Glyceryl Trinitrate (GTN) Spray

Question 1

GTN Indications

Answer 1

1. Myocardial ischaemia
2. Cardiogenic pulmonary oedema
3. Control of hypertension associated with autonomic dysreflexia
4. Control of hypertension (usually in conjunction with Labetalol) prior to fibrinolytic treatment for STEMI, or during inter-hospital transfer for STEMI
5. STEMI

Question 2

GTN Contraindications

Answer 2

1. Known severe allergy
2. Systolic BP less than 110 mmHg
3. Heart rate less than 40/minute
4. Heart rate more than 150/minute
5. Ventricular tachycardia

Question 3

GTN Cautions

Answer 3

1. STEMI, particularly STEMI involving the right ventricle. GTN may cause a significant fall in cardiac output and if there are signs of low cardiac output GTN should be withheld
2. The patient is frail
3. Signs of shock
4. Dysrhythmia
5. Has taken a phosphodiesterase inhibitor in the last 24 hours
6. Known aortic or mitral stenosis

Question 4

GTN Dose for Myocardial Ischaemia

Answer 4

0.4 mg every five minutes. Consider increasing interval to ten minutes if caution is present

Question 5

GTN Dose for STEMI

Answer 5

O.4 mg with caution. Withhold if signs of poor perfusion are present

Question 6

GTN Dose for cardiogenic pulmonary oedema

Answer 6

0.8 mg every five minutes. Consider increasing the dosing interval to ten minutes if a caution is present. Increase the dose and frequency is patient is not improving

Question 7

GTN Dose for Control of Hypertension

Answer 7

0.4 mg every five minutes

Question 8

GTN Route and Administration

Answer 8

• IS, sprayed under tongue
• If administered in presence of a caution;
  > patient should be sublime
  > IV assess should have been obtained whenever possible
  > the dosing interval should be increased to ten minutes
  > Be ready to administer 0.9% sodium chloride IV if there is a significant fall in cardiac output or blood pressure

Question 9

GTN Common Adverse Effects

Answer 9

1. Hypotension
2. Flushing
3. Headache
4. Tachycardia
5. Feeling light-headed

Question 10

GTN Mechanism of Action

Answer 10

• It is a vasodilator that acts on smooth muscle to cause venous and arterial vasodilation, with the predominant effect being on veins.
• The MOA is not clear, but it results in the formation of nitric oxide which is a vasodilator causing;
  > A reduction in venous return (preload) to the heart reducing the ventricular filling and cardiac output which reduces myocardial oxygen demand
  > Arterial dilation which reduces peripheral resistance (after load) to the heart hence reducing the myocardial oxygen demand