Relation Between Bioelectrical Impedance Analysis (BIA) and CT-scan Analysis in the ICU

Relation Between Bioelectrical Impedance-derived Muscle Mass and CT-derived Muscle Area in Critically Ill Patients

Aim of the present study is to determine whether muscle mass as assessed by bioelectrical impedance analysis correlates with and corresponds to muscle mass as assessed by CT scan analysis in critically patients admitted to the intensive care unit.

BIA measurements are performed in critically ill patients admitted to the ICU or MC, within 72 hours before or after CT scanning.

The BIA measurements are taken with the BIA 101 ASE, manufactured by Akern, Florence-7 Italy. This device is phase sensitive and injects an alternating current of 400 µA at 50 kHz. Measurements were performed while patients lay in supine position with a pillow supporting the head. The resistance, reactance, body weight and length are entered in the BIA algorithm, using BodyGram PRO. This algorithm calculated the body composition, with muscle mass being reported in kilogram (kg).

Abdominal CT scans are analyzed using the computer program SliceOmatic® version 4.3 and 5.0 (TomoVision, Montreal, QC, Canada) at the level of the third lumbar vertebra (L3). The muscle tissue was identified by using boundaries in Hounsfield Units (grayscale) set of -29 to +150(23). The program computes muscle surface area in cm2, by multiplying the pixel area by the amount of pixels identified as muscle.

For a direct comparison with the BIA-derived muscle mass, the CT-derived muscle area is converted to kg. This is done by following two steps. Firstly, the Shen equation is used for the conversion to litres.Secondly, the muscle volume is multiplied by its density, resulting in muscle mass expressed in kg.

Inclusion Criteria:

• Abdominal CT-scan made for diagnostic reasons

Exclusion Criteria:

• CT-scan not analysable
• Internal or external metal devices
• active pacemaker