Eagan's CH 18

What are the two most common errors committed during capillary sampling?

A. failure to properly warm the skin B. squeezing the puncture site

There are two common types of electrochemical analyzers. Name them.

A. galvanic B. polarographic

What are the three most common causes of oxygen analyzer malfunctions?

A. low battery B. sensor depletion C. electronic failure

What are the three primary parameters measured by a blood gas analyzer?

A. pH B. PCO2 C. PO2

Blood gases provide more information than other methods of gas exchange analysis. What are the three general areas that a blood gas helps to assess?

A. ventilation B. acid-base balance C. oxygenation

While performing end-tidal CO2 measurements, you notice that the baseline does not return to "0" on inspiration. Interpret this result.

An elevated baseline indicates rebreathing.

What precaution should you take when handling any laboratory specimen?

Apply standard or universal precautions such as wearing gloves. With blood gases you should avoid recapping and dispose of sharps properly. Double bag the blood for transport.

What is the gold standard of gas exchange analysis? What does this mean?

Arterial blood gases; this means ABGs are the standard against which other methods of analysis are measured.

Explain the differences between the two types of analyzers in terms of principle of operation and response time.

Galvanic analyzers use a gold anode and a lead cathode. Current flow across these poles is generated by the reduction of oxygen at the cathode. As there is no polarizing voltage the reaction is much slower than that of the polarographic analyzer. Polarographic analyzers use a silver anode and a platinum cathode. Current flow is generated by a polarizing voltage applied to these poles.

Which of the following would you perform after obtaining an arterial blood gas sample?

I. Remove air bubbles from the sample. II. Mix the sample by rotating the syringe.

Which of the following will affect the accuracy of pulse oximeter measurements?

II. decreased hematocrit levels III. dark skin pigmentation IV. exposure to sunlight

When would the transcutaneous monitor be preferred over the pulse oximeter?

In infants where hyperoxia is a concern; saturation measured by the pulse oximeter is not specific enough to monitor PO2.

A polarographic oxygen analyzer fails to calibrate when exposed to 100% oxygen. The first action the respiratory therapist should take would be to

Replace the battery.

Switching probes from one brand of pulse oximeter to another is strongly discouraged. What could happen if you do this?

Shock or burns to the patient

What problems may occur as a result of icing ABG samples?

Some analyzers (point of care, for example) require immediate analysis of unchilled blood. Accurate potassium analysis requires this, also. Thirty minutes of icing in a plastic syringe may erroneously increase PaO2. Glass syringes are recommended for long delays in analysis.

Describe the two-step process for calibrating an oxygen analyzer.

Step 1 is to expose the electrode to 100% O2 and calibrate the reading to 100%. Step 2 is to expose the electrode to 21% O2 and confirms a second reading of 21%.

A galvanic oxygen analyzer is being used as a check of the ventilator system to measure the delivered Fio2. The set Fio2 is 40%; however, the analyzer is reading 32%. Which of the following is the most likely cause of this discrepancy?

The electrode membrane has water condensation on its surface.

An end-tidal CO2 of "0" may indicate a serious problem. Name two life-threatening causes of a "0" value for end-tidal CO2.

A. cardiac arrest B. esophageal intubation --Could also indicate a leak or a disconnection

Never do this with a used needle

recap

Oxygen analyzer that measures the flow of electrons between negatively and positively charged poles

polarographic

What is the maximum ideal time between ABG sampling and analysis?

15 minutes

Name four other sites you can use if the radial artery is unavailable or has a poor pulse.

A. brachial B. femoral C. dorsalis pedis D. temporal (infants)

A 34-year-old firefighter is brought to the emergency department for treatment of smoke inhalation while fighting a house fire. His heart rate is 126, and respirations are 28 and labored. SpO2 is 100% on 6 L via nasal cannula. Blood pressure is 145/90 mm Hg. Breath sounds are coarse with inspiratory crackles in both bases. The patient's face is smudged with soot, and he is coughing up sputum with black specks in it. 37. What clinical signs of hypoxemia does the patient display? 38. Explain why the pulse oximeter is reading 100% despite these signs? 39. What is the most probable cause of the hypoxemia? 40. What blood test would you recommend to confirm your suspicions?

37. Tachycardia, tachypnea, abnormal breath sounds, labored breathing. 38. The pulse oximeter may be reading a falsely high %Hb O2 in the presence of carbon monoxide (HbCO) poisoning. 39. Elevated levels of carboxyhemoglobin will limit the oxygen carrying capacity of blood. Consider the carbonaceous sputum, history, breath sounds, and soot on Biff's face. 40. An ABG should be drawn and part of the sample analyzed with a co-oximeter (hemoximeter). Alternatively, you could use one of the new pulse oximeters that CAN measure carbon monoxide. These are not commonly available

A premature infant is wearing supplemental oxygen. Her physician is concerned about the effects of hyperoxia on her lungs and eyes. The infant is being monitored by a pulse oximeter, which shows a saturation of 100%. 41. What range of Po2 is possible with an Spo2 of 100%? 42. What type of noninvasive monitoring would you recommend in this situation?

41. PaO2 measurements of 100 to 600 are capable of giving pulse oximeter readings of 100%. 42. Transcutaneous monitoring will provide a noninvasive way to assess oxygenation in terms of keeping a minimally acceptable PaO2 and avoiding hyperoxia.

An elderly patient is admitted for acute exacerbation of his longstanding COPD. He is wearing a nasal cannula at 2 L/min. 43. What is the simplest way to quickly assess his oxygenation status? 44. Why would you recommend an arterial blood gas for this patient?

43. Pulse oximetry is a useful way to monitor the adequacy of arterial oxygenation. It is simple, quick, and noninvasive. 44. It is important to check the acid-base and ventilatory status of long-term COPD patients on admission to establish baseline values and to establish agreement between the SaO2 and the SpO2.

A patient was riding his motorcycle without a helmet when he crashed. Now he has a head injury and is being mechanically ventilated. His physician asks you to make recommendations regarding monitoring his gas exchange. 45. What are the advantages of using capnometry to monitor carbon dioxide in this situation? 46. Where would you place the capnometer probe in the ventilator circuit? 47. During monitoring, you notice that the capnograph does not return to "0" when the patient inhales. What does this indicate? 48. A few minutes later the patient's exhaled CO2 levels begin to rise. So does his blood pressure. Jimmy becomes agitated. What action would you take? 49. Why do rising CO2 levels cause increases in intracranial pressure?

45. Capnometry is continuous and noninvasive because you will be relying on maintaining a low PaCO2 for this patient. 46. Between the endotracheal tube and the wye connector of the circuit 47. Rebreathing 48. Manually ventilate or increase the ventilation provided by the ventilator to reduce the CO2. The capnometer will be useful in assessing this change. 49. CO2 is vasoactive. Increased levels cause vasodilation. As the blood vessels dilate, they take up more space in the head. Because the skull does not expand, the pressure (ICP) goes up.

If you wanted to measure actual hemoglobin saturation, what type of analyzer would be needed?

A hemoximeter (co-oximeter); although point-of-care devices can measure Hb, they do not measure the actual saturation; they calculate it.

Describe three noninvasive ways you can determine the reliability of a pulse oximeter at the bedside.

A. Assess perfusion at the monitoring site. B. agreement between the pulse oximeter heart rate and actual rate C. Confirm the adequacy of the output signal/stability of readings

Describe the three main quality assurance procedures used to maintain consistently accurate blood gas results. A. Automated calibration B. Control media C. Proficiency testing

A. Automated calibration. Gas electrodes are calibrated with precision mixtures of oxygen and carbon dioxide. The pH electrode is calibrated with standard pH buffer solutions. Calibration is a two-point process using high and low values. The analyzer automatically adjusts the response so the low output = the low input, etc. B. Control media. Once the machine is calibrated, control chemicals that mimic real blood samples are analyzed. At least two levels are tested every 8 hours, and three levels every 24 hours. Analyzed results are compared to expected values. C. Proficiency testing. Five unknown samples are analyzed at least three times per year. Results are reported. If the values are not acceptable, remediation must be performed and documented or reimbursement may be suspended.

While performing end-tidal CO2 measurements, you notice that no real plateau is reached. Give two possible interpretations of this result.

A. COPD/airway obstruction B. left ventricular failure/shock

List four reasons why the radial artery is the preferred site for ABG sampling?

A. It is near the surface and easy to palpate. B. Collateral circulation is provided by the ulnar artery. C. The radial artery is not near any large veins. D. This site may be less painful.

How long should you wait after changing the Fio2 before performing an ABG on a patient with healthy lungs? A patient with COPD?

A. Patients with healthy lungs reach steady state in 5 minutes B. COPD may be as long as 20 to 30 minutes

Which of the following is true concerning the use of a transcutaneous Po2 monitor?

A. TcPO2 should be checked with arterial blood samples.

Describe the modified Allen test, and give the definition of a positive result.

A. You occlude the radial and ulnar arteries and have the patient make a fist. The patient is then asked to relax his hand. It should be blanched or appear pale. Then release the ulnar artery. Observe the time required for the hand to "pink up". B. Flushing of the hand within 10 seconds is a positive result demonstrating adequate collateral circulation. (In the original test by Dr. Allen, a positive result was BADthus the confusion!)

What are the primary advantages and disadvantages of transcutaneous gas monitoring over arterial sampling? A. Advantages B. Disadvantages

A. advantages 1. noninvasive 2. continuous B. Disadvantages 1. poor correlation of values in some cases, such as older patients 2. not useful during short procedures or emergencies 3. labor intensive and complex

Name the four things you can do to avoid most preanalytical sampling errors. Hint: check Table 18-1 on page 371 of your text.

A. anaerobic sample B. anticoagulated sample C. immediate expulsion of air bubbles D. Analyze within 15 minutes or place on ice.

AARC's ABG sampling guidelines describe several medications that may result in prolonged bleeding. These are anticoagulants (clot preventors) and thrombolytics (clot busters). Give two examples of each of these classes of drugs. A. Anticoagulants B. Thrombolytics

A. anticoagulants 1. heparin 2. Coumadin (warfarin) (Don't forget Plavix and aspirin.) B. thrombolytics 1. streptokinase 2. tissue plasminogen activator (TPA)

What are the two primary benefits and hazards of indwelling peripheral arterial lines? A. Benefits B. Hazards

A. benefits 1. ready access for blood sampling 2. continuous pressure monitoring B. hazards 1. increased risk of infection 2. increased risk of thrombosis

Modify this test and perform before radial puncture

Allen

An arterial blood gas sample is drawn from a patient who is breathing room air. Analysis reveals the following results: pH 7.45 Paco2 35 mm Hg Pao2 155 mm Hg

An air bubble has contaminated the sample.

Why can you use a capnometer during CPR but not a pulse oximeter?

Capnometers are indicated to assess proper intubation and adequate blood flow generated during CPR because pulmonary blood flow is required to generate exhaled CO2. Pulse oximeters rely on perfusion at a peripheral site, which may not be available during CPR.

What is the difference between capnography and capnometry?

Capnometry is the measurement of CO2 in respiratory gases. A capnometer is the actual measuring device. Capnography is the real time graphic display of CO2 levels during breathing.

Oxygen analyzing electrode

Clark

External quality control testing program

proficiency

According to the AARC guidelines, what action should you take to verify the results when pulse oximetry is unreliable or does not confi rm suspicions about the patient's clinical state?

Make a direct measurement of SaO2 with an ABG and hemoximeter.

What are the normal values for end-tidal CO2 for health individuals and how do they compare with values for arterial CO2?

Normal end-tidal CO2 is approximately 35 to 43 mm Hg (5% to 6%), or about 1 to 5 mm Hg less than arterial values.

In your own words, explain how an electrochemical analyzer converts the number of oxygen molecules (Po2) into a measurable reading.

Oxygen molecules cross a membrane and enter an electrolyte solution. A chemical reaction, the reduction of oxygen at the cathode and oxidation of silver at the anode, causes current to flow between two electrodes. The amount of current reflects the amount of oxygen molecules present.

What is point of care testing, and what are the potential benefits of this method of testing blood samples?

Point-of-care testing allows for measurement of blood gas and other values at the bedside. This reduces turnaround time, may improve care, and may lower cost. It may also decrease the need for personnel and complex lab equipment.

How would you modify your technique if you had to perform ABGs on a patient receiving anticoagulants?

Post puncture, apply pressure to the site for longer. Check carefully for postpuncture bleeding. The text recommends checking all sites after 20 minutes. (This answer is not described in the text. The AARC guidelines list coagulopathy as a relative contraindication.)

Artery of choice for puncture or cannulation

Radial

What technique can help prevent hyperventilation from pain or anxiety from altering the sample results?

administration of a local anesthetic (lidocaine) prior to the arterial puncture

Measure blood values in the laboratory

analyze

Describe proper placement of a capnometer sampling chamber or adaptor for a patient who is being mechanically ventilated.

between the patient and the wye connector of the ventilator circuit

Systematic errors in measurement

bias

Artery in the arm that's not your first choice

brachial

Complications of arterial puncture include all of the following except

pulmonary embolus

Non-invasive oximeter commonly used to measure hemoglobin's saturation with oxygen

pulse

Alternative to arterial sampling in infants

capillary

Which of the following analyzers is calibrated to a value of zero when exposed to room air?

capnometer

Point-of-________: method of testing blood at the bedside

care

Oximeter used to measure carbon monoxide in the blood

co

A pulse oximeter is being used to monitor a patient who was rescued from a fi re. The Spo2 is 90%; however, the patient is unconscious and shows signs of respiratory distress. What additional test should the RT recommend?

co-oximetry

Quality control

qc

When would you choose a pulse oximeter for monitoring an infant's oxygenation status over a transcutaneous monitor?

during a short procedure, or during an emergency when results are needed immediately

Which of the following would be most useful in assessing proper tube placement following endotracheal intubation?

end-tidal CO2 monitoring

Which of the following sites would be the best for continuous monitoring of exhaled carbon dioxide during mechanical ventilation?

endotracheal tube connector

Preanalytical ones, bubble in sample for example

error

Big artery in the groin that is used for drawing blood when other choices fail

femoral

Oxygen analyzer that doesn't use a battery

glavanic

vivo, inside the body

in

vivo, outside the body

in

For which patients is capillary sampling appropriate?

infants and small children

Device that provides ongoing information to clinicians

monitor

invasive monitoring doesn't hurt

non

Sensor that works on optical detection instead of electrochemical properties

optode

Determine the saturation of hemoglobin with a photoelectric device

oximetry

Explain what variables are reliable and unreliable in capillary sampling compared to arterial sampling.

pH and PCO2 give rough estimates compared to arterial blood. PO2 is not valuable from a capillary sample.

A respiratory therapist is preparing to perform pulse oximetry. Which of the following would be least beneficial for assessing accuracy of the device?

performing an Allen test on the patient

Pulse oximeters use this principle to detect arterial pulsation

plethysmography

of care, testing blood at the bedside instead of in the lab

point

An infant is placed on a transcutaneous oxygen monitor. The Tcpo2 is reading 40 mm Hg less than the Pao2 obtained from an arterial sample. All of the following could cause this problem except

room air contamination of the transcutaneous electrode

Allen's, for example

test

clot buster

thrombolytic

What is the range of accuracy for most commercially available pulse oximeters?

±3% to 5%