Noradrenaline Equivalent Dose Calculator

Convert a multi-agent vasopressor infusion to a single noradrenaline-equivalent figure by four published formulas at once — because the published conversion ratios disagree, and this is a research comparability measure and not a prescribing tool.

Four published formulas, and where they disagree

Published conversion ratios, by source, and how far apart they are

The formulas written in µg/min, which cannot be read across

A comparability scale that four papers cannot agree on

A patient in vasodilatory shock is often on more than one vasopressor at once, and comparing their vasopressor burden with another patient’s, or with a trial population’s, needs them all on one scale. The noradrenaline equivalent is that scale: every other agent is multiplied by a ratio expressing its pressor effect relative to noradrenaline, and the products are added. It is used to describe shock severity, to define high-dose vasopressor therapy in cohort studies and to make trial arms comparable. Every paper that published a formula built it for that purpose.

The difficulty is that the published ratios do not agree. Kotani and colleagues set nine formulas side by side in 2023 and the disagreement is not marginal: phenylephrine is given a ratio of 0.06 in one formula, 0.1 in two others and 0.45 in a fourth, a 7.5-fold spread on a single drug; vasopressin is 2.5 per unit per minute in three formulas and 5 in another; dopamine is divided by 150 in one and by 100 in three. The disagreements come from the underlying evidence rather than from carelessness — the authors are explicit that their angiotensin II factor differs from Goradia’s fourfold because the two groups estimated it from different randomised trials. The consequence is that a noradrenaline-equivalent figure means nothing without the name of the formula that produced it, so this page prints four of them on every calculation and the ratio between the highest and the lowest.

There is a second, quieter trap in the units. Noradrenaline is infused in micrograms per kilogram per minute in some units and micrograms per minute in others; phenylephrine and vasopressin are usually per minute; dopamine is essentially always per kilogram. Five of the nine published formulas mix the two conventions inside a single sum, which is why VASST divides dopamine by 2 where Goradia divides it by 100, and why one paper’s vasopressin factor is 500 and another’s is 2.5. Neither is a different clinical claim; they are the same claim in different units. At 70 kg the two conventions differ seventyfold, which is the size of error available to anyone who enters a µg/min rate into a µg/kg/min field.

The most important thing here is what the number is not. These ratios were fitted to pressor effect in populations. They say nothing about receptor profile, and the agents are not interchangeable: noradrenaline is predominantly alpha-1, adrenaline adds substantial beta-1 and beta-2 activity and raises lactate, phenylephrine is pure alpha-1 and reflexly slows the heart, dopamine’s effect shifts with the infusion rate, and vasopressin acts on V1 receptors and not on adrenoceptors at all. Two infusions with the same equivalent figure can move cardiac output in opposite directions. Nothing here is a dose, a target or a conversion for switching a running infusion — that is done by titrating the new agent against the patient in front of you. A derived haemodynamic number is read alongside the patient — the history, the perfusion, the lactate, the trend across serial measurements — and never instead of them. It supports a clinician’s judgement rather than replacing it.

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References

1. Kotani Y, Di Gioia A, Landoni G, Belletti A, Khanna AK. An updated ‘norepinephrine equivalent’ score in intensive care as a marker of shock severity. Crit Care. 2023;27:29. The source of every ratio in the table on this page: its Table 1 reproduces nine published formulas side by side. Their own adds 0.06 × phenylephrine, 1/100 × dopamine, 2.5 × vasopressin (U/min), 1/8 × metaraminol and 0.0025 × angiotensin II (ng/kg/min) to the two catecholamines. The paper states the disagreement out loud: “the correction factors for angiotensin II are inconsistent even after the adjustment of the unit used (2.5 vs. 10)”.
2. Khanna A, English SW, Wang XS, et al. Angiotensin II for the treatment of vasodilatory shock (ATHOS-3). N Engl J Med. 2017;377(5):419–30. The norepinephrine-equivalent formula used in the trial, as reproduced in Kotani et al.’s Table 1: “Norepinephrine dose (µg/kg/min) + epinephrine dose (µg/kg/min) + 1/150 × dopamine dose (µg/kg/min) + 1/10 × phenylephrine dose (µg/kg/min) + 2.5 × vasopressin dose (U/min)”. The most widely reused of the formulas and the one this page’s headline figure follows.
3. Goradia S, Sardaneh AA, Narayan SW, Penm J, Patanwala AE. Vasopressor dose equivalence: a scoping review and suggested formula. J Crit Care. 2021. As reproduced in Kotani et al.’s Table 1: “Norepinephrine dose (µg/kg/min) + epinephrine dose (µg/kg/min) + 1/10 × phenylephrine dose (µg/kg/min) + 1/100 × dopamine dose (µg/kg/min) + 1/8 × metaraminol (µg/kg/min) + 2.5 × vasopressin dose (U/min) + 10 × angiotensin II dose (µg/kg/min)”.
4. Brown SM, Lanspa MJ, Jones JP, et al. Survival after shock requiring high-dose vasopressor therapy. Chest. 2013;143(3):664–71. As reproduced in Kotani et al.’s Table 1: “Norepinephrine dose (µg/kg/min) + epinephrine dose (µg/kg/min) + 1/100 × dopamine dose (µg/kg/min) + 5 × vasopressin dose (U/min) + 0.45 × phenylephrine dose (µg/kg/min)” — the outlier of the set on both vasopressin and phenylephrine.
5. Russell JA, Walley KR, Singer J, et al. Vasopressin versus norepinephrine infusion in patients with septic shock (VASST). N Engl J Med. 2008;358(9):877–87. Its equivalence formula, as reproduced in Kotani et al.’s Table 1, mixes the two unit conventions inside one expression: “Norepinephrine dose (µg/min) + 1/2 × dopamine dose (µg/kg/min) + epinephrine dose (µg/min) + 1/10 × phenylephrine dose (µg/min)”.

Not medical advice. For healthcare professionals and education. Reference intervals vary by laboratory and assay — always use your own laboratory's. Never base a dose or a treatment decision on this page alone. Full disclaimer at calcengines.com/disclaimer/