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RTT 215 - Ch. 6 (1)

Ch. 6 - Blood Gas and Related Tests

______ ____ analysis is the most basic test of lung function. blood gas
what does evaluation of the acid-base and oxygenation status of the body provide? important info about the function of the lungs themselves
what does anaeobic sampling involve? invasive that carries risks of blood-borne pathogens
calculating _______ _______ and the ______ ________ uses blood gas measurements to assess gas exchange as it applies to oxygenation. oxygen content; shunt fraction
____ is the negative logarithm of the hydrogen ion concentration in the blood, used as a positive number. pH
how is pH derived? converting H+ to a negative exponent of 10 and calculating its logarithm
what is the physiologic range of pH of blood in clinical practice? 6.90-7.80
what is PCO2? measures partial pressure exerted in CO2 in solution in the blood
what is the PCO2 in mixed venous blood? 40-46 mmHg
what is PO2? what is the normal mixed venous PO2? measures partial pressure exerted by O2 dissolved in blood; 37-43 mmHg
__________ _______ influences the expected arterial PO2. barometric pressures
how is blood pH measured? exposing blood to a glass electrode; light absorbance w/ optical pH indicator (anaerobic)
what temperature are pH measurements made at? 37 degrees
how is PCO2 measured? exposing blood to a modified pH electrode in jacket w/ teflon membrane at tip
what does the jacket contain? HCO3 buffer
the change in pH is measured by the electrode and is proportional to the ____. PCO2
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
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
what is BE the difference between? actual buffering capacity of the blood and expected value
what are the main buffers that affect the BE? HCO3 and Hb
how is PO2 measured? exposing whole blood to platinum electrode covered w/ polypropylene membrane
what is this type of electrode called? polarographic (clark)
what are blood gas values (pH, PCO2, PO2) influenced by? pt's temperature
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
what are common problems with spectrophotometric methods? mechanical/electrical failure, inadequate mixing
where are mixed venous samples drawn from? and what is a common problem? PAC; contamination w/ flush solution, displacement of catheter tip
venous samples from peripheral veins are not useful for assessing ___________. oxygenation
what does contamination often occur? air is left in syringe; poor fitting plungers; failure to properly cap
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
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
within how long should samples be analyzed? 15-20 mins (>20 mins - iced)
what are acid-base disorders arising from lung diseases often related to? PCO2 and its transport as carbonic acid
PaCO2 is inversely proportional to _________ __________. alveolar ventilation
________ is a common cause of hyperventilation. hypoxemia
O2 therapy is usually titrated to maintain PaCO2 values <___ mmHg without hypercapnia and acidosis. 60
what is the normal alveolar-arterial gradient? <20 mmHg
hyperventilation may increase PaO2 as high as ____ mmHg in a normal pt. 120
what can a decreased PaO2 result from? hypoventilation, diffusion abnormality, V/Q imbalance, high altitude
what does hypoxemia commonly result from? inadequate/abnormal Hb
what is the severity of impaired oxygenation indicated by? PaO2 at rest
what is PaO2 a good index of? lungs' ability to match pulm capillary blood flow w/ adequate ventilation
_______ _______ is the most accurate way to assess O2 delivery and the probability of tissue hypoxia. oxygen content
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
what does PVO2 change in response to? alterations in CO and O2 consumption
what can the degree of arterial desaturation NOT be predicted from? static pulmonary function measurements
___________ refers to the measurement of Hb and its derivatives by spectroscopy. hemoximetry
O2 saturation is the ratio of oxygenated Hb to etiher...? total Hb or functional Hb (binds O2)
what are the methods of measuring O2 saturation of Hb? spectrophotometer; measure SvO2
at PaO2 values of approximately ____, Hb becomes completely saturated. 150
______ changes in PaO2 result in ______ changes in saturation. small; large
what is P50? what is the P50 of normal adult Hb? partial pressure at which Hb is 50% saturated; 27 mmHg
how is P50 determined? equilibrating blood w/ several gases at low O2 tensions; compare measured SaO2 w/ expected
what is the normal COHb? 0.5%-2% of total Hb
when COHb is elevated, arterial blood appears ______ ____. bright red
what are the 2 ways COHb interferes with O2 transport? 1. binds competitively to Hb 2. shifts the O2Hb curve to the left
removal of CO from the blood depends on the _______ __________. minute ventilation
____________ 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
what do high levels of MetHb result from? oxidizing agents
what is the avg saturation of mixed venous blood in healthy pts? 75% at a PVO2 of 40 mmHg
____ is useful in assessing cardiac function in critical care setting and during exercise. what do values <60% indicate? SvO2; cardiovascular decompensation (tissue hypoxemia)
SpO2 estimates SaO2 by analyzing absorption of light passing through a capillary bed, either by __________ or ___________. transmission; reflectance
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
what is the accuracy of pulse oximetry? +/- 2% of actual saturation (SaO2 >90%)
when is pulse oximetry most useful? shown to correlate w/ blood oximetry in pt w/ known circumstance
when is blood gas analysis required? evaluate hyperoxemia or acid-base status
_________ includes continuous, noninvasive monitoring of expired CO2 and analysis of the single-breath CO2 waveform. capnography
what are the methods used to measure exhaled CO2 gas? infrared analyzers; mass spectrometer
what is the shape of the expired CO2 curve determined by? ventilation-perfusion matching
what does the absolute concentration of CO2 at the alveolar plateau depend on? minute ventilation and CO2 production
in healthy individuals, approx __% of th eCO is shunted past the pulmonary system. 5
what disease patterns is intrapulmonary shunting common in? atelectasis or foreign body aspiration; ARDS, pneumonia
what does the accuracy of clinical shunt measurement depend on? accuracy of PO2 determinations
Created by: christa_2008