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Clinical Importance of ABG
  • Physiological monitoring by means of PaCO2, pH, HCO3, and PaO2 measurement
  • Reflection of pt's need for oxygenation and/or ventilation.
ABG's should be drawn ______
  • As often as necessary to ensure safe and effective ventilation
  • When pt is as stable as possible
  • Reasonable time after ventilator change has been made (15 min)
ABG's should not be drawn ________
  • After pt has been transferred
  • After change in O2 status
  • After suctioning
ABG's should not be drawn unnecessarily due to :
  • Cost
  • Risk of infection
  • Pain
  • Loss of hemoglobin
  • Availibility of monitors
  • Pt Anxiety
Arterial blood analysis reveals :
  • The effect heart and lungs have on gas exchange before the oxygenated blood reaches the tissue
  • Compared to venous blood the amount of O2 consumed and CO2 produced at tissue level
Most desirable sites for ABG draws
  • Radial artery (preferred)
  • Brachial artery 2nd choice
  • Femoral artery
  • Dorsalis pedis (least preferred)
Radial artery ABG's
  • Most common site for ABG draw
  • Easiest site to palpate, stabilize, and puncture.
  • Modified Allen's test should always be performed before puncturing radial artery
Brachial artery ABG's
  • Second choice for draws
  • Very high risk of thromboembolism
  • Embolism can block blood flow to the radial and ulnar arteries
  • Embolism could lead to ischemia of the hand and forearm
Femoral artery ABG's
  • Third choice for draws
  • Usually done only on unconscious pts
  • Significant risk of hemotoma
  • Higher risk of infection
  • Artery is in close proximity to nerve and vein 
Dorsalis pedis ABG's
  • Least preferred site
  • Located on top of foot
  • Difficult to palpate, stabilize and puncture
Contraindications of arterial puncture
  • Failed Modified Allen's test
  • Pt's with abnormal bleeding time
  • Pt's receiving anticoagulant therapy
Complications of arterial puncture
  • Uncontrolled bleeding
  • Infection
  • Hematoma
  • Thrombosis
  • Hemorrhage
  • Pain
  • Peripheral nerve damage
  • Define Hematoma
  • Mass of blood
  • Usually clotted
  • Confined to tissue or space
  • Caused by break in blood vessel
Care following arterial puncture
  • Hold pressure on site for at least 3 min
  • Never recap a dirty needle
  • Never bend, break, or remove needles by hand
  • Always dispose of needles in appropriate containers
Reasons for continued bleeding
  • Pt is on anti-coagulant therapy
  • Pt has bleeding disorder
  • Pt has low platelet count
  • Artery has been lacerated
Results of ABG are most reliable when drawn by RRT because we know when:
  • The last vent change occured
  • The last O2 change occured
  • When the patient was last seen
  • When the tx was last given
  • What pts activity level has been
Modified Allen's Test
  • Have pt extend arm from which sample will be drawn
  • Squeeze wrist at site of radial and ulnar arteries to occlude blood flow
  • Have pt make fist
  • Have pt open hand maintain pressure
  • Palm should be blanched
  • Release pressure from ulnar artery
  • Color should return to palm within ten seconds
  • If color does not return select another site
Equipment needed for ABG
  • Appropriate doctor's order
  • ABG heparinized syringe
  • Needle
  • Gauze
  • Tape
  • Alcohol
  • Label
  • Cup/Ice
  • Towel
  • Gloves
Purpose of using local anesthetic
  • Lessen effect of nerves near the puncture site
  • Relax muscles near puncture site
  • Prevent or relax vasoconstriction of artery
Use of local anesthetic
  • For pts with extremely low pain tolerance
  • Inject a small amount of lidocaine. subcutaneously and peri-arterially
  • Wait 2 minutes for effect
Information required to report ABG
  • Name of pt
  • Date/ Time
  • Site of sample
  • Pts temp
  • FIO2
  • Your initials
ABG draw on infants/children < 5 yrs
  • Newborns within first 24 hrs umbilical artery
  • Infant/Pediatric arteries are difficult to locate
  • Preferred method is finger,toe or heel (Capillary Blood Gas)
Complications of a capillary stick
  • Tissuse damage due to squeezing the sample site
  • Infection
Capillary Boold Gas Values
  • pH  7.35-7.45
  • PCO2  26-41 torr
  • PO2  40-60 torr
  • HCO3  16-24 mEq/L
  • Approx values for adults and chldren over 8 yrs
  • Not a good monitor for assessing oxygenation
  • Used primarily for monitoring CO2 and pH
Factors affecting ABG results
  • Air contact
  • Clotting within sample
  • Pt Temperature
  • Suctioning
  • Change in FIO2
  • Machineo out of calibration
  • Delay in time between draw and sample anlaysis
Indications for arterial lines
  • Critically ill pts who require frequent ABG's
  • Pts with unstable cardiovascular system and require continous monitoring
Arterial line sites

  • radial artery

  • femoral artery

  • brachial artery

Rt's only do radial artery
Define anacrotic limb
Upstroke of the waveform that represents a rapid injection of blood from the ventricle into the aorta
Define dicrotic notch
Notch of waveform represents the point where pressure in ventricle is less than pressure in aorta, aortic valve closes
Define dicrotic limb
Down stoke of waveform that represents gradual fall in blood pressure as blood flows into the periphery
Causes of dampened waveform
  • Blood clot occluding catheter tip
  • Air bubbles in catheter or transducer
  • Catheter tip is against wall of artery
  • Catheter is kinked
Hemodynamic normal parameters
  • Systolic pressure 100-140 mmHg
  • Diastolic pressure 60-90 mmHg
  • Mean arterial pressure 105-70 mmHg
Blood pressure reading from a line may read :
5-15 mmHG higher than cuff blood pressure
Risks associated with art-lines
  • Infection
  • Massive blood loss
  • Thrombus formation
Sanz electrode
  • Measures H+ ion concentration (pH)
  • One reference electrode (known pH)
  • One measuring electrode contains electrolyte solution with a silver-silver chloride wire
Two point calibration (Sanz)
  • Low pH solution 6.840
  • High pH solution 7.384
Severinghaus electrode
  • Outer Lucite jacket capped w/teflon membrane
  • As CO2 crosses membrane it causes current change
  • measures PCO2
Clark electrode
  • Uses silver-silver chloride anode and platinum cathode
  • electrode capped with polypropylene membrane permits diffusion of O2
  • Measures PO2
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