To the Editor:-The ParaGraph Muscle Stimulator (Vital Signs, Totowa, NJ) is a new type of neuromuscular stimulator that uses a piezoelectric motion sensor. The sensor, when correctly applied, allows for the electronic interpretation and a computer screen display of the movement of a stimulated muscle. This permits monitoring of muscle relaxation without direct contact with the patient's extremity, a distinct advantage because an extremity is frequently not available during surgery.

The literature provided with the ParaGraph Muscle Stimulator* suggests placing the electric stimulator pad over the ulnar nerve at the wrist and the motion sensor over the bulk of the thenar eminence. We have found more satisfactory results by placing the motion sensor over the intersection of the hypothenar eminence and digit minimi (fifth digit). Stimulation of the ulnar nerve causes more motion of the fifth digit than the thumb. Another approach is to place the stimulating pad more lateral, so the median nerve is stimulated. This will cause the thumb to move more.

It is important to visually assess the response to stimulation before administering muscle relaxants, to determine where the motion sensor and stimulating pad should be placed.

Christopher Roberts, M.D., Resident in Anesthesia; Jerry A. Dorsch, M.D., Consultant in Anesthesia, Department of Anesthesia and Critical Care, Mayo Clinic, 4500 San Pablo Road, Jacksonville, Florida 32224.

(Accepted for publication August 21, 1996.)

*ParaGraph Operator's Manual. Vital Signs, Inc. 1993.