Vasopressor equivalents: why the formulas disagree

Norepinephrine equivalence is a research convention, not a pharmacologic fact — and phenylephrine’s conversion factor varies fifteen-fold across the trials it was derived from.

Reviewed and updated August 2026 · Written by Anastasia Jackson, DNAP, CRNA

Every clinical claim on this page is cited to its source below. How we source clinical content — including the corrections we have made and why.

Norepinephrine equivalence exists so that trials can describe vasopressor burden in one number. It is a research convention built on assumptions, and the assumptions differ enough between published formulas that the same patient can produce meaningfully different figures depending on which one you use.

The spread

A scoping review screened 16,315 articles and included 21 clinical trials comparing the potency of at least two intravenous vasopressors against a blood pressure outcome. The conversion ratios equivalent to one unit of norepinephrine:¹

The formulas

Goradia 2021 — the scoping review’s proposal

All in mcg/kg/min except vasopressin in units/min:¹

Kotani 2023 — the updated version

Differs chiefly in the phenylephrine and dopamine coefficients:³

Note that 0.06 is not 1/10 — it is closer to 1/16, at the far end of the reported phenylephrine range. Two published formulas, both current, differing by a factor of nearly two on the same drug.

VASST — the one embedded in trial protocols

Older, uses mcg/min rather than mcg/kg/min for most agents, and still appears in eligibility criteria for oncology and critical care trials:⁴

The mixed units are a genuine trap — dopamine is weight-indexed while the others are not.

What it is used for, and what it is not

Legitimate uses

• Trial eligibility and outcomes — vasopressor-free days, entry thresholds for shock trials.
• Tracking escalation in one patient over time, provided the same formula is used throughout.
• Describing severity in a way that is comparable across patients on different agents.

Where it misleads

Two further limits worth stating:

• The conversion factors rest on unclear evidence. No prospective study has been done with the primary objective of determining the norepinephrine equivalence of the other agents; the published factors are inferences drawn from trials designed to answer other questions.⁵
• Novel agents lack established conversions, angiotensin II most notably, where the reported range spans nearly twofold and the formulas differ on the coefficient by orders of magnitude.^1,3

Thresholds

Conventions vary, but a norepinephrine equivalent above roughly 0.25–0.5 mcg/kg/min is commonly treated as high-dose vasopressor support, and values above 0.5 mcg/kg/min indicate very high or refractory vasoplegic shock associated with elevated mortality.⁶

Trial protocols frequently define high-dose by monotherapy thresholds instead — norepinephrine ≥ 20 mcg/min, phenylephrine ≥ 200 mcg/min, epinephrine ≥ 10 mcg/min, dopamine ≥ 10 mcg/kg/min — with the VASST formula applied only for combinations.⁴

The obstetric exception

One setting has a directly measured potency ratio rather than an inferred one. In 100 consecutive patients treated for post-spinal hypotension during elective cesarean section, the potency ratio of phenylephrine to norepinephrine was 11.3 (95% CI 8.1–16.9), making phenylephrine 100 mcg approximately equivalent to norepinephrine 8.8 mcg.⁷

That sits at the upper end of the general range and is consistent with the ÷ 10 convention — which is reassuring, since it is one of the few figures derived from a study designed to measure exactly this. For the agent-selection question in that setting, see spinal anesthesia in elderly patients, where norepinephrine versus phenylephrine is discussed on cardiac output grounds.

Practical reading

• State which formula you used. A norepinephrine equivalent without a named formula is not a reproducible number.
• Use the same formula throughout a comparison. Most of the disagreement disappears when the question is escalation in one patient rather than comparison across studies.
• Do not use it as a bedside conversion. It exists to describe burden retrospectively, not to switch a patient from one agent to another.
• Read a low number skeptically in a patient on inotropes or mechanical support.

Frequently asked questions

How do you calculate norepinephrine equivalents?

The most commonly cited formula, from a 2021 scoping review, is: norepinephrine + epinephrine + phenylephrine/10 + dopamine/100 + metaraminol/8 + vasopressin×2.5 + angiotensin II×10, all in mcg/kg/min except vasopressin in units/min.¹ A 2023 update uses 0.06 × phenylephrine instead of ÷ 10, and the older VASST formula uses mcg/min with dopamine divided by 2.^3,4 Always state which formula was used.

What is the phenylephrine to norepinephrine conversion?

Conventionally 10:1 — phenylephrine divided by 10. But this is the least settled of all the conversions: the reported range across trials is 1.1 to 16.3 for one unit of norepinephrine, a fifteen-fold spread.¹ Some studies have used 2.2:1, which inflates the calculated norepinephrine equivalent substantially compared with the modern convention.²

What counts as a high dose of vasopressor?

A norepinephrine equivalent above roughly 0.25–0.5 mcg/kg/min is commonly treated as high-dose support, and above 0.5 mcg/kg/min as very high or refractory vasoplegic shock.⁶ Trial protocols often use monotherapy thresholds instead — norepinephrine ≥ 20 mcg/min, phenylephrine ≥ 200 mcg/min, epinephrine ≥ 10 mcg/min.⁴

What is the vasopressin norepinephrine equivalent?

Vasopressin in units per minute is multiplied by 2.5. This is one of the more consistent conversions — the reported range for the underlying ratio is narrow, 0.3 to 0.4 units equivalent to one unit of norepinephrine.¹

Can norepinephrine equivalents be used to switch a patient between agents?

No. It is a research convention for describing total vasopressor burden retrospectively, built on conversion factors inferred from trials designed to answer other questions.⁵ No prospective study has been done with the primary objective of establishing these equivalences.

Why does a patient on ECMO have a low norepinephrine equivalent?

Because the score cannot see mechanical circulatory support or inotropes. A patient on veno-arterial ECMO with moderate-to-high dose inotropes and low-dose norepinephrine will have a norepinephrine equivalent that is disproportionately low relative to the actual intensity of hemodynamic support.³

References

1. Goradia S, Sardaneh AA, Narayan SW, Penm J, Patanwala AE. Vasopressor dose equivalence: a scoping review and suggested formula. J Crit Care. 2021;61:233–240. PMID 33220576. 16,315 articles screened, 21 included.
2. High dose vasopressors: never surrender. PulmCrit / EMCrit. Discusses the effect of the 2.2:1 versus 10:1 phenylephrine convention on calculated norepinephrine equivalents.
3. Kotani Y, Belletti A, Maiucci G, et al. An updated “norepinephrine equivalent” score in intensive care as a marker of shock severity. Crit Care. 2023;27:29. doi:10.1186/s13054-023-04322-y. Includes the ECMO and inotrope limitation.
4. VASST trial vasopressor equivalent equation, per Russell JA, et al. (2008), as reproduced in trial protocols defining high-dose vasopressor use.
5. Norepinephrine equivalent dose of vasopressin, phenylephrine and epinephrine in septic shock. Trial rationale noting that no prospective study has primarily determined the norepinephrine equivalence of the other agents.
6. Norepinephrine equivalent dose. Methodological reference summarizing the conventional severity bands of 0.25–0.5 and above 0.5 mcg/kg/min.
7. Comparison of the potency of phenylephrine and norepinephrine bolus doses used to treat post-spinal hypotension during elective caesarean section. Int J Obstet Anesth. 2019. Potency ratio 11.3 (95% CI 8.1–16.9) in 100 consecutive patients.
8. Further reading. Surviving Sepsis Campaign: international guidelines for management of sepsis and septic shock 2021. Intensive Care Med. 2021. Norepinephrine first-line, vasopressin second-line.