Enteral and Parenteral Nutrition
Which critically ill patients should receive TPN? Prof R D Griffiths in conjunction with Fresenius-Kabi Why are these guidelines required? In the critical care setting, nutritional support influences the outcome for critically ill patients. This guideline seeks to outline the important role of parenteral nutrition in the critically ill patient. Enteral and parenteral nutrition The enteral route for nutrition delivery is preferred where it can be safely delivered in the absence of gastrointestinal intolerance.
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For a small proportion of patients enteral feeding is not possible but in addition for a larger proportion of patients research consistently shows that enteral nutrition does not always cover the total nutritional needs of intensive care unit patients. There has been a reluctance to use parenteral nutrition (PN) or to supplement enteral (EN) or oral nutrition with parenteral nutrition (PN) for the perceived risk that to do so increases the infection and mortality risk.
Systematic review evidence acquired from studies in the critically ill shows that while there may be an increased risk of infection there is no added mortality risk [ 1 ]. Parenteral nutrition has changed considerably over the last forty years and many of the complications were a feature of historical PN practice associated with its inappropriate use, unbalanced formulations and liberal overfeeding. Even the risk of infection may be more related to the underlying patient disease and indication for PN rather than modern PN formulations and delivery in ICU.
Malnourishment It has been estimated that around 40% of all patients in hospital are undernourished and this is associated with further complications. Acute critically ill patients lose on average approximately 5-10% of skeletal muscle mass per week during their ICU stay [ 3 ]. Complications such as septicaemia in these patients are to a large extent caused by malnutrition and impaired immunological function [ 2 ]. Complications versus choice of nutrition route When correctly applied, the complications of PN are less likely to result in death compared with those of EN.
Recent studies conclude that PN compared with early EN is risk-neutral overall [ 3 ]. It is reassuring that in critically ill patients, when used with EN in the ICU as a supplement, PN has been confirmed to be risk-neutral or may even offer benefits. However from current data it is not possible to justify the extra cost of supplemental PN when started concurrently with EN at the start of an ICU admission [ 1 ] but more importantly there are no studies where it has been started in the more appropriate situation after EN has been shown to fail in already malnourished ICU patients.
It has been demonstrated that nutritional goals were reached in 22% of ICU patients fed via EN compared with 75% with PN [ 2 ]. It must be remembered that under nutrition is a debt that must eventually be repaid and this is also worse if it is compounded! The ACCEPT study showed that survival from intensive care was improved when an evidence based guideline for nutrition was followed and more nutrition delivered more consistently. This was achieved by earlier introduction and more complete enteral nutrition delivery without any decline in the use of PN alone or in supplementation.
Using the guidelines These guidelines have been developed using a step-by-step approach as follows: Step 1ASSESSMENTDoes the patient require nutritional support? Step 2ADMINISTRATIONWhich route(s) should be used? Step 3ACHIEVEMENT (REVIEW)Are nutrition goals being met? Step 1 Nutritional Risk Screening (adapted from NRS 2002 ESPEN) Does this patient require nutritional support? Initial screening of patients is recommended in these guidelines but it is assumed that ALL patients fulfill the criteria for requiring a final screening assessment which follows.
The adaptation assumes an affirmative answer to the question “Is the patient severely ill? (e. g. in intensive care) Impaired nutritional statusSeverity of disease (increase in requirements) Score 0Normal nutritional statusScore 0Normal nutritional requirements Score 1 Wt loss >5% in 3 months or foodScore 1Hip fracture. Chronic patients in (Mild)intake below 50-75% of normal particular acute complications of requirements in preceding weekcirrhosis, COPD. Chronic diabetes haemodialysis, oncology. Score 2Wt loss >5% in 2 months or BMIScore 2Major abdominal surgery, stroke, (Moderate)18. -20. 5 + impaired general condition orsevere pneumonia, haematologic food intake 25-60% of normal requirement malignancy. in preceding week. Score 3Wt loss >15% in 3 months or BMI Score 3Head injury, Bone marrow transplant (Severe)<18. 5 + impaired general condition orIntensive Care Patients (APACHE >10) food intake 0-25% of normal requirement in preceding week SCORE+ SCORE= TOTAL SCORE AGE ADJUSTMENT (IF PATIENT ? 70 YRS ADD 1 TO TOTAL SCORE)= TAAS SCORE INTERPRETATION SCORE ? 3The patient is nutritionally at risk and a nutritional plan should be initiated.
SCORE< 3Weekly re-screening of the patient. If the patient is scheduled for a major operation a preventative nutrition plan should be considered to avoid associated risk status. Step 2Administration route(s) Nutritional support does influence the outcome of critically ill patients and evidence suggests that the consistent achievement of nutritional goals is important and this should if feasible be through the enteral route [ 7 ]. Evidence suggests that for most patients this is just as effectively and safely delivered through a naso-gastric tube compared to tubes sited after the stomach [ 1 ].
It must be recognized that problems do occur with all forms of enteral delivery and that delivery is more often attained by the parenteral route3 and this is apparent in critically ill patients where enteral nutrition is inappropriate, contraindicated or has failed. Parenteral nutrition should be used when the GI tract is not functional or cannot be accessed or when the patient’s nutrient needs are greater than those which can be met through the GI tract. However it should not be commenced in the non-malnourished as a supplement until approaches to enteral delivery have been optimized [ 1 ].
Assess the integrity and function of the bowel using the following prompts: IF THE ANSWER IS “NO” TO EITHER QUESTION – TIME TO CONSIDER PN Is the digestive tract functioning? Is the patient well nourished and recovery of gut function expected within 3 days? IF THE ANSWER IS “YES” TO EITHER QUESTION – TIME TO CONSIDER PN While using an enteral feeding protocol does the presence of excess gastric aspirates (e. g. persistently > 150mls after measures to improve gastric emptying) lead to reduced enteral intake. Does the nutrition equirements of the disease or injury exceed that which can be delivered safely via the enteral route? Some patients with an intact GI tract do not tolerate enteral feeds or do not receive sufficient intake enterally or orally to meet their energy and protein requirements. The reasons for poor gastric emptying should be considered. Simple measures such as turning to the right side or reducing opiate intake may be tried along with short trials of either Metoclopramide or Erythromycin if other causes have been excluded.
However gastrointestinal intolerance is an important and worrying sign and is associated with increased pneumonia and risk of death independently of illness severity . The supine posture is also associated with increased risk of aspiration pneumonia and if patients cannot be nursed in the semi-erect position parenteral nutrition may be a safer option whether it is used as a supplement or as the sole source of nutrition in these patients [ 6 ]. Choice of feed and amounts In the critical care setting estimation or measurement of precise requirements is fraught with error.
A target of 25 kcal/kg/day for the first week is acceptable. Protein intake is the central component as this cannot be stored metabolically. Most evidence supports 1. 5 gm/kg/day as a reasonable target. Requirements change during an illness and generally increase in the second week and when patients become more active. Simple methods using patient size bands based upon accessible measures of body size (height or weight) should be used to calculate target amounts. More sophisticated individual patient calculations have not been shown to be any more accurate.
Polymeric complete enteral feeds should be used for most patients and infused continuously. Evidence for the use of specific formulations is lacking, except that the immunonutrition cocktails that contain extra arginine should NOT be given [ 1 ] outside of the peri-operative setting where evidence exists. An all-in-one complete balanced parenteral formulation should be used and evidence based recommendations suggests where practical these should contain glutamine [ 1 ]. They should be delivered continuously through a dedicated lumen that should not be used for any other access.
Some of the energy should come from lipid sources but there is paucity of evidence to suggest any particular lipid formulations although this may change as more advanced formulations come on the market. Caution should be applied when other lipid containing infusions are also in use (e. g. propofol). Lipid infusion is safe at rates up to 1. 5 gm/kg/day, and glucose should be given at 3-4 gm/kg/day. Use simple standardized regimens for most patients. Within ICU acute electrolyte management (e. g. potassium and phosphate) is more readily managed by separate infusions if safe systems exist.
Patients on renal support will have increased nutritional losses so maintain on full feeding. Important when using either EN or PN Nutrition should be commenced at reduced rates especially in the malnourished until metabolic tolerance established. Increase to full target over a 3 day period and monitor for re-feeding syndrome. It is possible to overfeed with PN but unless glucose intake exceeds 4-5 gm/kg/day hyperglycaemia indicates peripheral insulin resistance and the need for additional insulin and not reduction in feed volume.
Step 3 Are nutrition goals being achieved? Set targets and check nutrition intake daily and act upon the findings. It is recommended that calorie (and nitrogen) intake is calculated daily in addition to the fluid balance. Has the patient received the amount of nutrition prescribed over previous days? Nutritional support, once instigated, should be monitored to confirm the safety of treatment. The following guide illustrates the type of monitoring required. The tests required will depend upon duration and method of feeding.
The frequency of testing will vary depending on the illness severity. Fluid balance and calorie intake and if possible weight. Urea and electrolytes daily (watch K+ as feeds may have only a modest K+ content) Blood glucose monitored frequently and preferably as part of a tight glycaemic control. Phosphate (This should be monitored closely especially when starting feeds in the malnourished) Plasma lipid clearance or triglycerides Full blood count Liver function tests, Calcium & Magnesium
Calculation or measurement of nitrogen balance is not reliable in the routine setting. Nutrition support algorithm summary ASSESS Is nutritional support required? 40% of patients admitted to hospital are undernourished REASSESS Supplemental PN? ADMINISTER Which route? Is enteral feeding practical and safe? If not consider PN ACHIEVE and REVIEW Are you satisfying the nutrient needs of the patient? N Y WEANING STRATEGY If on EN can oral intake be started? If on PN can EN be started?