Changes of Skin Resistance After Midazolam and After the End of Anaesthesia

Introduction Before anaesthesia, benzodiazepines are routinely used to reduce anxiety before anaesthesia and surgery. Usually anxiolysis is preferable to sedation, which may interfere with recovery after short procedures. Unfortunately, although anxiolytic sedatives are widely used in clinical practice, the methodology for assessing treatment effect of these compounds has not been well developed. Psychologic tests like the Hamilton Anxiety Rating Scale (HARS), the Wang Anxiety Rating Scale (WARS), or Zung Self-Rating Anxiety Scale (SAS) were used to assess changes in anxiety were developed for measuring effect of long-term therapy and are rather cumbersome and difficult to use in routine anaesthetic praxis.

More commonly used test in clinical perioperative use are the Ramsay sedation scale (RSS), the Richmond Agitation-Sedation Scale (RASS) and the Observer's Assessment of Alertness and Sedation scale (OAASS), but they focus mainly on level of sedation and not the level of anxiolysis. There are several reports demonstrating that there is a correlation between level of anxiety and changes in skin resistance.

Changes of skin resistance (SI) were first used in criminology in 1897 and in 1921 the method was used in criminology by August Larson together with changes of heart rate, respiratory rate and blood pressure for construction of polygraph. This method was many times validated and polygraph is still used as a "lie detector". More recently sever studies appeared demonstrating correlation between changes of skin resistance and sedation grade, bispectral index, reaction to stimulation, pain and motor activity.

The present double-blinded study was designed to refine methodology for objective evaluating effect of sedative and anxiolytic agents. The primary aim of our study was to examine if of changes in skin resistance after placebo pre-screening can be used for objective assessment of an anxiolytic effect of drugs compared to commonly used subjective scales like Ramsay sedation scale (RSS), or The Richmond Agitation-Sedation Scale (RASS) and Observer's Assessment of Alertness and Sedation scale(OAASS). The secondary aim was to evaluate if changes of skin resistance can be used for assessing recovery from anaesthesia.

Patients The study was performed in adult patients scheduled for knee arthroscopy or minor plastic surgery under general anaesthesia. Consent was obtained the day before surgery during pre-anaesthetic visit. Exclusion criteria were previous history of taking drugs affecting mental functions, history of psychic illness, implanted electrical device, know allergy to benzodiazepines, myasthenia gravis, ASA classification ASA 3 and more. All patients consented not to use any medication for sedation or anxiety, opioid analgesics, ethanol and illicit drugs 24 hours before surgery. Patients were instructed that they will be administered by a random order first sedative agent or placebo and will be observed for their level of sedation.