ABGs and Oxygenation

1
ABGs and Oxygenation

• RC 290

2
ABG Sampling Sites

• Umbilical artery catheter (UAC)
• Clots may form on the end
• Remember, it is post-ductal blood so the PaO2 may
  be lower than pre-ductal PaO2

3
ABG Sampling Sites Punctures

• Radial artery and temporal artery
• Can be hard to hit
• Brachial should not be used
• NEVER use the femoral artery in an infant!

4
ABG Sampling Sites Capillary

• Easier to puncture than radial or temporal artery
• PO2 may not correlate well to PaO2
• Heel has to be warmed prior to puncture to
  arterialize the site

5
ABG Values Well Baby

• pH 7.30 7.45
• PaCO2 35-45
• PaO2 60-90

• HCO3 18-21
• B.E. /- 2
• sat 90 orgt

6
Acceptable ABGs Sick Baby

• pH 7.25 7.35
• PaCO2 35-55
• Depends on pH
• PaO2 50-70

• HCO3 18-21
• B.E. /- 2
• sat 90 or gt

7
Capillary gases use the same values EXCEPT for PO2

• Capillary PO2 35-50
• Capillary sat 75-85

8
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!

9
Cyanosis

• Classic definition 5 grams of unsaturated
  hemoglobin
• Infant may not show signs of cyanosis until PaO2
  lt 40 (sat between 75-85)

10
Effects of Hypoxia

• Decreased tissue oxygenation
• Lactic acidosis
• Hypoglycemia
• Increased PVR and PAP
• May allow shunting across ductus arteriosus or
  foramen ovale

• Decreased surfactant
• Worsening of hypoxemia
• Decreased thermogenesis
• Cold stress/hypothermia
• Brain CNS damage

11
Hyperoxia PaO2 gt 100

• Hyperoxia may damage the neonates eyes and/or
  lungs

12
Retinopathy of Prematurity (ROP)

• 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 (its the PaO2, not the
  FIO2), and the duration of O2
• Vitamin A and/or E may help prevent it

13
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
  (why?)
• Increased surface tension due to decreased
  surfactant
• Inflammatory exudate and hyaline membrane
  formation
• Sloughing of alveolar epithelium
• Fibrosis

14
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 Flip-Flop
• It is not unusual to limit changes in FIO2 to
  1-2!

15
O2 Therapy Devices
16
Nasal Cannula

• Should be used with a blender
• 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

17
Hoods

• 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
  hearing

Note A heated, humidified flow of 10-12 LPM may
be used in isolette