chapter 23 Anatomy for Venipuncture
Venipuncture is a technique separate and distinct from intravenous (IV) sedation. All health care professionals should become proficient with this route of drug administration whether IV sedation is practiced or not because the ability to establish an IV line may prove to be important in emergency situations.
Venipuncture is not a difficult technique to learn. Indeed, Malamed demonstrated that the initial attempt at venipuncture by untrained dental students had a greater than 90% success rate.1 However, proficiency requires practice. Once learned, knowledge of the technique remains with the dentist forever; yet because it is an acquired skill, if not used regularly, the level of the dentist’s ability will diminish.
In theory, venipuncture may be attempted in any superficial vein of a size sufficient to accommodate the needle. Figure 23-1 illustrates the major superficial veins in the human body. In practice, however, elective venipuncture is usually confined to one of the patient’s extremities. Either an arm or leg may be used. The usual preference is the arm, with the leg used when arm veins are inadequate or in emergency situations in which the arm may be unavailable or unsuitable for use.
IV sedation in the dental setting in an ambulatory patient is almost always an elective procedure. Selection of a venipuncture site will therefore usually be limited to one of the arms. Use of the leg for venipuncture is usually reserved for the infant or child, in whom arm veins are smaller and less superficial than in the adult, or the adult with a disability, in whom a venipuncture site in the foot may be more easily secured than one on the arm.
In this chapter, the anatomy of the circulation to the arm is described in detail. Both the venous circulation and the arterial circulation are discussed because it is necessary to be aware of those sites where anatomically important structures, such as arteries and nerves, lie in close proximity to veins. Knowing where not to attempt a venipuncture is valuable knowledge.
Blood to the right upper limb leaves the aortic arch through the short, wide brachiocephalic (innominate) trunk, which divides into the right common carotid and right subclavian arteries, the latter delivering arterial blood to the upper limb. On the left side, the subclavian artery is a direct branch of the arch of the aorta. From this point onward, the arteries of the two sides are symmetric.2
At the outer border of the first rib, the subclavian artery turns laterally to enter into the axilla. At this point, it is termed the axillary artery. The axillary artery leaves the axilla at the lower border of the teres major muscle to enter the arm or brachium as the brachial artery. Approximately 1 inch below the antecubital fossa, the brachial artery bifurcates into the radial and ulnar arteries (Figure 23-2), which travel distally in the forearm and terminate in the palm as an arterial arch. The ulnar artery forms the superficial palmar arch, which travels to the level of the web of the thumb, where it is completed by a small branch arising from the radial artery, the superficial palmar branch. The radial artery crosses the bottom of the so-called snuffbox (the hollow at the base of the thumb), reaching the dorsum of the hand and then entering the palm. There it forms the deep palmar arch, which is completed by a small branch from the ulnar artery, the deep palmar branch.
The location of these arteries has great clinical significance. Within the antecubital fossa, the brachial artery is commonly found beneath the median basilic vein, usually the most prominent vein in the antecubital fossa. The brachial artery is located just medial of the midline in the antecubital fossa and is the primary reason that the medial aspect of the antecubital fossa is low on my list of preferred venipuncture sites for the neophyte phlebotomist.
Approximately 2.5 cm (1 inch) below the antecubital fossa, the radial and ulnar arteries arise from the brachial artery. The radial artery lies on the lateral aspect of the ventral surface of the forearm, the ulnar on its medial aspect. Although it is not superficial at its origin, approximately 5% of the population does possess a recurrent radial artery, which is located on the lateral side of the antecubital fossa and is relatively superficial.
The radial artery continues down the ventral aspect of the forearm, not lying near the surface until it reaches the lateral aspect of the wrist, at the base of the snuffbox. At this point, on the ventral surface of the wrist, the radial artery is quite superficial. It is at this point that the radial pulse and arterial blood for blood gas analysis may be obtained. Care must be exercised whenever venipuncture is contemplated in this region. Fortunately, venous anatomy does not readily lend itself to venipuncture at this site.
The ulnar artery descends through the forearm lying more deeply within the tissues than does the radial. It lies on the medial aspect of the forearm, but at no point does it become superficial enough to be palpable.
The veins of the arm may be divided into two groups: deep veins and superficial veins. The deep veins, for the most part, accompany arteries within the fascial sleeve, whereas the superficial veins lie for most of their course outside the fascial sleeve.
Deep veins, except for the axillary veins, are arranged in pairs, one on either side of the various arteries. The axillary vein, which is a direct continuation of the basilic vein, crosses the axilla and becomes the subclavian vein at the outer border of the first rib. Its branches correspond to those of the axillary artery, except for the thoracoacromial, which joins the cephalic vein. The axillary vein receives the brachial veins in the lower portion of the axilla and the cephalic vein in the upper portion of the axilla. These deep veins will not be of significance in venipuncture.
Blood to the digits is drained through an anastomosis of palmar and dorsal digital veins. From the palmar aspect of the hand, most blood flows to the dorsum of the hand, especially through the intercapitular veins that lie between the heads of the metacarpal bones (aka knuckles) and around the margins of these heads. Blood from the digits and palm therefore drains primarily into the dorsal venous network on the back of the hand. Two major veins arise from this dorsal venous network. The cephalic vein arises from the radial aspect of this network, and the basilic vein rises from the ulnar side. These veins ascend the forearm, the cephalic on the lateral aspect, the basilic medially. Within the forearm, the median vein of the forearm arises and ascends the forearm on its medial aspect.
At the antecubital fossa, a number of veins, somewhat superficial, are usually visible. From lateral to medial are the cephalic vein, the median cephalic, the median vein, the median basilic, and the basilic. The cephalic vein continues upward through the clavipectoral fascia to drain into the axillary vein, and the basilic vein runs to the axilla, where it continues directly as the axillary vein.
Clinically the arm provides the phlebotomist with four distinct areas for venipuncture. At the upper part of the arm is found the antecubital fossa, which is discussed as two separate areas: (1) the medial aspect of the antecubital fossa and (2) the lateral aspect of the antecubital fossa. In our descent down the arm, the ventral aspect of the forearm is next, followed by the dorsum of the wrist and the dorsum of the hand. Each of these potential venipuncture sites presents its own advantages and disadvantages.
The dorsum of the hand is the preferred site for venipuncture of anesthesiologists (Figure 23-3). It has several distinct advantages over other sites and few disadvantages. It is one of my two preferred sites.
Anatomically, it is extremely rare to find arteries on the dorsal aspect of the hand; most arteries are located on its palmar aspect. In addition, most blood returning to the heart is routed into the veins/>