A Comparison of 18-Gauge and 20-Gauge Short Peripheral Catheters in Terms of Pain and Procedural Difficulty: A Randomized Controlled Trial in the Emergency Department

Background and Objectives: Clinicians often default to the narrower short peripheral catheter (SPC), believing wider catheters to be more painful and harder to insert. One previous randomized trial found no difference, but it neither selected patients by measured access risk nor interpreted the result against a prespecified threshold of clinical importance. We conducted a confirmatory trial addressing both, comparing 18-gauge and 20-gauge SPCs in adult emergency department patients at low-to-moderate risk of difficult access. Materials and Methods: In a single-center, parallel-group superiority randomized controlled trial with 1:1 allocation (ClinicalTrials.gov NCT07629427), adults with an Adult Difficult Intravenous Access (A-DIVA) score from 0 to 3 were allocated to an 18-gauge or a 20-gauge SPC by block randomization. Patients were blinded by goggles until dressing, and the data analyst was also blinded. Co-primary outcomes were patient-reported pain and nurse-reported procedural difficulty on 100 mm visual analog scales immediately after the first attempt; first-attempt success was secondary. The trial was powered for a 13 mm difference in pain. Results: In total, 204 patients were randomized, 102 per group. Median pain was 32.5 vs. 30.5 mm (median difference 1 mm, 95% CI -4 to 6; p = 0.65) and median procedural difficulty was 12.0 vs. 15.0 mm (-1 mm, 95% CI -4 to 1; p = 0.28). The first attempt succeeded in 92.2% and 90.2% of patients (absolute risk difference 2.0 percentage points, 95% CI -5.8 to 9.7; p = 0.62); no prespecified subgroup showed a treatment interaction. Conclusions: In adults at low-to-moderate risk of difficult intravenous access, we did not detect a difference between 18-gauge and 20-gauge SPCs in terms of insertion pain, procedural difficulty, or first-attempt success, and the confidence interval for pain lay well within the minimum clinically important difference. Formal equivalence was not tested; the trial was designed to detect superiority. SPC size can therefore be chosen on the anticipated therapy rather than the expected discomfort.