TY  - CHAP
M1  - Book, Section
TI  - Chapter 14. Adrenergic Agonists & Antagonists
A1  - Butterworth, John F.
A1  - Mackey, David C.
A1  - Wasnick, John D.
PY  - 2013
T2  - Morgan & Mikhail's Clinical Anesthesiology, 5e
AB  - Adrenergic  agonists  can  be  categorized  as  direct  or  indirect.  Direct  agonists  bind  to  the  receptor,  whereas  indirect  agonists  increase  endogenous  neurotransmitter  activity.  The  primary  effect  of  phenylephrine  is  peripheral  vasoconstriction  with  a  concomitant  rise  in  systemic  vascular  resistance  and  arterial  blood  pressure.  Clonidine  seems  to  decrease  anesthetic  and  analgesic  requirements  and  to  provide  sedation  and  anxiolysis.  Dexmedetomidine  is  a  lipophylic  α-methylol  derivative  with  a  higher  affinity  for  α2-receptors  than  clonidine.  It  has  sedative,  analgesic,  and  sympatholytic  effects  that  blunt  many  of  the  cardiovascular  responses  seen  during  the  perioperative  period.  Long-term  use  of  these  agents,  particularly  clonidine  and  dexmedetomidine,  leads  to  supersensitization  and  up-regulation  of  receptors;  with  abrupt  discontinuation  of  either  drug,  an  acute  withdrawal  syndrome  manifested  by  a  hypertensive  crisis  can  occur.  Ephedrine  is  commonly  used  as  a  vasopressor  during  anesthesia.  As  such,  its  administration  should  be  viewed  as  a  temporizing  measure  while  the  cause  of  hypotension  is  determined  and  remedied.  Small  doses  (approximately  2  mcg/kg/min)  of  dopamine  (DA)  have  minimal  adrenergic  effects  but  activate  dopaminergic  receptors.  Stimulation  of  these  nonadrenergic  receptors  (specifically,  DA1  receptors)  vasodilates  the  renal  vasculature  and  promotes  diuresis.  Favorable  effects  on  myocardial  oxygen  balance  are  believed  to  make  dobutamine  a  good  choice  for  patients  with  the  combination  of  congestive  heart  failure  and  coronary  artery  disease,  particularly  if  peripheral  vascular  resistance  is  elevated.  (There  are  some  recent  debates  regarding  this  beneficial  effect.)  Labetalol  lowers  blood  pressure  without  reflex  tachycardia  because  of  its  combination  of  α-  and  β-effects.  Esmolol  is  an  ultrashort-acting  selective  β1-antagonist  that  reduces  heart  rate  and,  to  a  lesser  extent,  blood  pressure.  Discontinuation  of  β-blocker  therapy  for  24-48  hr  may  trigger  a  withdrawal  syndrome  characterized  by  hypertension,  tachycardia,  and  angina  pectoris.  
SN  - 
PB  - The McGraw-Hill Companies
CY  - New York, NY
Y2  - 2021/03/08
UR  - accessanesthesiology.mhmedical.com/content.aspx?aid=57231933
ER  -