The daily replacement dose of cortisol is approximately 5 to 7.5 mg of prednisone. Suppression of the hypothalamic–pituitary–adrenal (HPA) axis by exogenous steroids for more than a few weeks may produce relative adrenal insufficiency. When systemic steroids are used for longer periods, adrenal insufficiency may persist for up to 1 year. Short courses of low-dose oral steroids (<5mgof prednisone in a single morning dose for any duration of time, alternate-day dosing of short-acting glucocorticoids, and any dose of corticosteroids given for less than 3 weeks) are not thought to cause clinically significant suppression of the HPA axis (151,172). Use of inhaled corticosteroids of over 0.8 mg per day or class I topical glucocorticoids of 2 g per day or more may cause suppression (172).
Table 22.13 Guidelines for Adrenal Supplementation Therapya
IV, intravenously. aPatients receiving 5 mg/d or less of prednisone should receive their normal daily replacement but do not require supplementation. Patients who receive greater than 5 mg/d of prednisone should receive the above therapy in addition to their maintenance therapy. Reprinted from Coursin DB, Wood KE. Corticosteroid supplementation for adrenal insufficiency. JAMA 2002;287:236–240, with permission.
If either the dose or duration of glucocorticoid administration exceeds the preceding regimen, biochemical tests are recommended to preoperatively evaluate the function of the adrenal gland. The easiest and safest test to assess HPA function is the cosyntropin stimulation test. Cosyntropin, a synthetic analogue of adrenocorticotropic hormone, is given in a dose of 250 μg intravenously, and a blood sample is collected 30 minutes after the injection and assayed for plasma cortisol. A plasma cortisol value of greater than 18 to 20 μg/dL indicates adequate adrenal function (151,154). If the history regarding exogenous steroid use is unclear, the cosyntropin stimulation test should be considered as a preoperative test to determine whether the patient will need perioperative glucocorticoid coverage. The amount of glucocorticoid replacement should be equivalent to the normal physiologic response to surgical stress (Table 22.13) (173).
For minor surgical stress, such as colonoscopy, the glucocorticoid target is approximately 25 mg of hydrocortisone equivalent on the day of the procedure (173). For moderate surgical stress, for example, open cholecystectomy, the glucocorticoid target is 50 to 75 mg of hydrocortisone equivalent on the day of the procedure and tapered quickly for 1 to 2 days (173). The patient should receive her normal daily dose preoperatively, followed by 50 mg of hydrocortisone intravenously administered intraoperatively. For major surgical stress, such as liver resection, the glucocorticoid target range is 100 to 150 mg hydrocortisone equivalent on the day of the procedure, tapering rapidly over the next 1 to 2 days to the usual dosage (173). The patient should receive her normal daily dose preoperatively.