RT Book, Section
A1 Rosow, Carl
A1 Dershwitz, Mark
A2 Longnecker, David E.
A2 Mackey, Sean C.
A2 Newman, Mark F.
A2 Sandberg, Warren S.
A2 Zapol, Warren M.
SR Print(0)
ID 1144118652
T1 Opioid Analgesics
T2 Anesthesiology, 3e
YR 2017
FD 2017
PB McGraw-Hill Education
PP New York, NY
SN 9780071848817
LK accessanesthesiology.mhmedical.com/content.aspx?aid=1144118652
RD 2024/04/19
AB KEY  POINTSAn  opioid  is  any  natural  or  synthetic  compound  that  has  effects  similar  to  those  of  morphine  or  that  acts  as  an  antagonist  at  the  same  receptors  to  which  morphine  binds.  Opioids  are  analgesics.  Unlike  local  anesthetics  and  the  anti-inflammatory  inhibitors  of  cyclooxygenase,  they  alter  the  perception  of  pain  as  a  noxious  entity.The  “classical”  pharmacologic  effects  of  morphine,  such  as  analgesia  and  ventilatory  depression,  are  mediated  by  μ  receptors.  κ  and  δ  receptors  are  more  important  in  mediating  the  effects  of  some  endogenous  opioids.Opioids  relieve  prolonged,  burning  pain  more  effectively  than  the  sharp  pain  of  an  incision.  Neuropathic  pain  can  be  resistant  to  opioid  treatment.  Intraoperative  opioids  can  reduce  or  abolish  autonomic  and  somatic  responses  to  surgical  stimuli.Opioids  produce  drowsiness  and  difficulty  concentrating.  They  do  not  usually  produce  anterograde  amnesia.  Doses  sufficient  to  produce  apnea  and  profound  analgesia  do  not  reliably  produce  unconsciousness.Opioids  produce  dose-related  depression  of  the  ventilatory  response  to  CO2  as  well  as  to  hypoxia.  A  decrease  in  ventilatory  rate  is  not  a  sensitive  indicator  of  opioid  effect.  Sleep  will  further  potentiate  the  ventilatory  depression.  Equianalgesic  doses  of  all  full  agonists  produce  equivalent  amounts  of  ventilatory  depression.Opioids  suppress  cough  by  depressing  putative  cough  centers  in  the  medulla.  This  effect  is  not  mediated  through  classical  opioid  receptors.  Dextrorotatory  isomers  of  opioid  analgesics  retain  antitussive  activity.Opioids  produce  complex  effects  on  vomiting  centers  in  the  medulla.  There  is  direct  stimulation  of  the  chemoreceptor  trigger  zone.  The  emetic  effects  are  potentiated  by  stimulation  of  the  vestibular  apparatus.Hypertonus  of  skeletal  muscle  may  be  produced  by  large  intravenous  doses  of  opioids,  especially  fentanyl  and  its  derivatives.  “Lead  pipe”  muscle  rigidity  may  prevent  mechanical  ventilation.  The  primary  etiology  is  supraglottic  obstruction  from  constriction  of  laryngeal  and  pharyngeal  muscles.Morphine  and  meperidine  produce  a  nonimmunologic  release  of  histamine  from  tissue  mast  cells,  often  mistaken  for  allergy.  There  may  be  transient  hypotension.Opioids  decrease  propulsive  movements  in  the  gastrointestinal  tract  while  increasing  sphincter  tone.  Chronic  administration  usually  requires  laxatives  or  stool  softeners  to  treat  constipation.When  tolerance  to  an  opioid  occurs,  there  is  simultaneous  cross-tolerance  to  other  agonists.  Tolerance  develops  to  the  depressant  effects  (analgesia,  ventilatory  depression,  euphoria),  but  less  so  to  the  stimulant  effects  (constipation,  pupillary  constriction).Physical  dependence  is  not  the  same  thing  as  psychological  dependence  or  addiction  that  includes  compulsive  drug-seeking  behavior.  The  risk  of  addiction  can  be  minimized  by  careful  medical  management.Morphine  is  the  least  lipophilic  of  the  opioids.  It  penetrates  biologic  membranes  more  slowly  than  lipophilic  opioids.  In  spite  of  its  rapid  distribution  and  elimination  from  plasma,  changes  in  brain  concentration  are  small  and  delayed,  and  its  onset  and  offset  are  slow.Meperidine  or  its  metabolites  inhibit  SERT  (the  presynaptic  serotonin  γ-aminobutyric  acid  [GABA]  family  transporter)  and  may  produce  serotonin  syndrome,  especially  in  patients  taking  monoamine  oxidase  inhibitors.  A  metabolite  has  proconvulsant  activity.Methadone  is  long  lasting  due  to  its  long  terminal  half-life.  It  has  high  oral  bioavailability  (approximately  80%).  Repeated  doses  result  in  substantial  accumulation;  subsequent  doses  appear  to  last  much  longer  than  the  initial  dose.Fentanyl  is  extremely  fat  soluble,  resulting  in  rapid  onset  and  relatively  short  duration.  Duration  ...