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Bioelectrical Impedance Analysis |
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Troubleshooting Trouble shooting readings on the spot will prevent
much of your data from being lost or inadequate to use in your overall patient
evaluation. Differences in resistance readings are relatively small in taking
BIA measures, ranging from 8.3 to 14.0 ohms (1.8-2.9%) in one test.[80]
Intraobserver and intraobservation error using standardized techniques is
minimal, even over a period of days to weeks.[81]
A description of troubleshooting information is shown in Table 3. Items that
can significantly change BIA readings fall into the following categories:
patient position, environment, electrode placement, and data input. Minor
influences can include patient activity, meals, menstrual cycle, and others.
The following table discusses each of these situations. Table 3. Troubleshooting Guide for BIA Measures
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Patient position |
Patient lying flat
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The patient should be lying on his/her back perfectly flat and relaxed for the reading. Lounge chairs, wheel chairs, and exam tables that do not allow for the patient to lie flat on their back will change the electrical pathway and alter the resistance and reactance readings |
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Do not let arms or legs touch
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The arms and legs should be slightly apart and not touching other body parts. The electrical pathway can be altered or shortened by arm or leg skin touching other skin. If this seems to happen, place a thin towel or other buffering object between the arms and body or between the thighs to prevent this problem. |
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Be aware of metal objects |
Metal tables (and even cement floors) should be adequately covered with a blanket or other covering; metal jewelry should not touch the electrode and if in doubt of the effect on the BIA readings, remove the jewelry during the test. |
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Environment |
Avoid hot and cold rooms
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Because most of the resistance reading is provided by the arm and leg (and most of that is from the elbow down and from the knee down), it is important to make sure that peripheral blood flow is not significantly changed by hot or cold environments. Allow the patient to lie quietly in ambient temperature for a couple of minutes to allow settling of excess or deficient blood supply in peripheral limbs prior to obtaining a reading. |
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Minimize sweat and lotion
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The presence of sweat or lotion can alter the readings by not allowing the electrode sufficient connection to the skin. Lotion and sweat can increase the variable of what is referred to as “surface resistance” when you really want the reading to reflect a more “deep resistance” of body tissues under the skin. To alleviate this problem, use alcohol swabs to wipe away sweat or lotion and dry the skin surface that will be used for electrode placement. |
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Avoid rooms with electronics
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For the most part, small amounts of electrical activity in the room used for testing is not a problem. But if the office supply of electricity or large numbers of appliances or other electrical equipment are active in close proximity, you may want to change the room you are using for BIAs to see if it helps to get more reasonable measurements. |
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Electrode placement |
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The electrodes should be placed in the same position on each patient. Remember “red head” and “black foot” and the leads will always be in the right place. Red-wired leads should be placed on the back of the hand with the red clip at the wrist and black clip between the two center knuckles. The black-wired leads should be placed on the top of the foot with the red clip at the ankle and the black clip above the toes at the center “knuckle.” |
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Data input |
Recording data Write it down
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Wrong numbers give wrong results. Keep the paper and pencil for recording data close by and record your readings before you remove the electrodes. Trying to remember numbers can be a problem, especially if you are having a lively conversation with the patient. Resistance readings are 3 digits usually ranging from 250-850. Reactance readings are 2 digits usually ranging from 30-80. Do a quick QC check if the readings seem out of range to make sure that connections are good, battery is okay (little grey squares show up between the numbers when the battery is low), and everything noted above is according to standards. If the report looks incorrect (gee, he seemed a bit over fat but the report says he has “–20” pounds of fat!), then check your data input. Height is the most crucial measure on the report. Remember that a person who is 5 foot 8 inches tall is 68 inches (not 58 inches tall). It is also worth checking to see that weight is put in correctly and that resist/react numbers are not transposed. |
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Minor effects |
Activity, recent meals, menstrual cycle |
Activity tends to increase peripheral circulation, and that can change BIA readings. However, it is usually slight and even the most strenuous exercise is not noticeable within about an hour or so. Just make sure that the person is lying flat and has a chance to let the peripheral blood supply settle for a couple of minutes before taking the reading. Recent meals and beverages tend to be reflected in the abdomen before quickly exiting through the bladder. Either way, the influence of abdominal blood supply and bladder contents only minimally affect the mostly peripherally-influenced resistance and reactance readings. The same holds true for menstrual cycles. The slight alterations should not be enough to affect your interpretation of the report. |
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Others |
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There are bound to be other circumstances that affect readings not mentioned here. This box is just to recognize that those may exist and recommend that a good QC check on methods and data input is in order before deciding that a particular patient has outlier readings. |
