Infusion Basics for Nurses: Concentrations, Dilutions, and Titrated Drips

1) Calculating Infusion Concentration (mg/mL) From the Bag

Infusion concentration tells you how much drug is in each milliliter of fluid. This is the key bridge between a provider order written in mg/hr (or units/hr) and the pump setting in mL/hr.

Core formula

Concentration = total drug in bag ÷ total volume in bag

For mg-based drips:

mg/mL = total mg ÷ total mL

For unit-based drips:

units/mL = total units ÷ total mL

Step-by-step workflow (bedside-ready)

• Step 1: Read the label as a “whole bag” statement. Example: “Heparin 25,000 units in 250 mL.”
• Step 2: Identify the two totals. Total drug = 25,000 units; total volume = 250 mL.
• Step 3: Divide to get concentration. 25,000 ÷ 250 = 100 units/mL.
• Step 4: Write the concentration clearly in your notes or on your calculation line (e.g., 100 units/mL).

Examples

Example A (mg/mL): A bag is labeled “Diltiazem 125 mg in 125 mL.”

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• Concentration = 125 mg ÷ 125 mL = 1 mg/mL

Example B (mg/mL): A bag is labeled “Amiodarone 900 mg in 500 mL.”

• Concentration = 900 ÷ 500 = 1.8 mg/mL

Example C (units/mL): “Insulin 100 units in 100 mL.”

• Concentration = 100 ÷ 100 = 1 unit/mL

2) Converting Ordered mg/hr or units/hr to mL/hr Using the Prepared Concentration

Once you know the prepared concentration (mg/mL or units/mL), you can convert an ordered dose rate (mg/hr or units/hr) into a pump rate (mL/hr). The logic is: how many mL each hour are needed to deliver the ordered amount each hour?

Core formula

mL/hr = (ordered dose per hour) ÷ (concentration per mL)

So:

• mL/hr = (mg/hr) ÷ (mg/mL)
• mL/hr = (units/hr) ÷ (units/mL)

Step-by-step workflow

• Step 1: Confirm the concentration from the bag label (or pharmacy prep).
• Step 2: Confirm the order is per hour (mg/hr or units/hr).
• Step 3: Divide ordered dose rate by concentration.
• Step 4: Apply pump rounding rules per policy (often to the nearest tenth for many pumps; verify your device/unit standard).
• Step 5: Sanity-check: If you increase the ordered dose/hr, the mL/hr should increase proportionally (unless concentration changes).

Examples

Example A (mg/hr → mL/hr): Diltiazem bag concentration is 1 mg/mL. Order: 10 mg/hr.

• mL/hr = 10 mg/hr ÷ 1 mg/mL = 10 mL/hr

Example B (mg/hr → mL/hr): Amiodarone concentration is 1.8 mg/mL. Order: 54 mg/hr.

• mL/hr = 54 ÷ 1.8 = 30 mL/hr

Example C (units/hr → mL/hr): Heparin concentration is 100 units/mL. Order: 1,200 units/hr.

• mL/hr = 1,200 ÷ 100 = 12 mL/hr

3) Titration Scenarios: Adjusting Rates Safely and Documenting Changes

Titrated drips change over time based on patient response and a protocol. Safe titration is less about “doing math fast” and more about following a consistent workflow that prevents skipped steps and documentation gaps.

A safe titration workflow (repeat every time)

• 1) Verify the titration order and protocol language. Identify: target (e.g., BP range, HR range, lab goal), increment size (e.g., “increase by 2 mg/hr”), and minimum time between changes.
• 2) Identify your current dose rate and current pump rate. Record both (e.g., “currently 8 mg/hr at 8 mL/hr”).
• 3) Apply the protocol increment to the dose rate (not the mL/hr). This prevents errors when concentration is not a clean number.
• 4) Convert the new dose rate to a new pump rate using the concentration.
• 5) Round appropriately for the pump and policy. If rounding changes the delivered dose meaningfully, re-check with a second nurse or pharmacy per policy.
• 6) Document the change clearly. Include: time, assessment trigger, old dose/rate, new dose/rate, and patient response plan (e.g., “recheck BP in 5 min”).

Example titration (mg/hr increments)

Scenario: Diltiazem concentration 1 mg/mL. Protocol: “Titrate by 2 mg/hr every 15 minutes to HR goal.” Current dose: 6 mg/hr.

• New dose after one increase: 6 + 2 = 8 mg/hr
• New pump rate: 8 mg/hr ÷ 1 mg/mL = 8 mL/hr
• Document: “Time, HR, increased from 6 mg/hr (6 mL/hr) to 8 mg/hr (8 mL/hr) per protocol; reassess HR/BP in 15 min.”

Example titration (units/hr increments)

Scenario: Heparin concentration 100 units/mL. Protocol: “Increase by 200 units/hr based on anti-Xa/aPTT nomogram.” Current dose: 1,000 units/hr.

• New dose: 1,000 + 200 = 1,200 units/hr
• New pump rate: 1,200 ÷ 100 = 12 mL/hr
• Document: “Nomogram adjustment: increased from 1,000 units/hr (10 mL/hr) to 1,200 units/hr (12 mL/hr); next lab due at ___.”

Mini-checklist for documentation (dose + rate)

4) Common Pitfalls (and How to Avoid Them)

Pitfall 1: Mixing up total drug in the bag vs. concentration

What it looks like: Using “900 mg” (the whole bag) as if it were “900 mg/mL.”

Prevention: Always write concentration with units: mg/mL or units/mL. If you can’t attach “per mL,” you’re not done.

Pitfall 2: Misreading labels like “___ in 250 mL”

What it looks like: Treating “in 250 mL” as an extra volume to add, or ignoring it and assuming a standard concentration.

Prevention: Translate the label into a fraction immediately: total drug / total mL. Example: “25,000 units in 250 mL” becomes 25,000 units ÷ 250 mL.

Pitfall 3: Confusing mg/hr with mL/hr during titration

What it looks like: Protocol says “increase by 2 mg/hr,” but the nurse increases the pump by 2 mL/hr without checking concentration.

Prevention: Titrate in the ordered dose unit first (mg/hr or units/hr), then convert to mL/hr.

Pitfall 4: Inappropriate rounding for pump settings

What it looks like: Rounding 33.3 mL/hr to 35 mL/hr “for simplicity,” unintentionally changing the dose.

Prevention: Round only according to pump capability and unit policy. When in doubt, keep one decimal place if the pump allows it, and verify the delivered dose after rounding by multiplying back: (mL/hr) × (mg/mL) = mg/hr delivered.

Pitfall 5: Skipping the “multiply-back” check

What it looks like: A calculated mL/hr is entered without verifying it delivers the intended mg/hr or units/hr.

Prevention: Quick check after rounding:

delivered dose/hr = pump mL/hr × concentration

If the delivered dose/hr is not acceptably close to the ordered dose/hr, re-calculate and clarify rounding expectations.

5) Integrated Case Exercises (Initial Rate → Titration → Dose Delivered Over Time)

Work these like you would at the bedside: find concentration, set the initial pump rate, apply one titration change, then verify how much drug the patient received over a defined time interval.

Case 1: mg-based drip with clean concentration

Bag: Diltiazem 125 mg in 125 mL

Order: Start at 10 mg/hr. Titrate by +2 mg/hr after 15 minutes if HR remains above goal. After titration, the drip runs at the new setting for 45 minutes.

Step 1: Concentration

• 125 mg ÷ 125 mL = 1 mg/mL

Step 2: Initial pump rate (mL/hr)

• mL/hr = 10 mg/hr ÷ 1 mg/mL = 10 mL/hr

Step 3: One titration increase

• New dose: 10 + 2 = 12 mg/hr
• New pump rate: 12 ÷ 1 = 12 mL/hr

Step 4: Verify final dose delivered over 45 minutes at the new setting

• Convert time: 45 min = 0.75 hr
• Dose delivered: 12 mg/hr × 0.75 hr = 9 mg
• Cross-check via volume: 12 mL/hr × 0.75 hr = 9 mL; at 1 mg/mL → 9 mg

Case 2: mg-based drip with non-integer concentration (rounding + multiply-back)

Bag: Amiodarone 900 mg in 500 mL

Order: Infuse at 72 mg/hr. Protocol: if ectopy persists, increase by 18 mg/hr. After the increase, run for 30 minutes. Pump accepts tenths (0.1 mL/hr).

Step 1: Concentration

• 900 ÷ 500 = 1.8 mg/mL

Step 2: Initial pump rate

• mL/hr = 72 ÷ 1.8 = 40 mL/hr

Step 3: Titration increase

• New dose: 72 + 18 = 90 mg/hr
• New pump rate: 90 ÷ 1.8 = 50 mL/hr

Step 4: Dose delivered over 30 minutes at the new setting

• 30 min = 0.5 hr
• 90 mg/hr × 0.5 hr = 45 mg

Case 3: units-based drip with titration and delivered dose check

Bag: Heparin 25,000 units in 250 mL

Order: Start at 1,100 units/hr. Titrate by +200 units/hr per nomogram. After titration, the infusion runs for 2 hours.

Step 1: Concentration

• 25,000 ÷ 250 = 100 units/mL

Step 2: Initial pump rate

• mL/hr = 1,100 ÷ 100 = 11 mL/hr

Step 3: Titration increase

• New dose: 1,100 + 200 = 1,300 units/hr
• New pump rate: 1,300 ÷ 100 = 13 mL/hr

Step 4: Verify dose delivered over 2 hours at the new setting

• 1,300 units/hr × 2 hr = 2,600 units
• Cross-check via volume: 13 mL/hr × 2 hr = 26 mL; at 100 units/mL → 2,600 units

Quick self-check questions (use after each exercise)

• Did I write the concentration with correct units (mg/mL or units/mL)?
• Did I titrate the dose rate first (mg/hr or units/hr), then convert to mL/hr?
• After rounding, did I multiply back to confirm the delivered dose/hr matches the intended dose/hr?
• When calculating dose delivered over time, did I convert minutes to hours correctly?