Page 31 - Zoo Animal Learning and Training

Chapter 3: Minimum Database for Intracranial Surgery 23

Among the risk factors associated with mortality are high‐risk sur- electrolyte abnormalities are present that could cause arrhythmias
gery, history of ischemic heart disease, history of congestive heart (hyperkalemia, hypocalcemia).
failure, history of cerebrovascular disease, preoperative treatment Appropriate correction of fluid and electrolyte imbalances is
with insulin, and preoperative serum creatinine concentration necessary prior to anesthesia, and electrolytes and volume status
greater than 2.0 mg/dL [1]. It is unknown if any of these risk factors should be monitored to avoid rapid fluid shifts and iatrogenic
apply to the veterinary population. brain edema, hemorrhage, or encephalopathy. Acidosis from
intraoperative hypercapnea along with existing metabolic acidosis
Gastrointestinal System from renal disease could lead to significant respiratory depression
Although vomiting, regurgitation, diarrhea, and abdominal pain [1]. Blood pressure may be elevated in patients with renal disease
are all signs usually referable to gastrointestinal tract abnormalities, and could impact short‐term outcomes by influencing cerebral
vomiting is occasionally a manifestation of intracranial disease. perfusion pressure and surgical bleeding [7]. Anemia, depending
Patients with full stomachs or megaesophagus are at risk for aspira- on severity, may require preoperative or postoperative transfu-
tion pneumonia. Presence of megaesophagus should prompt con- sion. Mannitol is contraindicated in volume‐depleted or anuric
cern for paraneoplastic syndromes [10] or endocrinopathies patients.
manifesting with motor unit signs, e.g., hypothyroidism [11–14]. Urinary culture may be justified based on the presence of active
All patients are fasted at least 12 hours prior to surgery and kept nil sediment seen on preliminary urinalysis. Patients with a history of
by mouth for 24 hours postoperatively to minimize risk of aspira- urinary tract infection should also have a presurgical urine culture.
tion pneumonia. If mentation is not improved by 24 hours postop- Early identification and treatment of urinary tract infection is
eratively, food should continue to be withheld and alternative important to prevent hematogenous seeding of the surgical site.
nutrition considered.
Routine blood chemistry provides basic liver parameters. Hematological System
Hepatomegaly, jaundice, ascites and/or ecchymoses should cause Intraoperative or postoperative intracranial hemorrhage has the
alarm regarding adequate liver function. Decreased albumin and potential to be catastrophic with devastating clinical effects.
blood urea nitrogen (BUN) are biochemical changes often associ- Depending on the procedure the risk for hemorrhage varies.
ated with liver failure. Liver function tests such as preprandial and Minimally, CBC including a platelet count, blood type (for dogs),
postprandial bile acid concentration and prothrombin time (PT)/ and blood type and cross‐match (for cats) are recommended prior
partial thromboplastin time (PTT) may be advisable in some to most intracranial surgeries. Dogs that have previously undergone
patients. Abdominal ultrasound may distinguish between a focal blood transfusion will need to be cross‐matched in addition to
liver abnormality and a diffuse one. Aspirates or biopsies are done blood typing. The supervising surgeon should confirm that an
accordingly and clotting times are typically recommended prior to appropriate blood product is available should the need arise.
performing a liver biopsy.
Oral cavity inspection may identify a source of bacteria that Endocrine System
could contribute to postoperative infections. Effectively dealing Medical history of patients with endocrinopathies may include
with dental disease prior to intracranial surgery is often danger- unintentional weight gain or loss, abnormal hair growth/loss,
ous to the patient and impractical. Intraoperative antibiotics are polydipsia/polyuria, poor vision, and lethargy. On physical
warranted. examination one may find the coat sparse with abnormal pig-
mentation, skin pigmentation, redistribution of fat to the face
Renal System and abdomen, hepatomegaly, cataracts, and occasionally motor
Advanced imaging of the brain with MRI or CT often necessitates unit signs [11–14]. Abnormalities present on routine chemistry
the use of intravenous contrast (gadolinium or iodine based analysis can also provide evidence of concurrent endocrine dis-
respectively). Because these agents undergo renal excretion, renal eases. Some endocrine diseases such as hyperadrenocorticism
parameters and hydration status should be assessed in all patients and diabetes mellitus can predispose to development of urinary
prior to contrast administration. At the very least, BUN reagent tract infections, skin infections or cutaneous ulceration, and
strip, PCV, and urine specific gravity should be performed. This delayed wound healing. Hyperadrenocorticism can be confirmed
rapid and abbreviated assessment is most useful in young healthy with either an adrenocorticotropic hormone (ACTH) stimula-
animals or emergent situations. A more complete evaluation would tion test and/or low‐dose dexamethasone suppression test. Levels
include a complete blood count (CBC), full chemistry, and urinal- of serum thyroxine and thyroid‐stimulating hormone (TSH),
ysis. Renal complications associated with contrast agents include with or without free thyroxine, should be evaluated in patients
contrast‐induced nephropathy and worsening of existing renal demonstrating clinical signs and/or clinicopathological abnor-
disease. Hypovolemia may predispose to contrast‐associated or malities consistent with hypothyroidism. Hypothyroidism can
postanesthetic renal complications and should be corrected prior impair both central and peripheral nervous system function as
to anesthesia. well as contribute to myopathic changes [12], all of which may
Azotemia can be prerenal, renal, or postrenal and should be complicate patient management.
addressed prior to surgical consideration. Chronic renal failure is
typically due to primary kidney disease and poses significant Integument
anesthetic challenges. Patients with chronic renal disease may Skin infections should be identified and treated prior to surgery.
develop electrolyte abnormalities, encephalopathy, metabolic aci- Surgery should be postponed, if at all possible, if infection is present
dosis, gastrointestinal bleeding, nonregenerative anemia, hyper- at the expected incision site. Hematogenous spread of dermal infec-
tension, and fluid imbalances. A complete chemistry panel, tions is one of the most common sources of bacteria contributing to
urinalysis, CBC, and blood pressure are indicated in patients with catheter infections and surgical site infections, which may be devas-
known or suspected renal disease. The ECG should be reviewed if tating with intracranial procedures.