Hypermagnesemia may be associated with a number of a number of clinical findings that become more serious as the serum level of magnesium increases.


Neurologic findings secondary to decreased transmission across the neuromuscular junction:

(1) decreased or absent deep tendon reflexes

(2) depressed mental status, progressing from drowsiness to somnolence to coma

(3) flaccid paralysis

(4) difficulty with urination

(5) no response to painful stimuli


Cardiovascular changes:

(1) hypotension (associated with direct vasodilation and ganglionic blocking)

(2) bradycardia after a transient tachycardia

(3) abnormal ECG (increased PR interval, increased duration QRS, increased QT interval, heart block, other)

(4) cardiac arrest and asystole with severe hypermagnesemia


Respiratory changes:

(1) respiratory depression progressing to apnea

(2) hypoxemia


Gastrointestinal changes:

(1) nausea and vomiting

(2) ileus


Cutaneous changes:

(1) cutaneous flushing

(2) diaphoresis

Serum Magnesium Concentration


< 2 mmol/L

may be asymptomatic or show nausea, vomiting and cutaneous flushing

2 mmol/L

decreased deep tendon reflexes, drowsiness, diaphoresis

2.0 - 3.5 mmol/L

somnolence, bradycardia, hypotension

2.5 - 5.0

ECG changes, paralytic ileus

>= 5 mmol/L

flaccid paralysis, with respiratory depression

>= 7.5 mmol.L

complete heart block, respiratory paralysis, coma

>= 8.5 mmol/L

cardiac arrest, asystole



• 1 mg/dL magnesium = 0.4114 mmol/L = 0.8228 mEq/L


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