Enteral nutrition (EN) is an effective way to nourish patients; however, many barriers prevent consistent and effective delivery of EN in the hospitalized patient. Clinicians must focus on interventions that will make our patients comfortable while their EN is infusing. Part I of this four part series critically evaluates two of the most common barriers to EN: the use of bowel sounds to assess readiness for EN and gastric residual volumes to assess tolerance of EN. Strategies to manage such obstacles in the clinical setting will be provided.
Upcoming in the series:
- Part II Enteral Feeding: Eradicate Barriers with Root Cause Analysis and Focused Intervention
- Part III Jejunal Feeding: The Tail is Wagging the Dog(ma): Dispelling Myths with Physiology, Evidence, and Clinical Experience
- Part IV Enteral Feeding: Hydrating the Enterally-Fed Patient—It Isn’t Rocket Science.
Carol Rees Parrish MS, RDN Nutrition Support Specialist, Digestive Health Center, University of Virginia Health System, Stacey McCray RDN Coordinator, Nutrition Support Training Programs, University of Virginia Health System, Digestive Health Center, Charlottesville, VA
Enteral feeding is an effective way to nourish those patients unable to meet nutritional needs by mouth alone. However, many barriers exist in the hospital setting that interfere with the delivery of the prescribed EN (Table 1). Confirming our clinical experience, many studies have demonstrated that patients routinely receive only 45-65% of EN ordered,1-5 and only 84% was achieved in a recent study that set out to ensure a targeted level of EN was delivered.5 To overcome this track record, we must carefully examine each aspect of EN delivery for potential barriers to adequate nutrition support. Many current practices surrounding the provision of EN are not evidenced-based, nor physiologically sound. One of the most common reasons for EN to be held is “gastrointestinal (GI) intolerance.” Many reports of ‘GI intolerance” are based on unproven monitoring techniques and years of past assumptions about how the GI tract works. While it is true that hospitalized patients can have significant GI issues, little evidence exists to support many of the practices used to “monitor” tolerance to EN. Developing a successful EN regimen requires the following:
- Full understanding of normal GI anatomy and physiology
- Knowledge of current evidence behind the practice of enteral nutrition
- Clinical experience as a bedside practitioner
The goal of this four part series is to review basic GI anatomy and physiology, discuss how this relates to EN, identify common barriers to EN, and identify strategies to overcome these obstacles. With a better understanding of the GI tract and normal GI function, the clinician will be better equipped to address the root cause of EN delivery barriers and intervene appropriately to improve provision of EN. Part I critically evaluates two of the most common barriers to EN: the use of bowel sounds to assess readiness for EN and gastric residual volumes to assess tolerance of EN.
Auscultation of bowel sounds (BS) has historically been used to assess bowel function and readiness for oral diet or EN. Despite widespread use, the practice of auscultating BS has never been validated as a marker of GI function; hence its clinical value remains largely unstudied and subjective. In fact, no evidence exists supporting the correlation between bowel sounds and peristalsis, or the need to wait for BS prior to EN initiation.6 To the contrary, two studies have demonstrated that there is a great deal of inter-rater variability among physicians when listening to BS, and that auscultation of BS are unreliable as an indicator of peristalsis and GI function.7-8
Enhanced Recovery after Surgery (ERAS) protocols are multimodal peri-operative protocols aimed at enhancing organ function and decreasing surgical complications resulting in earlier hospital discharge. Most ERAS protocols include early initiation of an oral diet (often post-op day 1). Assessment of BS is not included in any ERAS protocols. This is in contrast to conventional care protocols that hold oral and EN until ‘bowel function returns’—most often assessed by BS or passage of gas. The recent implementation and advancement of ERAS protocols demonstrate that early oral or EN is not only possible, but beneficial to patients. ERAS protocols have demonstrated.9-11
- Earlier return of bowel function & decreased incidence of post-op ileus
- Less nausea (through prophylactic nausea medication)
- Decreased complication rates and shorter hospital length of stay
- Earlier resumption of normal activities
- Increased patient satisfaction
- Significant cost savings
In summary, experience from ERAS protocols suggests that there is no benefit to using BS as an indicator of GI function and it should be removed as a potential barrier to nutrition supports goals.
ASSESSMENT OF GASTRIC RESIDUAL VOLUMES
Gastric residual volumes (GRV) for decades have been used to ‘measure’ tolerance of EN. A recent nursing survey of 582 nurses in 5 major hospitals found that 89% of nurses would terminate EN for GRVs > 300mL.12 However, this practice is counterintuitive to normal gastric anatomy and physiology. The stomach is a reservoir and the idea that having some gastric residual is abnormal or a problem contradicts its physiologic role.
It is important to bear in mind that a GRV in an enterally-fed patient is not only comprised of EN (i.e. what goes in is not the only thing that comes out). The volume of endogenous secretions (salivary and gastric secretions) that pass through the stomach daily is approximately 2-4 liters (Table 2). Remember, when any volume is put into the stomach, the stomach responds by adding its own gastric juices as part of its physiologic role.13,14Borgstrom demonstrated a 3-5 fold dilution of a test meal from stomach into duodenum over a 4 hour period—500mL/625kcal test meal diluted to a volume of 1500-2500mL.15The total daily volume of endogenous secretions, oral intake, EN, medications, and water flushes can be > 6 liters per day (∼ 230mL/hr) above the pylorus alone. With this volume in mind, one might argue that standard GRV thresholds (60-150mL) are less than endogenous secretions, and therefore, by definition, emptying must be occurring. When evaluating the significance of GRV, all the components contributing to that volume should be considered.
In addition to the physiologic aspects of GRVs, there are practical and institutional limitations, as well. No standard definition of a GRV exists because the volume that constitutes a significant GRV has never been prospectively studied in a randomized fashion. EN is often held based on an arbitrary number chosen by the hospital or found in textbooks. There is little agreement on how frequently GRV should be checked and whether the GRV should be returned to the stomach (and, if so, how much should be returned?).16 The location of the tip of the feeding tube in the stomach will also affect the amount of GRV. For example, a PEG tube placed high in the stomach may not produce a significant residual because it sits above the air-fluid level of dependent gastric contents. Conversely, a nasogastric tube may produce more GRV simply due to its position in the stomach (see section on pooling effect below).
Gastric Emptying and the Pooling Effect
Normal gastric emptying is quite swift. Liquid emptying is preserved even in severe gastroparesis.17 However, liquids empty from the stomach by receptive relaxation and gravity; therefore, the supine positioning of many hospitalized patients is not optimal for gastric emptying. In the supine position, the anatomy of the stomach is such that the fundus is in the most posterior/superior/left portion and the antrum is in the anterior/inferior/right portion. When the patient is supine or semi-recumbent, liquids can collect in the fundus because it is posterior. Hence, when a patient is supine or at low backrest elevation, the stomach “drapes” over the spine, and with the addition of gravity, gastric secretions may pool in the most dependent portion. When the patient turns to the right side down position, liquids move past the spine to the more anterior antrum and thus can pass into the duodenum. In the upright position, the fundus empties into the more dependent body and antrum and into the duodenum. Therefore, the stomach generally empties best when the patient is on the right side when lying flat or semi-recumbent, or when the patient is fully upright. For radiology photo images illustrating this concept, see also the 2008 article in the Practical Gastroenterology series on GRVs.18
Most nasogastric feeding tubes fall into the most dependent part of the stomach, the fundus, which is not contractile and furthest from the pylorus. Aspirating a GRV from the fundus may retrieve a much greater volume than from the antrum. Although anecdotal, one intervention that is used at UVAHS should a patient’s residual be checked and be elevated beyond what the team is comfortable with, is to put the patient on their right side (while semi-recumbent) for 15-20 minutes, after which the residual is rechecked. Taking advantage of gravity by turning patients on their right side where the pylorus is located (while maintaining backrest elevation at 30 degrees or greater), may enhance liquid emptying from the stomach, and decrease the amount of GRV detected. For more information on this topic, ask your radiologist about how they perform a barium swallow (not to be confused with a modified barium swallow).
Back to GRVs
Monitoring of gastric residuals is often thought to reduce the risk of aspiration and pneumonia in higher risk, critically ill patients. However, several studies have shown that increasing the threshold for gastric residuals (up to 400-500mL) did not increase the incidence of pneumonia.19,20 Several studies have also shown that raising the level of GRV and decreasing the frequency (or eliminating checks altogether) results in more EN received21,22 without significantly increasing the incidence of ventilator associated pneumonia. The use of GRVs to prevent aspiration pneumonia suggests that only those patients who are enterally fed are at risk for aspiration. Do we check GRVs in patients on oral diets during the day, but supplemental EN overnight? What about patients receiving parenteral nutrition (PN) or IV fluids (often our sickest patients)? Some studies have shown that patients receiving PN have a higher rate of pneumonia than those enterally-fed.23,24
Despite the lack of evidence to support monitoring GRVs, a great deal of nursing time is spent on this task, and patients miss a significant amount of EN for what may be a clinically unimportant (and arbitrary) reason. At least one study has also shown that frequent GRV checks may lead to more frequent clogging of feeding tubes.25 Williams, et al. also concluded that reducing the frequency of residual checks saves nursing time, decreases risk of contamination of feeding circuit, and minimizes risk of body fluid exposure.26 Ultimately, not checking GRV allows the nurse more time with their patients to focus on steps that have been shown to decrease aspiration pneumonia (good oral hygiene, backrest elevation, etc.), while allowing patients to meet important nutrition goals.
Time To Move On?
In 2016, the American Society for Enteral and Parenteral Nutrition (ASPEN) and the Society for Critical Care Medicine (SCCM) jointly came out with practice guidelines questioning the practice of checking GRVs. Their conclusions can be summarized as follows:27
- GRVs should not be used as part of routine care to monitor ICU patients receiving EN.
- For those ICUs where GRVs are still utilized, holding EN for GRVs < 500mL in the absence of other signs of GI intolerance* should be avoided. *GI intolerance is defined as:
“Vomiting, abdominal distention, complaints of discomfort, high NG output, high GRV, diarrhea, reduced passage of flatus and stool, or abnormal abdominal radiographs.”
While GRVs are not an effective way to monitor tolerance to EN, it is still extremely important to monitor hospitalized patients for signs and symptoms of impaired gastric emptying which is common in the hospital setting. Clinicians should be aware of circumstances that put patients at risk for gastroparesis or altered GI function and develop an individualized plan accordingly. It is crucial to pay attention to abdominal symptoms such as distention, complaints of fullness, tenseness, guarding, firmness, bloating, pain, nausea or vomiting. Patients should also be monitored for constipation, especially in those on narcotics. If your institution does continue to check GRVs, see Table 3 for suggestions to intervene. Finally, see Appendix I for one institution’s justification to phase out routine GRV checks.
Additional Considerations Physiologic Response to Enteral Feeding Initiation and the Ileal Brake
An initial increase in GRV has been documented the first few hours of EN initiation, but this effect subsides rather quickly.28 Kleibeuker provided 15 healthy volunteers with 200mL/hr of EN for 450 minutes (7.5 hours).28 GRVs were checked every 30 minutes beginning at 120 minutes of EN infusion. The author found the highest GRVs occurred at 120 minutes, then decreased with continued infusion.
The ileal brake is a feedback mechanism within the ileum that regulates the passage of food through the gut.29 When the distal intestine identifies nutrients that seem to have escaped absorption higher up in the small bowel, a signal is sent to slow peristalsis (including gastric emptying).30,31 Therefore, it is not uncommon for patients to have an increase in nausea or other GI symptoms upon initiation of jejunal feedings if nutrients escape to the ileum.
In either circumstance above, if patients experience increased GRVs or an increase in nausea upon initiation of feeding, a brief decrease in rate with a slower advancement may help this transition. Use of a scheduled antiemetic for a few days can help also. However, patients should be able to quickly advance to goal flow as these mechanisms subside.
A Word About Backrest Elevation
While there is little evidence to support GRV checks, there is clear evidence available to support a decreased aspiration risk when backrest elevation (BRE) is maintained.32-39BRE of < 30 degrees is one of the most modifiable risk factors consistently and strongly associated with aspiration, especially in bedbound patients with altered sensorium or impaired swallow. This seemingly simple (but underutilized) intervention is not easy to accomplish. Two studies reported that critical care nurses consistently over-estimated the BRE level.37,40 Another study found that nurses self-reporting of BRE were consistent with observed levels of 28 degrees for intubated patients.41 In all of these studies, actual BRE fell far short of the recommended 45 degrees regardless of the nurses’ perceptions. A summary of studies evaluating BRE in hospitalized patients can be found in Table 4.
There are a number of things that clinicians can do to help ensure that backrest elevation is maintained. First, educate all members of the team that they share this responsibility—it really does take a village. Education should not be a one-time event, but should be ongoing at regular intervals (e.g. quarterly). Note that it is not necessarily accurate to use the head of bed gauge since the gauge measures the level of the head of bed and does not measure the patient’s level of BRE. For those who slide down in the bed, a technique might include elevation of the HOB to approximately 20-30 degrees, then changing the angle of the whole bed to assure BRE (i.e., reverse trendelenberg). Physician orders for backrest elevation may help with compliance. If not already a part of routine order sets, any member of the healthcare team can request such an order from the physician or nurse practitioner. Finally, regular monitoring of institutional practices is necessary, as adherence with guidelines fluctuates over time.
EN is an effective way to nourish patients unable to meet their nutritional needs, particularly in the acute inpatient setting. However, for EN to be effective, patients need to receive the goal (“dose”) intended. Many barriers exist in the hospital setting that thwart patients from meeting key nutrition goals, without good evidence to support holding EN for these issues. Instead of perpetuating the myth that EN causes complications, clinicians must focus on the underlying conditions and interventions that will make our patients comfortable while their EN is infusing. This article specifically addresses bowel sounds, gastric residual volumes and backrest elevation, and provides the reader with an opportunity to reevaluate how one approaches these barriers in order to maximize nutrient delivery in the enterally-fed patient.