What is the timeline for the triphasic reaction after transsphenoidal surgery?

From the Guidelines

The triphasic reaction after transsphenoidal surgery typically occurs within 7-10 days, with the first phase lasting 24-48 hours, the second phase from days 3-7, and the third phase starting around day 7-10.

Phases of the Triphasic Reaction

• The first phase, or diuretic phase, is characterized by polyuria due to temporary suppression of ADH secretion from surgical manipulation of the posterior pituitary 1.
• The second phase, or antidiuretic phase, is marked by SIADH with water retention, hyponatremia, and concentrated urine as the injured posterior pituitary releases stored ADH.
• The third phase begins around day 7-10, when normal water homeostasis is restored as the hypothalamic-pituitary axis recovers.

Management of the Triphasic Reaction

Management includes careful fluid and electrolyte monitoring throughout all phases, with fluid replacement during the diuretic phase and fluid restriction during the antidiuretic phase 1.

• Fluid replacement during the diuretic phase often requires hypotonic fluids at 0.5-1 mL/kg/hr above urine output.
• Fluid restriction during the antidiuretic phase typically involves limiting fluid intake to 800-1000 mL/day.
• Serum sodium levels should be monitored at least twice daily during the first week, with more frequent monitoring if significant fluctuations occur.

Importance of Monitoring and Management

Close monitoring and management of fluid and electrolyte balance are crucial to prevent complications and ensure a smooth recovery 1.

• Patients should be managed in a setting where close observations can occur, and any concerns can be flagged and raised with an expert endocrinologist at an early stage.
• The risk factors for AVP deficiency or SIADH, such as female sex, cerebrospinal fluid leak, drain after surgery, invasion of the posterior pituitary by the tumour, or manipulation of the posterior pituitary during surgery, should be carefully considered when managing patients after transsphenoidal surgery.

From the Research

Triphasic Reaction after Transsphenoidal Surgery

• The triphasic reaction after transsphenoidal surgery typically involves an initial phase of diabetes insipidus, followed by a phase of hyponatremia, and finally a return to normal sodium levels 2, 3.
• The timeline for this reaction can vary, but hyponatremia typically occurs around 8-10 days after surgery 2, 3.
• Studies have shown that the frequency of hyponatremia after transsphenoidal surgery can range from 2% to 25% 2, and it is often associated with the syndrome of inappropriate antidiuretic hormone secretion (SIADH) 3, 4.
• The hyponatremia phase can last for several days, with serum sodium levels normalizing within 3.8 +/- 1.7 days 3.
• Factors that may contribute to the development of hyponatremia after transsphenoidal surgery include hypoadrenalism, water retention, and natriuresis 4.
• In some cases, hyponatremia can be a life-threatening complication, and patients should be screened for serum electrolytes after transsphenoidal surgery 3, 5.
• The incidence of diabetes insipidus and SIADH after transsphenoidal surgery can be significant, with one study reporting an incidence of 26% and 14%, respectively, in pediatric patients 6.