Inconclusive evidence regarding the volume of gastric aspirate that can be safely reintroduced following residual volume measurements
- Correspondence to Norma A Metheny
Saint Louis University School of Nursing, 3525 Caroline Mall, St Louis, MO 63104, USA;
This randomised trial to assess risks associated with returning or discarding gastric residual volume (GRV) to tube-fed patients is similar to one reported in 2000 by Booker and colleagues. Although the current study had a larger sample size, neither study was able to provide definitive recommendations for practice.
The investigators randomised 125 critically ill adult patients to a ‘return’ or ‘discard’ group. The return group had up to 250 ml of gastric fluid returned to the stomach at each 6-hourly GRV measurement. Although not explicitly stated by the investigators, it appears that no gastric fluid was returned to subjects in the discard group. Outcome variables listed in the study's objectives were incidence of tube blockage, pulmonary aspiration, gastrointestinal intolerance (nausea, vomiting, abdominal distension and diarrhoea) and disturbances in potassium and glucose balance. None of the tubes became blocked during the study. Aspiration was not found in either group. No differences were found in signs of gastrointestinal intolerance to feedings. Finally, no difference was found in the incidence of hypokalaemia between the groups; however, a significantly higher incidence of hyperglycaemic episodes was reported in the control group.
In addition to the relatively large sample size, a strong feature of the study was the use of the same type of feeding tube (16 Fr Salem Sump) for each patient. This type of tube is recognised as facilitating more reliable measures of GRV than are allowed by small-diameter flexible tubes.1 The large-diameter tubes were unlikely to become clogged, especially as they were flushed periodically with water. Measurements selected for gastrointestinal intolerance to feedings were reasonable. However, the investigators did not indicate how much of an increase in abdominal girth was considered significant. A major weakness of the study was the use of glucose oxidase reagent strips to assess for aspiration. This method has been found to be ineffective in clinical and laboratory settings.2 3 For this reason, use of glucose strips to monitor for aspiration is not recommended.4 It is recognised that high GRVs are related to aspiration.5 As such, a reliable measure of aspiration is crucial to a study of how GRVs are managed. The investigators referred to fluid balance as an outcome but did not indicate how it was defined or measured; thus, it was impossible to determine what was meant by the values reported in their table 4. It was difficult to determine whether the investigators calculated the total mean volume of gastric aspirate discarded from each group. Some portions of the methodology were difficult to understand because of changes in terminology. For example, subjects were sometimes referred to as being in either the ‘return’ or ‘discard’ group; at other times, they were referred to as being in either the ‘intervention’ or ‘control group’.
The investigators' findings regarding the safety of returning up to 250 ml of gastric contents to the stomach of critically ill tube-fed patients are partially supported by a recommendation from the North American Summit on Aspiration in the Critically Ill Patient: Consensus Statement to return up to 500 ml of GRV to the patient.6 However, less supportive of the findings is a report in which aspiration occurred significantly more often in patients with two or more GRVs of at least 200 ml and one or more GRVs of at least 250 ml.5 The latter study used a highly sensitive marker (pepsin) for the aspiration of gastric contents.
In summary, a large randomised trial using a sensitive and specific assay for aspiration of gastric contents may shed more light on the relationship between aspiration and the volume of GRV returned to patients. Another desirable component of a future study is a comparison between groups of the volume of discarded fluid to assess more accurately the effect of this procedure on fluid and electrolyte status.
Competing interests None.