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What are the Acceptable Sites for Arterial Puncture?
- Radial Artery ( most preferred)
- Brachial Artery
- Femoral Artery
- Dorsalis Pedis
Why is the Radial Artery the Preferred Site?
- Artery is superficial
- Not adjacent to large veins
- Easy to palpate
- Presence of collateral blood flow
- Relative safety by being so distal on the limb
Why is the Brachial Artery is NOT the Preferred Site?
- Relative proximity to a large vein and nerve
- Contact with nerve can be very painful
- Inadvertent venous sampling
- Limited collateral circulation
Why draw from the Femoral Artery?
- The femoral artery is very large
- It is easy to find
- It is the only site available:
- - During CPR
- - Low QT
- - Hypotension / Hypovolemia
Why is the Femoral Artery is NOT the Preferred Site for blood draw?
- Potential trauma to the major arterial blood supply to the lower extremity
- Vessel Relative proximity to a large vein.
- It may be deep and difficult to locate.
- Lacks sufficient collateral circulation.
What readings will Air bubbles in sample give?
- Will normally decreased PaCO2
- Will normally increased pH
- Will normally increased PaO2
What readings will a Delay in analysis give?
- Will normally increased PaCO2
- Will normally decreased PaO2
- Will normally decreased pH
If properly iced, a blood gas sample will have little changed in values if analyzed within how long?
What will too much heparin left in the syringe cause to the readings of a blood gas?
- Will normally decreased pH
- Make sure expel all liquid from syringe
Why might we accidentally draw venous blood when sampling a blood gas?
- sometimes hard to distinguish arterial from venous in hypoxic pt.
- Sometimes the blood will not pulsate in the hypotensive pt.
What will Patient Anxiety cause to the result of a blood gas?
- Can lead to hyperventilation
- Hyperventilation normally
- increase O2
- decrease CO2
- increase pH
What may clots cause to a blood gas reading?
- Loss of blood gas sample
- Delays in running samples
- Delays in recording the blood gas results
- Causing the analyzer to "go down" for maintenance, further delaying blood gas analysis
What is the proper process of drawing an arterial blood gas?
- confirm the order and chart review
- Determine if the patient is anticoagulated
- - Normal platelet count 150,000-400,000/mm3
- - Rule of thumb: Normal clotting time 1-7 minutes
- Obtain needed equipment
- Perform Allen�s test
- If the radial artery is unsuitable as a puncture site:
- - The dorsalis pedis artery is the second choice
- - Followed by the posterior tibial artery
- Femoral artery punctures are performed only in emergency situations in children.
- Femoral artery punctures are never performed in neonates.
What are Contraindications to an ABG puncture?
- Abnormal modified Allen�s test
- should not be performed through a lesion or through or distal to a surgical shunt (e.g., as in a dialysis patient)
- evidence of infection or peripheral vascular disease involving the selected limb, an alternate site should be selected
- coagulopathy or medium-to-high-dose anticoagulation therapy
- - Heparin
- - Coumadin
- - Streptokinase
How are capillary sample sites choosen?
- A highly vascularized capillary bed:
- - Heel
- - Big Toe
- - Finger: do not use on infants
For a heel, only stick on the _________ side of the heel never over the ________ tendon, this will scar and cause painful walking later in life.
What is the proper process for drawing a capillary blood gas?
- Arterialize the heel by warming it to 42-45 degrees for 5-15 minutes prior to the stick via:
- - heat lamp
- - warm bath
- - chemical heat pack
- After the site is cleaned and prepped, a lancet is used to punch a single 2.5 mm deep hole in the heel, establishing a free flow of blood
- Do NOT squeeze of milk the site
- First amount of blood that comes out should be wiped away due to serous fluid
- A pre-heparinized capillary tube is inserted into the drops of blood and allowed to fill to the predetermined volume
- hand carry the sample to the ABG lab
- If the sample can not be hand carried to blood gas lab:
- - Both ends of the tube are capped or sealed after a flea is inserted.
- - The flea is used to mix the sample and prevent clotting.
- - The sample is iced until analyzed
Why should we not squeeze or milk a capillary blood gas puncture site?
- It de-arterializes the site.
- Will cause the sample to clot
What are the advantages of Arterial Catheter (A-Line) Sampling?
- Minimal trauma to patient
- Allows for repeated sampling
- Ability to monitor blood pressure in "real time"
What are the disadvantages of Arterial Catheter (A-Line) Sampling?
- Air emboli
- Tissue trauma
- Loss of volume
Continuous, non-invasive monitoring of carbon dioxide and oxygen levels is an example of what?
How Does Transcutaneous Monitoring Work?
- The major resistance to transcutaneous gas diffusion is the lipid structure of the skin.
- Heating an area of the skin to 41- 45o liquefies the lipid structure allowing the molecules to line up and creating the channels for gas diffusion.
- - Heat shifts the oxygen dissociation curve to the right, releasing O2.
- - Heat also causes vasodilation, arterializing the blood.
- - Adaptations of the Clark and Severinghaus electrodes are utilized.
Heat shifts the oxygen dissociation curve to the _______, releasing O2
Heat will cause vasodilation or vasoconstriction, which in turn arterializes the blood?
Pt___ tends to correlate better to arterial values than Pt__.
Why does PtCO2 tend to correlate better to arterial values than PtO2?
- CO2 diffuses easier than O2
- CO2 electrode has a larger surface area for diffusion
- PtO2 usually tends lower than PAO2
Why are transcutaneous monitors used (clinical application)?
- General trending
- Changes in vascular blood flow
- Monitor for ROP
- To reduce the number of blood gas "sticks"
- Ventilator management, especially during HFO
What are the limitations of transcutaneous monitors?
- Insufficient heat applied to skin
- Blistering of skin
- Vasopressive drugs
- Poor perfusion to skin, especially if placed over bony prominences, or distal extremities.
- Be sure to select fleshly sites with good capillary refill (<2 sec.)
What is another major limitaion of transcutaneous monitors?
- Can also be labor intensive:
- Requires frequent site changes (q 2-4 hours, minimum)
- Calibration q 8-12 hours
- Electrode will need to be cleaned, re-membraned, and re-calibrated between pts
How do we troubleshoot a transcutaneous monitor is they do not correlate to blood gas values?
- Check for air-leak around electrode site
- Need to change membrane
- Need to change site
- Edematous site and/or patient
- Check for vasoactive drugs (e.g. epinephrine)
Where is Conjunctival Transcutaneous Electrode placed?
under the eye lid
What is Capnography/Capnometry?
- Measurement of exhaled or end tidal PaCO2 (PetCO2)
- Provides continuous, accurate monitoring of PaCO2
What does Capnography/Capnometry use?
spectrophotometric infrared analyisis of Exhaled CO2
What are the two methods used to collect and analyze gas in Capnography/Capnometry?
- Sidestream analyzer
- Mainstream analyzer
What are the advantages and disadvantages of a Sidestream analyzer?
- Removes sample continuously through a small tube
- - Measurements are delayed
- Light weight, less likely to cause inadvertent extubation
What are the advantages and disadvantages of a Mainstream analyzer?
- Analyzes at the airway
- - Measurements are current
- Accidental extubation is a hazard
What tends to alter exhaled PaCO2?
End tidal CO2 monitors show changes in function, not condition. Some examples that help demonstrate this are things suchas?
- Deadspace: Causes decreased PetCO2 levels. PetCO2 will be lower than arterial levels
- Shunting: Often shows no change. CO2 diffuses 20 times faster than O2. ONLY decreases with SIGNIFICANT shunting.
What are some Conditions that increase deadspace?
- Pulmonary embolus
- High pressures from mechanical ventilation
What are some Conditions that cause shunting?
- Tetrology of Fallot (diseases that cause cardiac problems)
- Atrial Septal Defect
- Tricuspid Atresia
- Airway Obstruction
- Consolidation (Pneumonia)
What are Limitations to PetCO2 monitoring?
Can only show changes in ventilaotry condition, not improvement or deterioration
An increase in PetCO2 during PetCO2 monitoring may be due to?
- Decreased ventilation
- Decreased QT
- Worsening V/Q
A decrease in PetCO2 during PetCO2 may be due to?
- Improvement in ventilation
- Increased deadspace ventilation