TY  - CHAP
M1  - Book, Section
TI  - Respiratory Mechanics and Respiratory Failure
A1  - Rozenfeld, Ranna A.
PY  - 2018
T2  - The PICU Handbook
AB  - Developmental  considerationsBasal  metabolic  rate  is  higher  in  children  than  in  adults,  resulting  in  decreased  metabolic  reserve  in  the  face  of  increased  oxygen  consumption  during  critical  illnessMore  compliant  chest  wall  with  decreased  elastic  recoilIncomplete  alveolarization  and  lack  of  collateral  ventilation  (pores  of  Kohn  and  canals  of  Lambert  develop  at  ages  3–4)Airways  in  children  have  increased  resistance  and  lack  rigid  cartilageMore  susceptible  to  dynamic  compression  and  airway  obstructionCompliance:  Distensibility  of  the  lung;  ease  of  expansion  of  the  lungs  and  thorax,  determined  by  pulmonary  volume  and  elasticity;  measure  of  the  ratio  of  change  in  tidal  volume  and  the  pressure  it  produces:C=∆V/∆PHigh  compliance  =  healthy  lung,  neuromuscular  weakness  or  paralysisLow  compliance  =  acute  respiratory  distress  syndrome  (ARDS),  pneumoniaResistance  (Poiseuille's  law):  Resistance  to  flow  is  inversely  related  to  the  fourth  power  of  the  radius;  therefore,  if  the  radius  is  halved,  the  resistance  is  increased  16-fold.Results  in  profound  decrease  in  flow  as  laminar  flow  transitions  to  turbulent  flow  (see  Figure  18-1)Lung  volumes  (see  Figure  18-2)  Tidal  volume  (VT):  volume  of  air  moved  during  quiet  breathing.Vital  capacity  (VC):  maximal  volume  of  air  that  can  be  forcibly  exhaled  after  a  maximal  inspiration.Residual  volume  (RV):  volume  of  air  remaining  in  lungs  after  a  maximal  expiration.  It  cannot  be  expired  no  matter  how  vigorous  or  long  the  effort.Total  lung  capacity  (TLC):  volume  of  air  in  the  lungs  at  the  end  of  a  maximal  inspiration.Functional  residual  capacity  (FRC):  volume  of  air  remaining  in  the  lungs  at  the  end  of  a  normal  expiration.FRC  is  reduced  by  supine  positioning,  abdominal  distension,  restrictive  lung  disease,  and  sedation.Normal  gas  exchange  requires:Transport  of  oxygen  (O2)  to  the  alveolusDiffusion  of  O2  across  the  alveolar-capillary  membraneO2  transfer  from  the  blood  to  the  organsCarbon  dioxide  (CO2)  removal  from  blood  into  the  alveolusVentilation:  Refers  to  CO2  exchange  at  the  alveolar  level.Determined  by  minute  ventilation  and  anatomic  dead  space.Alveolar  Ventilation=[VT−Dead  Space  (Vd)]  ×Respiratory  Rate  (RR)Minute  Ventilation=VT×RRDead  Space  Volume  (Vd)=Anatomic+PhysiologicDead  space  =  the  sum  of  gas  volume  within  the  conducting  airways  that  does  not  reach  the  alveoli  (anatomic)  and  volume  of  gas  that  doesn't  participate  in  gas  exchange  secondary  to  inadequate  perfusion  (physiologic).Physiologic  causes  of  hypercapnia:Increased  CO2  production  (fever,  burns,  overfeeding)Decreased  alveolar  ventilationDecreased  VTDecreased  central  nervous  system  (CNS)  drive  (sedatives)Neuromuscular  weaknessFlail  chestIncreased  VdPulmonary  embolusHyperinflation  (asthma,  bronchiolitis,  cystic  fibrosis  [CF],  excessive  positive  end-expiratory  pressure  [PEEP])Decreased  cardiac  output  (dehydration,  dysrhythmia,  cardiomyopathy,  post-cardiopulmonary  bypass)Increased  pulmonary  vascular  resistance  
SN  - 
PB  - McGraw-Hill Education
CY  - New York, NY
Y2  - 2024/04/19
UR  - accesspediatrics.mhmedical.com/content.aspx?aid=1152487573
ER  -