ABGs and Oxygenation RC 290

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

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!

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

ABG Values: Well Baby pH: 7.30 – 7.45 PaCO2: 35-45 PaO2: 60-90 HCO3: 18-21 B.E.: +/- 2 %sat: 90% or>

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 >

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!

Cyanosis Classic definition: 5 grams% of unsaturated hemoglobin Infant may not show signs of cyanosis until PaO2 < 40 (%sat between 75-85%)

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

Hyperoxia may damage the neonate’s eyes and/or lungs Hyperoxia: PaO2 > 100 Hyperoxia may damage the neonate’s eyes and/or lungs

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 (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 (why?) Increased surface tension due to decreased surfactant Inflammatory exudate and hyaline membrane formation 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 Flip-Flop It is not unusual to limit changes in FIO2 to 1-2%!

O2 Therapy Devices

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

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