Gastric residual volume management in critically ill mechanically ventilated patients: A literature review

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1 598451PSH / Proceedings of Singapore HealthcareGuo research-article2015 Review Article PROCEEDINGS OF SINGAPORE HEALTHCARE Gastric residual volume management in critically ill mechanically ventilated patients: A literature review Proceedings of Singapore Healthcare 2015, Vol. 24(3) The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalspermissions.nav DOI: / psh.sagepub.com Bing Guo Abstract Measured gastric residual volume (GRV) is most commonly used as a marker to guide enteral feeding rate and prevention of pulmonary aspiration in gastric-fed, mechanically ventilated intensive care unit patients. However, there is little consensus on the practice standard, and controversies exist regarding its implications. A total of 17 papers were reviewed to evaluate the factors affecting the accuracy of GRV measurement, GRV measurement practices, and its correlations with clinically important complications. Multiple factors affect the accuracy of GRV measurement. GRV threshold and assessment frequency remain undefined. No direct correlation between measured GRV and incidences of pulmonary aspiration or pneumonia was found. However, higher incidences of pulmonary aspiration were observed in cases of higher GRV. Not measuring GRV could result in patient harm. Reducing GRV prior to position change and procedures associated with high risk for regurgitation could prevent aspiration incidences. Keywords Enteral nutrition, feed intolerance, gastric emptying, gastric residual volume, intensive care unit, literature review Introduction Critically ill, mechanically ventilated patients in intensive care units (ICU) are most likely to experience delayed gastric emptying, intolerance of enteral feeding, higher chances of malnutrition, 1 pulmonary aspiration, infections, 2 and mortality. 3-5 Gastrointestinal motility can be impeded by medications, hyperglycemia, electrolyte disturbances, hypoxia, sepsis, increased intra-cranial pressure, and administration of calorically dense or hyperosmolar formulas. 6 Measuring the gastric residual volume (GRV) is the most common practice in assessing the tolerance of a patient to enteral nutrition and preventing pulmonary aspiration. 7 However, there is little consensus on the practice standard, and several aspects related to its implementation are controversial. 1,7 Background and underlying rationale Nutrition management for critically ill patients has gained more attention with improved understanding of the molecular and biological effects of nutrients in maintaining homeostasis. 8 Early enteral nutrition supports the functional integrity of the gut and maintains structural integrity, which improves immunity and reduces disease severity, and therefore it is recommended. 1,8 Measured GRV is used as a marker for enteral nutrition tolerance and prevention of pulmonary aspiration, as constant infusion of feeds into the stomach with delayed gastric emptying causes increased gastric content, and predisposes patients to gastroesophageal reflux and pulmonary aspiration. 9 Some practitioners 10,11 recommended four-hourly assessments of GRV, and that a GRV of 200 ml should cause concern. However, some authors argue the total amount of upper gastrointestinal secretion is approximately ml/hour without any feeding, 12 therefore GRVs between 400 and 500 ml are more physiological. 13 A certain volume of gastric content is necessary for gastric emptying, 14 and Division of Nursing, Singapore General Hospital, Singapore Corresponding author: Bing Guo, Singapore General Hospital, 31 Third Hospital Avenue, Bowyer Block B, Level 2, , Singapore. bing.guo@sgh.com.sg Creative Commons CC-BY-NC: This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 3.0 License ( which permits non-commercial use, reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages ( com/en-us/nam/open-access-at-sage).

2 172 Proceedings of Singapore Healthcare 24(3) this volume varies from person to person. Thus some researchers recommend continuing feeding when GRV is less than 400 ml unless additional signs of intolerance occur 12 to prevent underfeeding, 15 worsening of nutritional status, and unnecessary initiation of parenteral nutrition. 16 Studies have since been conducted to test the effects of different levels of GRV, and to evaluate its role in reflecting feeding tolerance and preventing pulmonary aspiration. Aim The aim of this review was to survey the common techniques for measuring GRV, assessment intervals, optimal cut-off level (threshold) of GRV, management of high GRV, and the correlation between GRV and clinically important complications. By doing so, we aim to establish the most up-to-date consensus of the practice for using GRV to assess enteral nutrition tolerance and to prevent pulmonary aspiration in gastric-fed ICU patients. Methods Databases and keywords A search was performed on nursing, medical, and dietetic literature using CINAHL and Medline from 2000 to The keywords used both independently and in combination were: literature review, intensive care unit, critical care, critical care nurses, critical illness, critically ill, feed tolerance, feed intolerance, gastric emptying, enteral feeding, enteral nutrition, techniques, methods, and GRV. The references of all relevant review articles obtained through this search were examined to identify further studies which may potentially be relevant. Inclusion and exclusion criteria Articles in this review included studies focused on adult patients and the factors affecting reliability and accuracy of gastric content measurement by bedside nurses, clinical management of high GRV, and interpretations of elevated GRV in relation to enteral nutrition tolerance and incidence of complications. Articles which focused on bolus versus continuous, parenteral versus enteral, post-pyloric feeding, insulin, and prokinetic therapy were beyond the scope of this review. Results In this review 17 quantitative studies were examined (Table 1). Nine studies were observational or descriptive, and eight were experimental studies. ICU patients made up the population described in 16 articles, while one article surveyed ICU nurses for their current practice in relation to enteral nutrition. In this review, the following themes were identified: (1) factors affecting the accuracy of GRV measurement; (2) frequency of GRV assessment; (3) issues of managing high GRV; and (4) GRV threshold and its relation with feeding intolerance, and clinically important complications (pulmonary aspiration, nosocomial pneumonia, and mortality). Factors affecting measurement of GRVs Using GRV as a guide for gastric emptying and as a marker to predict the risk of pulmonary aspiration presumes that it reliably and accurately measures gastric contents. 9 However, patient position, tube position in the stomach, tube configuration, syringe size, and the aspiration technique may affect the measurement. In addition, when GRV is measured, the entire volume of gastric contents cannot be aspirated. Theoretically, GRV can be obtained from any gastric feeding tube, but it is easier to aspirate from large-diameter rigid tubes, and with multiple ports resting in the pool of gastric contents. 17 Higher GRVs are observed in patients with larger feeding tubes. 12,18 20 The mean GRV from large-diameter sump tubes ( Fr 14) may be more than two times higher than that obtained from small-diameter (Fr 10) tubes. 17 Patients with Fr 8 feeding tubes had the lowest mean GRV, but the highest percentage for positive regurgitation. 12 Methods in obtaining GRV are currently not standardized in practice and studies, while most nurses aspirate through a 50 or 60 ml syringe, 20 some use either passive drainage alone or a combination of passive drainage and syringe aspiration. 16,21 Metheny and colleagues 17 described using a 60 ml syringe to push in 30 ml of air to force the tube s distal ports away from the mucosal folds to facilitate aspiration. This was followed by aspirating GRV using a slowly withdrawing technique until no more fluid could be obtained. GRV threshold and assessment frequency In order to improve calorie delivery, researchers challenged the higher GRV threshold 12,18,21,22 and reduced the assessment frequencies. 16,22 In practice, nurses usually withhold or reduce the hourly enteral nutrition administration rate when GRVs are high, but there is little consensus on the GRV threshold. 23 A higher GRV threshold allows for a higher delivery of enteral nutrition calories. 12,16,18,21,22,24 While there is still no convincing evidence of significant benefits attributable to additional calories in critically ill patients, 5,24 26 the focus of whether or not to increase the GRV threshold is shifted by determining clinically important harm, such as pulmonary aspiration, nosocomial pneumonia incidences, and mortality. Evidence of regurgitation and pulmonary aspiration is identified in various ways (Table 2). However, observed feeds in the oral/nasal cavity, 16,18,21,22,24,27 testing glucose levels, 28,29 and detecting blue food coloring 12 are unreliable. 12,19 McClave and colleagues 12 used fluorometry to detect the presence of added yellow microspheres, coupled with a concurrent observation for blue food coloring in tracheal and oropharyngeal samples as evidence of regurgitation or pulmonary aspiration events. In another two studies, 19,20 Metheny and colleagues tested for the presence of pepsin in the trachea, as a proxy for aspiration. When compared with adding yellow microspheres in feeds, pepsin immunoassay is preferred for its high specificity (100%), sensitivity (93%), and most importantly, no potential for harm. 30 To understand the relationship between GRV and pulmonary aspiration, studies 12,19,20 have demonstrated that most pulmonary aspiration events are silent. Most patients had at

3 Guo 173 Table 1. Reviewed articles. Authors and year Type of, methodology Booker et al., 2000 Mentec et al., 2001 Randomized prospective experimental design Prospective observational Pinilla et al., 2001 Prospective, randomized controlled trial Morgan et al., 2004 Retrospective observational McClave et al., 2005 Randomized controlled trial Population studied, sample and sample size Factors affecting GRV measurement GRV threshold Aspirated GRV return amount Tube property Measuring method Frequency Key findings ICU patients in three hospitals (USA) Discard group: n=10 Return group: n=8 Patients in a medical and surgical ICU (France) n=153 Patients in medical/trauma/ surgical ICUs (Canada) Group 1: (n=36) 150 ml threshold with optimal prokinetics Group 2: (n=44) 250 ml theshold with mandatory prokinetics Patients in a trauma ICU (USA) Gastric tube group: n=45 Jejunostomy group: n=11 Patients in coronary/ medical/ surgical ICU (USA) Control group: n=20 NGT and OGT 14Fr NGT aspirate via 50ml syringe NGT: No description Q4H reduce Fr14-18, to Q12H Fr 10 when tolerated Gastric tube: n=45 Jejunostomy: n=11 GRV threshold: 200 ml Fr 12 n=19 Study group: n=20 PEG: n=19 GRV threshold: 400 ml Q4H 150 ml Discard group: Stop recheck discard all GRV 30 min later Return group: Day 1 5: Q4H ( ml) Day 6 twice: start onwards: prokinetics Q12H 500 ml stop Group1:150ml vs. Group2: 250ml return all GRV Return amount <500 ml No description Q6H 150 ml Return amount EN was held <150 ml for 4 h and then recheck GRV NGT: Fr 8 n=2 No description Q4H 200 ml vs. 400 ml - More complication days in return (32.6%) vs. discard group (23.4%) - Discard GRV low potassium - Sedation or catecholamines: risk factor for high GRV - High GRV: early marker for UDI - High pneumonia incidence in patients with UDI: 43% vs. 24% - Continuous monitoring of EN tolerance is necessary - Require intervention for GRV 100 ml No description - GRV 250ml+ mandatory prokinetics: feeding intolerance - High GRV cases: 53% in group 1 vs. 23% in group 2 (p<0.005) - 17% in group 1 vs. 43% in group 2 had Fr 10 tube (p<0.01) - HOB elevation correlates with better feeding tolerance - Reasons for discontinuing feeding: - High GRV: 11% - Surgery: 27% - Diagnostic procedure: 15% No description - No relationship between GRV and regurgitation/ aspiration events. - No correlation between pneumonia and regurgitation/ aspiration - 85% (34 of 40) had 1 regurgitation - 75% (30 of 40) had 1 aspiration % had GRV<150 ml, only 1.5%had GRV 400 ml - Lowest mean GRV in patients with Fr 8 tube but highest percentage for positive regurgitation (Continued)

4 174 Proceedings of Singapore Healthcare 24(3) Table 1. (Continued) Authors and year Type of, methodology Metheny et al., 2005 Descriptive Marshall and West, 2006 Descriptive survey Metheny et al., 2006 Prospective descriptive Metheny et al., 2008 Prospective, descriptive Juvé-Udina et al., 2009 Randomized, prospective, non-blinded, clinical trial Population studied, sample and sample size Patients from five ICUs in one hospital (USA) Concurrent presence of 10Fr and 14Fr /18Fr gastric tubes: n=62 Concurrent presence of 10Fr small bowel and 14Fr /18Fr gastric tubes: n=75 Random sample of 750 critical care nurses (Australia) Response rate 50.5% (n=376) 329 mechanically ventilated adult patients in five ICUs (USA) Patients in trauma/surgery/ medical/ coronary ICUs (USA) n=206 Patients in a medical/ surgical ICU (Spain) Intervention (return) group: n=61 Control (discard) group: n=61 Factors affecting GRV measurement GRV threshold Aspirated GRV return amount Tube property Measuring method Frequency Gastric and small bowel feeding tube: Fr 10 Fr14 Fr18 60 ml syringe push in 30 ml of air, then aspirate slowly Q4H 200ml Return amount 200 ml 87.5% assess GRV via aspiration NGT Fr 14: n=91 NGT Fr 10: n=88 Aspirate via 60 ml syringes Q4H-66.5% <50 to >400 ml Q4H ml (No consistent pattern) 80% return aspirated GRV (18.9% return all GRV, 40.7% return 200 ml) Return amount 200 ml NGT/OGT: Fr Gastrostomy tube: 20 Fr 60 ml syringe. push in 30 ml of air, then aspirate slowly Q4H Return amount 200 ml NGT Aspirating via 60 ml syringe Q6H 500ml Return amount 250 ml Key findings - Small-diameter tube underestimates GRVs - GRVs 150 ml occurred in post-pyloric feedings patients - GRV decreases overtime - Practice related to enteral feeding varies - Practice deviates from protocols - Large feeding tubes: higher GRVs. - Risk for pneumonia: high-aspiration group=4 times low-aspiration group % patients had 1 aspiration event - Most aspiration events are silent - More high GRVs ( 200 ml) in highaspiration than low-aspiration group - Aspiration occurred at all volumes of GRV - Mean GRV: 37.1 ± 36.6 ml - High GRV Significantly more aspiration incidence - Aspiration and GRVs-No correlation - High GRVs with other known risk factors has effect on aspiration - Large-bore tubes: more high GRVs - 93% patients aspirated once, only 6.8% vomited - Return 250 ml GRV does not increase total GRV - Return group had lower incidence and severity of delayed GE (p=0.001) - No significant differences in other outcome measurements

5 Guo 175 Table 1. (Continued) Authors and year Type of, methodology Population studied, sample and sample size Factors affecting GRV measurement GRV threshold Aspirated GRV return amount Tube property Measuring method Frequency Key findings Umbrello et al., 2009 Soroksky et al., 2010 Poulard et al Montejo et al., 2010 Hsu et al., 2011 Rice et al., 2012 Reignier et al., 2013 Descriptive Pilot prospective cohort Prospective before after intervention Randomized, prospective. Prospective, observational Randomized, open-label prospective Randomized controlled trial Patients in a general ICU (Italy) n=78 Patients in a medical/ surgical ICU (Israel) n=52 Patients in a medical/ surgical ICU (France) Control group: n=102 GRV >250 ml or vomiting Intervention group: n=103 vomiting only Patients from 28 ICUs (Spain) Control (GRV 200ml): n=165 Study (GRV 500ml): n=157 Patients from a medical ICU (Taiwan) n=61 Acute lung injury patients from 44 hospitals in US Trophic feeding n=508 Full feeding n=492 Patients from 9 ICU (French) Intervention group n=208 Control group n=215 Gastric tube No description Q2-4H No description No description - UDI not related to aspiration pneumonia - 2 consecutive air 150 ml =More pneumonia incidences - GRV: 158 ± 117 ml - Air volume: 140 ± 110 ml NGT Passive drainage to bag, then aspirate via 50 ml syringe NGT: Aspirate via 50 ml 14-Fr syringe NGT: range from <Fr 8 to >Fr 12 Gravity drainage to a bag for 10 min or aspirate via 50 ml syringe NGT Stop feeding for 30 min before check GRV, then aspirate using a 50 ml syringe GT postpyloric tube<20% Q4H after commencing feeding, then Q24H if GRV <500 ml No description First 6 days 400 kcal/day- Q12H 1300 Kcal/day- NGT Aspirate using a 50 ml syringe 6H Control group: 250 ml Intervention group: NA 1 st day: 6H 200 ml (control) vs. 2 nd day: 8H 500 ml () After 3 rd day: 24H if tolerated Every 4 hours Stop feeding if >500 ml or GRV >200 ml with feeding complications Q6H 500 ml Return amount 500ml Return amount 250 ml Return amount 200 ml (control) 500 ml () 400 ml Return all aspirated amount Every 6 hours Vomiting (intervention) vs. (control) Vomiting/ GRV>250 ml - No correlation: GRV values and complications (ICU LOS, mechanical ventilation days, ICU/ hospital mortality) - No GRV monitoring: receive more feeding without increased vomiting and pneumonia (control 19.6% vs. intervention 18.4%; p=0.86) - Vomiting occurs when GRV<100 ml - No difference in gastrointestinal complications / outcome variables. - Pneumonia incidence 27.3% (control) 28.0% () - No correlation: GRV and nosocomial pneumonia No description - GRV is higher in more severely ill patients - GRV typically increases then plateaus in first 3 6 h after feeding - Change in GRV trend is useful to predict patient outcomes Return amount 250 ml - No difference in clinical outcome - Less feeding intolerance in trophic feeding group despite receiving fewer medications to treat intolerance - More vomit in intervention group - Higher calorie target achieved in intervention group - No difference between groups in complications ICU: intensive care unit; GRV: gastric residual volume; GT: gastric tube; NGT: nasogastric tube; OGT: orogastric tube; Fr: French; HOB: head of bed; UDI: upper digestive intolerance; GE: gastric emptying; LOS; length of stay; h: hour.

6 176 Proceedings of Singapore Healthcare 24(3) Table 2. Methods for identification of complications. Authors and year Aspiration/regurgitation Diarrhea Pneumonia Radiology Microbiological Hematology Temperature Booker et al., 2000 Blood glucose monitors to check pulmonary aspirate (>1.1 mmol/l) Single liquid stool 300 ml or >3 liquid stool/24 h Mentec et al., 2001 No description >3 loose or liquid stools in 24 h CXR infiltration CXR infiltration Purulent tracheal aspirates or +ve distal bronchial sampling culture Leukocytosis or leucopenia Pinilla et al., 2001 Observed vomiting Observation Morgan et al., 2004 Feeds present in oral/ nasal cavities 3 liquid stools, or 250 McClave et al., 2005 Metheny et al., 2006 Metheny et al., 2008 Juvé-Udina et al., 2009 Umbrello et al., 2009 Soroksky et al., 2010 Presence of yellow microspheres and food coloring in tracheal or oropharyngeal samples ml stool in rectal/ colostomy bag, or 1500 ml effluent in ileostomy bag in 24 h CXR infiltration +ve pulmonary secretion cultures 38 C or 36.5 C Pepsin immunoassay (sensitivity 93%, Simplified clinical pulmonary infection score and bronchoalveolar lavage confirmation (refer to Table 3) specificity 100%) Pepsin immunoassay Standard blood glucose monitors soft blob-like, mushy/ liquid stools in 24 H No description No description No description Feeds present in oral cavity Observation for vomit US Centers for Disease Control definition of nosocomial pneumonia Poulard et al., 2010 Observed vomiting CXR infiltration Purulent tracheal aspirates and +ve secretion culture via bronchoscopy or tracheobronchial aspirate Montejo et al., 2010 Feeds present in oral or nasal cavities 5 liquid stools, Or 2000 ml stool in 24 h Reignier et al., 2013 Spontaneous vomit/regurgitation vomiting episode excludes regurgitation during procedures associated with vomiting reflex CXR infiltration Purulent tracheal secretions (no microbiological confirmation) No description CXR infiltration Purulent tracheal aspirates and +ve secretion culture via bronchoscopy or tracheobronchial aspirate Leukocytosis or leucopenia Leukocytosis or leucopenia Leukocytosis or leucopenia 38.5 C or 35.5 C >38 C 38.5 C or 35 C CXR: chest X-ray; +ve- positive; h: hour.

7 Guo 177 least one pulmonary aspiration event, and only a few episodes of vomiting were observed. 12,19,20 None of the studies found any correlation between pulmonary aspiration and GRV. However, patients with higher GRVs ( 200 ml) had significantly higher incidence of pulmonary aspiration. 19,20 It is worth noting that the percentage of pulmonary aspiration incidence was relatively high (33.7%) even when GRVs were between 0 and 50 ml. 20 This percentage increased as the GRVs increased, and nearly 45% of patients experienced pulmonary aspiration when the GRVs were between 151 and 200 ml. 20 McClave and colleagues 12 also noted that 93.2% of patients had a GRV less than 150 ml, with only 1.5% experiencing a GRV more than 400 ml. The risk for pneumonia among the high-aspiration group was four times higher than for the low-aspiration group. 19 This affirmed the supposition that sustained small-volume aspirations of gastric contents predispose to chemical pneumonitis and later to infectious pneumonia. 19 Reports in the literature show that the frequency of GRV checks for continuously fed patients ranges from 2 to 24 h, with most practicing every 4 6 h. 12,17,18,20,24,27 29 Mentec et al. 3 recommended continuous monitoring of GRVs, as a high GRV was an early marker for upper digestive intolerance, and GRVs tend to be more prevalent during the first few days of tube feeding. 3,20 Some institutions conducted frequent assessments initially which progressively decreased when the patients were able to tolerate feeding. 3,18,21 Since there was no evident relationship between GRV and aspiration pneumonia, Soroksky and colleagues 16 reduced assessments to every 24 h based on a single GRV assessment 500 ml after commencing gastric feeding. In addition, Poulard et al. 22 and Reignier et al. 24 tested the effects of not assessing GRV and concluded that it was beneficial, as patients received more feeding without increased complications. Management of aspirated GRV Practice varies among ICUs with regards to whether aspirated gastric contents should be discarded or reintroduced to patients. 20 Studies have shown that this decision might depend on the nurses personal belief or unit protocol. 20,31 Proponents for reintroducing GRV to patients believe that discarding gastric aspirate may result in a loss of gastric fluids and electrolytes. On the contrary, supporters reason that discarding GRV prevents contamination, tube occlusion, and volume retention secondary to delayed gastric emptying. 31 Booker et al. 31 studied the effect of discarding and reintroducing GRVs. The sample size was small, and no significant differences were found in this. More patients suffered from hypokalemia in the discard group; however, the high incidence rate of complications in the reintroduction group (tube clogging and episodes of diarrhea and nausea) repressed the recommendation of reintroducing aspirated GRV. In a larger, Juvé-Udina and colleagues 29 found that the reintroduction group experienced a significant reduction in delayed gastric emptying. In addition, tube clogging was prevented by regular feeding tube flushing. Complications such as more patients suffering from diarrhea in the reintroduction group and higher incidence of hypokalemia in patients in the discard group were reported in both studies, although both were statistically insignificant. Reasons for diarrhea in ICU patients were multifactorial: feeding contamination, pharmacotherapy, illness state, feeds composition, and continuous feeding methods. 32 Conversely, electrolyte results could be affected by loss of body fluids (especially in surgical patients), or other forms of replacement (intravenous or renal replacement therapy). The researchers of both studies did not attempt to document these factors in their studies. Nevertheless, reintroducing aspirated GRV has been adopted by most clinicians in practice. 20 This practice is also described in most studies, 3,16,17,19 21,22,24,27,28 although the reintroduction amount differs just as the GRV threshold does. Management of patients with high GRVs also varies; some institutions chose to begin prokinetics and allow feedings to continue at the same or a reduced rate, while others ceased feeding and reassessed the GRV at a later time. 19,20 McClave et al. 12 argued that observing the trend of gradually increasing GRV is more meaningful than stopping feeding based on a single high volume. Discussion With emerging evidence leaning toward nutritional therapy in modulating the underlying disease process and impact on patient outcomes, 33 it was observed that recent attention on enteral nutrition was predominantly regarding the improvement in its delivery. GRV measurement and management is perceived as a barrier to adequate calorie delivery. 24,34 However, in practice, most delays in feeding also occurred as a result of patients underlying condition, 28 surgery, and diagnostic procedures. 27 Can we do without monitoring GRV? Does increasing delivery of feeds by reducing GRV monitoring and increasing GRV threshold improve patients outcome without complications? Are current GRV management practices rational? With the known limitations of measuring GRV, methods using scintigraphy, paracetamol absorption test, breath tests, ultrasound, gastric impedance monitoring, and refractometry have been reviewed to accurately assess enteral feeding tolerance. 35 Although these tests are more reliable or sensitive, they can be expensive and may cause harm to patients, hence they are not feasible for use in clinical areas. Therefore, measuring GRV is still the most common assessment for gastric emptying. The methods used to obtain GRV are not standardized and reliable in these studies. More GRVs may be obtained by connecting feeding tubes to low wall suction for 15 min, 7 and in supine position. 36 However, these methods were not observed in the available studies. Therefore, attempts to the relationship between underestimated GRVs and pulmonary aspiration incidence would be ineffectual. Studies 18,21,22,24 have shown that increasing the GRV threshold or not assessing GRV did not increase adverse effects. However, a high GRV was considered as intolerant, which was the major difference identified between control and intervention groups in all these studies. As an example, a GRV of 250 ml in the control group (threshold 200 ml) was considered a feeding intolerance, but in the intervention group (threshold 400 ml), it was not. On the other hand,

8 178 Proceedings of Singapore Healthcare 24(3) Table 3. Simplified clinical pulmonary infection score. Chest radiograph Tracheal secretions Oxygenation: PaO 2 /FIO 2 mm Hg Blood leukocytes per mm 3 Temperature, C No infiltrate: 0 Few: 0 >240 or presence of 4000 and 11,000: and 38.4: 0 ARDS: 0 Patchy or diffuse infiltrate: Moderate: and absence of <4000 or >11,000: and 38.9: 1 1 ARDS: 2 Localized infiltrate: 2 Large: and 36.0: 2 Purulent: 1 ARDS: Acute Respiratory Distress Syndrome. Table 4. Mortality outcome. Authors and year Mortality Control Intervention p-value Poulard et al., 2010 ICU 24.5% 35% p = 0.13 Hospital 35.3% 42.7% p = 0.32 Montejo et al., 2010 ICU 15.7% 19.8% p = 0.28 Hospital 33.6% 33.9% p = 0.53 Soroksky et al., 2010 ICU 21% 40% p = 0.24 Hospital 35% 40% p = 1.0 Reignier et al., 2013 Day % 27.8% Day % 36.3% evidence shows that most pulmonary aspiration incidences occurred when the GRVs were below 200 ml, and only a few patients GRVs reached 400 ml. Thus there may be little difference for clinical implications when comparing the effect of GRV threshold of 200 ml and above 400 ml. More feeds were delivered in intervention groups, but vomiting incidences were also higher in these patients. The amounts of vomited feeds were not recorded, thus the higher calories achieved could not be accurately calculated. There was no evidence of improved patient outcomes compared with control groups in all these studies, even with increased delivery of enteral nutrition. 37 As the self-reported nosocomial pneumonia rate was defined by different guidelines (Table 2), comparisons between studies are difficult. Despite specific definitions, nosocomial pneumonia may still be unconsciously (or even consciously) under-reported due to non-blinding designs. 38 It was observed that mortality in these intervention groups increased despite being statistically insignificant (Table 4). This could be seen as a trend of patient harm. However, these studies might be small to evaluate. 38 Current studies have focused on finding the best GRV, but have rarely looked into nursing practices which might affect GRV management, and rarely developed strategies to effectively prevent complications which were brought on by high GRVs. Nursing activities are major parts of ICU care. In studies, it is emphasized that patients should be maintained in a semi-recumbent position to reduce the risk of pulmonary aspiration. However, maintaining a semi-recumbent position at all times is unrealistic during clinical practice. 39 A safe GRV in a semi-recumbent position might not be safe when the patient is in a supine position. 30,40 Furthermore, procedures such as oral or endotracheal suctioning elicit gag reflex and vomiting. More incidences of regurgitation and vomiting occur during positioning change and such procedures. This would greatly increase the risk of pulmonary aspiration. 41 Not assessing the GRV could lead to an accumulation of air in the stomach, and a high volume of air against the lower esophageal sphincter could also increase the risk of aspiration. 42 Metheny et al. 19 noted that 70% of patients who received concurrent gastric suction during small-bowel feedings displayed lower pulmonary aspiration incidence. Thus, low GRV does reduce incidences of aspiration. Therefore it is sensible to effectively remove the gastric contents before undertaking procedures associated with vomiting reflex, and only return the feeds to the patient when procedures are completed and the patient is in a semi-recumbent position. Limitations and strengths The reviewed articles were limited to research articles written in English, hence leaving out valuable opinions about enteral nutrition practices documented in other languages. Weak design, unreliable GRV measuring methods, and non-standardized complication evaluation tools used in the studies affected the research quality. 37 The notion of do no harm and the lack of convincing evidence in recent research impede ICU practitioners decisions in changing practice despite the recommendations from the 2009 SCCM and ASPEN guidelines, 8 and practice often deviates from protocols. 20,43 Hence, reliable studies with standardizations to reduce variability are needed to produce strong evidence. Strategies to improve gastric emptying and prevent pulmonary aspiration, such as maintaining a semi-recumbent position, might not be feasible with all ICU patients. 39,44,45 Furthermore, they may put patients at risk of developing

9 Guo 179 pressure ulcers, 39,46 which is another major risk for infection and poor patient outcome. The GRV threshold should be considered in the context of the individual patient setting. 37,47 In addition, improved gastric emptying by using prokinetics does not equal an improvement in nutrient absorption. 48 Good clinical practice requires the complications and benefits of therapies to be carefully weighed and balanced. It is pointless to focus on improving enteral nutrition delivery while neglecting other complications. Nevertheless, various studies have provided remarkable insights into factors affecting GRV measurement, reliable tools for pulmonary aspiration identification, and other risk factors for pulmonary aspiration. These insights offer important considerations in the advancement of clinical practice. Conclusion In summary, variations in GRV measurement practices make it unreliable for monitoring gastric emptying and predicting pulmonary aspiration. The safe GRV threshold and assessment frequency remain undefined. Intervention studies with improved methodology are needed in future research related to pulmonary aspiration prevention to ensure internal validity. Meanwhile, the monitoring of GRV is still necessary due to its possible role in the prevention of pulmonary aspiration. It is imperative to review current nursing practices and to adopt sound strategies for effectively removing gastric contents prior to procedures associated with high risk for regurgitation to prevent pulmonary aspiration. As pulmonary aspiration can still happen to patients despite lower GRV levels, prevention of aspirates from entering the pulmonary system through other strategies, such as regular removal of subglottic secretions, should be adopted. Ultimately, improving clinical outcomes of patients is the eventual goal of care in the ICU. Acknowledgements The author would like to acknowledge Ms Yeo Ai Ling from SingHealth Academy and the SGH Nursing Research Unit for assistance in medical writing. Conflicts of interest None declared. Funding This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors. Reference 1. Heyland D, Dhaliwal R, Drover J, et al. Canadian clinical practice guidelines for nutrition support in mechanically ventilated, critically ill adult patients. JPEN 2003; 27: Rubinson L, Diette GB, Song X, et al. Low caloric intake is associated with nosocomial bloodstream infections in patients in the medical intensive care unit. Crit Care Med 2004; 32: Mentec H, Dupont H, Bocchetti M, et al. Upper digestive intolerance during enteral nutrition in critically ill patients: Frequency, risk factors, and complications. Crit Care Med 2001; 29: Hsu CW, Sun SF, Lee DL, et al. Impact of disease severity on gastric residual volume in critical patients. World J Gastroenterol 2011; 17: Alberda C, Gramlich L, Jones N, et al. The relationship between nutritional intake and clinical outcomes in critically ill patients: Results of an international multicenter observational. Intensive Care Med 2009; 35: Landzinski J, Kiser TH, Fish DN, et al. Gastric motility function in critically ill patients tolerant vs intolerant to gastric nutrition. JPEN 2008; 32: McClave SA and Snider HL. Clinical use of gastric residual volumes as a monitor for patients on enteral tube feeding. JPEN 2002; 26(6Suppl): S43 S8; discussion S49 S 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 2009; 33: Parrish CR and McClave SA. Checking gastric residual volumes: A practice in search of science? 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