INTRODUCTION — The maintenance of appropriate nutrition in patients with acute and chronic illness is well recognized as a fundamental part of standard medical and surgical care [1]. Malnourished patients have poorer clinical outcomes, more complications and infections, and use more resources than well-nourished patients [2-4]. Because of lower energy reserves and proportionately higher energy and nutrient needs, children are more susceptible than adults to malnutrition and its multiple complications; as a result, nutritional interventions are even more important in pediatric patients. Thus, in both adult and pediatric patients, every effort should be made to support normal nutritional status throughout illness.
Enteral nutrition is generally preferred to parenteral nutrition because of its relative simplicity, safety, and lower cost, as well as its ability to maintain mucosal barrier function. There are several ways to deliver enteral nutrition (figure 1). This topic review will focus on the theoretical and practical aspects of pre- and post-pyloric enteral nutrition in children and adults. The advantages and disadvantages of each approach will be discussed, with particular reference to the decisions that lead to a choice of feeding method (algorithm 1). The American Gastroenterological Association (AGA) guideline for enteral nutrition [5], as well as other AGA guidelines, can be accessed through the AGA website.
ISSUES FOR DECIDING UPON THE TYPE OF ENTERAL NUTRITION — Nasoenteric tubes are the first means of gaining enteral access in the vast majority of patients. Orogastric feeds are often used in neonatal practice, since infants are predominantly obligate nasal breathers. A more permanent feeding tube should be considered if enteral support will be needed for more than four to five weeks [6]. (See "Inpatient placement and management of nasogastric and nasoenteric tubes in adults" and "Gastrostomy tubes: Uses, patient selection, and efficacy in adults".)
However, the transnasal approach may not always be possible. Anatomic anomalies, tumors, and trauma may impede the passage of a tube from the nose into the stomach and can lead to complications (table 1). Furthermore, placing a nasoenteric tube may be hazardous in patients with altered consciousness who may not be able to cooperate adequately with swallowing or indicate inadvertent misplacement of the tube into the trachea. Special precautions should be taken particularly in intubated patients, since cuffed endotracheal tubes do not sufficiently protect against pulmonary intubation during passage of a feeding tube. Nasoenteric tubes have also been associated with an increased risk of bacterial sinusitis [7].
In addition to the above considerations, the following must be established prior to deciding upon the type of access and site of administration:
●The patient should be unwilling or unable to maintain adequate nutrition with oral feeds alone. In most cases nutritional support should be considered if recommended daily requirements will not be met for more than about seven days in adults, three to five days in children, and one to three days in infants [8]. Earlier intervention is necessary in patients who are already malnourished.
●There must be a functional gut. The only absolute contraindication to enteral nutrition is mechanical obstruction. Other disease entities (eg, multiple traumas, postoperative state, gastrointestinal bleeding, congenital gastrointestinal anomalies, malabsorption, and short bowel syndrome among others) all require careful management but are not absolute contraindications to providing enteral nutrition.
●A route of enteral access must be safely obtainable.
GASTRIC FEEDING — Most patients tolerate intragastric feeding well. However, it is important to consider the factors that make this possible. The stomach must be structurally and functionally able to act as a reservoir, a propulsive and a digestive organ. Ideally, the lower esophageal sphincter should have adequate tone and function to prevent significant gastroesophageal reflux (GER). Gastric motility should be intact, with coordinated contraction, normal antroduodenal progression, and adequate gastric emptying of liquids. Because this information is usually unavailable, the decision to begin gastric feedings is typically made based upon the history and clinical evaluation. Although most patients can be started on low volume continuous intragastric feeds, a significant history of any of the following would favor starting with jejunal feeding:
●Recurrent aspiration of gastric contents
●Esophageal dysmotility with a history of regurgitation
●Delayed gastric emptying
The initial feeding regimen should be dictated by the patient's clinical status. A patient in a stable condition can usually be started on bolus nasogastric feeds, whereas less stable patients may be started with continuous gastric feeds.
Feeding tolerance must be continually assessed irrespective of the feeding regimen. Stool frequency, the presence of diarrhea, abdominal distension, urinary output, and vomiting are all factors that may be influenced by the feeding regimen. Diarrhea is commonly described as a complication of any route or type of enteral feeding. There are multiple factors that may precipitate diarrhea in tube-fed patients, not least of which are the patient's primary illness and concomitant medications. The composition, rate, and total volume of the feed may be responsible [9], while contamination of feed by bacteria [10] and small bowel bacterial overgrowth may also contribute. Monitoring of gastric residual volumes can also be used to assess tolerance, although a single high residual volume should not lead to unnecessary interruption of feed [11].
Introduction of continuous intragastric feeds is commonly used to assess feeding tolerance, especially if GER is suspected. Patients may be rapidly advanced to bolus feeds once continuous feeds are tolerated at full volume and strength. A more gradual transition to bolus feeds may be necessary in smaller children or in those where upper gastrointestinal motility is poor [12]. It may be necessary to formally assess GER (eg, by esophageal pH or multichannel intraluminal impedance monitoring) in some cases. Since GER often coexists with poor gastric motility in the critically ill, transpyloric feeding is often preferred from the outset in these patients [13]. (See 'Role in critically ill patients' below.)
Post-pyloric feeding — Four meta-analyses of randomized trials that compared post-pyloric feeding with gastric feeding have been published. Two of the meta-analyses found no benefit from post-pyloric feeding [14,15], while the other two found some benefits, including a reduction in the incidence of pneumonia [16,17]. Gastric feeding continues to be recommended for nutritional support of critically ill children where possible [18]. Post-pyloric feeding should be reserved for those intolerant of this feeding route or those with a high risk of aspiration.
Advantages of gastric feeding — Gastric feeding has a number of advantages. It is more physiological, is easier to begin, and more convenient.
More physiological — Intragastric feeding has the clear advantage of providing nutrition by the more physiological route. Intragastric feeds buffer gastric acid better than post-pyloric feedings. In one study, continuous gastric pH measurements among 10 critically ill patients fed intragastrically were greater than 5.0 significantly more often compared to those fed intraduodenally (54 versus 23 percent) [19]. In addition, both gastropancreatic reflexes and gastrin release contribute to pancreatic responses prior to food reaching the upper small bowel.
The osmolality, pH, and fat content of the substrate reaching the proximal small bowel regulate gastric emptying by both humoral and neural pathways. Bolus intragastric feeding thus more closely mimics physiological normality by allowing intrinsic mechanisms to control delivery of gastric content to the upper small bowel. However, it appears that in critically ill adults the rate of glucose absorption is the same whether or not nutrition is delivered intra-gastrically or via a post-pyloric catheter [20].
Ease of placement — The placement of orogastric or nasogastric tubes is a relatively safe procedure, requires minimal training, and is possible at the bedside. Nasogastric tubes are frequently dislodged. The mean life span of a nasal tube has been reported in adults to be only 10 days [21]; up to 60 percent of tube removals occur accidentally [22]. Although this underscores their use as short-term devices, they do have a role in the long-term management of some patients.
In children requiring nighttime feedings, placement of a new tube every night has been suggested to avoid the daily cosmetic appearance of a nasogastric tube [23]. While complications with insertion do occur [6], the use of softer, more flexible materials has reduced the risks of perforation and local trauma.
Assessment of correct positioning should only be carried out with pH assessment. Aspiration of gastric content is mandatory to help avoid the tracheal instillation of feeds, even if the tube is replaced daily (advised by the United Kingdom National Patient Safety Agency 2011). As mentioned above, placing tubes in patients with altered consciousness is particularly hazardous; thus, radiographic confirmation of tube location may be indicated in some clinical settings. Radiologic confirmation of intragastric location is warranted as a second line test if placement is uncertain or if gastric aspirates show a pH ≥5.0, since neither capnography nor air insufflation are reliably accurate [24].
Convenience — The stomach is able to tolerate a larger volume and higher osmotic load than the upper small intestine. Its role as a reservoir and regulator of food passage into the duodenum gives the patient and clinician much greater flexibility in choosing the type of formula and feeding regimen. The regulation of gastric emptying is complex, yet in health this maintains optimal digestive activity as well as regulating metabolic processes such as glucose homeostasis. Caloric density may be increased more easily to accommodate certain nutritional demands, although the need for maintenance free water must be taken into account for each patient.
Gastric feeds allow the option of either bolus or continuous feeds. In the presence of intact physiological mechanisms, bolus feedings are preferable since they minimize disruption to lifestyle and the dependence upon pump devices. Intermittent bolus feeding permits a slower, pump-controlled infusion over several hours and is used as a compromise between rapid, gravity-dependent bolus feeds and continuous infusions. Continuous intragastric feeds may be better tolerated by certain groups of patients (eg, premature infants, patients with mild-moderate GER or mildly delayed gastric emptying). In most instances, isotonic, polymeric feeds are suitable for intragastric feeding. These are less costly and more widely available than the hydrolyzed/elemental feeds sometimes used for post-pyloric feeding.
Disadvantages of gastric feeds — The main disadvantages of gastric feeding are encountered in patients with delayed gastric emptying and those at risk for aspiration.
Delayed gastric emptying — Any factor that may delay gastric emptying should be taken into account prior to a trial of intragastric feeds (table 2). Continuous intragastric feeds may be necessary when delayed gastric emptying is suspected. Symptoms such as nausea, vomiting, heartburn, early satiety, belching, and epigastric fullness may all precede actual vomiting as signs of delayed gastric emptying. Treatment with prokinetic agents such as metoclopramide, domperidone, or azithromycin/erythromycin can be beneficial [25]. In a randomized trial of more than 300 patients, metoclopramide did not reduce the incidence or the long-term mortality from aspiration pneumonias in intragastrically fed patients in the intensive care unit (ICU), although it did delay their onset [26]. (See "Treatment of gastroparesis", section on 'Prokinetics'.)
Gastroesophageal reflux and aspiration — A poorly functioning lower esophageal sphincter may become even less competent with passage of a nasogastric tube and the onset of gastric feeding. Fine bore tubes (<9 French) cause much less GER and aspiration than large bore tubes (>12 French) [27]. In some settings, it is important to define whether episodes of aspiration are truly gastroesophageal in origin. Aspiration in adults following a stroke, for example, may be due to disordered swallowing and/or GER. Oropharyngeal aspiration may be a particular concern in patients with neurogenic dysphagia (such as those with cerebral palsy) and be unrelated to enteral feeding. Videofluoroscopy and isotope salivagrams may help define the source of aspiration [28]. In children, upper airway endoscopy and findings of erythema are not predictive of GER, for instance [29].
Simple measures to minimize gastroesophageal reflux should be tried initially in patients suspected of having GER. The head of the bed should be elevated by 30º, the rate and volume of feeds should be reduced, and their composition modified to a more hydrolyzed or a lower osmolarity formula. The addition of acid blockade and prokinetic agents may also be useful. As mentioned above, significant symptoms of GERD (such as a history of apnea, recurrent aspiration, regurgitation, or moderate to severe esophagitis) might favor a therapeutic trial of post-pyloric feeding [30].
POST-PYLORIC FEEDING — The most common indications for post-pyloric feedings include:
●Pulmonary aspiration.
●Severe gastroesophageal reflux (GER) and esophagitis.
●Recurrent emesis.
●Post surgery/multiple trauma.
●Abnormal gastric or antroduodenal dysmotility.
●Patients with decreased bowel sounds or those on paralytic agents. In both settings gastric motility may be impaired more than intestinal motility.
Passing a feeding tube beyond the pylorus is necessary in children and adults who are intolerant of intragastric feeds. This is most often due to a combination of GER, poor gastric motility and/or concerns about pulmonary aspiration. Patients in the intensive care unit (ICU) are also frequent candidates for post-pyloric feedings due to their underlying illness and frequent finding of gastric ileus. In trauma patients, early enteral nutrition is associated with fewer infectious complications than parenteral nutrition [31,32]. A variety of in vitro and in vivo data also support the superiority of enteral over parenteral nutrition in a wide range of critical illnesses [33,34].
In children, jejunal feeds have traditionally been elemental or hydrolyzed and less viscous due to the narrow lumen of tubes needed to pass the pylorus, although polymeric feeds have also been tolerated [35]. In adults, polymeric formulas are usually used except for those with malabsorptive disorders. The sudden arrival of a hyperosmolar feed is likely to lead to abdominal cramping, hyperperistalsis, and diarrhea since the jejunum relies on a controlled delivery of isotonic substrate. In addition, the small bowel cannot expand its capacity as does the stomach, so jejunal feeds should be administered continuously by pump and never by bolus.
Advantages of post-pyloric feeding — Jejunal feeding has several advantages.
Minimize aspiration risk — The main advantage of post-pyloric feeding is that it may reduce the risk of GER and pneumonia [36,37].
Role in critically ill patients — Post-pyloric feeding has theoretical advantages in critically ill patients. Impaired gastric emptying is relatively common and thus feeding beyond the pylorus has the potential to deliver adequate nutrition without the need for parenteral nutrition [38]. In addition, compared to gastric feeding, it may reduce the risks associated with high gastric residuals such as aspiration pneumonia. The delivery of a continuous feed to the jejunum also prevents gastric distension, thus potentially allowing for better respiratory function [37]. The main disadvantages are the inconvenience, risks, and costs associated with placement of the tube beyond the pylorus. The rates of complications also depend on the severity of the underlying illness. As an example, prospective data show that critically ill children with shock had a higher incidence of gastrointestinal complications (eg, diarrhea, distension) with post-pyloric feeds than children without shock [39].
Several studies have examined these issues in critically-ill patients; not all of which reached the same conclusion [14,15,36,40]. A 2015 meta-analysis included 14 randomized controlled studies that compared gastric versus post-pyloric feeding in 1109 critically ill patients [17]. There were no significant differences in duration of mechanical ventilation or mortality but post-pyloric feeding was associated with a reduction in pneumonia as compared with gastric feeding (RR 0.65, 95% CI 0.51-0.84).
Canadian clinical practice guidelines also noted that small bowel feedings were associated with a lower incidence of pneumonia in critically ill adults, and therefore recommend routine use of small bowel feedings in centers where this is feasible [40]. Canadian ICUs using these guidelines reported higher rates of adequacy of enteral nutrition (percentage of prescribed energy needs actually received) compared with sites less compliant with these guidelines [41].
Benefits in acute pancreatitis — By bypassing the mouth, stomach and duodenum, jejunal feeds minimize the stimulation of pancreatic exocrine secretions [42]. Accumulating evidence has suggested that post-pyloric feeding is safe and may also reduce complications. The hypothesis underlying this benefit is that enteral nutrients maintain the intestinal barrier. Bacterial translocation from the gut is probably a major cause of infection in the setting of acute pancreatitis. In addition, another major advantage of the intestinal route is the elimination of the complications of parenteral nutrition such as catheter sepsis (2 percent even if the catheter is managed appropriately) and less frequent complications such as arterial laceration, pneumothorax, vein thrombosis, thrombophlebitis, hyperglycemia, and catheter embolism. Although the results of large controlled trials are awaited, cautious use of post-pyloric feeds in acute pancreatitis should be strongly considered. A meta-analysis of 27 randomized controlled trials confirmed that enteral nutrition in the setting of acute pancreatitis was associated with significant reductions in length of stay and infectious complications [43]. Indeed, guidelines recommend enteral feeding rather than parenteral nutrition in patients with moderately severe and severe acute pancreatitis who cannot tolerate oral feeding [44]. (See "Pathogenesis of acute pancreatitis" and "Management of acute pancreatitis".)
Disadvantages of post-pyloric feeding — The main disadvantages of post-pyloric feeding are related to difficulty with the placement of the tubes, clogging, and maintenance of their proper positions. In practice, success rates at post-pyloric placement can exceed 90 percent, regardless of technique (air insufflation, or use of erythromycin as a prokinetic agent) [45]. Feeding intolerance may also be a problem. A systematic review of transpyloric feeding in preterm infants found no significant growth benefit, but noted an increased mortality rate and an increased rate of feeding cessation due to gastrointestinal symptoms among those infants assigned to receive transpyloric feeding [46].
Difficulty with placement and ease of displacement — As with nasogastric tubes, nasojejunal tubes are very prone to accidental removal. Jejunal tubes are generally of finer bore than gastric tubes and thus frequently occlude, particularly if more viscous feeds and medications are given via this route.
Ideal positioning of post-pyloric feeding tubes is into the distal duodenum or jejunum (ie, beyond the ligament of Treitz). An adequately sited post-pyloric tube (verified radiographically) virtually eliminates tracheal aspiration [37] and is less likely to become dislodged, even in patients with persistent cough or vomiting. Nasal bridles allow more secure fixation of a nasal tube, however, the need for fixation around the vomer bone in the nasal cavity precludes it from routine use in pediatrics [47]. Although feeds can be given through tubes located more proximally in the duodenum, this is not an ideal location: a precise location in the duodenum is difficult to maintain, allows duodenogastric reflux of feed, and hence can contribute to gastroesophageal reflux and aspiration. Tubes in the proximal duodenum may also recoil into the stomach.
Intestinal perforation occurs more often with jejunal tubes than with intragastric tubes, although the introduction of softer and more flexible materials reduced the incidence of this complication [48,49]. Formation of an enterocutaneous fistulae has also been described [50]. Most reports of this type of complication have been in premature infants [51,52].
Other complications of jejunal feeding tubes include nonmechanical bowel ischemia, intussusception, and volvulus [53].
There are several methods used for placing post-pyloric tubes. Endoscopic placement of a jejunal feeding tube is commonly carried out and allows placement under direct vision. Fluoroscopy facilitates the placement of jejunal feeding tubes, particularly of gastro-jejunostomy tubes, but requires skilled radiologic support and exposure to radiation [54,55]. More recently, an electromagnetic-guidance technique proved faster (1.7 hours versus 21 hours) and more successful (82 versus 38 percent) than "blind" placement of a post-pyloric enteral feeding tube [56]. In general, small-bore tubes are more easily placed than larger tubes.
There are several less invasive techniques that have been described. Jejunal tubes with a pH sensitive tip have been successfully passed in children [57]. Weighted tubes have generally been no more successful than unweighted ones [58]. Gastric insufflation of 20 mL of air with an unweighted tube allowed 23 of 25 tubes to be advanced into the small bowel, compared to 11 of 25 in the control group in one study [59]. Other authors have used either erythromycin [60] or metoclopramide [61] to advance transpyloric tubes with some success. A meta-analysis of metoclopramide for this purpose noted that efficacy has not been demonstrated but that studies have been generally unpowered [62].
Feeding intolerance — A significant problem in some patients occurs with rapid entry of formula into the jejunum. This may follow the rapid infusion of feeds via jejunal tubes, or rapid gastric emptying of gastric bolus feeds. These patients develop a "dumping syndrome," with symptoms of faintness, palpitations, and sweating, often accompanied by pallor, tachycardia, rebound hypoglycemia, and diarrhea. It usually requires slowing of the rate of feeding or a change in formula. Although whole protein, complex carbohydrate feeds can be infused into the jejunum at low volumes, caloric requirements often require hydrolyzed protein formulas with medium-chain triglycerides and corn syrup/glucose polymer as sources of fat and carbohydrate, respectively. The addition of complex carbohydrates (eg, cornstarch) can reduce rapid glucose shifts and "dumping" symptoms that occur in patients given standard intragastric feeding regimens [63].
LONG-TERM PRE- AND POST-PYLORIC FEEDING — The indications for pre- and post-pyloric feeding also apply to the more permanent enteral feeding tubes. The placement of a percutaneous endoscopic gastrostomy (PEG) has now become common practice in patients requiring enteral feeding for more than four to five weeks. A feeding jejunostomy tube generally requires surgical placement, although endoscopic placement of jejunostomy tubes has been described (PEJ) [64-67]. One series in children has found this technique to be feasible in children as young as four years [68]. In adults with a body mass index (BMI) >25, the success rates of direct endoscopic jejunostomy placement was lower (67 versus 87 percent) than in patients with a BMI <25, and four out of five serious adverse events occurred in those with a BMI >25 [69]. In the presence of any esophageal obstruction, radiological gastrostomy placement has been used with some success [70], although the choice over a surgical gastrostomy clearly depends upon availability of local expertise.
Both surgical gastrostomies and PEGs differ from the nasogastric feeding in that they tether the gastric wall to the anterior abdominal wall. This is a theoretical problem with patients who already have disordered upper gastrointestinal motility, since this tethering can potentially worsen gastroesophageal reflux. If a motility disorder is strongly suspected, formal motility assessment of the upper gastrointestinal tract may be carried out prior to the procedure. If there is significant delay in gastric emptying or disordered antroduodenal motility, placement of a PEJ or surgical jejunostomy may be indicated instead of PEG.
In settings where gastrostomy feeds are no longer tolerated, a trial of jejunal feeds can be performed by placing a jejunal tube alongside an existing PEG, or by placing a PEG tube with transgastric jejunostomy tube (PEG-J), through which where a jejunal extension tube allows transpyloric feeding. These techniques provide a short-term feeding solution and may predict the response to a surgical jejunostomy or PEJ. However, they are seldom a long-term solution since these tubes also tend to recoil into the stomach, become clogged, and may be of little value in preventing pre-existing oropharyngeal aspiration [6,71]. PEJ tubes have significantly better long-term patency and stability of feeding access compared with PEG-J tubes [66,72].
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Nutrition support (parenteral and enteral nutrition) in adults".)
SUMMARY AND RECOMMENDATIONS
●The choice and route of enteral feeding is based upon the clinical setting, expected duration that support will be required, and assessment of the risk of complications. Enteral rather than parenteral nutrition is preferred in most patients (unless there are specific contraindications) since it is a safer and more physiological means of nutritional support. (See 'Issues for deciding upon the type of enteral nutrition' above.)
●Most patients can be started on low volume continuous intragastric feeds. However, we suggest beginning with jejunal feeding in patients with any of the following features: recurrent aspiration of gastric contents, esophageal dysmotility with a history of regurgitation, or delayed gastric emptying (Grade 2C). (See 'Gastric feeding' above.)
●Additional settings in which post-pyloric feeding can be considered include: severe gastroesophageal reflux (GER) and esophagitis, recurrent emesis, post-surgery/multiple trauma, gastric, antroduodenal dysmotility, patients with decreased bowel sounds and those on paralytic agents (where gastric motility may be impaired more than intestinal motility). The main disadvantages of post-pyloric feeding are related to difficulty with the placement of the tubes, clogging, and maintenance of their proper positions. (See 'Post-pyloric feeding' above.)
●There continues to be practice variation in use of post-pyloric versus gastric feedings in critically ill patients. In a pediatric intensive care unit (ICU), post-pyloric feeding is often used due to relative ease of placement, whereas in many adult ICUs, gastric feedings are often used initially because of the inconvenience of placing and maintaining post-pyloric feeding tubes in older patients.
●Enteral feeding can be associated with complications. The importance of assessing each individual's risk of GER and possible aspiration pneumonia cannot be overstated. (See 'Disadvantages of gastric feeds' above and 'Disadvantages of post-pyloric feeding' above.)