Nutritional options in the critically ill patient (Proceedings)

Adequate nutrition is essential for the critically ill patient. Nutrients are necessary to provide substrates for normal cellular functions, protein synthesis, and daily metabolic processes. The critical patient is often in a hypercatabolic state, so early nutrition is essential to prevent glycogen depletion, immune dysfunction, and loss of body mass, and to provide substrates for wound healing.

Common indications for nutritional supplementation in veterinary patients include hepatic disease, chronic renal disease, trauma, chemotherapy, radiation therapy, esophageal disease (megaesophagus, strictures, ulcers), and face or mouth pathology (trauma, neoplasia, etc.).

Enteral vs. Parenteral Nutrition

Whenever possible, enteral nutrition is preferred over parenteral nutrition, as it is a more physiologic, safer, and less expensive route. Enteral nutrition has also been shown to decrease bacterial translocation by maintaining gut mucosal integrity. Early enteral nutrition has been shown to blunt the release of stress hormones, thus reducing the elevation in metabolic rate.

Enteral nutrition should be considered any time that the gut is functional. Parenteral nutrition should be substituted when the gut is not accessible or is not functioning adequately. Examples include GI obstruction, severe peritonitis, intractable vomiting, acute pancreatitis, short bowel syndrome, and ileus.

Enteral feeding provides the necessary calories, protein, and nutrients to the patient as well as glutamine, an essential amino acid for enterocyte growth. Enteral nutrition enhances enteric IgA production for gut immune function, decreases bacterial translocation, and decreases stress ulcer production.

Enteral Feeding Routes and Tubes

If a patient is willing and able to eat, oral feeding is the best option. If the patient is unwilling to eat, but can tolerate oral feedings, syringe feeding is an option. However, this can be very stressful to a patient, it is very difficult to get adequate calories into the patient via this route, and it poses a risk for aspiration.

In a patient that is unwilling or unable to eat, an indwelling feeding tube is the preferred delivery route for nutrition. The type of feeding tube will depend on the underlying disease, length of estimated time tube feeding will be necessary, whether or not anesthesia is an option, whether or not abdominal surgery is being performed, and cost and experience of the clinician. Types of feeding tubes include nasoesophageal, nasogastric, esophagostomy, gastrostomy, and jejunostomy tubes.

In the postoperative patient, esophageal or gastric feeding tubes may be less useful due to vomiting and higher risks of aspiration in the depressed patient. Gastric motility and absorptive capacity may not return for 1-2 days post surgery, precluding the use of this route in the early postoperative period. The small intestines will have motility and absorptive capacity within hours of surgery, so jejunal feedings may be the best route postoperatively and whenever there is ongoing vomiting.

Nasoesophageal or nasogastric tubes are indicated for short term feeding of a liquid diet (<1 week). These tubes may also be useful for suctioning air or liquid from the esophagus or stomach. These tubes also may be indicated if anesthesia is not an option due to cost or condition of the animal or decompression of the stomach or esophagus is needed. Nasogastric is preferable over nasoesophageal whenever the esophagus is not functioning.

Contraindications of nasogastric or nasoesophageal tubes include severe thrombocytopenia or platelet dysfunction, head trauma, or protracted vomiting. Advantages of these tubes are that they do not require heavy sedation, do not require expensive equipment, and they are easily removed when no longer needed. Disadvantages are that they can only can be used for short-term feeding, they are not easy to use at home for most owners, they have a small diameter so only liquid diets can be used, they pose a risk of gastric reflux, erosive esophagitis, and aspiration, they can be irritating to the patient, and they are easily displaced by vomiting or patient interference.

Placement of nasogastric or nasoesphageal tubes is relatively easy to learn. First, numb the nostril with lidocaine (2%) or proparacaine. Choose a 3-12 Fr sialastic or red rubber feeding tube, depending on the size of the nares (Often a 5 Fr works in cats, and an 8 Fr for medium and larger dogs). For nasoesophageal, pre-measure to the level of the xiphoid and mark the tube with pen or tape. For nasogastric, pre-measure to the level of the last rib. Lubricate the tube with lidocaine gel.

In a dog, push upwards on the nasal planum and insert the tube at the ventral nasal meatus and pass in a ventromedial direction. Hold the head in a neutral or flexed position to allow passage into the esophagus. Gently insert the tube to the pre-placed mark and suction the tube to check placement. If continuous air is suctioned, the tube may be in the trachea or may have looped back up into the mouth. Open the mouth and look for the tube in the back of the throat or check to see if is has gone down the trachea. If negative pressure is reached immediately, the tube may still be in the esophagus, or it may have kinked. If the tube is in the stomach, it is most common to suction bile-colored liquid and varying amounts of air. A radiograph should always be taken to check tube placement. You can also inject a small amount of air or water to check placement. If this induces a cough, remove the tube and start over.

Pre-place a stay suture just lateral to the alar fold of the external nares, and wrap the tube around this fold. Wrap the ends around the tube and perform a Chinese finger trap pattern to secure the tube. Alternatively, place a butterfly tape around the tube, and secure the suture to this. Tissue glue is not recommended, as this can be irritating to the skin and does not have strong holding power. Place at least two additional sutures in the skin alongside the face or bridge of nose to secure the tube.

Esophagostomy tubes are indicated for short or long term (>5days) tube feeding when the esophagus and stomach are working. Advantages of these tubes is that they are inexpensive and don't require special equipment, they can be used on short-term or long-term bases, they are easily cared for at home by owners, and they have a large diameter, so blended canned diets can be used. Disadvantages are that they require general anesthesia to place, and they may be uncomfortable to some patients.

Method for placement of the esophagostomy tube requires general anesthesia and intubation. Clip and prep the left side of neck from jaw line to just cranial to shoulder. Use 10-12 Fr tube for cats and small dogs and up to 22 Fr in large dogs. Pre-measure so the tip will be at level of base of the heart. Insert curved hemostats into the proximal esophagus (just distal to wing of atlas). Turn tips of hemostats and place enough pressure to tent the esophagus and covering skin outward. Make a very small skin incision with a number 11 blade over the tips, just big enough to accommodate the tube, then push the hemostat tips through esophagus bluntly. Grasp the proximal tip of the esophagostomy tube and pull through incision and cranially out the mouth. Redirect the tube into the esophagus and slide the tip back down the esophagus. Feed the tube into the esophagus to the pre-measured point. Anchor the tube to skin around the ostomy site and to wing of atlas. Place a light bandage around the neck. Once the tube is no longer needed the tube is removed and the wound allowed to heal by second intention

Gastrostomy tubes are indicated when long term feeding is required (>10-12 days), decompression of the stomach or with esophageal disorders. Advantages of these tubes are they can be used on a long-term basis, they are comfortable, can be cared for easily at home by owners, can use blended commercial canned food, and they bypass the esophagus and lower esophageal sphincter. Disadvantages are that they require general anesthesia to place, they require specialized and expensive equipment, they require more expertise, they cannot be removed before days 10-14, and they pose a risk for peritonitis if dislodged before seal is formed.

Gastrostomy tubes are either placed endoscopically (percutaneous endoscopic gastrostomy or PEG tubes) or with a special device that allows percutaneous placement without the use of an endoscope. For PEG tube placement, the scope is placed into the stomach and insufflated with air. The assistant indents the body wall and stomach behind the last rib with a finger, so the indentation can be seen endoscopically. At this site, a 14-guage 2-inch catheter is placed into the stomach. A long wire loop in inserted through the catheter into the stomach, and a snare is used to grasp the wire loop. The scope and wire loop are removed from the stomach as a unit, thus pulling the wire loop out of the mouth. Use the loop to secure to the tapered end of the PEG tube. The wire is then used to pull the tube into the stomach and then out the body wall. The tube is retained in the stomach by an internal retention disk. The end of the tube is cut and a feeding adapter placed.

Jejunostomy tubes are indicated for immediate postoperative feedings of a liquid diet in patients with protracted vomiting, pancreatitis, or any time the stomach and duodenum need to be bypassed, such as gastric or duodenal surgery or proximal gastrointestinal tract disorders.

Advantages of these tubes are that the stomach, duodenum, and pancreas are bypassed and they can be used to feed immediately postoperatively, even if gastric motility is negligible. Disadvantages are that they must be in for a minimum of 7-10 days prior to removal to allow a good seal to form between the GI tract and abdominal wall, they require general anesthesia, require either abdominal surgery or the use of an endoscope to place, require special expertise for placement, they cannot be used at home by most owners, they have a small diameter so only commercial liquid diets can be fed, and they are easily dislodged, and pose a risk for peritonitis if dislodged before seal is formed.

These tubes can be placed directly into the jejunum during laparotomy, or can be passed through an existing gastrostomy tube with the use of an endoscope (percutaneous endoscopic jejunostomy or PEJ tube), or inserted through the external naris and terminating in the jejunum with the aid of an endoscope (endoscopically assisted NJ tube).

For placement of a PEJ tube, an endoscope is inserted into the PEG tube then guided into the duodenum. A guide wire is placed through the channel of the tube, and the scope is removed, leaving the guide wire in place. A 12 F jejunostomy tube is then inserted over the guide wire to an appropriate position (confirm with fluoroscopy or radiograph).

For NJ tube placement, the scope is placed into the duodenum, and a guide wire inserted into the jejunum. The scope is removed leaving the guide wire in place exiting the mouth. This is then back loaded into the nose by inserting a no. 5 French red rubber catheter into the external naris and grasping it with a hemostat as it exits the pharynx. The guide wire is placed into the tube, and the tube and guide wire removed as a unit to pull the guide wire retrograde through the nose. The jejunostomy tube is then inserted over the guide wire into the jejunum. Placement can be determined with the aid of fluoroscopy.

Diets

Only liquid diets (Clinicare Abbott laboratories) can be fed through small-bore tubes (<10 Fr). Blenderized canned foods (Hill's a/d, Eukanuba Maximum calorie) can be fed through larger bore tubes; but it may be best to start with liquid until the animal is tolerating the feedings well, then switch to canned food.

The determination of the amount to feed requires calculation of the basal energy rate (BER) = 30 x kg + 70. It is rarely necessary to feed more than this, as overfeeding can led to increased CO2 production and potentially ventilatory stress.

Microenteral nutrition involves the delivery of small amounts of 0.1 to 0.25 ml/lb/hour of a glucose and electrolyte solution into the gut through a gastric, nasogastric, or nasoesophageal tube. This is a good option for the patient who is fairly intolerant of oral nutrition (vomiting patient, pancreatitis patients, patients with severe esophageal injury, and those with short bowel syndrome). This helps to feed the gut and prevent mucosal atrophy and bacterial translocation.

Techniques for Enteral Feeding

In the trauma patient, early enteral feeding is very beneficial so should be started as soon as the patient will tolerate it. Postoperatively, if a jejunostomy tube has been placed, feeding can be started immediately. If another type of tube is being used, there will be a lag time of 1-2 days before there is gastric motility, so may need to delay feeding to avoid vomiting and aspiration. All diets should be warmed to room temperature.

Constant rate infusions are often tolerated better than bolus feedings, however this is less physiological, so should not be continued long term if avoidable. An enteral feeding pump or regular fluid pump can be used. For a constant rate infusion, place 8 hours worth of food in a bag. Flush the tube with 2-5ml of warm water at least every 6 hours. Initial delivery rate should be 0.25-0.5ml/lb/hour, slower if the GI is compromised or if there has been a long anorexic period. This rate can be increased by increments of 30% every 12 hours or so until full caloric requirements are met.

If the animal will be going home with a feeding tube, they will need to be switched to bolus feedings. Bolus feedings should start slow with a dilute solution at only around half the caloric requirements. This can be increased over the next 3-4 days to full caloric requirements and full concentrated feedings. It is best to divide daily feedings into 6-8 feedings per day to meet caloric requirements without going over the volume limit. Always administer bolus feedings over a period of 5 minutes or more, and always flush the tube after each feeding.

Caring for Feeding Tubes

Dressing should be changed whenever wet and a minimum of every 72 hours. Careful to not cut the tube while changing the bandage. Examine the ostomy site daily. Clean the site with antibacterial solution and examine closely for signs of discharge or inflammation and palpate for swelling or crepitus. Place an antibacterial ointment over the site before replacing the bandage.

Possible Complications of Enteral Nutrition

Kinking is common with small diameter tubes. Use care looping the tube when bandaging and don't bandage too tightly.

Clogging of the tube is a very common complication. The tube must be flushed a minimum of once every 6 hours. Always use commercial liquid diets in all small tubes (less than 10 Fr). Diets must be properly blenderized when using E tube or G tube. Use the largest bore tube possible. Tubes can often be unclogged with water, carbonated beverages, pancreatic enzymes, or meat tenderizer. Flush with smaller syringes to build up higher pressure in tube. Passing an angiographic wire down the lumen can be tried if other methods fail. Take radiographs to look for internal kinking if unclogging is unsuccessful.

Infection is a less common but more serious complication of feeding tubes. Mild wound infections can be treated locally with gentle cleaning with antibacterial solution. Warm compressing daily may be helpful as well. Avoid systemic antibiotics unless systemically ill.

Necrotizing fasciitis occurs when bacteria travel along fascial planes. This is a possibly fatal complication. Early warning signs include swelling, inflammation around the tube and in dependent areas near the tube, fluid or crepitus under the skin, and fever. This complication requires aggressive surgical debridement.

Tube dislodgement is common with nasal tubes, and an Elizabethan collar may be needed. Dislodgment is also common with vomiting. You may choose to avoid passing the tube through lower esophageal sphincter, especially in cats, as this may trigger vomiting. Early dislodgement of gastrostomy or jejunostomy tubes can lead to peritonitis.

Aspiration is common in humans. Always confirm placement of a tube with a radiograph. Monitor for moist lung sounds, areas of dullness on auscultation or percussion of the lungs, coughing or fever. Discontinue feeding, provide oxygen if necessary, and take chest radiographs. Transtracheal wash may help identify infectious agents.

Vomiting can be related to placement of the tube, the feeding process, the underlying disease, or a hyperosmolar diet. Avoid placing nasal and esophageal tubes into the stomach unless necessary, as this may trigger vomiting. Feed food at room temperature and don't feed too rapidly. Consider switching to a lower fat diet or diluting the diet with water. Consider suctioning the tube prior to feeding. Refrigerate all enteral diets after opening, and discard any opened diets after 24 hours.

Diarrhea is usually related more to the underlying disease. Liquid diets can often result in a liquid stool. Don't discontinue feeding unless absolutely necessary.

Refeeding syndrome occurs secondary to severe hypophosphatemia as malnourished patients receive aggressive nutritional support. It is characterized by acute cardiopulmonary decompensation leading to death. Refeeding leads to fluid retention, increases in heart rate, blood pressure, and oxygen consumption that may cause the demands on the heart to exceed supply. Increased carbon dioxide production leads to respiratory distress, CNS dysfunction (including seizures), diarrhea, red blood cell dysfunction and leukocyte dysfunction.

References available upon request.