Pediatric emergency medicine trisk 2869 2869
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though the dose must be retained for 15 to 30 minutes to be effective.
Kayexalate should not be provided to patients within 1 week of bowel
surgery due to risk of intestinal necrosis. In patients with normal renal
function, providing isotonic saline and loop diuretics may increase
potassium excretion. Isotonic expansion may be particularly effective in
patients who are hypovolemic with decreased effective renal perfusion. In
cases of hypovolemia, diuretics should only be provided once volume status
is restored to avoid prerenal insult. Thereafter, close monitoring of volume
status will allow appropriate adjustment of fluid rate and diuretic dosing. In
those patients with significantly impaired renal function, dialysis may be
indicated. Hemodialysis provides more rapid clearance of potassium,
though peritoneal dialysis may be more practical depending on the size of
the child, center preference, and comorbidities such as cardiovascular
instability or congenital heart disease.
DISORDERS OF CALCIUM HOMEOSTASIS
Goals of Treatment
Calcium is the most abundant cation in the body with approximately 99%
present in bone. Of the small fraction in the ECF compartment,
approximately half of the calcium is free or ionized, and it is this fraction
that exerts physiologic effect and is under physiologic regulation. Of note,
the fraction of calcium bound to plasma proteins is affected by the
extracellular pH. Acidemia causes hydrogen ions to displace calcium from
proteins and increases ionized calcium levels. Alkalemia will promote the
opposite effect.
Calcium homeostasis is dependent on endocrine control of three primary
organ systems: intestines, kidneys, and the skeletal system. The parathyroid
gland allows for the rapid regulation of ionized calcium concentration. Low
concentrations of ionized calcium stimulate parathyroid hormone (PTH)
secretion. PTH will increase serum calcium levels through mobilization of
calcium from the bone, increased calcium reabsorption in the distal renal
tubule, and stimulation of the conversion of 25-hydroxyvitamin D to 1,25dihydroxyvitamin D, the active metabolite of vitamin D. 1,25Dihydroxyvitamin D promotes calcium and phosphorus absorption from the
