Nutrition is an important aspect of a patient’s health and is overlooked during medical school as you are learning exciting pathophysiology of weird and wonderful diseases. One never thinks about nutrition until you are placed on a ward where you need to manage patients in need of nutritional support. Various studies show that doctors and nurses on wards with greater access to clinical dietitians had better focus on clinical nutrition and were able to care better for their patients.

What is nutrition?

So, what is nutrition? It is dependent on the consumption and absorption of necessary micro and macronutrients. Malnutrition is defined as a state that occurs when there is an imbalance between nutritional intake and requirements., and It has deleterious effects on patients as it increases their risk of mortality and morbidity. It can be chronic or acute. Critically ill patients are at an increased risk of malnutrition secondary to their increased metabolic demands as their bodies are in a catabolic state for a prolonged period. The management of this requires adopting a multidisciplinary approach.

Calorie requirements

Metabolic rate can be measured by indirect calorimetry; however, indirect calorimeters are not routinely available for calculating energy requirements in the NHS, so dietitians use evidence-based energy equations to calculate these. These equations take into account physiological stress (caused by medical conditions/disease state) and an activity factor that accounts for ‘diet-induced thermogenesis’ and the amount of physical activity the patient is able to perform. Typically, energy requirements for most patients range between 1600-2300 kcal per day. Patients with burns require more kcals per day.

NutrientAmount Required
Water25 – 35 ml/kg
Nitrogen0.17 – 0.30 g/kg
Glucose210 g
Lipid140 g
Sodium70 – 140 mmol
Potassium50 – 120 mmol
Calcium5 – 10 mmol
Magnesium5 – 10 mmol
Phosphate 10 – 20 mmol
Normal Daily Requirements (for a 70 kg healthy adult)

Carbohydrate metabolism and physiology

Carbohydrates are required by the body and used as the first source of energy to maintain a normal blood glucose level. During starvation, carbohydrates are generated from glycogen in the liver and skeletal muscles and used as a source of energy.


Micronutrients are defined as “nutrients present and required in the body in minute quantities (e.g., vitamins, trace elements).” Micronutrients include vitamins and certain minerals such as calcium, magnesium, and phosphorus. One of the most common functions of micronutrients and some minerals are to serve as necessary cofactors for enzymatic reactions. Various trace elements such as arginine and glutamine are essential in wound healing pathways.

Consequences of malnutrition

  • Inflammation and immunosuppression
  • Opportunistic infections
  • Catabolism, muscle wasting and weight loss
  • Impaired gut integrity
  • Delayed wound healing
  • Increased risk of morbidity and mortality

Screening for Malnutrition

In the NHS, malnutrition is monitored using the Malnutrition Universal Screening Tool (MUST). Patients are screened within 24 hours of admission and again every 7 days.

  • BMI
  • % of weight loss in the preceding 3-6 months
  • Effect of disease on nutritional intake: either there has been or will be no nutritional intake for ≥5 days

A patient scoring 2-6 requires a referral to the dietitian. Please follow your local Trust policy for more details.

Types of Nutrition

1. Oral Nutritional Support

Oral Nutritional Supplements (ONS) is used when where oral dietary intake is not adequate. If you or your team think your patient would benefit from these, refer the patient to your ward dietitian. They will then assess the patient and prescribe the most appropriate Oral Nutritional Supplements.

2. Enteral Feeding

Enteral Feeding (EF) includes any method of delivering nutrients for the gastrointestinal tract absorption. This can be via Nasogastric, Nasojejunal, PEG/gastrostomy or Jejunostomy or a PEG-J. Enteral feeding should be considered in patients who are malnourished or at risk of malnutrition and have (1) an inadequate or unsafe oral intake and (2) a functional accessible GI tract. (NICE 2006)

  • Composed of carbohydrates (glucose polymers), whole protein or oligopeptides, medium-chain or long-chain triglycerides as fats. A standard feed is formulated at 1kcal/ml. More concentrated feeds can be used to reduce the volume of fluid provided or to reduce the hours of feeding. In some cases, overnight feeding regimens may be put in place by dietitians to allow a patient to build up an appetite for better oral intake during the day.
  • Other special feeds are available such as high fibre, high protein-calorie, low sodium and peptide-based ones.
  • Some patients are given immune enhanced feeds (supplemented by arginine, fish oils, nucleotides) . There is evidence of benefit to a select group of patients e.g. burns patients being given immune enhanced feeds.
Types of Tubes
A. Nasogastric
  • • Most common
  • • Suitable for short term use such as post operatively or a patient who is being ventilated on critical care units.
  • • Can be wide bore or narrow bore
  • • Nasal bridles can be used to secure NG/NJ feeding tubes- discuss this with your dietitian/enteral nurse CNS.
Wide Bore Narrow Bore
Allows aspiration in patients with Bowel obstruction or pancreatitis Replaces wide bore for long term feeding
Uncomfortable for patient More comfortable for patient
Can aspirate small amounts
B. Gastrostomy (PEG/ jejunostomy)
  • • Long term feeding
  • • No discomfort of nasogastric or nasoduodenal tubes
  • • Risk of site infection
Gastrostomy/PEG Jejunostomy
Inserted into stomach Inserted into jejunum
Complications of Enteral Feeding
  • Blockage of tube
  • Trauma to the nose
  • Pulmonary aspiration
  • Tube misplacement
  • Reflux
  • Altered gut motility: constipation or diarrhoea
  • Pseudo obstruction and abdominal distention
  • Overfeeding leading to hepatic steatosis, liver failure and respiratory failure.
  • Metabolic: Dehydration, hyperglycemia and electrolyte imbalance
3. Parenteral Nutrition
  • Parenteral Nutrition (PN) refers to the administration of nutrients intravenously
  • Essential nutrients required to meet the patient’s nutritional demands are calculated and infused directly into the venous circulation, bypassing the gut.
  • Carbohydrates in PN are provided majorly by glucose and nitrogen is provided by amino acid solutions.
  • Lipids, essential vitamins, electrolytes (Sodium, Potassium, Magnesium, Calcium, Phosphate), trace elements and minerals make up the rest of the solution. These must be prepared in a sterile environment.
  • Most of these solutions are hyperosmotic and therefore poorly tolerated by peripheral veins leading to thrombophlebitis, pain and thrombosis. Therefore, they need to be administered centrally via a central venous line (CVP) or via a peripherally inserted central catheter (PICC)
Who needs it?

NICE 2006 ‘Nutrition Support in Adults’ is a good reference for the indications for PN.

Consider PN in patients who are malnourished or at risk of malnutrition with either (1) Inadequate or unsafe oral and/or enteral nutritional intake or (2) A non-functioning, inaccessible or perforated/leaking GI tract.

Some good examples of indications for PN include:

  • Short Bowel Syndrome
  • Bowel obstruction
  • Bowel perforation
  • Ileus/motility disorders
  • High output small bowel fistulae
  • MucositisIschaemic bowel

Broadly divided into three categories: insertion related, line related and patient related.

Insertion relatedLine relatedPatient related
BleedingOcclusionInfection (particularly fungal!)
Misplaced linesTranslocation of the gut flora
PneumothoraxFluid overload
Early infectionHyperglycaemia
Electrolyte disturbances
Complications of Parenteral Nutrition

Refeeding syndrome

This refers to fluid and electrolyte shifts and related metabolic implications in malnourished patients undergoing feeding. It results from a sudden administration of glucose that can result in a surge of insulin secretion, causing a massive cellular uptake of phosphate, magnesium, and potassium and a consequent fall in serum levels. Typical high-risk patients include malnourished patients, alcoholics and those on chemotherapy. The management includes the slow introduction and build-up of nutrition (glucose) provision towards target requirements. It also includes close monitoring and replacement of low levels of electrolytes as required. As well as additional vitamin and mineral supplementation. See the trust guidance on Refeeding Syndrome and refer to your dietitian for advice.

Take away points for junior doctors

  1. If unsure, always ask!
  2.  If a patient is septic, think do they have a CVP/PICC line?
  3. If a patient is on TPN, always document how many days they have had, any specific changes in the content of TPN and the rate it is being administered at. It contributes to their fluid requirements so should be taken into account when prescribing IV fluids
  4. Always look out for electrolyte abnormalities (they need daily TPN profile bloods taken!)
  5. Liaise with the Nutrition team regarding what bloods are needed and how frequently. ‘High refeeding risk’ patients will need daily nutrition profile bloods and supplementation as required.  
  6. Note: if no other access is available for taking bloods from PN patients, and using a PICC line is the only option, ensure to take bloods during a PN break as this avoids contamination of the sample. If the PN runs over 24 hours, aim to take the sample between PN bags leaving a 30min break off PN and ensure to flush the line before and after. Use of the PICC line should be done using aseptic technique to prevent line sepsis.  
  7. Always escalate any concerns to the nutrition team (it will help you learn)
  8. Where safe and possible, enteral and/or oral intake should always be given in preference to PN. Therefore ensure PN is indicated and consider it only if oral/enteral feeding options have been explored and ruled out

Written by Miss Swati Bhasin (Surgical SpR) & Jaci Chapman (Deputy HOD nutrition and dietetics at Royal Wolverhampton NHS trust)
Editing by Mudassar Khan (Y3 Medical Student)

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