Context and outcomes in distal radial artery sampling: A comparative perspective

Dear Editor,

We read with great interest the rigorous randomized trial by Sharma et al. comparing anatomical snuffbox (ASB) and distal forearm (DF) approaches for arterial blood gas (ABG) sampling in the emergency department (ED). ¹ Their finding that ASB did not meet non-inferiority criteria (first-pass success: 60.7% vs 74.7%, p = 0.006) provides important evidence for clinical practice.

We wish to offer complementary perspectives based on recent ICU-based randomized trials (n = 180 and n = 197, respectively)^2,3 conducted by our research group, comparing distal radial artery access (DRA; anatomically corresponding to ASB) with conventional radial access. Three considerations merit discussion: clinical context, non-inferiority margin interpretation, and hemostasis efficiency.

First, clinical setting significantly influences performance. These trials^2,3 achieved a first-pass success rate of 77.8% for ASB versus 80.0% for conventional radial access (p = 0.72), substantially exceeding the 60.7% ASB success rate observed by Sharma et al. in the ED. ¹ While the anatomical challenges of a smaller-caliber artery with a more tortuous course in the anatomical snuffbox are undeniable, this discrepancy likely reflects environmental factors rather than inherent technique limitations. The ICU setting offers more controlled conditions and adequate time for meticulous palpation, whereas the time-pressured ED environment may compromise the precision this technique requires. Notably, both studies implemented standardized operator training—Sharma et al. required ⩾25 successful ABG samples via each approach plus a 10-procedure simulation audit, while operators in our trials completed >20 supervised DRA procedures during pre-experimental training. Despite comparable training thresholds, differences in operator volume and continuous DRA exposure across clinical settings may have contributed to the observed discrepancy in first-pass success rates.

Second, non-inferiority margin selection fundamentally shapes conclusions. Sharma et al. employed a stringent −5% margin and observed a −14.0% difference (95% CI: −23.5% to −4.5%). ¹ Our study used a −15% margin—chosen to reflect clinically acceptable trade-offs when vessel preservation is valued—and observed a mean difference of −2.2% (95% CI: −14.1% to 9.7%). ² This highlights a key methodological question: What performance difference in first-pass success is acceptable when balanced against benefits in other outcome domains such as hemostasis efficiency and vessel preservation? The field would benefit from consensus on appropriate margins for vascular access procedures, considering multiple outcomes beyond initial success rates.

Third, hemostasis efficiency is a critical but often overlooked patient-centered outcome. Sharma et al.’s study did not measure hemostasis time. In our ABG sampling trial, ² the ASB approach dramatically reduced post-procedure compression time: 86 ± 16 versus 215 ± 36 s (p < 0.001). Our parallel arterial catheterization study demonstrated similar benefits: 224 ± 55 versus 418 ± 71 s (p < 0.001). ³ This consistent 50%–60% reduction translates to substantial clinical benefits: reduced patient discomfort during manual compression, decreased nursing workload, faster patient mobilization, and potentially lower risk of compression-related nerve injury. For patients requiring serial ABG analyses—common in both ED and ICU settings—these time savings accumulate significantly. We strongly recommend that future comparative studies of arterial access sites include hemostasis time as a co-primary endpoint.

Finally, neither trial formally assessed procedural pain or patient comfort—ours because ICU patients were largely sedated or had altered consciousness. This represents a unique opportunity for ED-based research, where alert patients enable patient-reported outcome assessment. We encourage Sharma et al. or other ED investigators to incorporate validated pain scales in future studies.

In conclusion, while we concur that the ASB approach presents technical challenges—particularly in time-pressured ED settings—our ICU-based data suggest it remains a viable option when multiple outcome domains are considered. The optimal arterial access site likely varies based on clinical context, patient characteristics, and outcome prioritization. Rather than universal recommendations, evidence-based, context-dependent approaches may better serve diverse patient populations.