Nitroglycerin Cautions
Objective: Nitroglycerin drops preload. That helps some ischemic and wet-lung patients and wrecks right-ventricular infarcts, PDE5 users, and anyone already hypotensive.
Why This Is Hard
Nitro is a habit drug: chest pain, spray, repeat. It is a venodilator. Patients who depend on preload — right-ventricular infarct, hypotensive ACS, volume-depleted — can crash. PDE5 inhibitors (erectile-dysfunction and some pulmonary-hypertension meds) plus nitro can produce refractory hypotension.
Before You Give It (Education)
- Indication in your protocol (ischemic pain and/or pulmonary edema — systems differ).
- Blood pressure above your protocol floor. Recheck after every dose.
- PDE5 / recent “that little blue pill” / pulmonary HTN meds — ask specifically. Common teaching windows: sildenafil or vardenafil within about 24 hours, tadalafil within about 48 hours (avanafil is shorter). Many EMS protocols use a single conservative window — follow yours.
- 12-lead when feasible before nitro in ACS: inferior ST elevation should make you think about a right-sided tracing and RV infarct caution.
- IV access is nice to have if they tank — know your local rule.
Key Points
- Headache and a BP drop are expected pharmacology, not a surprise.
- This lesson does not authorize a dose, spray count, or paste amount.
- Pulmonary edema patients who are hypertensive are a different picture from hypotensive cardiogenic shock — do not treat them the same.
- BP above protocol floor — recheck after every dose
- PDE5 / “little blue pill” / pulmonary HTN meds asked
- 12-lead territory — inferior STE → think RV caution
- Indication matches protocol (ischemic pain and/or wet lungs)
Field Pitfalls
- Nitro into SBP 80 because “chest pain gets nitro.”
- Never asking about PDE5.
- Skipping the 12-lead, then discovering inferior STE after they are hypotensive.
Practice
60-second drill
Three scenes — say nitro: go / hold / ask control and name the caution: (1) ischemic pain, BP well above your floor, no PDE5, clean 12-lead so far; (2) chest pain, SBP under your protocol floor; (3) inferior STE — right-sided tracing / RV caution before dropping preload. Related: STEMI, CHF.
Sources & Further Study
Named guidelines for further study. They are not clinical orders and do not replace your protocol or medical direction.
- 2025 ACC/AHA/ACEP/NAEMSP/SCAI ACS Guideline
- NASEMSO National Model EMS Clinical Guidelines (2022)
- Nitroglycerin is contraindicated with hypotension and recent PDE5 use (commonly taught ~24 h sildenafil/vardenafil, ~48 h tadalafil). Use caution in inferior/right-ventricular infarct. Protocol owns dose and BP cutoffs.
Education only. Apply learning within your protocols and medical direction. This is not clinical care guidance.
Check Your Understanding
Street decisions from this lesson only. After you check, the key is highlighted. Education practice — not a certification exam.