Chapter 70: Controversies: Enteral Nutrition—Pyloric Versus Postpyloric

Critically ill patients are often in hypermetabolic states with increased nutritional needs. At the same time, however, such patients are often unable to take adequate oral intake, necessitating the use of supplementary nutrition. Maintaining adequate nutrition in the critically ill patient has shown to decrease infectious complications.¹ Early enteral nutrition in the critically ill mechanically ventilated patient has shown to decrease ICU and hospital mortality rates with the greatest benefit derived in the sickest of patients.² Malnutrition on the other hand is known to adversely impact the length of ICU and hospital stay.³ It is because of the benefits seen with providing optimal nutrition in the ICU that nutritional support therapy has now become an indispensable component in the management of the critically ill patient. Although nutrition can be provided via the enteral or parenteral route, the enteral route is preferred over the latter due to its lower cost, ease of institution and decreased infectious complications.⁴ Not using the gastrointestinal tract predisposes to gut mucosal atrophy, resulting in translocation of the bacteria across the gut wall leading to bacteremia.

Shock, sepsis, traumatic brain injury as well as pharmacologic agents commonly used in the ICU setting (opioid analgesics, vasoactive, and paralytic agents), all predispose critically ill patients to develop impaired gastric emptying and decreased enteral motility that is seen in up to 60% of this patient population.⁷ As a consequence of impaired gastrointestinal motility, high gastric residual volumes (GRVs) are frequently encountered. Finding high GRVs is often used clinically, as an indication of intolerance to enteral feeds. Feeds are thus held or stopped altogether upon encountering high GRVs. It is thought that feeding past the pylorus may result in a lower incidence of high GRVs leading to fewer interruptions in enteral feeding and ultimately in increased nutritional delivery to the patient. However, whether routine monitoring of GRVs is warranted in the critically ill is yet another area of controversy.

Enteral nutrition in the critically ill is usually delivered via an enteric tube which is inserted either through one of the nares or through the oral cavity. The distal tip of this tube may terminate in the stomach (nasogastric or orogastric tube) or in the duodenum (nasoduodenal tube) or alternatively in the jejunum (nasojejunal tube). These feeding tubes can be placed by surgical techniques as well, namely, gastrostomy (percutaneous endoscopic gastrostomy (PEG) if placed via an endoscopic technique) and jejunostomy (percutaneous endoscopic jejunostomy (PEJ) when placed via an endoscopic technique).

Feeding into the stomach is often termed pyloric or prepyloric feeding, where as feeding into the duodenum or the jejunum is appropriately called postpyloric feeding because the distal end of the feeding tube rests past the pylorus. Although there are a relatively few clinical conditions (Table 70–1) in which feeding via the postpyloric route may be indicated, in a vast majority of the critically ill patients, the issue of pyloric versus postpyloric feeding has been an area of debate. Controversies surround issues of delivery of nutritional goals, time, and resources expended in placement of feeding tubes, as well as rates of infectious and noninfectious complications seen with the 2 modes of enteral feeding.

Before enteric feeds can be initiated, enteral access must first be obtained. Although the placement of nasogastric or orogastric tubes may be somewhat cumbersome for the patients, they are placed with a relative ease by the clinicians. Often air insufflation, although considered unreliable by many, and pH testing of the gastric contents are undertaken to confirm the placement of the nasogastric tube in the stomach. A chest X-ray (CXR) is also performed in order to confirm that the tip of the feeding tube is in its intended location and not in the lung.

Multiple techniques exist for the placement of postpyloric feeding tubes, and no one technique has been adopted as the standard. Methods employed in the placement of postpyloric feeding tubes range from blind placement at the bedside, placement under fluoroscopy guidance in the radiology suite, to placement by endoscopy under direct visualization. Techniques utilizing prokinetic agents, magnets, weighted-tip tubes, have been well described in literature for small bowel feeding tube placement at the bedside. Recently, CORPAK MedSystems, Inc. have introduced the CORTRAK 2 Enteral Access System to place postpyloric feeding tubes at the bedside. This method uses an electromagnetic sensing device placed on a patient’s chest to track the path that the tip of the feeding tube takes and displays it on a visual monitor. Once the tube is placed in its intended location, the electromagnetic transmitting stylet, preinstalled in the feeding tube, is removed.

TIME AND RESOURCES UTILIZED IN PLACING POSTPYLORIC TUBES

Placement of postpyloric enteral tubes may take a considerable amount of time especially when these tubes are placed via endoscopy or fluoroscopic guidance as opposed to bedside techniques. Delays in placing small bowel or duodenal tubes primarily happen when the radiologist or the endoscopist is not available after-hours or during weekends or holidays. Scheduling difficulties with radiology or endoscopy suites also, at times, may contribute to delays in the placement of small bowel tubes. Delays of up to 24 hours to initiate feeds are not uncommon when postpyloric tubes are placed via the endoscopic method.⁸ Such delays in the initiation of feeds ultimately affect the amount of nutrition a critically ill patient receives during her or his stay in the ICU. Adequately trained ICU staff skilled in placing postpyloric tubes at the bedside, however, ameliorates the need to take the patient to radiology or endoscopy suites for placement of tubes. Median times as low as 6.6 hours from admission to the ICU or initiation of mechanical ventilation to begin feeding while achieving 80% success rate in placement of postpyloric tubes by bedside nurses has been reported.⁸ Placement of postpyloric tubes at the bedside also forgoes the risks associated with transporting a critically ill patient, along with the paraphernalia of tubes and machines, in and out of the ICU. Cost reductions of greater than 60% have been noted when postpyloric tubes are placed at the bedside by dieticians as opposed to placement by the radiologist under fluoroscopic guidance.⁹ It is advisable, thus, that an attempt to place a postpyloric feeding tube should ideally be made at the bedside by an adequately trained professional, preferably a nurse or a dietician. If it proves difficult to obtain enteral access at the bedside, only then should alternate means to obtain enteral access be pursued.

ACHIEVING NUTRITIONAL GOALS IN THE CRITICALLY ILL PATIENTS

A number of studies have looked in to whether differences exist in achieving nutritional goals based on whether a patient is fed into the stomach or past the pylorus.

A fair number of studies have found that patients fed past the pylorus received greater amount of nutrition overall^10,11,12,13 compared to those fed in to the stomach. Another set of studies, however, found no difference between the 2 groups.^14,15 Evidence also exists which shows that those fed past the pylorus received less overall nutrition than those fed in to the stomach.⁸ One study found no difference over all, but upon a subgroup analysis found that in centers which have previous experience with postpyloric feeding, patients fed via the postpyloric route met nutritional goals more frequently than those fed in to the stomach.¹⁴ In a retrospective review of 150 episodes of postpyloric feeding in 146 patients, including 20 patients fed at home for various durations of time, nutritional requirements were met in 90% of the patients.¹⁶ The results of these studies are summarized in Table 70–2.

Meta-analyses that have evaluated this issue have yielded mixed results as well, with some that have reported no difference in achievement of nutritional goals^17,18 while others that have reported a signal toward increased nutritional intake with postpyloric feeding.¹⁹

PNEUMONIA IN PYLORIC VERSUS POSTPYLORIC FEEDS

Given that critically ill patients have a high incidence of delayed gastric emptying, up to 60% in some studies,⁷ high GRVs are frequently encountered when these patients are fed in to the stomach. High GRVs are thought to predispose a critically ill patient to a higher chance of developing gastroesophageal reflux, leading to an increased incidence of macroaspiration and microaspiration of gastric contents ultimately resulting in greater incidence of pneumonia. The idea of feeding past the pylorus to decrease reflux, aspiration, and ultimately prevent pneumonia is not an unfounded one. It has been shown in clinical studies that feeding a patient past the pylorus significantly reduces gastroesophageal reflux and results in a trend toward decreased pulmonary aspiration.²⁰ Whether this decreased incidence of reflux and aspiration of gastric contents leads to clinically important outcomes such as decreased incidence of nosocomial and ventilator associated pneumonias, has been extensively debated in multiple studies.

CURRENT EVIDENCE VALUATING RISK OF PNEUMONIA IN PYLORIC VERSUS POSTPYLORIC FEEDING

A number of studies have found no significant difference in the incidence of pneumonia in patients fed via the pyloric versus the postpyloric route.^{8,11,14,15,21} One of the earlier studies did however show a decreased incidence of pneumonia with postpyloric feeding compared to gastric feeding.¹⁰ Two additional studies have also shown a significant decrease in pneumonia with the use of postpyloric feeding as compared to prepyloric feeding.^12,13

Mostly, studies evaluating controversies surrounding pyloric versus postpyloric feeding have been relatively small. Given the plausibility of how postpyloric feeding can theoretically decrease the incidence of pneumonia and a number of studies showing both benefit and no benefit at all, a number of meta-analyses been carried out to investigate this issue further. Two of the earlier meta-analyses,^17,18 which utilized 9 and 11 studies, respectively; found no difference in rates of pneumonia between the pyloric and postpyloric feeding groups. More recent meta-analyses,^19,22 however, both of which are from 2013, with each including 15 studies, did show significant reduction in incidence of pneumonia with postpyloric feeds. Table 70–3 summarizes the results of the studies exploring pneumonia in pyloric versus postpyloric feeding.

A few studies have reported lower incidence of increased GRVs in the postpyloric group.^13,14,26 Higher incidence of diarrhea, however, has been reported in the postpyloric group.¹⁰ This is at times attributed to the inability of the small bowel to handle high osmotic loads in polymeric feeds. Thus partially hydrolyzed or semielemental feeds may prove to be useful in these instances. Complications related to tube maintenance have been noted to be higher in the postpyloric group.^14,16 Due to their smaller caliber, postpyloric tubes clog more frequently than gastric tubes. Tube blockage with postpyloric feeding tubes can be seen in up to 17% of the cases.¹⁶ Fifty-milliliter water flushes every 4 to 6 hours can help avoid clogging of the tubes. A meta-analysis¹⁸ found that proportion of patients needing an alternate form of feeding because of tube placement or tube blockage was significantly higher in the postpyloric group.

Most of the studies done to date have found no statistically significant difference in rates of mortality, ICU, or hospital lengths of stay.^{8,11,12,14,21} In addition, none of the meta-analyses conducted to date has a shown a difference in mortality between the 2 groups.

The 2009 American Society for Parenteral and Enteral Nutrition (ASPEN) guidelines²³ for nutrition support therapy in the critically ill do not make any specific recommendation for gastric or small bowel feeding and note that either of the two is an acceptable strategy. They do, however, recommend small bowel feeding for those at high risk of aspiration or intolerant of gastric feeding (grade C). These guidelines further recommend that withholding enteral feeds for multiple episodes of high gastric residuals is sufficient for one to consider initiating small bowel feeding (grade E).

The 2013 Canadian critical care nutrition guidelines²⁴ suggest that feeding critically ill patients through the small bowel may be associated with a lower incidence of pneumonia. These guidelines recommend that in ICUs where placement of postpyloric tubes is feasible, critically ill patients should be routinely fed through the postpyloric route. In ICUs where logistical difficulties exist in obtaining postpyloric access, postpyloric feeding should be considered only in patients who are at high risk for intolerance to enteric nutrition such as those on continuous infusion of sedatives and opioids, vasoactive agents and paralytics. If small bowel access is not feasible due to lack of fluoroscopy or endoscopy or due to lack of expertise in blind techniques, postpyloric feedings should be considered only in those patients who are intolerant of gastric feeds and those who repeatedly demonstrate high GRVs.

With the current evidence that is available, it is clear that the controversy about pyloric versus postpyloric is far from over. Larger studies in the future may show clearer differences in clinical outcomes between pyloric and postpyloric feeding. There is evidence to suggest that differences in clinical outcomes from pyloric versus postpyloric feeding may not be achieved in less critically ill patients and that the benefit of postpyloric feeding may be primarily seen in those with ASPEN II scores greater than 20.²⁵