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Poor validity of residual volumes as markers for risk of aspiration in critically ill patients
Australian Critical Care
Research Review Poor validity o f residual volumes as markers for risk o f aspiration in critically ill pat/ents Andrea Marshall
• Senior Research Fellow Critical Care N u r s i n g Professorial U n i t Royal N o r t h Shore H o s p i t a l a n d The U n i v e r s i t y of Technology, S y d n e y
McClave SA, Lukan JK, Stefater JA, Lowen CC, Looney SW, Matheson PJ, Gleeson K & Spain DA. Poor validity of residual volumes as markers for risk of aspiration in critically ill patients. Critical Care Medicine 2005; 33:1014-1017. injury. The remaining patients were admitted with chronic obstructive pulmonary disease (n=3), pneumonia (n=3) acute respiratory distress syndrome (n 3) and sepsis (n=6).
OBJECTIVES OF THE STUDY The aim of this study was to determine whether gastric residual volume (GRV) accurately predicts the risk for aspiration, to determine the most appropriate designated level of residual volume at which enteral feeding should be withheld, and to determine whether certain clinical factors and physical findings correlate with aspiration risk.
One episode of regurgitation was experienced by 85% of patients (n=34) and 75% (n=30) had at least one episode of aspiration. The mean frequency of regurgitation per patient was 31.3% (0%94%). W h e n regurgitation occurred, the mean GRV was 35.1mL (0-700mL). For aspiration, the raean frequency per patient was 22.1% (0%-94%) and the mean GRV was 30.6mL (0-700mL). The median GRV for all regurgitation and aspiration events was 5mL. The fi'equency of regurgitation and aspiration remained stable over a wide range of GRV. Aspiration risk and bowel function scores did not correlate with the incidence of regurgitation and aspiration. Blue food colouring was rm-ely detected (0.27%).
SETTING A N D SAMPLE The study was conducted in the medical, surgical and coronary intensive care units at the University of Louisville Hospital, a university-based tertiary care centre. Patients were eligible for the study if they were >18 years of age, mechanically ventilated and placed on intragastric enteral tube feeding through nasogastric or percutaneous endoscopic gastrostomy (PEG) tubes. Patients were excluded if access to the gut for tube feeding was not possible, if any portion of their caloric intake was achieved through oral intake, or if there was evidence of clinical shock requiring pressor agents. Pregnant patients and those who had mechanical obstruction of the gastrointestinal tract were also excluded from the study.
GRV was less than 50mL 84.1% of the time and 1.4% of the GRV were >400mL. The low GRV did not equate with low incidence of regurgitation or aspiration (frequency of aspiration was 23.0% when GRV was -<150mL. There was no increase in risk for aspiration between the control (21.6%) and the study group (22.6%). The frequency of regurgitation was less for patients with PEG tubes compared to nasogastric tubes (20.3% vs 40.7%; p=0.046). There was no correlation between the incidence of pneumonia and the frequency of regurgitation or aspiration.
METHOD Patients were fed Probalance (Nestl~ USA) to provide up to 25 kcal/kg per day. Yellow Microscopic beads (109) and 4.5mL of blue food colouring per 1,500mL were added to the feeding solution. Patients were randomised to one of two groups: the control group had enteral feeding stopped for gastric residual volumes >200mL and the study group had feeding stopped for GRV >400mL. Bedside evaluation of GRV was done every 4 hours for 3 days. Additional data was collected to detect blue food colouring, to check patient position and to collect secretions from the trachea and the oropharynx. Acute Physiology and Chronic Health Evaluation (APACHE) III, bowel function and aspiration risk scores were determined.
CRITIQUE The consequence of aspiration is considerable and includes the development of hypoxia and/or pneumonia. Consequently, monitoring GRV is cotmnon[y used in an attempt to mininlise the risk of aspiration. While it is presumed that the measurenlent of GRV is accurate and that this measurement is an appropriate marker for the risk of aspiration, this has never been validated in clinical studies. The definition of a 'high' gastric aspirate - one that is believed to be a cause of aspiration - is extremely variable in clinical practice 1 and there is no consensus on what a safe or normal GRV is in the critically ill z There is no data to suggest that high gastric aspirates predict aspiration o1 that aspiration does not occur with low aspirates 3, 4. In the critically ill, there are a number of factors that can impact on gastric emptying and thus increase GRV. Some of these factors include vasopressor use, sedation, narcotic use and sepsis 2, 5. Despite the lack of data to support the use of GRV in evaluating the risk for aspiration, this practice continues.
RESULTS Forty patients (21 with nasogastric feeds and 19 with percutaneous endoscopic gastrostomy feeds) were enrolled in the study. In total 1,118 samples (531 oral, 587 tracheal) were taken. The majority of patients in the study were admitted to ICU for trauma (62.5%; n=25) and 17 of these 25 patients had experienced a closed head Volume 18
Number 3
A u g u s t 2005
130
Australian Critical Care
This study by McClave e t al. presents data on an infrequently explored area and this data raises further questions regarding the
aspirate 2. It is often assmned that the aspirated GRV represents
validity of GRV as a marker for the risk for aspiration.
demonstrate that this is not the case.
the complete contents of the stomach; however previous studies
Patients
in this study were randomised to one of two study groups. These patients were from either a medical, surgical or coronary intensive care unit. Data on age, sex, A P A C H E III score was obtained
Zaloga and colleagues
demonstrated that aspiration of gastric contents consistently underestimates the GRV. More complete emptying was found to occur using continuous suctioning and rolling the patient from
allowing for comparisons between this study population and patients admitted to other ICUs. However, the majority of patients had experienced trauma and nearly half had a closed head injury. There is evidence to suggest that brain injury can decrease gastric emptying 6 and this raises questions about the applicability of these
While questions about GRV remain, McClave and colleagues have
results to the general ICU population. All patients were followed up for the full 3 days of the study.
us to reflect critically on our knowledge and beliefs about the role
side to side 2.
added to our knowledge in this area. While the data in this paper is insufficient to widely change clinical practice, it perhaps allows of GRV in predicting aspiration or for assessing feed tolerance and to question the routine and ritualistic practice surrounding the
In addition to the demographic data obtained for these patients, a calculated bowel function score (6 items) and an aspiration risk
measurenlent of gastric residual volumes.
score (9 items) were used. The authors describe these scores as being based on previous studies and arbitrarily weighted each item within each score. There are no details on the content or construct
REFERENCES 1.
Marshall A &. West S. Nutritional intake in the critically ill: hnproving practice through research. Australian Critical Care 2004; 17(1):6-15.
2.
Zaloga G. The myth of the gastric residual volume. Crit Care Med 2005; 33(2):449-450.
3.
Pinilla JC, Samphire J, Arnold C, Liu L & Thiessen B. Comparison of gastrointestinal tolerance to two enteral feeding protocols in critically ill patients: a prospective, randomized controlled trial. Jpen: J Parenter Enteral Nutr 2001; 25(2):81-6.
4.
McClave SA, Snider HL, Lowen CC, McLaughlin AJ, Greene LM, McCombs RJ, et al. Use of residual volume as a marker for enteral feeding intolerance: Prospective blinded comparison with physical examination and radiographic findings. Journal of Parenteral and Enteral Nutrition 1992; 16(2):99-105.
5.
Schuster-Bruce M. Gastric emptying in the critically ill Crit Care Med 2001;29(6):1293-4.
6.
Rhoney DH, Parker D Jr, Formea CM, Yap C & Coplin WM. Tolerability of bolus versus continuous gastric feeding in brain-injured patients. Neurol Res. 2002; 24(6):613-620.
validity of these tools, making the meaningfulness of this data difficult to determine. The results of this study appear compelling and suggest that GRV has a poor sensitivity for the risk for aspiration over a wide range of residual volumes. However, data was analysed for only 40 patients. Because repeated measures of GRV were obtained from each of these 40 patients, the results of the study become less certain. This is because if a patient is prone to aspiration (or not), they are more likely to consistently demonstrate similar findings with each clinical assessment - the measurements obtained in this study are not independent of one another. It is also not clear from the paper how GRV was measured in these patients and how consistently this was done for each of the patients across the three days of study. This technique may vary between clinicians and is dependent on tube position, the size and type of tube, number of tube openings and the syringe used to
131
Volume 18
Number 3
A u g u s t 2005
Research Review Poor validity o f residual volumes as markers for risk o f aspiration in critically ill pat/ents Andrea Marshall
• Senior Research Fellow Critical Care N u r s i n g Professorial U n i t Royal N o r t h Shore H o s p i t a l a n d The U n i v e r s i t y of Technology, S y d n e y
McClave SA, Lukan JK, Stefater JA, Lowen CC, Looney SW, Matheson PJ, Gleeson K & Spain DA. Poor validity of residual volumes as markers for risk of aspiration in critically ill patients. Critical Care Medicine 2005; 33:1014-1017. injury. The remaining patients were admitted with chronic obstructive pulmonary disease (n=3), pneumonia (n=3) acute respiratory distress syndrome (n 3) and sepsis (n=6).
OBJECTIVES OF THE STUDY The aim of this study was to determine whether gastric residual volume (GRV) accurately predicts the risk for aspiration, to determine the most appropriate designated level of residual volume at which enteral feeding should be withheld, and to determine whether certain clinical factors and physical findings correlate with aspiration risk.
One episode of regurgitation was experienced by 85% of patients (n=34) and 75% (n=30) had at least one episode of aspiration. The mean frequency of regurgitation per patient was 31.3% (0%94%). W h e n regurgitation occurred, the mean GRV was 35.1mL (0-700mL). For aspiration, the raean frequency per patient was 22.1% (0%-94%) and the mean GRV was 30.6mL (0-700mL). The median GRV for all regurgitation and aspiration events was 5mL. The fi'equency of regurgitation and aspiration remained stable over a wide range of GRV. Aspiration risk and bowel function scores did not correlate with the incidence of regurgitation and aspiration. Blue food colouring was rm-ely detected (0.27%).
SETTING A N D SAMPLE The study was conducted in the medical, surgical and coronary intensive care units at the University of Louisville Hospital, a university-based tertiary care centre. Patients were eligible for the study if they were >18 years of age, mechanically ventilated and placed on intragastric enteral tube feeding through nasogastric or percutaneous endoscopic gastrostomy (PEG) tubes. Patients were excluded if access to the gut for tube feeding was not possible, if any portion of their caloric intake was achieved through oral intake, or if there was evidence of clinical shock requiring pressor agents. Pregnant patients and those who had mechanical obstruction of the gastrointestinal tract were also excluded from the study.
GRV was less than 50mL 84.1% of the time and 1.4% of the GRV were >400mL. The low GRV did not equate with low incidence of regurgitation or aspiration (frequency of aspiration was 23.0% when GRV was -<150mL. There was no increase in risk for aspiration between the control (21.6%) and the study group (22.6%). The frequency of regurgitation was less for patients with PEG tubes compared to nasogastric tubes (20.3% vs 40.7%; p=0.046). There was no correlation between the incidence of pneumonia and the frequency of regurgitation or aspiration.
METHOD Patients were fed Probalance (Nestl~ USA) to provide up to 25 kcal/kg per day. Yellow Microscopic beads (109) and 4.5mL of blue food colouring per 1,500mL were added to the feeding solution. Patients were randomised to one of two groups: the control group had enteral feeding stopped for gastric residual volumes >200mL and the study group had feeding stopped for GRV >400mL. Bedside evaluation of GRV was done every 4 hours for 3 days. Additional data was collected to detect blue food colouring, to check patient position and to collect secretions from the trachea and the oropharynx. Acute Physiology and Chronic Health Evaluation (APACHE) III, bowel function and aspiration risk scores were determined.
CRITIQUE The consequence of aspiration is considerable and includes the development of hypoxia and/or pneumonia. Consequently, monitoring GRV is cotmnon[y used in an attempt to mininlise the risk of aspiration. While it is presumed that the measurenlent of GRV is accurate and that this measurement is an appropriate marker for the risk of aspiration, this has never been validated in clinical studies. The definition of a 'high' gastric aspirate - one that is believed to be a cause of aspiration - is extremely variable in clinical practice 1 and there is no consensus on what a safe or normal GRV is in the critically ill z There is no data to suggest that high gastric aspirates predict aspiration o1 that aspiration does not occur with low aspirates 3, 4. In the critically ill, there are a number of factors that can impact on gastric emptying and thus increase GRV. Some of these factors include vasopressor use, sedation, narcotic use and sepsis 2, 5. Despite the lack of data to support the use of GRV in evaluating the risk for aspiration, this practice continues.
RESULTS Forty patients (21 with nasogastric feeds and 19 with percutaneous endoscopic gastrostomy feeds) were enrolled in the study. In total 1,118 samples (531 oral, 587 tracheal) were taken. The majority of patients in the study were admitted to ICU for trauma (62.5%; n=25) and 17 of these 25 patients had experienced a closed head Volume 18
Number 3
A u g u s t 2005
130
Australian Critical Care
This study by McClave e t al. presents data on an infrequently explored area and this data raises further questions regarding the
aspirate 2. It is often assmned that the aspirated GRV represents
validity of GRV as a marker for the risk for aspiration.
demonstrate that this is not the case.
the complete contents of the stomach; however previous studies
Patients
in this study were randomised to one of two study groups. These patients were from either a medical, surgical or coronary intensive care unit. Data on age, sex, A P A C H E III score was obtained
Zaloga and colleagues
demonstrated that aspiration of gastric contents consistently underestimates the GRV. More complete emptying was found to occur using continuous suctioning and rolling the patient from
allowing for comparisons between this study population and patients admitted to other ICUs. However, the majority of patients had experienced trauma and nearly half had a closed head injury. There is evidence to suggest that brain injury can decrease gastric emptying 6 and this raises questions about the applicability of these
While questions about GRV remain, McClave and colleagues have
results to the general ICU population. All patients were followed up for the full 3 days of the study.
us to reflect critically on our knowledge and beliefs about the role
side to side 2.
added to our knowledge in this area. While the data in this paper is insufficient to widely change clinical practice, it perhaps allows of GRV in predicting aspiration or for assessing feed tolerance and to question the routine and ritualistic practice surrounding the
In addition to the demographic data obtained for these patients, a calculated bowel function score (6 items) and an aspiration risk
measurenlent of gastric residual volumes.
score (9 items) were used. The authors describe these scores as being based on previous studies and arbitrarily weighted each item within each score. There are no details on the content or construct
REFERENCES 1.
Marshall A &. West S. Nutritional intake in the critically ill: hnproving practice through research. Australian Critical Care 2004; 17(1):6-15.
2.
Zaloga G. The myth of the gastric residual volume. Crit Care Med 2005; 33(2):449-450.
3.
Pinilla JC, Samphire J, Arnold C, Liu L & Thiessen B. Comparison of gastrointestinal tolerance to two enteral feeding protocols in critically ill patients: a prospective, randomized controlled trial. Jpen: J Parenter Enteral Nutr 2001; 25(2):81-6.
4.
McClave SA, Snider HL, Lowen CC, McLaughlin AJ, Greene LM, McCombs RJ, et al. Use of residual volume as a marker for enteral feeding intolerance: Prospective blinded comparison with physical examination and radiographic findings. Journal of Parenteral and Enteral Nutrition 1992; 16(2):99-105.
5.
Schuster-Bruce M. Gastric emptying in the critically ill Crit Care Med 2001;29(6):1293-4.
6.
Rhoney DH, Parker D Jr, Formea CM, Yap C & Coplin WM. Tolerability of bolus versus continuous gastric feeding in brain-injured patients. Neurol Res. 2002; 24(6):613-620.
validity of these tools, making the meaningfulness of this data difficult to determine. The results of this study appear compelling and suggest that GRV has a poor sensitivity for the risk for aspiration over a wide range of residual volumes. However, data was analysed for only 40 patients. Because repeated measures of GRV were obtained from each of these 40 patients, the results of the study become less certain. This is because if a patient is prone to aspiration (or not), they are more likely to consistently demonstrate similar findings with each clinical assessment - the measurements obtained in this study are not independent of one another. It is also not clear from the paper how GRV was measured in these patients and how consistently this was done for each of the patients across the three days of study. This technique may vary between clinicians and is dependent on tube position, the size and type of tube, number of tube openings and the syringe used to
131
Volume 18
Number 3
A u g u s t 2005