What is the procedure for performing a pharmacological penile Doppler for erectile dysfunction?

Pharmacological Penile Doppler Ultrasound Procedure for Erectile Dysfunction

Perform an in-office intracavernosal injection test with alprostadil (starting at 10-15 μg) followed by serial Doppler measurements at 5-minute intervals up to 25 minutes to assess peak systolic velocity (PSV), end-diastolic velocity (EDV), and resistive index (RI). 1

Pre-Procedure Preparation

Patient Selection and Counseling

• Counsel patients about the test procedure, potential adverse events, and the need for dose titration before performing the diagnostic study. 1
• Exclude patients with active bleeding disorders, those on anticoagulation therapy (use with caution), or history of priapism 1
• Obtain baseline stretched penile length (SPL) in the flaccid state before injection, as failure to reach this length during peak erection predicts veno-occlusive dysfunction 2

Medication Preparation

• Use intracavernosal alprostadil (prostaglandin E1), which is the only FDA-approved agent for intracavernosal injection in the U.S. 1
• Alternative agents include papaverine, phentolamine, or atropine in combination, though these are typically not used as single agents 1

Injection Technique

Initial Dosing Strategy

• Begin with 10-15 μg of alprostadil injected into the corpus cavernosum 3, 4
• The dose should be titrated based on patient response and underlying etiology of ED 4
• Different ED etiologies require different dosing approaches: patients with veno-occlusive dysfunction may need higher doses (up to 20 μg) compared to those with psychogenic or neurogenic ED 4

Enhanced Protocol for Difficult Cases

• Consider combining oral sildenafil 100 mg administered before the procedure with alprostadil 15 μg injection to improve diagnostic accuracy 3
• This combination approach significantly improves PSV, EDV, and RI measurements compared to alprostadil alone 3
• The combined approach reduces false-positive diagnoses of arterial ED from 31.67% to 15.00% and mixed ED from 23.33% to 8.33% 3

Doppler Measurement Protocol

Timing of Measurements

• Measure penile hemodynamic parameters continuously at baseline (before injection), then at 5,10,15,20, and 25 minutes post-injection 3
• Peak systolic velocity (PSV) typically occurs within 5-10 minutes of injection 3
• Continue monitoring until maximum erection is achieved or 25 minutes elapsed 3

Key Parameters to Assess

• Peak Systolic Velocity (PSV): Assesses arterial inflow; abnormal values suggest arterial insufficiency 3, 2
• End-Diastolic Velocity (EDV): Elevated EDV (>12.0 cm/s) suggests veno-occlusive dysfunction 2
• Resistive Index (RI): Calculate as (PSV-EDV)/PSV; values <0.6 indicate veno-occlusive dysfunction 2
• Measured penile length at peak erection: Compare to baseline SPL; failure to reach SPL predicts veno-occlusive dysfunction with OR 2.255 2

Interpretation of Results

Diagnostic Criteria

• Veno-occlusive dysfunction is diagnosed when EDV >12.0 cm/s, RI <0.6, and failure to achieve stretched penile length despite adequate tumescence 2
• Arterial insufficiency is suggested by low PSV values 3
• The combination of elevated EDV (OR 1.281) and low RI (OR 0.694) independently predicts veno-occlusive dysfunction 2

Response Assessment

• Document the duration of erection from application to detumescence, as this varies significantly by ED etiology 4
• Psychogenic ED: expect 32-98 minutes duration with dose-dependent response 4
• Arteriogenic ED: expect 40-82 minutes with significant dose-response relationship 4
• Veno-occlusive ED: expect only 8-17 minutes even at maximum doses 4
• Neurogenic ED: expect 40-101 minutes with dose-dependent response 4

Common Pitfalls to Avoid

• Do not rely solely on rigidity or tumescence measurements—these do not correlate with veno-occlusive dysfunction as reliably as the combination of EDV, RI, and failure to achieve SPL 2
• Avoid using insufficient doses of alprostadil—start at 10-15 μg and titrate up to 20 μg if needed, as response is dose-dependent across all ED etiologies 4
• Do not perform the test in patients with untreated urinary tract infections, systemic infections, or cutaneous infections 1
• Monitor for prolonged erection or priapism, which are potential adverse events requiring immediate intervention 1