Patient nutrition is an often-neglected aspect of the overall management of patients, but 50% of surgical patients suffer protein energy malnutrition. Sepsis, injury and starvation are the main contributors to postoperative morbidity and mortality. Following the initial resuscitation of a critically ill patient, the nutritional status should be assessed and a plan of nutritional management made. It is best to use the enteral route if possible, however, adequate calorie intake is often difficult to achieve. The currently available intravenous feeding regimens present a confusing array of mixtures of fat, carbohydrate, amino acids, vitamins and minerals and there are several steps to follow to initiate treatment safely. Many hospitals have a nutrition team, which assists with the management of enteral feed or total parenteral nutrition and helps with monitoring during treatment, but the clinician should have a working knowledge of patient nutrition to initiate a good management plan.
Nutritional requirements
In illness or after surgery, burns or trauma, the following sequence occurs.
• Energy requirements are increased by up to 30%. • Metabolism is affected by altered levels of catecholamines and cortisol. • Blood sugar control becomes deranged as patients develop an apparent increased resistance to insulin. • There are major fluid and electrolyte losses from diarrhoea, vomiting or nasogastric losses, excessive sweating, stoma losses and surgical drains. • Fluid shifts, caused by leaky membranes or fluid moving into the third space, create difficulties in assessing fluid balance.
Assessing nutritional status
The following identify patients at risk of protein energy malnutrition:
• Clinical history (e.g. nausea, vomiting, diarrhoea, abdominal distension, previous surgery, weight fluctuations) • Dietary history (types and amounts of food taken, dysphagia) • Physical examination (weight: height, body mass index (BMI), general appearance). • The following tests can be used to establish the severity of protein energy malnutrition and the response to nutritional intervention: • Anthropometric (skin fold thickness) • Biochemical (albumin, transferrin and pre-albumin) • Immunological (lymphocyte count).
Enteral feeding
If the patient has any functional bowel, the enteral route should be used if possible. The best nutrition comes from a balanced diet that is chewed, swallowed and digested. Gut motility is influenced by hormones released during mastication. Stomach emptying controls the delivery of food to the jejunum to maximize absorption. The gut mucosa is more likely to retain its normal function if it is bathed in the correct nutrients. The large bowel requires an adequate amount of fibre to ensure regular soft bowel actions. As soon as any of these aspects of feeding are defective, the absorption of nutrients is affected.
Approximate combinations of nutrients in enteral feeds
Elderly / Frail
Normal
Critical Illness
Protein
8 - 10 g
10 - 16 g
16 - 20 g
CHO
700 Cal
1000 Cal
1200 Cal
Fat
700 Cal
1000 Cal
1200 Cal
Total Calories
1400 Cal
2000 Cal
2400 Cal
Total Volume
2.5 Lt.
205 Lt.
3.0 Lt.
Some specialist feeds (e.g. Pulmocare) provide a greater percentage of calories as fat (by providing fewer calories derived from carbohydrate, the amount of carbon dioxide produced is reduced, thereby assisting ventilatory weaning in some patients). Other specialized feeds (e.g. elemental solutions of amino acids or peptides) are available for patients with short-bowel syndrome, malabsorption or severe inflammatory bowel disease. Extra food supplements can also be used to provide extra fat or carbohydrate.
Parenteral feeding
When the bowel is not functioning, unable to be used or all attempts at feeding using this route have failed, parenteral nutrition is indicated. A multidisciplinary nutrition team including doctors, nurses, pharmacists and dietitians can improve the efficacy of total parenteral nutrition (TPN). Insertion of a feeding line is usually undertaken by doctors and cared for by nurses; the dietitian can advise on nutritional requirements and the pharmacist can recommend nutritional preparations and additives. The whole team has a role to play in the continuing care of the feeding line, monitoring of response to therapy and audit of complications.
Patient selection
Common reasons for requiring TPN are:
• Post surgery – if bowel function is likely to be disturbed
• Short-bowel syndrome
• Gastrointestinal fistulae
• Prolonged paralytic ileus
• Inflammatory bowel disease
• Preoperatively – in malnourished patients with ineffective bowel function.
Sepsis, severe burns and pancreatitis were also considered reasons for using the parenteral route, but enteral nutrition is now recognized as more appropriate. In some cases, a combination of parenteral nutrition and enteral feed may be used.
Recent advances
The constituents of TPN have been modified and simplified over the past few years. The use of a single bag every 24 hours reduces the infection risk by reducing the need to handle the line connections. Several companies have special bags that allow mixing of the constituents immediately before use without the risk of contamination, this increases the shelf-life of the product and enables the pharmacy to supply TPN almost on demand. The vitamins and minerals required are available in single-day vials for addition immediately before use.
Recent research on immunotherapy suggests that the addition of substances such as glutamine, arginine and the omega-3 fatty acids, may enhance the immune response during critical illness. Recent work suggests that blood sugar control in a tight range reduces mortality in critical care patients.
