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Cairo: Mosby’s Respiratory Care Equipment, 9th EditionChapter 10: Blood Gas MonitoringAnswer Key to the WorkbookAchieving the Objectives1A. A modified Allen’s test should always be performed before obtaining a sample from the radial artery.1B. If she clenches her fist, this action forces the blood out of her hand.1C. (A) Radial artery; (B) ulnar artery1D. The purpose is to momentarily stop blood flow to the hand.1E. His hand should appear blanched.1F. The ulnar artery should be released first.1G. If the palm does not blush, the ulnar artery is either absent or partially or totally occluded. This is a negative result, meaning that there is poor or no collateral circulation.1H. A blushing of the palm when the ulnar artery is released demonstrates that the ulnar artery is patent, and that there is collateral circulation to that hand.1I. A negative result to Allen’s test dictates that the arterial blood gas should be sampled from another site, such as the brachial artery. A positive result for Allen’s test indicates that there is collateral circulation and that an arterial puncture can be performed using that particular radial artery.2A.2B. Mixed venous blood samples can be obtained through a flow-directed intracardiac catheter (i.e., a Swan-Ganz catheter).2C. Earlobe or side of the heel3A.1. Electronic display2. Amplifier3. Sample inlet4. 6.840 buffer5. Constant-temperature water bath6. pH-sensitive glass7. Sampling chamber8. pH membrane9. Contact bridge10. KCl solution11. Ceramic tip12. Mercurous chloride13. Mercury bead14. Slope potentiometer15. Balance potentiometer3B.1. Silicon elastic membrane2. Sample pathway3. Nylon spacer4. pH-sensitive glass5. Measuring half-cell6. Reference half-cell7. HCO3 solution3C.1. Silver anode2. PO2 electrolyte3. Platinum wire cathode4. Polypropylene membrane5. Cathode tip4A. Polarographic (Clark) electrode (PO2)4B. Stow-Severinghaus electrode (PCO2)4C. Sanz electrodes (pH)4D. The measuring electrode, Ag/AgCl, is immersed in a phosphate buffer solution with a pH of 6.840. The reference electrode, calomel, is immersed in a solution of saturated KCl.4E. The partial pressure of carbon dioxide (PCO2) electrode uses a bicarbonate buffered solution. 4F. The partial pressure of oxygen (PO2) electrode uses a solution of KCl.4G. The pH electrode measurement is made as a result of the electrical activity on the pH-sensitive glass of the measuring electrode. This electrical activity is converted to pH units. This type of system of voltage measurement is termed a potentiometer.4H. The PCO2 measurement is made as a result of a potential difference created by the formation of hydrogen ions. This potential difference is measured by a voltmeter calibrated to read millimeters of mercury.4I. The PO2 electrode measures the current change that occurs between the anode and the cathode when the electrode is exposed to a blood sample containing oxygen. Measurement using current changes is termed amperometric.4J. EH+ = 0.0615 × pH or a voltage of 61.5 mV will be developed for every pH unit difference between the sample and the measuring electrode (constant 6.840).4K. CO2 + H2O → H2CO3 → H+ + HCO34L. Henderson-Hasselbalch equation: pH = pK + log (HCO3/PCO2)5A. Acid-base balance: uncompensated respiratory acidosis (acute respiratory acidosis); oxygenation status: uncorrected hypoxemia5B. Acid-base balance: partially compensated metabolic acidosis;oxygenation status: within normal limits5C. Acid-base balance: fully compensated metabolic alkalosis;oxygenation status: corrected hypoxemia5D. Acid-base balance: partially compensated respiratory alkalosis;oxygenation status: within normal limits5E. 21 mm Hg5F. 25 mm Hg5G. 33 mm Hg5H. A left shift in the oxyhemoglobin dissociation curve5I. A right shift in the oxyhemoglobin dissociation curve6A. Oxyhemoglobin, carboxyhemoglobin, methemoglobin, sulfhemoglobin, and fetal hemoglobin6B. Spectrophotometry is based on the relative transmission or absorption of portions of the light spectrum.6C. The Lambert-Beer law, which states that the transmission of a specific wavelength of light through a solution is a logarithmic function of the concentration of the absorbing species in the solution6D. The blood sample is heated to 37° C and hemolyzed. 6E. The translucent solution created in the first step is placed in a cuvette. 6F. Monochromatic light beams are simultaneously directed through the blood-filled cuvette and a reference blank solution without hemoglobin. Electrical current is proportional to the intensity of the light transmitted through the solutions. The absorbance of the blank solution is then subtracted from the absorbance of the blood sample. The resultant values are used to calculate the concentration of each type of hemoglobin in the blood sample.6G. The presence of incompletely hemolyzed red blood cells, lipids, air bubbles, bilirubin (>20 mg/dL of whole blood), intravenous dyes, and fetal hemoglobin can produce erroneous measurements of hemoglobin.7A. The Joint Commission, the Centers for Medicare & Medicaid Services, and the College of American Pathologists publish the standards.7B. It is a system that involves analyzing control samples (with known pH, PCO2, and PO2), assessing the measurements against defined limits, identifying problems, and specifying corrective actions.7C. It is a program that involves testing the proficiency of both personnel and equipment and providing a dynamic process of identification, evaluation, and resolution of problems that affect blood gas measurements.7D. (1) Assessing blind samples periodically (proficiency testing); (2) assessing the technical competence of laboratory personnel; and (3) providing a means of reporting the variability of individual blood gas analyzers7E. A minimum of three times each year laboratories receive three to five unknown samples. The laboratory analyzes and forwards the results to the sponsoring organization. The sponsoring organization collates the results from all laboratories. Each laboratory is notified of its performance.7F. pH ± 0.04 of the target value; PCO2 ± 3 mm Hg or ± 8% of the target value, whichever is greater; and PO2 ± 3 standard deviations of the target value8A. The partial pressure of oxygen in the arteries (PaO2) changes approximately 7% for each degree Celsius. 8B. 4% per degree Celsius8C. 0.0146 per degree Celsius8D. Hypothermia causes a left shift in the curve. The hemoglobin does not let the oxygen go as readily.8E. Hyperthermia causes a right shift in the curve. The hemoglobin lets go of the oxygen more readily.9A. Low perfusion causes a decrease in blood flow and pulsatile signal in the extremities.9B. Physiologic causes of low perfusion: (1) hypovolemia; (2) peripheral vasoconstriction from drugs; and (3) hypothermia. Technical causes of low perfusion: extracorporeal membrane oxygenation9C. Place the oximeter probe in the patient’s ear instead of on the finger.9D. Oxyhemoglobin and carboxyhemoglobin (COHb) have similar absorption coefficients for red light (660 nm). Therefore, the presence of COHb will lead to false high SpO2 values.9E. Methemoglobin9F. If enough methemoglobin is present in the blood, the SpO2 will read approximately 85% because the pulse oximeter will measure a red-to-infrared (IR) ratio of 1:1. This could either be underestimating or overestimating the patient’s actual oxyhemoglobin saturation.9G. Administration of nitrites, benzocaine, or dapsone can cause increased levels of methemoglobin (MetHb).9H. Administration of methylene blue and indigo carmine may falsely drop SpO2 because these dyes absorb a portion of the incident light emitted by the pulse oximeter diodes.9I. Dark nail polishes may cause the shunting of light around the finger periphery. This can cause the SpO2 to be erroneously high or low depending on whether the light is pulsatile.9J. Heat lamps, fluorescent lights, fiberoptic light sources, and surgical lamps9K. Pulse oximeters will measure the amount of light present when both red and IR light sources are off. This value is subtracted from the red and IR light absorption values.10A. A heater failure will decrease gas diffusion across the skin, causing an erroneously low PO2 reading. 10B. The accuracy of transcutaneous PO2 (PtCO2) measurements are directly related to cardiac output and cutaneous resistance. An increase in cutaneous resistance and a decrease in cardiac output reduce the accuracy of PtCO2 measurements.10C. Septic shock, hemorrhage, heart failure, and hypothermia10D. A decreasing cardiac index will decrease the accuracy of PtCO2 measurements, which is shown by a decrease in the PtCO2/PaO2 index.10E. The heat causes a higher metabolic rate at the site of the electrode, which will cause the slightly higher transcutaneous PCO2 (PtcCO2) measurement.10F. Hair and dirt adversely affect the transcutaneous signals.10G. Heat will cause the electrolyte solution to evaporate, which can potentially decrease the gas diffusion between the skin and electrode.10H. Cleaning rids the electrode of silver that may deposit on the cathode.10I. To check for evaporation of the electrolyte or tears in the membrane11A.Type of metabolic acidosispHPCO2HCO3-Acute<7.35Normal<22Partly compensated<7.35<35<22Compensated7.35-7.40<35<2211B.Type of respiratory acidosispHPCO2HCO3-Acute<7.35>45NormalPartly compensated<7.35>45>26Compensated7.35-7.40>45>2611C.Type of metabolic alkalosispHPCO2HCO3-Acute>7.45Normal>26Partly compensated>7.45>45>26Compensated7.40-7.45>45>2611D.Type of respiratory alkalosispHPCO2HCO3-Acute>7.45<35NormalPartly compensated>7.45<35<22Compensated7.40-7.45<35<22pHPCO2HCO3-Interpretation11E.7.286024Acute respiratory acidosis11F.7.389632Compensated respiratory acidosis11G.7.522820Partly compensated respiratory alkalosis11H.7.442819Compensated respiratory alkalosis11I.7.463423Acute respiratory alkalosis11J.7.288037Partly compensated respiratory acidosis11K.7.594948Partly compensated metabolic alkalosis11L.7.343821Acute metabolic acidosis11M.7.444833Compensated metabolic alkalosis11N.7.363015Compensated metabolic acidosis11O.7.513931Acute metabolic alkalosis11P.7.343418Partly compensated metabolic acidosisAnswers to NBRC-Type Questions1. C2. A3. D4. A5. B6. B7. D8. B9. C10. A11. D12. A13. C 14. B15. D ................
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