Malnutrition is a significant problem in critically ill patients in the intensive care unit (ICU). Studies suggest that only 50-60% of patients receive the proper nutritional needs in intensive care. Nutrition is the cornerstone of healing and is one of the many interventions that impact a patient’s recovery journey.

Healthcare clinicians have struggled to assess patients’ energy needs accurately. A new technology—indirect calorimetry (IC)—is promising to improve this problem. Thanks to the support of Surrey Hospitals Foundation, this ground-breaking device has now been made available to dietitians working in the critical care unit at Surrey Memorial Hospital (SMH).

Critically ill patients benefit from Indirect Calorimetry (IC)

Indirect Calorimetry measures Resting Energy Expenditure (REE). REE refers to the amount of energy a patient uses during 24 hours to maintain involuntary functions like breathing, digestion, and body temperature. Indirect calorimetry calculates the exact calories a patient’s body requires to function at rest by measuring oxygen inhalation and carbon dioxide exhalation. “It connects to a patient’s ventilator and measures their gas exchange,” explains Julie Jamieson, a dietitian at SMH’s critical care unit. “It’s a real game changer.”

Determining the nutritional needs of critically ill patients in the ICU is challenging. Each patient’s caloric needs depend on the severity of the illness and other factors, including their demographics, illness duration, and medications. Body mass index (BMI) also plays a crucial role in determining the energy needs of intensive care patients and developing a personalized nutrition plan.

Patients with low or high BMIs are at an increased risk of complications if they consume too much protein, carbohydrates, or fats, as it can have adverse effects. Additionally, research has shown that the energy needs of obese patients vary day to day and can alternate between hyper- and hypo-metabolism during their care journey in the ICU. This patient population benefits significantly from IC-guided nutrition therapy as it precisely measures the resting energy expenditure (REE) of these patients, which helps dieticians create an individualized nutrition plan.

“We do indirect calorimetry around day three or five when patients are out of the acute phase of their illness. If the patient remains on a ventilator, we repeat it weekly because we know that energy needs change and fluctuate throughout the ICU stay,” says Jamieson.

Loss of muscle mass affects healing

All of these factors can affect resting energy expenditure (REE). Indirect calorimetry provides the dietician with the precise calorie count each patient needs. “We know that as our patients recover, they can lose 1-2% of their muscle mass daily. So, anything we can do to mitigate that is significant, and this is meeting their energy needs,” says Jamieson.

In the past, dieticians used complicated formulas called predictive equations to calculate the nutritional needs of critically ill patients. However, the results were often flawed, leading to patients being under or overfed by 500-1,000 calories a day. “Research has shown that those equations are very inaccurate and are correct only 50% of the time. Indirect calorimetry is very accurate within 3%,” says Jamieson.

Underfeeding linked to poor outcomes

Indirect calorimetry-based nutrition protocols mitigate the delicate balance of under and overfeeding patients in the ICU. Underfeeding critically ill patients can result in poor wound healing, immunosuppression, and increased risk of infection. On the other hand, overfeeding can result in hyperglycemia and fatty liver disease and can also worsen respiratory failure by increasing carbon dioxide production, thus impairing the patient’s ability to wean off the ventilator. “Indirect calorimetry allows us to know the exact calories our patients need to prevent these ICU complications,” says Jamieson.

Short-term mortality significantly reduced

Indirect calorimetry is the gold standard for measuring REE and guiding nutrition support for ICU patients. A study done in 2021 showed a 23% reduction in short-term mortality when energy targets were based on IC.

Another benefit of IC is that it allows dietitians to track the nutritional needs of critically ill patients as they transition out of critical care. Surrey Hospitals Foundation also funded an additional piece of equipment called a canopy hood for this purpose. As patients move to acute care, the device also measures REE when the individual is no longer on a ventilator and can breathe independently.

“There is a lot of research going into how we improve the outcomes of our patients as they recover from critical illness,” Jamieson says. The canopy hood “allows us to personalize patients’ nutrition prescription and follow their journey as they transition out of critical care and recover from their illness.”

A new feature of IC is the ability to calculate resting energy expenditure in patients breathing on their own without a ventilator. Jamieson believes this is a huge benefit to the hospital, as the new IC can be used in other departments for non-critically ill patients.

“We’re training dieticians in acute care to use indirect calorimetry when patients move out of the ICU or even if they have a patient who they think will benefit from it,” says Jamieson.

IC testing completed in minutes

The critical care department started using the new IC device in August 2023. Previously, Jamieson and her team used a first-generation IC that took two hours to complete and was conducted at night. The new IC only takes 10 minutes and can be done anytime throughout the day.

“With this new device, we’re able to do more tests than we ever could before,” says Jamieson. “Previously, we would do one a week, and now we are doing a couple a day, if not more. So, the use of indirect calorimetry has increased significantly.”

Gratitude for generous contributions

Indirect calorimetry holds tremendous promise for the future. Nutrition for critically ill patients is not a one-size-fits-all plan. With IC, healthcare professionals can accurately measure energy expenditure and customize patient calorie needs quickly and accurately. The dieticians at Surrey Memorial Hospital Critical Care say they are grateful to have access to this transformative technology.

“We are thankful to Surrey Hospitals Foundation for providing this equipment,” says Jamieson. “We use it daily and have a lot more confidence knowing that we are providing patients with the calories they need and can personalize nutrition support, thus improving their ICU outcomes,” Jamieson says.

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About the Author

This article is a guest post by Denise Moulton, a registered nurse that works at the Jim Pattison Outpatient Care and Surgery Centre in Surrey. Denise is passionate about writing. Her background in journalism allows her to create compelling and informative content that resonates with anyone interested in healthcare. In her free time, Denise can be found exploring British Columbia’s hiking trails.