Considerable time may be saved depending on the specific procedure and the experience of the surgeon.
POSTOPERATIVE CONSIDERATIONS Monitoring and Support During the postoperative period, respiratory, cardiovascular, and renal compensatory mechanisms may be diminished and susceptible to dys-
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function. Repetitive monitoring and evaluation of circulatory and metabolic parameters can clearly show the progression of a normal recovery or allow early detection of abnormalities that threaten normal recovery. Immediately following surgery, the animal should be placed on a preheated circulating water blanket and monitored constantly until extubation. Continuous monitoring of body temperature is advised until core body temperature reaches 37.8° C (100° F). Pulse and capillary refill time, respiration rate, and anesthetic depth are monitored closely until the animal is sternal, alert, and responsive. Thoracic auscultation is indicated, especially if aggressive fluid therapy is being administered. Blood pressure, central venous pressure, urine output, and electrocardiography monitoring may be indicated in animals whose condition is critical. Fluid therapy is continued for at least 12 hours following any major surgical procedure; however, duration and volume ultimately depends on the animal’s needs. After surgery, a packed cell volume and total solids should be recorded to establish a baseline for monitoring hydration status. Fluids at maintenance rates (40 to 60 ml/kg/day) are administered routinely; however, significant blood loss or concerns about renal function may dictate that higher rates be used. Supplemental oxygen should be available for animal support as needed. Placement of a nasopharyngeal oxygen tube may be indicated in brachycephalic animals or geriatric animals with preexisting respiratory disease. Supplemental oxygen may also be administered by oxygen cage or face mask, although the latter is labor intensive. The need for mechanically assisted ventilation or placement of a tracheostomy tube is rare but should be anticipated and prepared for in some critical care cases.
Analgesia Appropriate administration of analgesics to the geriatric animal can eliminate or reduce the stress and distress of postoperative pain. Opioids are the most reliable and predictable drugs for the relief of major postoperative pain. They may be administered parenterally or orally in some cases, and opioid cutaneous patches are available for longer duration analgesia. NSAIDs are useful for minor postoperative pain but should not be used concurrently with corticosteroids because of the risks of gastrointestinal ulceration. Caution is advised if NSAIDs are used in animals with chronic renal failure.
Other methods of postoperative analgesia include the use of epidurally administered drugs and blocking of the pain response by local injection of lidocaine or marcaine.
Nutrition Anticipation of the geriatric animal’s nutritional needs in the perioperative period is important. Animals that have questionable nitrogen balance or those animals undergoing a surgical procedure that may impair eating should have a feeding tube placed while the animal is under anesthesia. Esophagostomy, percutaneous gastrostomy, or endoscopically assisted gastrostomy tubes have all been placed and used successfully to support animals nutritionally. It is important that nutritional therapy be administered early in the course of the animal’s anorexia rather than after it has not eaten for several days.5 References 1. Kraft W: Geriatrics in canine and feline internal medicine, Eur J Med Res 3:31, 1998. 2. Goldston RT: Introduction and overview of geriatrics. In Goldston RT, Hoskins JD, eds: Geriatrics and gerontology of the dog and cat, Philadelphia, 1995, WB Saunders. 3. Harvey RC, Paddleford RR: Management of geriatric patients: a common occurrence, Vet Clin North Am Small Anim Pract 29:683, 1999. 4. Paddleford RR: Anesthetic considerations for the geriatric patient, Vet Clin North Am Small Anim Pract 19:13, 1989. 5. Hosgood G: Surgical protocol. In Goldston RT, Hoskins JD, eds: Geriatrics and gerontology of the dog and cat, Philadelphia, 1995, WB Saunders. 6. Aucoin DP: Drug therapy in the geriatric animal: the effect of aging on drug disposition, Vet Clin North Am Small Anim Pract 19:41, 1989. 7. Krawiec DR: Urologic disorders of the geriatric dog, Vet Clin North Am Small Anim Pract 19:75, 1989. 8. Dodman NH, Deeler DC, Court MH: Aging changes in the geriatric dog and their impact on anesthesia, Compend Contin Educ Pract Vet 6:1106, 1984. 9. Meurs KM, Miller MW, Slater MR: Arterial blood pressure measurement in a population of healthy geriatric dogs, J Am Anim Hosp Assoc 36:497, 2000. 10. Hamlin RL: Identifying the cardiovascular and pulmonary diseases that affect old dogs, Vet Med 85:483, 1990. 11. Robinson NE, Gillespie JR: Lung volumes in aging beagle dogs, J Appl Physiol 35:317, 1973. 12. Meyer RE: Anesthesia for neonatal and geriatric patients. In Short CE, ed: Principles and practice of veterinary anesthesia, Baltimore, 1987, Williams & Wilkins. 13. Muravchick S: Preoperative assessment of the elderly patient, Anesthesiol Clin North Am 18:71, 2000. 14. Sawyer RG, Pruett TL: Wound infections, Surg Clin North Am 74:519, 1994.
Chapter 8 Surgery and Its Application 15. Brown DC: Personal communication, February, 2002. 16. Holt DR, Kirk SJ, Regan MC et al: Effect of age on wound healing in healthy human beings, Surgery 112:293, 1992. 17. Quirinia A, Viidik A: The influence of age on the healing of normal and ischemic skin wounds, Mech Ageing Dev 5:221, 1991. 18. Petersen TI, Kissmeyer-Nielsen P, Laurberg S et al: Impaired wound healing but unaltered colonic healing with increasing age: an experimental study in rats, Eur Surg Res 27:250, 1995. 19. Hunt TK, Hopf HW: Wound healing and wound infection: what surgeons and anesthesiologists can do, Surg Clin North Am 77:587, 1997. 20. Waldron DR, Budsberg SC: Surgery of the geriatric patient, Vet Clin North Am Small Anim Pract 19:33, 1989. 21. MacDonald J: Neoplastic diseases of the integument, Proc Am Anim Hosp Assoc, 1987.
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22. Rutteman GR, Withrow SJ, MacEwen GE: Tumors of the mammary gland. In Withrow SJ, MacEwen GE, eds: Small animal clinical oncology, Philadelphia, 2001, WB Saunders. 23. Pavletic MM, Schwartz A: Stapling instrumentation, Vet Clin North Am Small Anim Pract 24:247, 1994. 24. Brickman KR, Lambert RW: Evaluation of skin stapling for wound closure in the emergency department, Ann Emerg Med 18:122, 1989.
Supplemental Readings Willard MD: Endoscopy of body cavities. In Fossum TW, ed: Small animal surgery, St Louis, 2002, Mosby.
Surgery and Its Application DON R. WALDRON
The increased numbers of animals under veterinary care has seemingly increased the number of geriatric animals presented for medical and surgical care.1 Improvement in veterinary nutrition, the quality of veterinary care, and the numbers of owners seeking improved veterinary care are likely causes of this increase in geriatric patients. It has been stated repeatedly that aging is not a specific disease but rather a complex process influenced by genetics, environment, and nutrition.2 The veterinary profession has advanced over the past dozen years, allowing a distinction to be made between processes of aging as opposed to age-related disease. Nevertheless, increasing age does negatively affect an animal’s ability to respond to stress. Furthermore, the geriatric animal is more likely to have multiple organ system disease and less functional organ reserve capacity than the young patient.3,4 Surgery should not be viewed as impractical or prohibitive in the aged patient; however, complete and thorough evaluation of the animal is necessary to identify subclinical organ dysfunction that may become significant after hospitalization, anesthesia, and surgery. Similarly, there are known physiologic changes that occur in the aging animal that may affect the morbidity or mortality associated with surgical procedures. Identification of specific problems that may affect an animal requires a complete and thorough history and physical examination, and collection of data regarding both the animal’s surgical problem and any other clinical disease (Table 8-1). Focusing on the surgical problem is to be avoided initially; rather, the emphasis should
be placed on identification of covert clinical disease by means of appropriate laboratory testing and imaging techniques.5 Complete evaluation of the animal as a whole and specific evaluation of the surgical problem will allow the veterinarian to develop a rational plan of therapy that may or may not include surgery. If surgery is deemed necessary or appropriate, proper surgical planning should include consideration of the preoperative, intraoperative, and postoperative needs of the animal.
PHYSIOLOGY OF THE GERIATRIC ANIMAL AND ITS CLINICAL SIGNIFICANCE Many organ systems undergo change with aging. Organ changes have been described in geriatric humans, and it is thought these same changes occur in animals.3 In addition to physiologic changes in organ systems, aging may increase the role of other extrinsic factors that may affect the morbidity related to surgery in the aged animal. The risk of any surgical procedure is the sum of risks inherent in the animal’s physical condition and the direct risk factors associated with the specific surgical procedure. In many cases, increased risk in the geriatric patient is due to the previously described impaired ability to maintain normal homeostasis. The stress of disease, hospitalization, anesthesia, and surgery may cause a compensated geriatric animal to decompensate, thus causing overt clinical disease in addition to the primary surgical problem. 87
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TABLE 8-1. GERIATRIC SURGICAL DISEASE SYSTEM OR ORGAN Digestive System Oral cavity
Tongue Salivary gland Esophagus Stomach
PATHOLOGY
THERAPEUTIC OPTIONS
Neoplasia Inflammation or abscess Gingival hyperplasia Oronasal fistula Neoplasia Mucocele Neoplasia Neoplasia
Maxillectomy or mandibulectomy Dentistry Gingivectomy Mucoperiosteal flap Partial glossectomy Mandibular or sublingual salivary gland, excision, drain mucocele Excision of affected gland Resection and anastomosis, local excision for benign lesions (leiomyomas) Partial gastrectomy or gastroduodenostomy Decompression, permanent gastropexy Local excision or partial gastrectomy, consider underlying cause (nonsteroidal antiinflammatory drugs, mast cell tumor, gastrinoma, hepatic disease) Gastroduodenostomy, Y-U pyloroplasty if benign Resection and anastomosis if localized, chemotherapy for lymphosarcoma Typhlectomy Resection and anastomosis for malignancy, colonoscopic polyp excision Subtotal colectomy Submucosal resection, partial pull-through, Swenson’s pull-through, dorsal approach for resection and anastomosis or extramural tumor excision Herniorrhaphy with internal obturator muscle flap and castration Surgical excision and castration for adenomas, castration and delayed local aggressive resection for sebaceous adenocarcinoma, excision for large adenomas Anal sacculectomy and abdominal lymphadenectomy, chemotherapy Anal sacculectomy Partial or total lobectomy if disease is localized to one lobe Cholecystectomy Cholecystectomy Tumor excision, metastases are functional; corticosteroids, diazoxide, or streptozotocin Partial pancreatectomy if localized Partial pancreatectomy, H2 blockers, octreotide, proton pump inhibitors Drainage, lavage
Neoplasia Gastric dilation-volvulus Ulceration
Small intestine
Outlet obstruction Neoplasia
Cecum Colon
Neoplasia Neoplasia
Rectum
Idiopathic megacolon Neoplasia
Perineum
Perineal hernia Perianal neoplasia
Anal sac
Neoplasia
Liver Gall bladder Pancreas
Abscess or inflammation Neoplasia Cholelithiasis Cholecystitis Beta-cell neoplasia Adenocarcinoma Gastrinoma Abscess
Respiratory System Nasal planum Nasal cavity
Neoplasia Neoplasia
Larynx
Paralysis Collapse
Trachea
Collapse
Lung Pleural space
Neoplasia Chylothorax
Cardiovascular System Cardiac Right atrial neoplasia Atrioventricular block Pericardial effusion Urologic System Renal
Lithiasis Neoplasia Chronic renal failure or acute renal failure
Nosectomy Radiation therapy (megavoltage or cobalt), rhinotomy plus orthovoltage radiation Unilateral arytenoid lateralization Permanent tracheostomy, unilateral arytenoid lateralization, partial laryngectomy Prosthetic rings for extrathoracic collapse, intraluminal stent for intrathoracic collapse Lobectomy, lymph node biopsy Thoracic duct ligation or embolization, pleuroperitoneal shunt Excision of right atrial appendage and tumor and pericardiectomy Pacemaker implantation if second or third degree Pericardiectomy if caused by neoplasia or idiopathic Lithotripsy or nephrotomy and calculus removal if obstructive disease is present, “watchful waiting” if no infection or obstruction, nephrectomy if kidney is nonfunctional Nephrectomy if unilateral Medical management, renal transplantation
Chapter 8 Surgery and Its Application
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TABLE 8-1. GERIATRIC SURGICAL DISEASE—cont’d SYSTEM OR ORGAN
PATHOLOGY
Urologic System—cont’d Ureter Lithiasis Urinary bladder Lithiasis Neoplasia Urethra
Endocrine System Thyroid Parathyroid Adrenal Pituitary Reproductive System Testes Prostate
Mammary Uterus or ovary Vagina
Incontinence Lithiasis Neoplasia Stricture Neoplasia, canine Neoplasia, feline Neoplasia Neoplasia Neoplasia Neoplasia Hyperplasia Cyst Inflammation Abscess Neoplasia Neoplasia, canine Neoplasia, feline Pyometra Neoplasia Neoplasia
Hematopoietic System Spleen Neoplasia Hematoma Nervous System Brain Spinal Cord
Neoplasia Disk Neoplasia
Nerve
Neoplasia Cauda equina
Skeletal System Joints
Degenerative joint disease
Coxofemoral
Hip dysplasia
Stifle
Cranial cruciate rupture
Bone
Neoplasia
Special Senses Skin Ear Eye
Neoplasia Neoplasia Inflammation Hypertrophy Neoplasia Cataracts
THERAPEUTIC OPTIONS Ureterotomy, lithotripsy Cystectomy, lithotripsy, or medical management if calculi are magnesium ammonium phosphate Partial cystectomy if possible and/or chemotherapy, tube cystostomy for palliation Colposuspension if unresponsive to medical management Urohydropulsion, scrotal, perineal, or antepubic urethrostomy Vaginourethroplasty Tube cystostomy for palliation Thyroidectomy if freely movable and noninvasive, radiation I-131 therapy, thyroidectomy or medical management with methimazole Parathyroidectomy Adrenalectomy Hypophysectomy Neutering Neutering Drainage procedure, excision of cyst Omentalization of abscess Lumpectomy, regional or unilateral mastectomy, ovariohysterectomy Regional or unilateral mastectomy Ovariohysterectomy Ovariohysterectomy Excision of tumor, with or without episiotomy Splenectomy Splenectomy, partial splenectomy Excision, radiation therapy Medical treatment or laminectomy if motor impairment or chronic pain Excision by laminectomy if extradural or intradural or extramedullary Excision with or without amputation Laminectomy with or without foraminotomy Treatment of underlying cause, weight control, exercise modification, analgesics, arthrodesis, excision arthroplasty, joint replacement Weight control, exercise modification, medical management, total hip arthroplasty, femoral head ostectomy Arthrotomy, joint stabilization, tibial plateau leveling osteotomy, fibular head transposition, conservative in small dogs and cats Amputation plus chemotherapy, limb-sparing treatment plus chemotherapy Excision, laser ablation, cryosurgery Excision of tumor, vertical or total ear canal ablation Lateral ear canal resection, vertical or total ear canal ablation Lateral ear canal resection, vertical or total ear canal ablation Observation or enucleation Observation, phacoemulsification, intraocular lens implantation
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Hepatic System Altered hepatic microsomal enzyme systems may cause a decreased ability to metabolize drugs in the geriatric animal.4 Elimination of some drugs is dependent on hepatic blood flow, which decreases with aging.6 This decreased metabolic function may be present in spite of normal laboratory values. A decreased ability to metabolize or eliminate drugs has obvious implications from an anesthetic point of view but also affects administration of other drugs in the perioperative period such as antimicrobial and nonsteroidal antiinflammatory agents (NSAIDs). Severe liver disease may be responsible for hypoproteinemia, which delays wound healing. Similarly, severe disease may result in a decrease in blood clotting factors, thereby prolonging normal clotting times. Serum liver enzymes, albumin, and total protein levels and prothrombin and partial thromboplastin times may assist in assessing liver function. Fasted and postprandial serum bile acids more accurately reflect true liver function.
Renal System Decreased renal function and decreased renal reserve are of utmost concern in the geriatric animal in the perioperative period (Table 8-2).
The kidneys of the geriatric animal have decreases in glomerular numbers, tubular size and weight, and increased fibrosis.7 It should be recalled that decreases in renal function as indicated by abnormal elevations in laboratory values (blood urea nitrogen and serum creatinine) are not linearly related. At least 65% to 75% of renal function is lost before there are increases in the commonly obtained laboratory values; therefore small increases in blood urea nitrogen may indicate large decreases in glomerular filtration rate. As always, blood urea nitrogen and serum creatinine values are interpreted in conjunction with urinalysis. Chronic renal failure produces mild to moderate elevations in blood urea nitrogen and serum creatinine, an isosthenuric urine, and mild anemia in some cases. More specific testing for renal function involves the use of creatinine clearance or glomerular filtration rates as determined by nuclear scintigraphy. Even in the face of normal renal laboratory values, decreased renal blood flow as a result of less than normal cardiac output causes glomerular filtration rates of the kidneys to decrease. Glomerular filtration rates as determined by nuclear scintigraphy are not widely available in practice; however, they represent an excellent noninvasive means of evaluating the contribution of each kidney to overall renal function. This information is especially valuable when one is
TABLE 8-2. PRACTICAL GUIDE TO THE PREVENTION OF PERIOPERATIVE RENAL FAILURE IN GERIATRIC ANIMALS PRINCIPLE
METHOD OR MEASUREMENT
Assess renal function accurately
Blood urea nitrogen Serum creatinine Urine output Glomerular filtration rate measured via scintigraphy Physical examination Serial body weights Packed cell volume and total solids Central venous pressure Avoid hypotension by assuring normal volume status and surgical hemostasis Reverse severe hypotension with crystalloid fluids, blood products, and vasopressors Prompt radiographic diagnosis Catheter drainage Surgical correction Limit use of aminoglycosides or nonsteroidal antiinflammatory drugs Limit use of intravenous contrast agents Adjust drug doses Abscess drainage (local, pancreatic, prostate) Catheter care Appropriate antibiotics Crystalloid fluids in correct volume Mannitol, furosemide, dopamine Monitor urine output
Assess and monitor volume status
Control and maintain blood pressure Relieve urinary tract obstruction Avoid known nephrotoxins Prevent sepsis Consider diuresis
Modified from Monroe WE, Waldron DR: Renal failure: surgical considerations. In Bojrab MJ, ed: Disease mechanisms in small animal surgery, ed 2, Philadelphia, 1993, Lea & Febiger.
Chapter 8 Surgery and Its Application considering surgery on the kidney itself, for example, nephrotomy or nephrectomy. Animals with compensated renal disease may be anesthetized and operated on successfully; however, attention to perioperative fluid needs and urine production is critical in ensuring that the animal is not pushed into decompensated renal failure or that, conversely, overly zealous fluid administration does not cause pulmonary edema. Drugs that are potentially nephrotoxic such as NSAIDs and aminoglycoside antibiotics are used cautiously in the geriatric animal.
Cardiopulmonary Function As with other organ systems, there is a decrease in cardiac reserve in geriatric patients compared with healthy young animals.3 Although animals are not routinely diagnosed with primary vascular disease and hypertension as geriatric humans are, there is a decrease in cardiac output, baroreceptor activity, and circulation time in the geriatric animal.8,9 Although the geriatric heart has normal contractile elements, its ability to respond to catecholamines is reduced.5 The changes that occur negatively affect the animal’s ability to maintain blood pressure during stress and anesthesia.3,10 Valvular disease is extremely common in the geriatric canine, and myocardial disease may be seen in both the aging canine and feline. Valvular disease by itself, as evidenced by cardiac murmurs detected on physical examination, does not prohibit anesthesia or surgery; however, judicious use of crystalloid fluids is indicated, especially if renal function is also compromised. In addition to careful auscultation and pulse examination, thoracic radiography, electrocardiography, and ultrasonography of the heart may aid in identifying specific disease, which may affect anesthesia and surgical planning. Respiratory function decreases as the animal ages. Respiratory rate, tidal volume, lung elasticity, and partial pressure of arterial oxygen all decrease in the geriatric animal.11,12 Gas exchange is less efficient, and ventilation-perfusion mismatch is potentially more prevalent and severe than in the young animal.13 Clinically, the decreased function may result in hypoxia and hypercarbia, which may in turn negatively affect cardiac function by predisposing the animal to arrhythmias. Mild anesthetic depression of respiration in the normal young animal may be critical to the geriatric animal.3 Pulmonary function testing is not routinely performed in animals. Auscultation, thoracic
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radiography, and blood-gas analysis are available to aid in assessment of pulmonary function. Aspiration pneumonia may occur more commonly in geriatric humans and is especially common in the perioperative period in animals with laryngeal paralysis or esophageal disease.
Endocrine Disease Endocrine diseases are diagnosed more commonly in the geriatric dog and cat. Diseases of the endocrine system often have a primary affect and also may affect other organ systems important in anesthesia and surgery. For example, parathyroid adenomas cause hypercalcemia, which may cause peripheral weakness and renal disease. Hyperthyroidism in cats causes primary gastrointestinal disturbances but has profound secondary effects on cardiac function. Hyperadrenocorticism, either naturally occurring or iatrogenic, may affect wound healing or wound infection rates in surgery of any type performed in the geriatric animal. Some of the endocrine diseases diagnosed in geriatric animals are potentially surgical in nature, such as beta-cell tumors of the pancreas, hyperthyroidism in the cat, parathyroid adenomas, and functional adrenal tumors. Careful assessment of multiorgan systems before surgery is indicated in these animals. In some cases, the animal can be treated medically in the short term before surgery, and the risks associated with anesthesia and surgery are reduced. A hyperthyroid feline made euthyroid with methimazole and an animal with hyperadrenocorticism that is treated medically are examples of geriatric disease states in which the animal may be improved with medical therapy prior to definitive surgical therapy.
INFECTION AND WOUND HEALING Wound infection rates in geriatric humans with clean or clean-contaminated wounds have been reported to be higher than in the younger population. Other authors, however, have not found age to be an independent predictor of wound infection.14 Similarly, wound infection rates in animals, when assessed by univariate analysis, appear increased in the geriatric animal. However, when the same data are assessed by multivariate analysis, infection rates in the geriatric population appear the same as in younger populations; therefore, it appears that other factors including concurrent infections at distant sites or
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the presence of endocrinopathies likely influence wound infection rates.15 Wound healing is reported as delayed in geriatric humans16 and in rats.17,18 The effect of increasing age on wound healing in dogs and cats is questionable and probably not clinically significant; however, concurrent pathologic problems such as hyperadrenocorticism, diabetes mellitus, or hypoproteinemia negatively affects wound healing.5 Supplementation with vitamin A and anabolic steroids may correct the adverse effects of diabetes mellitus, corticosteroids, or radiation on healing and is commonly used in human surgical patients.19
PREOPERATIVE ASSESSMENT History and Physical Examination A thorough history and detailed physical examination are essential in assessing the geriatric animal’s surgical needs. Information acquired may affect both the anesthesia and surgical protocols. Attention to possible drug interactions or their specific effects is especially important. Prolonged administration of corticosteroids or certain antibiotics for dermatologic disease or NSAIDs for degenerative joint disease is common in geriatric animals. These agents may affect wound healing, wound infection, renal function, microbial susceptibility, and blood clotting.5,20 History or physical findings of polydipsia, polyuria, lack of exercise tolerance, persistent cough, lameness, or undiagnosed mass may indicate a serious problem that requires further attention prior to surgery. History regarding the primary clinical problem is also important. A spontaneously occurring long bone or facial fracture in a geriatric animal with minor trauma may be secondary to neoplasia, infection, dental disease, or metabolic bone disease. Acute clinical signs seemingly associated with chronic problems may, in fact, be due to secondary disease. An acute rear limb lameness in a canine with a chronically luxating patella may indicate a cranial cruciate ligament injury. Similarly, a dyspneic geriatric animal of a brachycephalic breed may have an obstructed airway from laryngeal collapse or neoplasia rather than an elongated soft palate. Physical examination includes careful thoracic auscultation and abdominal palpation. Superficial palpation of the entire body is advised to diagnose skin and mammary tumors, both of which have an increased prevalence in the geriatric animal.21,22
Preoperative Evaluation The extent of preoperative evaluation is dictated by the primary surgical problem and any problems identified historically or on physical examination. A problem list should be made to guide the veterinarian in formulating differential diagnoses and a diagnostic plan. For elective surgery, a minimum database for geriatric animals should include a complete blood count, serum chemistry panel, urinalysis, and a lead II electrocardiogram. Thoracic radiographs are taken in many animals to identify cardiac or lung pathology that may affect anesthetic administration, although the value of such screening has been questioned in asymptomatic animals.13 Three-view thoracic radiographs are considered mandatory in the animal with suspected or known cancer to identify possible metastatic disease prior to surgery. Thoracic metastatic lesions must be 3 to 5 mm in diameter before they are visible radiographically. A lead II electrocardiogram tracing is valuable as a screening tool for cardiac arrhythmias. Undiagnosed lesions or masses identified on or within an animal can be initially assessed by fine needle aspiration and cytologic examination. Aspiration of superficial masses is routine; aspiration of abdominal or thoracic masses may require ultrasound guidance. In many animals, these procedures may be performed without anesthesia; however, sedation may be required for aspiration of masses within body cavities. Similarly, tissue biopsies from a sedated animal may be obtained using ultrasound guidance, local anesthesia, and a biopsy punch or Tru-Cut needle (Travenol Laboratories, Deerfield, Ill) technique. Biopsies of the liver, spleen, prostate, and kidneys are commonly performed by this method. A diagnosis obtained from biopsy specimens can be vital to constructing a rational therapeutic plan that may or may not include surgery. Ultrasonography, magnetic resonance imaging, and computed tomography are valuable noninvasive tools for more complete evaluation of the geriatric animal. Sonographic evaluation of the abdomen by a skilled examiner is a sensitive means of screening for either primary or metastatic masses in the animal with suspected or known cancer. Advanced imaging techniques, such as magnetic resonance imaging or computed tomography, require general anesthesia but allow for more accurate assessment of normal and diseased tissue than conventional radiography and may further assist the surgeon in developing a
Chapter 8 Surgery and Its Application therapeutic plan. The increased ability to image diseased tissue accurately may allow the surgeon to avoid unnecessary surgery when successful resection of diseased tissue is not possible. Endoscopic examination of the upper and/or lower gastrointestinal tract may provide tissue for diagnosis of enteric disease. Endoscopic examination may also characterize disease as focal or more diffuse in nature, thereby contributing to accurate therapeutic planning.
Preoperative Care In the case of elective geriatric surgery, it is desirable that the animal be as “normal” as possible for anesthesia and surgery. This implies that any current therapy for preexisting defined disease be optimal. In addition to treatment of defined disease, provision of preoperative nutrition may be indicated to improve the overall health of the animal, especially if the animal has had chronic disease.5 The stress of anesthesia and surgery can increase the basal metabolic rate significantly; therefore, attention to nutritional needs preoperatively and postoperatively is important. A high-energy, high-protein diet can meet these needs. Alternatively, a nasogastric, esophagostomy, or gastrostomy tube may be placed to assure that caloric and energy needs are met in the perioperative period. The importance of maintaining adequate nutrition in the feline to prevent hepatic lipidosis is well known. Attention to fluid and electrolyte needs is important in the perioperative period. Electrolyte abnormalities should be corrected by oral or parenteral means prior to general anesthesia. During the preoperative fasting period, the wellhydrated animal is allowed free access to water until anesthesia is induced. If the animal’s hydration status is questionable or there is evidence of renal disease, preoperative fluid therapy is advisable prior to anesthesia. Effects of fluid therapy may be monitored by packed cell volume and total solids measurement, body weight, serum chemistries, and quantitative urine production. The latter requires placement of an indwelling urinary catheter that is connected to a closed collection system. The need for blood transfusion is a clinical judgment; however, existing anemia in which the packed cell volume is less than 25% is an indication for cross-matched packed cells or whole blood transfusion prior to general anesthesia and surgery.
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Surgical Planning The critical periods for the geriatric animal undergoing surgery are at anesthesia induction, intraoperatively, and in the immediate postoperative period.5 Every effort is made to minimize stress on the animal preoperatively. For elective surgery, geriatric animals may be evaluated as outpatients and then presented fasted (free-choice water) on the morning of surgery. Proper planning and preparation for both general and specific needs during surgery will allow the surgeon to minimize the animal’s time under general anesthesia. Consideration of the following guidelines may decrease anesthesia time and improve operative efficiency in the geriatric animal.5,20 • Consider the need for equipment appropriate to the specific surgery. • Have a specific operative goal or goals prior to surgery; have contingency or alternative plans should problems arise. Plan on biopsy of diseased tissue if resection is not possible. • Be familiar with the surgical procedure and know the appropriate anatomy. • Consider the need for cross-matching and possible intraoperative or postoperative blood transfusion if blood loss is likely. Consider the possibility of using colloids such as plasma or hetastarch. • If the animal is cooperative clip the surgical site immediately prior to induction of anesthesia; alternatively the clip may be performed in the premedicated animal. • Once anesthesia is induced and the animal is stabilized, complete the preoperative surgical site preparation as expeditiously as possible and move the animal to the operating room. • Consider the need for appropriate antibiotics in the intraoperative and postoperative periods. Surgical procedures that are expected to last longer than 90 minutes have a higher rate of bacterial wound contamination, and prophylactic antibiotic therapy is indicated. In addition, procedures that are clean-contaminated (entry into the gastrointestinal, respiratory, or infected urinary tract) or contaminated (entry into the colon) require the administration of antibiotics effective against suspected pathogens. Perioperative antimicrobial agents should be given in these cases in the immediate preoperative period after anesthetic induction and intraoperatively if the procedure exceeds 90 minutes; one or two doses should be given postoperatively.
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Intraoperative Monitoring and Support Close monitoring of the animal is indicated during surgery. Routine intraoperative monitoring should include electrocardiogram and pulse oximetry in addition to physical monitoring of pulse quality (Figure 8-1). End-tidal CO2 monitoring is a sensitive means of measuring the adequacy of ventilation, but the equipment is expensive. Blood pressure may be monitored noninvasively with Doppler equipment or oscillometric monitoring using a pneumatic cuff. Urine production as measured by use of an indwelling urinary catheter and closed collection system is an indirect measure of the adequacy of blood pressure and a direct measure of renal function, which is important in any animal with renal compromise or in an animal that undergoes renal surgery. Normal urine output should be at least 1 to 2 ml/kg/h. Intraoperative administration of crystalloid intravenous fluids is routinely provided at 10 to 20 ml/kg/h to provide cardiovascular and renal support. In general, a balanced electrolyte solution such as lactated Ringer’s is used, although specific disease processes may dictate the selection of other fluids. Pharmacologic management of oliguria during surgery is indicated in some cases. If the animal has been adequately volume expanded, the use of a dopamine drip (2 to 5 μg/kg/min), furosemide (2 to 4 mg/kg bolus), or mannitol 0.5 g/kg given over 15 minutes) may be considered to increase urine production. The older animal has less efficient thermoregulatory control, so attempts should be made during surgery to keep the animal warm.5 Core body temperature is usually monitored with rectal
Figure 8-1. Intraoperative monitoring of electrocardiographic tracing, heart rate, and pulse oximetry with one monitor.
or esophageal thermometers or by other intermittent manual methods. Maintenance of body temperature is especially difficult in animals weighing <5 kg when body cavities are opened. Warm water–circulating blankets (Gaymar Industries, Orchard Park, N.Y.) (Figure 8-2), circulating hot air blankets (Bair Hugger, Augustine Medical, Eden Prairie, Minn.) (Figure 8-3), and warm lavage solutions are useful in prevention and treatment of hypothermia.
SURGICAL PRINCIPLES Appropriate surgical planning, as suggested previously, will expedite the surgical procedure and reduce the need for crisis-based decisions. In addition to a surgical plan, specific techniques and equipment are available to maximize the surgeon’s efficiency. Maximizing the efficiency of
Figure 8-2. Circulating warm water blanket that is useful in preventing hypothermia.
Figure 8-3. Circulating hot air blankets also assist in preventing hypothermia and provide more uniform body coverage than water blankets.
Chapter 8 Surgery and Its Application the surgical procedure will reduce anesthesia time and stress on the geriatric animal.5 Adequate surgical exposure is extremely important for any surgical procedure. A generous incision that is appropriate for the specific procedure is made. Small incisions made in an effort to decrease operative time compromise surgical exposure and tend to increase operative time. Another technique to assist in exposure involves the use of self-retaining retractors. Balfour retractors are especially valuable to maintain exposure during abdominal procedures; Gelpi or Weitlander retractors are useful for orthopedic or neurologic cases. Direct surgical assistance from and tissue retraction by a technician are invaluable during many surgical procedures. Appropriate tissues should be excised or biopsies obtained. If neoplastic masses or organs are excised, regional lymph nodes should be excised or biopsied to stage the disease. Liver biopsies are easily obtained by the “guillotine” method using a loop of absorbable suture to attain hemostasis and cut through the edge of a liver lobe. Simple incisional biopsies are appropriate for obtaining renal, intestinal, bladder, or prostatic biopsies. Simple interrupted or mattress sutures of 3-0 or 4-0 polydioxanone (PDS II, Ethicon, N.J.) are used postbiopsy for hemostasis and to provide a leak-proof closure of hollow viscus. The use of mechanical surgical stapling equipment saves considerable time for the surgeon and results in decreased anesthesia time. Thoracoabdominal surgical instruments (TA, United States Surgical Corporation, Norwalk, Conn.) are easy to use and place two or three staggered rows of staples that provide good hemostasis and leakproof closure of soft tissues. These instruments place staple lines measuring 90, 55, or 30 mm in length and have been used for complete lung lobectomy, partial lung lobectomy, partial hepatectomy and splenectomy, closure of the stomach following partial gastrectomy, cecal removal, and prostatic and paraprostatic cyst removal.23 Ligateand-divide staplers (LDS, United States Surgical Corporation, Norwalk, Conn.) place two staples while a cutting blade cuts between them. This instrument is extremely useful for procedures such as splenectomy or in which the wellvascularized omentum must be dissected from abdominal masses. Vascular staples (Surgiclips, United States Surgical Corporation, Norwalk, Conn.) place a single vascular clip on vessels and are very convenient for use in deep cavities. The LDS stapler and Surgiclips are “user friendly” with essentially little or no learning curve for the surgeon.
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Other stapling devices such as the gastrointestinal anastomosis (GIA, United States Surgical Corporation, Norwalk, Conn.) and endto-end anastomosis (EEA, United States Surgical Corporation, Norwalk, Conn.) can save time when one performs gastrointestinal anastomoses, but efficient and safe use of these instruments requires considerable training and experience. Simple continuous suture closure of the linea alba is a safe and quick alternative to simple interrupted patterns. Monofilament absorbable suture with prolonged tensile strength such as polydioxanone or polyglyconate (Maxon, United States Surgical Corporation, Norwalk, Conn.) or nonabsorbable material such as polypropylene (Prolene, Ethicon, NJ) or nylon (Dermalon, Ethicon, N.J.) is recommended for continuous closure. General suture size guidelines for continuous closure are as follows: for animals weighing <5 kg, use 3-0 suture; for those weighing 5 to 25 kg, use 2-0 suture; for those weighing 25 to 50 kg, use 0 suture; and for animals weighing >50 kg, use size 1 suture. Skin staples are a time-saving adjunct to efficient surgery, especially when long linear incisions such as celiotomy or thoracotomy incisions are closed. Skin stapling is reported to be three to five times faster than suturing for wound closure.24 Staplers are available from several manufacturers and generally come in two widths. Wide staples are preferred for use in animals and are most easily placed after an intradermal closure of the incision, which enhances skin alignment. In recent years, minimally invasive surgical techniques have become more widely used in veterinary surgery. Arthroscopy, laparoscopy, thoracoscopy, and urethrocystoscopy have been used for diagnosis and therapy of some disease processes. Advantages include less morbidity and mortality than with open surgical techniques, and definitive tissue biopsy is possible under direct visualization. Disadvantages include the expense of the equipment, the need for training in specialized techniques, and in some cases limited visualization of complete body cavities. Considerable time may be saved depending on the specific procedure and the experience of the surgeon.
POSTOPERATIVE CONSIDERATIONS Monitoring and Support During the postoperative period, respiratory, cardiovascular, and renal compensatory mechanisms may be diminished and susceptible to dys-
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function. Repetitive monitoring and evaluation of circulatory and metabolic parameters can clearly show the progression of a normal recovery or allow early detection of abnormalities that threaten normal recovery. Immediately following surgery, the animal should be placed on a preheated circulating water blanket and monitored constantly until extubation. Continuous monitoring of body temperature is advised until core body temperature reaches 37.8° C (100° F). Pulse and capillary refill time, respiration rate, and anesthetic depth are monitored closely until the animal is sternal, alert, and responsive. Thoracic auscultation is indicated, especially if aggressive fluid therapy is being administered. Blood pressure, central venous pressure, urine output, and electrocardiography monitoring may be indicated in animals whose condition is critical. Fluid therapy is continued for at least 12 hours following any major surgical procedure; however, duration and volume ultimately depends on the animal’s needs. After surgery, a packed cell volume and total solids should be recorded to establish a baseline for monitoring hydration status. Fluids at maintenance rates (40 to 60 ml/kg/day) are administered routinely; however, significant blood loss or concerns about renal function may dictate that higher rates be used. Supplemental oxygen should be available for animal support as needed. Placement of a nasopharyngeal oxygen tube may be indicated in brachycephalic animals or geriatric animals with preexisting respiratory disease. Supplemental oxygen may also be administered by oxygen cage or face mask, although the latter is labor intensive. The need for mechanically assisted ventilation or placement of a tracheostomy tube is rare but should be anticipated and prepared for in some critical care cases.
Analgesia Appropriate administration of analgesics to the geriatric animal can eliminate or reduce the stress and distress of postoperative pain. Opioids are the most reliable and predictable drugs for the relief of major postoperative pain. They may be administered parenterally or orally in some cases, and opioid cutaneous patches are available for longer duration analgesia. NSAIDs are useful for minor postoperative pain but should not be used concurrently with corticosteroids because of the risks of gastrointestinal ulceration. Caution is advised if NSAIDs are used in animals with chronic renal failure.
Other methods of postoperative analgesia include the use of epidurally administered drugs and blocking of the pain response by local injection of lidocaine or marcaine.
Nutrition Anticipation of the geriatric animal’s nutritional needs in the perioperative period is important. Animals that have questionable nitrogen balance or those animals undergoing a surgical procedure that may impair eating should have a feeding tube placed while the animal is under anesthesia. Esophagostomy, percutaneous gastrostomy, or endoscopically assisted gastrostomy tubes have all been placed and used successfully to support animals nutritionally. It is important that nutritional therapy be administered early in the course of the animal’s anorexia rather than after it has not eaten for several days.5 References 1. Kraft W: Geriatrics in canine and feline internal medicine, Eur J Med Res 3:31, 1998. 2. Goldston RT: Introduction and overview of geriatrics. In Goldston RT, Hoskins JD, eds: Geriatrics and gerontology of the dog and cat, Philadelphia, 1995, WB Saunders. 3. Harvey RC, Paddleford RR: Management of geriatric patients: a common occurrence, Vet Clin North Am Small Anim Pract 29:683, 1999. 4. Paddleford RR: Anesthetic considerations for the geriatric patient, Vet Clin North Am Small Anim Pract 19:13, 1989. 5. Hosgood G: Surgical protocol. In Goldston RT, Hoskins JD, eds: Geriatrics and gerontology of the dog and cat, Philadelphia, 1995, WB Saunders. 6. Aucoin DP: Drug therapy in the geriatric animal: the effect of aging on drug disposition, Vet Clin North Am Small Anim Pract 19:41, 1989. 7. Krawiec DR: Urologic disorders of the geriatric dog, Vet Clin North Am Small Anim Pract 19:75, 1989. 8. Dodman NH, Deeler DC, Court MH: Aging changes in the geriatric dog and their impact on anesthesia, Compend Contin Educ Pract Vet 6:1106, 1984. 9. Meurs KM, Miller MW, Slater MR: Arterial blood pressure measurement in a population of healthy geriatric dogs, J Am Anim Hosp Assoc 36:497, 2000. 10. Hamlin RL: Identifying the cardiovascular and pulmonary diseases that affect old dogs, Vet Med 85:483, 1990. 11. Robinson NE, Gillespie JR: Lung volumes in aging beagle dogs, J Appl Physiol 35:317, 1973. 12. Meyer RE: Anesthesia for neonatal and geriatric patients. In Short CE, ed: Principles and practice of veterinary anesthesia, Baltimore, 1987, Williams & Wilkins. 13. Muravchick S: Preoperative assessment of the elderly patient, Anesthesiol Clin North Am 18:71, 2000. 14. Sawyer RG, Pruett TL: Wound infections, Surg Clin North Am 74:519, 1994.
Chapter 8 Surgery and Its Application 15. Brown DC: Personal communication, February, 2002. 16. Holt DR, Kirk SJ, Regan MC et al: Effect of age on wound healing in healthy human beings, Surgery 112:293, 1992. 17. Quirinia A, Viidik A: The influence of age on the healing of normal and ischemic skin wounds, Mech Ageing Dev 5:221, 1991. 18. Petersen TI, Kissmeyer-Nielsen P, Laurberg S et al: Impaired wound healing but unaltered colonic healing with increasing age: an experimental study in rats, Eur Surg Res 27:250, 1995. 19. Hunt TK, Hopf HW: Wound healing and wound infection: what surgeons and anesthesiologists can do, Surg Clin North Am 77:587, 1997. 20. Waldron DR, Budsberg SC: Surgery of the geriatric patient, Vet Clin North Am Small Anim Pract 19:33, 1989. 21. MacDonald J: Neoplastic diseases of the integument, Proc Am Anim Hosp Assoc, 1987.
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22. Rutteman GR, Withrow SJ, MacEwen GE: Tumors of the mammary gland. In Withrow SJ, MacEwen GE, eds: Small animal clinical oncology, Philadelphia, 2001, WB Saunders. 23. Pavletic MM, Schwartz A: Stapling instrumentation, Vet Clin North Am Small Anim Pract 24:247, 1994. 24. Brickman KR, Lambert RW: Evaluation of skin stapling for wound closure in the emergency department, Ann Emerg Med 18:122, 1989.
Supplemental Readings Willard MD: Endoscopy of body cavities. In Fossum TW, ed: Small animal surgery, St Louis, 2002, Mosby.