What is the recommended infusion rate for Glyceryl Trinitrate (GTN) in ml/hr?

GTN Infusion Rate Guidelines

Start intravenous nitroglycerin at 5 mcg/min (not ml/hr), titrate by 5 mcg/min every 3-5 minutes up to 20 mcg/min maximum for hypertensive emergencies, or up to 200 mcg/min for acute coronary syndrome/pulmonary edema. 1, 2, 3

Critical Clarification: Dosing is in mcg/min, NOT ml/hr

The infusion rate in ml/hr depends entirely on your concentration preparation. You must calculate ml/hr based on your specific GTN concentration (typically 50-100 mcg/ml). 4

Example calculation:

• If using 50 mg GTN in 250 ml = 200 mcg/ml concentration
• To deliver 10 mcg/min: (10 mcg/min ÷ 200 mcg/ml) × 60 min/hr = 3 ml/hr

Initial Dosing Algorithm

For Hypertensive Emergency (without ACS/pulmonary edema):

• Start: 5 mcg/min 1
• Titrate: Increase by 5 mcg/min every 3-5 minutes 1
• Maximum: 20 mcg/min 1
• Use only if acute coronary syndrome or acute pulmonary edema present 1

For Acute Coronary Syndrome or Acute Pulmonary Edema:

• Start: 5-10 mcg/min using non-absorbing tubing 2, 3
• Initial titration: Increase by 10 mcg/min every 3-5 minutes for first 20 minutes 2, 3
• If no response at 20 mcg/min: Use larger increments of 10 mcg/min, then 20 mcg/min 2, 3
• Once partial response: Reduce increment size and lengthen intervals 3
• Commonly recommended ceiling: 200 mcg/min 2, 3
• Absolute maximum: Up to 400 mcg/min may be used with careful monitoring in refractory cases 2

Mandatory Safety Parameters - Absolute Contraindications

Do not initiate GTN if: 1, 2, 3

• Systolic BP <90 mmHg or >30 mmHg below baseline
• Phosphodiesterase inhibitor use within 24 hours (sildenafil) or 48 hours (tadalafil) - risk of profound hypotension and death
• Marked bradycardia or tachycardia
• Suspected right ventricular infarction (these patients are critically preload-dependent)
• Volume depletion

Blood Pressure Targets During Titration

For previously normotensive patients: 2, 3

• Do not reduce systolic BP below 110 mmHg

For hypertensive patients: 2, 3

• Do not reduce mean arterial pressure by more than 25% from baseline

Stop titrating when: 3

• Symptoms resolve (no need to continue increasing for BP effect alone)

Practical Administration Considerations

Cannula Size Matters:

• Large bore cannulas (e.g., grey/14G) have significant dead space - drug takes >6 minutes to reach patient at 1 ml/hr 4
• Smaller cannulas (e.g., pink/20G) reduce lag time to ~1.5 minutes 4
• If using large cannula, start with faster initial infusion rate (higher ml/hr) to ensure drug reaches patient quickly, then adjust 4

Onset of Action:

• Hemodynamic effects begin within 2-5 minutes of infusion start 5
• Peak venous effects occur around 20 minutes 6
• Steady-state plasma concentration achieved by 30 minutes 5

Tolerance Management

Tolerance develops predictably: 2, 3

• Becomes significant after 24 hours of continuous therapy
• Is dose and duration dependent
• Requires periodic rate increases if therapy extends beyond 24 hours

Transition strategy: 3, 7

• Switch to oral/topical nitrates within 24 hours once patient stable and symptom-free for 12-24 hours
• Transition to oral isosorbide dinitrate prevents rebound vasoconstriction
• Use nitrate-free intervals if ischemia recurs during continuous therapy

Common Pitfalls to Avoid

1. Confusing mcg/min with ml/hr - always calculate based on your specific concentration 4
2. Using GTN for hypertensive emergency without ACS/pulmonary edema - other agents preferred 1
3. Continuing to titrate after symptom resolution - unnecessary and increases hypotension risk 3
4. Forgetting to ask about phosphodiesterase inhibitors - can be fatal 2, 3
5. Using in right ventricular infarction - can cause cardiovascular collapse 2, 3
6. Starting with large cannula at slow ml/hr rate - significant delay in drug delivery 4