Which factor is a possible cause for constipation in a patient who is prescribed enteral feedings?

February 2011 Issue

Enteral Nutrition Intolerance in Critical Illness
By Megan Tempest, RD, LDN
Today’s Dietitian
Vol. 13 No. 2 P. 30

A dietitian’s role in the critical care setting is uniquely challenging, frequently rewarding, at times frustrating, and unquestionably valuable. Feeding difficulties abound when caring for the complex, heterogeneous critically ill patient population. Intolerance to gastric feeding has been reported in up to 60% of patients in the ICU.1 A host of telltale signs and symptoms may signal intolerance to enteral feeding, including vomiting, nausea, abdominal pain and/or distention, constipation, and diarrhea. Research has shown that gastrointestinal (GI) complications and feeding intolerance often result in decreased provision of enteral nutrition (EN) and prolonged ICU stay. The etiology of GI dysmotility is not clearly understood but is believed to be multifactorial. Contributing factors may include impaired function of the enteric nerve and smooth muscles of the GI tract, inflammation, surgery, medications such as opioids, electrolyte imbalances, hyperglycemia, sepsis, increased cranial pressure, and the presence of disease itself.1

It cannot be overemphasized that enteral feeding is the preferred route of nutrition for critically ill patients with a functional GI tract. When compared with parenteral nutrition administration, enteral feeding is considered safer and is correlated with better patient outcomes, prevents atrophy of the intestinal villi, and maintains the normal gut mucosal barrier, thereby discouraging bacterial translocation. The initiation of early EN within 24 hours of ICU admission is recommended and believed to reduce infectious complications.1 Dietitians may find themselves plagued and frustrated by the host of barriers that make the provision of adequate and timely enteral feeding difficult to achieve.

Recognizing EN Intolerance
While patients who are alert and lucid may verbalize their GI symptoms, more often than not, factors such as chemical sedation, altered mental status, and reliance on mechanical ventilation require a clinician to objectively assess the presence of EN intolerance. Tal Kleiner, RD, CDN, CNSC, a critical care dietitian at Montefiore Medical Center in New York City, stresses the importance of timely assessment. “I usually follow up with the patient within 24 hours after enteral feeding was started to check for early signs of intolerance,” Kleiner says. “I look for symptoms like abdominal distention, cramping, tenderness, patient complaints—if they’re able to communicate them—nausea and vomiting, constipation, and so on. If they have diarrhea, we try to rule out infectious etiologies or medications that may be contributing. If they are constipated, I check to ensure a bowel regimen is in place. I typically talk to a nurse first; they usually know best what is going on with the patient.”

Distinguishing between true vs. suspected EN intolerance requires diligence. Patient intolerance accounts for one third of EN cessation time, approximately one half of which represents true intolerance.2 Medications commonly prescribed to patients who are critically ill (eg, sedatives, analgesics) often underlie delayed GI motility. On the flip side, diarrhea is frequently observed in patients who are critically ill and is often immediately presumed to reflect intolerance to tube feeding. To accurately determine whether diarrhea is related to EN, infection, or medications, American Society for Parenteral and Enteral Nutrition (ASPEN) guidelines suggest a thorough abdominal exam, fecal leukocyte determination, quantification of stool, stool culture for Clostridium difficile and/or toxin assay, serum electrolyte panel to evaluate for excessive electrolyte losses or dehydration, and a review of medications.2

Drug Therapy to Promote EN Tolerance
Delayed gastric emptying affects approximately 50% of mechanically ventilated patients and 80% of patients with increased cranial pressure following head injury.1 For this reason, prokinetic/promotility medications are commonly prescribed to patients who are critically ill. Although the precise role of prokinetic medications in promoting EN tolerance remains somewhat misunderstood, the existing body of evidence continues to favor their use for this purpose. Annie Widlicka, MS, RD, LDN, CNSD, a critical care dietitian at the University of Chicago Medical Center, states, “Our first line of defense is often a promotility medication.”

Per ASPEN guidelines, adding prokinetic agents such as erythromycin or metoclopramide has been shown to improve gastric emptying and EN tolerance but has resulted in little change in clinical outcome for patients in the ICU.2

Looking beyond prokinetics, the use of opiate antagonists may counteract the GI dysmotility that often results from the prolonged administration of medications such as morphine. Also per ASPEN guidelines, the use of naloxone (an opiate antagonist) infused through a feeding tube to counteract effects of opioid narcotics on the gut and thus improve intestinal motility was shown in one level 2 study to significantly increase the volume of EN infused, reduce gastric residual volumes (GRVs), and decrease the incidence of ventilator-associated pneumonia.2

Perhaps even more promising is the use of sedative medications that don’t have the side effect of slowing down GI motility. Dexmedetomidine (Precedex) is specifically indicated for use in intubated and mechanically ventilated patients in the ICU setting. Widlicka reports dexmedetomidine has elicited positive results in her ICU. “The good news is there are sedatives out there that might not put the GI system to sleep. There is hope in the future of intubated sedated patient,” she says.

Feeding Tube Placement
A significant potential consequence of delayed gastric emptying is aspiration, which may result in life-threatening aspiration pneumonia. Fear of aspiration may be one of the strongest underlying motivations behind the frequent, and often unnecessary, cessation of enteral tube feeding in the ICU. To reduce the risk of aspiration, ASPEN guidelines indicate that diverting the level of feeding by postpyloric tube placement should be considered.2 However, this practice continues to be met with much resistance in many ICUs. According to Kleiner, “Postpyloric placement definitely helps support tolerance, and I wish it were done more often. Physicians are slowly becoming more open to small bowel or postpyloric feeds—and we’ve seen it work well—but it can be hard to get the team on board.”

Widlicka’s thoughts parallel the resistance that Kleiner describes. “Placing a postpyloric tube is often low on the list of strategies to improve EN tolerance, in part due to physician inexperience,” Widlicka explains, “although we do have a handful of physicians who’ve been willing to just go for it and are subsequently more willing to do it again. Postpyloric placement doesn’t happen as often as I would like it to.”

Welpe and colleagues sought to assess the safety, success, and time efficiency of establishing jejunal feeding in ICU patients via a fluoroscopy-guided technique, as discussed in the March 2010 issue of the Journal of Parenteral and Enteral Nutrition. Based on the results of their study, the authors concluded fluoroscopy-guided placement of jejunal feeding tubes by adequately trained ICU staff to be a fast and safe procedure, one that facilitates the initiation of EN in the critically ill population in the face of gastroduodenal dysfunction.

Another study by Taylor and colleagues compared the gastric emptying in patients fed via an electromagnetically guided nasointestinal tube (EGNT) or a standard nasogastric tube plus prescribed prokinetics. They found that nasointestinal feeding using EGNT achieved a higher percentage of the EN goal than using prokinetics alone. Specifically, their results indicated an immediate effect: 80% of the median EN goal was met by day one of feeding and was maintained at greater than 88% until day 10, a rate that may reduce ICU stay and complications by reducing the energy deficit.3

Gastric Residuals: What Is Significant?
In the critical care setting, this may qualify as the so-called million-dollar question. Many critical care dietitians have undoubtedly experienced frustration over unwarranted interruptions in EN due to the presence of gastric residuals and fears of aspiration. Both ASPEN and the Society of Critical Care Medicine advise that holding EN for GRVs less than 500 mL in the critically ill adult patient should generally be avoided. ASPEN guidelines state: “Four level II studies indicate that raising the cutoff value for gastric residual volume (leading to automatic cessation of EN) from a lower number of 50-150 mL to a higher number of 250-500 mL does not increase risk for regurgitation, aspiration, or pneumonia. Decreasing the cutoff value for gastric residual volume does not protect the patient from these complications, often leads to inappropriate cessation, and may adversely affect outcome through reduced volume of EN infused. Gastric residual volumes in the range of 200-500 mL should raise concern and lead to the implementation of measures to reduce risk of aspiration, but automatic cessation of feeding should not occur for gastric residual volumes <500 mL in the absence of other signs of intolerance.”1

Despite established guidelines, inconsistent practices for measuring and interpreting gastric residuals continue. Given the drawbacks of monitoring GRV, is it ever appropriate to forgo this practice? Poulard and colleagues raised this question in their prospective before-after study, published in a 2010 issue of the Journal of Parenteral and Enteral Nutrition. They challenged the assumption that GRV monitoring is an accurate method of assessing EN tolerance, one that decreases the risk of vomiting and ventilator-assisted pneumonia. They analyzed 205 medical-surgical ICU patients who had received EN via a nasogastric tube within 48 hours after starting endotracheal mechanical ventilation. They compared two methods of assessing EN tolerance: measuring GRVs at six-hour intervals (the control phase) vs. recording vomiting episodes without monitoring GRV. The study showed that those patients who did not receive GRV monitoring received larger feeding volumes without an increased rate of vomiting or ventilator-assisted pneumonia.

According to the researchers, the results indicate that monitoring GRV may hinder EN delivery, leading to underfeeding, by causing unnecessary interruptions. They conclude that the practice of holding EN delivery when GRV reaches an arbitrarily determined cutoff level is not justified by scientific evidence, increases nurse workload, and doesn’t decrease the risk of ventilator-assisted pneumonia. The results suggest that the cessation of GRV monitoring in mechanically ventilated ICU patients may be discontinued; however, more studies are warranted to substantiate these findings.4

The implementation of evidence-based protocols could clear up the confusion over GRV and potentially reduce the incidence of enteral feeding interruptions. Past research has shown that the use of an enteral feeding protocol can result in significant improvement in nutrient delivery, although frequent tube feeding interruptions due to GRVs, suspected GI intolerance, and routine procedures may still occur.5

Kleiner is playing an active role in the implementation of an up-to-date protocol for assessing GRV in her ICU at Montefiore Medical Center. Following ASPEN guidelines and with support from the ICU attending physicians, the protocol uses greater than 500 mL GRV as a precautionary cutoff level for cessation of feeding. “The nurses are very attached to a protocol,” Kleiner explains. “They really do try to follow it; it’s not every nurse doing her own thing. But the actual protocol is one thing; educating and reinforcing the protocol is very important. We are slowly trying to change practice and provide lots of in-services, with the goal of not holding the tube feeding as much as we can.”

An education-focused approach has produced positive results for Jessica LaRosa, RD, CNSC, a clinical dietitian based in Las Vegas. “In general, in-services and education are the key. At our facility, allowing for higher gastric residuals required a culture change. It took a lot of education until we saw a shift in practice in our ICU,” she says.

Widlicka describes valid drawbacks to the absence of a feeding protocol in the ICU setting. She explains that gastric residuals may be checked by nursing staff, but if doing so is not mandated by a formal protocol or policy, the practice is likely to be inconsistent and unreliable. “Some nurses may hold tube feeding for a GRV that is double the ordered infusion rate. For example, if the feeding is running at 40 mL/hour, then the nurse may hold the feed for an 80 mL GRV. Another may routinely hold tube feeding for GRV greater than 200 mL. If a physician doesn’t actively write an order to hold tube feeding, then it may be held indefinitely until someone decides to restart. In this case, it takes a fairly proactive nurse to go to the physician to obtain an order to resume feeding. That’s where not having a protocol really handicaps the ICU in terms of feeding patients adequately.”

Final Thoughts From the Experts
Adherence to evidence-based guidelines is crucial to standardizing practices for preventing, assessing, and treating EN intolerance. Yet the role of using sound clinical judgment and proactively gauging the “big picture” is vital to tackling EN intolerance in patients who are critically ill. Kleiner alludes to using this approach. “For our sicker, more septic patients, we often start feeding at a low infusion rate and increase slowly—a less-aggressive approach than we may take with more stable patients. If the patient has symptoms of slow gastric emptying, we may try prokinetic medications, decreased rate of sedation, or adjust the enteral formula. When transitioning off of parenteral nutrition, I may start the patient on a predigested, elemental formula to be on the safe side and better ensure tolerance, then switch to a standard formula if appropriate. For any patient with GI-related condition or surgery, I might choose a formula that is low residue, low fiber, lower fat, more isotonic—whichever I think may be more easily tolerated.”

Widlicka also employs a well-rounded approach. “For example, if the patient is frequently having GRVs greater than 200 mL, I may try a formula that is hypo-osmolar, lower fat, elemental, or semielemental. I may also recommend lowering the feeding infusion rate, with the knowledge that a trickle feed is preferable to holding the feeding indefinitely. If the patient is on heavy sedation or a poorly controlled diabetic, I would get on board sooner rather than later with recommending a postpyloric tube and perhaps not even go the route of prokinetics.” Further reminding us of the relationship between elevated blood glucose and delayed gastric emptying, Widlicka states, “When I see a patient with blood glucose in the 200 to 300 mg/dL range [who] seems to have delayed gastric emptying, I would certainly talk with the physician about improving the patient’s glycemic control in some way, shape, or form.”

LaRosa summarizes the challenge dietitians confront when treating individuals who are critically ill with intolerance to EN. “When a patient is poorly tolerating enteral feeding, [he or she is] not able to reap the benefits of adequate nutrition,” she says. “Poor enteral tolerance may trigger many negative consequences—from patients not receiving the prescribed amount of nutrition to poor wound healing or development of wounds. Furthermore, the gut is the largest immune organ in your body, and when it is not able to fully protect a patient, a vicious cycle may follow.”

— Megan Tempest, RD, LDN, works at Presbyterian/St. Luke’s Medical Center in Denver and is a freelance writer.

References
1. Ukleja A. Altered GI motility in critically ill patients: Current understanding of pathophysiology, clinical impact, and diagnostic approach. Nutr Clin Pract. 2010;25(1):16-25.

2. McClave SA, Martindale RG, Vanek VW, et al. Guidelines for the Provision and Assessment of Nutrition Support Therapy in the Adult Critically Ill Patient: Society of Critical Care Medicine (SCCM) and American Society for Parenteral and Enteral Nutrition (A.S.P.E.N.). JPEN J Parenter Enteral Nutr. 2009;33(3):277-316.

3. Taylor SJ, Manara AR, Brown J. Treating delayed gastric emptying in critical illness:
Metoclopramide, erythromycin and bedside (Cortrak) nasointestinal tube placement. JPEN J Parenter Enteral Nutr. 2010;34(3):289-294.

4. Poulard F, Dimet J, Martin-Lefevre L, et al. Impact of not measuring residual gastric volume in mechanically ventilated patients receiving early enteral feeding: A prospective before-after study. JPEN J Parenter Enteral Nutr. 2010;34(2):125-130.

5. Btaiche IF, Chan LN, Pleva M, Kraft MD. Critical illness, gastrointestinal complications, and medication therapy during enteral feeding in critically ill adult patients. Nutr Clin Pract. 2010;25(1):32-49.

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