When should hydrocortisone be administered to treat presumed adrenal insufficiency? What is the dose of hydrocortisone?

• hypotension out of proportion to the severity of illness
• other clinical features suggestive of primary adrenal insufficiency (where hemodynamic collapse is most prominent secondary to both cortisol and aldosterone depletion) include hyperkalemia, hyponatremia, non-anion gap acidosis, hyperpigmentation and hypoglycemia. 

Hydrocortisone dose is 100 mg IV for adults and 1 - 3 mg/kg IV for children.

Source 

Burgess, B. and Roe, J.  "Adrenal Insufficiency"  Critical Decisions in Emergency Medicine.  July 2012.