What are the central nervous system (CNS) toxicities of a Stellate Ganglion Block?

CNS Toxicity of Stellate Ganglion Block

The primary CNS toxicity of stellate ganglion block is convulsions resulting from inadvertent intra-arterial injection of local anesthetic, with retrograde flow delivering high concentrations directly to the cerebral circulation. 1, 2, 3

Mechanism of CNS Toxicity

The stellate ganglion block carries unique CNS toxicity risks due to its anatomical location in the head and neck region. Small doses of local anesthetics injected during stellate ganglion blocks can produce adverse reactions similar to systemic toxicity seen with unintentional intravascular injections of larger doses 1. These reactions occur due to intra-arterial injection with retrograde flow to the cerebral circulation, delivering concentrated local anesthetic directly to the brain 1, 3.

The severity of CNS toxicity depends on the concentration of local anesthetic presented to the brain, not just the total dose administered. 3

Specific CNS Manifestations

Acute CNS Toxicity Symptoms

The CNS toxicity from stellate ganglion block presents in a characteristic progression:

• Early warning signs include restlessness, anxiety, tinnitus, dizziness, blurred vision, tremors, depression, or drowsiness 1
• Severe manifestations include confusion, agitation evolving to frank seizures, convulsions, CNS depression, respiratory depression, and/or respiratory arrest 4, 1, 2
• Cardiovascular effects may accompany CNS toxicity, including cardiovascular stimulation or depression 1

The incidence of severe CNS complications from stellate ganglion block is approximately 1.7 per 1000 blockades, with convulsions being the most common severe complication 2.

Clinical Context and Risk Factors

Why Stellate Ganglion Block Has Higher CNS Risk

Unlike peripheral nerve blocks that are not expected to exacerbate hemodynamic instability 4, stellate ganglion blocks pose unique risks because of their proximity to major cerebral vessels. The vertebral artery lies in close proximity to the injection site, making inadvertent intra-arterial injection a constant risk 5, 2.

Even with negative aspiration tests and test doses, proper administration is not guaranteed, as aspiration for blood can be negative despite intravascular needle placement. 1, 2

Management of CNS Toxicity

Immediate Response Protocol

When CNS toxicity occurs during stellate ganglion block:

• Ensure resuscitative equipment and personnel are immediately available for treating adverse reactions 1
• Monitor circulation and respiration constantly during and after the procedure 1
• Have oxygen and other resuscitative drugs available for immediate use 1
• Administer intravenous lipid emulsion (ILE) therapy for severe local anesthetic systemic toxicity, as higher doses can improve outcomes 4, 5

The American Heart Association guidelines support ILE administration for cardiac arrest resulting from local anesthetic toxicity, as it creates a lipid compartment in the serum that reduces the concentration of lipophilic medications in tissues by sequestration 4.

Prevention Strategies

Essential Safety Measures

To minimize CNS toxicity risk during stellate ganglion block:

• Place an intravenous line before the procedure (recommended by 72% of surveyed departments) 2
• Use ECG monitoring routinely (recommended by 28% of departments, though this should be higher) 2
• Perform aspiration tests before injection (universally recommended) 1, 2
• Administer a test dose of 0.5-2 mL local anesthetic before full injection 2
• Have an assistant present during the procedure (73% of departments follow this practice) 2
• Keep anticonvulsant drugs immediately available 2
• Use ultrasound guidance to improve feasibility and safety 6

Dosing Considerations

Use the lowest dosage that results in effective anesthesia to avoid high plasma levels and serious adverse effects. 1 Repeated doses of local anesthetic may cause significant increases in blood levels with each dose due to slow accumulation 1.

Common Pitfalls to Avoid

• Do not rely solely on aspiration tests to confirm proper needle placement, as they can be falsely negative 1, 2
• Do not proceed without continuous monitoring of cardiovascular and respiratory vital signs and the patient's state of consciousness 1
• Do not ignore early warning signs such as restlessness, anxiety, or tinnitus, as these may herald impending severe CNS toxicity 1
• Do not perform stellate ganglion block without immediate access to resuscitation equipment, including equipment for intubation and ventilation 2

Additional Considerations

While stellate ganglion block is contraindicated or not recommended for routine long-term treatment of non-CRPS neuropathic pain 4, it may be used as a component of multimodal treatment for CRPS when there is consistent improvement and increasing duration of pain relief 4, 7. However, the CNS toxicity risks remain constant regardless of the indication.