How to start an intravenous glyceryl trinitrate (GTN) infusion

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.