RT Book, Section
A1 Butterworth IV, John F.
A1 Mackey, David C.
A1 Wasnick, John D.
SR Print(0)
ID 1161431915
T1 Spinal, Epidural, & Caudal Blocks
T2 Morgan & Mikhail's Clinical Anesthesiology, 6e
YR 2018
FD 2018
PB McGraw-Hill Education
PP New York, NY
SN 9781259834424
LK accessmedicine.mhmedical.com/content.aspx?aid=1161431915
RD 2024/04/16
AB KEY  CONCEPTS  Neuraxial  anesthesia  greatly  expands  the  anesthesiologists’  armamentarium,  in  many  cases  providing  alternatives  to  general  anesthesia.  Neuraxial  anesthesia  may  also  be  used  simultaneously  with  general  anesthesia  or  afterward  for  postoperative  analgesia.  Neuraxial  blocks  can  be  performed  as  a  single  injection  or  with  a  catheter  to  allow  intermittent  boluses  or  continuous  infusions.  Performing  a  lumbar  (subarachnoid)  spinal  puncture  below  L1  in  an  adult  (L3  in  a  child)  usually  avoids  potential  needle  trauma  to  the  spinal  cord.  The  principal  site  of  action  for  neuraxial  blockade  is  believed  to  be  the  nerve  root,  at  least  during  initial  onset  of  block.  Differential  blockade  typically  results  in  sympathetic  blockade  (judged  by  temperature  sensitivity)  that  may  be  two  segments  or  more  cephalad  than  the  sensory  block  (pain,  light  touch),  which,  in  turn,  is  usually  several  segments  more  cephalad  than  the  motor  blockade.  Interruption  of  efferent  autonomic  transmission  at  the  spinal  nerve  roots  during  neuraxial  blocks  produces  sympathetic  blockade.  Neuraxial  blocks  typically  produce  variable  decreases  in  blood  pressure  that  may  be  accompanied  by  a  decrease  in  heart  rate.  Deleterious  cardiovascular  effects  should  be  anticipated  and  steps  undertaken  to  minimize  the  degree  of  hypotension.  However,  volume  loading  with  10  to  20  mL/kg  of  intravenous  fluid  in  a  healthy  patient  before  initiation  of  the  block  has  been  shown  repeatedly  to  fail  to  prevent  hypotension  (in  the  absence  of  preexisting  hypovolemia).  Excessive  or  symptomatic  bradycardia  should  be  treated  with  atropine,  and  hypotension  should  be  treated  with  vasopressors.  Major  contraindications  to  neuraxial  anesthesia  include  lack  of  consent,  coagulation  abnormalities,  severe  hypovolemia,  elevated  intracranial  pressure,  and  infection  at  the  site  of  injection.  For  epidural  anesthesia,  a  sudden  loss  of  resistance  (to  injection  of  air  or  saline)  is  encountered  as  the  needle  passes  through  the  ligamentum  flavum  and  enters  the  epidural  space.  For  spinal  anesthesia,  the  needle  is  advanced  through  the  epidural  space  and  penetrates  the  dura–subarachnoid  membranes,  as  signaled  by  freely  flowing  cerebrospinal  fluid.  Continuous  epidural  anesthesia  is  a  neuraxial  technique  offering  a  range  of  applications  wider  than  single  dose  spinal  anesthesia.  An  epidural  block  can  be  performed  at  the  lumbar,  thoracic,  or  cervical  level.  Epidural  techniques  are  widely  used  for  surgical  anesthesia,  obstetric  analgesia,  postoperative  pain  control,  and  chronic  pain  management.  Epidural  anesthesia  is  slower  in  onset  (10–20  min)  and  may  not  be  as  dense  as  spinal  anesthesia,  a  feature  that  can  be  useful  clinically.  The  quantity  (volume  and  concentration)  of  local  anesthetic  needed  for  epidural  anesthesia  is  larger  than  that  needed  for  spinal  anesthesia.  Toxic  side  effects  are  almost  guaranteed  if  a  “full  epidural  dose”  is  injected  intrathecally  or  intravascularly.  Caudal  epidural  anesthesia  is  a  common  regional  technique  in  pediatric  patients.