Nutrition Support Traineeship
We have had a slow transition to spring weather here in Virginia , and our recent trainees had a cold, wet start to their week. However, by Thursday the sun was out, and they were able to appreciate the Dogwoods and Redbuds in bloom here.
Our journal club article this month was a recent JPEN article.
This study is a little different than our usual, and I would like to point out the involvement of Dr. Stephen McClave, who was the first person to randomize patients with pancreatitis to enteral feeding, one of the few researchers to study residuals in an organized manner, and has investigated use of indirect calorimetry.
This is a pilot study that examined the use of a refractometer to measure how much of a gastric residual was made up of feeding formula, versus how much is body fluid. A refractometer measures “total soluble solids in solution” and a Brix value (0-32 in this study) is assigned to the liquid. The authors demonstrated with in-vitro studies, that saliva, gastric juice and 0.9% normal saline all had a similar Brix value (1.0-1.9), while Osmolite had a Brix value of 23. The in-vitro studies demonstrated that they could reliably determine the degree of dilution of Osmolite with these substances using the Brix value.
The authors then examined the Brix values in a group of ICU patients on mechanical ventilation after receiving a 240 mL bolus feeding of Osmolite via a 14 french nasogastric tube. The patients were fed for 24 hours before the Brix values were checked, and separated into two groups based on gastric residuals (< 75 mL or > 75 mL). Twenty-five patients had residuals less than 75 mL during the previous 24 hours of feeding, and 18 patients had residuals > 75 mL during the previous 24 hours of feeding.
The study reported that one patient with low residuals had a high Brix value, and that 13 of the 18 patients with residuals >75mls had a low Brix value. The authors discuss the possible implications of these findings, suggesting that a patient with low residuals but a high Brix value might have gastric dysmotility (> 20% of the bolus of formula remaining in the stomach after 180 minutes). They also suggest that a low Brix value in the setting of high residuals implies that the patient has adequate gastric emptying because the patient has cleared the feeding from the stomach, and the residual is actually gastric secretions and not feeding formula.
The use of a “residualometer” initially struck me as a
weird, not clinically useful article, but once you look carefully you
realize that that this is the first time anyone has investigated how
much of a residual is made up of tube feeding, and how much is gastric
fluid/saliva. It also discusses the possibility that some
patients have low measured residuals because the tip of the
tube is not down in the “pool” of feedings, but actually have very slow
gastric emptying (and actually high residuals, and
questionably at risk of emesis if feedings
continued). It has a good discussion in the article, and many of
the weaknesses of the study are reviewed by the authors.
The authors also did not consider the possibility that bile (or blood) can reflux into the stomach, and this can affect refractometer readings. The biggest limitation is that none of the measurements (residuals or Brix value) correlated with symptoms or clinical outcomes.
Take home message:
Don’t start looking to buy a refractometer (“residualometer”) to predict tube feeding tolerance- we will need to see an outcome study demonstrating the labor and expense involved would lead to meaningful improvement in care.
This is, however, a very valuable study to read because it discusses the limitations to the monitoring of residuals, and it can be useful if you need “evidence” to prove to some other member of the healthcare team that some patients have intact gastric emptying, and their residuals are actually gastric fluid. Do not get bogged down in the technical aspects of the refractometer, or the in-vitro data. There is wisdom to help you feed the sick people in the discussion section.
“New knowledge is the most valuable commodity on earth. The more truth we have to work with, the richer we become.”
Kurt Vonnegut Jr.
Joe Krenitsky MS, RD