Background and Aims The ideal agent for subarachnoid anaesthesia is still a matter of research. Subarachnoid administration of pethidine hydrochloride has been successfully administered (dose of 1mg/kg^-1).This study aims to assess the efficacy of low dose of pethidine hydrochloride (0.4mgkg^-1) compared to administration of ropivacaineand fentanyl which is nowadays the common practice.

Ethical approval has been granted by the ethics committee.

Methods Patients undergoing transurethral resection of bladder tumor were blindly randomly allocated into 2 groups. Group I patients received low dose of pethidine hydrochloride (0,4mgkg^-1) and Group II patients received 15mg ofropivacainewith 15 mcg of fentanyl.Catheter-related bladder discomfort (CRBD) was evaluated.

Results 101 patients were enrolled in the study. There was no difference between the demographic profile and duration of operation between the groups(p >0.05).There was a difference regarding the motor block which was present only in 10,2% of Group I patients and in all of Group II patients (p<0,01). Length of stay in postanaesthesia care unit was significantly higher in Group II patients (p<0,01) with no difference in adverse events. No difference in analgesic requirements was observed for postoperative pain management in either group yet there was a significant difference in time to postoperative analgesic administration(p<0,01) in favor of Group I patients.The incidence of CRBD was 36,7% in Group I and 78,8% in Group II.

Conclusions Subarachnoid anaesthesia with low dose pethidine administration presents as a suitable alternative to current practice.