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RTT 213 - Ch. 18
Ch. 18 - (Egan's) Analysis and Monitoring of Gas Exchange
| Question | Answer |
|---|---|
| what is the most common approach to analyzing gas exchange between the blood and tissues? | measure O2 levels in the mixed venous (pulmonary artery) blood |
| what is the term analysis broadly defined as? | study or interpretation |
| in clinical practice, what does laboratory analysis refer too? | discrete measurements of fluids or tissue that must be removed from the body |
| what are these measurements made by? | laboratory analyzer |
| what does monitoring mean? | ongoing process by which clinicians obtain and evaluate dynamic physiologic processes in a timely manner |
| a ________ is a device that provides the important date to the clinician in real time, usually without the removal of samples from the body. | monitor |
| _________ procedures require insertion of a sensor or collection device into the body, whereas ___________ monitoring is a means of gathering data externally. | invasive; noninvasive |
| what does the analysis of gas exchange begin with? | knowledge of the system inputs - inspired O2/CO2 |
| what are the two common types of electrochemical O2 analyzers? | 1. Clark electrode 2. galvanic fuel cell |
| what is the clark electrode similar to? | those used in blood gas analyzers and transcutaneous monitors |
| what are the response times for Clark electrode O2 analyzer? galvanic fuel cell? | 10-30 seconds; 60 secs |
| the clark electrode and galvanic fuel cell are suitable for basic _____ monitoring. | FiO2 |
| what should be selected when greater accuracy or faster response times are needed? | paramagnetic, zirconium cell, Raman scattering, or mass spectroscopy |
| what must first be done to obtain accurate results with an O2 analyzer? | calibration |
| although procedures differ according to the manufacturer, the basic steps are similar, what are these steps? | exposure of the sensor to two gases w/ different O2 concentrations (100% O2/21% room air) |
| what should be adjusted in order for the analyzer to read 100% O2? | calibration |
| after exposing to 100% O2, what should the clinician do? | expose the sensor to room air and confirm a second reading of 21% |
| when should the clinician know that an analyzer is not working? | fails to calibrate or gives an inconsistent reading |
| what are the most common causes of analyzer malfunction? | low batteries (Clark), sensor depletion, electronic failure |
| what causes inaccurate readings with electrochemical analyzers? | condensed water vapor or pressure fluctuations |
| what type of O2 analyzer is particularly sensitive to condensation? | galvanic cells |
| how can this problem be avoided during continuous use in humidified circuits? | place the analyzer sensor proximal to any humidification device |
| what are fuel cell and Clark electrode readings also affected by? | ambient pressure changes |
| what conditions cause the devices to read lower than the actual O2 concentrations? | low pressure (high altitude) |
| what causes the devices to read higher than the actual FiO2? | high pressures (positive pressure ventilation) |
| what is the definition of respiratory failure still largely based on? | blood gas measurements |
| how can blood gas samples be obtained? | percutaneous puncture of a pulmonary artery, catheter (arterial, central venous, or PA), capillary sampling |
| results obtained from sampling ABG are the cornerstone in the diagnosis and management of wht? | oxygenation and acid-base disturbances |
| what are ABGs considered? | gold standard of gas exchange analysis |
| what does arterial puncture involve? | drawing blood from a peripheral artery through a single percutaneous needle puncture |
| what is the preferred site for arterial blood sampling? | radial artery |
| why is the radial artery most often used? | 1. near surface, easy to stabilize 2. collateral circulation 3. no large veins near 4. pain free |
| what are the indications for ABG? | evaluate ventilation, acid-base, oxygenation, ozygen-carrying capacity of blood; assess response to therapy/tests; monitor disease |
| what are the contraindications of ABG? | negative Allen's test results; surgical shunt; no femoral outside of hospital; coagulopathy/anticoagulation (heparin, warfarin) |
| what are 5 precautions and/or possible complications of ABG? | 1. hematoma 2. contamination 3. hemorrhage 4. trauma to the vessel 5. pain |
| what are examples of assessments for the need of an ABG? | history/physical indicators, diagnostic tests, initiation, change, discontinuation of therapy, pulmonary rehabilitation program |
| what are 5 examples of monitoring during an ABG? | 1. FiO2 2. O2 device 3. air bubbles 4. RR 5. temperature |
| what are the 2 purposes of a needle capping device? | 1. isolates from air exposure 2. prevent needle stick injuries |
| what should be performed before any radial puncture? | modified Allen test |
| when is the modified allen test positive? | skin flushes pink within 10 secs |
| if other conditions make interpreting allen test results difficult, what should be used to assess the pulsatile flow of the thumb? | Doppler pulse transducer |
| in most cases, a sample volume of __-__ mL of blood is adequate. | 2-4 |
| what does the actual sample volume needed depend on? | 1. anticoagulant 2. requirements of specific analyzer 3. if other tests will be performed on sample |
| what are the rules for careful handling of the needle that will help avoid transmission of blood-borne diseases? | never recap used needle without safety device, never handle it using both hands or point it toward body; never bend, break, or remove used needles from syringe by hand; always dispose of used syringes |
| what are the first 5 steps for radial artery puncture? | 1. check chart 2. confirm steady-state conditions 3. equipment 4. wash hands 5. explain to pt |
| what are the next 5 steps for radial artery puncture? | 6. position pt (extend wrist 30 degrees) 7. Allen test 8. cleanse site (70% alcohol) 9. heparinize the syringe 10. palpate/secure artery with one hand |
| what are the next 5 steps for radial artery puncture? | 11. insert needle, bevel up, 45 degree angle 12. 2-4 mL of blood 13. apply pressure (5-10 mins) 14. expel bubbles, cap syringe 15. mix sample |
| what are the next 5 steps for radial artery puncture? | 16. place sample in transport container 17. dispose waste 18. document 19. check site 20 mins later for hematoma |
| what are 5 clinical indications for ABG? | 1. cyanosis 2. dyspnea 3. abnormal breath sounds 4. tachypnea 5. heavy use of accessory muscle |
| what are the 2 problem areas associated with arterial puncture? | 1. difficulties in getting a good sample 2. preanalytical error |
| what are the problems with getting a good sample? | inaccessible artery, absent pulse, deficient sample return, alteration of test results |
| when should the tip of the needle be redirected? | after it is first withdrawn to the subcutaneous tissue |
| what can alter the blood gas results? | excessive suction |
| ___________ _______ are problems occurring before sample analysis, which can alter the accuracy of the blood gas results. | preanalytical errors |
| how can clinicians avoid most preanalytical errors? | ensuring the sample is obtained anaerobically, anticoagulated, analyzed within 15 mins |
| what is the traditional method used to avoid errors caused by blood cell metabolism? | quickly chill the sample by placing it in ice slush |
| when is this needed? | if the sample is not analyzed within 10-15 mins |
| when should chilled samples be disposed? | after 60 mins |
| how long do pts with healthy lungs take to achieve a steady state? COPD pts? | 5 mins after changes; as long as 20-30 mins |
| to document the pt's status, what should be recorded? | 1. date, time, site of sampling 2. allen test results 3. body temp, position, activity level, RR 4. FiO2 |
| what is the first step of interpretation of the results? | ensure you're looking at the results of the correct pt |
| what are the 2 basic steps of interpretation of the results? | 1. interpretation of the oxygenation status 2. interpretation of the acid-base status |
| what is the oxygenation status determined by examining? | PaO2, SaO2, CaO2 |
| what does SaO2 represent? | the degree to which the hemoglobin is saturated with O2 |
| what does CaO2 represent? | the content of O2 in 100mL of arterial blood and is a function of SaO2 |
| what is the normal SaO2? CaO2? | 95%-100%; 18-20 mL of O2 per 100mL of arterial blood (16-20 vol%) |
| what is the acid-base status of the pt determined by examining? | pH, PaCO2, HCO3 |
| what do indwelling catheters provide? | continuous monitoring of vascular pressures |
| whats more likely to happen with indwelling catheters than they are with intermittent punctures? | infections and thrombosis |
| what are the most common routes for indwelling vascular lines? | peripheral artery, central vein, pulmonary artery |
| in an indwelling catheter, what does the catheter connect to? | a disposable continuous-flush device |
| how does this device keep the line open? | by providing a continuous low flow (2-4 mL/hr) of heparinized IV fluid |
| what is connected to the flush device that provides an electrical signal to an amplifier or monitor, which displays the corresponding pressure waveform? | strain-gauge pressure transducer |
| what provides access for sampling blood from most intravascular lines? | three-way stopcock |
| what is the first step in the procedure of an indwelling catheter? | ensure that the balloon is deflated and prepare to draw the sample directly from the catheter's distal port |
| what is the second step in the procedure of an indwelling catheter? | clinician slowly withdraws the sample |
| what can dilute the blood sample and affect O2 content measures? | rapid flow of IV fluid |
| what is capillary blood gas sampling sometimes used as? | an alternative to direct arterial access in infants/small children |
| what can properly obtained capillary blood from a well-perfused pt provide rough estimates of? | arterial pH and PaCO2 levels |
| the capillary PO2 is of no value in estimating _________ __________. | arterial oxygenation |
| capillary blood values are meaningful only if what? | the sample site is properly warmed |
| what is the most common technical error is capillary sampling? | inadequate warming and squeezing of the puncture site |
| a sample obtained from a warmed capillary site is often referred to as ___________ ______. | arterialized blood |
| what part of the body do capillary blood samples reflect arterial PCO2 and PO2 better than a finger stick? | earlobe |
| what is the equipment required for a capillary blood sampling? | lancet, preheparinized glass capillary tubes, metal "fleas," magnet, clay/wax sealant/caps, gauze, bandages, ice, gloves, skin antiseptic, warming pads, sharps container, labeling |
| what is the most common site of capillary sampling? | heel, specifically the lateral aspect of the plantar surface |
| what do analyzers use the measurements of pH, PaCO2, and PO2 to compute? | plasma bicarbonate, base excess, hemoglobin saturation |
| if actual measurement of Hb saturation, methemoglobinm and HbCO is required, the sample usually must be analyzed separately using ___________. | hemoximetry |
| what are the key components that blood gas analyzers typically share? | 1. operator interface 2. measuring chamber 3. calibrating gas tanks 4. reagent containers 5. waste container 6. results display, storage, transmittal system |
| to measure PO2, blood gas analyzers use...? | the Clark polaragraphic electrode |
| what does the pH electrode actually consist of? | two electrodes or half-cells |
| what is used to measure PaCO2? | Severinghaus electrode |
| to provide accurate and clinically useful data, how must blood gas analysis be performed? | 1. on a sample free of preanalytical errors 2. properly functioning analyzer 3. procedure that follows manufacturer's recommendations |
| what does quality pt care depend on? | acurate blood gas results |
| what does the accuracy of blood gas testing depend on? | rigorous quality control |
| what is the hallmark of a comprehensive quality control program? | RECORDKEEPING and clearly written and comprehensive policies and procedures |
| __________ _________ is the process of testing a new instrument to confirm a manufacturer's claims. | PERFORMANCE VALIDATION |
| _________ is examining the repeatability of the results. | precision |
| what is the best way to avoid problems associated with analyzers, filters, membranes, or electrolyte solution deteriorating and failing? | scheduling regular PREVENTIVE MAINTENCE |
| _________ is the only fully automated element of blood gas quality control. | CALIBRATION |
| in most units, the media used to calibrate the gas electrodes are...? | precision mixtures of O2 and CO2. |
| what is used for the pH electrode? | standard pH buffer solutions |
| ___________ ______ must meet the requirements set by nationally recognized standards organizations. | calibration media |
| what is calibration performed to ensure? | that the output of the analyzer is both accurate and linear across the range of measured values |
| what are the 2 steps of calibration? | 1. adjusting the offset of the instrument so that low output = low input 2. the gain (slope) is adjusted to ensure that high output = high input |
| _____________ ___________ establishes and periodically confirms the validity of blood gas analyzer results. | CALIBRATION VERIFICATION |
| what does calibration verification require? | analysis of at least 3 materials with known values spanning the entire range of values expected for clinical samples ("controls") |
| _______ _______ _______ takes calibration verification a step further by applying statistical and rule-based procedures to help detect, repond to, and correct instrument error. | INTERNAL QUALITY CONTROL |
| what are the 2 categories of analytical error? | 1. random 2. systematic |
| random errors are errors of precision, or more precisely, __________. | imprecision |
| what does bias plus impercision equal? | total instrument error, or inaccuracy |
| _________ ________ requires analysis and reporting on externally provided control media with unknown values, usually three times per year, with five samples per test. | PROFICIENCY TESTING |
| ________ _______ is the ongoing process of applying appropriate measures to correct errors identified through the quality assurance cycle. | REMEDIAL ACTION |
| ____________ ______ takes blood gas analysis from the specialized laboratory to the pt's bedside. | point-of-care testing |
| besides blood gas analysis, what can other devices measure during point-of-care testing? | serum electrolytes, blood glucose levels, blood urea nitrogen, hematocrit, prothrombin, partial thromboplastin time |
| where does analysis take place? | a disposable cartridge, which is inserted into a chamber in the body of the unit |
| a ______ ____ _______ is a bedside tool that can provide measurements either continuously or at appropriate intervals without permently removing blood from the pt. | blood gas monitor |
| what are the 3 such systems in current clinical use? | 1. transcutaneous blood gas monitor 2. intraarterial (in vivo) 3. on-demand (ex vivo) |
| _____________ blood gas monitoring provides continuous, noninvasive estimates of arterial PO2 and PCO2 through a surface skin sensor. | transcutaneous |
| what is the comparison of transcutaneous blood gas monitoring and capillary sampling? | the device arterializes the underlying blood by heating the skin |
| what are the two most important factors that influence the agreement between arterial blood and transcutaneous gas measurements? | age and perfusion status |
| in terms of age, the _________ the pt, the better is the agreement between the PaO2 and PTCO2. | younger |
| in perfusion status, when are the PaO2 and PTCO2 similar? | in pts with normal cardiac output and fluid balance |
| agreement between PTCO2 and ______ is a little better. | PaCO2 |
| when is transcutaneous monitoring a reasonable choice? | when there is a need for continuous, noninvasive, analysis of gas exchange in hemodynamically stable infants/children |
| transcutaneous monitoring also is useful for monitoring _________ in neonates. | hyperoxia |
| instead of measuring gas tensions in a blood sample, transcutaneous electrodes measure PO2 and PCO2 in...? | an electrolyte gel between the sensor and skin |
| what is the response time for these electrodes? | 20-30 secs |
| what are the most common sites for electrode placement? | abdomen, chest, lower back |
| what are the steps to take care to avoid thermal injury to the pt's skin? | 1. careful monitoring of sensor temp (42 degrees C) 2. regularly rotating the sensor site |
| proper _____-________ contact is essential, as is proper application to the skin surface. | sensor-electrolyte |
| with intraarterial (in vivo), rather than using electrochemistry, ______ measure blood gas parameters by photochemical reactions, which alter light transmission through optical fibers. | optodes |
| light transmitted to this dye can be absorbed, reflected, or even re-emitted at a different wavelength called ___________. | fluorescence |
| most photochemical blood gas systems used both ___________ and __________-based optodes. | absorbance; fluorescence |
| because O2 "quenches" the dye's fluorescence, the intensity of this return signal is inversely proportional to the arterial _____. | PO2 |
| ________ (__ ____) blood gas monitoring systems are a logical compromise between bench-top and in vivo blood gas analysis. | on-demand (ex vivo) |
| what is the only major shortcoming of ex vivo systems? | their inability to provide real-time continuous data |
| _________ is the measurement of blood hemoglobin saturations using ______________. | oximetry; spectrophotometry |
| a substance's pattern of light absorption varies predictably with the amount of pressure; what law is this known as? | Lambert-Beer law |
| the particular pattern of light absorption exhibited by a substance at different wavelengths is called its _________ ________. | absorption spectrum |
| what are the two types of oximetry used in clinical practice? | 1. hemoximetry (co-oximetry) 2. pulse oximetry |
| what is hemoximetry? | laboratory analytical procedure requiring invasive sampling of arterial blood |
| how are the specific wavelengths needed for analysis yielded? | light generated by a thallium cathode lamp passes through a series of lenses and filters |
| s beam splitter then divides the light into two portions, directing one through a reference solution and the other through a sample chamber, or _______. | cuvette |
| because a laboratory hemoximeter used three different wavelengths of light, it can simultaneously compute the relative concentrations of multiple hemoglobin species, such as...? | Hb, HbO2, HbCO, metHb |
| what is the first step in hemoximetry? | blood is introduced into the sampling port of the analyzer, usually either by aspiration or injection |
| what is the next step? | hemolysis (then, to cuvette for analysis) |
| what is a major assumption underlying hemoximetry? | the measured changes in light absorbance result only from variations in the relative concentrations of various hemoglobins |
| a ______ ________ is an inexpensive and portable noninvasive monitoring device that provides estimates of arterial blood oxyhemoglobin saturation levels. | pulse oximeter |
| the pulse oximeter combines the principle of spectrophotometry, as used by hemoximetry, with ______________. | photoplethysmography |
| what does the pulse oximeter use? | two wavelengths of light (one red, one infrared) |
| pulse oximeter actually measures transmission through...? | living tissue, such as a finger or an earlobe |
| what does a baseline component represent? | the stable absorbance pf the tissue bed, which mainly is the result of venous and capillary blood |
| the ______ the actual SaO2, the less accurate and reliable is the SpO2 measurement. | lower |
| most clinicians consider pulse oximeter readings unreliable at saturations below ___%. | 80 |
| what are the two problem categories with pulse oximetry? | 1. those inherent in the technology itself 2. those associated with clinical interpretation and use of data |
| what is the most common source of error and false alarms? | motion artifact |
| what can minimize this problem? | relocation of the sensor |
| how are the low alarms set for dark skin pigmentation? | 3% - 5% higher |
| the pulse oximeter does not measure ____. | PCO2 |
| ___________ is the measurement of CO2 in respiratory gases. | capnometry |
| a __________ is the device that measures the CO2. | capnometer |
| ___________ is the graphic display CO2 levels as they change during breathing. | capnography |
| what is the primary use of capnography? | monitoring during general anesthesia or MV |
| what is the key component in a capnograph? | rapidly responding CO2 analyzer |
| what is the most common rapid CO2 analyzer? | infrared capnometer |
| what are the two different methods to sample respiratory gases that capnometers use? | 1. mainstream sampling 2. sidestream sampling |
| what can interpretation of the capnogram be useful in assessing trends in? | alveolar ventilation and detecting V/Q imbalance |
| what is gas sampled at the end of exhalation? | end-tidal gas |
| what is the normal PETCO2 | 1-5 mmHg less than the PaCO2 or b/t 35-43 mmHg |
| what is the first step in assessing the capnogram? | determine the actual PETCO2 and whether it has changed over time |
| what does a PETCO2 of zero usually indicate? | system leak, esophageal intubation, cardiac arrest |
| once the capnogram as been assessed for changes in PETCO2, the _________ and its pattern should be analyzed. | waveform |
| what does a normal capnogram have? | starts with a sharp upstroke, followed by a plateau, then a rapid downstroke |
| what does an elevated baseline indicate? | rebreathing |
| what is the most significant error with capnogram? | assuming that the end-expired CO2 levels can substitute for actual PaCO2 measurements |
| what is the most common problem? | contamination or obstruction of the sampling system or monitor by secretions or condensate |
Created by:
christa_2008