Metaraminol (Critical Care Formulary)

For use in Critical Care Areas for Adults only.  Administer via syringe pump via central line or a large peripheral vein.

MECHANISM OF ACTION:

• Metaraminol exhibits marked vasopressor (alpha-1) as well as positive inotropic (beta) effects.

USES:

• Severe hypotension associated with low peripheral resistance eg in sepsis (correct hypovolaemia first).

CAUTIONS:

• Hypotension due to uncorrected hypovolaemia.
• Tachycardia or reflex bradycardia.
• Cardiac arrhythmias.
• Sustained use can result in cumulative effects that persist even when therapy is discontinued.
• Some brands contain sodium metabisulphite; caution if previous sensitivity.

PRESENTATION:

• Pre-filled syringe: 2.5mg/5mL (0.5mg/mL).
• Ampoule: 10mg/1mL.

ADMINISTRATION:

For IV Injection (bolus) [EMERGENCY USE ONLY]:

• Use the pre-filled syringe.

For Infusion:

• Dilute 2mL (20mg) of metaraminol to 40mL with sodium chloride 0.9% or glucose 5% to provide a concentration of 0.5mg/mL
• Administer infusion via a syringe driver via central line (use a dedicated port) or a large peripheral vein
• When stopping the infusion, reduce the rate of infusion gradually. Abrupt withdrawal can cause acute hypotension
• Note, this concentration of 0.5mg/mL has been updated from previous NHS Highland Critical Care policy and is aligned with the Standardised Concentration Document published by the Intensive Care Society in 2020.
• If patient is on a high rate of metaraminol for a prolonged duration consideration can be given to making up a 3mL (30mg) in 60mL syringe.

DOSE AND RATE:

For IV Injection (bolus) [EMERGENCY USE ONLY]:

• 1 to 2mL (0.5 to 1mg) can be given as a rescue bolus in an emergency while infusion is being prepared.  The effect begins approximately 1 minute after IV bolus.

For Infusion:

• Start with a low infusion rate (commonly in the range of 6 to 10mL/hour but lower rates may be required for elderly/frail patients) then dose titrated to achieve clinical target (blood pressure or mean arterial pressure [MAP]).  The infusion rate should normally be kept within the range 1 to 20mL/hour (0.5 to 10mg/hour).
• If dose is escalating rapidly or if clinical target is not being met, the doctor must be contacted to discuss further management.  Options include:
  • Fluid resuscitation.
  • Switch to alternative therapies as appropriate such as noradrenaline if there is a central line (CVC) in place.
  • If necessary consult ICU staff.

STABILITY:

• 24 hours.
• Do not allow the syringe or infusion to run out.  A syringe or infusion can be made up to a maximum of one hour in advance and labelled clearly with contents and expiry.  Refer to local nursing guidance for switching over infusions or syringes.
• Due to duration of action of metaraminol of 20 to 60 minutes, double pumping is not required when changing over syringes.

EXTRAVASATION:

• This medicine has a low pH and may cause venous irritation and tissue damage in cases of extravasation.  Resite catheter at first signs of inflammation.
• Please refer to NHS Highland Extravasation Protocol on intranet. 

SIDE EFFECTS:

• Bradycardia (reflex to the increase in blood pressure).
• Arrhythmias.
• Peripheral ischaemia.
• Headaches.

MONITORING:

• Ensure ECG and blood pressure monitoring is in place.  Invasive blood pressure monitoring is preferred as in hypoperfused or shock states with cool peripheries, non invasive BP recordings are less reliable.

ADDITIONAL INFORMATION:

• Metaraminol has a longer duration of action than noradrenaline so an excessive vasopressor response may cause prolonged rise in blood pressure.
• Metaraminol is the vasopressor of choice where only peripheral access is available.  If central access is available consider switching to noradrenaline.