Dose calculation with brief-pulse ECT demystified

Abstract

Byline: Chittaranjan. Andrade There are two important categories of electroconvulsive therapy (ECT) devices: constant voltage, sinusoidal wave devices and constant current, brief-pulse devices. The sinusoidal wave devices are currently considered obsolete for the following reasons. [sup][1] *Current flows almost continuously with the sinusoidal waveform. As a result, far more electrical charge is delivered than is necessary to trigger the seizure. The extra charge may not increase efficacy but does increase the cognitive adverse effects of the treatment. In contrast, with constant current, brief-pulse ECT devices, current is delivered in short pulses. The seizure which is triggered can be as effective as that with sinusoidal wave ECT, and is associated with less cognitive adverse effects. *According to Ohm's law, the current in a circuit is inversely proportional to the resistance. As resistance varies from patient to patient, at constant voltage the current in the circuit and hence the electrical charge delivered during ECT will also vary from patient to patient. Consequently, there is no way that a clinician can deliver a planned ECT dose (in units of charge) to the patient; this, however, is possible with constant current devices which automatically adjust the strength of the current to the resistance in the circuit. The administration of a planned dose is necessary because it is now known that the electrical dose administered during ECT is just as important to therapeutics as the dose of a drug administered during pharmacotherapy. What is the relationship between dosing and outcome with ECT? There are three fairly consistent findings: [sup][1] *Higher electrical doses are associated with a greater proportion of responders in patients who receive right unilateral ECT. *Higher electrical doses are associated with faster response to ECT with both unilateral and bilateral electrode placements. *Higher electrical doses are associated with greater cognitive adverse effects. Dosing is usually estimated in units of charge (millicoulombs), although both units of energy (joules) and power (watts) have been suggested as alternatives. The ideal unit remains elusive; [sup][2] nevertheless, for most practical purposes, units of charge suffice. Many clinicians feel intimidated by the choices available with brief-pulse apparatuses and lack the knowledge necessary to calculate the ECT dose. This article demystifies the subject; all the background that the reader requires is a very basic knowledge of mathematics and physics. Consider the following facts: *Brief-pulse ECT delivers a train of identical pulses of electricity [Figure 1]. *Each pulse has certain amplitude (pulse height). This is measured in units of current; that is, amperes (A) or milliamperes (mA). *Each pulse has certain duration (pulse width). This is measured in milliseconds (ms). *There is a specific number of pulses delivered each second. This is determined from the stimulus frequency, which is measured in hertz (Hz) or cycles per second (cps). If the stimulus is unidirectional, the number of pulses per second is the same as the stimulus frequency. If the stimulus is bidirectional, the number of pulses per second is double the stimulus frequency (this is because each cycle is made up of one positive and one negative pulse). Most constant current, brief-pulse ECT devices deliver bidirectional pulses. *The ECT stimulus is passed for a specific duration. This is known as the stimulus duration, or the duration of the stimulus train, and is measured in seconds.{Figure 1} Calculating stimulus dose Step 1: To calculate the ECT dose, the first step is to determine the following: *Current, or pulse amplitude (A or mA) *Pulse width (ms) *Number of pulses per second (determined from the stimulus frequency) *Stimulus duration Some ECT devices allow the clinician to adjust the value of all these settings. …