The ulnar artery: A site suitable for arterial cannulation in pediatric patients.

Background: Historically, the ulnar artery has rarely been considered for arterial cannulation as it is less easily palpated than the radial artery. With the current routine use of ultrasound in pediatric patients, the ulnar is as accessible as the radial and could be viewed as an equivalent site for cannulation.

Aims: The purpose of this study was to compare ulnar and radial artery suitability for arterial cannulation in pediatric patients using 2-dimensional ultrasound.

Methods: We examined the ulnar and radial arteries of pediatric patients aged birth to 6 years who were scheduled to undergo general anesthesia. Following anesthesia induction, the investigators positioned the patient's wrist to 30-45 degrees of extension and obtained images of the ulnar and radial arteries in the transverse and longitudinal planes. Assessments of the arteries' anterior-posterior diameter, cross-sectional area and depth were made by visual inspection at the time of image acquisition and by electronic caliper measurement of recorded images.

Results: In 108 patients, mean anterior-posterior diameter of the ulnar artery was larger than the radial artery in the transverse view, longitudinal view, and cross-sectional area in 63.6%, 59.4%, and 60.4% of patients (p = .002, .004, and .006, respectively). Mean ulnar artery size was, on average, larger than the radial artery by 7.7%, 8.1%, and 12.9% in the transverse AP diameter, longitudinal AP diameter, and cross-sectional area (95% CI 3.1-12.4%; 3.2-13.0%; 4.4-21.5%). The investigator's visual evaluation of vessel size at the bedside showed substantial agreement with the measured cross-sectional area (linear-weighted kappa of 0.73). In a subset of 13 patients age <24 months, the mean depth of the ulnar artery was 2.13 mm compared to 1.65 mm for the radial artery (difference -0.48 mm 95% CI 1.08-0.12).

Conclusions: The ulnar artery was larger than the radial artery in 60% of pediatric patients thus may offer an arterial cannulation site advantage due to its larger size. The use of 2-dimensional ultrasound examination allows accurate assessment of upper extremity distal arteries in order to optimize site selection for arterial cannulation in pediatric patients.