Does the resistive index of the radial artery change after arterial cannulation in patients undergoing abdominal surgery? A prospective observational study.

Background and aims: To evaluate the flow at the cannulation site in the radial artery, the resistive indices (RIs) before cannula insertion and 6 h after decannulation were measured (primary outcome). The secondary outcomes were measurement of the artery size by anteroposterior (AP) diameter at the insertion site, RI and AP diameter at a point 4 cm proximal and in the ipsilateral ulnar artery before insertion and 6 h after cannula removal.

Methods: In 96 patients requiring an arterial line during surgery, peak systolic velocity (PSV) and end-diastolic velocity (EDV) were measured to derive RI using a linear ultrasound transducer. The RI was measured at R1 (insertion point), R2, 4 cm proximal to R1, and U1 on the ipsilateral ulnar artery. The AP diameter of the arteries at baseline R1₀, R2₀ and U1₀ was measured and repeated 6 h after removal of the cannula, R1₆, R2₆ and U1₆.

Results: RI or AP diameter in R1 or R2 did not differ pre- and post-cannulation. Mean R1₀ 1.143 [standard deviation (SD: 0.239)] versus R1₆ 1.181 (SD: 0.260) m/sec [mean difference (MD): -0.0372 (95% confidence interval (CI): -0.098, 0.023), P = 0.230]. Mean AP diameter at baseline versus 6 h decannulation 0.177 (SD: 0.042) versus 0.172 (SD: 0.045) cm [MD: 0.005 (95% CI: 0.003, 0.013), P = 0.222] was also similar. The mean PSV in U1₀ versus U1₆ was higher: 0.480 (SD: 0.178) versus 0.528 (SD: 0.316) m/sec [MD: 0.120 (95% CI: -0.185, -0.054), P = 0.002] and AP diameter was also higher than baseline (P = 0.001).

Conclusion: The flow in the radial artery did not change following cannulation. The PSV and AP diameter in the ulnar artery increased after decannulation, suggesting a compensatory increase in flow.