Vagus Nerve Stimulation: Anesthetic Strategies for Left vs. Right Nerve Navigation

Ink & Air

Introduction

Vagus Nerve Stimulation (VNS) is a neuromodulation therapy used in patients with treatment-resistant conditions such as epilepsy and depression. The anesthesiologist’s role is central to ensuring safe perioperative management, given the vagus nerve’s complex anatomy and physiology. This chapter reviews anesthetic considerations, with emphasis on differences between right- and left-sided stimulation.

Overview of Vagus Nerve Stimulation

VNS involves implantation of an electrode around the cervical vagus nerve, connected to a pulse generator implanted subcutaneously in the chest. The device delivers programmed electrical impulses to modulate neural activity.

Primary Indications

• Pharmacoresistant epilepsy: Reduces seizure frequency in refractory cases.
• Treatment-resistant depression: Improves mood in patients failing conventional therapies.
• Cluster headaches: Provides relief in refractory cases.

Emerging Indications

• Post-traumatic stress disorder (PTSD)
• Inflammatory diseases (rheumatoid arthritis, Crohn’s disease)
• Heart failure
• Tinnitus
• Obesity
• Modulation of inflammatory pathways in ongoing trials

References: Groves DA, Brown VJ. Neurosci Biobehav Rev. 2005;29(3):493-500.

Ben-Menachem E. Lancet Neurol. 2002;1(8):477-82.

Johnson RL, Wilson CG. Front Neurosci. 2018;12:897.

Right vs. Left Vagus Nerve Stimulation

Left Vagus Nerve

• Standard and preferred site for VNS implantation.
• Primarily influences the atrioventricular (AV) node rather than the sinoatrial node.
• Carries a lower risk of bradycardia and asystole.
• Associated with a safer perioperative profile.

Right Vagus Nerve

• Provides dominant innervation to the sinoatrial (SA) node.
• Increases risk of severe bradyarrhythmias, asystole, or cardiac arrest.
• Rarely used, reserved for cases where left-sided access is not feasible.
• Requires preoperative cardiology evaluation and intraoperative cardiac monitoring.

References: Ardell JL, et al. J Physiol. 2016;594(14):3877-3909.

Yuan H, Silberstein SD. Headache. 2016;56(1):71–78.

Vagus Nerve Anatomy and Physiology

Anatomy

• The vagus nerve (cranial nerve X) is a mixed nerve with motor, sensory, and parasympathetic fibers.
• Exits the medulla via the jugular foramen.
• Contributes to the cardiopulmonary and abdominal plexuses.
• Left vagus nerve: Mainly supplies the AV node and thoraco-abdominal viscera.
• Right vagus nerve: Dominantly supplies the SA node, with stronger cardiac effects.

Physiology

• Approximately 80% of fibers are afferent, projecting to the nucleus tractus solitarius (NTS).
• The NTS integrates inputs to higher centers, influencing the amygdala, hypothalamus, and locus coeruleus.
• Stimulation enhances GABAergic and noradrenergic activity, suppressing hyperexcitability in epilepsy and mood disorders.

References: Kandel ER, et al. Principles of Neural Science. 5th ed. McGraw-Hill; 2013.

Bonaz B, et al. Neuron. 2016;89(6):1131-1146.

Preoperative Evaluation

• Cardiac assessment: Review arrhythmias, conduction abnormalities, or pacemakers.
• Neurological status: Assess seizure control, antiepileptic drug (AED) levels.
• Psychiatric medications: Consider interactions with anesthetics (SSRIs, TCAs, antipsychotics).
• Device history: Confirm previous implant details, need for battery replacement or revision.
• Diagnostics: Baseline ECG for all patients; mandatory cardiology consult for right-sided VNS.

Reference: DeGiorgio CM, et al. Seizure. 2000;9(7):448–451.

Intraoperative Anesthetic Management

Choice of Technique

• General anesthesia: Standard, with endotracheal intubation for airway protection. Short-acting agents (propofol, remifentanil) favored.
• Monitored anesthesia care (MAC): Limited to minor procedures (e.g., generator replacement) in stable, cooperative patients.

Pharmacologic Considerations

• Avoid agents that lower seizure threshold (ketamine, enflurane).
• TIVA with propofol preferred for stable hemodynamics.
• Be prepared for sudden bradycardia; atropine or glycopyrrolate should be immediately available.

Positioning and Airway

• Supine, with head rotated for surgical exposure.
• Avoid hyperextension to minimize venous congestion.
• Endotracheal intubation ensures airway security.

Monitoring

• Standard ASA monitors plus continuous ECG.
• External defibrillator/pacing pads must be available.
• NIM endotracheal tubes may help monitor recurrent laryngeal nerve function.

Device Interference

• Electrocautery: Prefer bipolar; monopolar used with caution, away from generator.
• Magnet usage: Surgeons may test or disable the device intraoperatively; anesthesiologists must monitor hemodynamic effects.

Reference: Rychlicki F, et al. Paediatr Anaesth. 2006;16(2):143–149.

Intraoperative Challenges

• Vagal manipulation can induce bradycardia, hypotension, or asystole.
• Treat bradycardia with atropine (0.5–1 mg IV) or glycopyrrolate (0.2–0.4 mg IV).
• Asystole requires immediate cessation of stimulation and ACLS protocols.
• Hemodynamic instability: Optimize fluids and use vasopressors as required.
• Airway complications: Recurrent laryngeal nerve stretch may cause postoperative hoarseness or laryngospasm.
• Device testing: Coordinate with surgeons; stop testing if significant bradycardia or hypotension occurs.

Reference: Wheless JW, et al. Epilepsy Res. 2001;46(1):1–10.

Postoperative Care

• Monitor in PACU for:
• Recurrent laryngeal nerve dysfunction (hoarseness, dysphagia).
• Respiratory compromise (rare, requires urgent evaluation).
• Resume AEDs and psychiatric medications promptly.
• Provide patient education on wound care, device titration, and expected sensations.

Reference: Handforth A, et al. Neurology. 1998;51(1):48–55.

Special Considerations for Right-Sided VNS

• Indicated only if left vagus access is not possible.
• Requires preoperative cardiology evaluation.
• Intraoperative precautions:
• Continuous ECG monitoring.
• Immediate availability of pacing and defibrillation.
• Greater vigilance needed due to high arrhythmia risk.

Reference: Engineer ND, et al. Nature. 2011;470(7332):101–104.

Clinical Takeaway Checklist

Preoperative

• Baseline ECG and cardiac assessment.
• Confirm AED and psychiatric medication status.
• Cardiology consult for right-sided VNS.

Intraoperative

• TIVA or balanced anesthesia, avoid seizure-threshold-lowering drugs.
• Continuous ECG, atropine/glycopyrrolate ready.
• Use bipolar cautery when possible.
• Coordinate with surgeons during device testing.

Postoperative

• Monitor for laryngeal nerve complications and respiratory compromise.
• Resume AEDs and psychiatric medications promptly.
• Educate patient on device function and wound care.