5.4 Status Epilepticus Seizure Protocols

Status Epilepticus Seizure Protocols

Definition and Classification

Status Epilepticus (SE) is a life-threatening neurological emergency characterized by prolonged or repetitive seizure activity. Classically defined as a seizure lasting more than 30 minutes, the clinical definition has been updated to facilitate rapid intervention: continuous seizure activity lasting >= 5 minutes, or two or more discrete seizures without a complete return to baseline neurological status between episodes.

SE is divided into convulsive (generalized tonic-clonic activity with motor manifestations) and non-convulsive (absence of motor convulsions, characterized by altered mental status and electrographic seizure activity). Convulsive SE is a medical emergency that leads to systemic complications, including hyperthermia, rhabdomyolysis, severe lactic acidosis, respiratory failure, and irreversible neuronal injury from metabolic exhaustion.

Cellular Pathophysiology of Status Epilepticus

At the cellular level, status epilepticus is characterized by a failure of normal inhibitory mechanisms and an excess of excitatory neurotransmission. Normally, the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) binds to GABA-A receptors, causing an influx of chloride ions that hyperpolarizes the postsynaptic membrane. Excitatory transmission is mediated by glutamate binding to N-methyl-D-aspartate (NMDA) and AMPA receptors, causing sodium and calcium influx that depolarizes the neuron.

As a seizure persists beyond 5 minutes, a critical transition occurs:

1. GABA-A Receptor Downregulation: GABA-A receptors are internalized into the postsynaptic cell, making them unavailable for binding. Consequently, the brain becomes progressively resistant to benzodiazepines (which rely on these receptors to work).
2. NMDA Receptor Upregulation: Glutamate receptors are recruited to the synaptic membrane, leading to sustained calcium influx, excitotoxicity, and neuronal death. This explains why second-line and third-line agents must be initiated quickly, and why ketamine (an NMDA receptor antagonist) is highly effective in refractory status epilepticus.

Phase 1: First-Line Therapy (Benzodiazepines)

Benzodiazepines are the established first-line treatment for acute status epilepticus. They act as positive allosteric modulators of GABA-A receptors, enhancing inhibitory chloride conductance.

• Lorazepam (Ativan):
  • Dose: 2–4 mg IV (0.1 mg/kg, max single dose 4 mg) administered over 2 minutes. May repeat in 5-10 minutes if seizures persist.
  • Clinical Rationale: Lorazepam is the preferred agent when IV access is established. It has a lower lipid solubility compared to diazepam, meaning it redistributes out of the brain tissue much slower, providing a longer duration of anticonvulsant activity (up to 12 hours).
• Midazolam (Versed):
  • Dose: 5–10 mg IV (0.2 mg/kg), or 10 mg IM (for patients >40 kg; 5 mg for 13–40 kg).
  • Clinical Rationale: Midazolam IM is the treatment of choice in the absence of intravenous access. Because it is water-soluble, it is rapidly absorbed from the muscle tissue. It can also be administered intranasally or buccally.
• Diazepam (Valium):
  • Dose: 5–10 mg IV (0.15 mg/kg).
  • Clinical Rationale: Highly lipid-soluble, resulting in a very rapid onset (<1 minute). However, it rapidly redistributes into peripheral fat stores, causing its brain levels to drop quickly. The effective duration of anticonvulsant activity is often only 20–30 minutes, leading to a high rate of seizure recurrence.

Phase 2: Second-Line Therapy (Anticonvulsants)

If benzodiazepines fail to terminate the seizure, or if the seizure is controlled but a long-acting maintenance agent is required, second-line non-sedating anticonvulsants should be administered immediately.

• Levetiracetam (Keppra):
  • Dose: 60 mg/kg IV (max 4,500 mg) infused over 10–15 minutes.
  • Clinical Rationale: Highly favored due to its excellent safety profile, lack of hepatic metabolism, minimal drug-drug interactions, and absence of cardiovascular side effects.
• Fosphenytoin (Cerebyx):
  • Dose: 20 mg PE (phenytoin equivalents)/kg IV.
  • Rate: Infused at a maximum rate of 150 mg PE/min.
  • Clinical Rationale: A water-soluble prodrug of phenytoin. Unlike phenytoin, it can be diluted in both normal saline and dextrose-containing solutions. It carries a lower risk of local tissue necrosis and cardiac arrhythmias.
• Phenytoin (Dilantin):
  • Dose: 20 mg/kg IV.
  • Rate: Infused at a maximum rate of 50 mg/min.
  • Clinical Rationale: Must be diluted only in Normal Saline (NS) to prevent precipitation. It contains propylene glycol as a solvent, which can cause severe hypotension, bradycardia, and cardiac conduction blocks. It is contraindicated in patients with second- or third-degree heart blocks.
• Sodium Valproate (Depacon):
  • Dose: 40 mg/kg IV (max 3,000 mg) over 5–10 minutes. Avoid in patients with acute hepatic failure or suspected mitochondrial disorders.

Phase 3: Refractory Status Epilepticus (RSE) and Anesthetic Infusions

Refractory Status Epilepticus occurs when seizures persist despite first-line benzodiazepine and second-line anticonvulsant therapies. This stage requires advanced airway protection, mechanical ventilation, and continuous anesthetic infusions titrated to burst suppression on EEG.

• Propofol (Diprivan): Loading dose of 1–2 mg/kg IV bolus, followed by a continuous infusion of 20–200 mcg/kg/min. Paramedics must monitor for Propofol Infusion Syndrome (PRIS), which presents with metabolic acidosis, rhabdomyolysis, hyperkalemia, renal failure, and cardiac dysfunction.
• Midazolam Infusion: Loading dose of 0.2 mg/kg IV, followed by an infusion of 0.05–2.0 mg/kg/h.
• Ketamine: Loading dose of 1-2 mg/kg, followed by 0.5-5.0 mg/kg/h. Ketamine acts as an NMDA antagonist, targeting the upregulated glutamate receptors found in prolonged status.
• The Paralysis Caveat: If a neuromuscular blocker (e.g., Rocuronium) is used to facilitate intubation, it will eliminate the motor manifestations of the seizure, but will not stop the electrical seizure activity in the brain. Flight crews must maintain continuous sedation and anticonvulsant therapy to prevent subclinical status epilepticus and subsequent brain injury.

Special Contexts: Eclampsia and Reversible Causes

• Eclampsia: Defined as new-onset seizures in a pregnant patient (>20 weeks gestation to 4 weeks postpartum) with preeclampsia. The drug of choice is Magnesium Sulfate (4–6 g IV bolus over 15–20 minutes, followed by a 1–2 g/h infusion). Magnesium acts by blocking NMDA receptors and causing cerebral vasodilation. Benzodiazepines are reserved for seizures refractory to magnesium.
• Reversible Metabolic Causes: Always check a bedside blood glucose. Treat hypoglycemia with D10W or D50W. For seizures secondary to severe hyponatremia, administer 3% hypertonic saline (100–150 mL IV over 10–15 minutes).