Extra Topic 2.7 -- Stellate Ganglion Block (Local Anesthetic Toxicity)

Question 1

What is your differential diagnosis?

(Shortly after receiving a stellate ganglion block with bupivacaine, a 28-year-old female patient is noted to have difficulty speaking and reports dizziness, difficulty swallowing, and shortness of breath.)

Answer 1

Given the symptomatology described,

the most likely cause of the patient’s distress is –

local anesthetic toxicity secondary to unintentional vascular injection

(since the presentation of local anesthetic toxicity is extremely variable in onset and initial symptomatology, this complication should be considered in any situation where a patient experiences an altered mental state, neurologic symptoms, or cardiovascular instability following the administration of local anesthetic for regional anesthesia).

Other potential causes and/or contributing factors of his symptomatology include:

1. paralysis of the recurrent laryngeal nerve, which is located near the stellate ganglion (would result in hoarseness);
2. pneumothorax could lead to respiratory distress and hypotension (the latter occurring with a tension pneumothorax); and
3. accidental epidural or subarachnoid injection could result in this symptomatology before progressing to loss of consciousness and apnea.

Clinical Notes:

• Classically, the signs and symptoms of local anesthetic toxicity progress in the following manner –
  
  • Nonspecific neurologic symptoms = metallic taste, circumoral paresthesias, tongue numbness, visual disturbances (i.e. blurred vision and difficulty focusing), auditory disturbances (i.e. tinnitus), lightheadedness, dizziness, and a feeling of “impending doom”
  • CNS excitation = agitation, shivering, muscle twitching, tremors of the face and distal extremities, and tonic-clonic convulsions
  • CNS depression = resolution of seizure activity, respiratory depression, loss of consciousness, coma, and respiratory arrest
  • Cardiovascular depression = hypotension, bradycardia, ventricular dysrhythmias, and cardiovascular collapse

Question 2

Assuming this were local anesthetic toxicity,

what would you do?

(Shortly after receiving a stellate ganglion block with bupivacaine, a 28-year-old female patient is noted to have difficulty speaking and reports dizziness, difficulty swallowing, and shortness of breath.)

Answer 2

Assuming the effects were secondary to vascular uptake of local anesthetic, I would:

1. call for help and a lipid rescue kit;
2. ensure adequate ventilation and oxygenation to correct and/or avoid factors that enhance the systemic toxicity of local anesthetics, such as –
   
   • hypercarbia (increased cerebral blood flow, intra-neuronal ion trapping of the drug, and decreased plasma protein binding of the drug),
   • acidosis (decreased plasma protein binding of the drug), and
   • hypoxemia;
3. administer a benzodiazepine to stop the seizure
   
   • (seizure activity increases metabolism, which may lead to hypoxemia, hypercarbia, and acidosis);
4. administer succinylcholine and intubate her if –
   
   • ventilation were inadequate,
   • the risk of aspiration was significant (history of GERD or hiatal hernia), or
   • if tonic-clonic movements persisted despite benzodiazepine administration (succinylcholine would minimize the metabolic acidosis associated with seizure-induced muscle activity, it would not, however, affect the acidosis that develops secondary to seizure-induced increases in cerebral metabolism);
5. alert the nearest facility with cardiopulmonary bypass capability; and
6. treat hypotension, bradycardia, and dysrhythmias as indicated
   
   • (avoid procainamide, lidocaine, B-blockers, vasopressin, and calcium channel blockers when treating bupivacaine-induced cardiac arrhythmias).
7. Moreover, I would – initiate lipid emulsion therapy if –
   
   • the signs and symptoms of local anesthetic toxicity appeared to be rapidly progressing,
   • she experienced prolonged seizure activity, or
   • she developed signs of cardiac toxicity (i.e. bradycardia, heart block, hypotension, asystole, or ventricular arrhythmia).
8. Finally, if the patient did not respond adequately to these therapies, I would – consider utilizing cardiopulmonary bypass to provide “bridging” therapy until her tissue levels of local anesthetic were no longer toxic.

Clinical Notes:

• Lipid Emulsion Therapy Dosing:
  
  • Bolus 1.5 mL/kg of 20% lipid solution over 1 minute (roughly 100 mL in adults) and start a continuous infusion at 0.25 mL/kg/minute.
  • If cardiovascular instability persists after 5 minutes, repeat the bolus and double the infusion rate.
  • Maintain the infusion for at least 10 minutes after attaining circulatory stability.
  • The recommended upper limit for initial lipid dosing is approximately 10 mL/kg over 30 minutes.

Question 3

The patient progresses to asystole. What would you do?

(Shortly after receiving a stellate ganglion block with bupivacaine, a 28-year-old female patient is noted to have difficulty speaking and reports dizziness, difficulty swallowing, and shortness of breath.)

Answer 3

I would immediately:

1. start chest compressions,
2. call for a defibrillator (in case a shockable rhythm developed during resuscitation),
3. secure the airway with an endotracheal tube, and
4. provide 100% oxygen.
5. Next, I would – attempt to confirm true asystole (make sure all cables are connected properly, ensure adequate monitor gain, check another lead, check for pulse – very fine ventricular fibrillation can look like asystole),
6. initiate lipid emulsion therapy (if not already done),
7. administer a 1 mcg/kg intravenous bolus of epinephrine, recognizing that higher doses of epinephrine have been associated with poorer outcomes in the setting of bupivacaine-induced asystole (epinephrine is highly arrhythmogenic and may reduce the efficacy of lipid emulsion therapy), and
8. correct any potential contributing factors, such as hypoxia, hypercarbia, and acidosis.
9. I would then – continue to monitor the patient for the development of a shockable rhythm,
10. notify the nearest facility with cardiopulmonary bypass capabilities, and
11. consider pacing her on bypass if she remained inadequately responsive to these interventions.

Question 4

Would you consider administering vasopressin in place of additional doses of epinephrine?

(Shortly after receiving a stellate ganglion block with bupivacaine, a 28-year-old female patient is noted to have difficulty speaking and reports dizziness, difficulty swallowing, and shortness of breath.)

Answer 4

While vasopressin is normally an acceptable alternative to epinephrine in the treatment of asystole,

I would NOT administer it in this case because in animal studies it has been associated with – poor outcomes and pulmonary hemorrhage in the setting of local anesthetic toxicity.

Therefore, if she did not respond adequately to the first dose of epinephrine, I would –

• administer additional doses of epinephrine and/or
• consider pulmonary bypass.

Question 5

What are the most important factors affecting systemic absorption of local anesthetic?

(Shortly after receiving a stellate ganglion block with bupivacaine, a 28-year-old female patient is noted to have difficulty speaking and reports dizziness, difficulty swallowing, and shortness of breath.)

Answer 5

The most important factors affecting systemic absorption of a local anesthetic include:

1. the amount of blood flow at the site of injection (intravenous > tracheal > intercostal > caudal > paracervical > epidural > brachial plexus > sciatic/femoral > subcutaneous),
2. the dose,
3. the properties of the injected local anesthetic
   
   • (the higher the lipid solubility and protein binding of a drug, the lower the rate of systemic absorption), and
4. the addition of vasoconstrictors to the local anesthetic solution (the vasoconstriction associated with the addition of epinephrine decreases the rate of systemic absorption).

• Clinical Note:*
• Since the lungs extract a significant amount of local anesthetic from the systemic circulation, the threshold for systemic toxicity is much higher for an intravenous injection of local anesthetic as compared to a similar intra-arterial injection.

Question 6

Could local anesthetic toxicity have been prevented in this patient?

(Shortly after receiving a stellate ganglion block with bupivacaine, a 28-year-old female patient is noted to have difficulty speaking and reports dizziness, difficulty swallowing, and shortness of breath.)

Answer 6

The best way to avoid toxicity is to – limit the administered dose of local anesthetic drug, especially at sites of high systemic absorption or in patients with hypercapnia, advanced age, poor cardiac function, ischemic heart disease, cardiac conduction abnormalities, metabolic disease, and/or abnormally low plasma protein concentration (pregnancy).

Other preventative measures include – the use of ultrasound, aspiration prior to injection, the use of small incremental drug dosing, the addition of physiologic markers of excessive systemic absorption (i.e. epinephrine and/or fentanyl), and the avoidance of excessive sedation (which could mask the signs and symptoms of local anesthetic toxicity).