[Severe hypercalcemia in intensive care medicine]

Hypercalcemic crisis is a rare but life-threatening complication of severe hypercalcemia. In most cases (> 90%), primary hyperparathyroidism or malignancy are the causes of a hypercalcemic crisis. Prodromes are often nonspecific and can present as nausea, vomiting, or a lack of concentration. The transition from hypercalcemia to a hypercalcemic crisis is often caused by a dysregulated volume status. As rapid treatment is essential, differential diagnostics should not delay treatment. In the human body, there is a complex system that keeps the extracellular calcium concentration within a narrow range (total calcium level: 2.1-2.5 mmol/L), whereby only about 50% of the total extracellular calcium is ionized and, therefore, biologically active. The remaining 50% is mostly bound to albumin and globulins. A hypercalcemic crisis is defined as a (albumin-corrected) total calcium over 3.5 mmol/L with accompanying severe symptoms. In addition to the measurement of the albumin-corrected total calcium concentration and ionized calcium, measuring the (intact) parathyroid hormone level is also crucial, as the causes of the hypercalcemic crisis can be roughly divided into parathyroid hormone (PTH)-dependent and PTH-independent causes. Initially, treatment is primarily symptomatic; in patients with a hypercalcemic crisis, the focus is on evaluation and appropriate emergency treatment according to the ABCDE scheme (e.g., securing the airway). At the same time, the calcium level should be lowered as quickly as possible in a controlled manner. Therefore, differentiated volume therapy is recommended. In addition, treatment with loop diuretics such as furosemide can be considered (after correcting hypovolemia). If therapy is not successful quickly or if there are contraindications to increased fluid administration (e.g., cardiac or renal insufficiency), the start of (calcium-free) dialysis is usually unavoidable. Calcitonin can be used to rapidly reduce calcium levels. Depending on the clinical cause of the severe hypercalcemia, cinacalcet, bisphosphonates, and denosumab are also drugs that can effectively reduce calcium levels within 2-3 days. The long-term prognosis depends on the underlying disease. A cohort of patients with primary hyperparathyroidism showed a 3-year survival rate of 80%.