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Questions and Answers
What distinguishes laboratory analysis from monitoring?
What distinguishes laboratory analysis from monitoring?
Which of the following statements about invasive procedures is true?
Which of the following statements about invasive procedures is true?
What is the primary advantage of invasive procedures compared to noninvasive procedures?
What is the primary advantage of invasive procedures compared to noninvasive procedures?
What principle is commonly used in bedside systems for measuring FIO2?
What principle is commonly used in bedside systems for measuring FIO2?
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Which electrochemical device requires a battery to function?
Which electrochemical device requires a battery to function?
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What is a common troubleshooting step for O2 analyzers?
What is a common troubleshooting step for O2 analyzers?
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What might indicate that an O2 analyzer is malfunctioning?
What might indicate that an O2 analyzer is malfunctioning?
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Which of the following is a preventative maintenance step for O2 analyzers?
Which of the following is a preventative maintenance step for O2 analyzers?
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What is a characteristic of the response time of Clark electrodes?
What is a characteristic of the response time of Clark electrodes?
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What is a significant risk factor associated with invasive procedures?
What is a significant risk factor associated with invasive procedures?
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What is the main reason the radial artery is preferred for arterial blood sampling?
What is the main reason the radial artery is preferred for arterial blood sampling?
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What does a normal Modified Allen test indicate?
What does a normal Modified Allen test indicate?
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Which of the following is a precaution to take when handling needles?
Which of the following is a precaution to take when handling needles?
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How much blood is generally adequate for sampling during arterial blood gas analysis?
How much blood is generally adequate for sampling during arterial blood gas analysis?
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Which statement about the Modified Allen test is true?
Which statement about the Modified Allen test is true?
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What is NOT a characteristic of the radial artery as a site for blood sampling?
What is NOT a characteristic of the radial artery as a site for blood sampling?
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What precautions should be taken regarding the use of syringes after obtaining blood samples?
What precautions should be taken regarding the use of syringes after obtaining blood samples?
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Which patients should NOT undergo a Modified Allen test?
Which patients should NOT undergo a Modified Allen test?
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What factors may affect the required volume of blood for sampling?
What factors may affect the required volume of blood for sampling?
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Why is arterial cannulation performed?
Why is arterial cannulation performed?
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What is a key reason for using the radial artery for blood gas sampling?
What is a key reason for using the radial artery for blood gas sampling?
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Which aspect of the Modified Allen test indicates normal collateral circulation?
Which aspect of the Modified Allen test indicates normal collateral circulation?
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Why should the Modified Allen test not be performed on critically ill patients?
Why should the Modified Allen test not be performed on critically ill patients?
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What is the recommended blood sample volume for arterial blood gas analysis?
What is the recommended blood sample volume for arterial blood gas analysis?
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What should be done with used syringes and needles?
What should be done with used syringes and needles?
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What anticoagulant factors can influence the required blood volume for sampling?
What anticoagulant factors can influence the required blood volume for sampling?
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What is a safety precaution to take when handling needles?
What is a safety precaution to take when handling needles?
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When is arterial cannulation typically necessary?
When is arterial cannulation typically necessary?
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Which statement is true regarding the safety handling of used needles?
Which statement is true regarding the safety handling of used needles?
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What determines the adequacy of the blood sample volume in arterial sampling?
What determines the adequacy of the blood sample volume in arterial sampling?
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What is a key difference between laboratory analysis and monitoring?
What is a key difference between laboratory analysis and monitoring?
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Which of the following best describes the typical response time of a Clark electrode?
Which of the following best describes the typical response time of a Clark electrode?
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In what way do invasive procedures typically differ from noninvasive procedures?
In what way do invasive procedures typically differ from noninvasive procedures?
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What must be done before using an oxygen analyzer to ensure accurate measurements?
What must be done before using an oxygen analyzer to ensure accurate measurements?
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What can indicate that an oxygen analyzer may be malfunctioning?
What can indicate that an oxygen analyzer may be malfunctioning?
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Regarding noninvasive monitoring, what is one significant advantage highlighted?
Regarding noninvasive monitoring, what is one significant advantage highlighted?
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What is a common characteristic of galvanic fuel cells used in measuring FIO2?
What is a common characteristic of galvanic fuel cells used in measuring FIO2?
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What is the best approach to prevent issues with oxygen analyzers?
What is the best approach to prevent issues with oxygen analyzers?
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What does a consistent trend in changes detected through a noninvasive method indicate?
What does a consistent trend in changes detected through a noninvasive method indicate?
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What is a potential issue that could arise if an analyzer fails to calibrate?
What is a potential issue that could arise if an analyzer fails to calibrate?
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Study Notes
Analysis and Monitoring of Gas Exchange
- Analysis involves discrete measurements of body fluids or tissues, requiring removal from the body.
- Measurements are performed using an analyzer.
- Monitoring is a continuous process, evaluating physiological processes at the bedside.
- Monitoring uses bedside monitors.
Analysis vs. Monitoring
- Laboratory analysis provides discrete measurements of fluids or tissues, requiring removal from the body.
- Monitoring is a continuous process, evaluating dynamic physiological processes in a timely manner, usually at the bedside.
Invasive vs. Noninvasive Procedures
- Invasive procedures require insertion of a sensor or collection device into the body.
- Noninvasive methods gather data externally.
- Invasive procedures provide more accurate data but carry a higher risk compared to noninvasive methods.
- Noninvasive trends are useful in making clinical decisions after establishing a gradient between invasive and noninvasive methods.
Measuring FIO2
- Most bedside systems use electrochemical principles to measure FIO2.
- Two common methods are polargraphic (Clark) electrodes, requiring batteries, and galvanic fuel cells, not needing batteries.
- Clark electrodes have response times between 10-30 seconds.
- Galvanic fuel cells have response times of 60 seconds.
Troubleshooting O2 Analyzers
- Calibration must be performed according to the manufacturer's instructions before use.
- Failure to calibrate or inconsistent readings indicate malfunction.
- Preventative maintenance is the best way to avoid problems.
- Analyzer calibration failures could be due to low batteries, sensor depletion, or electronic failure.
Sampling & Analyzing Blood Gases
- Analyzing arterial blood samples is crucial in diagnosing and treating respiratory failure.
- Radial artery is the most common site due to its superficial location, stabilizable collateral circulation (confirmed with the Allen test), and minimal pain during puncture.
- Arterial cannulation is an option when frequent sampling is needed.
Arterial Sampling
- The Modified Allen's test is performed before radial artery puncture to confirm adequate collateral circulation.
- The test involves occluding both the radial and ulnar arteries, then releasing the ulnar artery, observing the hand for return of blood flow within 5-10 seconds.
- The test cannot be performed on critically ill or uncooperative/unconscious patients.
- The appropriate blood sample volume is 0.5 to 1 mL, depending on anticoagulants used and further testing.
- Proper needle handling, syringe disposal, and sharps container usage are crucial for safety and infection control.
Indications for Arterial Sampling
- Unexplained dyspnea, acute dyspnea/tachypnea, abnormal breath sounds, cyanosis, heavy use of accessory muscles, ventilator setting changes, CPR, diffuse/new chest infiltrates in CXR, sudden cardiac arrhythmias, and acute hypotension.
Blood Sample Analysis
- Clinicians can avoid pre-analytical errors by obtaining samples anaerobically.
- Samples must be properly anticoagulated and analyzed within 10-30 minutes.
Interpretation of ABGs
- PaO2 (partial pressure of oxygen) is significant in evaluating oxygenation status.
- SaO2 (oxygen saturation) is typically normal at 95-100%.
- CaO2 (arterial oxygen content) ranges between 18-20 volume percent when normal.
- PaO2 values ranging from 60 to 79 mm Hg indicate mild hypoxemia; 40-59 mm Hg, moderate hypoxemia; and below 40 mm Hg, severe hypoxemia.
Indwelling Catheters
- Indwelling catheters provide ready access for blood sampling and continuous monitoring of vascular pressures.
- Infection and thrombosis risks are higher compared to intermittent punctures.
- Common catheterization routes include peripheral arteries (radial, brachial, and pedal), femoral artery, central vein, and pulmonary artery.
- Three-way stopcocks provide sampling access for most intravascular lines.
- Pulmonary artery catheters include separate blood sampling and IV infusion ports with a balloon at the tip.
Brachial Artery Catheter Image
- (Diagram with labeled parts).
3-way Stopcock Image
- (Diagram with labeled parts).
Capillary Blood Gases
- Capillary samples accurately reflect arterial pH and PCO2 levels.
- Capillary PO2 is not suitable for assessing arterial oxygenation and needs to be evaluated using pulse oximetry.
- Common errors during capillary sampling include inadequate warming and squeezing of the puncture site, resulting in venous/lymphatic sample contamination.
Analyzing
- Analyses of blood samples measure pH, PCO2, and PO2 levels.
- Supporting secondary values are calculated, such as plasma bicarbonate, base excess, and hemoglobin saturation.
- Some systems combine blood gas and hemoximetry (total hemoglobin) measurement.
Instrumentation
- Instrumentation is based on several types of sensor technology for measuring pH, PCO2, and PO2.
- Examples include electrochemical electrodes, optical fluorescence, and photoluminescence.
Electrodes
- PaO2: Clark polarographic electrode.
- PaCO2: Severinghaus electrode.
- pH: pH electrode consisting of a measuring and reference electrodes.
Point-of-Care Testing
- Point-of-care testing performs blood gas analysis at the patient's bedside, reducing turnaround time and improving care/lowering costs.
- Blood chemistry and hematology parameters are also analyzed through this method.
GEM Premier 4000
- (Image/diagram of the device)
Oximetry
- Oximetry measures hemoglobin saturation using spectrophotometry.
- Substances absorb light differently, leading to distinct patterns.
- Hemoglobin forms (HbO2, HbCO, metHb) absorb light differently.
- For example, HbO2 absorbs less red light and more infrared light.
Oximetry (cont.)
- Types of oximetry used in clinical practice include hemoximetry (co-oximetry) requiring invasive arterial blood sampling.
- Pulse oximetry, a non-invasive monitoring technique.
- A fiberoptic catheter inserted into the vena cava or pulmonary artery allows for venous oximetry.
- Tissue oximetry is a non-invasive technique measuring hemoglobin saturation at the tissue level.
Tissue Oxygen Probe (diagram)
- A diagram of the device.
- Numbers/labels corresponding to device parts.
Hemoximetry
- Hemoximetry measures blood oxygen levels and hemoglobin saturations using a hemoximeter.
- Multiple lights pass through the sample to analyze different hemoglobin species (HbO2, HbCO, or metHb).
- Highly accurate measurements with good quality assurance.
Pulse Oximetry
- Pulse oximetry combines photometry and plethysmography for noninvasive estimates of SaO2.
- Results are reported as SpO2 (pulse oximetry oxygen saturation).
- The method uses light absorption patterns to measure "pulsed" (arterial) blood oxygen saturation.
- Pulse oximetry results are not as accurate as hemoximetry.
Pulse Oximetry (cont)
- The accuracy of pulse oximetry is ±3% to 5% of hemoximetry.
- Finger probes are unreliable in shock.
- Pulse oximetry cannot distinguish HbCO from HbO2 (falsely high readings in CO poisoning).
- Pulse oximetry does not measure CaO2 or PCO2, so for suspected O2 transport issues, patients with hypoventilation should undergo ABG analysis.
Pulse Oximetry (cont.)
- Two types of pulse oximetry sensors are transmission and reflectance:
- Transmission sensors: two-sided sensors with LEDs and photodetectors, placed on the finger, toe, or earlobe.
- Reflectance sensors: one-sided sensors containing LEDs and a photodetector, commonly placed on the forehead.
Venous Oximetry
- Venous oximetry assesses the balance between oxygen delivery, utilization, and perfusion by indirectly measuring global tissue oxygenation.
- Normal values for mixed venous (pulmonary artery) oxygen saturation (SvO2) range from 60% to 80%.
Venous Oximetry (cont.)
- (Diagram of venous oximetry).
Tissue Oximetry
- Tissue oximetry measures oxygen saturation (StO2) at the tissue level, evaluating adequacy of circulation and oxygen delivery.
- Early detection of low StO2 can identify tissue hypoperfusion, particularly in patients with traumatic injuries.
Capnometry
- Capnometry measures carbon dioxide (CO2) in respiratory gases.
- A capnometer provides a graphic display (capnography) of CO2 levels during breathing.
- This method is frequently used in patients undergoing general anesthesia or mechanical ventilation.
Capnometry (cont)
- CO2 absorbs infrared light proportionally to its concentration measured via capnometry;
- Two techniques:
- Mainstream: patient's breathing circuit has an analysis chamber.
- Sidestream: small gas volumes from the circuit are pumped into a nearby analyzer.
Capnometry (cont.)
- A normal capnogram shows a CO2 pattern with zero at the start of exhalation, then a sharp rise (Phase II), and a plateau as alveolar gas is exhaled (Phase III).
- End-tidal PCO2 (ETCO2) usually averages 3-5 mm Hg below PaCO2, estimating deadspace ventilation.
Capnometry (cont.)
- (Diagram of capnogram).
Capnometry (cont.)
- (Diagram of capnogram showing different patterns associated with lung diseases and/or disorders).
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Description
Explore the differences between analysis and monitoring in gas exchange. This quiz covers the processes of invasive and noninvasive procedures, along with their implications in clinical settings. Understand how these methodologies impact physiological evaluations and decisions.
