Definition

Status epilepticus is defined as a seizure lasting more than 5 minutes, or two or more discrete seizures between which consciousness is not fully recovered. This definition reflects the evidence that seizures lasting more than 5 minutes rarely terminate spontaneously and require pharmacological intervention. The neuronal injury caused by prolonged seizure activity is cumulative — each additional minute of status epilepticus results in further neuronal death and makes the seizure progressively more difficult to terminate.

Non-convulsive status epilepticus (NCSE) is an important and frequently overlooked diagnosis in the ICU. Patients with NCSE may not have visible convulsive movements — they may simply appear deeply sedated, confused, or subtly obtunded. NCSE accounts for a significant proportion of unexplained coma in the ICU, and the diagnosis requires EEG. Any intubated ICU patient with unexplained impaired consciousness or failure to wake up appropriately after sedation holds should be considered for EEG to exclude NCSE.

Treatment Algorithm

The UK treatment algorithm for status epilepticus follows a time-based stepwise approach:

Time Phase	Stage	Treatment
0–5 min	Premonitory / immediate	ABCDE assessment; O2; IV access; blood glucose (treat <4 mmol/L immediately); blood tests including anticonvulsant levels; position patient safely
5–10 min	Early status	IV lorazepam 4 mg over 2 minutes. Repeat once after 10 minutes if seizure continues. If no IV access: buccal midazolam 10 mg OR rectal diazepam 10 mg.
10–30 min	Established status	IV levetiracetam 60 mg/kg (max 4500 mg) over 10 minutes. OR IV sodium valproate 40 mg/kg over 10 minutes. OR IV phenytoin 20 mg/kg at ≤50 mg/min (with continuous ECG monitoring).
30–60 min	Refractory status	General anaesthesia: IV propofol infusion, OR IV midazolam infusion, OR IV thiopental infusion. Intubate and ventilate. Continuous EEG monitoring. ICU admission. Neurology input.
>60 min	Super-refractory status	Ketamine infusion; isoflurane inhalation; immunotherapy (methylprednisolone, IVIg, plasma exchange if autoimmune aetiology suspected). Specialist neuro-ICU.

Pharmacology of Key Anticonvulsants

Understanding the mechanism of action, dosing, and side effects of the drugs used in status epilepticus is essential for safe prescribing:

Lorazepam works by enhancing the effect of GABA at the GABAA receptor, increasing chloride conductance and hyperpolarising the neuronal membrane. It has a longer duration of action than diazepam due to less rapid redistribution, making it more effective than diazepam as a first-line agent. Its main adverse effects are respiratory depression and sedation — have airway equipment ready before administering.

Levetiracetam has become the preferred second-line agent in UK practice following studies (including ESETT and CONSE-PT) showing equivalent efficacy to phenytoin and valproate with a more favourable adverse effect profile. Its mechanism involves binding to the synaptic vesicle protein SV2A, modulating neurotransmitter release. It does not cause QTc prolongation, does not require cardiac monitoring during infusion, and has no significant haemodynamic effects. It is renally cleared, so doses should be reduced in significant renal impairment.

Sodium valproate acts via multiple mechanisms including sodium channel blockade, GABA enhancement, and modulation of NMDA receptors. It is effective in generalised and focal epilepsy and is particularly useful when the seizure type is unclear. It should be avoided in women of childbearing potential without contraception (teratogenic), in mitochondrial disorders, and in patients with liver disease.

Phenytoin and fosphenytoin act by blocking voltage-gated sodium channels, reducing repetitive high-frequency neuronal firing. Phenytoin must be given slowly (maximum 50 mg/min) because rapid infusion causes cardiac arrhythmias and hypotension — continuous ECG monitoring is mandatory. The therapeutic plasma level is 10–20 mg/L. Fosphenytoin is a prodrug that can be given more rapidly and is less irritant to veins.