CONDUCTION BLOCKS IN MAN ARE DEPENDENT ON THE STIMULATION FREQUENCY

The action of local anaesthetics on isolated nerves is enhanced by hig h stimulation frequencies. The aim of our study was to investigate whe ther high-frequency stimulation enhances regional anaesthesia in man. Methods. Seven healthy volunteers underwent three ulnar nerve blocks w hile non-noxious electrical stimulation with high (10, 50 Hz) or low ( 0.2 Hz) frequencies was applied via a widespread cutaneous electrode i n the area supplied by the ulnar nerve. Perception was monitored conti nuously by means of a visual analogue scale. Skin temperature (infrare d telethermometry) was evaluated every minute as an indicator of vasom otor block. After complete loss of perception or after 45 min, the spr ead of anaesthesia was determined by sharp-dull discrimination. The ne rve block was preceded by a control stimulation of 45 min under otherw ise identical conditions. Results. During stimulation with 10 and 50 H z, perception was lost significantly earlier than with 0.2 Hz. The spr ead of sensory block at the end of the experiments was also enhanced b y stimulation with high frequencies, whereas the onset of vasomotor bl ock (rise in skin tempeature) remained unaltered. Conclusion. Non-oxio us electrical stimulation with high frequencies significantly accelera tes the onset of anaesthesia and extends the spread of sensory block.