Stellate Ganglion Block (SGB): Mechanism, Clinical Use, and Effects
Stellate Ganglion Block (SGB): Mechanism, Clinical Use, and Effects
The stellate ganglion block (SGB) is a medical procedure in which a local anaesthetic is injected around the stellate ganglion, a cluster of sympathetic nerves located in the neck, near the sixth and seventh cervical vertebrae (C6–C7). This ganglion, part of the sympathetic nervous system, regulates autonomic functions such as heart rate, blood flow, and sweating in the head, neck, upper chest, and upper limbs.
Clinical relationship with the vagus nerve
The stellate ganglion and the vagus nerve represent opposing but complementary branches of the autonomic nervous system.
The stellate ganglion mediates sympathetic “fight-or-flight” activity, while the vagus nerve governs parasympathetic “rest-and-digest” functions. For this reason, both stellate ganglion block (SGB) and vagus nerve stimulation (VNS) can influence mood, anxiety, and PTSD symptoms: but through opposite directions of autonomic modulation.
Their functional differences are summarised in the table below.
| Feature | Stellate Ganglion | Vagus Nerve (Cranial Nerve X) |
|---|---|---|
| System | Part of the sympathetic nervous system (“fight or flight”). | Part of the parasympathetic nervous system (“rest and digest”). |
| Location | Formed by fusion of the inferior cervical and first thoracic sympathetic ganglia, located at the base of the neck (C6–C7 level) in front of the vertebral transverse process. | Originates in the medulla oblongata of the brainstem and descends through the neck, thorax and abdomen to innervate major organs. |
| Main Function | Regulates sympathetic output: increases heart rate, constricts blood vessels, dilates pupils, and heightens alertness and blood flow to muscles. | Regulates parasympathetic output: slows heart rate, stimulates digestion, modulates inflammatory responses and emotional calm. |
| Type of Nerve Fibres | Contains post-ganglionic sympathetic neurones. | Contains mixed sensory and motor fibres with mostly preganglionic parasympathetic neurones. |
| Effect of Medical Intervention | Stellate Ganglion Block (SGB) reduces excessive sympathetic tone, dampening hyperarousal, pain, and stress-related vascular constriction. | Vagus Nerve Stimulation (VNS) increases parasympathetic signalling, promoting calmness, digestion, and autonomic regulation. |
| Clinical Relevance | Used to treat Complex Regional Pain Syndrome, PTSD hyperarousal, and vascular disorders. | Used to treat epilepsy, depression, inflammation and stress-related disorders. |
| Relationship Between Them | They are functionally complementary but anatomically distinct. The Stellate Ganglion is sympathetic; the Vagus Nerve is parasympathetic. Both influence autonomic balance and emotional regulation from opposite directions. | |
By temporarily inhibiting sympathetic nerve activity, an SGB modulates the body’s fight-or-flight response and can influence physiological arousal and emotional regulation. A successful block produces transient signs of sympathetic inhibition, including eyelid drooping (ptosis), pupil constriction (miosis), facial warmth, and nasal congestion, a constellation known as Horner’s syndrome, which confirms correct anaesthetic placement.
Procedure
The procedure is performed by an anaesthetist or pain specialist under ultrasound or fluoroscopic guidance to ensure precision and avoid vascular injury. After antiseptic preparation and local skin anaesthesia, a fine needle is inserted into the neck near the transverse process of C6 or C7, close to the stellate ganglion. Typically, 5–10 ml of local anaesthetic (e.g., lidocaine, bupivacaine, or ropivacaine) is injected.
The effects begin within minutes and last for several hours, though repeated blocks may have cumulative effects. Modern approaches often use image guidance to reduce risks such as inadvertent injection into blood vessels or the epidural space. The procedure generally takes 15–30 minutes, and patients are monitored for 30–60 minutes afterwards for safety and confirmation of block success.
Physiological Mechanism
Blocking the stellate ganglion interrupts sympathetic outflow to the head, neck, and upper thorax, producing a temporary shift toward reduced sympathetic activity and altered autonomic balance rather than true 'parasympathetic dominance'. This alters autonomic tone and is associated with reduced sympathetic signalling and may contribute to decreased central hyperarousal. Neuroimaging and functional MRI studies suggest that SGB can reduce activity in the amygdala, a brain region involved in fear and threat processing, thereby dampening exaggerated stress responses.
Because the stellate ganglion connects indirectly to limbic and hypothalamic circuits, SGB may modulate emotional reactivity, sleep patterns, and heart rate variability. The mechanism is therefore viewed as both autonomic and neuroendocrine, influencing systemic levels of adrenaline and cortisol through sympathetic inhibition.
Clinical Uses
SGB was originally developed for pain management, particularly in conditions involving sympathetic overactivity. Current clinical applications include:
- Complex Regional Pain Syndrome (CRPS) – to reduce neuropathic pain and vasospasm in the arm or hand.
- Post-traumatic Stress Disorder (PTSD) – to reduce hyperarousal, intrusive memories, and sleep disturbance by resetting autonomic balance.
- Hot flashes and menopausal symptoms – through modulation of sympathetic tone in thermoregulatory centres.
- Refractory angina – to reduce cardiac sympathetic drive and pain signalling.
Use in PTSD
Interest in SGB for Post-traumatic Stress Disorder has increased over the past decade, especially among veterans and first responders. The rationale is that hyperactivity in the sympathetic nervous system contributes to the persistent hypervigilance, anxiety and sleep disturbance characteristic of PTSD. By temporarily blocking sympathetic output, SGB appears to modulate autonomic regulation and reduce physiological hyperarousal in some individuals.
Several controlled and observational studies, including controlled trials from the US Department of Defense and VA research groups, have found that SGB can lead to a clinically meaningful reduction in PTSD symptom scores in approximately 70–80% of participants, often within days of the procedure. Improvements are most notable in anxiety, irritability, and sleep quality. The benefits may last from weeks to several months, and repeat injections can sustain the effect.
Functional imaging studies have shown that patients receiving SGB exhibit decreased activity in the amygdala and increased prefrontal cortical regulation, suggesting improved emotional control. However, while early results are encouraging, reviews by academic bodies such as the American Psychiatric Association caution that SGB remains an adjunctive treatment - not a substitute for psychotherapy or pharmacotherapy - until long-term, large-scale data are available.
Risks and Side Effects
SGB is generally well tolerated when performed by experienced clinicians. Common transient effects include:
- Temporary Horner’s syndrome (drooping eyelid, small pupil, facial warmth)
- Hoarseness or mild difficulty swallowing
- Localised neck soreness
- Light-headedness or tingling sensations
Serious complications are rare but can include intravascular injection, seizure (from anaesthetic toxicity), or pneumothorax if the needle passes too deeply. Modern image-guided methods have significantly reduced these risks.
Clinical Disclaimer: Stellate ganglion block is a medical procedure that must be performed only by trained and licensed clinicians. It is an adjunctive intervention that should not replace evidence-based psychiatric or psychological treatment. Patient suitability must always be determined by a qualified physician based on medical history and current clinical condition.