NG-tube feeding ramp for an inappetent cat
An 8 kg cat is hospitalized for hepatic lipidosis. You place an NG tube and plan a 3-day ramp to 100% RER using a liquid diet at 1.0 kcal/mL, delivered as four boluses per day. Calculate RER, the Day 3 daily volume, and the per-bolus volume on Day 3. Compare the per-bolus volume to the 10 mL/kg per-feeding cap.
Hint
RER is not linear in body weight. It uses an exponent: the metabolic rate scales with body mass to the 3/4 power. You'll need to compute 8 raised to the 0.75 power (or use a calculator).
Another hint
Three steps. (1) RER = 70 × BW^0.75 (BW in kg). For 8 kg, BW^0.75 ≈ 4.76. (2) Day 3 is 100% RER in a 3-day ramp; daily volume = RER kcal/day ÷ diet kcal/mL. (3) Per-bolus = daily ÷ 4 feedings. The 10 mL/kg cap = 10 × 8 = 80 mL per feeding.
Show worked answer
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Compute RER from the standard formula. The 0.75 exponent reflects allometric scaling: metabolism rises with body mass but more slowly than linearly.
$$\text{RER} = 70 \times (8)^{0.75} \approx 70 \times 4.76 \approx 333 \,\tfrac{kcal}{day}$$ -
The 3-day ramp delivers 33% / 66% / 100% of RER on Days 1, 2, 3 respectively. The ramp is conservative: it gives the GI tract time to tolerate enteral nutrition and reduces refeeding-syndrome risk in chronically inappetent patients.
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Day 3 daily kcal target = 100% × 333 = 333 kcal. Convert to volume of liquid diet at 1.0 kcal/mL:
$$\frac{333 \,\cancel{kcal}}{1.0 \,\cancel{kcal}/mL} = 333 \,\tfrac{mL}{day}$$ -
Divide by 4 feedings per day for the per-bolus volume.
$$\frac{333 \,mL}{4 \,\text{feedings}} \approx 83 \,\tfrac{mL}{\text{feeding}}$$ -
Compare to the 10 mL/kg per-feeding cap. For an 8 kg cat, the cap is 80 mL. 83 mL slightly exceeds the cap.
$$\text{cap} = 10 \,\tfrac{mL}{\cancel{kg}} \times 8 \,\cancel{kg} = 80 \,\tfrac{mL}{\text{feeding}}$$ -
The fix is to add a fifth feeding rather than push the individual bolus higher. 333 mL ÷ 5 = ~67 mL per feeding, comfortably below the 80 mL cap. Boluses larger than the cap raise the risk of regurgitation and aspiration.
RER ≈ 333 kcal/day. Day 3 (100% RER) = 333 mL/day at 1.0 kcal/mL. Split across 4 feedings, that's ~83 mL per bolus, which slightly exceeds the 10 mL/kg per-feeding cap (80 mL). Either add a fifth feeding (drops bolus to ~67 mL) or accept the marginal overage with close monitoring for regurgitation.