The effect on blood pressure of an acute fall in ionized calcium during hemodialysis. A randomized study in two patients

Aim: Elevating serum ionized calcium levels is known to stabilize blood pressure during and after a hemodialysis session. The data on lowering calcium levels is limited. Subjects and methods: This study examined the responses to an acute drop in ionized calcium during a four hour hemodialysis session in two subjects who differed in the presence (patient 1) or absence (patient 2) of anti-hypertensive medication and average weight loss of 4 kg (patient 1) or 2 kgs (patient 2) with each dialysis. Parathyroid hormone (PTH) levels were normal (patient I) or very high (patient 2). A calcium free dialysate was used and the calcium infusion rate distal to the dialyzer was varied to produce either no change in ionized calcium for 10 dialyses, or a fall of at least 0.2 mmol/l for 10 dialyses. The sequence was randomized and was blinded to the observers and patients. Results: The fall in ionized calcium was similar in each individual, 0.37 +/- 0.11 and 0.34 +/- 0.05 mmol/l. PTH rose from 8.6 +/- 1.6 to 24.2 +/- 6.6 pmol/l for patient 1 and 144.6 +/- 59.9 to 234.8 +/- 32.3 pmol/l for patient 2: patient 1 showed a fall in blood pressure after dialysis associated with the fall in calcium. This was most pronounced in the upright position whereas there was no change for Patient 2. For Patient 1 standing mean blood pressure post-dialysis was 104 +/- 6 mmHg when the calcium was stable and 94 +/- 10 mmHg with hypocalcemia p < 0.01. Mean blood pressure during dialysis was also lower with hypocalcemia 100 +/- 7 versus 92 +/- 9 p < 0.05. There were no significant changes in blood pressure for patient 2. Neither of the patients had any symptoms attributable to hypotension or hypocalcemia. Conclusion: It was concluded that modest falls in ionized calcium were associated with a drop in standing blood pressure only when combined with other factors predisposing to vascular instability. Even so these decreases were small enough to be asymptomatic.