Intake and Output Measurement (I&O)
Key Points
- I&O monitoring detects fluid volume deficit or excess early, before major clinical manifestations develop
- Intake = all fluids entering the body; Output = all measurable fluids leaving the body; Insensible losses (sweat, respiration) cannot be measured
- In typical daily adult balance, about 60% of output is urine and about 40% is insensible loss from skin, lungs, and GI pathways
- Total intake should nearly equal total output daily; fluid balance = intake − output
- Combine I&O trend with daily weight; greater than 1 kg change in 24 hours is significant and should be reported
- All fluids documented in milliliters (mL); 1 oz = 30 mL; ice chips count as half volume
- Critical care patients: I&O monitored hourly; general patients: per shift (every 8–12 hours)
- Timely documentation is required; delayed charting can miss early negative or positive balance trends
Equipment
- Measuring container (graduated in mL) — for urine, drainage, emesis
- Toilet collection hat (commode hat) — to measure voided urine or liquid stool
- Urinal — for male patients
- I&O documentation record or electronic health record flow sheet
What Counts as Intake
All fluids taken in through any route:
| Route | Examples | Special Rules |
|---|---|---|
| Oral fluids | Water, juice, milk, broth, soups | Record full volume in mL |
| Foods liquid at room temperature | Ice cream, yogurt, custard, pudding, gelatin | Record full volume |
| High-water-content foods | Watermelon, cantaloupe, ice chips, popsicles | Count as half volume |
| Enteral feedings | NG tube feeds, gastrostomy tube feeds, free-water flushes | Record full volume |
| IV fluids | Maintenance fluids, antibiotics in piggyback, IV pushes, flushes, TPN | Record all volumes including flush amounts |
| Irrigation fluids | Bladder irrigation (IUC), wound irrigation | Include — will appear in output |
What Counts as Output
All measurable fluids leaving the body:
| Output Type | Documentation |
|---|---|
| Urine | Freely voided, catheter drainage bag (drain and measure at end of shift or hourly in ICU), urinary diversion, nephrostomy |
| Liquid stool | Measure with commode hat; document each episode of incontinence |
| Gastric output | NG suction, emesis (vomiting) |
| Wound/surgical drains | Jackson-Pratt (JP), Hemovac, chest tube — empty and measure per shift |
| Blood | Surgical blood loss estimate, blood transfusion output |
| Incontinence events | If volume cannot be measured, document each urine or liquid-stool occurrence for trend interpretation |
| Insensible losses | NOT documented — sweat, normal respiration, formed stool |
Procedure Steps
- Identify patients requiring I&O monitoring — ordered by provider for: fluid imbalance risk, diuretic therapy, fluid-volume-deficit-hypovolemia-and-dehydration, fluid-volume-overload-hypervolemia, renal conditions, cardiac conditions, post-operative status
- Gather measuring equipment — place measuring container in patient bathroom; provide commode hat, urinal, or collection receptacle as appropriate
- Educate patient and family — instruct patient to call nurse before flushing toilet; explain importance of saving all urine and liquid stool; explain that swallowing, urinating, or discarding fluids without measuring prevents accurate monitoring
- Measure and record intake — document all oral fluid amounts in mL (convert oz to mL: 1 oz = 30 mL); record IV fluids from pump totals; note special rules for ice chips (half volume) and enteral feeds
- Measure and record output — pour urine or drainage into graduated container at eye level to read measurement; document emesis and liquid stool volume
- Total and document I&O — calculate totals at end of each shift; in critical care, calculate hourly; document in flow sheet
- Calculate fluid balance — Intake − Output = Fluid Balance; positive balance = more in than out (risk for fluid overload); negative balance = more out than in (risk for dehydration); notify provider of significant imbalance
- Assess output quality, not only quantity — trend urine concentration/color changes (for example dark yellow or tea-colored urine can indicate concentration with fluid deficit)
- Report deviations — report sustained urine output <30 mL/hr (or <0.5 mL/kg/hr) over 8 hours to provider promptly (possible dehydration, renal hypoperfusion, or kidney dysfunction)
- Protect daily-weight accuracy when used with I&O trends — use the same scale/time/clothing-bedding baseline, zero bed/sling scales with standard linens, and keep drains/catheter bags off the scale during measurement.
Common Errors
- Forgetting to count IV flush volumes → falsely low intake total
- Counting ice chips as full volume → falsely high intake total (ice chips = half volume)
- Failing to include irrigation volumes in intake → falsely negative fluid balance
- Assuming incontinence episodes can be estimated without documentation → inaccurate output record
- Not monitoring urine output hourly in ICU patients → delayed recognition of oliguria (sepsis, AKI)
Related
- fluid-volume-deficit-hypovolemia-and-dehydration — I&O is essential monitoring tool for hypovolemia detection
- fluid-volume-overload-hypervolemia — Positive fluid balance trends indicate fluid overload risk
- intravenous-fluid-categories-tonicity-and-infusion-regulation — IV fluid volumes are part of intake record
- sepsis — Urine output ≥30 mL/hr is a key monitoring target in sepsis management
- bladder-assessment — Urinary output norms and abnormalities
- focused-assessment-for-fluid-electrolyte-and-acid-base-imbalance — I&O as component of fluid assessment