Updated July 2026 · 7 min read

IV Hydralazine: The ICU Nurse's Guide

Part of the ICU Emergencies Hub — browse every related guide in one place.

Hydralazine is the intermittent IV push you give for a high blood pressure when a drip isn't set up yet — convenient, but deceptively tricky. Its onset is slow, its peak is late, and its response varies wildly between patients, which is exactly how people get stacked doses and an unexpected crash. Here is how to use it safely.

How hydralazine works

Hydralazine relaxes arteriolar smooth muscle directly, dropping systemic vascular resistance and therefore blood pressure. Because it works on arterioles and not veins, it lowers afterload without much effect on preload. The trade-off is a reflex response: as pressure falls, the baroreceptors drive up heart rate and contractility, which can be a problem in a patient with coronary disease or aortic dissection, where the goal is to lower shear, not raise it.

Dosing and the timing trap

This delayed, variable pharmacology is hydralazine's central hazard. Unlike a titratable drip that lets you match effect to a target continuously, an intermittent push commits you to a dose before you can see the full response. That is why for a patient who needs precise, sustained control — dissection, hypertensive emergency with end-organ damage — a continuous, fast-titrating agent is usually preferred.

Side effects to monitor

Reflex tachycardia and flushing are the most common acute effects, sometimes with headache and palpitations. In ischemic hearts the tachycardia can worsen demand.

Hypotension from stacked or over-vigorous dosing is the main serious risk — watch the trend, not just the single reading.

Drug-induced lupus can occur with chronic oral use (dose- and acetylator-status dependent), which is a long-term outpatient consideration rather than an acute-care one.

Where it fits — and where a drip wins

Hydralazine is genuinely useful for a quick knock-down of a moderately high pressure when IV access is limited or a pump isn't ready, and it is a first-line agent in severe preeclampsia and eclampsia, where it has a long track record. But when the situation calls for a tight target held over hours — aortic dissection, hypertensive emergency, neuro cases — a titratable infusion like nicardipine or labetalol or clevidipine gives control that intermittent hydralazine cannot.

Why CRNA students should know it

On the CRNA path, hydralazine is a common intraoperative and PACU tool for treating hypertension, and its delayed, unpredictable onset is a classic anesthesia teaching point — the drug that punishes impatience. Understanding afterload reduction, reflex tachycardia, and when a titratable infusion beats an intermittent push is exactly the hemodynamic reasoning you carry from the ICU into the OR.

Bottom line

Hydralazine is the convenient IV push for acute hypertension with a catch: slow, variable onset that punishes re-dosing too soon, plus reflex tachycardia. It earns its place in preeclampsia and as a quick knock-down, but for precise, sustained control a titratable drip is safer. Respect the timing and you will avoid the crash.

This article is general educational information for licensed clinicians and students, not medical advice or a substitute for your institution's protocols, pharmacy guidance, or a provider's orders. Always follow facility policy and verify every dose independently.