Calcium Hemostasis

Question 1

Causes of post-thyroidectomy hypocalcemia?

How calcium is transported in the blood?

Hormones involved in Ca +2 homeostasis?

Physiologic role of calcium in the body?

Answer 1

• Removal of parathyroid glands
• Ischemia of parathyroid glands

• 50% unbound and ionized
• 45% bound to plasma proteins
• 5% is associated with anions such as citrate and lactate

Hormones involved in Ca +2 homeostasis?
“Calcium homeostasis is mainly regulated by three hormones — parathyroid hormone (PTH), vitamin D₃ (calcitriol), and calcitonin.”

1. Parathyroid hormone (PTH):
   • Bone: Stimulates osteoclastic activity → releases calcium and phosphate into blood.
   • Kidney: Increases calcium reabsorption, increases phosphate excretion, and activates 1-α-hydroxylase → increases calcitriol formation.
   • Net effect: Increases serum calcium.
2. Vitamin D₃ (Calcitriol):
   • Gut: Increases absorption of calcium and phosphate.
   • Bone: Promotes mineralization by stimulating osteoblastic activity.
   • Kidney: Increases reabsorption of calcium and phosphate.
   • Net effect: Raises calcium and phosphate levels.
3. Calcitonin:
   • Bone: Inhibits osteoclastic activity → decreases bone resorption.
   • Kidney: Increases excretion of calcium and phosphate.
   • Net effect: Lowers serum calcium.

• Physiologic processes o Neuromuscular transmission o Smooth and skeletal muscle contraction o Cardiac automaticity o Nerve function o Cell division and movement o Certain oxidative processes
• Co-factor for many steps during blood coagulation
• Involved in the action of other intracellular messengers, e.g. CAMP, and thus mediates the cellular response to numerous hormones, including epinephrine, glucagon, ADH, secretin.
• Calcium binding proteins e.g. troponin, calmodulin
• Mineralization of bone

Question 2

Q: Why this patient may have abdominal pain?

Q: How CKD cause 2ndry hyperparathyroidism?

How is vitamin D formed

Answer 2

As complication of hypercalcemia:
- peptic ulcer
- Renal stones
- Acute pancreatitis

• Due to hypocalcemia induced by phosphate retention
  and reduced Vitamin D synthesis as consequence of
  reduced renal function

Vitamin D metabolism occurs in three main steps — in the skin, liver, and kidney.”

1. Skin:
   7-dehydrocholesterol → (by UV light) → Previtamin D₃, which is converted to Vitamin D₃ (cholecalciferol).
2. Liver:
   Vitamin D₃ → (by 25-hydroxylase) → 25-hydroxycholecalciferol (calcidiol).
3. Kidney:
   Calcidiol → (by 1α-hydroxylase) → 1,25-dihydroxycholecalciferol (calcitriol) — the active form.
   Alternatively, 24-hydroxylase forms 24,25-dihydroxycholecalciferol, an inactive metabolite.

Question 3

Signs of hypocalcemia
ECG changes in hyper and hypocalcemia
How to treat tetany

Answer 3

• Neurological: irritability manifest as peripheral and circumoral paresthesiae
• Muscular: cramps
• Tetany: spasms
• Chvostek’s sign: twitching of the facial muscles on tapping of the facial nerve anterior to the tragus
• Trousseau’s sign: tetanic spasm of the hand upon tapping the median nerve following blood pressure cuff-induced arm ischemia

“Calcium mainly affects the QT interval on ECG.”

👉 Hypercalcemia:
• QT interval shortens due to shortened ST segment.
• In severe cases: widened T wave, possible arrhythmias.

👉 Hypocalcemia:
• QT interval prolongs due to prolonged ST segment.
• May lead to T wave changes and risk of torsades de pointes.

• IV calcium replacement: 10m 10% calcium gluconate in 50ml of D5 or NS given over 10min (90 mg of elemental calcium per 10 mL) with ECG monitoring, repeat till patient is asymptomatic.
  Followed by calcium gluconate infusion – dilute 100ml of 10% calcium gulconate in 1L of NS and infuse at 50ml/h, titrate to achieve normocalcaemia.
  Concurrent hypomagnesemia: 2g of 10% magnesium sulphate over 10-20min