The superficial ulnar artery—a potential hazard in patients with difficult venous access

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Editor—Anatomical variations in the arterial supply of the upper limb pose a hazard for inadvertent intra-arterial cannulation and drug administration. Although the superficial radial artery (SRA) is most at risk, owing to its proximity to the cephalic vein, anaesthetists should be aware that other superficial variant arteries also exist. Here we report an unusual case of accidental intra-arterial cannulation occurring at a site other than the SRA.

A 53-yr-old former i.v. heroin addict presented for elective total hip replacement. I.V. access was known to be difficult, and was not established before arrival in the operating theatre. The patient underwent an inhalational induction with sevoflurane, and a prolonged search for a suitable vein in his upper limbs ensued. An invisible but palpable, non-pulsatile superficial vessel was eventually located in the right ventro-medial forearm. An 18-gauge i.v. cannula was successfully inserted, but upon release of the tourniquet, blood was observed to flow rapidly up into the i.v. fluid tubing. A diagnosis of intra-arterial cannulation was promptly made, and the cannula was removed. I.V. access was obtained in the left external jugular vein and the operation proceeded uneventfully. The patient suffered no sequelae as a result of the incident.

Identifying a superficial blood vessel as an artery or vein is not always easy, even for experienced anaesthetists. Although palpation has been recommended to distinguish one from the other,1 our experience and that of others suggests that the absence of pulsation is an unreliable sign.2 3 Partial occlusion of arterial flow by an applied tourniquet may be one reason for this. Once intra-arterial cannulation has occurred, indicators include pulsatile retrograde flow of blood, intense pain on injection of drugs and cutaneous signs of distal ischaemia. Early detection is also facilitated by awareness that an artery may be present and anaesthetists should be aware of the common patterns of anatomical variation. This has recently been reviewed.4 5

The artery cannulated here was likely to have been the superficial ulnar artery (SUA). The SUA arises from the axillary, brachial or superficial brachial arteries, and runs superficial to the superficial forearm flexor muscles on the ventro-medial aspect of the forearm. Like the SRA, the SUA is closely related to a major vein (basilic) throughout its course and hence is also at risk of unintended vascular puncture. From its origin, the SUA runs superficial to the median nerve, under the brachial fascia. It may pass either deep or superficial to the bicipital aponeurosis at the elbow. Thereafter, it usually runs beneath the deep antebrachial fascia of the forearm, but has also been observed to adopt a subcutaneous course in some individuals. It eventually comes to lie in its normal position between the ulnar nerve and the tendon of flexor carpi ulnaris, usually at the level of the mid-forearm.

The SUA is a more common anomaly than the SRA. In a large cadaveric survey, a SUA was observed in 3.75% (18/480) of specimens whereas a SRA occurred in only <0.2% (1/480).5 Although the ventro-medial aspect of the forearm is an uncommon site in which to attempt venipuncture, this may be required in patients with difficult venous access.

In summary, the SUA is the most commonly observed superficial aberrant artery in the forearm and hand, occurring in almost 4% of individuals. The absence of vessel pulsation on palpation is unreliable when attempting to differentiate between a superficial vein and artery. Hence, the possibility of inadvertent intra-arterial cannulation should be kept in mind whenever venipuncture is performed in the antecubital fossa or on the ventro-medial aspect of the forearm.

K. J. Chin and K. Singh

Singapore

References

1 Lirk P, Keller C, Colvin J, et al. Unintentional arterial puncture during cephalic vein cannulation: case report and anatomical study. Br J Anaesth 2004; 92: 740–2[Abstract/Free Full Text]

2 Duggan M, Braude BM. Accidental intra-arterial injection through an ‘intravenous’ cannula on the dorsum of the hand. Paediatr Anaesth 2004; 14: 611–12

3 Ghouri AF, Mading W, Prabaker K. Accidental intra-arterial drug injections via intravascular catheters placed on the dorsum of the hand. Anesth Analg 2002; 95: 487–91[Abstract/Free Full Text]

4 Rodriguez-Niedenfuhr M, Vazquez T, Nearn L, Ferreira B, Parkin I, Sanudo JR. Variation of the arterial pattern in the upper limb revisited: a morphological and statistical study, with a review of the literature. J Anat 2001; 199: 547–66[CrossRef][ISI][Medline]

5 Rodriguez-Niedenfuhr M, Vazquez T, Parkin IG, Sanudo JR. Arterial patterns of the human upper limb: update of anatomical variations and embryological development. Eur J Anat 2003; 7 (Suppl. 1): 21–8





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