A Pilot Study to Assess the effects of Propofol on Patient Reaction Time.

 

Chapman R, Anderson K, Kenny GNC.

University Department of Anaesthesia, Glasgow Royal Infirmary, Glasgow.

 

Background and Goal of Study Previous studies on patient maintained propofol sedation by this group demonstrated that patients are capable of over sedating themselves (1). In this study we assessed the feasibility of using patient reaction time as part of a safety feedback loop to prevent over sedation.

 

Materials and Methods 10 patients were recruited. propofol was administered using an effect-site target controlled infusion. The patients were given a handset with a push button, the handset vibrated and the patients pressed the handset button in response to vibration. Reaction time, sedation scores and the corresponding effect site concentration were recorded. Sedation was commenced at an effect site of 1.0mcg.ml^-1 and was increased in a stepwise fashion. Measurements of reaction time were made after each increment.

 

Results All 10 patients completed the study. The mean effect-site concentration achieved prior to being unable to respond with a button push was 2.41mcg.ml^-1 (standard deviation 0.6). At the point where there was no response with a button push none of the patients had lost verbal contact. Fig 1 shows reaction time against effect site for the 10 patients.

 

Conclusions This study demonstrates that increasing the effect site concentration of propofol leads to an increase in reaction time that becomes markedly prolonged just prior to the patient being unable to respond with a button push. The mean effect-site concentration achieved prior to failure to respond to the vibration was higher than the level required for dental sedation (2). Reaction time appears to be more sensitive than sedation scoring as a tool for preventing over sedation. Further studies are required to confirm if reaction time could be utilized in a safety mechanism in patient maintained sedation.

 

    

Fig 1

 

 

 

References

1.        Anderson KJ, Leitch JA, Green JS, Kenny GN. Effect-site controlled patient maintained sedation: a volunteer safety study. Anaesthesia 2005; 60: 235-8.

2.        Leitch JA, Sutcliffe N, Kenny GN. Patient-maintained sedation for oral         surgery using a target-controlled infusion of propofol – a pilot study. British Dental Journal 2003; 194: 43-5.