Normal parathyroid hormone responses to hypocalcemia during cardiopulmonary bypass

• Published in: Anesthesiology (Philadelphia) 1991-07, Vol.75 (1), p.43-48
• Main Authors: ROBERTIE, P. G, BUTTERWORTH, J. F, ROYSTER, R. L, PRIELIPP, R. C, DUDAS, L, WARD BLACK, K, COLE, L. R, ZALOGA, G. P
• Format: Article
• Language: English
• Subjects: Anesthesia; Anesthesia depending on type of surgery; Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy; Biological and medical sciences; Calcitriol - blood; Cardiopulmonary Bypass; Humans; Hypocalcemia - metabolism; Magnesium - blood; Magnesium Sulfate - administration & dosage; Magnesium Sulfate - metabolism; Medical sciences; Parathyroid Hormone - blood; Radioimmunoassay; Thoracic and cardiovascular surgery. Cardiopulmonary bypass
• ISSN: 0003-3022; 1528-1175
• DOI: 10.1097/00000542-199107000-00008

To determine whether the calcium-magnesium-parathyroid hormone-calcitriol (vitamin D) axis responds appropriately to the hypocalcemia that routinely follows initiation of cardiopulmonary bypass (CPB), we measured blood ionized calcium (CaI), total calcium (CaT), total magnesium (MgT), ultrafilterable magnesium (MgI), total protein, intact parathyroid hormone (PTH), and calcitriol concentrations at eight defined time points in 28 patients undergoing elective cardiac surgery. With the onset of CPB, CaI decreased from 1.14 +/- 0.02 to 0.91 +/- 0.03 mM, P less than 0.05) (n = 17), and then gradually returned to a normal value by the time of separation from CPB (0.98 +/- 0.01 mM). CaT, MgI, MgT, and total protein concentrations declined significantly upon initiation of CPB and remained depressed thereafter. PTH initially decreased upon initiation of CPB (from 50 +/- 8 to 24 +/- 9 pg/ml, n = 9, P less than 0.05), remained inappropriately decreased during the early phases of CPB, and then gradually increased to maximal concentrations in response to hypocalcemia (103 +/- 15 pg/ml) before emergence. Calcitriol concentrations (n = 8) were unchanged during surgery. Based on these initial results, which suggested an association between hypomagnesemia and the slow PTH response to hypocalcemia, measurements were repeated in 10 additional patients, to whom magnesium (Mg) (1 g MgSO4 in two separate intravenous doses) was administered. Mg administration neither altered the PTH response to ionized hypocalcemia nor hastened the return of CaI to normal.