RESUMO
BACKGROUND: While sleeping, humans frequently change their position; this is done to avoid direct and excessive pressure on the body surface, and is considered to be very important for the prevention of pressure sores. A patient who is under general anesthesia, however, cannot perform this reflex movement; maintaining the same position during an entire operation causes concentrated pressure on specific body surfaces, and this may result in complications such as allopecia, back pain, pressure sores and peripheral nerve damage. Because little is known about the relationship between surgical position and pressure on the body surface, position is in most clinical situations decided on the basis of experience and informed guesswork. In order to qualitatively and quantitatively determine weight-bearing areas, pressure on the body surface of patients was evaluated under general anesthesia. METHOD: Ten patients scheduled for elective surgery were selected for this study. They were all aged over 20 and ASA class 1. A mattress equipped with a force sensing resistor was placed on the operating table and used to determine pressure on the body surface. Pressure was measured before and after anesthesia was induced in the supine, lateral and prone position. The signal generated by this mattress was processed using an analogue-digital (AD) converter, then displayed as pressure distribution on a computer screen. Pressure points were compared qualitatively, and for quantitative measurement were digitally expressed. 'Pressure' here is mean pressure at each point calculated among ten patients. RESULTS: In the supine position, pressure was concentrated on the shoulder and sacral areas. Pressure distribution in these areas was 29.8% (shoulder) and 26.0% (sacral area) before anesthesia was induced, and 20.3% (shoulder) and 25.8% (sacral area) after induction. In the lateral position, the shoulder and trochanteric areas were identified as the main weight-bearing areas; pressure distribution was 11.2% and 8.1% before induction, and 21.6% and 15.3% after induction, respectively. In the prone position, the chest and abdomen were the main weight-bearing areas. Pressure distribution in the chest area was 30.8% before induction and 24.4% after. Operating table tilt in each surgical position also produced marked changes in pressure distribution. CONCLUSIONS: In each surgical position, weight-bearing areas were qualitatively and quantitatively determined before and after anesthesia.