Prior to the commencement of TPN, patient assessment is done to find out if he/she requires nutrition support. This can be done using the ESPEN guidelines for nutrition screening 2002.
If the patient requires a nutrition plan, the next step will be to decide if oral, enteral or parenteral means of nutrition support is suitable.
1st choice in postoperative artificial nutrition: enteral feeding or a combination of enteral & supplementary parenteral feeding. This is because
enteral nutrients maintain GI mucosal structure & function,is less costly and less invasive.
Indications for Postoperative Parenteral Nutrition:
Undernourished pt in whom enteral nutrition is not feasible/not tolerable
Patient with postoperative complications impairing gastrointestinal function who are unable to receive adequate amounts of oral/enteral feeding for at least 7 day
Patient is undernourished if ≥1 criteria present:
Weight loss >10-15% within 6 months
BMI < style="line-height: 115%;">
Serum albumin <>(with no evidence of hepatic or renal dysfunction)
Contraindications for Enteral Nutrition:
- Intestinal obstruction
- Multiple fistulas with high output
- Intestinal ischaemia
- Severe shock with impaired splanchnic perfusion
- Fulminant sepsis
25 kcal/kg ideal body weight gives an approximate estimate of daily energy expenditure & requirements
Severe stress: may require 30kcal/kg ideal body weight
In patient unable to be fed via enteral route after surgery, a full range of vitamins & trace elements should be supplemented on a daily basis.
Weaning from PN is not necessary.
However it has been shown that even after prolonged PN, the beta-cells remain sensitive to changes in glucose levels & adaptation of glucose levels and insulin secretion occurs very quickly.
In some other institutions, the non-protein calories to nitrogen (NPC: N) ratio is used in TPN compounding.
NPC/N = Non-protein calories (kcal)/nitrogen (g)
1g N= 6.25 g protein
1g dextrose = 4kcal
1g protein = 4 kcal
1g lipid = 9kcal
The calculations below are what I was taught in my uni days by an experienced TPN pharmacist.
1. Decide NPC:N ratio for patient (e.g. 100: 1 for severely stressed patients)
2.Estimate total protein requirement. (1.5 g/kg/day; 1.5 x 50kg =75 g protein= 75/6.25=12g N)
If 12g N is to be given, 12 x 100 = 1200 kcal non-protein calorie is required for reach a NPC: N of 100.
1200 kcal --> 600 kcal dextrose, 600 kcal lipid
4. Dextrose = 600kcal/4kcal= 150 g
Lipid = 600kcal/9kcal = 67g
Desirable NPC:N ratios
80:1 the most severely stressed patients
100:1 severely stressed patients
150:1 unstressed patient
Increasing the amount of amino acids administered is particularly effective under surgically stressed conditions due to the increase in amino acid requirements.
The optimal NPC/N ratio is estimated to be about 100 (50 g as amino acids), when the IV solution is administered at the anticipated daily dose in clinical use (1000 kcal/day)
- Test solutions with NPC/N ratio 50, 100, 150 or 200 were administered parenterally at a rate of 120 kcal/kg/day for 5 days to normal rats
- Protein synthesis rate in the liver increased with a decrease in the NPC/N ratio
- NPC/N: 50, the levels of serum urea nitrogen and serum branched chain amino acids were high, implying an excessive accumulation of amino acids.
How is the TPN practice in your hospital?
- Holcombe BJ. Adult parenteral nutrition. In Yong LL, Koda-Kimble MA (editors). Applied therapyeutics-the clinical use of drugs. Pennsylvania: Lippincott Williams & Wilkins;1995. p. 35-1—35-15.
- ESPEN guidelines on parenteral nutrition: surgery. Clin nutr 2009; 28: 376-386.
- Kondrup J, Allison SP, Elia M, Plauth M. ESPEN guidelines for nutrition screening 2002. Clin nutr 2003; 22 (4): 415-421.
- California State University Northridge. Parenteral nutrition total [Online]. 2000 September 7 [accessed 2010 July 14]; Available from: URL: http://www.csun.edu/~cjh78264/parenteral/calculation/calc05.html
- Nakayama M., Motoki T, Kuwahata T and Onodera R. The optimal nitrogen proportion to non-protein calories in normal rats receiving hypocaloric parenteral nutrition. Nutrition Research 2002; 22: 1091–1099.