Infusion Rate Calculator (mcg/kg/min)

The formula

Rate (mL/hr) = (dose mcg/kg/min × weight kg × 60) ÷ (drug mcg ÷ bag mL). The 60 converts minutes to hours; the (drug mcg ÷ bag mL) is the concentration. The two unit conversions everyone gets wrong are mg→mcg (multiply by 1000) and per-min→per-hour (multiply by 60). Most pumps want mL/hr, not mcg/min.

Worked example — norepinephrine

Order: norepinephrine 0.1 mcg/kg/min, patient weight 80 kg. Bag: 4 mg / 250 mL. Dose per minute: 0.1 × 80 = 8 mcg/min. Dose per hour: 8 × 60 = 480 mcg/hr. Concentration: 4 mg = 4,000 mcg, in 250 mL = 16 mcg/mL. Pump rate: 480 ÷ 16 = 30 mL/hr.

Common pressor concentrations and starting doses

Norepinephrine: 4 mg / 250 mL (16 mcg/mL); start 0.05 mcg/kg/min. Epinephrine: 4 mg / 250 mL (16 mcg/mL); start 0.05 mcg/kg/min. Phenylephrine: 50 mg / 250 mL (200 mcg/mL); start 0.5-1 mcg/kg/min. Vasopressin: 20 units / 100 mL (0.2 units/mL); fixed 0.03-0.04 units/min, NOT weight-based. Dobutamine: 250 mg / 250 mL (1,000 mcg/mL); start 2.5-5 mcg/kg/min.

Reading a pump display

Most ICU pumps (Alaris, Plum, Baxter Sigma) display both mcg/kg/min and mL/hr. The dose is set in mcg/kg/min; the pump computes mL/hr from the entered concentration. ALWAYS verify the entered concentration matches the actual bag — wrong concentration setting is one of the most common medication errors with continuous infusions.

How to titrate a vasoactive drip safely

Titration of vasoactive infusions is one of the most consequential things bedside nurses do. The principle is simple: change one variable at a time, wait for steady-state response (usually 3–5 minutes for short half-life agents like norepinephrine, longer for vasopressin), and reassess MAP, heart rate, perfusion markers, and any in-line cardiac index data before the next change. Avoid the temptation to make multiple titrations in rapid succession because the lag between rate change and physiologic response masks which adjustment is actually working. Document every change with the time, the new rate, the MAP/HR before and after, and any concurrent events (fluid bolus, sedation change, position change).

For most adult ICUs, norepinephrine is the first-line vasopressor for septic and most types of distributive shock per Surviving Sepsis 2021 guidelines. Vasopressin is added at a fixed 0.03 units/min when norepinephrine cannot be weaned below 0.25–0.5 mcg/kg/min, both to spare adrenergic receptors and to add a non-adrenergic vasoconstrictor. Phenylephrine is preferred when tachycardia limits norepinephrine titration. Epinephrine is added or substituted in refractory shock, especially when low cardiac output coexists with vasoplegia. Knowing the order matters because changing the wrong drip can make the patient worse.

Concentration mistakes and bag-swap pitfalls

The single deadliest error pattern with continuous infusions is a concentration mismatch between the bag and the pump library. ISMP recommends standard concentrations precisely to eliminate this — but pharmacy sometimes sends a non-standard concentration during shortages or for fluid-restricted patients (e.g., 8 mg in 250 mL norepinephrine for a CHF patient on fluid restriction). When that bag arrives, the pump library still defaults to the standard 4 mg/250 mL setting. If the nurse hangs the new bag and forgets to update the concentration entry, the patient receives half the prescribed dose. The reverse error — entering a more dilute concentration than the actual bag — overdoses by twofold or more.

Always perform a bag-pump-line crosscheck before starting a new bag: confirm the drug name, the concentration on the label, the concentration in the pump library, the rate displayed, and that the line is traced from bag to patient. Independent double-check by a second nurse for any high-alert vasoactive drip is non-negotiable. Many EHR-integrated smart pumps now require a barcode scan of the bag against the order, which catches most concentration errors automatically — but the human verification step still matters because barcode systems fail when a label is wrinkled, a scanner is unavailable, or a pharmacy override has been entered.

Weaning and discontinuation

Weaning vasoactive infusions is as nurse-driven as starting them. The common wean is to reduce the rate by ~10–25% every 15–30 minutes as long as MAP stays at goal. If MAP drops, return to the prior rate and try again in 30–60 minutes. Many ICUs use formal "weaning protocols" that allow nurse-titrated reductions without a physician order each time, which speeds liberation and reduces ICU length of stay. When the rate is at the lowest setting (often 0.02 mcg/kg/min for norepinephrine) and MAP remains adequate without additional volume or oxygen support, the drug can be discontinued. After discontinuation, monitor for rebound hypotension over the next 30–60 minutes, particularly in patients on prolonged infusions where adrenergic receptor downregulation may have occurred.