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Dosing ECT Stimulus Ahmad al-Ajhuri, MBChB MScMed Emory University ECT mini-fellowship Director of ATP
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Dosing ECT StimulusAhmad al-Ajhuri, MBChB MScMed Emory University ECT mini-fellowship
Director of ATP
Cairo, May 2011 2
Related Electricity principles
• V = I × R “Ohm’s Law”V: voltage in volts, I: current intensity in milliamperes, R: resistance (impedance) in ohms
• U = Q × I × RU: energy in joules, Q: charge in millicoulombs, I: current intensity in milliamperes, R: resistance (impedance) in ohms
• Q = I × PW × 2F × DQ: charge in millicoulombs, I: current intensity in milliamperes, PW: pulse width, F: frequency in hertz (cycles pairs per
second), D: duration of stimulus train in seconds
• 1 mC = 1 mA / 1 sec• Constant current devices: safe• Summary metric: J / mC?• Energy (J): unpredictable
Ohm’s law triangle
Cairo, May 2011 3
Electrical waveforms of ECT
• Waveform: the “shape” of the stimulus as a function of time.
• Sine wave ECT: 1930s Cerletti and Bini, wall outlets, continuous, neurotoxic!
• Brief pulse ECT: 0.5 – 2 ms, late 1970s• Ultra-brief pulse ECT: < 0.5 ms, late 1990s
Cairo, May 2011 5
Seizure Threshold (ST)
• The total amount of electricity necessary to induce a seizure ie CONVULSIVE THRESHOLD.
• IMPEDANCE: static (200 – 3000 Ω) and dynamic (120 – 350 Ω). Electrodes, scalp and skull.
• IMPEDANCE: automatic self-test in MECTA devicesFemales > MalesRUL > BT > BF
• Scalp SHUNTING of current: a lower proportion of current entering the brain. It is a short-circuit
Cairo, May 2011 7
ST
• ST variance: up to 50 folds, a lot of factors, strong evidence for gender and electrode placement
• Titration session : up to 4-5 restimualtions with 20 seconds apart
• STIMULUS INTENSITY: moderately suprathreshold ie 1.5 – 2.5 × ST in BT/BF, 2.5 – 6 × ST in RUL
Cairo, May 2011 11
STIMULUS DOSING• Why?
– Cerebral generalization: more effective– Barely suprathreshold (just above ST): ineffective– Markedly suprathreshold (far beyond ST): hazardous– ST is increasing along index ECT course: fixed dosing is
inappropriate• EMPERICAL TITRATION: most precise• PRE SELECTED (FORMULA-BASED) METHOD: pts do not
tolerate titration, eg cardiac, severely suicidal. etc• FIXED DOSING: may be a malpractice, esp if randomly
assigned.
Cairo, May 2011 12
STIMULUS DOSING: MECTA devices
• Stimulus 1: RUL, Female• Stimulus 2: BT/BF Female, RUL Male• Stimulus 3: BT/BF Male• After 3rd failed stimulus (uncommon): jump 2 levels for
4th one• Preselected stimulus: calculated dose
Stimulus 3: RUL, FemaleStimulus 4: All others
• Dial the device knob: 1 / 2 – 1 × pt age ( poor method with no evidence)
Cairo, May 2011 13
STIMULUS DOSING: MECTA devices
• Remember : therapeutic STIMULUS INTENSITY is moderately suprathreshold for next sessions:1.5 – 2.5 × ST in BT/BF, 2.5 – 6 × ST in RUL
• General rule: restimulate increasing 50 – 100 % of the previous stimulus when needed, eg missed seizure, brief seizure, etc
Cairo, May 2011 14
SEIZURE ADEQUACY
• Pattern & Duration: motor & EEG• Pattern: generalization both motor & EEG• Duration: 20 – 60 sec motor, 30 – 120 sec EEG• MISSED: no activity both motor & EEG• BRIEF (ABORTIVE): < 20 sec motor, < 30 sec EEG• PROLONGED: > 60 sec motor, > 120 EEG• Post-ictal suppression: a valid parameter• Although: seizure adequacy parameters are still
unclear, and lacking good evidence
Cairo, May 2011 16
How to manage inadequate seizure?
• MISSED / ABORTIVE: – Check device and connections– Restimulate: 20 sec apart, up to 5 times ( very rare), vary the
duration and frequency, then pulse width– Hyperventilate: 15 – 20 / min– IV Flumazenil: if pt is on BZD– DC / Taper drugs interfering: eg AEDs– Decrease IV anesthetic dose / switch to less anticonvulsant one.
Consider xanthines: Caffeine, theophylline, aminophylline.– Space the schedule– Check recent stimulus increase: paradoxical area of curve
Cairo, May 2011 17
PROLONGED / TARDIVE seizures
• More than 60 sec motor / 120 sec EEG (APA Task Reprot 2001: 180 sec both !) – Abort with IV anesthetic (thiopental) / BZD
(midazolam). If no response (rare): intubate, IV loading phenytoin and refer to ICU.
– Good ventilation– Additional dose of muscle relaxant– Decrease stimulus– Check pt drugs: eg xanthines
