In this episode, I’ll discuss the dose–response of intravenous calcium in surgical ICU patients.
How much does the ionized calcium value of a patient with hypocalcemia change when given a replacement dose of IV calcium? A group of authors published a retrospective cohort study in the International Journal of Clinical Pharmacy in an attempt to answer this question.
The authors looked at almost 200 patients who were admitted to the surgical ICU of a single center and given IV calcium in response to hypocalcemia. Patients were evaluated to determine the association between IV calcium dose and subsequent change in ionized calcium level.
Linear regression was used and confounders were controlled for as best as possible before a model was produced.
After controlling for confounders, the authors found that the initial calcium level, the calcium dose, the patient’s age, and whether or not the patient had a diagnosis of pancreatitis were the factors that belonged in the model to predict the change in ionized calcium after replacement.
The model was then reduced into this equation: Change in iCa level = 0.462 − 0.011 × [Ca dose] − 0.0007×[Age] − 0.259×[Initial iCa] + 0.076×[initial iCa × Ca dose] − 0.076×[Pancreatitis].
This model was able to explain 76.9% of the response to a dose of calcium.
The authors then went further and looked at a simplified model that only considered baseline ionized calcium and calcium dose given.
The simplified model uses the following equation: Change in iCa level = 0.335 − 0.013 × [Ca dose − 0.247 × [Initial iCa] + 0.082×[initial iCa×Ca dose].
This simplified model was able to explain 75.6% of the response to a dose of calcium using 2 fewer variables.
It should be noted that the amount of calcium in the formula was converted to the equivalent in grams of calcium gluconate. This means if a patient received 1 gram of calcium chloride it was looked at as receiving 2.92 grams of calcium gluconate for the purposes of modeling the data for the formula.
The authors emphasize that their data suggests if a patient has significant hypocalcemia and requires IV replacement, a dose of only 1g of calcium gluconate is unlikely to normalize a patient’s ionized calcium.
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