ABGs and Oxygenation

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					  ABGs and Oxygenation

RC 290
ABG Sampling Sites
         • Umbilical artery
           catheter (UAC)
            – Clots may form on the
            – Remember, it is post-
              ductal blood so the
              PaO2 may be lower
              than pre-ductal PaO2
ABG Sampling Sites: Punctures
               • Radial artery and
                 temporal artery
                  – Can be hard to hit
               • Brachial should not be
               • NEVER use the
                 femoral artery in an
ABG Sampling Sites: Capillary
               • Easier to puncture
                 than radial or temporal
               • PO2 may not correlate
                 well to PaO2
               • Heel has to be warmed
                 prior to puncture to
                 “arterialize” the site
      ABG Values: Well Baby
• pH: 7.30 – 7.45   • HCO3: 18-21
• PaCO2: 35-45      • B.E.: +/- 2
• PaO2: 60-90       • %sat: 90% or>
   Acceptable ABGs: Sick Baby
• pH: 7.25 – 7.35    • HCO3: 18-21
• PaCO2: 35-55       • B.E.: +/- 2
   – Depends on pH   • %sat: 90% or >
• PaO2: 50-70
Capillary gases use the same
 values EXCEPT for PO2
      Capillary PO2: 35-50
     Capillary %sat: 75-85%
    Why lower PO2 values Are
     acceptable in the neonate
• O2 dissociation curve is shifted to the left
  so affinity is increased – hemoglobin
  saturates at a lower PaO2
  – Presence of HBF
  – Decreased 2,3-DPG
• Neonate not considered hypoxemic until
  PaO2 is less than 50!
• Classic definition: 5 grams% of unsaturated
• Infant may not show signs of cyanosis until
  PaO2 < 40 (%sat between 75-85%)
           Effects of Hypoxia
• Decreased tissue          • Decreased surfactant
  oxygenation                  – Worsening of
• Lactic acidosis                hypoxemia
• Hypoglycemia              • Decreased
• Increased PVR and           thermogenesis
  PAP                          – Cold
  – May allow shunting           stress/hypothermia
    across ductus
    arteriosus or foramen   • Brain & CNS damage
  Hyperoxia: PaO2 > 100

Hyperoxia may damage the neonate’s
         eyes and/or lungs
     Retinopathy of Prematurity
• Hyperoxia causes vasospasm and ischemia in
  retinal arterioles
• Ischemia and compensatory vasodilation and
  proliferation causes retinal edema which may lead
  to detachment and blindness
• ROP incidence increases with these three factors:
   – Prematurity, hyperoxia (it’s the PaO2, not the FIO2),
     and the duration of O2
   – Vitamin A and/or E may help prevent it
      O2 Toxicity in the Lungs
Here it is the FIO2 which causes high PAO2
This causes the following pathological changes:
• Decreased alveolar volume, ie decreased FRC
• Increased surface tension due to decreased
• Inflammatory exudate and hyaline membrane
• Sloughing of alveolar epithelium
• Fibrosis
    Management of O2 Therapy
• Keep PaO2 between 50-70!
   – For hypoxemia on 21%, start FIO2 between 25-35%
   – Use guideline that 1% change in FIO2 will maximally
     change PAO2 by 7 mmhg
• Avoid Flip-Flop phenomenon
   – Changing FIO2 by more than 5-10% at one time may
     cause sudden deterioration
   – The longer the infant is on O2, the more prone he is to
• It is not unusual to limit changes in FIO2 to 1-2%!
O2 Therapy Devices
Nasal Cannula
       • Should be used with a
       • One or both prongs may
         be removed
       • Special flowmeters allow
         flows of less than 1 LPM
         to be used
       • Vapotherm– high
         humidity and flow through
         cannula, e.g. 5-6 LPM
                                    • Best to use a blender
                                      to flood the hood with
                                      a precise FIO2
                                    • Flow needs to be 5-7
                                      LPM to flush out CO2
                                    • Noise inside hood may
                                      be damaging to infants
Note: A heated, humidified flow of 10-12 LPM may be used in isolette

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