Endocrine Abstracts

A 56 year old man with history of Hypertension, “Pre-diabetes” and Osteoarthritis was noted to have a low morning Cortisol of 31 nmol/l at 0912 hrs and <28 nmol/l at 0741 hrs on the first and 4th postoperative days respectively following a left total knee replacement. His regular medications were Amlodipine 5mg OD, Ramipril 5mg OD, Bisoprolol 3.75mg OD, Atorvastatin 20mg HS, Gabapentin 100mg TDS. Post operatively he was also given Zomorph 10mg BD with Oramorph PRN for pain control and Low Molecular Weight Heparin for Venous Thromboembolism prophylaxis. The patient did not receive any steroids peri operatively. Intra operatively blood pressure was consistently around 120/70 mmHg. Apart from an intra articular steroid injection 2 years before, he was not taking any steroid in any form. He reported no sickness/vomiting/dizziness. His postoperative pain was under control with opioids. On examination pulse was 63/mt, regular, BP 125/70mmHg (receiving his usual anti hypertension medications), Temperature 36.7 C, no altered pigmentation noted, capillary blood glucose was 5.8 mmol/l. Laboratory investigations showed Sodium 135 mmol/l (133-146), Potassium 4.4 mmol/l (3.5-5.3), Urea 5 mmol/l (1.7-7.1), Creatinine 74 umol/l (59-104). Without any steroid replacement, a stimulation test with Tetracosactide 250 microgram (Short Synacthen® Test) was done on 5th postoperative day (in the evening) which showed normal adrenal response-- 0 minute Cortisol 30 nmol/l, 30 minutes (post Tetracosactide) Cortisol 465 nmol/l. Adrenocorticotropic Hormone(ACTH) level was 6 ng/l (normal <47). Though a very low 9 am Cortisol would suggest hypocortisolism (in those not taking any steroids) and warrant immediate steroid replacement, the fact that the patient had an uneventful major surgery made us to look for another explanation. The normal adrenal response to the stimulation with Tetracosactide reassured us that we were not dealing with hypocortisolism. Most probably the Gabapentin was suppressing the stress response in our patient. Significant reduction in the plasma cortisol level have been noted in patients given Gabapentin one hour before surgery¹. The likely explanation why the first morning Cortisol checked is that it was probably incorrectly requested or tested (The Cortisol printed just above the Full Blood Count in the Blood Sciences paper request form in our Trust, now replaced with electronic requests). The patient was reassured and discharged. Reference1. Gabapentin-induced changes of plasma cortisol level and immune status in hysterectomized women; December 2014; International Immunopharmacology 23(2):530-6