Circulating ionized calcium and parathyroid hormone levels following coronary artery by-pass surgery

In critically ill patients, hypocalcaemia is a common finding. Also variabl e derangements in the normally tight Ca2+-mediated control of the parathyro id hormone (PTH) secretion have been found. Utilizing coronary artery by-pa ss grafting (CABG) as a standardized model of severe trauma, 18 patients un derwent determinations of blood levels of calcium, magnesium (Mg), ionized calcium (Ca2+), serum levels of intact PTH, procalcitonin (PCT) and the pro inflammatory cytokines tumour necrosis factor alpha (TNF-alpha) and interle ukin-6 (IL-6). Samples were collected before, directly after, the morning a fter and 5 days after surgery. A significant, but minor, decrease in blood Ca2+ levels (mean 0.04 mmol/L, p<0.05) was seen shortly after CABG, not acc ompanied by any significant change of serum PTH levels. This alteration of the Ca2+ control of the steady-state PTH levels contrasted with the mainten ance of the PTH secretory response to a sequential citrate and calcium infu sion (CiCa clamp), which was normal in two patients evaluated in the mornin g following surgery. Serum Mg levels were transiently increased after opera tion (+0.25 mmol/L, p<0.001) and correlated to the TNF-alpha (r = 0.62, p<0 .01) and PCT (r = 0.67, p<0.006) levels in the morning after surgery. Serum levels of IL-6 and TNF-alpha were significantly (p<0.0001) increased immed iately after surgery, while the peak in serum PCT levels (p<0.001) occurred in the morning after CABG. Serum PTH levels correlated positively with IL- 6 (r = 0.68, p<0.008) 5 days after surgery. In conclusion, CABG caused a de crease in ionized calcium levels without a rise in steady-state PTH levels, but rapid changes in Ca2+ during CiCa clamping revealed a normal PTH secre tory response. These findings might relate to elevated serum Mg levels, whi le a direct action of TNF-alpha or IL-6 on the PTH release seem less possib le.