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
1. [Combining the two] • use invasive to establish baseline
• apply noninvasive for ongoing monitoring of STABLE patient
• trends in change of noninvasive useful in making clinical decisions
2. Define analysis. Measurement of fluid or tissue that must be permanently removed from the body
3. Define invasive Invasive procedures require insertion of a sensor or collection device into the body
4. Define monitoring. Ongoing process by which clinician obtains and evaluates dynamic physiologic processes, “Real time”
5. Define noninvasive Noninvasive is a means of gathering data
externally
6. Describe methods for blood gas monitoring. Transcutaneous PO2 and PCO2
Intraarterial (in vivo) monitoring
On Demand (ex vivo
7. Describe methods for blood gas monitoring for Intraarterial (in vivo) monitoring Uses indwelling fiberoptic photochemical sensor
(optodes)
Optode contains a dye at one end and the amount
of light the dye absorbs, reflect or re‐emits,
determines the concentration of different
substances
8. Describe methods for blood gas monitoring for On Demand (ex vivo) Optodes are located in a sensor cassette inserted
in‐line with the arterial catheter
Blood is pulled into the cassette, measured, then
placed back into the body
9. Describe methods for blood gas monitoring for Transcutaneous PO2 and PCO2 Uses an electrode placed directly on skin to
measure skin PO2 and PCO2
Used primarily on infants because their skin is
more permeable to O2 and CO2
10. Differentiate between capnometry and capnography
11. Differentiate between pluse-oximetry and co-oximetry. Pulse-oximetry is non-invasive

 

 

Co-oximetry is invasive

12. Differentiate between pulse-oximetry and co-oximetry. Co-oximetry
Laboratory analytical procedure requiring invasive sampling of arterial blood
Utilizes light at special wavelength to measure
Oxyhemoglobin
Deoxyhemoglobin
Carboxyhemoglobin
Methemoglobin
Pulse Oximetry
Most appropriate noninvasive technique for continuous monitoring of O2 saturations
(SpO2)
Utilizes Beer’s Law
Linear relationship between absorbency of a
solution and its concentration
13. The end? • the End-tidal PCO2 (PETCO2) is used to estimate deadspace ventilation
14. Explain capnometry Capnometry is used to measure CO2 at the patient’s airway

 

 

Disadvantages
Needs to be calibrated periodically
Water can occlude sample lines

15. Explain capriography Capnograph is the graphic waveform display of CO2 as a function of time
Measured at bedside by infrared absorption Should correlate with PCO2 onABG
Useful for tube placement on intubation and monitoring patient’s ventilatory status
16. Explain criteria for Collateral Blood Flow. Arterial punctures may cause vessel spasm, intraluminal
clotting, or bleeding with the formation of a periarterial
clot (hematoma)
Any of these factors may result in decreased blood flow to
the tissues
Collateral blood flow is an important consideration in
choosing arterial puncture sites in the event of arterial
obstruction
17. Explain criteria for PeriarterialTissues Muscle, tendon, and fat are reasonably insensitive to pain;
bones and nerves are very sensitive to pain
Arteries surrounded by relatively insensitive tissues are
desirable so that the puncture can be as free from pain as
possible
Arteries that are not adjacent to veins are preferable to
minimize the chance of inadvertent venous puncture
18. Explain criteria for Vessel accessibility. It is easier to palpate, stabilize, and puncture a
superficial artery than a relatively deep one
Superficial arteries are found at the distal ends of
the extremities
19. Explain how a co-oximetry works. Laboratory analytical procedure requiring invasive
sampling of arterial blood
Utilizes light at special wavelength to measure
Oxyhemoglobin
Deoxyhemoglobin
Carboxyhemoglobin
Methemoglobin
20. Explain how Pulse Oximetry works Most appropriate noninvasive technique for continuous monitoring of O2 saturations (SpO2)
Utilizes Beer’s Law
Linear relationship between absorbency of a solution and its concentrationHow it works
Uses a probe that passes light through a pulsating tissue bed
Consists of two light sources that must be lined up correctly
Light passes through tissue and measures both red and infrared wavelengths
Accurate in patients with good perfusion and saturations of 70% or higher
21. Explain problems encountered during arterial punctures as well and troubleshooting techniques. Getting a good sample
▪ Inaccessible artery ‐ choose a different site
▪ Absent pulse ‐ choose a different site
▪ Small spurt of blood ‐ needle has gone through the
artery so pull back. If redirection is needed pull out until
bevel is seen then redirect
▪ If patient is in pain or has increased anxiety this will
cause hyperventilation and altered results
22. Explain temperature correction in regards to blood gas analysis. If patient’s temp is abnormal corrections should
be made
▪ If patient has a fever:
▪ When analyzed CO2 & O2 will be decreased and pH will be
increased (due to temperature of machine)
▪ Must correct to patient’s body temp which will cause the CO2 and
O2 to increase and pH to decrease
▪ If patient is hypothermic:
▪ When analyzed CO2 & O2 will be increased and pH will be
decreased (due to temperature of machine)
▪ Must correct to patient’s body temp which will cause the CO2 and
O2 to decrease and pH to increase
23. Explain the components of a blood gas analyzer. Blood gas analyzers measure 3 values
pH (Sanz electrode)
PO2 (Clark electrode)
PCO2 (Severinghaus electrode)
All other values are calculated
HCO3
BE
Oxygen saturation
24. Explain the function and principles of a Galvanic O2 Analyzer Creates a current as a result of oxidation and reduction of
O2
Measures partial pressures and converts to a percentage
Accuracy is affected by water on the sensor, high pressure,
and altitude
Can measure continuous flow
2‐point calibration required (21% and 100%)
If unable to calibrate check the fuel cell
Disadvantage
▪ Powered by a fuel cell which must be changed on
occasion
25. Explain the function and principles of an electrical oxygen analyzer. Oxygen analyzers are used to measure inspired oxygen concentration (FiO2)
26. Explain the function and principles of an electrochemical oxygen analyzer Electrochemical oxygen analyzer
Rely on a chemical reaction to produce a flow of electrons (current)Two types:
Galvanic
Polarographic
27. Explain the function and principles of a physical oxygen analyzer. Oxygen analyzers are used to measure inspired oxygen concentration (FiO2)
28. Explain the function and principles of a Polorgraphic Similar to galvanic fuel cell but requires a battery
to speed up the reduction reaction
▪ Allows for a faster response time
Measures partial pressure and converts to a
percentage
Affected by water on sensor, altitude, and
pressure
Calibrate same as galvanic
If unable to calibrate, change the battery
29. Explain the procedure for arterial punctures
30. For accurate ABG results, what are components of QUALITY CONTROL? • record keeping (policies, procedures)
• performance validation (testing new instrument)
• preventative maintenance / function testing
• automated calibration and verification
• internal statistical quality control
• external quality control (proficiency testing)
• remedial action (correct errors)
31. Give an example of OXIMETRY? HbO2 absorbs LESS red light and MORE infrared light.
32. How are the results reported? • as SpO2 -> NOT SaO2!
• p = pulse
33. How does a Pulse Oximeter work? • photodector placed opposite LED across arterial vascular bed
• light transmitted through tissue and partially absorbed
• absorption is constant except during arterial pulsation
• ignores constant sources of light, concentrates on pulsatile absorption
• measures intensity of light @ each wavelength
34. How does hemoximetry work? • INVASIVE
• multiple lights pass through the sample to measure multiple Hb species (HbO2, HbCO, and metHb)
35. How does it work? sensor warms underlying sking to increase arerial blood flow
36. How does pulse oximeter work? uses light absorption patterns
• indicate saturation of “PULSED” arterial blood
37. How does Pulse Oximeter work (con’t)? • compares light absorption with red and infrared light to yeild %HbO2
• Accuracy within 3-5% of actual
• the lower the SpO2, the less accurate
• <70% = unreliable
• signal extraction w/adaptive filter technology -> separates arterial signal from non-arterial noise
38. How does the capnometer function? • CO2 absorbs infrared light
39. How do we analyze gas exchange between lungs and blood? • O2 and CO2 levels in ARTERIAL blood
• CO2 levels in expired air
40. How do we analyze gas exchange levels between blood and tissue? O2 levels in mixed venous (pulmonary artery) blood
41. How do you calibrate an ELECTROCHEMICAL analyzer? [Clark & galvanic] • 2-point calibration
• Calibrate to known source of 21%
-> use control to adjust
• Then calibrate to known source of 100%
42. [How do you calibrate an O2 analyzer?] • use 2 sample method
• expose sensor to 100% & 21% O2
43. How else does OXIMETRY work? Each FORM of hemoglobin has own pattern of light absorption.
44. How good are results of pulse oximeters? not as accurate as hemoximetry
• within 3-5% of hemoximetry
45. In high altitudes, what inaccuracy will the oxygen analyzer read? lower % than actual
• because lower pressure in higher altitudes
46. In high pressures, what inaccuracy will the oxygen analyzer read? And what conditions make for high pressure? • higher % than actual
• some mechanical ventilation
47. In Pulse Oximetry what’s the difference between HbO2 and deoxygenated (reduced) Hb? HbO2 absorbs less light and more infrared light, than deoxygenated (reduced) Hb.
48. Interpret arterial blood gas values Blood gas analyzers measure 3 values
pH (Sanz electrode)
PO2 (Clark electrode)
PCO2 (Severinghaus electrode)
All other values are calculated
HCO3
BE
Oxygen saturation
49. Is it a good way to measure oxygen levels? if good quality assurance is used -> accurate!
50. List complications of arterial punctures. Arteriospasm
Air or blood emboli
Patient or sampler
contamination
(infection)
Hematoma
Hemorrhage
Trauma to vessel
Arterial occlusion
Vasovagal response
Pain
Tissue trauma
Peripheral nerve
damage
51. List criteria for site of arterial puncture. Criteria for site of arterial puncture
Collateral Blood Flow
Vessel Accessibility
PeriarterialTissue
52. List indications for an arterial puncture. Sudden, unexplained dyspnea
Cyanosis
Abnormal breath sounds
Severe, unexplained tachypnea
Heavy use of accessory muscles
Changes in ventilator settings
CPR
Diffuse infiltrates in the CXR
53. List methods of sampling for gas analysis. Blood can be obtained by analysis by
Percutaneous puncture of a peripheral artery
From an indwelling catheter
Capillary sampling
54. List primary site for arterial puncture. Radial
▪ safest and most accessible
▪ located superficially
▪ collateral circulation via ulnar artery
Brachial
▪ no collateral circulation
Femoral
▪ no collateral circulation
55. List the recommended equipment for arterial punctures.
56. Most bedside systems use what to measure FIO2? electrochemical principles
57. Our clinical focus is on gas exchange between what? • lungs and blood
• blood and tissues
58. Some rules of Thumb? • wait 20-30 min. after major change in ventilatory support before sampling
• set alarm at 92%, NOT 90%
• but ICUs may set alarm levels @ 90%
• patients w/chronic hypoxia may be set at 88%
59. Soon afterward? • PCO2 level rises sharply and plateaus
(as alveolar gas is exhaled)
60. True saturation equals what? (reduced Hb+HbO2) + HbO2 + HbCO + metHb
61. What 3 ways are there to interpret oxygenation status? • PaO2
• SaO2
• CaO2
62. What affects the accuracy of a pulse oximetry Accuracy affected by
Perfusion (shock, hypotension, hemodynamics)
Things interfering with light transmission
▪ Fingernail polish
▪ Acrylic nails
▪ Erythema
▪ Bright ambient light
Patient motion
63. What are 2 important factors that influence accuracy of transcutaneous measurements? • age
• perfusion status
64. What are 2 techniques used in capnometry? • mainstrem – analyzing chamber is in breathing circuit
• sidestream – pump small volume of gas from circuit into analyzer (not done often)
65. What are indications for arterial sampling in patient? • acute SOB (tachypnea)
• abnormal breath sounds
• cyanosis
• heavy use of accessory muscle
• changes in ventilator settings
• CPR
• diffuse infiltrates in radiograph
66. What are oximetry LIMITATIONS? • motion artifact
• abnormal hemoglobins (CO & met)
• intravascular dyes
• ambient light
• low perfusion states
• skin pigmentation
• nail polish
• inaccurate below 83%
67. [What are PREANALYTIC ERRORS?] • problems occuring BEFORE sample analysis that alter accuracy
68. What are some disadvantages of pulse oximetry? • finger probes not reliable in patients with SHOCK
• cannot distinguish HbCO from HbO2 -> false high reading w/CO poisoning
• does not measure CaO2 or PCO2 -> patients w/O2 transport issues of hypoventilation need ABG
69. [What are some Preanalytic Errors?] • air in sample -> visible bubbles
• venous admixture
• excess anticoagulant
• metabolic effects -> time lag of collection
70. What are the 2 most common technical errors? • not warming site properly
• squeezing of puncture site (causes venous and lymphatic contamination)
71. What are the 2 most common types of electrochemical O2 analyzers that analyze FIO2? • polargraphic (Clark) electrode
• galvanic fuel cell
72. What are the different forms of Hb? • Hb (reduced hemoglobin)
• HbO2 (oxyhemoglobin)
• HbCO (hemoglobin carboxy hemoglobin)
• metHb (methemoglobin–nitrogen hemoglobin)
73. What are the effects of HUMIDITY on Miniox O2 analyzer? • it DECREASES the concentration of O2
-like diluting sample with another gas!
-if 100% O2 is saturated with 100% humidity, then actual O2 concentration drops to 96-97%!
-> using a Humidifier
74. What are the EFFECTS OF PRESSURE on Miniox O2 analyzer? • Yes! Because it responds to partial pressure of O2 (not %)
– changes in barometric pressure change the readings
– higher altitude => lower reading
75. What are the effects of TEMPERATURE on Miniox O2 analyzer? • minimal
-it has internal thermistor
-varies less than 3%
* Note: don’t handle unnecessarily, cuz body heat can affect its accuracy!
76. What are the response times for Clark electrodes? 10 – 30 seconds
77. What are the response times for galvanic fuel cells? 60 seconds
78. What causes inaccurate readings of oxygen analyzers? • H2O condensation (on probe)
• Pressure fluctuations
79. What does a greater difference between PETCO2 and PaCO2 mean? obstructive lung disease
• can’t expirate CO2
• [possible acidosis]
80. What does a normal capnogram show at start? • a PCO2 of zero at start of expiration
81. What does CaO2 represent? content of O2 in 100 ml of arterial bloodj
• amount of Hb present and degree of saturation
82. What does NONINVASIVE monitoring mean? gathering data EXTERNALLY
83. What does PaO2 represent? partial pressure of O2 in arterial blood
• result of gas exchange between lung and blood
84. What does PETCO2 normally average? • 1-5 mmHG less than PaCO2 (arterial CO2) ~34-39 mmHg
• PaCO2 = 40 mmHg normal
85. What does SaO2 represent? degree to which Hb is saturated with O2[can have 100% saturation in low amount of blood!]
86. What does the modified Allen test test for? • collateral circulation in the ulnar artery
87. What do INVASIVE procedures require? INSERTION of sensor or collection device into body
88. [What do you do with an electrochemical O2 analyzer?] measure a patient’s FiO2
• after calibration
• to see if they’re getting the prescribed amount
89. What if analyzer doesn’t calibrate? -> possible low battery in polarographic (galvanic uses batter to run only alarms)
-> sensor depletion (galvanic fuel cell dying; clean polarographic anode/cathodes and replace electrolyte solution)
-> electronic failure
90. What is a capnometer? measures CO2
91. What is a FAULTY ASSUMPTION of pulse oximetry reading? • everytime 97% reading = 14.5 gm/dL HbO2
-> patient may be anemic (blood has less than normal # RBC)
-> pulse oximeter doesn’t look at all types of Hb (may only look at reduced Hb and HbO2)
92. What is a PROBLEM of pulse oximetry? • pulse oximeter only reads REDUCED Hb and HbO2
-97% but patient still in distress. Patient has 15 g/dL but only 8 available for O2 carrying.
-Thus: • patient has CO poisoning, gm/dL is HbCO
93. What is CAPILLARY BLOOD GAS ANALYSIS? alternative to direct arterial
• used in infants and small children
94. What is capillary blood gas NOT good for? NO VALUE in estimating PO2 (arterial oxygenation)
95. What is capnography? graphic display of CO2 levels
• as they change during breathing
96. What is CAPNOMETRY? measurement of CO2 in respiratory gases
97. What is characteristic of MONITORING? • ongoing process, dynamic physiologic process in timely manner
• done w/MONITOR
• no removal of samples from body
98. What is characteristics of LABORATORY ANALYSIS? • removed from the body
• discrete measurements
• made with ANALYZER
99. What is CO-OXIMETRY? • measures more than 2 types of Hb-> more wavelengths needed
• 3 wavelengths measure:
-Hb&HbO2, HbCO, metHb
100. What is HEMOXIMETRY? • uses a hemoximeter to measure blood O2 levels and Hb saturations
• a type of oximetry
101. What is it capillary blood gas used for? rough estimate of arterial pH and PCO2
• needs to be warmed
102. What is most often used? radial artery
103. What is normal CaO2? 16-20 ml per 100 ml = 16-20%
104. What is normal PaO2? 80-100 mm Hg
105. What is normal SaO2? 95-100%
106. What is normal saturation for pulse oximetry? • 97% saturation
• 15 g/dL Hb -> per 100 mL of blood
107. What is OXIMETRY? measurement of blood Hb hemoglobin saturations using SPECTROPHOTOMETRY
108. What is pulse oximetry? • noninvasive portable monitoring device
109. What is reduced CaO2 a result of? • low PaO2 and SaO2
• reduced Hb level
• or both
110. [What is the definition of respiratory failure based on? blood gas measurements
111. [what is the only true way to measure VENTILATION?] • arterial CO2
112. What is the PaO2 for mild hypoxemia? 60-80 mm Hg
113. What is the PaO2 for moderate hypoxemia? 40-60 mm Hg
114. What is the PaO for severe hypoxemia? <40 mm Hg
115. What is the PERFUSION INDEX? • the pulsatile signal indexed against the non-pulsatile signal
• ratio: PS/NPS
• should be at least 1.00
• can range from .01 to 20
116. What is TRANSCUTANEOUS BLOOD GAS MONITORING? • skin sensor
• provides continuous, noninvasive estaimates of PO2 & PCO2
117. What is transmission vs. reflectance oximetry? • transmission: LED goes through tissue to detector
• reflectance: LED light reflects back to detector
118. What other LIMITATIONS? • can’t quantify degree of hypoxemia present
• Hyperbilirubinemia does NOT affect accuracy of SpO2 readings
119. What reduces the agreement between PtcO2 and PaO2? • low perfusion
• increasing age
120. What should one do so HUMIDITY does not affect Miniox O2 analyzer? • position sensor UPSTREAM of humidifier
• Mount sensor with deflector pointing downward, so water doesn’t collect (condensation)
121. What’s the best way to avoid problems with O2 analyzers? preventive maintenance
122. What’s the most common causes of anlayzer malfunction? low batteries, sensor depletion, electronic failure
• fix: replace batteries, replace sensor, repair electronic system
123. What type of OXYGEN ANALYZERS are there? • Physical (Beckman: outdated but accurate)
• Electrical (Mira: outdated)
• Electrochemical
• chemical
• mass spectrometer
• Blood Sampling Analyzers
• Spectrophotometric (pulse oximeter)
124. What types of blood sampling analyzers are there? • polarographic (Clark electrode)
• Arterial blood gas samples
• Transcutaneous monitoring
125. What types of electrochemical oxygen analyzers are there? • galvanic (fuel cell)
• polarographic (Clark electrode); faster
126. When is capnograpy used? in patients undergoing:
• general anesthesia
• mechanical ventilation
127. [Where does analysis of gas exchange begin?] with system inputs:
• inspired O2 concentrations
• CO2 concentrations
128. [Where do we get blood gas samples?] • peripheral artery
• indwelling catheter (arterial, central venous, or PA)
• capillary sampling
129. [Where do you put the probe?] use a T-tube and place in circuit downstream from inspiratory tube
• between output and mouth
130. Where else can arterial blood be taken? • brachial
• femoral
• posterior tibial
• dorsalis pedis
131. Where is a transcutaneous monitor placed on an infant? normally over the sternum
132. Which is better? • invasive more accurate
• but carries greater risk
133. Why does OXIMETRY work? every substance has a unique pattern of light absorption
134. Why is radial artery most often used? • collateral circulation! (confirm with Allen test)
• near surface, easy to stabilize
• no large veins near
• relatively pain free
1. Benefits of Point-of-Care Testing… Reduces turnaround time, thus should improve care and lower costs.
2. How can tissue O2 be measured? Can be measured by invasive probes-Tissue Oxygen (PtO2) Monitor, inserted directly into organs, tissue, and body fluids.
3. How do you prevent pre-analytical errors in ABG samples? Make sure the sample is:
Obtained anaerobically
Properly anticoagulated
Bubbles removed
Analyzed within 10 to 30 minutes
4. How is CO2 transported? 45-55 ml of CO2 per 1 dl blood is transported by ionized bicarb, dissolved in plasma, and plasma protein transport.
5. How much blood is needed for an adequate ABG sample? 0.5-1 mL of blood. (usually enough to perform two tests)
6. In regards to accurate ABG results what are the components of quality control? **Record keeping (policies and procedures)
**Performance validation (testing new instrument)
**Preventative maintenance and function checks
**Automated calibration and verification
**Internal statistical quality control
**External quality control (proficiency testing)
**Remedial action (to correct errors)
7. Intra-arterial (In Vivo) continuous blood gas analysis is beneficial because it provides… Real time monitoring
**Reduction in therapeutic decision making time
**Less blood loss
**Lower infection risk
**Improved accuracy
**Elimination of specimen transport
8. Invasive procedures are… insertion of a monitoring device into a patient
9. Laboratory Analysis is… discrete measurements of fluids or tissue that has been removed from patient
10. Monitoring is defined as… an ongoing process by which clinicians obtain and evaluate dynamic physiological processes in a timely manner (bedside)
11. Noninvasive procedures are… external monitoring without insertion of devices INTO the patient.
12. Possible anatomical sites for blood draws Brachial
Radial
Femoral
Posterior tibial
Dorsalis pedis
13. Pressure values for oxygenation PaO2 (normal = 80-100)
PaO2 60-79 mm Hg = mild hypoxemia
PaO2 40-59 mm Hg = moderate hypoxemia
PaO2 <40 mm Hg = severe hypoxemia
SaO2 (normal = 95-100%)
CaO2 (normal = 18-20 vol%)
14. Procedure for initiating indwelling catheterization… First sample of indwelling catheter would be a waste sample.
15. Reasons for drawing an ABG Sudden, unexplained dyspnea
Acute shortness of breath / tachypnea
Abnormal breath sounds
Cyanosis
Heavy use of accessory muscles
Changes in ventilator settings
CPR
Diffuse infiltrates in chest radiograph
New infiltrates in CXR
Sudden cardiac arrhythmias
Acute hypotension
16. Syringe safety precautions… Do NOT recap the needle without a safety device, handle with both hands, point the needle at people when not performing a puncture, bend/break/remove needles from syringes by hand or dispose of used syringes in anything but an appropriate puncture resistant sharps container.
17. What are common technical errors associated with capillary blood sampling? inadequate warming and squeezing of puncture site. Squeezing the puncture site may result in venous and lymphatic contamination of sample.
18. What are secondary values to ABGs that need to be CALCULATED? Bicarbonate (HCO3-)
Base excess (BE) or deficit
Hemoglobin saturation (HbO2%)
19. What are the 2 most important factors influencing accuracy of transcutaneous measurements? Age and perfusion status
20. What are the benefits of indwelling catheters? (ie. A-Line) **Provides ready access for blood sampling.
**Allow continuous monitoring of vascular pressures.
21. What are the site locations for indwelling catheters? Normal routes are peripheral arteries (radial, brachial, pedal), femoral artery, central vein, and pulmonary artery.
22. What are two techniques of capnometry? 1. Mainstream technique places an analysis chamber in patients breathing circuit.
2. Sidestream technique pumps small volume of gas from circuit into nearby analyzer.
23. what can a good capillary blood gas sample provide and reflect? estimated arterial oxygenation and PCO2
24. What can be used if frequent blood sampling is needed? Arterial cannulation
25. What can PtO2 monitors indicate? **Monitor brain tissue oxygen as an early sign of ischemia.
**Monitor adequacy of brain perfusion in patients with traumatic brain injury.
26. What does capnometry measure? CO2 in respiratory gasses

 

 

**Capnometer functions on basis that CO2 absorbs infrared light proportion to amount of CO2 present.

27. What does Extra-arterial (Ex Vivo) blood gas analysis provide? **Eliminates all problems associated with indwelling sensors.
**Provides quick results.
**Determine further justification of costs and patient benefits.
28. What does oximetry measure? Hb saturation using spectrophotometry.
29. What does transcutaneous monitoring provide? continuous, noninvasive estimates of PO2 and PCO2 using a skin sensor. Also PtcO2 levels
30. What do most beside systems to measure FiO2 utilize? electrochemical principles (O2 analyzers)
31. What is a downfall of indwelling catheters? Infection and thrombosis are more likely than intermittent punctures.
32. What is Hb measurements expressed as and what is its O2 capacity when compared to what is dissolved in plasma Always expressed in grams/dl. dl=100 ml. The O2 capacity of Hb is 7x greater than what is dissolved in plasma.
33. What is Hemoglobin (Hb or Hgb) a protein (metalloprotein) with Fe+2 (ferric Iron) made up of globulin chains (2 alpha and 2 beta). Each of these chains have a central structure called the Heme molecule. Hb helps maintain the shape of the RBC. Abnormal Hb will change the shape of the RBC impeding the function and flow of the blood.
34. What is hemoximetry? laboratory analytical procedure requiring invasive sampling of arterial blood.

 

 

**Measures blood oxygen levels and hemoglobin saturations using a hemoximeter.
**Multiple lights pass through sample to measure multiple hemoglobin species such as HbO2, HbCO, and metHb.
**If good quality assurance measures are used, measurements are very accurate!

35. What is Point-of-Care Testing? Performing blood gas analysis at the patient’s bedside.
36. What is pulse oximetry? noninvasive monitoring technique performed at bedside.

 

 

**Combines principles of spectrophotometry with photoplethysmography.
**Noninvasive portable monitoring device providing estimates of SaO2
**Results are reported as SpO2
**Pulse oximetry uses light absorption patterns to indicate saturation levels of “pulsed” blood (arterial blood, not venous blood)
**Results are not as accurate as hemoximetry
**Accurate to within ±3% to 5% of hemoximetry.
**Finger probes are not reliable in patients with shock.
**Cannot distinguish HbCO from HbO2, so there will be a false high [SpO2] in CO poisoning.
**Does not measure CaO2 or PCO2, so patients suspected of having O2 transport issues or hypoventilation should have an ABG.

37. What is responsible for the color of our blood? The Fe in Hb is responsible for the color of our blood which varies depending on the amount of O2 that is bound to it.
38. What is the benefit to invasive procedures over noninvasive procedures? Greater accuracy
39. What is the downfall to invasive procedures? Greater risk
40. What is the drawback of Ex Vivo blood gas analysis? Unable to provide real-time continuous data.
41. What is the importance of the Heme Molecule in Hb? Heme molecule contains iron that transports O2 and CO2.
42. What is the normal range for proper collateral circulation? (time wise) Pink in 5-10 seconds
43. What is Tissue oximetry? noninvasive (TCM) method of measuring saturation of hemoglobin at tissue level.

 

 

**Oxygen saturation at tissue level (StO2) assesses adequacy of circulation & oxygen delivery.
**Early detection of low StO2 can be used as an early detection method of tissue hypoperfusion in patients with traumatic injuries.

44. What is used to measure CO2 levels in capnometry? Capnometer
45. What patients usually require capnometry? patients undergoing general anesthesia or mechanical ventilation.
46. What should you do if you get a negative reading on the modified Allen’s test? Redo the test on the other hand and if you get another negative call the doctor.
47. What situation is noninvasive methods appropriate? clinical decisions
48. What value is useless in regards to Capillary blood samples PO2 and SaO2. (SaO2 must be evaluated via pulse oximetry.
49. When do you do a modified Allen’s test? Prior to radial puncture ONLY.
50. Why does Oximetry work? each substance has its own unique pattern of light absorption. (ie each form of hemoglobin HbO2, HbCO)
51. Why do we use Point-of-Care Testing? **Reduces turnaround time, thus should improve care and lower costs.
**Used for blood chemistry and hematology parameters.
**Used increasingly in hospitals and physician offices.
52. Why is the radial artery the most often used site for ABG puncture? **near surface
**Collateral circulation usually exists
**No large veins nearby
**Radial puncture is RELATIVELY pain free