Objective To investigate the appropriate venous access for obese patients undergoing metabolic and bariatric surgery by comparing the clinical outcomes of different lengths of peripheral intravenous catheters.Methods Inpatients who underwent bariatric surgery in a tertiary hospital in Zhejiang from August 2022 to December 2022 were selected as the study population using a fixed-point continuous convenience sampling method.A stratified block randomisation method was used to divide the group into an experimental group 1(mini-midline catheters),an experimental group 2(midline catheters)and a control group(short peripheral intravenous catheters,Short PIVCs).The incidence of catheter-related complications,the rate of extubation due to complications,the duration of catheter retention,the time to first catheter-related complication were compared in the 3 groups.Results A total of 186 patients were included,with 62 patients in each group.The overall incidence of catheter-related complications in experimental group 1,experimental group 2,and control group were 25.81％,8.06％,and 58.06％.The extubation rates due to complications were 19.35％,4.84％,and 41.94％,and the duration of catheter retention was 7.00(6.00,7.00)d,7.00(6.00,7.00)d,6.00(3.00,6.25)d.The differences were statistically different(P＜0.05)when comparing the 3 groups.Among them,the differences in the overall incidence of catheter-related complications and the rate of extubation due to complications were statistically significant when comparing experimental group 1 with the control group,experimental group 2 with the control group,and experimental group 1 with experimental group 2(P＜0.017);the duration of catheter retention in both experimental group 1 and experimental group 2 were higher than it in the control group,and the differences were statistically different(P＜0.017).Conclusion The complication rate of mini-midline catheters and midline catheters is lower than that of short ones,and the indwelling time is consistent with the perioperative period of metabolic and bariatric surgery,which is suitable for use in patients undergoing metabolic and bariatric surgery.