Intraarterial Nitroglycerin Dosing for Lower Extremity Vasospasm
For lower extremity vasospasm, administer intraarterial nitroglycerin as bolus injections of 40-100 mcg (0.4-1.0 mL of 100 mcg/mL solution) directly into the affected artery, which can be repeated every 10 minutes as needed, or alternatively use continuous intraarterial infusion at rates similar to intravenous protocols (starting at 5-10 mcg/min and titrating upward).
Bolus Dosing Strategy
Intraarterial bolus administration of 40-100 mcg nitroglycerin has demonstrated efficacy in reversing acute arterial vasospasm in transplant and vascular surgery settings 1, 2.
In pediatric renal transplantation, two aliquots of 40 mcg (0.4 mL of 100 mcg/mL solution) injected directly into the renal artery 10 minutes apart resulted in dramatic improvement in organ perfusion and blood flow 1.
For refractory coronary vasospasm, intracoronary (intraarterial) nitroglycerin successfully reversed spasm when sublingual and intravenous routes failed, though specific doses ranged from bolus injections during catheterization 2.
Bolus injections should be spaced at least 10 minutes apart to assess response and avoid excessive systemic hypotension 1.
Continuous Intraarterial Infusion Protocol
For severe, refractory lower extremity vasospasm after peripheral bypass, continuous intraarterial nitroglycerin infusion can be administered for 24 hours using standard intravenous dosing protocols 3.
The FDA-approved initial dosing when using non-absorbing tubing is 5 mcg/min, with titration in 5 mcg/min increments every 3-5 minutes until response is observed 4.
If no response occurs at 20 mcg/min, increase increments to 10 mcg/min, and subsequently to 20 mcg/min as needed 4, 5.
The maximum concentration for nitroglycerin infusion should not exceed 400 mcg/mL, with typical maximum infusion rates of 200 mcg/min (though doses up to 400 mcg/min have been used safely in specific situations) 4, 6.
Preparation and Administration
Nitroglycerin must be diluted from concentrated vials: transfer 50 mg into 500 mL of either 5% dextrose or 0.9% sodium chloride to yield 100 mcg/mL concentration 4.
For intraarterial bolus administration, use the 100 mcg/mL concentration and inject 0.4-1.0 mL directly into the affected artery via catheter 1.
Non-absorbing (non-PVC) tubing must be used for continuous infusions, as PVC tubing absorbs significant amounts of nitroglycerin and requires higher doses 4, 5.
Hemodynamic Monitoring Requirements
Continuous blood pressure monitoring is mandatory during intraarterial nitroglycerin administration 5, 7.
Systolic blood pressure should not fall below 90 mmHg or decrease more than 30 mmHg from baseline 4, 5.
In previously normotensive patients, do not reduce systolic BP below 110 mmHg; in hypertensive patients, do not reduce mean arterial pressure by more than 25% from baseline 5, 7.
Monitor for transient systemic hypotension, which typically resolves quickly after intraarterial bolus administration 1.
Critical Contraindications
Absolute contraindication exists if the patient has used sildenafil within 24 hours or tadalafil/vardenafil within 48 hours due to risk of profound hypotension and death 5, 6.
Avoid in patients with initial systolic BP <90 mmHg or marked bradycardia (<50 bpm) or tachycardia (>100 bpm without heart failure) 5, 7.
Use extreme caution in suspected right ventricular infarction, as these patients are dependent on adequate preload 5, 6.
Tolerance Considerations
Tolerance to nitroglycerin develops within 7-8 hours and becomes clinically significant after 24 hours of continuous therapy 5, 6.
For continuous intraarterial infusions lasting beyond 24 hours, periodic increases in infusion rate may be necessary to maintain efficacy 6, 5.
If using continuous infusion for refractory vasospasm, plan for 24-hour duration as demonstrated in successful case reports 3.
Alternative Vasodilators
If nitroglycerin boluses are ineffective, consider intraarterial calcium channel blockers: verapamil 5-10 mg or diltiazem 0.15 mg/kg 8.
Nicardipine and verapamil boluses may be attempted before escalating to continuous nitroglycerin infusion 3.
Clinical Pitfalls to Avoid
Do not use intravenous or sublingual nitroglycerin for severe arterial vasospasm when intraarterial access is available, as direct intraarterial administration is more effective for localized vasospasm 2, 3.
Ensure adequate flushing of infusion sets when changing nitroglycerin concentrations, as residual drug in tubing can delay delivery of new concentrations by minutes to hours 4.
Do not mix nitroglycerin with other drugs in the same infusion 4.