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No Benefit Seen From Monitoring Gastric Volume in Ventilated Patients on Tube Feedings
Early enteral nutrition for patients on mechanical ventilation is considered the standard of care. It's been assumed that delayed gastric emptying, resulting in a stomach full of liquid nutrition, predisposes patients to have aspiration events and develop ventilator associated pneumonia (VAP). Therefore, expert bodies recommend we regularly "check residuals" on these patients, aspirating their stomach contents to see how much tube feeding is pooling there, and stopping the feeding if the volume seems high. The practical result is that patients often don't receive their goal caloric intake, because tube feedings are so often stopped for these so-called "high residuals." Prokinetic drugs like metoclopramide (Reglan) are also often given in these situations.
But this practice is based mostly on theoretical grounds and old physiological studies, not on any large outcome-driven clinical study. Some observational evidence suggests that checking gastric volumes is actually associated with underfeeding and worse clinical outcomes, while others call the supposed threat of high gastric residuals a "myth."
Jean Reignier et al addressed the question with a randomized trial in JAMA, concluding that not monitoring gastric volumes was non-inferior to monitoring them, in its effect on the development of ventilator associated pneumonia.
What They Did
Investigators randomized 452 mechanically ventilated patients at 9 French ICUs to undergo either gastric volume residual checks every 6 hours, with tube feeds pausing for regurgitation, vomiting, or residual volumes >250 mL; or no checks. In the "no check" control group, feedings were still paused for regurgitation or vomiting. Patients began tube feedings within 36 hours of admission. The measured outcome was the rate of ventilator associated pneumonia within 90 days, as defined by a blinded adjudication committee.
What They Found
There was no difference in the development of VAP between the groups: 35 of 222 (16%) of patients getting frequent gastric volume checks developed VAP, while among those not receiving any residual checks, 38 of 227 patients (17%) experienced a VAP. There were also no differences in prespecified secondary outcomes such as infections, ICU stay, mortality, or ventilator days.
However, significantly more patients in the "no checks" group got 100% of their intended calories (an odds ratio of 1.77).
What It Means
Studies on ventilator associated pneumonia are notoriously non-replicable. Their findings are highly sensitive to the rate of VAP at a given institution, which in turn is dependent on patient population, the prevalent local microbiologic flora, and the methods and case definition used to diagnose VAP. Since all these can vary widely even in hospitals across town from each other, it's tough to conclude much from any individual study.
It may be hard to replicate such a study in the U.S., where reported VAP rates are lower and anecdotal evidence suggests they are falling further -- making it more difficult (expensive) to design a trial to find a meaningful difference in VAP from an intervention. Our improving reported VAP rates may be due to effective prevention measures, reclassification of VAPs as tracheobronchitides to game the "quality" measurement system, or both.
All that said, this well-done study stoutly challenges the existing dogma asserting the need for checking gastric residual volumes in patients receiving tube feedings on mechanical ventilation. Medicolegally speaking, since aspiration events are more obvious and litigable than nonspecifically worse outcomes due to underfeeding, and since (as this study shows) aspiration events and VAP will occur with or without gastric volume checks, I don't expect many people to change their practice ... barring a change in the SCCM nutrition guidelines.
Jean Reignier et al. Effect of Not Monitoring Residual Gastric Volume on Risk of Ventilator-Associated Pneumonia in Adults Receiving Mechanical Ventilation and Early Enteral Feeding. A Randomized Trial. JAMA. 2013;309(3):249-256.