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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 137–200 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 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 occur¹² 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 2013. 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 study population described in 16 articles, while one article surveyed ICU nurses for their current practice in relation to enteral nutrition.

Table 1.

Reviewed articles.

Authors and year	Type of study, methodology	Population studied, sample and sample size	Factors affecting GRV measurement			GRV threshold	Aspirated GRV return amount	Key findings
Authors and year	Type of study, methodology	Population studied, sample and sample size	Tube property	Measuring method	Frequency	GRV threshold	Aspirated GRV return amount	Key findings
Booker et al., 2000	Randomized prospective experimental design	ICU patients in three hospitals (USA) Discard group: n=10 Return group: n=8	NGT and OGT		Q4H	150 mlStop recheck 30 min later	Discard group: discard all GRVReturn group: return all GRV	- More complication days in return (32.6%) vs. discard group (23.4%) - Discard GRV → low potassium
Mentec et al., 2001	Prospective observational study	Patients in a medical and surgical ICU (France) n=153	14Fr NGT	aspirate via 50ml syringe	Day 1–5: Q4HDay 6 onwards: Q12H	(150–500 ml) ⩾twice: start prokinetics500 ml stop	Return amount <500 ml	- 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
Pinilla et al., 2001	Prospective, randomized controlled trial	Patients in medical/trauma/ surgical ICUs (Canada)Group 1: (n=36) 150 ml threshold with optimal prokineticsGroup 2: (n=44) 250 ml theshold with mandatory prokinetics	NGT:Fr14-18, Fr 10	No description	Q4H reduce to Q12H when tolerated	Group1:150ml vs. Group2: 250ml	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)
Morgan et al., 2004	Retrospective observational study	Patients in a trauma ICU (USA) Gastric tube group: n=45Jejunostomy group: n=11	Gastric tube: n=45Jejunostomy: n=11	No description	⩽Q6H	150 mlEN was held for 4 h and then recheck GRV	Return amount <150 ml	- HOB elevation correlates with better feeding tolerance - Reasons for discontinuing feeding: - High GRV: 11% - Surgery: 27% - Diagnostic procedure: 15%
McClave et al., 2005	Randomized controlled trial	Patients in coronary/ medical/surgical ICU (USA) Control group: n=20GRV threshold: 200 mlStudy group: n=20GRV threshold: 400 ml	NGT: Fr 8 n=2Fr 12 n=19PEG: n=19	No description	Q4H	200 ml vs. 400 ml	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 - 93.2% 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
Metheny et al., 2005	Descriptive study	Patients from five ICUs in one hospital (USA) Concurrent presence of 10Fr and 14Fr /18Fr gastric tubes: n=62Concurrent presence of 10Fr small bowel and 14Fr /18Fr gastric tubes: n=75	Gastric and small bowel feeding tube: Fr 10Fr14Fr18	60 ml syringe push in 30 ml of air, then aspirate slowly	Q4H	200ml	Return amount ⩽200 ml	- Small-diameter tube underestimates GRVs - GRVs ⩾150 ml occurred in post-pyloric feedings patients - GRV decreases overtime
Marshall and West, 2006	Descriptive survey	Random sample of 750 critical care nurses (Australia) Response rate 50.5% (n=376)	–	87.5% assess GRV via aspiration	Q4H-66.5%	<50 to >400 ml	80% return aspirated GRV (18.9% return all GRV, 40.7% return ⩽200 ml)	- Practice related to enteral feeding varies - Practice deviates from protocols
Metheny et al., 2006	Prospective descriptive study	329 mechanically ventilated adult patients in five ICUs (USA)	NGT Fr⩾14: n=91NGT Fr 10: n=88	Aspirate via 60 ml syringes	Q4H	150–200 ml (No consistent pattern)	Return amount ⩽200 ml	- Large feeding tubes: higher GRVs. - Risk for pneumonia: high-aspiration group=4 times low-aspiration group - 88.9% patients had ⩾1 aspiration event - Most aspiration events are silent - More high GRVs (⩾200 ml) in high-aspiration than low-aspiration group - Aspiration occurred at all volumes of GRV
Metheny et al., 2008	Prospective, descriptive study	Patients in trauma/surgery/ medical/ coronary ICUs (USA) n=206	NGT/OGT: 10–18 FrGastrostomy tube: 20 Fr	60 ml syringe. push in 30 ml of air, then aspirate slowly	Q4H	–	Return amount ⩽200 ml	- 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
Juvé-Udina et al., 2009	Randomized, prospective, non-blinded, clinical trial	Patients in a medical/ surgical ICU (Spain) Intervention (return) group: n=61Control (discard) group: n=61	NGT	Aspirating via 60 ml syringe	Q6H	500ml	Return amount ⩽250 ml	- 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
Umbrello et al., 2009	Descriptive study	Patients in a general ICU (Italy) n=78	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
Soroksky et al., 2010	Pilot prospective cohort study	Patients in a medical/ surgical ICU (Israel) n=52	NGT	Passive drainage to bag, then aspirate via 50 ml syringe	Q4H after commencing feeding, then Q24H if GRV <500 ml	500 ml	Return amount ⩽500ml	- No correlation: GRV values and complications (ICU LOS, mechanical ventilation days, ICU/ hospital mortality)
Poulard et al. 2010	Prospective before–after intervention study	Patients in a medical/ surgical ICU (France) Control group: n=102GRV >250 ml or vomitingIntervention group: n=103 vomiting only	NGT:14-Fr	Aspirate via 50 ml syringe	6H	Control group: 250 mlIntervention group: NA	Return amount ⩽250 ml	- 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
Montejo et al., 2010	Randomized, prospective study.	Patients from 28 ICUs (Spain) Control (GRV 200ml): n=165Study (GRV 500ml): n=157	NGT: range from <Fr 8 to >Fr 12	Gravity drainage to a bag for 10 min or aspirate via 50 ml syringe	1^st day: 6H2^nd day: 8HAfter 3^rd day: 24H if tolerated	200 ml (control) vs. 500 ml (study)	Return amount ⩽200 ml (control) ⩽500 ml (study)	- No difference in gastrointestinal complications / outcome variables. - Pneumonia incidence 27.3% (control) 28.0% (study) - No correlation: GRV and nosocomial pneumonia
Hsu et al., 2011	Prospective, observational study	Patients from a medical ICU (Taiwan) n=61	NGT	Stop feeding for 30 min before check GRV, then aspirate using a 50 ml syringe	Every 4 hours	Stop feeding if >500 ml or GRV >200 ml with feeding complications	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
Rice et al., 2012	Randomized, open-label prospective study	Acute lung injury patients from 44 hospitals in USTrophic feeding n=508Full feeding n=492	GT post-pyloric tube<20%	No description	First 6 days 400 kcal/day- Q12H1300 Kcal/day-Q6H	400 ml	Return all aspirated amount	- No difference in clinical outcome - Less feeding intolerance in trophic feeding group despite receiving fewer medications to treat intolerance
Reignier et al., 2013	Randomized controlled trial	Patients from 9 ICU (French) Intervention group n=208Control group n=215	NGT	Aspirate using a 50 ml syringe	Every 6 hours	Vomiting (intervention) vs. (control)Vomiting/ GRV>250 ml	Return amount ⩽250 ml	- 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.

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 colleagues¹⁷ 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 coloring¹² are unreliable.^12,19 McClave and colleagues¹² 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

Table 2.

Methods for identification of complications.

Authors and year	Aspiration/regurgitation	Diarrhea	Pneumonia
Authors and year	Aspiration/regurgitation	Diarrhea	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	CXR infiltration	–	–	–
Mentec et al., 2001	No description	>3 loose or liquid stools in 24 h	CXR infiltration	Purulent tracheal aspirates or +ve distal bronchial sampling culture	Leukocytosis or leucopenia	⩾38°C or ⩽36.5°C
Pinilla et al., 2001	Observed vomiting	Observation	–	–	–	–
Morgan et al., 2004	Feeds present in oral/ nasal cavities	⩾3 liquid stools, or ⩾250 ml stool in rectal/ colostomy bag, or ⩾1500 ml effluent in ileostomy bag in 24 h	–	–	–	–
McClave et al., 2005	Presence of yellow microspheres and food coloring in tracheal or oropharyngeal samples	–	CXR infiltration	+ve pulmonary secretion cultures	–	–
Metheny et al., 2006	Pepsin immunoassay (sensitivity 93%, specificity 100%)	–	Simplified clinical pulmonary infection score and bronchoalveolar lavage confirmation (refer to Table 3)
Metheny et al., 2008	Pepsin immunoassay		–	–	–	–
Juvé-Udina et al., 2009	Standard blood glucose monitors	⩾soft blob-like, mushy/ liquid stools in 24 H	–	–	–	–
Umbrello et al., 2009	No description	No description	No description	–	–	–
Soroksky et al., 2010	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	Leukocytosis or leucopenia	⩾38.5°C or ⩽35.5°C
Montejo et al., 2010	Feeds present in oral or nasal cavities	⩾5 liquid stools, Or ⩾2000 ml stool in 24 h	CXR infiltration	Purulent tracheal secretions (no microbiological confirmation)	Leukocytosis or leucopenia	>38°C
Reignier et al., 2013	Spontaneous vomit/regurgitation vomiting episode excludes regurgitation during procedures associated with vomiting reflex	No description	CXR infiltration	Purulent tracheal aspirates and +ve secretion culture via bronchoscopy or tracheobronchial aspirate	Leukocytosis or leucopenia	⩾38.5°C or ⩽35°C

CXR: chest X-ray; +ve- positive; h: hour.

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 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 colleagues¹² 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 colleagues¹⁶ 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 study. 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 study, Juvé-Udina and colleagues²⁹ 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 study 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, 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 study 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

Table 3.

Simplified clinical pulmonary infection score.

Chest radiograph	Tracheal secretions	Oxygenation: PaO₂/FIO₂ mm Hg	Blood leukocytes per mm³	Temperature, °C
No infiltrate: 0	Few: 0	>240 or presence of ARDS: 0	⩾4000 and ⩽11,000: 0	⩾36.5 and ⩽38.4: 0
Patchy or diffuse infiltrate: 1	Moderate: 1	⩽240 and absence of ARDS: 2	<4000 or >11,000: 1	⩾38.5 and ⩽38.9: 1
Localized infiltrate: 2	Large: 2			⩾39.0 and ⩽36.0: 2
	Purulent: 1

ARDS: Acute Respiratory Distress Syndrome.

Table 4.

Mortality outcome.

Authors and year		Mortality
Authors and year		Control	Intervention	p-value
Poulard et al., 2010	ICU	24.5%	35%	p = 0.13
Poulard et al., 2010	Hospital	35.3%	42.7%	p = 0.32
Montejo et al., 2010	ICU	15.7%	19.8%	p = 0.28
Montejo et al., 2010	Hospital	33.6%	33.9%	p = 0.53
Soroksky et al., 2010	ICU	21%	40%	p = 0.24
Soroksky et al., 2010	Hospital	35%	40%	p = 1.0
Reignier et al., 2013	Day 28	27.5%	27.8%
Reignier et al., 2013	Day 90	34.2%	36.3%

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 study 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 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.

Footnotes

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.

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

Abstract

Keywords

Introduction

Background and underlying rationale

Aim

Methods

Databases and keywords

Inclusion and exclusion criteria

Results

Factors affecting measurement of GRVs

GRV threshold and assessment frequency

Management of aspirated GRV

Discussion

Limitations and strengths

Conclusion

Footnotes

Acknowledgements

Conflicts of interest

Funding

References