E. Laakso et al., BLOOD-FLOW IN THE LOWER-LIMBS IN THE KNEE-CHEST POSITION - ULTRASONOGRAPHIC STUDY IN UNANESTHETIZED VOLUNTEERS, Anaesthesia, 51(12), 1996, pp. 1113-1116
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.