Sir: Having abandoned the use of electrolyte solution in favour of gel, our local monitoring and recording systems showed a marked increase in impedance. Despite adequate skin preparation and electrode placement and the use of greater mechanical pressure in the application of the electrodes, impedance levels remained higher by a factor of approximately times four compared to previous levels.

As impedance provides a measure of the resistance to current flow from the electrode to the patient, the change in method (and hence impedance) is likely to necessitate a significant increase in the current required for effective treatment (Royal College of Psychiatrists, 1995).

In addition, increased side-effects may be a result. The two patients treated during the cross-over period complained of significantly more side-effects of headache, memory impairment and general feelings of ‘unwellness’ when the impedance levels rose.

For the time being, in the absence of better evidence, we have chosen to return to the use of pads and electrolyte solution for the comfort of our patients.