Nitrous oxide (entonox) inhalation and tolerance of transrectal ultrasound guided prostate biopsy: A double-blind randomized controlled study

Purpose: We performed a randomized, placebo controlled double-blind trial to evaluate the effectiveness of Entonox (BOC Gases, Manchester, United Kingdom), that is 50% nitrous oxide and oxygen, as analgesia during transrectal ultrasound guided prostate biopsy. Materials and Methods: Patients referred for transrectal ultrasound guided prostate biopsy for the first time as an outpatient procedure were recruited subject to exclusion criteria and randomized to breathe Entonox or air via similar breath activated devices. At the end of the procedure patients completed a visual pain analog scale. Patients who refused study participation also completed the visual analog pain scale to assess the placebo effect of receiving gas through a mask. Results: A total of 110 patients were studied. Statistical analysis using 1-way analysis of variance showed a highly significant difference in pain perception among the 3 groups (F [2,107] = 73.348, p < 0.001). This significant decrease in pain was noted in the Entonox versus air and Entonox versus placebo groups. There was no significant difference in the air and placebo groups. Seven of the 51 patients receiving Entonox complained of feeling drowsy during the procedure, which resolved at completion of the procedure. In this group 49 patients would undergo this procedure again if needed. In 2 of the 45 patients in the group receiving air the procedure was abandoned due to pain, while another 19 would prefer more analgesia and 2 would prefer general anesthesia if the procedure was to be repeated. Conclusions: Our study shows that Entonox is a safe, rapidly acting and effective form of analgesia for the pain of prostate biopsy. We believe that it should be the analgesia of choice for this procedure.