Abstract Background Bronchoscopy can be a distress for the patient. There have been few studies on the combination of sedatives and opioids. The aim of this study was to demonstrate the usefulness and safety of administration of the combination of midazolam and pethidine during bronchoscopy. Methods In this prospective randomized single (patient)-blind study, we randomly assigned 100 patients who were scheduled to undergo bronchoscopy biopsy to receive treatment with either the midazolam/pethidine combination (combination group) or midazolam alone (midazolam group) during examinations. After the end of bronchoscopy, patients completed a questionnaire and the visual analogue scale was measured. The primary outcome was the patients’ acceptance of re-examination assessed by visual analogue scale. We also assessed pain levels, vital signs, midazolam use, xylocaine use, and adverse events. Univariate analyses were performed using Fisher’s exact test for categorical data, and the t-test or Mann-Whitney test was carried out for analysis of numeric data. All P-values were two-sided, and values < 0.05 were considered statistically significant. Results We analyzed 47 patients in the combination group and 49 patients in the midazolam group. The primary outcome was a good trend in the combination group, but not significantly different (3.82 ± 2.3 in combination group versus 4.17 ± 2.75 in midazolam alone, P = 0.400). In the combination group, the visual analog scale score for pain during bronchoscopy was significantly lower (1.10 ± 1.88 versus 2.13 ± 2.42, P = 0.022), and the sedation level score per the modified observer’s assessment of alertness/sedation scale was significantly deeper (3.49 ± 0.98 versus 3.94 ± 1.03, P = 0.031). Maximal systolic blood pressure during testing was significantly lower (162.39 ± 23.45 mmHg versus 178.24 ± 30.24 mmHg, P = 0.005), and the number of additional administrations of midazolam was significantly lower (2.06 ± 1.45 versus 2.63 ± 1.35, P = 0.049). There were also significantly fewer adverse events (30 versus 41, P = 0.036). Conclusions The combination uses of midazolam and pethidine for sedation resulted in significant improvements in the pain, blood pressure, additional use of midazolam, and safety during bronchoscopy among patients. Trial registration This study was registered in the University Medical Hospital Information Network in Japan (UMINCTR Registration number: UMIN000032230 , Registered: 13/April/2018).
