Nutritional considerations when commencing TPN

Mary Peck, Dietitian

Nutritional considerations when commencing TPN

• Assessment of nutritional requirements• Assessment of re-feeding risk• Safe introduction of TPN

Case study

• Mrs A• Wt 50kg, ht 150cm, BMI 22• Small bowel resection with anastomosis

10days ago. Now has septic picture, ?anastomotic leak. Minimal diet since surgery. Pt currently in bed or sitting in a chair.

• Bloods: creat 50, urea 5, Na 139, k3.9, PO4 1.0, mg 0.73, CRP 190

Assessment of nutritional requirements

• Energy (fat and glucose}• Nitrogen• Electrolytes• Micronutrients• Fluid

Energy

• The components of energy expenditure are:• Basal metabolic rate (BMR)• Disease state/stress• Activity level

Calculation of BMR

• Use equations based on gender, age and weight.• Henry/Oxford (2005) equations currently used. F M• 18-30 13.1W+558 16.0W+545• 30-60 9.74W+694 14.2W+593• 60-70 10.2W+572 13.0W+567• 70+ 10W+577 13.7W+481

• Mrs A BMR: 10.2x50+572=1082kcals

Weight

• Weight can be deceptive

• Oedema: minimal 1.0kg,moderate 5.0kg, severe 10.0kg

• Ascites: minimal 2.2kg, moderate 6.0kg, severe 14.0kg

Adjusting for stress

• Adjust BMR to account for stress

• Examples:• Infection 25-45%• Surgery (uncomplicated ) 5-20%• Surgery (complicated) 25-45%

• Mrs A (BMR 1082kcals)25% infection= 270kcals

Activity

• Adjust BMR to account for activity level

• Sedated and ventilated 0%• Bed bound immobile 10%• Bed bound mobile/sitting 15-20%• Mobile on ward 25%

• Mrs A (BMR 1082kcals): 20% activity= 216kcals

Energy requirements of case study

• Mrs A, 62yrs, wt 50kg, CRP 190, sitting in chair

• BMR: 10.2x50+572=1082kcals• 25%infection: 270kcals• 20% activity: 216kcals • Total energy requirements 1568kcals

(1600kcals)

Calculation of nitrogen requirements

• Normal requirements 0.17g/kg/day (0.14-0.2)

• Hypermetabolic• 5-25% 0.2 (0.17-0.25)• 25-50% 0.25 (0.2-0.3)• >50% 0.3 (0.25-0,35)

• Mrs A: 50x0.25=12.5g nitrogen per day

Electrolyte requirements

• Na: 1mmol/kg• K: 1mmol/kg: (2-4mmols/kg in re-feeding)• Mg: 0.1-0.2mmol/kg: (0.2mmol/kg in re-

feeding)• P04: 0.5-0.7mmol/kg: no specific re-feeding

guideline, but will need to give maximum P04 limit in small TPN bags

• Ca: 0.1-0.15mmol/kg

Daily fluid requirements

• 18-60 yrs: 35ml/kg• >60yrs : 30ml/kg

• Re-feeding: consider prescribing: 20-25mls/kg. (NICE-Intravenous fluid therapy in adults in hospital, 2013)

Mrs A requirements

• Mrs A: 62yrs, 50kg, BMI 22• Energy: 1600 kcals• Nitrogen: 12g• Na: 50 mmols• K: 50 mmols • P04: 25-35 mmols• Mg: 5-10 mmols• Ca: 5-7.5 mmols• Fluid approx 1500ml

Assessment of re-feeding risk (NICE)

• At risk

• Little or no intake > 5 days

• Introduce feeding at maximum of 50% requirements for the first 2 days.

• Monitor biochemistry• Meet full requirements for electrolytes and

micronutrients.

High re-feeding risk (NICE)

• Starved state plus any of the following:• BMI<16• Unintentional weight loss >15% within the last 3-6 months• Little or no nutrition >10days• Low levels K, Mg or P04 prior to feeding

• Starved state plus 2 of the following:• BMI<18.5• Unintentional weight loss >10% within the last 3-6 months.• Very little or no nutrition for >5 days• History of alcohol abuse

Management of high re-feeding risk (NICE)

• Start nutrition at 10kcals/kg/day• Build up over 4-7days• Monitor K, Mg, P04, supplement if necessary • 1 pair pabrinex o.d for 10 days

Mrs A: re-feeding risk

• High risk since minimal nutrition for 10 days.• K, Mg, P04 currently normal, but likely to drop

• Pabrinex: 1pair od for 10days• Start feeding at 10kcals/kg: 500kcalsday• Increase nutrition over minimum of 4 days.

Mrs A: increase in TPN

• Requirements: 1600kcals, 12gN

• Day 1: smof 4 (500kals, 4gN)• Day 2: smof 4 (500kals, 4gN)• Day 3 :smof 8 (1100kcals, 8gN)• Day 4: smof 12 (1600kcals, 12gN)

• Full complement of electrolytes and micronutrients

Summary

• Nutritional assessment to determine requirements.

• Assess re-feeding risk before starting nutrition.• Increase nutrition cautiously as per NICE

(2006 CG32) on re-feeding.