Name of the Procedure:

Oxygen Uptake, Expired Gas Analysis; Rest, Indirect (Commonly known as Indirect Calorimetry)

Summary

Indirect calorimetry is a non-invasive procedure used to measure the amount of oxygen the body consumes and the amount of carbon dioxide it produces while at rest. This analysis provides insights into a patient's metabolic rate and energy expenditure.

Purpose

Indirect calorimetry addresses issues related to metabolic function and energy requirements. The goals are to evaluate the patient's resting metabolic rate (RMR), assess nutritional needs, and aid in managing conditions like obesity, malnutrition, and metabolic disorders.

Indications

• Unexplained weight loss or gain
• Malnutrition or undernutrition
• Obesity management
• Pre- and post-bariatric surgery assessment
• Chronic diseases affecting metabolism (e.g., respiratory or cardiac conditions)

Preparation

• The patient should fast for at least 8 hours prior to the test.
• Avoid strenuous exercise for 24 hours before the procedure.
• Medication adjustments may be needed as per the healthcare provider’s instructions.
• A baseline assessment may include basic blood tests and nutritional reviews.

Procedure Description

1. The patient is asked to rest comfortably in a supine position.
2. A face mask or mouthpiece connected to a metabolic cart is placed over the nose and mouth.
3. The equipment measures the volume of expired gases and their oxygen and carbon dioxide content.
4. The patient breathes normally while the data is collected over a period of 15-30 minutes.
5. No anesthesia or sedation is required as the procedure is completely non-invasive.

Duration

The procedure typically takes around 30-45 minutes, including preparation and data collection.

Setting

Indirect calorimetry is performed in a hospital, outpatient clinic, or specialized metabolic laboratory setting.

Personnel

• Respiratory therapist or clinical technician
• Registered dietitian
• Supervising physician (optional)

Risks and Complications

• The procedure is considered very safe with minimal risk.
• Rare instances of discomfort or anxiety due to the face mask or mouthpiece.

Benefits

• Provides accurate measurements of metabolic rate and energy expenditure.
• Helps in designing personalized nutritional and metabolic interventions.
• Supports the management and treatment of metabolic and nutritional disorders.

Recovery

• No recovery time is needed; patients can resume normal activities immediately after the procedure.
• Follow-up may include consultation with a dietitian or healthcare provider for results interpretation and action plans.

Alternatives

• Direct calorimetry (more invasive, requires specialized facilities)
• Predictive equations for metabolic rate (less accurate)

Pros of Indirect Calorimetry

• Non-invasive and quick
• Provides precise measurements

Cons of Indirect Calorimetry

• Requires specific equipment and trained personnel

Patient Experience

• The patient may feel slight discomfort from wearing the face mask or mouthpiece but can breathe normally throughout the test.
• The test is painless, and there are no immediate aftereffects.
• Staff will ensure the patient’s comfort and explain each step clearly.