Intraoperative Seizures

Introduction

• Seizures are caused by abnormal, synchronous depolarization of neurons in the cortex, resulting in motor symptoms, sensory symptoms, or both.^1-3
• They can be classified into the following subcategories: tonic-clonic generalized seizures (otherwise known as grand mal), temporal lobe seizures (complex partial), partial focal motor seizures, and absence seizures.^1-3
• Seizure disorder is defined as the presence of at least two unprovoked seizures.
• Seizures that occur while under general anesthesia are exceptionally rare (less than 1 in 10,000-20,000 anesthetics), largely due to the antiepileptic qualities of many common anesthetic agents.
• In a single-center retrospective review of patients with documented seizure disorders undergoing anesthesia, the overall frequency of a perioperative seizure was 3.4%.⁴
  • Patients with frequent seizures at baseline and with recent seizures before surgical admission were at an increased risk for perioperative seizure activity.
  • Neither the type of surgery nor the type of anesthetic affected the frequency of perioperative seizures.
• However, when intraoperative seizures do occur, they can be extremely dangerous due to their impact on oxygenation, metabolism, and intraoperative monitoring. Thus, anesthesia providers must understand how to recognize and treat an intraoperative seizure adequately.⁵

Etiology

Seizures occur due to abnormal synchronous neuronal activity. Causes can be grouped into the following:

• Structural: brain tumors, stroke, trauma, intraparenchymal malformations
• Metabolic: electrolyte disturbances (↓Na⁺, ↓Ca²⁺, ↓Mg²⁺), hypoglycemia, uremia, hepatic encephalopathy
• Toxic: drug intoxication or withdrawal (e.g., alcohol, benzodiazepines), local anesthetic systemic toxicity (LAST)
• Infectious/Inflammatory: meningitis, encephalitis, autoimmune causes.
• Genetic/Idiopathic: primary epilepsy syndromes

Intraoperative Causes

• Intraoperative seizures are rare but potentially dangerous because they can compromise oxygenation, increase intracranial pressure, affect metabolism, and disrupt intraoperative monitoring
• In the intraoperative setting, seizures can be further classified.
• Drug-related causes
  • LAST
  • Pro-convulsant anesthetics
    • Etomidate, ketamine, and methohexital can lower seizure threshold
  • Withdrawal or missed doses of anticonvulsants preoperatively
• Physiologic and metabolic causes
  • Hypoxia or hypercarbia
  • Metabolic or electrolyte derangements: hypoglycemia, hyponatremia, hypocalcemia, hypomagnesemia
  • Hypothermia or hyperthermia
  • Acid-base disturbances
• Surgical or procedural causes
  • Direct cortical stimulation (e.g., during awake craniotomy)
  • Cerebral ischemia or embolism
  • Irrigation with hypotonic fluids or contrast agents (especially during neuro or cardiac surgery)
• Preexisting neurologic conditions
  • History of epilepsy or prior neurologic pathology/dysfunction

Clinical Presentation

• Generalized seizures: uncontrolled tonic-clonic motor activity in all extremities, loss of consciousness, loss of bowel and/or bladder function, airway obstruction, forced gaze preference
• Partial focal motor seizures: tonic-clonic motor activity similar to that of generalized seizures, however, usually restricted to one limb. These seizures can often progress to generalized seizures
• Temporal lobe seizures: unpredictable, bizarre behavior or movements
• Absence seizures: blank stare

Seizure Presentation in the Intraoperative Setting

• Of note, seizures can present quite differently in the intraoperative setting, especially while under general anesthesia. The following can be signs of a potential seizure; however, other causes of these findings must be ruled out before making a seizure diagnosis:
  • Unexplained tachycardia and/or hypertension
  • Increased end-tidal CO₂
  • Elevated core temperature
  • Sudden increase in oxygen consumption (increased FiO₂ requirement)
  • Electroencephalography (EEG) or processed EEG (Bispectral Index Score) changes
• If the patient is not paralyzed by neuromuscular blockade, tonic-clonic movements, uncontrolled involuntary muscle contractions, facial twitching, or eye deviation, and nystagmus may also be observed.
• It is important to note that several intraoperative clinical situations may present as seizures or seizure-like activity, and it is imperative that anesthesia providers can distinguish between these scenarios.
• Similar events can include nonepileptic myoclonus after etomidate administration, muscle fasciculations after succinylcholine administration, opioid-induced chest wall rigidity, incomplete reversal of neuromuscular blockade, light anesthesia, shivering, loss of consciousness for alternative reasons, and cardiac arrest.
• Once the various “seizure mimickers” are ruled out and a primary diagnosis of a seizure is established, it is important to identify the underlying cause to appropriately manage and treat the seizure.

Management of Intraoperative Seizures⁵

Recognize and Terminate the Seizure

• Signs while under anesthesia (as listed above): tonic-clonic movements (if not under neuromuscular blockade), facial or ocular twitching, unexplained tachycardia, hypertension, increased end-tidal CO₂, or changes in EEG or BIS monitor
• If under neuromuscular blockade, electrical or autonomic signs may be the only clues
• Terminate the seizure pharmacologically
  • First line: Benzodiazepines
    • Midazolam 0.05–0.1 mg/kg IV (typical 2–5 mg bolus)
    • Diazepam 0.1–0.2 mg/kg IV
    • Lorazepam 0.05 mg/kg IV
  • If ongoing:
    • Propofol 1–2 mg/kg IV bolus
    • Thiopental 1–3 mg/kg IV if propofol unavailable

Stop Potential Triggers

• Cease surgical stimulation (let the surgery team know, pause surgery if possible)
• Discontinue any proconvulsant agents: enflurane, etomidate, methohexital, ketamine
• Stop any local anesthetic infusion (if using a peripheral nerve block catheter or a neuraxial catheter)
• Check for and correct:
  • Hypoxia (↑FiO_₂, ensure airway and ventilation)
  • Hypercarbia (adjust minute ventilation as necessary)
  • Hypoglycemia (check bedside glucose)
  • Electrolyte abnormalities (Na⁺, Ca²⁺, Mg²⁺)
  • Acid-base derangements

Maintenance and Monitoring

• Secure airway, oxygenation, and hemodynamics
• Deepen anesthesia if appropriate (e.g., volatile anesthetic, propofol)
• Continuous EEG monitoring if feasible
• Treat hyperthermia and acidosis if present

Search for and Treat the Underlying Cause

• Check labs: glucose, electrolytes, arterial blood gas
• Assess drug doses: local anesthetic plasma levels if LAST suspected
• Consider neuroimaging postoperatively if a new focal deficit or an unexplained event occurs
• If LAST is suspected: initiate lipid emulsion therapy per protocol

Postoperative Management

• Notify the neurology team for further workup
• Evaluate for structural, metabolic, or pharmacologic causes
• Resume or optimize anticonvulsant therapy if the patient has known epilepsy