Ultrasound-Guided Peripheral Intravenous Access Using Different Vein-Selection Strategies in Difficult Emergency Department Patients: A Systematic Review

Ultrasound guidance has become the reference approach to peripheral intravenous cannulation in emergency department (ED) patients with difficult intravenous access (DIVA), yet the single decision that ultrasound uniquely enables -which vein to choose -remains poorly codified.This review synthesises primary evidence on how vein-selection strategies influence cannulation success and catheter longevity.Four databases were searched from inception to 30 June 2026 for original studies of adult ED patients with DIVA in whom a target-vein selection variable (anatomical site, sonographic depth, sonographic diameter, or catheter-to-vein geometry) was related to an access outcome.Study selection, extraction and risk-of-bias assessment using Risk Of Bias In Non-randomised Studies of Interventions (ROBINS-I) were performed in duplicate.Findings were synthesised narratively; meta-analysis was not appropriate.Ten studies (1,952 patients or cannulation encounters) met the criteria.Larger vessel diameter predicted insertion success, but no statistically significant association with longevity was detected in the single study that examined it.Increasing vessel depth was consistently associated with poorer catheter survival in the three cohorts that examined longevity, with a threshold near 1.2 cm, and limited insertion success beyond approximately 1.5-1.6 cm in two further studies.Deep proximal upper-arm veins delivered the highest firstpass success but the poorest durability, while forearm and antecubital targets showed the reverse.Three of four studies found that maximising the intraluminal catheter length -a direct consequence of vein choiceprotected against premature failure.Overall risk of bias was low in four studies, moderate in two and serious in four.Vein selection appears to be a modifiable determinant of both obtaining and retaining peripheral access in DIVA patients, and the optimal target differs according to whether the immediate priority is cannulation or dwell time.A prospectively validated, sonographically anchored selection rule has yet to be tested, and the thresholds identified here, which derive from separate cohorts, should be regarded as an evidence-informed approach pending prospective validation rather than a clinical decision rule.