Arterial Blood Gases

Arterial puncture of peripheral to obtain arterial blood for direct measure of , , and PO2
To assess and
3 Primary Sites: (1st choice d/t accessibility and collateral blood flow), , (last choice)

Capillary Stick
Used in
Wrap area in warm wet cloth 5-7 min to the site
Consistent correlation with Arterial and
Do not use for monitoring – values will not match

ABG Kit
5 mL syringe
Needles - ga
Rubber stopper or needle capping device
Adhesive Strip
Alcohol prep
Gauze
Plastic Bag
Container for
Lidocaine if ordered
Label
Sharps

Modified Allen’s test
allen’s test confirms that blood flow is present
1. Hand should pink up within in seconds
2. If color does not return in seconds use a different site
3. Do not attempt or on pt with dialysis shunt

Hazards/Complications
Disruption of blood flow.
Clotting
Bleeding, hold pressure for min
Vessel
Tissue
Anticoagulation

Problems
Air bubble in ABG :
PaCO2 will toward 0.
PaO2 will or decrease towards .
pH will

Improper Cooling of Sample
PaCO2 will
PaO2 will
pH will

Excess Heparin
PaCO2 will towards 0
PaO2 will towards
pH will towards

Flush Solution Dilution
PaCO2 will
PaO2 will
pH will

Assessing Ventilation
Respiratory
Volume
Chest
Breath Sounds
PaCo2
EtCo2

Ventilation:
Abnormal CO2 with normal pH – increase ventilation or start mechanical vent
CO2: – : Normal – Do not change settings. Do not initiate mechanical ventilation
CO2: >: Not ventilating – ventilation. Remove or reduce deadspace. Increase ventilation
CO2: <: Hyperventilation – Don’t initiate mechanical ventilation. Decrease . Consider cause.

Oxygenation assessment:
rate
Color
Sensorium
PaO2
SaO2

Oxygenation: , FiO2
PaO2: - on FiO2 of .21 – 1: Acceptable. Maintain settings
PaO2: < on FiO2 of .21 - .59: Poor Ventilation if PaCO2 in increased. Increase ventilation, increase FiO2 up to 60%
PaO2: < on FiO2 of .60+ - , Refractory Hypoxemia, Venous admixture. Start CPAP or increase PEEP
PaO2: > on FiO2 of .22 – 1: Over oxygenation. Decrease FiO2, or CPAP.

Acid Base Balance: pH
– : Acceptable
< : Acidosis. Uncompensated if CO2 is increased or HCO3- is decreased.
> : Alkalosis. Uncompensated if CO2 is decreased or HCO3- is increased.

Uncompensated vs Compensated
: If pH is in acceptable range
: pH is out of range

Respiratory Acidosis/Alkalosis
pH is abnormal because of a change in the

Metabolic Acidosis/Alkalosis
pH is abnormal because of a change in the

Partially Compensated
pH is out of range and both the and are moving in the same direction
Examples:
Respiratory Acidosis: pH 7.3 CO2 and HCO3- are
Metabolic Alkalosis: pH is 7.5 CO2, and HCO3- are

Troubleshooting
If pt is on room air: Add PaO2 and PaCO2 together. Should be - torr

PaO2 – VQ Mismatch, Diffusion defect, shunting
PaO2 – supplemental O2, bubbles

Type #1 Special Pathology: ABG looks good but pt looks and feels bad

: Measure COHb with co-oximeter. Treat with 100% O2 and hyperbaric O2
: Watch for low Hb. Treat with O2 and transfusion
: Increased deadspace. Vd/Vt is increased. Look for in post op, bed ridden, Hx of DVT, pregnancy, obesity, venous stasis, varicose veins, trauma, atrial fibrillation. Treat with support ventilation and oxygenation, thrombolytics
: Accidental ingestion. Causes methemoglobanemia. Increased levels of methemoglobin interferes with co-oximeter.

Type #2 Special Pathologies: ABG looks bad but patient feels fine

: Chronic respiratory acidosis with decreased

High FiO2 can cause O2 induced

O2 – Hb Disassociation Curve
is method of expressing position of the curve

Left Shift: < P50
O2 affinity
Decreased H+ (increased pH)
Decreased
Decreased Temp
Decreased 2-3 DPG

Right Shift: > P50
O2 Affinity
H+ (decreased pH)
PCO2
Increased Temp
Increased 2-3 DPG

Oximetry
SpO2 – Pulse
Most appropriate non invasive method
Probe attaches to patient and transmits light through capillary beds
Normal: – %
Needs good
Affected by: poor , erythema, bright ambient lights.
Clean probe with alcohol
Will read higher if poisoning is present

Overnight POX
Assesses O2 sats
Sleep related breathing disorders, Sleep apneaUse the time interval for measurement

Co-Oximeter/hemoximeter
Diagnses poisoning
Normal is 0-2% but is higher in smokers (-%)
CO Poisoning is >% SaO2 is calculated in ABG so it won’t be

Capnography
Methods/Procedures
Measures exhaled CO2 content with spectrophotometer or mass .
Calibrated every hours using low and high concentrations
EtCO2 %: Normal is - %
PetCO2 will read lower than

Monitoring PetCO2
PetCO2 means there is a decrease in ventilation.
PetCO2 means there is an increase in ventilation or a decrease in .

Troubleshooting
Moisture or secretions can obstruct tube and give false readings
Condensation can sample flowrate
sampling lines will dampen waveform
Low sampling will dampen waveform

Quality assurance
ABG Controls
2 Types of commercially prepared controls
Based
Aqueous/ Based

ABG methodology
3 commonly used levels of controls: , normal,
All Ran per day
Roles encompass all situations encountered in determining whether a specific value is in or out of control.

Gas Analyzers
2 parameters: range to be measured and conditions of test.
point cal is most common. Multipoint calibration will verify if it is or not.
Involve 1 of 2 techniques: Known concentration of the gas, using lung volume or DLCO simulator.

Other QC methods
testing: unknown control specimens are sent to different labs using same make and model of analyzers
: Labs that have more than 1 ABG analyzer can process samples on 2 or more and compare results.
: Tonometry, allows precision gas mixtures to be equilibrated with whole blood or buffer solution