Ch. 6 - Blood Gas and Related Tests
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| ______ ____ analysis is the most basic test of lung function. | blood gas
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| what does evaluation of the acid-base and oxygenation status of the body provide? | important info about the function of the lungs themselves
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| what does anaeobic sampling involve? | invasive that carries risks of blood-borne pathogens
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| calculating _______ _______ and the ______ ________ uses blood gas measurements to assess gas exchange as it applies to oxygenation. | oxygen content; shunt fraction
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| ____ is the negative logarithm of the hydrogen ion concentration in the blood, used as a positive number. | pH
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| how is pH derived? | converting H+ to a negative exponent of 10 and calculating its logarithm
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| what is the physiologic range of pH of blood in clinical practice? | 6.90-7.80
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| what is PCO2? | measures partial pressure exerted in CO2 in solution in the blood
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| what is the PCO2 in mixed venous blood? | 40-46 mmHg
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| what is PO2? what is the normal mixed venous PO2? | measures partial pressure exerted by O2 dissolved in blood; 37-43 mmHg
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| __________ _______ influences the expected arterial PO2. | barometric pressures
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| how is blood pH measured? | exposing blood to a glass electrode; light absorbance w/ optical pH indicator (anaerobic)
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| what temperature are pH measurements made at? | 37 degrees
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| how is PCO2 measured? | exposing blood to a modified pH electrode in jacket w/ teflon membrane at tip
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| what does the jacket contain? | HCO3 buffer
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| the change in pH is measured by the electrode and is proportional to the ____. | PCO2
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| newer blood gas analyzers use a ______________ to measure the absorbance of CO2 in the infrared portion of the spectrum. PCO2 may also be estimated using a ____________ electrode. | spectrophotometer; transcutaneous
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| if the hemoglobin is measured or estimated, the _____ _______ can be calculated. what is the normal at a pH of 7.40? | base excess; 48 mEq/L
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| what is BE the difference between? | actual buffering capacity of the blood and expected value
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| what are the main buffers that affect the BE? | HCO3 and Hb
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| how is PO2 measured? | exposing whole blood to platinum electrode covered w/ polypropylene membrane
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| what is this type of electrode called? | polarographic (clark)
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| what are blood gas values (pH, PCO2, PO2) influenced by? | pt's temperature
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| what are the technical problems with blood gas electrodes and related measuring devices? electrode-based analyzers? | contamination by protein or blood products; depletion of buffers, tears/ruptures
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| what are common problems with spectrophotometric methods? | mechanical/electrical failure, inadequate mixing
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| where are mixed venous samples drawn from? and what is a common problem? | PAC; contamination w/ flush solution, displacement of catheter tip
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| venous samples from peripheral veins are not useful for assessing ___________. | oxygenation
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| what does contamination often occur? | air is left in syringe; poor fitting plungers; failure to properly cap
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| how long does a glass syringe sample last in ice water? within how long should plastic syringe sampled be analyzed? | 1-2 hours; 30 mins
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| when a blood gas specimen is placed in an ice-water bath, the ________ of O2 increases, as does the affinity of Hb for O2. | solubility
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| within how long should samples be analyzed? | 15-20 mins (>20 mins - iced)
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| what are acid-base disorders arising from lung diseases often related to? | PCO2 and its transport as carbonic acid
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| PaCO2 is inversely proportional to _________ __________. | alveolar ventilation
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| ________ is a common cause of hyperventilation. | hypoxemia
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| O2 therapy is usually titrated to maintain PaCO2 values <___ mmHg without hypercapnia and acidosis. | 60
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| what is the normal alveolar-arterial gradient? | <20 mmHg
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| hyperventilation may increase PaO2 as high as ____ mmHg in a normal pt. | 120
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| what can a decreased PaO2 result from? | hypoventilation, diffusion abnormality, V/Q imbalance, high altitude
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| what does hypoxemia commonly result from? | inadequate/abnormal Hb
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| what is the severity of impaired oxygenation indicated by? | PaO2 at rest
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| what is PaO2 a good index of? | lungs' ability to match pulm capillary blood flow w/ adequate ventilation
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| _______ _______ is the most accurate way to assess O2 delivery and the probability of tissue hypoxia. | oxygen content
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| what is the mixed venous oxygen tension (PVO2) normal range? what is the avg mixed venous O2 content? CaO2? | 37-43 mmHg; 15 ml/dl; 20 ml/dl
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| what does PVO2 change in response to? | alterations in CO and O2 consumption
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| what can the degree of arterial desaturation NOT be predicted from? | static pulmonary function measurements
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| ___________ refers to the measurement of Hb and its derivatives by spectroscopy. | hemoximetry
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| O2 saturation is the ratio of oxygenated Hb to etiher...? | total Hb or functional Hb (binds O2)
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| what are the methods of measuring O2 saturation of Hb? | spectrophotometer; measure SvO2
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| at PaO2 values of approximately ____, Hb becomes completely saturated. | 150
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| ______ changes in PaO2 result in ______ changes in saturation. | small; large
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| what is P50? what is the P50 of normal adult Hb? | partial pressure at which Hb is 50% saturated; 27 mmHg
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| how is P50 determined? | equilibrating blood w/ several gases at low O2 tensions; compare measured SaO2 w/ expected
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| what is the normal COHb? | 0.5%-2% of total Hb
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| when COHb is elevated, arterial blood appears ______ ____. | bright red
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| what are the 2 ways COHb interferes with O2 transport? | 1. binds competitively to Hb 2. shifts the O2Hb curve to the left
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| removal of CO from the blood depends on the _______ __________. | minute ventilation
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| ____________ forms when iron atoms of the Hb molecule are oxidized from Fe++ to Fe+++. what is the normal level? | methemoglobin; <1.5% of total Hb
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| what do high levels of MetHb result from? | oxidizing agents
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| what is the avg saturation of mixed venous blood in healthy pts? | 75% at a PVO2 of 40 mmHg
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| ____ is useful in assessing cardiac function in critical care setting and during exercise. what do values <60% indicate? | SvO2; cardiovascular decompensation (tissue hypoxemia)
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| SpO2 estimates SaO2 by analyzing absorption of light passing through a capillary bed, either by __________ or ___________. | transmission; reflectance
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| pulse oximeters measure the light absorption of a mixture of 2 forms of Hb...? the relative absorptions at ____ nm (red) and ____ nm (near infrared) can be used to calculate the combination of the two Hb forms. | 1. O2Hb 2. reduced Hb; 660; 940
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| what is the accuracy of pulse oximetry? | +/- 2% of actual saturation (SaO2 >90%)
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| when is pulse oximetry most useful? | shown to correlate w/ blood oximetry in pt w/ known circumstance
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| when is blood gas analysis required? | evaluate hyperoxemia or acid-base status
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| _________ includes continuous, noninvasive monitoring of expired CO2 and analysis of the single-breath CO2 waveform. | capnography
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| what are the methods used to measure exhaled CO2 gas? | infrared analyzers; mass spectrometer
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| what is the shape of the expired CO2 curve determined by? | ventilation-perfusion matching
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| what does the absolute concentration of CO2 at the alveolar plateau depend on? | minute ventilation and CO2 production
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| in healthy individuals, approx __% of th eCO is shunted past the pulmonary system. | 5
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| what disease patterns is intrapulmonary shunting common in? | atelectasis or foreign body aspiration; ARDS, pneumonia
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| what does the accuracy of clinical shunt measurement depend on? | accuracy of PO2 determinations
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