Is the Upper Shoulder Highly Vascular?
Yes, the upper shoulder region is highly vascular, containing major vessels including the subclavian artery and vein, and this vascularity creates significant risk for inadvertent intravascular injection of local anesthetics like lidocaine, which can cause immediate seizures if the drug enters the bloodstream directly.
Vascular Anatomy of the Upper Shoulder
The upper shoulder region contains critical large-caliber vessels that make it a highly vascular area:
The subclavian vein and artery traverse the upper shoulder region, representing major central vessels with high blood flow that can rapidly distribute injected medications systemically 1.
Inadvertent arterial puncture during procedures in this region carries significant hemorrhagic risk, as evidenced by guidelines recommending that insertion sites allowing easy vessel compression be chosen when coagulopathy is present, with femoral access sometimes preferred over subclavian approaches 1.
The Association of Anaesthetists guidelines specifically note that bleeding risks vary with anatomical site, with the subclavian region having higher complication rates including pneumothorax (0.3-2.3%, highest with subclavian route) and hemothorax from vascular trauma 1.
Clinical Significance for Lidocaine Injections
The high vascularity of the upper shoulder creates specific risks when administering local anesthetics:
Inadvertent intravascular injection of lidocaine causes immediate seizures through direct systemic absorption, as documented in multiple case reports where seizures occurred "immediately after injection" or "shortly after" lidocaine administration 2, 3.
Lidocaine concentrations above 15 μg/mL frequently result in seizures in both laboratory animals and humans, and intravascular injection bypasses normal tissue absorption, delivering toxic concentrations directly to the central nervous system 4, 5.
Seizures from lidocaine toxicity are almost invariably generalized tonic-clonic seizures without focal features, despite experimental models showing focal amygdala onset, suggesting rapid systemic distribution when vascular injection occurs 4.
Risk Mitigation Strategies
Given the high vascularity of the upper shoulder region:
Always aspirate before injecting lidocaine to detect intravascular needle placement, as the presence of blood return indicates vascular puncture requiring needle repositioning 1.
Use ultrasound guidance with color Doppler to visualize vascular structures before needle insertion in the upper shoulder region, as this significantly reduces the risk of vascular puncture 1.
Administer lidocaine slowly in divided doses rather than as a single bolus, as this allows early detection of systemic toxicity symptoms (perioral numbness, tinnitus, altered mental status) before full toxic dose is delivered 1.
Have immediate seizure management capabilities available, including IV benzodiazepines (lorazepam 0.1 mg/kg IV, maximum 4 mg at 2 mg/min) and airway equipment, whenever performing injections in highly vascular regions like the upper shoulder 6, 7.
Common Pitfalls
Assuming that aspiration alone is sufficient: Even with negative aspiration, the needle tip may migrate into a vessel during injection, so slow incremental injection with frequent re-aspiration is essential 1.
Underestimating the speed of systemic absorption: In highly vascular areas like the upper shoulder, intravascular injection causes seizures within seconds to minutes, not the 30+ minutes typical of tissue absorption 2, 3.
Failing to recognize that a history of seizures is NOT a contraindication to lidocaine use: The evidence shows that partial seizure history does not increase risk of lidocaine-induced seizures, as these are generalized and concentration-dependent rather than related to underlying seizure disorders 4.