How to Calculate Tube Feeds Per Hour
To calculate the hourly rate for enteral tube feeds, divide the patient's total daily caloric requirement (typically 30 kcal/kg/day for most patients) by the caloric density of the feed (usually 1.0 kcal/mL for standard formulas), then divide this total daily volume by the intended infusion hours (traditionally 24 hours, though volume-based approaches using 20 hours are superior).
Basic Calculation Framework
Step 1: Determine Daily Caloric Needs
- Standard requirement: 30 kcal/kg/day (or 30 mL/kg/day of standard 1.0 kcal/mL feeds) 1
- Severely malnourished patients: Start at <10 kcal/kg/day to prevent refeeding syndrome 1
- Protein requirements: 0.2–0.3 g nitrogen/kg/day (equivalent to 1.25–1.875 g protein/kg/day) 1
Step 2: Calculate Total Daily Volume
- Most commercial feeds contain 1.0 kcal/mL (standard) or 1.5 kcal/mL (high-energy versions) 1
- Formula: Total daily volume (mL) = Daily caloric requirement ÷ Feed caloric density
- Example: For a 70 kg patient needing 2100 kcal/day using standard 1.0 kcal/mL feed = 2100 mL/day
Step 3: Determine Hourly Rate
Traditional Rate-Based Method (Less Effective)
- Divide total daily volume by 24 hours
- Example: 2100 mL ÷ 24 hours = 87.5 mL/hour
- Problem: This approach leads to significant underfeeding when interruptions occur, with mean volume deficits of 247 mL/day 2
Volume-Based Method (Strongly Recommended)
- Divide total daily volume by 20 hours (not 24), but still infuse over 24 hours
- Example: 2100 mL ÷ 20 hours = 105 mL/hour
- Rationale: This compensates for inevitable feeding interruptions (procedures, extubations, etc.) 2, 3, 4
- Evidence: Volume-based feeding delivers 92.9% of goal calories vs. 80.9% with rate-based feeding, with significantly lower caloric deficits (-776 kcal vs. -1934 kcal, P = 0.01) 3
- Recent data shows volume-based protocols achieve 102% of energy goals vs. 75% with rate-based (P < 0.001) 4
Mode-Specific Considerations
Continuous Infusion (Post-Pyloric/Jejunal Feeds)
- Required for post-pyloric feeding due to loss of gastric reservoir 1
- Use volume-based calculation with maximum rate up to 150 mL/hour when catching up 5
- Avoid overnight continuous feeds in aspiration-risk patients 1
Intermittent Infusion (Gastric Feeds)
- Moderate rates via gravity or pump
- Include feeding breaks of ≥6 hours based on patient needs 1
- Can use overnight feeding schedules
Bolus Feeding (Gastric Only)
- Volume: 200–400 mL per bolus over 15–60 minutes 1
- Never use for jejunal feeds - causes dumping syndrome 1
- Administered via 50 mL syringe with or without plunger (gravity feeding) 1
- Normal subjects tolerate bolus volumes of 250–750 mL at 30 mL/min without distress 6
Fluid Requirements
- Standard: 30–35 mL/kg body weight per day 1
- Adjust for excessive losses (drains, fistulae, high-output stomas)
- Most feeds contain adequate electrolytes when meeting full energy needs 1
Critical Safety Points
Avoid Overfeeding
- Both inadequate and excessive feeding can be harmful 1
- Volume-based protocols may result in some overfeeding but without significant adverse outcomes 2, 3, 4
- No significant differences in hyperglycemia, emesis, diarrhea, or high gastric residual volumes (>400 mL) with volume-based vs. rate-based feeding 4, 5
Consult Dietitians
- Expert advice should be sought for feed prescription, especially in complex cases 1
- Adjust for organ failure (renal, hepatic, respiratory) with disease-specific formulations 1
Micronutrient Supplementation
- Standard feeds meet micronutrient needs only at full feeding volumes 1
- Give additional balanced supplements during early feeding when full volumes aren't tolerated 1
Practical Algorithm
- Calculate: Patient weight (kg) × 30 kcal = Daily caloric requirement
- Determine volume: Daily calories ÷ Feed density (1.0 or 1.5 kcal/mL) = Total mL/day
- Set hourly rate: Total mL ÷ 20 hours = Hourly rate (for volume-based approach)
- Adjust mode: Continuous for jejunal; intermittent or bolus for gastric
- Monitor: Aim for ≥80% of prescribed volume delivery = adequate nutrition 5, 7