Evolution of blood magnesium and phosphorus ion levels following thyroidectomy and correlation with total calcium values

Abstract

CONTEXT AND OBJECTIVE: Magnesium ion concentration is directly related and phosphorus ion concentration is inversely related to calcemia. The aim of this study was to evaluate the evolution of magnesium and phosphorus ion levels in patients undergoing thyroidectomy and correlate these with changes to calcium concentration. DESIGN AND SETTING:Prospective study at the Alpha Institute of Gastroenterology, Hospital das Clínicas, Universidade Federal de Minas Gerais. METHODS:The study included 333 patients, of both genders and mean age 45 ± 15 years, who underwent thyroidectomy between 2000 and 2005.Total calcium, phosphorus and magnesium were measured in the blood preoperatively and 24 and 48 hours postoperatively. Ionic changes were evaluated according to the presence or absence of postoperative hypocalcemia.RESULTS: There were statistically significant drops in blood phosphorus levels 24 and 48 hours after thyroidectomy, compared with preoperative values, in the patients without hypocalcemia. In the patients who developed hypocalcemia, there was a significant drop in plasma phosphorus on the first postoperative day and an increase (also statistically significant) on the second day, in relation to preoperative phosphorus levels. A significant drop in postoperative magnesium was also observed on the first and second days after thyroidectomy in the patients with hypocalcemia, in relation to preoperative levels. In the patients without hypocalcemia, the drop in magnesium was significant on the first day, but there was no difference on the second day.CONCLUSION: Despite the postoperative changes, neither magnesium nor phosphorus ion levels had any role in post-thyroidectomy calcemia. RESUMO CONTEXTO E OBJETIVO:A concentração do íon magnésio está diretamente e a do íon fósforo inversamente relacionada à calcemia. O objetivo foi avaliar a evolução das concentrações dos íons magnésio e fósforo nos pacientes submetidos a tireoidectomia, e relacioná-los com as alterações da concentração do cálcio. TIPO DE ESTUDO E LOCAL: Estudo prospectivo realizado no Instituto Alfa de Gastroenterologia, Hospital das Clínicas, Universidade Federal de MinasGerais. MÉTODOS:O estudo incluiu 333 pacientes de ambos os sexos, com média de idade de 45 ± 15 anos, submetidos a tireoidectomia no período de 2000 a 2005. Cálcio total, fósforo e magnésio foram dosados no pré-operatório e com 24 e 48 horas de pós-operatório. As alterações dos íons foram avaliadas de acordo com a presença ou ausência de hipocalcemia pós-operatória. RESULTADOS:Houve queda estatisticamente significativa dos níveis sanguíneos de fósforo 24 horas e 48 horas após a tireoidectomia em relação ao pré-operatório nos pacientes que não tiveram hipocalcemia. Quanto aos pacientes que evoluíram com hipocalcemia, houve queda significativa do fósforo plasmático no primeiro dia de pós-operatório e elevação, também estatisticamente significativa, no segundo dia em relação ao fósforo pré-operatório. Foi também observada queda significativa do magnésio pós-operatório em relação ao p...

Perioperative magnesium levels in total thyroidectomy and relationship to hypocalcemia

“…In a previous paper, we reported hypomagnesemia (<0.7 mmol/L) to be a relatively common (12.9%) occurrence after thyroidectomy, and to be a strong predictor of post‐thyroidectomy hypocalcemia . Other authors have reported similar findings . In our previous paper, we examined the association between magnesium levels taken on the first postoperative day and incidence of biochemical and symptomatic hypocalcemia during the course of the 2‐night postoperative stay .…”

“…Hypocalcemic patients also showed a significant drop in magnesium levels on POD2 from preoperative values; however, this drop was not significant among patients not developing hypocalcemia. In this study, there was no analysis performed for association between hypomagnesemia and hypocalcemia, or correlation between magnesium and calcium levels …”

“…In this study, there was no analysis performed for association between hypomagnesemia and hypocalcemia, or correlation between magnesium and calcium levels. 15 Although reasons for the fall in calcium levels after thyroidectomy are well documented, reasons for a fall in magnesium levels is less clear. It is notable that there is significant variability in the reported incidence of postoperative hypomagnesemia, ranging from 10.1% 16 to as high as 72% 5 (12.9% in our previous study, using 0.7 mmol/L as cutoff 1 ).…”

“…1 Other authors have reported similar findings. 2,5,[13][14][15] In our previous paper, we examined the association between magnesium levels taken on the first postoperative day and incidence of biochemical and symptomatic hypocalcemia during the course of the 2-night postoperative stay. 1 Less is known, however, regarding the trend of magnesium levels after thyroidectomy, and the correlation of same with trends in calcium levels.…”

Serum phosphorus values for early prediction of hypocalcemia in total thyroidectomy

“…PTH controls intestinal and renal absorption and excretion of phosphorus. PTH acts directly on proximal tubules of nephron and reduce phosphorus reabsorption and increasing phosphaturia (2,3). The drop in serum phosphorus in response to PTH stimulation is earlier than increase in calcium.…”