Arterial Blood Gases

Arterial puncture of peripheral [blank_start]artery[blank_end] to obtain arterial blood for direct measure of [blank_start]pH[blank_end], [blank_start]PACO2[blank_end], and PO2 To assess [blank_start]ventilation[blank_end] and [blank_start]oxygenation[blank_end] 3 Primary Sites: [blank_start]Radial[blank_end] (1st choice d/t accessibility and collateral blood flow), [blank_start]Brachial[blank_end], [blank_start]Femoral[blank_end] (last choice)

Capillary Stick Used in [blank_start]infants[blank_end] Wrap area in warm wet cloth 5-7 min to [blank_start]arterialize[blank_end] the site Consistent correlation with Arterial [blank_start]pH[blank_end] and [blank_start]PCO2[blank_end] Do not use for [blank_start]O2[blank_end] monitoring – values will not match

ABG Kit 5 mL [blank_start]heparinized[blank_end] syringe Needles [blank_start]20[blank_end]-[blank_start]25[blank_end] ga Rubber stopper or needle capping device Adhesive Strip Alcohol prep Gauze Plastic Bag Container for [blank_start]Ice[blank_end] Lidocaine if ordered Label Sharps

Modified Allen’s test [blank_start]Positive[blank_end] allen’s test confirms that [blank_start]collateral[blank_end] blood flow is present 1. Hand should pink up within in [blank_start]2[blank_end] seconds 2. If color does not return in [blank_start]5[blank_end] seconds use a different site 3. Do not attempt [blank_start]radial[blank_end] or [blank_start]brachial[blank_end] on pt with dialysis shunt

Hazards/Complications Disruption of blood flow. [blank_start]Hematoma[blank_end] Clotting Bleeding, hold pressure for [blank_start]5[blank_end] min Vessel [blank_start]spasm[blank_end] Tissue [blank_start]trauma[blank_end] Anticoagulation [blank_start]therapy[blank_end]

Problems Air bubble in ABG : PaCO2 will [blank_start]decrease[blank_end] toward 0. PaO2 will [blank_start]increase[blank_end] or decrease towards [blank_start]150[blank_end]. pH will [blank_start]increase[blank_end]

Improper Cooling of Sample PaCO2 will [blank_start]increase[blank_end] PaO2 will [blank_start]decrease[blank_end] pH will [blank_start]decrease[blank_end]

Excess Heparin PaCO2 will [blank_start]decrease[blank_end] towards 0 PaO2 will [blank_start]increase[blank_end] towards [blank_start]150[blank_end] pH will [blank_start]decrease[blank_end] towards [blank_start]7.0[blank_end]

Flush Solution Dilution PaCO2 will [blank_start]decrease[blank_end] PaO2 will [blank_start]increase[blank_end] pH will [blank_start]decrease[blank_end]

Assessing Ventilation Respiratory [blank_start]Rate[blank_end] [blank_start]Tidal[blank_end] Volume Chest [blank_start]movement[blank_end] Breath Sounds PaCo2 EtCo2 Ventilation: [blank_start]PaCO2[blank_end] Abnormal CO2 with normal pH – [blank_start]do not[blank_end] increase ventilation or start mechanical vent CO2: [blank_start]35[blank_end] – [blank_start]45[blank_end]: Normal – Do not change settings. Do not initiate mechanical ventilation CO2: >[blank_start]45[blank_end]: Not ventilating – [blank_start]Initiate[blank_end] ventilation. Remove or reduce deadspace. Increase ventilation CO2: <[blank_start]35[blank_end]: Hyperventilation – Don’t initiate mechanical ventilation. Decrease [blank_start]ventilation[blank_end]. Consider cause.

Oxygenation assessment: [blank_start]Heart[blank_end] rate Color Sensorium PaO2 SaO2 Oxygenation: [blank_start]PaO2[blank_end], FiO2 PaO2: [blank_start]80[blank_end] - [blank_start]100[blank_end] on FiO2 of .21 – 1: Acceptable. Maintain settings PaO2: <[blank_start]80[blank_end] on FiO2 of .21 - .59: Poor Ventilation if PaCO2 in increased. Increase ventilation, increase FiO2 up to 60% PaO2: <[blank_start]80[blank_end] on FiO2 of .60+ - [blank_start]Shunting[blank_end], Refractory Hypoxemia, Venous admixture. Start CPAP or increase PEEP PaO2: >[blank_start]100[blank_end] on FiO2 of .22 – 1: Over oxygenation. Decrease FiO2, [blank_start]PEEP[blank_end] or CPAP.

Acid Base Balance: pH [blank_start]7.35[blank_end] – [blank_start]7.45[blank_end] : Acceptable <[blank_start]7.35[blank_end] : Acidosis. Uncompensated if CO2 is increased or HCO3- is decreased. >[blank_start]7.45[blank_end] : Alkalosis. Uncompensated if CO2 is decreased or HCO3- is increased. Uncompensated vs Compensated [blank_start]Compensated[blank_end]: If pH is in acceptable range [blank_start]Uncompensated[blank_end]: pH is out of range Respiratory Acidosis/Alkalosis pH is abnormal because of a change in the [blank_start]PaCo2[blank_end] Metabolic Acidosis/Alkalosis pH is abnormal because of a change in the [blank_start]HCO3-[blank_end] Partially Compensated pH is out of range and both the [blank_start]CO2[blank_end] and [blank_start]HCO3-[blank_end] are moving in the same direction Examples: Respiratory Acidosis: pH 7.3 CO2 and HCO3- are [blank_start]high[blank_end] Metabolic Alkalosis: pH is 7.5 CO2, and HCO3- are [blank_start]high[blank_end]

Troubleshooting If pt is on room air: Add PaO2 and PaCO2 together. Should be [blank_start]110[blank_end]-[blank_start]140[blank_end] torr [blank_start]Decreased[blank_end] PaO2 – VQ Mismatch, Diffusion defect, shunting [blank_start]Increased[blank_end] PaO2 – supplemental O2, bubbles

Type #1 Special Pathology: ABG looks good but pt looks and feels bad [blank_start]CO Poisoning[blank_end]: Measure COHb with co-oximeter. Treat with 100% O2 and hyperbaric O2 [blank_start]Anemia[blank_end]: Watch for low Hb. Treat with O2 and transfusion [blank_start]Pulmonary Embolism[blank_end]: 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 [blank_start]Nitrate Poisoning[blank_end]: Accidental ingestion. Causes methemoglobanemia. Increased levels of methemoglobin interferes with co-oximeter. Type #2 Special Pathologies: ABG looks bad but patient feels fine [blank_start]COPD[blank_end]: Chronic respiratory acidosis with decreased [blank_start]PaO2[blank_end] High FiO2 can cause O2 induced [blank_start]hypoventilation[blank_end]

O2 – Hb Disassociation Curve [blank_start]P50[blank_end] is method of expressing position of the curve Left Shift: <[blank_start]27[blank_end] P50 [blank_start]Increased[blank_end] O2 affinity Decreased H+ (increased pH) Decreased [blank_start]PCO2[blank_end] Decreased Temp Decreased 2-3 DPG Right Shift: > [blank_start]27[blank_end] P50 [blank_start]Decreased[blank_end] O2 Affinity [blank_start]Increased[blank_end] H+ (decreased pH) [blank_start]Increased[blank_end] PCO2 Increased Temp Increased 2-3 DPG

Oximetry SpO2 – Pulse [blank_start]Oximeter[blank_end] Most appropriate non invasive method Probe attaches to patient and transmits light through capillary beds Normal: [blank_start]93[blank_end] – [blank_start]97[blank_end]% Needs good [blank_start]perfusion[blank_end] Affected by: poor [blank_start]perfusion[blank_end], erythema, bright ambient lights. Clean probe with alcohol Will read higher if [blank_start]CO[blank_end] poisoning is present Overnight POX Assesses O2 sats [blank_start]overnight[blank_end] Sleep related breathing disorders, Sleep apneaUse the [blank_start]shortest[blank_end] time interval for measurement Co-Oximeter/hemoximeter Diagnses [blank_start]CO[blank_end] poisoning Normal is 0-2% but is higher in smokers ([blank_start]5[blank_end]-[blank_start]10[blank_end]%) CO Poisoning is >[blank_start]20[blank_end]% SaO2 is calculated in ABG so it won’t be [blank_start]accurate[blank_end]

Capnography Methods/Procedures Measures exhaled CO2 content with [blank_start]infrared[blank_end] spectrophotometer or mass [blank_start]spectrometer[blank_end]. Calibrated every [blank_start]8[blank_end] hours using low and high [blank_start]CO2[blank_end] concentrations EtCO2 %: Normal is [blank_start]3[blank_end] - [blank_start]5[blank_end]% PetCO2 will read lower than [blank_start]PaCO2[blank_end] Monitoring PetCO2 [blank_start]Increased[blank_end] PetCO2 means there is a decrease in ventilation. [blank_start]Decreased[blank_end] PetCO2 means there is an increase in ventilation or a decrease in [blank_start]perfusion[blank_end]. Troubleshooting Moisture or secretions can obstruct tube and give false readings Condensation can [blank_start]slow[blank_end] sample flowrate [blank_start]Long[blank_end] sampling lines will dampen waveform Low sampling [blank_start]rates[blank_end] will dampen waveform

Quality assurance ABG Controls 2 Types of commercially prepared controls [blank_start]Blood[blank_end] Based Aqueous/[blank_start]Flourocarbon[blank_end] Based ABG methodology 3 commonly used levels of controls: [blank_start]Acidotic[blank_end], normal, [blank_start]alkalotic[blank_end] All Ran [blank_start]once[blank_end] per day [blank_start]Westgaurd[blank_end] Roles encompass all situations encountered in determining whether a specific value is in or out of control. Gas Analyzers 2 parameters: [blank_start]Physiologic[blank_end] range to be measured and [blank_start]sampling[blank_end] conditions of test. [blank_start]2[blank_end] point cal is most common. Multipoint calibration will verify if it is [blank_start]linear[blank_end] or not. Involve 1 of 2 techniques: Known concentration of the gas, using lung volume or DLCO simulator. Other QC methods [blank_start]Profeciency[blank_end] testing: unknown control specimens are sent to different labs using same make and model of analyzers [blank_start]Multi Machine Analysis[blank_end]: Labs that have more than 1 ABG analyzer can process samples on 2 or more and compare results. [blank_start]Gas exchange validation[blank_end]: Tonometry, allows precision gas mixtures to be equilibrated with whole blood or buffer solution