Bioelectric Impedance Analysis
To estimate and assess body composition.
There are no food, fluid, activity, or medication restrictions unless by medical direction.
- Healthy adults.
Critical Findings and Potential Interventions
(Study type: Electrophysiologic; related body system: Multisystem.)
Electrical impulses run continuously through the cells, tissues, and organs involved in any type of metabolic process. A few examples include the musculoskeletal, cardiovascular, and nervous systems. The impulses are conducted and sustained through complex chain reactions involving electrolytes such as sodium, potassium, calcium, and magnesium. The ability of tissues to conduct or prevent the passage of electrical energy varies with changes in the concentration of electrolytes in intra- and extracellular fluids, changes in cell membrane permeability, cellular composition, and water content. When an electric current is passed through the body, it is conducted through the intra- and extracellular fluids containing water and electrolytes. Lean tissue contains more water than fatty tissue; therefore, the flow of current occurs easily through muscle but is impeded by fat, which is the basis for bioelectric impedance analysis (BIA).
Bioelectric impedance measurements are a reflection of the structure, composition, and function of specific tissues. Measurements of the electrical properties of normal tissue have been expanded to explore tissue profiles along a continuum of cellular change from damaged to expired. These advances may make it possible to diagnose diseases earlier, predict survival, and guide the progress of therapeutic interventions. The technology has appeal because it is simple, portable, noninvasive, relatively inexpensive, and has rapid turnaround to results. In practice, it is usually conducted by contact with electrodes at the site of interest, such as wrist to ankle, hand to hand, or foot to foot. Estimates of body fat percentage are derived from the measurements set against validated formulas that consider factors to include a person’s age, height, weight, gender, and ethnicity.
The development of medical applications based on BIA include impedance plethysmography; electroencephalography; hydration management for patients with hemodynamic disturbances; nutritional interventions for malnourished, critically ill patients; and assessment of body composition as a risk factor for developing diseases such as heart disease, diabetes, hypertension, and some types of cancer. Nutritionists, athletic club trainers, and members of sports organizations are using BIA to assess health and assist patients in successful weight management. Health assessment has become part of some employee wellness programs. Participation in health assessment is also tied to some employer-sponsored health insurance plans that offer discounts to employees who participate and penalties for those who do not participate. Drawbacks to some of the simpler equipment used to measure body composition in healthy individuals are inconsistent readings due to variations in hydration level, skin temperature, and testing environment, as well as the skill level of the person administering the measurements.
- Assessment of nutritional therapy for the treatment of a chronic disease.
- Assist in evaluating prognosis for patients with chronic conditions such as cancer or liver disease or who are critically ill with an infectious disease.
- Estimation of body composition as part of a biophysical health assessment.
Patients who are pregnant may be excluded from participating in the study; protocols vary among facilities. Fluid volumes change significantly throughout the course of a pregnancy, and interpretation of results may not be accurate or useful.
Patients with cardiac implantable electronic devices (e.g., pacemaker, defibrillator); while this is a generally accepted recommendation there is not a large body of scientific evidence documenting electrical interference related to BIA.
Patients with extremely abnormal body weight (obese or emaciated) or physical deformities that present an irregular distribution in body composition may be excluded from participating in the study; protocols vary among facilities. Interpretation of results may not be accurate or useful.
Patients with a skin condition that would interfere with placement of electrodes.
Patients with sudden and significant changes in hydration status (hyper- or hypovolemia).
Young patients (neonate to adolescent) and older adult patients may be excluded from participating in the study; protocols vary among facilities. Validated formulas for younger and older adult patients may not be available, and interpretation of results may not be accurate or useful.
Factors that may alter the results of the study
- The quality of the BIA study is dependent on the skill of the person performing the study.
- Poor electrode conduction.
Potential Medical Diagnosis: Clinical Significance of Results
Abnormal Findings In:
- Chronic conditions (e.g., cancer, HIV, liver disease) (related to diminished electrical conductivity as a result of cachexia)
- Patients receiving nutritional therapy related to weight issues or chronic conditions (in order to assess and monitor the efficacy of therapy)
Nursing Implications, Nursing Process, Clinical Judgement
Before the Study: Planning and Implementation
Teaching the Patient What to Expect
- Discuss how this procedure is performed to measure the amount of fat and lean muscle mass in the body.
- Explain that the procedure takes about 3 to 5 min.
- Review the procedure with the patient.
- Advise that the application of an electrical current is brief, will not be felt, and is not harmful.
- Some studies require standing and holding a device containing hand-to-hand electrodes to record body composition.
- Other types of studies require standing on a device used to record body composition using foot-to-foot measurements.
- The patient is placed in a supine position for 5 to 10 min prior to the study in order to achieve a relatively even distribution of body fluids.
- Precise positioning requires lying facing up, arms abducted 30 degrees from the sides of the body, and legs positioned so that the thighs do not touch.
- A thin piece of acrylic fabric between the arms and trunk or between the thighs if necessary.
- Skin is thoroughly cleansed where the electrodes will be placed with alcohol pads to remove any fatty substances (ex. lotion) or other types of residue that may interfere with the study measurements.
- Two sets of electrodes are placed: one to the patient’s right hand and one to the patient’s right foot.
- Each set of electrodes has one electrode that provides the source of the current and another that serves as a voltage detector.
- When the procedure is complete, the electrodes will be removed.
After the Study: Implementation & Evaluation Potential Nursing Actions
- Monitor electrode sites for inflammation.
- Chronic illness can often require significant diet changes to maximize health.
- Make dietary changes based on a specific diagnosis and individual study results.
- Consider how weight management can be a very emotional issue, making it difficult for individuals to adhere to nutritional treatment plans.
Followup Evaluation and Desired Outcomes
- Acknowledges that depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy.
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