The endocrine systems throughout the body play crucial rolls in the maintenance and metabolism that are required to maintain
health. Perturbations in many of these symptoms occur in dogs and cats and veterinarians are often required to diagnose and
treat these conditions that may last throughout the lifetime of a pet. In addition, many of these patients will require anesthesia
for diagnostics and treatments that may or may not be related to underlying endocrine diseases. Veterinarians should have
an understanding of how these conditions can affect physiology, anesthesia and how anesthetic and analgesic medications can
affect these conditions.
Physiologic changes commonly seen in patients with hyperadrnocroticism include poor tissue and wound healing, PU/PD, hypercoagulability,
muscle wasting, lethargy, hypoxemia, polyphagia, abdominal enlargement, excessive lipid deposits, and electrolyte abnormalities.
This condition can be either from an intrinsic disease or iatrogenic from steroid administration. Stabilization of the disease
state should be done prior to any anesthesia for routine or elective procedures. Many of these patients can be hypertensive
as well due to increased systemic vascular resistance. The can put an additional stress on the heart that may already have
weakened cardiac muscle. Complications can include difficult catheterization, fluid retention, excessive bleeding, pulmonary
thromboembolism, and ineffectual ventilation.
Patients with hypoadrenocorticism can have physiologic abnormalities including bradycardia, dehydration, collapse, PU/PD,
weight loss, weakness, lethargy, and shock. Stabilization of these patients with intravenous fluid and electrolyte therapy
and replacement steroid therapy can be easily achieved and these patients respond quickly to treatment. In most of these
patients, additional doses of glucocorticoids, for the stress of anesthesia and surgery, are warranted even if the patients
are well regulated.
Diabetic patients present to the veterinarian for anesthesia for procedures often unrelated to glucose disorders. However,
as the prevalence of obesity continues to increase in our population of patients, the prevalence of glucose disorders will
also increase. It is therefore essential that veterinarians be able to safely anesthetize these patients. Well controlled
patients are usually uncomplicated to get back on their regular insulin and eating schedule. Poorly or uncontrolled patients
can be very difficult and should be regulated prior to anesthesia, especially where the anesthesia can be delayed. There
are various protocols available for the administration of feed and insulin on the day of the anesthetic event that can be
used successfully. It is probably more important that diabetic patients are anesthetized early in the morning to limit the
fasting period and allow for the remainder of the day to be recovered and reregulated.
Unlike simple diabetics, patients with diabetic ketoacidosis are very poor anesthetic candidates and have high complication
and mortality rates. These patients are severely dehydrated, hypovolemic, acidotic and have electrolyte abnormalities. They
are also often extremely hyperglycemic as well that can result in hyperosmolarity. Animal that are positive for urine or
blood ketones should not be anesthetized unless it is for a life saving procedure. Even then, if at all possible stabilization
with large volumes of intravenous fluids and insulin should be performed to correct hypovolemia and bring blood glucose levels
to less than 300 mg/dL. Repeated monitoring of glucose should be performed to dictate therapy preventing wide swings in glucose.
Hyperthyroidism is usually seen in older cats and can be accompanied by behavioral changed such as hyperactivity, nervousness,
and aggression. These patients may also have dyspnea and become easily stressed when handled or restrained. In cats that
have conditions secondary to hyperthyroidism such as hypertrophic cardiomyopathy and renal disease, anesthetic care can becomes
extremely difficult. These patients are often in a fragile state and can progress to cardiac arrhythmias and heart failure
when overly stressed, sometimes resulting in death. Preanesthetic medical therapy is advised to stabilize patients prior
to elective procedures. Anesthetic protocols are based around opioids and drugs that can increase heart or precipitate arrhythmias
such as atropine and ketamine should be avoided. Fluid and electrolyte therapy is also recommended throughout the peri-anesthetic
Canine hypothyroidism is usually slow in onset and has minimal impact on anesthetic concerns compared to other endocrine diseases.
These patients can be obese and have signs consistent with a decreased metabolic rate. Bradycardia, hypotension, decreased
stroke volume, decreased drug metabolism, and hypothermia are common concerns. Many of these concerns can be alleviated with
thyroid hormone supplementation and regulation of the condition is recommended prior to elective procedures.
Anesthesia for patients with a pheochromocytoma can be one of the most challenging for the veterinarian. Excessive catecholamine
put these patients at risk for wide swings in heart rate and cardiac output as well as blood pressure. These patients are
extremely unstable and can have cardiac arrest at any time. Preoperative stabilization for a minimum of two weeks with phenoxybenzamine
can help reduce hypertension and restore circulating blood volume. The use of beta blockers such as propanolol to reduce
tachycardia can be administered as well. It is critical that beta blockers are not administered until after a minimum of
one week of phenoxybenzamine administration. Administration of beta blockers without prior alpha blockade with phenoxybenzamine
can result in worsening of hypertension. Fluid and electrolyte therapy should be performed prior to anesthesia as well to
ensure a proper circulating volume. During surgery, complications from catecholamine release from tumor manipulation can
be managed with administration of nitroprusside for hypertension and esmolol for tachyarrhytmias.