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Magnesium Sulfate Administration

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Administration of Magnesium Sulfate for Vasospasm Prevention After Aneurysmal Subarachnoid Hemorrhage


To prevent vasospasm and improve outcome after aneurysmal subarachnoid hemorrhage by maintaining a magnesium level of 3-4.5mEq/l

Inclusion Criteria

  • CT proven subarachnoid hemorrhage
  • CTA or angiogram proven berry aneurysm
  • Less than 72 hours post subarachnoid hemorrhage
  • Hunt and Hess grade I-IV Fisher group II-III
  • Age greater than or equal to18 years old
  • Secured aneurysm

Exclusion Criteria

  • Pregnancy
  • Age less then 18
  • Congestive Heart Failure (NY Heart Association Class 3 or 4)
  • 2nd or 3rd degree heart block (caution in digitalized patients)
  • Renal insufficiency (calculated creatinine clearance rate < 30ml/min)
  • Known neuromuscular disease
  • Concomitant use of neuromuscular blocking agents (cisatracurium, vecuronium etc.)
  • Serum K > 6mmol/L
  • Ionized Ca<1.1mmol/l
  • Hypotension (SBP < 90mmHg or MAP < 60mmHg unresponsive to the administration of IV fluids and/or pressors)
  • Ordered nifedipine (hypotension and NM blockade risk)

Guidelines for Use

  • All magnesium administration must have a signed physician order, including a specific dose and rate. All rate changes require a physician order.
    • Abbreviated orders, "per protocol" and "as directed" should not be accepted
  • To be used only in an ICU setting
    • Not for general care unit use
  • Central line suggested, not required
  • MgSO4 40gm/L SWI is a piggyback solution, NOT a mainline infusion
  • Bolus Dose: 2g MgSO4 (50cc) over 30 minutes
    • Record BP, HR, RR every 10 mintues during bolus infusion
  • Initial Maintenance Rate: 1g MgSO4/hr (25cc/hr)
  • The Magnesium drip may be stopped and restarted at the discretion of the Neuro ICU fellow.
  • Goal: serum Mg level = 3-4.5 mEq/l
    • The ICU fellow/resident must be called if Mg not within range.
    • Calcium po/ngt supplements administered during MGSO4 administration.
  • Cardiac monitoring performed per ICU routine

Serum Mg levels are checked

  • before starting the infusion
  • 2 hours after initiation
  • 2 hours after a dose or rate change
  • every 12 hours afterwards (including dose changes)
    • special note that MGH labs may notify us that Mg levels are out of range
  • Ionized Ca and serum K levels are checked twice a day
  • Calcium repletion is desired if Calcium < 1.1mmol/L. Calcium maybe repleted over 30 minutes.

Protocol is discontinued for

  • Ionized Ca less then 1.1mmol/L
  • Serum K greater then 6 mmol/L
  • Systolic blood pressure less then 80mmHg
  • Patient need to go for neuro-interventional vasospasm treatment - require general anesthesia
  • New prolongation of PR interval or onset of new AV block
    • Covering physician is to be notified with any of the above


  • 14 days after aneuysmal subarachnoid hemorrhage
  • transferring out of ICU

Potential side effects of MgSO4 infusions and goal serum Mg levels

  • hot and/or flushed feeling
  • nausea, vomiting, diarrhea
  • local venous irritation
  • generalized feeling of drowsiness
  • hypotension (can be treated with Ca gluconate 0.5-2g infusion): cardiac depression, negative ionotropy, PR prolongation, AV block
  • respiratory arrest
  • hypocalcemia
  • hyperkalemia

Serum Magnesium levels

  • 1.4 - 2.1mEq/l
    • Normal
  • 3 - 4.5mEq/l
    • Target
  • 5 - 10mEq/l
    • EKG changes (PR and QRS prolongation)
  • >10mEq/l
    • Loss of DTRs
  • > 15mEq/l
    • Respiratory paralysis
  • > 25mEq/l
    • Cardiac Arrest

Physician guide for titration

  • Rate changes may only be made with a physician order

Most current Serum Mg level

  • < 3mEq/l
    • Current infusion rate change: increase rate 0.5g/h (+12.5cc/h)
  • 3-4.5mEq/l
    • Current infusion rate change: no change (target range)
  • 4.6-5.5mEq/l
    • Current infusion rate change: decrease rate 0.5g/h (-12.5cc/h)
  • > 5.5mEq/l
    • Current infusion rate change: stop infusion until < 5.5mEq/l then decrease rate 1g/h (-25cc/h)

Other Information

  • please refer to MGH Critical Care IV Medication Guidelines
  • MgSO4 comes from Material Management: 40gm in 1000cc sterile water injection (324.8mEq/L) and is stocked in the Blake 12 medication closet
  • Y-site/co-administration compatible with: dobutamine, dopamine, esmolol, heparin, insulin, labetalol, mannitol, nicardipine, nitroprusside, norepinephrine, phenylephrine, potassium chloride, vasopressin. Please page the pharmacist covering for additional compatibilities or information.
  • incompatible with: argatroban, hypertonic saline (1.5% & 1.5%, 3%, 23.4%), methylprednisolone, others
  • 500mg MgSO4 = 48mg Mg++ = 4.06mEq = 2.03mmol
  • Materials Management re-order #________________


  1. Magnesium Sulfate in Aneurysmal Subarachnoid Hemorrhage. A randomized Controlled Trial. Stroke 2005; 36:1011-1015
  2. Magnesium Sulfate Therapy after Aneurysmal Subarachnoid Hemorrhage. J Neurosurg 2002; 96: 510-514
  3. Hypomagnessemia after Aneursysmal Subarachnoid Hemorrhage. Neurosurgery 2003; 52: 276-282
  4. Magnesium Sulfate Reverses Experimental Delayed Cerebral Vasospasm after Subarachnoid Hemorrhage in Rats. Stroke 1991; 22: 922-927
  5. Manual of High Risk Pregnancy and Delivery. Gilbert and Harmon; Mosby, 1993; 398
  6. Magnesium and Its Therapeutic Uses: A Review; The American Journal of Medicine; 1994; 96: 63-76
  7. MGH protocol for administration of MgSO4 for the Pre-Eclamptic/PIH patients

MGH Committee Review & Policy Updates

  • MGH MESAC reviewed, amended & approved 10/25/05
  • MGH Critical Care Committee submitted 10/05
  • MGH Critical Care IV Medication Guidelines amendment submitted 11/05

Authoring Information

Reviewed/Approved by: Schwamm, Lee, M.D. on behalf of ASQT

Last updated: 7/7/2010

   Authors: Guy Rordorf, MD; Mary Guanci, RN CNS; John Murphy, RN; Michael Bodock; RPh

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