Metabolic Cart Periprocedural Care

Patient Instructions

Thoroughly explaining the procedure to the patient is important, and preprocedure preparation is important. Outpatients are asked to fast overnight, and studies should be performed first thing in the morning. Patients should be instructed to avoid any drinks with caffeine or sugar and to avoid strenuous activity or exercise until the test is completed. They should also be instructed to wake and dress in comfortable clothes and to be driven to the facility with minimal effort, if possible.

Upon arrival, the patient should be placed on a stretcher or recliner for 30-45 minutes before the test. The patient needs to be in a resting state. There should be no interruptions during measurement and no nursing care for at least 1 hour before the test (including suctioning) in an environmentally neutral room.

In ventilator-dependent patients, ventilator settings should not be changed for at least 90 minutes before the procedure.

All sources of supplemental oxygen (eg, nasal cannula, masks, aerosol delivery) are turned off, if possible, to avoid a falsely low metabolic rate.

Diet or tube feedings should remain unchanged for 48 hours prior to measuring the REE.

Patient must take nothing by mouth (NPO) for at least 2 hours before testing owing to the increased metabolic rate caused by the thermogenesis effect following meals. The exception is for patients receiving continuous tube feedings, as this does not affect the testing.

Equipment

Many commercial devices for this type of testing are available. It is advisable that the types of patients to be studied reflect the needs of the institution. Patients on ventilators require a device that measures elevated oxygen levels. Some institutions use a metabolic cart for cardiopulmonary stress testing and/or research-level data collection. It is with these classes of advanced systems that a canopy system is also available. These devices also have robust databases and can perform advanced data collection and analysis, such as body-fat percentage or breakdown of substrate utilization.

Another group of devices is easier to operate but can be used only in individuals who do not require oxygen therapy and cannot be used for exercise testing. These devices usually do not have extensive databases or trending capabilities.

Other equipment includes the following:

• Disposable 22-mm ventilator tubing
• Precision calibration gases and volume calibration syringe
• Thermometer, barometer, and hygrometer (built into most metabolic systems)
• Canopy, valve with mouthpiece, or facemask for nonintubated patients
• Heart rate monitors (only for exercise testing)
• Treadmill or ergometer (for exercise measurements)
• Anthropometric equipment for measurement, when necessary (eg, calibrated skinfold calipers, measuring tape, bioimpedance)

Anesthesia

Anesthesia is not required, as this would alter the patient’s metabolic rate.

Positioning

The patient should be awake throughout the procedure in a supine or semi-Fowler position and in an environmentally neutral comfortable area or quiet room.

Complications

Measurement of REE via metabolic cart is a safe procedure, but some potential complications or limitations include the following:

• Reduction in alveolar ventilation

• Increased work of breathing

• Hypoxemia or bradycardia secondary to disconnection of the patient from the ventilator