Electroconvulsive therapy — seizure threshold, brief anaesthetic, haemodynamic management

Overview and Framework

Electroconvulsive therapy (ECT) remains one of the most effective biological treatments for severe depression, yet it is also one of the most misunderstood. For the anaesthetist, ECT presents a unique intersection of psychiatric, physiological, and technical challenges, brief but repeated general anaesthetics in patients whose underlying illness and medications carry significant cardiorespiratory and pharmacological implications. The consultant anaesthetist must be able to articulate both the evidence supporting ECT's use and the anaesthetic considerations that determine its safety and efficacy, and should be capable of discussing the evidence with patients, psychiatrists, and trainees.

Depression affects approximately 5-10% of adults at some point in their lives, and a significant minority will have illness refractory to antidepressant pharmacotherapy and psychotherapy. ECT was introduced in 1938 by Cerletti and Bini and, despite decades of controversy, has accumulated a substantial evidence base demonstrating superior efficacy in specific clinical contexts. Modern ECT bears little resemblance to its unmodified origins, electrical parameters, electrode placement, and anaesthetic technique have all evolved considerably.

From a consultant anaesthetic perspective, the role extends beyond simply providing safe anaesthesia. It includes pre-procedure optimisation, awareness of how anaesthetic agents modify seizure threshold and duration, monitoring for cardiovascular responses, and participation in decisions about ongoing fitness for a course of treatment. Understanding why ECT works, insofar as this is known, contextualises the physiological targets that anaesthetic management must respect.

Mechanism of Action

The precise mechanism by which ECT exerts antidepressant effect remains incompletely understood, but several neurobiological pathways have been identified:

• Seizure-mediated neuromodulation: The generalised tonic-clonic seizure is necessary for therapeutic effect; subconvulsive stimulation is ineffective. Seizure duration of 20-50 seconds (EEG) is generally considered adequate, though the relationship between seizure duration and clinical outcome is imperfect
• Monoaminergic effects: ECT increases synaptic availability of serotonin, noradrenaline, and dopamine, consistent with the monoamine hypothesis of depression
• Neuroendocrine changes: ECT normalises dysregulated hypothalamic-pituitary-adrenal axis activity, reduces hypercortisolaemia, and increases brain-derived neurotrophic factor (BDNF), promoting neuroplasticity
• Anticonvulsant properties: Paradoxically, ECT progressively raises seizure threshold over a course of treatment, an effect correlated with clinical response; this is thought to involve GABAergic upregulation
• Neuroimaging evidence: Functional MRI and PET studies demonstrate increased connectivity in prefressive-associated neural circuits (including the default mode network) and normalisation of prefrontal hypoactivity following successful ECT

Key principle: The adequacy of the induced seizure is central to therapeutic outcome. Anaesthetic management must balance amnesia and patient safety against excessive suppression of seizure activity.

Clinical Indications

Primary Indications for ECT in Depression

Other Psychiatric Indications

ECT is also evidence-supported in bipolar disorder (manic and depressive phases), schizoaffective disorder, treatment-resistant schizophrenia (particularly with prominent affective or catatonic features), and neuroleptic malignant syndrome. Parkinson's disease with comorbid depression represents another recognised indication.

Evidence Base for Efficacy

Randomised Controlled Trials, Active vs Sham ECT

The most methodologically rigorous evidence comes from studies comparing real ECT with anaesthesia alone (sham ECT), ensuring blinding of patients and raters:

• Multiple RCTs from the 1970s-1990s (principally UK, Scandinavian, and American multicentre trials) consistently demonstrated that real ECT produces significantly greater reductions in depressive symptom scores (Hamilton Depression Rating Scale, Montgomery-Åsberg Depression Rating Scale) than sham ECT
• The Leicestershire and Northwick Park trials are among the most cited, both demonstrated clear superiority of real over sham ECT, with response rates approximately 60-80% for real ECT vs 30-40% for sham, though exact figures vary by population studied
• A systematic review and meta-analysis incorporating these trials estimated an overall response rate of 60-80% for acute ECT in unipolar and bipolar depression

ECT vs Pharmacotherapy

• ECT demonstrates superior short-term response rates compared to tricyclic antidepressants, MAOIs, and, in most comparative studies, modern antidepressants including SSRIs and SNRIs
• Comparative trials are complicated by ethical constraints (crossover designs, short treatment durations, heterogeneous populations)
• ECT response is particularly marked in melancholic, psychotic, and catatonic subtypes, where pharmacotherapy alone is substantially less effective
• Meta-analyses suggest ECT is 1.5-2× more likely to produce remission compared to antidepressant monotherapy in treatment-resistant cohorts

Maintenance ECT

• Acute ECT produces rapid response, but relapse rates without ongoing treatment are high (approximately 50-80% within 12 months in some series)
• Maintenance ECT (weekly to monthly treatments) reduces relapse rates and is supported by RCT evidence, notably the Continuation ECT (CORE) study, which demonstrated significantly lower relapse rates with continuation ECT plus pharmacotherapy compared to pharmacotherapy alone
• Maintenance ECT is particularly valuable for patients with recurrent severe depression who have failed multiple pharmacological maintenance strategies

Speed of Response

• One of ECT's most clinically significant advantages is rapidity of antidepressant effect, meaningful symptom reduction typically occurs within 2-4 treatments (3-5 days with thrice-weekly schedules)
• This is unmatched by any currently available antidepressant, making ECT potentially life-saving in acutely suicidal or nutritionally compromised patients
• Ketamine infusions have emerged as a comparably rapid but shorter-lasting alternative; comparative trials are ongoing

Cognitive Side Effects and Tolerability

A balanced appraisal of the evidence must address cognitive adverse effects, which are the primary concern for patients and clinicians:

• Acute confusional state following each treatment is universal and typically resolves within 30-60 minutes
• Anterograde amnesia during a course is common; most patients experience measurable impairment in new learning that resolves over weeks following treatment completion
• Retrograde amnesia, loss of memories from the period around ECT, is the most persistent concern; autobiographical memory gaps may persist for months in a minority
• Electrode placement significantly influences cognitive outcomes: unilateral (right) electrode placement (d'Elia position) causes less cognitive impairment than bilateral placement, though bilateral ECT may be more rapidly effective in severe illness
• Ultra-brief pulse stimulation (pulse width ≤0.5 ms, compared to brief pulse at 0.5-2 ms) reduces cognitive side effects without substantially compromising efficacy, now the dominant technique in most Australasian centres
• Subjective memory complaints may persist beyond objective testing abnormalities; patient-reported outcomes are important but complex to interpret in the context of depression itself (which impairs memory)

Examination tip: Candidates should know that cognitive side effects are reduced by right unilateral placement, ultra-brief pulse, and minimising electrical dose above seizure threshold. These modifications do not eliminate adverse effects but substantially reduce them.

Contraindications and Risk Stratification

There are no absolute contraindications to ECT, but the following conditions represent high-risk situations requiring careful pre-procedure assessment and optimisation:

Pregnancy is not a contraindication. Fetal wellbeing should be monitored during treatment; uterine contractions may occur and obstetric review is required.

Anaesthetic Management

Goals of Anaesthesia for ECT

1. Rapid onset of unconsciousness and amnesia
2. Adequate muscle relaxation to prevent injury during convulsion
3. Minimal suppression of seizure duration and quality
4. Rapid offset, patient must be assessable and recoverable promptly
5. Blunting of the cardiovascular response to electrical stimulation

Induction Agents and Seizure Effects

Key principle: Propofol is the most commonly used agent in Australian practice but its anticonvulsant properties are the primary anaesthetic contributor to inadequate seizures. Dose-reduction strategies, or substitution with ketamine (0.5-1.5 mg/kg IV), are appropriate when seizures are consistently brief or inadequate.

Muscle Relaxation

• Succinylcholine 0.5-1.0 mg/kg IV remains the standard relaxant, rapid onset, ultra-short duration, complete paralysis to prevent orthopaedic injury
• Isolated arm technique (tourniquet inflated before succinylcholine) allows visual observation of motor seizure activity in one limb
• Rocuronium with sugammadex reversal is an alternative where succinylcholine is contraindicated (hyperkalaemia, personal or family history of malignant hyperthermia, pseudocholinesterase deficiency)

Cardiovascular Management

• Immediate bradycardia (vagal) may follow electrical stimulus, usually transient; atropine 0.3-0.6 mg IV (or glycopyrrolate) available
• Tachycardia and hypertension follow, peak at 1-3 minutes post-stimulus; mediated by sympathetic surge
• Blunting agents: labetalol 5-20 mg IV, esmolol 0.5-1.0 mg/kg IV, glyceryl trinitrate infusion; choice depends on baseline cardiovascular status
• Patients with known ischaemic heart disease require careful attenuation of the hypertensive response

Airway Management

• LMA is standard in most Australian ECT suites, mask ventilation with 100% O₂ pre-oxygenation, LMA inserted after induction
• ET intubation reserved for high aspiration risk, difficult airway, or obesity with poor mask seal
• Bite block mandatory to protect teeth and secure airway during convulsion
• Supplemental O₂ augments seizure quality and duration

Special Populations and Practical Considerations

Concurrent Medications

• Lithium, increases risk of prolonged seizure, delirium, and neurotoxicity; typically withheld on the morning of treatment
• Benzodiazepines, raise seizure threshold significantly; should be weaned or withheld where psychiatrically safe
• Anticonvulsants (including valproate, lamotrigine), raise seizure threshold; psychiatrist and anaesthetist must collaborate on whether dose reduction is appropriate
• MAOIs, significant interactions with vasopressors and opioids; most centres require washout before commencing ECT, though some experienced centres manage with careful technique
• Antidepressants, SSRIs and SNRIs generally continued; tricyclics may lower seizure threshold and increase arrhythmia risk

Course Length and Treatment Frequency

• A standard acute course comprises 6-12 treatments, delivered two to three times per week
• Response is assessed after 6 treatments; continuation beyond 12 requires documented ongoing benefit
• Frequency affects cognitive load, twice-weekly scheduling offers a better cognitive side-effect profile with comparable efficacy to three-times-weekly

Summary and Examination Strategy

ECT occupies a unique position in psychiatric therapeutics, a treatment with a robust RCT evidence base demonstrating superiority to sham and to pharmacotherapy in specific populations, yet one that remains underutilised due to stigma, cognitive concerns, and logistical barriers. For ANZCA Fellowship, candidates should be able to:

• Articulate the level of evidence supporting ECT (multiple RCTs, systematic reviews, meta-analyses) and distinguish it from anecdote
• Identify which depressive presentations derive greatest benefit, psychotic, melancholic, catatonic, treatment-resistant, high-suicide-risk
• Explain the physiological basis of therapeutic effect and the reasons seizure adequacy matters anaesthetically
• Describe how induction agent choice (particularly propofol vs ketamine) directly influences seizure quality, and how this is monitored (EEG, motor activity via isolated arm)
• Demonstrate awareness of cognitive side effects and the modifications (ultra-brief pulse, unilateral placement) that mitigate them without abolishing efficacy
• Discuss cardiovascular management, both the vagally mediated bradycardia and the sympathetically mediated hypertensive surge, and appropriate pharmacological strategies

The anaesthetist's role in ECT is not passive. The choice of agent, dose, and adjuncts directly determines whether a therapeutic seizure occurs, making the anaesthetist an active contributor to psychiatric treatment outcome.

Sources

• ANZCA Professional Documents (PS series)
• ANZCA clinical guidelines