Complications of enteral nutrition

Under exam conditions, asked about the risks and benefits of enteral nutrition, one may be expected to quote a list of the more common complications.

The college has previously asked about this in Question 25 from the second paper of 2014. The question was mainly about nutrition in severe pancreatitis; only part b) asked to "list the complications that need to be considered with the use of enteral nutrition". M.D. Bastow's hymn to the complications of enteral nutrition is available as a free full text article. It is my primary source for the below information.

Aspiration

Yes, having something in your stomach is always a risk of aspiration. But this does not increase the risk of ventilator-associated pneumonia.
The normal 10-100ml of fasting stomach juice is sterile, but still acidic enough to cause chemical pneumonitis. The presence of enteral feeds can buffer this acidity (especially the protein, because protein is a good buffer) but the feeds themselves are excellent substrate for bacterial growth, and if they end up in the lungs, badness ensues.
For some considerable time, people assumed that all ventilator-associated pneumonia was the result of aspirated feeds.

However, changes to post-pyloric feeding, PEJ feeding or using pro-motility agents has failed to reduce the incidence of ventilator-associated pneumonia. Rather, ANY FEEDING at all is actually protective - there seems to be a decreased risk of ventilator-associated pneumonia.
In a meta-analysis, this protective effect failed to reach statistical significance, but the bottom line is that nasogastric feeding, though responsible for some vomity behaviour, does not doom your patient to inhaling their Jevity.

Instead, VAP appears to be more related to the microaspiration of oropharyngeal secretions. There are many strategies which are useful in improving feed tolerance, but none of them seem to protect you from VAP.

Diarrhoea

The incidence of diarrhoea in the enterally fed patient does certainly seem to be higher.
One paper puts the risk at 18%, vs only 6% among normally fed hospitalized adults. Still, not as high as constipation.

Why is this so?

• Some of it must be due to changes in intestinal transit time associated with a totally fluid diet.
• Some of it must be due to villous damage which is inevitable with critical illness
• Some must be due to the inevitable genocide of intestinal microflora, associated with the use of nightmarish antibiotics.
• Some must be due to the fact that most nasogastrically-administered drug suspensions present as a sorbitol or mannitol syrup, and thus act as osmotic laxatives.
• Some may be due to the hyperosmolarity of the feeds themselves. This is suspected of the high calorie feeds which are more concentrated, delivering something like 1.5kcal per ml. However, Bastow reports that feeds up to 600mosm/Kg are easily tolerated. This makes a certain wicked sense. lets face it, the osmolarity of a steak dinner must be significantly higher than 600mosm/Kg, and most of us can tolerate this without torrential diarrhoea.
• Additionally, the delivery of feeds as a bolus rather than as a constant infusion results in a rapid gastric emptying, and rapid small bowel transit (because a large bolus stimulates peristalsis). Its another argument against bolus feeding.

"ICU diarrhoea" is less frequent than "ICU constipation". However, mixing up your feed volume to contain 2% soluble guar gum seems to be the panacea to treat them both. A trial of this stuff promises to reduce the frequency of liquid stools to a manageable average of 1(+/- 0.7) per day. The dose, in the setting of a 60ml/hr goal rate, is therefore about 1.2g per hr, or 20g per bottle.

Incidentally, the above-linked material safety data sheet for guar gum recommends one apparel oneself in with a full environmental suit including boots gloves and dust respirator in order to deal with a large scale spill of this ground-up nut product. The oral LD50 in rats is about 7g per kg, which means that one would need to feed an average human about half a kilogram of this stuff before they die of guar gum overdose. I can only expect the cause of death would be some sort of gummy bowel obstruction.

In spite of using sensible amounts of fibre, problems still occur. A"fibre bezoar" may form if the patient has impaired peristalsis.

Constipation

The ICU patient has many reasons to be constipated, not the least of which is the massive amounts of infused opiates, the oedematous gut, the vasopressors, the immobility, the inability to sense the urge, or to strain while sedated, et cetera. Enteral feeds are way down on the list of reasons. This BJA article places the rate of constipation in the critically ill adult at 83%, and mentions enteral nutrition as a solution, rather than the cause. Ideally, one would be forced to admit that enteral nutrition will probably only cause constipation in a patient who is dehydrated.

Dehydration

The chance of becoming dehydrated in the ICU is surprisingly high, depending on how cavalier one is with their ultrafiltration goals and diuretic use. Dehydration due to feeds is probably more likely in the setting of some sort of chronically tube-fed patient whose enteral feeds form their sole source of fluid intake. The concentration of water in most enteral feeds is quite a bit lower than the recommended daily intake.

Malnutrition due to feed intolerance

One should aim to provide at least 50-65% of one's goal dose to achieve the benefits of enteral nutrition. This is the dose required to get the various protective benefits from enteral nutrition, such as the decreased risk of infection and improved return of cognitive function in head injury. However, even if one achieves this volume (which would end up being about 100 kcal for a normal-sized person) one would typically still lose weight. The adaptation to this sort of malnutrition would not result in massive protein catabolism (unlike total starvation) but the response to injury would be diminished, and the delay in recovery may be significant for people with abnormally high caloric requirements (such as septic patients and burns patients).

Complications relating to the feeding tube

This is discussed at greater length elsewhere. In summary, feeding tube insertion complications are:

• Poor placement, eg. into the lung
• Oesophageal or gastric perforation
• Increased tendency towards gastro-oesophageal reflux
• Pressure areas due to prolonged tube dwell time (eg. pressure on the nares)
• Sinusitis (for nasal tubes)
• Poor oral hygiene( for oral tubes)
• Oesophageal stricture
• Discomfort in the awake patient