Persing: Ch 10 ABGs
6. The respiratory therapist has received an order to obtain an ABG sample from a patina, but an Allen test indicates collateral circulation is not present in the right wrist. At this time, the therapist would: A. obtain blood from the right radial artery B. obtain blood from the right brachial artery C. Wait for the physical to evaluate collateral circulation D. Check collateral circulation in the left wrist
* D. Check collateral circulation in the left wrist.*
Which of the following conditions shifts the HbO2 dissociation curve to the right? A. Hypercapnia B. Hypothermia C. Alkalemia D. HbCO
*A. Hypercapnia* (Right shift indicates Hb has less affinity for O2 and releases it more readily to the tissues, thus increases tissue Oxygenation.)
What is the Haldane effect?
*As O2 combines with Hb, the release of CO2 is enhanced. * (The lower the PO2 and hemoglobin saturation with O2, the more CO2 can be carried in the blood.)
8. The respiratory therapist is reviewing ABGs obtained earlier in the day from a patient on 35% air- entrainment mask. The ABG values are as follows: pH 7.43 PaCO2 29 torr PaO2 70 torr HCO3- 18 mEq/L What is the correct interpretation of this blood gas? A. Partially compensated metabolic acidosis normal oxygenation B. Fully. compensated respiratory alkalosis mild hypoxemia C . Uncompensated respiratory alkalosis normal oxygenation D. Fully compensated metabolic acidosis mild hypoxemia
*B. Fully compensated respiratory alkalosis mild hypoxemia*
9. The following blood gases are obtained on a sever cyanotic COPD patient on a 2 L/min NC: pH 7.51 PaCO2 29 torr PaO2 155 torr HCO3- 34 mEq/L Which of the following most likely accounts for these ABG values? A. The patient's cannula flow was higher than 2 L/min at the time of the arterial stick B. There is air in the blood sample C. The blood was inadvertently obtained from the vein D. These represent normal blood gases for a severe COPD patient
*B. There is air in the blood sample*
Which of the following ABG measurements determines how well a patient's lungs are being ventilated? A. pH B. paCO2 C. paO2 D. HCO3
*B. paCO2* (A value <35 mmHg indicates hyperventilation; >45mmHg indicates hypoventilation)
10. A patient on a mechanical al ventilator has the following ABG results: pH. 7.27 PaCO2 28 torr PaO2 88 torr HCO3- 27 mEq/L Based on this data, the respiratory therapist should recommend which of the following? A. Increase Vt B. Decrease the ventilator rate C. Repeat the blood gas evaluation since these results indicate a lab error. D. Decrease the FiO2
*C. Repeat the blood gas evaluation since these results indicate a lab error* (pH is acidic and both PaCO2 and HCO3- are alka )
The information below has been obtained from a patient on an aerosol mask at 40% O2: pH 7.42 PaCO2 36 mmHg PaO2 122 mmHg HCO3- 26 mEq/L What is the patient's P(A-a)O2? Barometric pressure (PB) = 747 mmHg A. 45 mmHg B. 77 mmHg C. 113 mmHg D. 235 mmHg
*C.* PAO2 = ((Pb -47 mmHg) x FiO2) - (PaCO2 x 1.25) PaO2 = (747 -47) x 0.40 - (36 x 1.25) = (700 x 0.40) - 45 = 280 - 45 = 235 mmHg = 235 mmHg - 122 mmHg = 113 mmHg
A patient with 2 L/min nasal cannula has the following ABG results: *pH 7.51* *PaCo2 27 mmHg* *PaO2 62 mmHg* *HCO3- 23mEq/L* These results indicate which of the following conditions? A. Uncompensated respiratory acidosis B. Chronic respiratory alkalosis C. Compensated metabolic alkalosis D. Acute respiratory alkalosis
*D. Acute respiratory alkalosis*
Which of the following blood gas measurements determines the level of tissue oxygenation? A. pH B. PaCO2 C. PaO2 D. PvO2
*D. PvO2* (Normal values = 35-45mmHg; decreased values indicate inadequate oxygenation of tissues)
7. The following ABGs have been recorded for a patient on 35% air- entrainment mask: pH. 7.51 PaCo2 42 mmHg PaO2 79 mmHg HCO2- 33 mEq/L What is the correct interpretation of this blood gas? A. Partially compensated respiratory alkalosis B. Fully compensated metabolic alkalosis C. Uncompensated respiratory alkalosis D. Uncompensated metabolic alkalosis
*D. Uncompensated metabolic alkalosis*
What the steps taken when obtaining ABG sampling via radial artery puncture?
1. Explain procedure to patient 2. Put gloves on 3. Perform the modified Allen's test 4. Place a folded towel under the patient's wrist to keep wrist hyperextended (for easier access to artery) 5. Clean the puncture site with isopropyl (70%) or some other appropriate disinfectant. 6. *optional *. If anesthetic (lidocaine (Xylocaine))needs to be used (pain management/ patients punctured several times) administer subcutaneously around puncture site and allow 3-5 min to take effect. 7. With the needle and heparinized syringe in one hand, palpate the artery with other hand. The needle should enter the skin at a 45- degree angle with the bevel pointed up. Advance the needle until blood pulsates into the syringe. 8. After obtaining 1mL of blood, apply a sterile gaze pad with pressure over the puncture site for 3-5 minutes or until bleeding has stopped 9. If an air bubble is present, ensure to remove from syringe since it can cause in accurate reading (↑ PaO2 and ↓ PaCo2 levels). 10. Place a cap/ rubber stopper over the needle, or remove the needle and place a cap over the end of syringe, This prevents air from entering the syringe. 11. Roll the syringe back and forth in hands to ensure proper mixing of blood and heparin to prevent clotting. 12. *optional* place sample on ice if sample can't be tested within 30 min. 13. Record the following info. after sample is drawn: FiO2, Vt, RR, Mode of ventilation (Mechanical, CMV, SIMV), PEEP level, patient's temperature.
What are some conditions that may cause a right shift of the oxyhemoglobin curve?
1. Hypercapnia 2. Acidemia 3. Hyperthermia 4. Increased levels of 2,3- DPG
What are some factors for the HbO2 Dissociation curve to shift to the right?
1. Hypercapnia 2. Acidosis 3. Hyperthermia 4. Increased levels of 2,3 DPG
What are some factors for the HbO2 Dissociation curve to shift to the left?
1. Hypocapnia 2. Alkalosis 3. Hypothermia 4. Decreased levels of DPG 5. HbCO
What are the steps when performing a modified Allen's test?
1. Instruct the patient to close his/her hand while occluding both radial & ulnar arteries 2. Instruct the patient to open his/her hand as you release the pressure on the ulnar artery while watching for the hand to regain normal color. 3. In order for a positive result, the hand should pink within 10-15 seconds 4. If the color is not restored within 10-15 sec the test is negative, meaning collateral circulation is not present and blood must not be obtained from the radial artery. The test should be repeated on the opposite hand if negative.
What does the HbO2 Dissociation curve show?
1. The relationship between PaO2 and SaO2 and the affinity the Hb has for O2 at various saturation levels. 2. The S-shaped curve indicates that the PaO2 levels of <60 mmHg, small increases in PaO2 result in fairly large increases in SaO2 3. The flat portion of curve shows PaO2 levels above 60mmHg saturation rises slowly a PaO2 of 70 mmHg yields an SaO2 of 93% PaO2 levels between 80-100 mmHg result in SaO2 of 95%-100% 4. If curve shifts to right = ↓ affinity of Hb for O2 If to the left = ↑affinity of Hb for O2
What is the normal A-a gradient on room air (persing)?
4-12 mmHg
What are the levels of hypoxemia?
60-79mmHg= Mild hypoxemia 40-59mmHg= Moderate hypoxemia < 40 mmHg = Severe hypoxemia
What are the normal PaO2 levels?
80-100mmHg
Why might the temperature be recorded for blood gas results?
A fever shifts the HbO2 curve to the right, which indicates Hb more readily releases O2 to the tissues bit does not pick up the O2 easily. This may affect the PaO2 but not to a significant degree.
What is the Bohr effect?
As the RBC travels to the tissue, it releases O2 because elevated CO2 levels, which are present around the tissues, decrease the affinity of Hb for O2.
What is the most common cause of a decreased PvO2? and How?
Cause: *Decreased Cardiac Output* How: cardiac output drops, blood flow to the tissues slows while tissue O2 uptake remains at the same rate, so some tissue takes more O2 from the blood than normal which deprives other tissues of the normal O2 amount when blood returns from the body to pulmonary artery it contains less O2 than it should and is reflected by PvO2 drop.
Blood gas analysis monitors which of the following physiological variables: 1. Arterial oxygenation: PaO2 2. Alveolar ventilation: PaCO2 3. Acid-base status: pH 4. Tissue oxygenation: pvO2 A. 2 and 3 only B. 1 and 3 only C. 1 and 2 only D. 1,2, and 3 only E. All of the above
E. All of the above
What is the PAO2 calculation?
PAO2 = [(PB-47mmHg)(FiO2) ]- (paCO2 x 1.25)
Changing Vt, RR, and dead space alters what levels?
PaCO2
What is known as the portion of O2 that is dissolved in the plasma of blood?
PaO2 (for every 1 mmHg of PaO2 there is 0.003 mL of dissolved O2)
What are the common sites from which an arterial blood gas is obtained?
Radial, femoral, and dorsalis pedis arteries
Which artery is the most common site to draw an ABG from and why?
Radial: it provides good collateral circulation and is easily accessed.
If the needle passes through the artery and only a small amount of blood enters the syringe, what should be done?
The needle should be slowly withdrawn until it is in the artery, and if the needle needs to be redirected, it should first be withdrawn to the subcutaneous tissue.
Why are arterial samples used?
The values reflect the patient's total cardiopulmonary status
Mixed venous blood obtained from the pulmonary artery vial a pulmonary artery catheter, is used to determine what?
Tissue oxygenation
What test is performed to determine collateral circulation?
modified Allen's test
