Parenteral nutrition
From WardWiki - Foundation Doctor Helper
Contents |
Indication
Parenteral nutrition (PN) may be indicated in the following circumstances:
- acute severe pancreatitis - this is not universal and to be considered only when oral input is not tolerated.
- high output, small bowel fistula
- prolonged ileus (greater than 1 week)
- inability to be fed orally or enterally for more than 1 week
- short bowel
- radiation enteritis
Disadvantages
The sole advantage of TPN is the ability to feed a patient while there is gut failure or there is need to rest the gut while an enterocutaneous fistula heals. There are many more reasons NOT to consider TPN than to consider it and these are listed below:
- Loss of use and direct nutrition to the gut can lead to translocation of gut flora into the circulation casing sepsis
- Risks of establishing central venous access such as pneumothorax
- High fluid load of peripheral TPN limits its use considerably
- Lipaemia and cholestasis can result from lipid infusion
- Risks of venous thrombosis and occlusion
- Risk of line sepsis is very real and frequently happens; microbes are usually staphylococcal.
Starting Parenteral Nutrition
Patients starting PN are at risk of developing refeeding syndrome and PN should be started slowly to try & minimise complications (NICE guidelines 2006). All patients should be given Pabrinex before starting PN See page 4 & then daily for up to 5 days in the most severely undernourished. Patients should be prescribed half a Kabiven K11 Standard 1 daily for the first 48 hours and monitored carefully for refeeding syndrome with daily bloods for U&E, Ca, Mg, PO4 and IV supplementation as required.
Patients will need additional fluid & electrolyte supplementation during this time. Please be cautious in the quantity and use of additional IV fluid. Use normal saline or Hartmann’s Solution in place of Dextrose or 5% Dextrose as the PN solution will provide a high concentration of glucose once commenced. DO NOT OVERLOAD THE PATIENT by failing to include TPN volume on the fluid balance chart.
Refeeding Syndrome
Refeeding syndrome is defined as severe fluid and electrolyte shifts and related metabolic implications in malnourished patients undergoing refeeding (Solomon and Kirby, 1990). Refeeding syndrome is caused by a switch from starvation to anabolism, with glucose as the major energy source.
Metabolic abnormalities include:
- Hypophosphataemia
- Hypokalaemia
- Hypomagnesaemia and occasionally hypocalcaemia
- Altered glucose metabolism (hyperglycaemia)
- Vitamin deficiency
- Cardiac failure, pulmonary oedema and dysrhythmias
- Acute circulatory fluid overload or fluid depletion
These abnormalities can lead to cardiac, respiratory, neuromuscular, haematologic, hepatic and gastrointestinal complications. If untreated they can be fatal.
Patients at high risk of refeeding syndrome include: Patients with one of the following:
- BMI < 16 kg/m2
- Unintentional weight loss > 15% within last 3-6 months
- Little or no nutritional intake for > 10 days
- Low levels of potassium, phosphate or magnesium prior to feeding
OR Patients with two or more of the following:
- BMI < 18.5kg/m2
- Unintentional weight loss > 10% within last 3-6 months
- Little or no nutritional intake for > 5 days
- A history of alcohol abuse or medicine including insulin, chemotherapy, antacids or diuretics
(NICE 2006)
Patients at high risk of refeeding syndrome should receive adequate doses of thiamine, Vitamin B and multivitamins/trace elements immediately before and for the next three days of feeding (NICE 2006) or for longer is the patient is severely malnourished). This may also be administered intravenously once daily as a pair of Pabrinex ® intravenous high potency (vitamin B & C injection BPC) ampoules. These contain 250 mg of thiamine. Ensure ampoules are for intravenous administration. Mix 1 pair (ampoules 1 & 2) together in a syringe. Add to a minimum of 50 -100ml normal saline or glucose 5% and infuse over 30 minutes.
Caution: Repeated injections of Pabrinex or large doses: >400mg, have been associated with anaphylaxis. Facilities for treating anaphylactic reactions should be available. Patients on enteral feeds should receive oral thiamine 200-300mg/day, vitamin B co-strong 1-2 tablets tds and a balanced multivitamin/trace element supplement once daily. For those unable to swallow safely may have oral thiamine tablets crushed and dispersed in water and Vigranon B Syrup (Oral vitamin B complex) given via the enteral tube feeding.
Patients at high risk of refeeding syndrome require oral/enteral/intravenous supplements of potassium (likely requirement 2-4mmol/kg/day), phosphate (likely requirement 0.3-0.6mmol/kg/day) and magnesium (likely requirement 0.4mmol/kg/day). In such patients the FY1 should monitor bloods (U & E’s, Ca, Mg & Phosphate) daily and correct abnormalities where necessary.
Nutrition support should be started slowly in seriously ill patients requiring enteral feeding. It should be started no more than 50% of the estimated target energy and protein requirements and be built up to meet their full needs over 24-48 hours. In patients at high risk of refeeding syndrome feed should start at a maximum of 10kcal/kg/day increasing slowly to full requirements over 4-7 days. In extreme cases use only 5kcal/kg/day restoring circulatory volume and monitoring fluid balance and overall clinical status closely. In all patients full requirements of fluids, electrolytes, vitamins and minerals should beprovided from the outset of feeding.
Replacement Therapy in Refeeding Syndrome
(Adapted from Dewar & Horvath, 2001, Terlevich et al. 2003, NICE 2006) The following are guidelines only and should not replace the clinical judgement of the doctor and pharmacist. NICE (2006) no longer recommends delaying the start of the feed in patients at risk of refeeding syndrome to replace electrolytes – but does recommend starting the feed cautiously whilst replacing the electrolytes. All patients at risk of refeeding syndrome should be given oral thiamine or Pabrinex before starting the feed.
Low phosphate
Serum phosphate <0.5mmol/l represents severe deficiency and needs correcting regardless of the route of feeding. Serum phosphate >0.5mmol/l in patients on enteral feeding - phosphate can be corrected with the use of oral phosphate preparations e.g. Phosphate-Sandoz (effervescent tablets – 1 tablet = 16.1 mmol phosphate).
Correcting phosphate intravenously
Infuse 500ml Phosphate Polyfusor (giving 50mmol phosphate, 81mmol sodium, 9.5mmol potassium) through a dedicated cannula over 24 hours Monitor phosphate levels daily Further infusions of the phosphates polyfusor can be given (as above) if phosphate is still <0.5mmol/l. (Note IV phosphate should not be given to hypocalcaemic patients).
Low Magnesium
Serum magnesium <0.6mmol/l requires IV replacement. Serum magnesium levels 0.6 – 0.8 mmol/l in patients on enteral feeding may be supplemented orally/enterally using magnesium glycerophosphate tablets (4 mmol magnesium per tablet) or Magnesium glycerophosphate liquid 1mmol/ml.) The initial dose is 1-2 tablets 3 times a day, up to 3 tablets four times a day. The tablets can be dispersed in water for tube administration. For tube administration: Flush the tube well before and after magnesium or the drug may precipitate and block the tube. N.B. these preparations are unlicensed, therefore, the doctor must sign a disclaimer form
Correcting Magnesium intravenously
Give 8-12mmol magnesium (4 ml 50% magnesium sulphate injection) in 100 ml 5% glucose or 0.9% sodium chloride over eight hours, or 60 minutes in a HDU / ITU The second dose should be 8-12 mmol (20 ml 50% magnesium sulphate) in a minimum of 100 ml over 20 hours. Recheck magnesium levels. Higher infusions than this do really require specialist input.
Incompatabilties
Magnesium or calcium, & phosphate may be given simultaneously via the intravenous route however these should be given via separate cannula. Ideally these should be placed in opposing limbs as precipitation of insoluble phosphates results.
Hyperglycaemia during Parenteral nutrition and insulin treatment
Parenteral nutrition will be given continuously and hence need for gylcaemic control is contant and predictable.
- If BM greater than 8-10mmol/l, use intravenous insulin regime as per hospital insulin sliding scales, available in all hospital departments routinely. Insulin resistance is seen in many ill patients, even when not previously known to be diabetic.
- Do not avoid prescribing IV dextrose in case of hypoglycaemia if patient is on insulin. The PN is a constant source of glucose but cannot be safely bolused as fat embolism or other complications due to it's viscosity and cation content can occur. It is dangerous to attempt speeding up of TPN for many reasons but this is certainly one of them!!
- Insulin must never be stopped in IDDM or uncontrolled NIDDM.
- This means that insulin must not be stopped during feeding, though may be reduced or stopped when not feeding.
- BM 4 hourly is usually sufficient when patient has held a stable plasma glucose.
Management of known diabetics during parenteral nutrition
- All previously known or newly diagnosed diabetics who are referred to the dietetic department for parenteral feeding should have an urgent (same day) referral written by a dietitian or member of the nutrition team to the Diabetologist.
- For diabetic patients that are diet controlled or oral hypoglycaemics, conversion to insulin is almost always required upon starting parenteral feeding. For patients on insulin, their regimen may need substantial adjustment to accommodate the hyperglycaemia caused by parenteral feeding and by the constant rather than intermittent carbohydrate intake. All carbohydrate intake from TPN is from glucose and this is in part to reduce its viscosity.
- Diabetes team referral is always required
- Non-diabetic patients who are referred for parenteral feeding should have their BM monitored once a day at different times of the day for 3-5 days whilst receiving the enteral feeding and recorded on the green blood glucose monitoring charts attached to the drug charts. Blood glucose recording is to be done while on feeding, not during a break. Monitoring can stop if the blood glucose is less than 10mmols on full feeding rate for 48 hours.
- If a blood glucose level of greater than 10 mmol/l is recorded then an urgent referral should be written and sent to the diabetologist.
When commencing a parenteral feed on a diabetic patient, hyperglycaemia occurs within a few hours and can be marked. If no concomitant insulin treatment is started patients can become grossly polyuric and dehydrated, and may progress to HONK (hyper-osmolar nonketosis)in type 2 diabetics, or DKA (diabetic ketoacidosis) in type 1 diabetics.
- Commence IV Insulin sliding scale infusion on starting parenteral feed, and adjust the sliding scale according to chart instructions to keep blood glucose under control.
- Blood glucose monitoring should be dependent on previous results and as per protocol. It is often useful to continue insulin sliding scale for a few days while reintroduction of enteral feeding rate is progressively increased until full feeding rate is achieved.
Reintroduction of enteral feeding
This is desired to aid discharge and use the working gut. There are many advantages to using the gut rather than TPN and these should be sought as early as possible. Reintroduction may be slow and unsteady in some patients and close support from a dietician is essential to success. In diabetic patients, further input is required as listed below.
- Once full feeding rate is achieved and patient stable the insulin treatment can be converted to a subcutaneous regimen to suit the feeding regimen. Dietitians should directly liaise with the diabetologists involved, to agree on the most suitable feeding regimen for the patient. A variety of insulin preparations and regimens may be employed to suit the individual patient’s insulin sensitivity and feeding duration.
- Most patients are initially commenced on 20 hours of feed per day although overnight feeding is also commonly employed. If blood glucose levels are poorly controlled and unstable on 20 hours feeding regimen despite use of IV insulin sliding scale, always consider 24 hours feeding. Discuss directly with the diabetologists if this is the case - a small amount of background long acting insulin may help against such peaks and troughs.
- It is crucial that once feeding regimen is agreed and subcutaneous insulin regimen is decided, to keep to the same feed break hours each day. Break times should not be changed greatly without informing the diabetes team and insulin dose and timing adjusted concomitantly. Failure to do so puts patients at risk of hypoglycaemia. Pure short acting insulins should be analgoes such as Lispro so that they can be given with meals rather than trying to predit when a patient will eat.
- Use red feed break signs to specify feed break times and place on pumps to aid ward staff compliance to fixed feed breaks
- If diabetic patient or patient with a BM> 10 mmol/l is discharged quickly, write to the GP requesting blood glucose monitoring in the community. Inform the diabetes nurses and consultant involved BEFORE discharge.
Sources
Luton & Dunstable Hospital NHS Foundation Trust - Guidelines for PARENTERAL/ENTERAL NUTRITION
