Haemodynamics and oxygen tension in the microcirculation of ischaemic skinflaps after neural blockade and haemodilution

The aim of this study was to evaluate the effects of neural, blockade and e xtended normovolaemic haemodilution on haemodynamics and oxygenation in the microcirculation of ischaemic skin flaps using a recently developed island flap on the back of Syrian golden hamsters. One part of the flap was made ischaemic by inducing a random perfusion pattern following interruption of the axial blood supply. The model permitted quantitative assessment of the microhaemodynamics and oxygen tension in all microvascular segments by the use of intravital microscopy. Oxygen tension was measured with the phosphor escence decay method. Neural blockade was induced by applying 2% lidocaine to the neurovascular flap pedicle. Haemodilution was achieved by isovolaemi c exchange of 50% of the total blood volume with dextran 70. One hour after surgery (baseline), centreline velocity was significantly reduced to 20-44 % in all the microvessels in the randomly as compared to the axially perfus ed part, whereas the diameters were slightly larger (ns). In the control gr oup, blood flow declined by 20-75% (P < 0.01 vs. baseline) over time in the entire flap. Flow reduction was significantly attenuated by haemodilution in the entire flap, but more pronounced in the ischaemic part. Neural block ade caused marked vasodilatation and significantly improved blood flow in t he axially but not in randomly perfused microvessels. After 8 h, oxygen ten sion ranged from 4.0 to 6.1 mmHg in the axial part (means, ns between group s), whereas in the ischaemic part, it was 0.8-1.0 mmHg (P < vs. axial) in t he control and neural blockade groups, and 1.7 mmHg (P vs. axial and betwee n groups) after haemodilution. Our findings indicate that neural blockade d oes not improve microcirculation and oxygenation in randomly perfused flap tissue because the sympathetic regulation of its microcirculation is overru led by autoregulatory mechanisms. Normovolaemic haemodilution, even after a 50% exchange, augments oxygenation in ischaemic flap tissue due to increas ed blood flow particularly in the randomly perfused tissue. (C) 1999 The Br itish Association of Plastic Surgeons.