Enteral and Tube Feeding: If the Gut Works, Use It

Why nutrition support matters

Malnutrition is one of the commonest untreated diagnoses on a hospital ward. A malnourished patient heals more slowly, fights infection less well, loses muscle (including the muscles of breathing and coughing), and stays in hospital longer. Yet the deficit is easy to miss because it looks like "just being unwell." That is why every admission should carry a simple screen — the most widely used is MUST (Malnutrition Universal Screening Tool), which scores body-mass index, recent unplanned weight loss, and any acute illness that has stopped eating for more than five days. A high score flags a patient who needs a plan, not just a diet chart. The principle throughout is escalation: try the least invasive route that works, and only step up when it fails.

The governing rule: if the gut works, use it

There are two ways to feed a patient who cannot eat normally: enteral (into a working gut, by mouth or tube) and parenteral (nutrients delivered straight into a vein, bypassing the gut entirely). Whenever the gut works, enteral wins — and it wins on almost every axis. It is more physiological: nutrients arrive the way evolution intended, digested and absorbed in sequence. It keeps the gut lining alive; an unused bowel atrophies, its barrier weakens, and bacteria can translocate across it. It is far cheaper, and it carries fewer serious complications — no central line, no line sepsis, far less metabolic derangement. Parenteral nutrition is powerful but is reserved for the gut that genuinely cannot be used — obstruction, a high-output fistula, short bowel — as the Parenteral nutrition chapter sets out in detail. Enteral is not merely the cheaper option; it is the safer and more physiological one.

Start with the mouth: oral nutritional support

Before any tube, exhaust the simplest route — the patient's own mouth. Much can be done with food itself: fortifying meals with extra energy and protein (cream, butter, milk powder, cheese added to ordinary dishes), offering small frequent snacks, and removing the well-meaning but harmful "low-fat, low-sugar" restrictions from someone who is wasting away. When food alone falls short, oral nutritional supplements — the familiar high-energy "build-up" drinks — bridge the gap. These are cheap, need no procedure, and preserve normal eating. Only when a patient cannot swallow safely (like our stroke patient) or cannot take enough by mouth despite genuine effort do we escalate to a tube.

The routes of tube feeding

Two questions decide the route: how long, and where must the feed land? For short-term feeding (weeks), a nasogastric (NG) tube — passed through the nose into the stomach — is the workhorse. Its great danger, and the reason it dominates the exam, is misplacement: the tube can slip into the trachea and lung, and pouring feed down a mislocated tube can drown a patient. Confirming the tip is in the stomach before every use is therefore mandatory: aspirate fluid and test it on pH paper (a pH of 5.5 or below means gastric acid — safe to feed), and if there is any doubt, a chest X-ray is the definitive check. Feeding through a wrongly placed NG tube is classed as a "never event" — an error so serious it should never happen. If the stomach must be bypassed — severe reflux, high aspiration risk, gastroparesis — the tube is advanced past the stomach into the jejunum (a nasojejunal, NJ, tube). For long-term feeding (beyond about four weeks) a tube through the nose is neither comfortable nor durable, so a feeding tube is placed directly through the abdominal wall: a gastrostomy (often a PEG — percutaneous endoscopic gastrostomy) into the stomach, or a jejunostomy into the jejunum.

What flows down the tube: feed types

Most patients receive a polymeric feed — nutrients in their whole form (intact protein, complex carbohydrate, fat), which a normal gut digests just as it would food. When digestion or absorption is impaired — pancreatic insufficiency, short bowel, severe malabsorption — an elemental or semi-elemental feed is used instead, with the protein already broken down to amino acids or short peptides and fat partly pre-digested, so it needs little enzymatic work to be absorbed. Beyond these, disease-specific feeds exist (for example lower-volume, higher-energy formulas for fluid-restricted patients, or altered protein content in some organ failures), though the evidence for many is modest and a standard polymeric feed suits the great majority.

The four families of complication

Tube feeding goes wrong in four broad ways — mechanical, gastrointestinal, metabolic, and drug-related. Mechanical problems are the tube itself: misplacement (into the airway — the never event above), blockage of a narrow lumen (usually from feed residue or crushed drug left to set), and displacement. Aspiration — feed or gastric contents refluxing up and into the lungs — sits at the mechanical–GI border and causes pneumonia; nursing the patient sat up and not over-filling the stomach reduces it. Gastrointestinal complications are led by diarrhoea, which too often triggers a reflexive fear of "intolerance" when the real cause is usually more prosaic: too fast a feed rate, the sorbitol used as a sweetener in many liquid medicines given down the tube, or — most commonly of all — antibiotics and the Clostridioides difficile they can unleash. This connects directly to the Gastrointestinal section, where antibiotic-associated and C. difficile diarrhoea are worked through. Nausea and bloating round out the GI group.

The metabolic danger: refeeding syndrome

The metabolic complication that must never be forgotten is refeeding syndrome — the single most dangerous consequence of feeding the severely malnourished. During starvation the body runs on fat and depletes its intracellular stores of phosphate, potassium and magnesium, even while blood levels look deceptively normal. Reintroduce carbohydrate and the resulting insulin surge drives glucose — and phosphate, potassium and magnesium with it — rushing into cells, collapsing their blood concentrations. The fall in phosphate is the hallmark and can be lethal, causing cardiac and respiratory failure, arrhythmias, and seizures. The defence is discipline: identify the at-risk patient, give thiamine before and during feeding, start feed low and slow, and monitor and replace electrolytes daily. The Refeeding syndrome chapter is devoted to this; the one-line rule for the tube-feeding prescriber is start low, go slow, and check the phosphate. Hyperglycaemia is the milder metabolic cousin — overfeeding carbohydrate, especially in the stressed or diabetic patient, raises blood glucose and needs monitoring.

The practical pharmacology: giving drugs down a tube

A feeding tube is not a shortcut for the drug round — it is a trap for the unwary prescriber. When a patient cannot swallow, their regular tablets must somehow go down the tube — and this is where pharmacology meets the bedside. First, not every tablet can be crushed. Modified-release (slow-release) formulations crushed into a tube dump their entire dose at once, converting a smooth 24-hour release into a dangerous peak; enteric-coated tablets lose the coating that protected the drug from stomach acid or protected the stomach from the drug. Where a solid cannot be given, a liquid formulation or a different route must be found, ideally with pharmacy advice. Second, some drugs bind to the feed itself and lose their effect. The two classic culprits are phenytoin and levothyroxine, whose absorption is markedly reduced by enteral feed sitting in the gut — the practical fix is to hold the feed for a window before and after the dose and flush the tube well, an interaction the Central nervous system chapter (phenytoin) and the Endocrine chapter (levothyroxine) both return to. The crushing pitfalls tie back to the Principles of pharmacology, where modified-release and enteric-coated design are explained. Third, and most mundane but most common, the tube blocks if it is not flushed with water before and after every drug and every feed; a crushed drug left in a narrow lumen sets like cement.

Watching the patient: monitoring

Feeding is titrated, not set and forgotten. Track the trend of weight and, at first, daily bloods — especially phosphate, potassium and magnesium in anyone at refeeding risk, plus glucose, sodium, urea, and liver and renal function. Watch tolerance at the bedside: is there diarrhoea, vomiting, distension, a rising aspirate volume? Reassess the route regularly — a patient who recovers a safe swallow should be moved back up the ladder to oral intake, because the least invasive route that meets the need is always the goal. Nutrition is a live prescription, reviewed like any drug.