The impact of operative duration and intraoperative fluid dynamics on postoperative hypocalcemia after total thyroidectomy: a prospective non-randomized study

Background Postoperative hypocalcemia after total thyroidectomy (TT) still remains common. This prospective observation study examined the role of intraoperative time period (IOP) and intravenous fluids (IVF) in transient and permanent (> 6 months) hypocalcemia post-TT. Subjects and method Consecutive patients (n = 328; age = median (IQR); 34 (15) years; M:F = 65:263) with benign or malignant thyroid disease undergoing TT were evaluated for IOP, intraoperative IVF, serum corrected calcium, intact parathormone (iPTH), and 25-hydroxyvitamin D (25OHD) levels at baseline, 48 h, and 6 months post-TT. Results The incidence of symptomatic transient and permanent hypocalcemia post-TT was 33.5% and 7.9% respectively. In multivariate logistic regression analysis, the independent risk factors for transient hypocalcemia were IOP (odds ratio: 11.6), 48-h iPTH (4.8), IVF (2.9), hyperthyroidism (2.8), and percent calcium decline (1.07), while 25OHD deficiency increased the risk by 10.5 odds in subset with preoperative hypocalcemia. In receiver operating characteristic analysis, IOP, and IVF strongly predicted transient hypocalcemia with a threshold of 123 min and 1085 mL. Area under the curve, sensitivity, and specificity were 0.883 (95% CI: 0.838-0.928), 88.1%, and 74.4% and 0.883 (0.840-0.926; each P = 0.001), 84.4%, and 74.4% respectively. Serum 48-h calcium Conclusion Operative duration > 123 min and IVF > 1085 mL increased the risk of transient hypocalcemia post-TT manyfold but not permanent hypocalcemia. Routine intraoperative identification, preservation of viable in situ parathyroid glands, and laryngeal nerves increased IOP and rates of transient hypocalcemia but improved long-term outcome.