Introduction #
Anesthetizing dogs with Addison’s disease (hypoadrenocorticism) requires special considerations due to their impaired ability to produce glucocorticoids and mineralocorticoids. This condition affects the adrenal glands’ ability to respond to stress, making anesthetic events particularly challenging. Careful pre-anesthetic assessment, medication management, and vigilant monitoring are essential to minimize risks and complications.
Pathophysiology Overview #
Addison’s disease results from insufficient production of mineralocorticoids (aldosterone) and glucocorticoids (cortisol) by the adrenal cortex. These hormones are crucial for maintaining electrolyte balance, blood pressure, glucose metabolism, and stress response. Without appropriate hormone supplementation, anesthetic procedures can trigger an Addisonian crisis, a potentially life-threatening condition.
Common Bloodwork Abnormalities #
Typical laboratory findings in Addisonian dogs (particularly before instituting medical management) include:
Electrolyte imbalances are hallmark findings, particularly a sodium:potassium ratio below 27:1. Specifically, hyponatremia (decreased sodium) and hyperkalemia (elevated potassium) are common. Severe hyperkalemia can lead to cardiac arrhythmias and decreased cardiac contractility.
Metabolic acidosis often develops secondary to impaired hydrogen ion excretion. Mild hypercalcemia may be present in approximately 30% of cases. Azotemia (elevated BUN and creatinine) frequently occurs due to decreased renal perfusion. Pre-renal azotemia is common as reduced aldosterone leads to sodium and water loss.
Mild, non-regenerative anemia may be observed due to decreased erythropoiesis and gastrointestinal blood loss. Eosinophilia and lymphocytosis can be present due to lack of cortisol’s suppressive effects on the immune system. Hypoglycemia occasionally occurs due to impaired gluconeogenesis and glycogenolysis in the absence of cortisol.
Clinical Signs Relevant to Anesthesia #
Dogs with poorly controlled Addison’s disease may present with several concerning clinical signs:
Lethargy, weakness, and collapse can occur, especially during stress. Gastrointestinal signs including vomiting, diarrhea, and decreased appetite are common. Cardiovascular abnormalities include weak pulses, hypotension, and bradycardia. Dehydration is frequently observed due to sodium and water loss. Hypothermia may develop, particularly during anesthesia.
Addisonian crisis manifests as severe lethargy, weakness, collapse, vomiting, diarrhea, hypothermia, bradycardia, weak pulses, and shock. Without prompt treatment, this can be fatal.
Pre-anesthetic Considerations #
Before anesthesia, several steps should be taken:
Comprehensive bloodwork should include a complete blood count, serum biochemistry, and electrolyte levels. Correct electrolyte abnormalities, particularly hyperkalemia and hyponatremia, prior to anesthesia. Fluid therapy with 0.9% NaCl (normal saline) is typically recommended to correct dehydration and electrolyte imbalances, although in well regulated individuals other crystalloids such as LRS and Normosol-R have been successfully used.
Supplemental glucocorticoids should be administered. For non-emergency procedures, oral maintenance (physiologic dose) prednisolone can be doubled for 1 day before and 1-2 days after the procedure. For emergency procedures, intravenous dexamethasone sodium phosphate (0.1-0.2 mg/kg) is preferred, as it doesn’t interfere with ACTH stimulation testing if needed.
If the patient is receiving ongoing mineralocorticoid supplementation (such as DOCP or fludrocortisone), ensure they’ve received their regular dose. Correct hypoglycemia if present with dextrose supplementation.
Anesthetic Protocol Recommendations #
In well managed cases many anesthetic protocols are reasonable. Avoiding alpha-2 agonists may be prudent due to their inhibition of the stress response.
Intraoperative Monitoring #
During anesthesia, monitoring is warrented:
Continuous ECG monitoring is essential to detect arrhythmias associated with hyperkalemia. Blood pressure should be monitored frequently due to increased risk of hypotension. Regular assessment of body temperature is necessary as hypothermia is common. Fluid therapy should continue throughout the procedure, typically with 0.9% NaCl or balanced electrolyte solutions containing potassium (e.g., Lactated Ringer’s) if medical management has been successful.
Postoperative Complications #
Common postoperative complications include:
Persistent or recurring hypotension may require adjustments to fluid therapy or vasopressor support. Electrolyte abnormalities, particularly hyperkalemia, can recur and require ongoing management. Hypoglycemia may develop, especially after longer procedures.
Immediate Postoperative Management #
Careful management in the immediate postoperative period includes:
Continue glucocorticoid supplementation, typically prednisolone or dexamethasone. Maintain intravenous fluid therapy until the patient is stable and eating. Monitor electrolytes, especially potassium and sodium, regularly in the postoperative period if recovery is prolonged.
Conclusion #
Successful anesthesia in dogs with Addison’s disease requires thorough preparation, appropriate medication selection, diligent monitoring, and careful postoperative care. Understanding the pathophysiology of the disease and anticipating potential complications allows for the development of an individualized anesthetic plan that minimizes risks and promotes a smooth recovery. With proper management, most Addisonian dogs can safely undergo anesthesia and surgical procedures.
