Intravascular injection during ultrasound-guided axillary block: negative aspiration can be misleading

Needle visualization is an advantage of ultrasound-guided nerve blocks compared to traditional methods of nerve localization. However, visualization of local anesthetic spread is also important. During an ultrasound-guided axillary block, there was negative aspiration for blood. However, the absence of local anesthetic spread on ultrasound imaging suggested possible intravascular injection. The ultrasound transducer was removed from the patient's arm and venous blood was aspirated from the nerve block needle. Pressure applied to an ultrasound transducer can occlude venous structures making negative aspiration of blood unreliable for excluding intravascular needle placement.