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RTT 215 - Ch. 6 (1)
Ch. 6 - Blood Gas and Related Tests
| Question | Answer |
|---|---|
| ______ ____ 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
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