Determination of Endotracheal Tube Size in a Perinatal Population

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Determination of Endotracheal Tube Size in a
Perinatal Population

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Anesthesiology, V104, No 5, May 2006
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• Advances in neonatal medicine have contributed to
  survival of extremely preterm infants
• Design on intubation was based on different type
  of lesions report and experimental studies
  dealing with development of postintubation
  lesions
• Injury occurs two levels posterior part of
  glottic plane( vocal process necrosis or
  cricoarytenoid ankylosis), subglottic level(
  cricoid necrosis and subglottic stenosis)

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• Etiologies injury of mucosa and ischemic lesions
  caused by pressure excess on laryngeal structures
  
• Subglottic lumen mucosa ischemic lesion(
  endotracheal tube and cricoid cartilage)
• Main determinant of injury( excessive tube size)
• Postintubation subglottic stenosis 04
• Posterior glottic lesions more frequent

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Materials and Methods
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• 150 postmortem examinations
• Free of malformative syndromes affecting the
  laryngotracheal structures and never been
  intubated
• Anatomical pieces study within 6 h after death
• No fixative agent or conservative agent
• Intubated to estimate largest tube size without
  glottic friction or cricoid deformation( Clinical
  ID)

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• Potex Blue Line endotracheal tubes( size 2.54.0)
  and Vygon endotracheal tube( size 2.0)
• lt tube size 2.0 could not be introduced without
  cricoid deformation considered high injury risk
  intubation

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• Second stage intubated with different calibrated
  inextensible ballons of increasing size
• Thermoformed polyvinyl chloride fixed on 18-gauge
  catheter
• Balloon connect to low-pressure manometer and
  inflated with 20 cm H2O pressure
• Positioned through laryngotracheal structures
  with proximal extremity 1cm over glottis and
  distal one sticking out under fifth tracheal ring

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• Pressure ID (pass through laryngotracheal
  structures without increasing balloon pressure or
  with normalization pressure at least 15 min)
• Optimal tube size corresponded to pressure ID
• High injury risk smallest balloon remained
  increased for at least 15 min

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• Dissected larynx for anatomical estimation
• Separated along inferior edge of cricoid
  cartilage
• Measure anteroposterior and lateral diameters of
  subglottic and trachea, interarytenoid distance(
  IAD)
• Optimal tube size corresponded to tube whose
  external perimeter less than or equal to
  subglottic or tracheal perimeter( SG ID)
• Maximal tube size pass through glottic plane OD
  less than or equal to IAD( IAD ID)

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Results
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• Causes of fetus death Neurologic malformation(43
  cases), Cardiac malformation( 31 cases),
  Urogenital malformation( 12 cases),
  polymalformative syndromes( 11 cases),
  intrauterine death( 17 cases), stillbirth( 8
  cases)
• Cause of infant death sudden death( 24 cases),
  nonreanimated neurologic disease( 4 cases)
• Laryngeal mask was used as resuscitation( 9
  cases)
• No infant was intubated

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• No statistical difference between males and
  females for subglottic and tracheal measures
• Interarytenoid distance in females was
  significantly less than population ( group E)

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• Clinical ID significantly greater than pressure
  ID
• Highest correlation coefficients with corrected
  GA and birth weight( respectively, clinical ID
  r0.841, r0.834 SG ID r0.825, r0.808 IAD ID
  r0.704, r0.663 pressure ID r0.770, r0.773)

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Discussion
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• Fresh autopsy specimens to ensure airway
  dimensions close to live patients
• Physicochemical characteristics of cartilaginous
  structures similar to physiologic conditions( for
  pressure evaluation)
• Embedded specimen( tissue shrinkage) impossible
  to realize( IAD correspond to abduction passive
  movement of cricoarytenoid joint)

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• Concerns premature babies less than 37 weeks
  gestation
• SG ID systemically lower those obtained with
  other methods( pressure, clinical, and IAD
  estimation)
• Dimensions of the cricoid lumen in preterm
  infants less than published previously in same
  age group
• Dimensions of cricoid lumen in term neonates
  consistent with published in some studies but
  less than published in others

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• Attributed to interindividual variablity due to
  small sample sizes, differences in measurement
• Differences Measuring luminal diameters at
  predetermined plans in the cricoid ring, Level of
  section and orientation of section plane

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• Ultrasound measurements of tracheal diameter in
  fetuses smaller diameter than the result
• Ultrasound smaller than anatomical measurements
• Cricoid lumen and age hyperbolic relation or
  quasi-linear relation

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• Absence of difference between males and females
  for laryngeal and tracheal, IAD no observation
• Some studies Anteroposterior dimension of
  glottis exceeds subglottis and tracheal lumen
• Only IAD potential limiting factor at the
  level of glottis
• Smaller size tube for females older than 40 weeks
  GA may be considered

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• Pressure study based on capillary pressure 2030
  mmHg in adults, venous end of capillary 12mmHg
• Nordin et al. ischemic lesions as result of
  excessive pressure after 15 min
• Normal pressure in preterm infants not report
  maximum inflation pressure 20 cmH2O(13 mmHg)
• Circumferential muscular structure and
  adipoconnective tissue not significantly affect
  pressure variation

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• Pressure study didnt define level of obstacle
  in case of pressure increase
• Didnt consider potential pressure induced by
  inclination of tube by upper structures( nasal
  fossa, oropharynx) and position of head
• Anatomical study thinner level of lumen
  corresponds to subglottic area
• High number of patients considered to have high
  injury risk according to anatomical estimation
  compared with pressure estimation

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• Premature laryngeal structures possess an
  elasticity allowing passage of a tube with higher
  size than that predicted by anatomical
  measurements
• Better tolerance of intubation in premature
  infants
• Limiting factor interarytenoid distance
• Risk of injury posterior glottis
• Elasticity disappears around 37 weeks GA,
  limiting parameter becomes cricoid area, risk of
  subglottic stenosis

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• Clinical estimation ID dose not seem to be valid
  criterion to determine tube size
• Correction of GA based on biometric parameters
  seems unrealistic in clinical practice.
  Guidelines based on birth weight seem more
  relevant
• Similar OD, difference of ID reach 1 mm
• Important for tube choice due to ventilation
  assistance
• Provide safe intubation and limit laryngeal
  injury for this study

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