RT Book, Section
A1 Boezaart, André P.
A1 Borene, Steven C.
A2 Hadzic, Admir
SR Print(0)
ID 3500994
T1 Chapter 22. Functional Evaluation of Motor Responses for Upper Limb Blocks
T2 NYSORA Textbook of Regional Anesthesia and Acute Pain Management
YR 2007
FD 2007
PB The McGraw-Hill Companies
PP New York, NY
SN 9780071449069
LK accessanesthesiology.mhmedical.com/content.aspx?aid=3500994
RD 2024/04/19
AB A  nerve  stimulator  delivers  a  charge  to  a  motor  nerve  fiber,  which  causes  a  flow  of  ions  through  the  nerve  membrane  and  initiates  an  action  potential  in  the  nerve  fiber.1  The  larger  the  delivered  charge,  the  more  motor  fibers  in  the  motor  nerve  fascicle  will  fire  and  the  stronger  the  resulting  motor  response  until  a  maximal  motor  response  is  reached.  Several  factors  influence  the  total  charge  delivered  to  a  nerve  fiber.  The  duration  and  intensity  of  the  current  are  the  main  variables.  The  impedance  of  the  tissue  between  the  stimulating  surface  (needle  or  catheter)  and  the  nerve  further  influence  the  current  intensity.  This  is  reduced  as  the  distance  from  the  stimulating  surface  to  the  nerve  is  reduced.  In  addition,  the  type  of  tissue  between  the  stimulating  surface  and  the  nerve,  the  type  of  electrode  used,  and  the  polarity  of  the  electrode  affect  the  total  impedance  of  the  system  and  thus  affect  the  motor  response  to  stimulation.  Muscle  mass  is  also  important,  such  that  a  stimulus  in  a  frail  80-year-old  woman  differs  substantially  from  a  motor  response  from  a  similar  electrical  response  delivered  to  a  young  muscular  patient.1