Hypermagnesium

Electrolyte約 6 分鐘4 個章節

Data from Uptodate Symptoms of hypermagnesemia Causes and treatment of hypermagnesemia

0.血鎂單位換算與毒性階梯(考試速記)#

單位換算: 1.0 mM = 2.0 mEq/L = 2.43 mg/dL
毒性階梯
- 2.0-3.0 mM(4-6 mEq/L, 4.8-7.2 mg/dL): 噁心、臉部潮紅、嗜睡、DTR 減弱、低血壓
- 3.0-5.0 mM(6-10 mEq/L, 7.2-12 mg/dL): DTR 消失、PR/QRS/QT 延長、低血鈣、呼吸抑制
- >5.0 mM(>10 mEq/L, >12 mg/dL): 呼吸肌麻痺、完全房室傳導阻滯
- >6.0-7.5 mM(>12-15 mEq/L, >15 mg/dL): 心跳停止
解毒劑: 10% calcium gluconate 10-20 mL IV push 拮抗神經肌肉與心臟毒性

1.S/S(neuromuscular, CV, hypocalcemia)#

Neuromuscular
- ↓ impulse transmission across the NM junction
  - 影響muscles(含smooth muscles), CNS, autonomic nerves(甚至可fixed and dilated pupils due to 副交感神經blockage)
CV
- Mg是intracellular and extracellular calcium channel blocker→BV dilate、hypotension；補鎂避免併用CCB(回思hypomagnesium會↑intracellular Ca->HTN...)
- 另intracellular Mg會block心臟多種K+ channels(回思在腎臟Mg可block ROMK...)且與Na-K ATPase function相關(hypomagnesium會Na-K pump dysfunction)
- >2-2.5mM可hypotension, conduction blocks, bradycardia
- >2.5mM可EKG change(PR interval↑, QRS interval↑, QT interval↑(!!))
  - 怎麼和hypomagnesium一樣??, 不過uptodate真的這樣寫
  - 註:cCa>4也可T wave widening而↑QT interval !!
- >7.5mM可CAVB
Hypocalcemia
- 可↓PTH secretion(why?應該是因為激活CaSR of parathyroid), 甚至造成osteomalacic renal osteodystrophy and adynamic bone disease
  - 回思hypomagnesium也可造成PTH resistance↑(先) + PTH secretion↓(後)
    - 所以高(>2.5mM)低(<0.5mM)血鎂iPTH都↓-->hypocalcemia
- Activate renal CaSR-->loss Ca2+
Others
- Hyperkalemia
  - Case reports after administration of Mg in pregnant women; maybe due to inhibit renal ROMK???
  - 回思hypomagnesium會disinhibit ROMK
- ↑ Uremic pruritus in dialysis Pts(註:高鈣高磷也會)
  - But study showed no benefits of Mg free dialysate
<2mM
- 多no S/S
2-3mM
- ↓DTR, conscious change, drowsiness, nausea(因為ileus?), ileus, urinary retention, flushing, headache(因為BV dilate?), hypotension(因為BV dilate and ↓norepinephrine release), conduction block, bradycardia
3-5mM
- No DTR, somnolence, EKG change, hypocalcemia
>5mM
- Paralysis(including respiratory failure), CAVB, cardiac arrest(多asystole)
  - Respiratory failure 多precedes cardiac arrest

2.Etiologies#

GFR↓ + Mg loading
- GFR↓...
  - 註:ESRD者Mg level多1-1.5mM
- Mg loading
  - Dead Sea water poisoning(因為含高量Ca, Mg, 所以會hypercalcemia and hypermagnesium)
  - Mg infusion for preeclampsia, eclampsia
    - Magpie Trial (Lancet 2002; PMID 12057549)：子癇前症產婦使用硫酸鎂使子癇發作風險顯著降低 58%｜子癇發作率 0.8% vs 1.9%(p<0.0001)，惟須密切監測深層腱反射以防高血鎂毒性〔PMID 12057549〕
  - MgO, Nacid(=Al+Mg) for (laxatives or antacid), Mg enema(colon吸收Mg不少)
  - Hypercatabolic/tumor lysis syndrome
    - Mg release from cells
  - 註:Nexium oral form也是magnesium based, 所以poor renal function者吃nexium會看到SMg↑一些
Adrenal insufficiency
- Due to volume depletion and hemoconcentration
Familial hypocalciuric hypercalcemia(FHH)
- 見hypercalcemiahypercalcemia-Familial hypocalciuric hypercalcemia
Lithium intake
- Why?機轉類似FHH?
GI disorders(PUD, gastritis, colitis, GI obstruction...)等↑Mg吸收率
- 好像是唯一一個GI發炎卻可能會↑吸收的...
- 但若malabsorption, diarrhea則hypomagnesium

3.Tx#

If normal/near normal renal function
- DC Mg sources
- Hydration +/- loop diuretics/thiazide
  - Thiazide理論上急性使用Mg吸收↑, 慢性使用才會使Mg吸收↓(↓TRPM6)
eGFR 15-45ml/min/1.73 m2 or mild AKI
- DC Mg sources
- Hydration + loop diuretics
- If refractory to above Tx
  - HD, especially if severe neuromuscular(paralysis, conscious change) or CV(EKG change, bradycardia, hypotension) S/S
(GFR <15ml/min/1.73 m2 or severe AKI) and symptomatic hypermagnesium
- (Hydration + loop diuretics) if non-anuria
- 多需要HD
  - More efficient than PD
  - High efficiency HD 3-4hrs可使(Serum dialyzable Mg(70%SMg)-dialysate Mg)↓1/3-1/2
    - 也就是說洗前SMg 3mM, dialysate 0.5mM, 洗完可↓(3*0.7-0.5)*(1/3-1/2)=0.53~0.8mM?
    - Bressendorff (Clin J Am Soc Nephrol 2018; PMID 30131425)：血液透析液鎂由 1.0 調升至 2.0 mEq/L 顯著改善血清鈣化傾向｜T50 鈣化傾向時間延長 73 分鐘(p<0.001)〔PMID 30131425〕
- IV Ca(5-10mEq over 5-10 mins) as a Mg antagonist to reverse the neuromuscular and CV effects while awaiting for HD