BLOOD-FLOW IN THE LOWER-LIMBS IN THE KNEE-CHEST POSITION - ULTRASONOGRAPHIC STUDY IN UNANESTHETIZED VOLUNTEERS

The knee-chest position for lumbar spine surgery is favoured because d ecreased filling of the epidural reins is associated with reduced pero perative bleeding. However, the position may be unfavourable from a ci rculatory point of view. In the present study, non-invasive assessment of circulation in the lower limbs was performed in 21 unanaesthetised , healthy volunteers who were placed in the surgical knee-chest positi on. Measurements included blood flow velocity (colour Doppler ultrason ography), oscillotonometric arterial blood pressure from upper and low er limbs and poise oximetry from a toe. There was a statistically sign ificant reduction in the posterior tibial artery flow velocity, maxima lly 31.6%, when the subject, was moved from the prone to the knee-ches t position. An enlargement of the trunk-femoral angle at the hip did n ot improve arterial flow. In 10 of the 21 volunteers, no flow in the p osterior tibial rein was detected in the knee-chest position. In spite of the deteriorated blood flow, pulse oximetry indicated sufficient c apillary flow in the very periphery of the lower limb. Tile change fro m prone to knee-chest position resulted in an increase in arterial blo od pressure of the upper limb; the increase in diastolic arterial pres sure was statistically significant (p < 0.001). It is concluded that t he surgical knee-chest position involves deterioration of both the art erial and venous flow of the lower limbs. This should be considered in patients undergoing surgery in this position and, in particular, in t hose at risk of developing cardiovascular complications.