TPN in Genery Surgery

Total parenteral nutrition (TPN) is an interesting aspect of pharmacy indeed. It is one of those areas whereby there is no overlap with the doctors (but with the dietitians! hehe) and pharmacists' roles are indispensable. My short stint at TPN unit was mind-opening indeed; not only does the TPN pharmacist needs to be well-versed with the clinical part and be skilful in compounding, he/she is also involved in stock procurement &control and his/her knowledge in aseptic room design is important.


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.

1^st 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
• Malabsorption
• 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.

It has been recommended that PN is tapered prior to discontinuation to prevent hypoglycaemia.

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)

Note:

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.

3.Non-protein calories (dextrose & lipid) = 1200 kcal

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?

References:

1. 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.
2. ESPEN guidelines on parenteral nutrition: surgery. Clin nutr 2009; 28: 376-386.
3. Kondrup J, Allison SP, Elia M, Plauth M. ESPEN guidelines for nutrition screening 2002. Clin nutr 2003; 22 (4): 415-421.
4. 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
5. 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.

The Other Indication of N-acetylcysteine

Apart from being the antidote to paracetamol poisoning, N-acetylcysteine is also used for the prevention of nephropathy associated with radiographic contrast media. (For instance, before and after primary angioplasty for acute myocardial infarction to reduce the risk of contrast-induced nephropathy.)

When it is used for such indication, the dose is 600mg bd orally before and the day of contrast media administration (total of 4 doses) [cf antidote to paracetamol poisoning: 150mg/kg over 15 min, then 50mg/kg over 4h, then 100mg/kg over 16h intravenously]. This indication is not in the MOH Formulary hence Ketua Pengarah Kesihatan (KPK) application is required.

Contrast agents reduce renal function by altering renal haemodynamics and by exerting direct toxic effects on tubular epithelial cells. It is on the assumption that reactive oxygen species in the pathogenesis of acute contrast-agent–induced reductions in renal function that the effects of the prophylactic oral administration of the antioxidant acetylcysteine have been studied in various trials.

According to EBSCO, to date, the outcomes for the use of acetylcysteine in the prevention of contrast nephropathy is of level 2 (mid level) and level 3 (lacking direct evidence). For those who are interested in the summary of various trials from EBSCO, you may email me at bpharmer05[at]gmail[dot]com.


References

1. Tepel M, van der Giet M, Schwarzfeld C et al. Prevention of radiographic-contrast-agent-induced reductions in renal function by acetylcysteine. N Engl J Med 2000; 343: 180-184.
2. Acetylcysteine. Dynamed-powered by EBSCOhost. 2010 May 8 [Accessed 2010 May 22]; Available from: URL: http://dynaweb.ebscohost.com/

Antibiotic Prophylaxis in Thalassaemia

The other day, I received a call from a house officer regarding penicillin V dose in thalassaemic children. She was unsure of the indication.


Findings
Splenomegaly (enlarged spleen) is common in thalassaemia major and intermedia due to the high rate of haemolysis (red blood cell destruction). This takes place because the spleen sees the defective red cells of the thalassaemic as deficient and the transfused red cells as invaders (much the same as with host vs graft disease) and removes them from circulation.

In some patients, splenectomy is performed as it may help decrease transfusion requirements for patients with splenomegaly.

The drug of choice for prophylaxis in patients with thalassaemia who have undergone a splenectomy is penicillin. This is because it is active against most microorganisms considered to be major pathogens in splenectomised patients (ie, streptococcal, pneumococcal, and some staphylococcal microorganisms) but not penicillinase-producing species.


Sanford Guide to Antimicrobial Therapy
Asplenic children to have antimicrobial prophylaxis until age 5:
Amoxicillin 20mg/kg/day OR
Penicillin V 125mg bd

Children over age 5:
Penicillin V 250mg bd for at least 1 year in children post-splenectomy

If allergic to penicillin:
-trimethoprim-sulfamethoxazole [National Antibiotic Guidelines states dose as 960mg od] OR
-clarithromycin
[NAG also recommends erythromycin 400mg bd OR azithromycin 250mg od]

The National Antibiotic Guidelines, based on article from BMJ 307, 1372-1373, recommends the duration of treatment to be minimum 2 years post splenectomy in adults and up to 16 years of age in children. Life long is not recommended.



References

1. Sanford Guide to Antimicrobial Thearpy 2006
2. National Antibiotic Guidelines
3. Yaish HM. Thalassaemia Intermedia. Emedicine. 2009 September 29 [Accessed 2010 May 22] Available from: URL: http://emedicine.medscape.com/article/959122-treatment