David J. Impastato

THE SAFEST POSSIBLE CLINICAL USE OF SUCCINYLCHOLINE IN ELECTROSHOCKTHERAPY

The usefulness of succinylcholine (SCh) in convulsive therapy is unquestioned. However, in spite of this some psychiatrists are fearful of using it because SCh at times causes prolonged apnea and even death (1-12). This article discusses the prevention of these complications. In order to understand clearly the physiologic function of SCh it is necessary to focus sharply on the mechanics of transmission of the nerve impulse (Figure 1)l) . The synaptic membrane (SM) of the motor end plate is a complex five-layered structure interposed between the nerve ending and the muscle fiber. It is here that, as the result of the nerve impulse, an actioncurrent originates which triggers the processes which lead to muscle contraction. The SM is said to be polarized when it is surrounded by sodium ions (Na+) lying in the pericellular spaces outside of the membrane and by potassium ions (K+) lying on the inside of the membranez). Acetylcholine (ACh), released within the membrane by the nerve impulse, alters the Na+K+ balance causing K+ ions to flow out of the membrane and Na+ to flow in. This ion exchange is the action current, which will flow so long as the membrane remains only partially depolarized. When the membrane is completely depolarized current flow ceases and muscular relaxation occurs. Prolonged action of ACh could give rise to complete depolarization. This is prevented by the presence, also within the SM, of acetylcholinesterase ( AChE) which hydrolyses and inactivates ACh. The destruction of ACh allows the repolarization of the SM. As soon as this occurs a fresh supply of ACh again partially depolarizes the SM and the sequence starts again ( 13). Muscle relaxant drugs cause relaxation by affecting the interplay of the