Intravascular Injections

Ultrasound guidance for regional blocks appears to reduce but not eliminate the vascular puncture risk. This is similar to what has been reported for ultrasound guidance for other interventions.¹

Small-volume test injections (0.5-1 mL) are useful for detecting intravascular injections.² If the injection is not visualized, it should be stopped immediately. It is best to presume intravascular injection or some other adverse event.

Systemic toxicity of local anesthetics is probably reduced with ultrasound guidance for several reasons. First, evidence suggests that regional blocks can be performed with lower volumes of local anesthetic. Second, the chance of vascular puncture by the needle tip is less. Third, it is possible to recognize intravascular injection. This detection occurs dynamically online (effectively in real time at frame rates >30 frames per second).

Despite this favorable safety profile, intravascular injection with systemic toxicity has been reported with ultrasound guidance.^3,4 Another concern is that probe compression may prevent detection of intravenous injection by collapsing the vein after puncture.⁵ It is difficult to assess the incidence of these problems from case reports, but these events are likely uncommon and primarily relate to limitations in needle tip visibility. Vascular puncture rates reported from clinical studies of ultrasound-guided regional blocks are listed in Table 63-1.^6–11

FIGURE 63-1 Ultrasound detection of intra-arterial injection of local anesthetic. The axillary artery is shown in short-axis view before (A) and after (B) injection of local anesthetic for out-of-plane axillary block.