Sunday 15 October, 2006

How to start an intravenous glyceryl trinitrate (GTN) infusion

Posted in Emergency, Emergency Dept., Medicine, Michael Tam at 20:20 by Michael Tam

Original article: Michael Tam :: Printer friendly

An understanding of how to start and setup an intravenous infusion of glyceryl trinitrate (GTN) is a rather useful skill. Unfortunately, setting up a GTN infusion is sufficiently complicated that it can’t be worked out in an emergency situation. In a nutshell:

Start with glyceryl trinitrate 5 mcg/min

then

increase infusion rate by 5 mcg/min every 3-5 minutes if needed

when infusion rate is GTN 20 mcg/min or more

increase infusion rate by 10 mcg/min every 3-5 minutes if needed

GTN infusions are not trivial. Call for help. It should best be performed under the supervision of someone who has experience with them (e.g., a medical registrar or emergency medicine registrar).

Step One: Indications

GTN infusions can be used in the following (1) (2):

  • hypertensive emergency / malignant hypertension
  • congestive cardiac failure with acute myocardial infarction
  • treatment of angina pectoris not responding to oral nitrates and/or beta blockers
  • control of perioperative hypertension

In hypertensive encephalopathy, aim to reduce the blood pressure slowly (3). There are substantial risks in reducing it quickly.

  • reduce the mean arterial pressure by 10% per hour;
  • by no more than 25% of the original value.

mean arterial pressure = diastolic + 1/3 (systolic – diastolic)

Step Two: Contraindications

Avoid in the following (1) (2):

  • hypotension or uncorrected hypovolaemia
  • raised intracranial pressure or cerebral haemorrhage
  • constrictive pericarditis or pericardial tamponade
  • severe anaemia and arterial hypoxaemia
  • concurrent use of phosphodiesterase-5 inhibitors, i.e., sildenafil (Viagra), tadalafil (Cialis) and vardenafil (Levitra)

Step Three: Initial stabilisation

Remember your “ABCs” of emergency management (3):

Position:

  • Comfortably;
  • in a monitored bed.

Airway:

  • Keep patent.

Breathing:

  • Administer high flow (i.e., > 6 L/min) via a Hudson mask or non-rebreather mask;
  • consider using CPAP if severe pulmonary oedema is present;
  • assess respiratory rate and effort (if inadequate, assist with ventilation, e.g., bag-valve-mask with oxygen).

Circulation:

  • Measure pulse rate, blood pressure (both arms if thoracic aortic dissection is suspected) and capillary refill;
  • attach cardiac monitoring equipment and correct any immediate life threatening arrhythmia;
  • insert intravenous cannulae x 2;
  • take bloods (FBC, UEC).

Perform a 12-lead ECG

Disability:

  • Measure Glasgow Coma Score (GCS); if less than or equal to 8 then consider endotracheal intubation to protect the airway.

Step Four: Draw up and dilute the GTN

GTN is absorbed into many plastics, especially PVC (2). Hence it is important to minimise the amount of tubing / filters in the giving sets and aim to use a glass bottle for dilution.

In Australia, GTN for injection comes in 50 mg/10 mL ampoules.

glyceryl trinitrate 50 mg in 500 mL of 0.9% NaCl solution (glass infusion bottle)

  • This yields a concentration of GTN of 100 mcg/mL;
  • a solution of 5% dextrose (D-glucose) can be used as an alternative.

Step Five: Start infusion

The dose of GTN needs to be carefully titrated for the patient according to response. The starting dose is low:

glyceryl trinitrate 5 mcg/min

which is

3 mL/h of the dilution (glyceryl trinitrate 100 mcg/mL)

Step Six: Upward titration

Start with small increases up to GTN 20 mcg/mL:

Increase infusion rate by glyceryl trinitrate 5 mcg/min every 3-5 minutes.

which is

3 mL/h of the dilution (glyceryl trinitrate 100 mcg/mL) every 3-5 minutes

When the infusion rate of GTN is greater than of equal to 20 mcg/mL (i.e., from the forth upward titration and beyond):

Increase infusion rate by glyceryl trinitrate 10 mcg/min every 3-5 minutes.

which is

6 mL/h of the dilution (glyceryl trinitrate 100 mcg/mL) every 3-5 minutes

  • There is no real maximum dose and the infusion rate should be adjusted to effect;
  • GTN has a wide therapeutic range;
  • it is suggested by McCowan and Shapiro (2006) (1) that the maximum rate to be GTN 200 mcg/min.

Step Seven: Arrange for definitive care

Once the patient has been stabilised, definitive care should be arranged. For a patient who requires a GTN infusion, this will be a monitored bed (i.e., a coronary care unit, intensive care unit or at least, a monitored bed).

Discussion

  • Beware in severe hypertension following head injury, intracranial bleed or cerebrovascular accident. The hypertension is in part the body’s response to maintain cerebral perfusion.
  • Some patients may respond fully to even the starting infusion rate of GTN (5 mcg/min) so careful titration and monitoring is required.
  • For patients requiring a high infusion dose of GTN, it can be helpful to increase the concentration of the infusion solution and then use the appropriate rate.

Reference articles

(1) McCowan C., Shapiro N. Hypertensive Emergencies. Emedicine. Last updated 13 April 2006. [Link]

(2) Glyceryl Trinitrate Concentrate Injection (DBL). MIMS Online. Last updated 13 September 2005.

(3) Hypertensive Emergencies, Treatment. Emergency Life Support (ELS) Course Manual. Second Edition. 2002.

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16 Comments »

  1. peter hughes said,

    re: GTN infusion, you say 500ml NaCL solution but it should be 500ml 5% Glucose

  2. Michael Tam said,

    According to the references used to write the article (and the product information for intravenous glyceryl trinitrate), the dilutant can either be saline or dextrose solution.

    Cheers.

  3. sue read said,

    We use NaCL as diluant.
    Do you have any info on comparable doses required when changing from oral to IV and back to oral as may be needed in an exacerbation or angina. If a patient is taking 120mg MR ISMO or 60 Imdur what is the comperable dose of IV GTN?…thanks

  4. Michael Tam said,

    Thank you for your question.

    My understanding is that there is no comparable dose conversion possible. Intravenous GTN infusions are highly variable between different people where equivalent doses may be different in orders of magnitude. Apart from physiological reasons why this might be the case, there are also large variabilities in the absorption of GTN from giving sets and tubing.

    Cheers.

  5. James said,

    “An understanding of how to start and setup an intravenous infusion of glyceryl trinitrate (GTN) is a rather useful skill. Unfortunately, setting up a GTN infusion is sufficiently complicated that it can’t be worked out in an emergency situation.”

    In a nutshell it is easy and often hindered by timid nurses.
    50mg of GTN (already in 50mls) in a 50mls syringe. 2-10mls per hour keeping systolic BP >90mmHg, at the maximum dose needed for therapeutic response in LVF or angina.

  6. Mandar said,

    They make GTN infusions unnecessarily complicated in Australia! As James said, start at 1ml/hr of the 1mg/ml GTN and titrate it carefully to the BP.

  7. nihad faisal said,

    regarding use of GTN in CCF or pulmonary oedema or Acute MI… what is our goal? to keep BP in normal limits? decrease the distress? im asking this cuz if i dont know the goal i cant say upto what level i need to increase the dose.
    and when to stop infusion, i think to stop infusion, u have to titre and decrese the dose and the omit.

  8. ahmad said,

    Excuse me gents.
    I’m looking for the oral dose for GTN ?
    And Why is anti-emitics usually taken with IHDs emergencies ?

    • Michael Tam said,

      For angina, one tablet of sublingual Anginine (GTN 600 mcg) every 5 minutes until relief of symptoms.

      Secondly, anti-emetics are NOT “usually” taken with acute coronary syndromes. However, you may choose to give an anti-emetic when giving intravenous morphine to reduce the likelihood or nausea and vomiting.

  9. Jun said,

    Thanks for the tips…Had a patient came in with BP 260/160 and reduce to 195/130 on IV GTN 100ug/min but suddenly it went up to 259/130 with HR 130/min. my question is can if I want to add IV labetolol how to titrate down the GTN or is there any guide on combine usage of labetolol and IV GTN. thanks a million!

  10. Jodie said,

    The guidelines for commencing the infusion are clear. However, once goal is reached how long do you maintain infusion at this level, providing BP is stable and how do you go about titrating down?
    Cheers.

  11. Stephen Judd said,

    Is there any information regarding the clinical effectiveness of IV GTN at high doses (say 30ml/hr) when it has been running at that dose for 24-48 hours? Does the patient become desensitized to it?

  12. Reza Rahman said,

    I’m presently revising for exams and this has really helped me get my head around GTN infusions. So thank you!

  13. junn said,

    which one is better dilution for infusion GTN?50mg GTN in 500 dextrose..or..50mg GTN in 50cc saline..?

    • adila said,

      n/saline

  14. nisha said,

    how does GTN work in a patient with positive D.Dimer and newly diagnosed RBBB?


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