What is the best way to feed a critically ill patient? Nutrition can be delivered either parenterally — directly into the veins – or enterally, e.g., via a tube that runs from the nose to the stomach. Both have potential and well-reported adverse consequences, along with potential benefits. It’s commonly believed that, if given the option, you should go with enteral feeding — in addition to being less invasive and more physiologically intuitive, it’s been associated with lower rates of infection and other complications.
But what if the adverse consequences that have hampered parenteral nutrition in the past aren’t a reflection of faulty strategy per se, but rather of poor execution? Rowan and her colleagues in the UK have hypothesized that, with advancements in feeding technology and better management of vascular access, parenteral nutrition may now be superior to enteral feeding, as it’s more likely to ensure delivery of the intended nutrition.
To test this theory, they conducted the CALORIES trial, enrolling 2400 adult patients with unexpected admissions to 33 intensive care units across England. The patients were randomized to receive nutritional support either parenterally (via a central venous catheter) or enterally (via a nasogastric or nasojejunal tube), initiated within 36 hours of admission and used exclusively for five days or until complete transition to oral feeding, discharge from the ICU, or death.
The results, published recently in NEJM, suggest there may not be a clear winner. All-cause mortality at 30 days, the primary outcome, was similar between the two groups: roughly a third of patients died (33.1% in the parenteral group, and 34.2% in the enteral group; relative risk 0.97, P=0.57). Patients in the parenteral group were less likely to become hypoglycemic than patients in the enteral group (3.7% vs. 6.2% of patients; absolute risk reduction 2.5%; P=0.006). They also had lower rates of vomiting (8.4% vs. 16.2%; absolute risk reduction 7.8%; P<0.001). For all other secondary outcomes — including the rate of infection, length of ICU and overall hospital stays, and 90-day survival – no significant difference was found between the two groups. The rate of adverse events was similar as well (4.9% in the parenteral group, and 4.8% in the enteral group; P=1.00).
“The reported increase in infectious complications that have been associated with the parenteral route was not observed,” the authors underscored. This could in part reflect improvements in the formulation, delivery, and monitoring of parenteral nutrition — in other words, better execution as compared to older studies.
But implementation issues may still be undermining the effectiveness of parenteral nutrition. The majority of patients in both study groups failed to achieve their targeted caloric intake (25kcal per kilogram per day). This finding was consistent with the results of previous studies, but still somewhat surprising: parenteral nutrition is supposed to be more reliable at guaranteeing delivery. The authors enumerated various logistical constraints that may have contributed to the shortfall, concluding, “There are substantial practical and organizational impediments for both routes of delivery, at least during an initial 5-day period.”
The CALORIES trial didn’t find parenteral nutrition to be superior to enteral nutrition as the investigators had hypothesized. Even by demonstrating comparable outcomes across the two routes, however, the study invites debate. The most important takeaway lesson from the study may be that for the critically ill patient, getting adequate nutrition early on — by any route — is hard. As for whether route matters, and to what extent, it’s likely still too soon to tell.
What is your approach to nutritional supplementation for patients who require intensive care? When enteral and parenteral nutrition are both available, what influences your decision to use one versus the other? How will the results of the CALORIES trial affect your practice?