B. M. Launer1, R. McIntyre1, L. J. Helmkamp1, C. D. Raeburn1, M. B. Albuja-Cruz1 1University of Colorado School of Medicine,GI, Tumor And Endocrine Surgery,Aurora, CO, USA
Introduction
Hypocalcemia is a frequent complication of thyroidectomy. Magnesium (Mg) and calcium metabolism are closely related. There is a paucity of studies evaluating the role of preoperative and postoperative Mg levels in post- thyroidectomy hypocalcemia.
Methods
Retrospective review of prospectively collected data of 389 patients who underwent thyroidectomy. We followed a standard protocol to manage hypocalcemia. Calcium, albumin, PTH and magnesium levels were checked immediately after surgery. Patients were stratified into 3 categories: high, intermediate, and low risk of hypocalcemia. High risk patients were started on oral calcitriol and calcium. Intermediate risk patients were given only oral calcium and low risk received no supplementation. Hypocalcemia was defined as corrected calcium level (CCL) < 8 mg/dl. Severe hypocalcemia was defined as a CCL < 7 mg/dl. Hypocalcemia event was defined as an episode of hypocalcemia at any point after the operation. Symptomatic hypocalcemia was defined as CCL <8 mg/dl plus symptoms of hypocalcemia. Hypomagnesemia was defined as Mg level <1.7mg/dl. Patients with and without hypomagnesemia preoperatively and immediately postoperatively were compared. Data were analyzed for demographics, operative procedure, calcium levels, PTH levels and complications of hypocalcemia.
Results
Seventy-eight patients (23%) had preoperative hypomagnesemia and 106 patients (37%) had postoperative hypomagnesemia. There was no difference in biochemical or symptomatic hypocalcemia, severity of symptoms of hypocalcemia, need for IV calcium, emergency department (ED) visits, readmissions, and permanent hypocalcemia between normal preoperative Mg and low preoperative Mg groups. Patients with low postoperative Mg levels had a significant higher risk of hypocalcemia (28% vs. 16%, p 0.007). Patients with low postoperative Mg levels also had a significantly higher rate of requiring I.V calcium (9% vs. 3%, p 0.023) based on our protocol. However, there was no difference between these two groups in regards to symptomatic hypocalcemia, severity of hypocalcemia, severity of symptoms of hypocalcemia, ED visits, readmissions, or permanent hypocalcemia. On multivariate analysis, postoperative hypomagnesemia was an independent predictor of hypocalcemia with 1.71 risk ratio (1.09, 2.68; 95% CI).
Conclusion
Postoperative hypomagnesemia is seen in more than one third of patients after thyroidectomy and it is associated with a significantly higher risk of hypocalcemia and need for I.V calcium. The risk of hypocalcemia is doubled for those patients with immediate postoperative hypomagnesemia. Therefore, postoperative Mg levels should be closely monitored and replaced as necessary in patients after thyroidectomy.