RT Book, Section
A1 Corripio, Manuel
A2 Atchabahian, Arthur
A2 Gupta, Ruchir
SR Print(0)
ID 57261431
T1 Chapter 73. Ophthalmology
T2 The Anesthesia Guide
YR 2013
FD 2013
PB The McGraw-Hill Companies
PP New York, NY
SN 978-0-07-176049-2
LK accessanesthesiology.mhmedical.com/content.aspx?aid=57261431
RD 2024/04/19
AB Regulation  of  intraocular  pressure  (IOP).  Normal  intraocular  pressure:  12–20  mm  HgClinical  pearl:  Pressure  from  a  tightly  fitted  mask,  improper  prone  position  or  retrobulbar  hemorrhage  can  lead  to  ↑  IOPMechanisms  for  the  decrease  of  IOP:  a  drop  in  BP  reduces  choroidal  volume,  relaxation  of  the  extraocular  muscles  (EOM)  lowers  wall  tension,  and  papillary  constriction  facilitates  aqueous  outflowClinical  pearl:  Succinylcholine  ↑  IOP  by  5–10  mm  Hg  for  5–10  minutes,  through  prolonged  contracture  of  the  EOM.  This  may  cause:Extrusion  of  ocular  contents  through  an  open  surgical  or  traumatic  woundAbnormal  forced  duction  test  for  20  minutes  (test  used  in  strabismus  surgery)The  oculocardiac  reflex:Pathway:  Afferent  trigeminal  nerve  (V1)/Efferent  vagus  nerve  (X)Most  common  scenarios:  pediatric  patients,  strabismus  surgerySymptoms/Signs:  Cardiac  dysrhythmias  ranging  from  bradycardia  to  ventricular  ectopy  to  sinus  arrest.  In  awake  patients,  somnolence  and  nauseaPrevention:Anticholinergic  medication.  IV  is  more  effective  than  IMRetrobulbar  block  and/or  deep  inhalation  anesthesia  may  also  helpLocal  infiltration  by  surgeonManagement:Immediately  notification  of  surgeon  and  temporary  cessation  of  surgical  stimulus  until  hemodynamic  stabilityConfirm  adequate  ventilation,  oxygenation,  and  depth  of  anesthesiaIV  atropine  (10  mcg/kg)  if  hemodynamic  instabilityIf  more  than  one  episode,  infiltration  of  the  rectus  muscle  with  local  anestheticIntraocular  gas  expansion:The  surgeon  may  inject  air  or  gas  into  the  posterior  chamber  to  flatten  a  detached  retina  and  allow  better  healingThe  air  bubble  is  usually  absorbed  in  5  days  by  diffusionIf  the  patient  is  breathing  nitrous  oxide  (N2O)  the  bubble  will  increase  in  size  →  ↑IOPN2O  is  35  times  more  soluble  than  nitrogen  (major  component  in  air)  in  bloodSulfur  hexafluoride  (SF6)  is  an  inert  gas  that  is  less  soluble  in  blood  than  nitrogen,  and  less  soluble  than  N2O.  It  has  a  duration  of  action  of  10  daysBubble  size  doubles  within  24  hours  after  injection  because  nitrogen  from  air  enters  the  bubble  more  rapidly  than  the  SF6  diffuses  into  the  bloodstreamUnless  high  volumes  of  SF6  are  injected,  the  slow  bubble  expansion  will  not  increase  IOPHowever,  if  a  patient  is  breathing  N2O,  the  bubble  will  rapidly  increase  in  size  and  ↑  IOPN2O  should  be  stopped  at  least  15  minutes  before  the  injection  of  air  and  should  be  avoided  until  at  least  5  days  after  the  injection  of  air  and  10  days  after  the  injection  of  SF6Systemic  side  effects  of  ophthalmic  drugs: