The hypercalcemia questions in the CICM fellowhsip exam are numerous, and largely focused on the treatment strategies available. Only the question from 2000 went indepth into the investigations of it, and in 2011 some detail about the mechanism of malignancy-associated hypercalcemia was expected.
Oh's manual only dedicates two short paragraph to this electrolyte disturbance. The LITFL page is an excellent replacement. If one has all the time in the world, one may also wish to explore the world literature, which is best represented by Carroll et al (2003) and the more detailed Shane et al (1999).
Primary endocrine causes
Random miscellaneous causes
*Yes, rhabdomyolysis is usually associated with hypocalcemia initially. However later in the evolution of the AKI there is hypercalcemia. This paper by Shane and Irani (2006) lists it as one of the causes in their table 2 on page 177. Looking deeper into it, one can find that this happens because sequestered calcium is released from the complexes which had formed in the injured muscle, during the convalescent phase of trauma.
It is also possible (perhaps, desirable) to organise the causes of hypercalcemia according to the tests which end up being abnormal. Classically, this is done by separating them into PTH-related and PTH-unrelated causes.
With raised PTH-related-protein:
With raised 25-hydroxyvitamin D levels
With lytic bone lesions, and normal PTHrp/Vit D
With raised 1,25-dihydroxyvitamin D levels
Random miscellaneous causes without malignancy or Vit D disturbances
In brief, in the exam one should write something about the following classical features:
Early manifestations (levels < 3.5mmol/L)
Late manifestations (levels over 3.5mmol/L)
If one has the appetite for detail, Table 1 from Shane et al (1999) offers an abundance of it. It has been reproduced below, with some omissions which the author thought were reasonable (for instance, "cardiac arrest" and "death" were omitted from the list of cardiovascular manifestations).
Causes such as renal failure and prolonged immobility can usually be ruled out (or in) immediately after meeting the patient. Similarly, one can easily look at their drugs and see whether something iatrogenic is responsible. Then, one is left with primary endocrine disturbances and malignancy.
Thus, one may wish to launch the following investigations:
For some reason, the college keeps asking about this; probably because it involves a formula for the trainees to memorise. This issue has come up in Question 14.2 from the first paper of 2009, and again in Question 9.2 from the first paper of 2019. Essentially, one was offered a hypercalcemic patient with a marginally elevated calcium and a severely depressed albumin (say, 15). What is the corrected calcium, the questions asked.
The correction formula was first described by Payne et al in 1973. It is a mathematical workaround from an era when calcium ion-selective electrodes were not widely available; it calculates the calcium level your patient would have if their albumin were normal, so you can decide whether their ionised calcium might be high.
Corrected calcium = (0.02 × (normal albumin - patient's albumin)) + serum calcium
This gives you a calcium value which - in a hypoalbuminaemic patient - is higher than the actual measured calcium. What the value says, in effect is that the patient is even more hypercalcemic than you think. This refers to the fact that the fraction of ionised calcium - the only biologically active form - would be higher in patients with low albumin levels, for any total calcium value.
What is thge point of this? Well. This is an anachronism from an era (the 1970s) when there were few calcium-sensing electrodes around, and the total calcium was the only available value. The physicians in those days would have relied on this formula to identify patients who were at risk of developing symptoms of hypercalcemia while having total calcium values which were still within the upper range of normal. These days, every ICU tends to have a blood gas analyser which reports ionised calcium values, and so there really is no point in looking at the corrected calcium value in any real clinical situation. Thus, in the modern era the only remaining purpose of the corrected calcium equation is to torture CICM Fellowship exam candidates.
The management of hypercalcemia follows a stepwise pattern, progressing from mild inoffensive interventions to invasive and dangerous methods. This chapter focuses on the management of the numerical calcium abnormality, because after all its all about the numbers. Particularly, numbers like 3.5mmol/L and other numbers of greater magnitude. Though the pursuit of numerical normality may seem meaningless to the non-critical-care physician population, the number representing calcium concentration does in fact have certain physiological correlations- such as coma and death- and so perhaps there is perhaps some value in paying attention to this isolated numerical abnormality.
In brief, these are the physiological aims for management of hypercalcemia, and the means to achieve them:
Dehydration could be contributing - perhaps not to the genesis of the hypercalcemia, but at least to its maintenance. The restoration of intravascular volume will bring about better renal perfusion, and with it perhaps some sort of tubular sanity. Calcium should start to be excreted. This intervention is cheap, largely harmless, and the results should be seen within hours.
If one is convinced that the source of the extra calcium is bone (which is usually the case - where else would it come from) then the inhibition of osteoclast activity is a sensible response. Locally, pamidronate infusion is used, and a protocol exists whereby a dose is calculated according to the magnitude of hypercalcemia. A range of 30-90mg is administered. This is not an intervention which favours immediate gratification - up to 3 days may pass before a meaningful decrease in calcium levels is observed.