2 ObjectivesList the normal values for parameters found in a blood-gas analysis.List the normal values for parameters found in a CO-Oximetry analysis.Differentiate between measured and calculated (derived) blood gas data.List the three physiologic processes assessed with blood gas data.State the PaCO2 equation.Describe how alveolar minute ventilation is derived.Describe the relationship between PaCO2, CO2 production and Alveolar Minute Ventilation.
3 ObjectivesDescribe the effects of altitude on partial pressure, barometric pressure and fractional concentrations.Given appropriate data, use Dalton’s Law to determine the resultant partial pressures of a gas in a mixture.Given appropriate data, calculate the Alveolar Air Equation.Explain how changes in the PIO2 or PaCO2 levels affect the PAO2.State the formula for Oxygen Content and Oxygen Delivery.
4 Arterial Blood-Gas Analysis Two ComponentsAcid Base Balance/VentilationpH, PaCO2, HCO3-, BEElectrolytes (primarily K+)OxygenationPaO2, Hb, CaO2, SaO2, MetHb%, COHb% & any other abnormal Hemoglobin species.Oxygenation Indices: PaO2/FIO2, A-aDO2, s/t.
22 High Altitude Response Increase Altitude¯ PBARO ¯ PIO2 ¯ PAO2 ¯ PaO2To adapt to high altitudesChange the environmentAirplanes are pressurized to feet.Increase FIO2 (above 20,000 feet).Adapt PhysiologicallyHyperventilation.Collateral Circulation.Shift the oxygen dissociation curve.Increase Hemoglobin levels.
23 Calculating PBaro at High Altitudes PBARO falls 120 mm Hg per mile of altitudeExample: Leadville is 2 miles above sea level. Calculate the PBARO & PO2120 x 2 miles = 240 mm Hg decline= 520 mm Hg (PBARO)PO2 = x .21109 mm Hg or torr (PO2)
24 Physiologic Processes ABG results provide information on the three physiologic processesAlveolar VentilationAcid-BaseOxygenation
25 Equations Used to Reflect the Physiologic Processes PaCO2 EquationHenderson HasselbalchAlveolar Air EquationOxygen Content (CaO2)Oxygen DeliveryAlveolar VentilationAcid BaseOxygenation
26 PaCO2 and Alveolar Ventilation Alveolar Ventilation is the amount of air in L/min that reaches the alveoli and takes part in gas exchange.The body eliminates the CO2 produced, during metabolism, via ALVEOLAR ventilation.
27 Metabolism Steady State The amount of CO2 added to the blood through metabolism = the amount of CO2 excreted by the lungs.200 mL/min
28 PaCO2 Equation PaCO2 = CO2 production x 0.863 Alveolar Minute Ventilation0.863 is a constant which equates dissimilar units.40 mm Hg = 200 mL/min x4.3 L/min
29 PaCO2 EquationIf CO2 production doubles (e.g. fever), alveolar minute ventilation must double to keep a normal PaCO2 level.40 mm Hg = 400 mL/min x8.6 L/min
30 Henderson-Hasselbalch Equation pH is defined as the negative log of the H+ concentrationpH = pK + Log HCO (Base)(PaCO2 x 0.03) (Acid)pH = pK + Log mEq/LmEq/L“Normal” pH implies 20 times more base than acid
31 PAO2 PAO2 = PBARO – 47 torr x FIO2 – PaCO2 0.8 PAO2 = PIO2 - PaCO2 PAO2 on room air = 100 – 104 mm HgPAO2 on 100% = 600’s
33 Effects of PaCO2 on PAO2 and PaO2 A rise in the PaCO2 will lower the PAO2 and therefore the PaO2.Hypoventilation is a cause of hypoxemia.
34 CaO2 CaO2 = (SaO2 x Hb x 1.34) + (PaO2 x 0.003) With normal values: Oxyhemoglobin (attached) represents 19.7 vol%.Dissolved oxygen (PaO2) represents 0.3 vol%.Total Oxygen present in the blood 20 vol%.
35 Vol %mL of oxygen/100 mL of bloodOrmL of oxygen/dL of blood
36 Oxygen Delivery Oxygen Delivery = CaO2 x CO x 10 Oxygen Delivery = CaO2 x SV x HR x 10Normal Value = 1,000 mL/minRepresents amount of oxygen delivered to the tissues each minute.
37 Factors that Influence Oxygen Delivery to the Tissues SaO2HbPaO2Stroke VolumeHeart Rate
38 Summary of Important Points ABG interpretation means evaluating the acid base and oxygenation status of the patient.Acid Base represent the metabolic and respiratory indices.FIO2 stays the same regardless of changes in PBaro.PBARO decreases as altitude increases.Dalton’s Law.PO2 is affected by FIO2, PBARO and age.
39 Summary of Important Points PAirway = PBARO.To interpret an ABG you need 3 areas of information.Oxygen delivery is influenced by five factors.ABG values are either measured or derived.Understand the 5 equations and the relationship among the parameters used.