Everyone has strong opinions about food. We all feel that we have some special, intuitive understanding of nutrition. Nonsense. Such intuitions have historically created a wide array of dogma regarding nutrition, complicating matters immensely.
Fortunately, the 2016 SCCM/ASPEN guidelines have stripped away much of the nonsense involved in nutritional support. This allows for a simple and effective approach to nutritional support in the ICU. Based on these guidelines, this post will attempt to sort out truth vs. fiction: which nutritional beliefs are valid, and which need to be discarded?
#1. Early enteral nutrition (within 24-48 hours) is helpful.
Benefits of early enteral nutrition may include maintence of gut integrity, reduction in bacterial translocation, and stress ulcer prophylaxis. Delayed initiation of nutrition may promote ileus, impeding later attempts to start feeding. Meta-analyses confirm benefits, including reduction of infectious complications.
Benefits of enteral nutrition largely relate to supporting bowel health, rather than necessarily providing nutritional fuel. This explains why enteral nutrition is generally superior to parenteral nutrition.
#2. The following are not contraindications to enteral nutrition.
- Lack of bowel sounds: This may simply indicate a lack of air in the bowel. The use of bowel sounds to drive any clinical decision has never been validated.
- Therapeutic paralysis: Paralytic infusions only affect the skeletal muscles, not smooth muscles (e.g. intestines, pupillary reflexes).
- Patient is required to lie flat: The evidence supporting feeding in a semi-recumbent position is somewhat weak. Semi-recumbent positioning is preferable but not mandatory (Marik 2014).
- Vasopressor use: Traditionally, it was feared that providing nutrition in the context of shock could cause intestinal ischemia. However, enteral nutrition actually appears to improve blood flow to the gut and preserve intestinal integrity. Once a patient has been fluid resuscitated and stabilized on vasopressors, enteral nutrition may be started at low rates (more on this below).
- Open abdomen: Enteral nutrition is recommended for patients with an open abdomen who don't have bowel injury.
- Pancreatitis: Evidence supports early enteral nutrition among patients with severe pancreatitis, similar to other critically ill patients.
Currently, the only major contraindications to enteral nutrition seem to be bowel obstruction, perforation, mesenteric ischemia, or major gastrointestinal bleeding. In short, the patient can be fed as long as they aren't having an intestinal catastrophe.
There is no known illness or disease that has been demonstrated to benefit from starvation. – Marik 2014.
#3. Starting feeds at 25-50% caloric goal and increasing to 100% over 3-7 days is reasonable.
The ideal initial rate for tube feeding is unknown.
- In previously well nourished patients, starting hypocaloric feeding appears safe (while targeting 100% protein goal). This was previously discussed here.
- In previously malnourished patients, starting at a lower rate may be wise to avoid refeeding syndrome.
- SCCM/ASPEN guidelines recommend starting with very low-level feeding (10-20 kCal/hr “trophic feeding”) for patients with septic shock or severe pancreatitis.
Hopefully this will eventually be clarified. For now, it seems reasonable to start feeding early, but at a reduced rate (e.g. 25-50% caloric goal). Subsequently, feeding can be advanced to 100% goal calories over 3-7 days, as tolerated. Efforts should be made to provide 100% protein requirements when possible. Determining a nutritional prescription that provides fewer calories yet adequate protein may be easily accomplished with the tube feed cheat sheet.
#4. Generally avoid fancy, designer tube-feed formulations.
Historically there has been much enthusiasm about a variety of specialized tube feeds. Evidence regarding these has generally been disappointing. Based on the SCCM/ASPEN guidelines, if you gave every patient a generic tube feed formulation, that would be fine.
These guidelines specifically recommend against the following designer tube feeds:
- High-fat formulations designed to help wean patients off ventilation.
- Anti-inflammatory formulations designed for patients with ARDS.
- Immune-modulating enteral formulations (e.g. with arginine) for patients in the medical ICU.
- Branched-chain amino acid formulations designed for patients with hepatic encephalopathy.
Specialty formulations may remain useful in the following situations:
- Fluid-restricted, energy-dense formulations may be useful in patients with volume overload (1).
- Renal formulations are recommended only for patients with renal failure who develop significant electrolyte abnormalities.
- Patients with diarrhea may be managed with tube feeds that contain fiber or small-peptide formulations (2).
- Immune-modulating enteral formulations with arginine may be useful in post-operative patients and patients with severe trauma.
#5. Don't check gastric residual volumes (GRVs).
GRVs are a poor predictor of with pneumonia, aspiration, or regurgitation. Between ~2000-2010, several RCTs showed that using a lower GRV cutoff wasn't any safer than a higher cutoff. Consequently, the 2006 SCCM/ASPEN guideline increased the GRV target to <500 ml. More recently, one RCTs and one before/after implementation trial demonstrated that it was safe to stop checking GRVs entirely (Reignier 2013, Poulard 2010). This has led the SCCM/ASPEN to currently recommend eliminating GRVs entirely from routine care.
Measuring GRVs is a significant impediment to effective enteral nutrition, since it often leads to unnecessary interruption of feeding. Eliminating GRVs entirely is probably easier than trying to figure out what to do with them. Discontinuing GRVs may also reduce the burden on nurses, who are required to check these repeatedly.
#6. Don't interrupt feeding for procedures or possible extubation.
There is little rationale to interrupt tube feeds for most procedures (e.g. interventional radiology procedures). With adequate procedural sedation and analgesia, most procedures shouldn't provoke vomiting. If vomiting should occur, these patients are intubated with a protected airway.
A common practice is to hold tube feeding at midnight if the patient might possibly be extubated the following morning. In the absence of evidence, my preference is to continue tube feeds until a definite decision is reached to extubate the patient. Prior to extubation, the stomach should be suctioned empty (if the patient is being fed via a nasogastric or orogastric tube)(3).
#7. Difficulty tolerating tube feeds (e.g., vomiting) may be managed with post-pyloric tube placement or prokinetics.
- Post-pyloric feeding generally produces similar outcomes compared to gastric feeding (similar mortality, ICU length of stay, and duration of mechanical ventilation). The first-line approach for feeding intubated patients is typically gastric feeding, because this is easier. However, if there is difficulty tolerating gastric feeding, post-pyloric feeding is a rational approach. This may be a viable strategy within a hospital capable of placing post-pyloric feeding tubes rapidly (e.g. with Cortrak electromagnetic guidance)(4).
- Metoclopramide or erythromycin may improve gastric motility. These agents have been shown to reduce gastric residual volume and feeding intolerance.
#8. Patients with pancreatitis, septic shock, hepatic failure, or renal failure can all be fed the same way you would feed any other patient in the ICU.
Feeding patients with renal or hepatic failure has always been a source of confusion. Will protein worsen uremia in renal failure? Could it exacerbate hepatic encephalopathy in cirrhosis? What do we do about pancreatitis?
According to the SCCM/ASPEN guidelines, you can feed these patients the same way you would feed any patient in the ICU. Protein administration shouldn't be restricted as a strategy to avoid dialysis or hepatic encephalopathy. Some minor differences are:
- Patients with renal failure may be started on a regular tube feed formulation. However, if significant electrolyte abnormalities develop (e.g. hyperkalemia, hyperphosphatemia), then switch to a renal tube feed formulation.
- In critically ill patients on dialysis, the amount of protein administered should be increased up to a maximum of 2.5 grams/kg daily (5).
#9. Patients with morbid obesity can be fed similarly to other ICU patients, based on their ideal body weight.
The ideal number of calories for a patient with morbid obesity remains unknown. Theoretically, underfeeding could promote weight loss. However, underfeeding patients in the ICU tends to backfire, because patients burn their own protein for fuel and become protein-malnourished (6).
The perfect approach may be to provide fewer calories than the patient needs, but an ample amount of protein. The SCCM/ASPEN guidelines therefore recommend:
- For BMI 30-50, provide 11-14 kCal/kg (using the actual body weight) and 2 grams/kg protein (using the ideal body weight)
- For BMI>50, provide 22-25 kCal/kg and 2.5 grams/kg protein, both utilizing the ideal body weight.
This may seem complicated, but it doesn’t have to be. The high-protein tube feed cheat sheet may be used for patients with morbid obesity (example below; details about how to use this here). This sheet calculates tube feed formulations providing 25 kCal/kg ideal body weight and 2.25 grams protein/kg ideal body weight. This will produce a reasonable nutritional prescription for these patients (7).
Over time, critical care nutrition is becoming progressively simpler and easier. Take-home messages from the 2016 SCCM/ASPEN guidelines include:
- Early enteral nutrition should be provided to nearly all intubated patients.
- The only strong contraindication to enteral nutrition is an intestinal catastrophe. The following are not contraindications: lack of bowel sounds, therapeutic paralysis, vasopressors, pancreatitis, or open abdomen.
- Don't check gastric residual volumes.
- Patients with pancreatitis, septic shock, hepatic failure, or renal failure can all be fed in essentially the same way that you would feed any patient in the ICU.
- Fancy, designer tube-feed formulations are rarely needed.
- SCCM/ASPEN 2016: Guidelines for the provision and assessment of nutrition support therapy in the adult critically ill patient.
- Related posts:
- Please note that in order for this to make a difference with edema and fluid balance, the key factor is the sodium content of the tube feeds (not the actual volume). In some cases, concentrated tube feed formulations actually have less sodium per kCal, but in other cases they don't (you have to look up the sodium content of the specific tube feed brand). Using a concentrated tube feed formulation that has less volume but lots of sodium doesn't actually get you anywhere – the patient will wind up being hypernatremic… and then you will be forced to give them free water to normalize their sodium.
- It is OK to use tube feed formulations that contain fiber. However, the best source of fiber appears to be soluble fiber products, which may be metabolized into short-chain fatty acids that nourish the colon (as opposed to insoluble fiber like Metamucil). Thus, the best approach to adding fiber may be add a specific supplement that contains soluble fiber (e.g. guar gum).
- For patients being fed via a small-bore nasal post-pyloric feeding tube, it is impossible to aspirate tube feeds. However, aspiration risk in this context may be lower because the feeding is being delivered distal to the stomach.
- At Genius General Hospital, the Cortrak system generally allows our nurses to place post-pyloric feeding tubes at the bedside in the ICU. Alternatively, if you're depending on interventional radiology or gastroenterology to place these, then this can be logistically challenging. (I have no conflicts of interest with Cortrak or any other company.)
- This may be achieved using the increased-protein version of the tube feed cheat sheet.
- Morbid obesity provides zero protection against protein-calorie malnutrition. It's not uncommon in the ICU to encounter patients who are hundreds of pounds overweight yet profoundly protein-depleted.
- For patients with BMI on the lower end (e.g. BMI 30-35), this table may provide a few hundred more calories than recommended by SCCM/ASPEN. It's doubtful that this will have a significant clinical impact, since the evidence surrounding this topic isn't very precise to begin with. Furthermore, most studies show that patients rarely receive 100% target calories.