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MMSC 407 Exam 3 Study Guide Solutions
1. pH: Negative log of the hydrogen activity pH
= -logH+
2. pH reference range: 7.35-7.
3. Calculate the pH of a solution which contains 4X 10^-8 mmol/L of hydrogen ion: pH = -
logH+ (4X10^-8) pH= -log10^-8 - log4 pH= 8-. pH= 7.
4. The in vivo blood pH is
influenced by the plasma and dissolved levels: bicarbonate carbonic acid
5. pH = pk + logHCO3 [(20) metabolic] + logH2CO3 [(1) respiratory]: pk: 6.1, dissociation constant
log20= 1. log 1= 0 pH= 6.1+1.3+0 = 7.
6. Henderson Hasselbalch Equation:: pH = pK + log[HCO3/(pCO2 X .03)] [20/1]
7. Step 1 pCO2 reference range: 35-45 mmHg
8. Step 1 HCO3 (bicarbonate) reference range: 21-28 mmol/L
9. Step 2 Acid criteria: ph < 7.
pCO2 > 45 mmHg HCO3 < 21 mmol/L
10. Step 2 Alkaline criteria: pH >
7.4 pCO2 < 35 mmHg HCO3 >28 mmol/L
11. Step 3: look at the two that are classified alike
EX
ph 7.36 acid pCO2 25 mmHg Alkaline HCO3 15 mmol/L acid
12. Bicarbonate (HCO3) is the parameter: metabolic
13. Step 4: what type of compensation if any exists?: Look at the parameter that was ditterent If the
value is not in the normal range, we know that some kind of compensation is occurring
14. Compensation: partial or complete: Look at the pH
is it in or out of ref range if it is in normal range: complete compensation; the parameter has moved out of the normal range enough to bring the pH back to
Ref value: 22-29 mmol/L
22. Buffer base definition: The sum of the concentration of all the butter anions in blood.
23. Blood Buffers are:: HCO3/H2CO3: 5%
HPO4/H2PO4: 1%
Hemoglobin: 80% Plasma proteins: 14% Ref value: 46-49 mEq/L
24. Base Excess definition: The concentration of titratable base when titrating the blood or plasma with a strong
acid or base to a plasma pH of 7.40 at a pCO2 of 40 mmHg at 37C. Used to estimate the amount of sodium bicarbonate to be given to correct pH problems 0.1 X (B.E.) X Patients weight (Kg)
25. Base Excess ref value: -2.5 - +2.5 mmol/L
26. Blood collection process: arterial samples: Patient must not begin to Hyperventilate due to anxiety
or pain. Syringe and Needle (Heparin) Not less than a 45 degree angle Anaerobic collection Mix well before analyzing No tourniquet Radial or Brachial arteries
27. Allen test: Check Radial Artery circulation before drawing
Drawing complications:
compensation
33. Major Limiting Factor in Accurate pH measurements: preanalytical errors
34. pH electrode measuring system ISE: The measurement of the electric potential (voltage) ditter- ence
between two electrodes in an electrochemical cell.
35. components of pH ISE: Calomel Reference Electrode
Salt Bridge Indicator Electrode
36. Calomel Reference Electrode: This reference electrode produces a constant reference potential to which the
indicator electrode potential can be compared. (244 mv)
37. Salt Bridge: Saturated KCL
This solution completes the circuit between the blood sample and both the reference and indicator electrodes.
38. Indicator Electrode: A glass membrane, specific for pH due to its mineral content, measures the electrical
potential at its surface due to the hydrogen ion activity.
39. Mineral Content for pH: Hydrogen Sensitive Glass: SiO2: 72.2%
Na2O: 21.4 % CaO: 6.4 %
40. Mineral Content for Sodium Sensitive Glass:: SiO2:
71% Na2O: 11% Al2O3: 18%
41. How to calibrate pH ISE: Known butters are used to calibrate the pH portion of blood gas analyzer
7.384 and 6.
42. Sources of error: pH ISE: 1. Instrument temp: 37C +/- .1 C
2. Bromide contamination of the KCL
3. protein build up on the pH glass surface
4. Scratched pH glass surface
5. Incorrect pH butters used in calibration
43. ref value for VENOUS pCO3: 38-50 mmHg
44. Hypercapnia: Increased
CO2 Caused by Hypoventilation It causes: Respiratory Acidosis pCO2 > 50 mm Hg
45. Hypoventilation can be brought on by:: Decrease in Alveolar Ventilation
The rate of gas exchange across the respiratory membrane depends upon the following:
1. surface area of the respiratory membrane
2. thickness of the respiratory membrane
3. solubility of the gas
4. ditterence in partial pressure of the gas on both sides of the membrane.
53. Treatment for Hypoventilation: Ventilate
54. Hypocapnia: Decreased
CO2 Caused by Hyperventilation It causes: Respiratory Alkalosis pCO values Less than 35 mmHg
55. Hyperventilation is caused by:: Secondary to Hypoxemia: high altitudes
Salicylate Poisoning Temperature / Fever Hysteria/ Anxiety/ Chronic Pain
56. Treatment for hyperventilation: Breath in own CO
57. pCO2 Electrode Measuring System:: The pCO2 electrode is an adapted pH electrode
Components
1. Ag/AgCl Reference Electrode
2. Salt/ Electrolyte Bridge
3. pCO2 membrane
4. pH sensitive glass/ indicator electrode
58. pCO2 is measured by: an increase in H+ activity at the pH sensitive glass electrode
greater H, the less pH
59. Calibrate pCO2 electrode: Gases are used to calibrate the pCO2 electrode on a blood gas instrument. (5.00%
and 10.00%) pCO2 mm Hg = (Barometric Pressure - Water Vapor Pressure) X % pCO2 gas
60. sources of error when measuring pCO2: membrane holes
Temp of instrument Calibrating glass
61. venous blood pO2 ref range: <40 mmHg
62. Blood pO2 with age and high altitudes: decreases
63. how to treat increased pO2 levels (over 110): Enriched oxygen
can be toxic
64. Retrolental Fibroplasia: Occurs in infants
May contribute to glaucoma, and retinal detachment in adulthood.
69. pO2 measuring electrode system: Polarography:: Supplying a constant voltage to an
electrode and monitoring the current change (amps) as oxygen is reduced at the cathode.
70. pO2 electrode Components: Cathode: Platinum wire enclosed in glass
Anode: Ag/AgCl wire pO2 membrane pO2 electrolyte solution: acts as a bridge to complete the circuit between the anode and the cathode Voltage source Ammeter: measures electric current in amperes
71. pO2 electrode measures: the rate of current flow which is proportional to the oxygen tension of the sample.
Cathode: reduction Anode: oxidation
72. pO2 electrode calibration: Gases are used to calibrate the pO2 electrode on a blood gas instrument
(0.00% and 12.00%) pO2 mmHg = (Barometric Pressure - Water Vapor Pressure) X % pO2 gas
73. Sources of error when measuring pO2: Membrane Holes
Temperature Instrument Calibrating Gases Silver Build up on the cathode Protein Build Up Increased WBC
74. pO2 Saturation: A ratio, expressed as a percentage of the volume of oxygen bound to Hemoglobin.
Reference Value: 95 - 98%
75. Clinical Significance of pO2 saturation: It is useful for predicting the amount of oxygen that is
available for tissue perfusion It also helps determine the effectiveness of oxygen therapy. It is a calculated parameter on most blood gas instruments Can be measured directly: Co-oximetry
76. co-oximeter: Sample is aspirated into the Co-oximeter and is lysed with lysing reagent to release hemoglo- bin.
The sample is drawn into a cuvette where absorbance is measured at ditterent wavelengths to determine the following fractions:
1. Oxyhemoglobin (O2Hb)
2. Deoxyhemoglobin (HHb)
3. Carboxyhemoglobin (COHb)
4. Methemoglobin (MetHb)
5. Sulfhemoglobin (SulfHb)
Each fraction has a characteristic absorption spectra. Each fraction is derived from a calculation based upon absorbance and total hemoglobin. Total Hemoglobin (tHb) = O2Hb + HHb + COHb + MetHb
77. Oxygen Saturation Calculation:: O2Hb/ (O2Hb + HHb) X 100%
78. Oxygen Content of Hemoglobin: Total amount of oxygen that hemoglobin can carry.
1.34 mL of Oxygen per gram of Hemoglobin.
85. Calculation of Plasma Bicarbonate by a Blood Gas Instrument: HCO3 = 0.03 X pCO
X 10 ^(pH - pK)
86. Metabolic Disorders: Primary Change in Bicarbonate (HCO3-)
Bicarbonate is a base Metabolic Acidosis: decreased bicarbonate Metabolic Alkalosis: increased bicarbonate
87. Respiratory Disorders: Primary Change in
pCO2 pCO2 is primarily acidic Respiratory Acidosis: increased pCO Respiratory Alkalosis: decreased pCO
