10) Blood gases and pH Flashcards
(100 cards)
1
Q
2 components of bicarb buffer system
A
Dissolved carbon dioxide gas (CO2)
Bicarbonate ion (HCO3-)
2
Q
1 atm = —- mmHg
A
760
3
Q
gas solubility constant
A
How much gas dissolves for each 1 mmHg of partial pressure of that gas.
4
Q
CO2 solubility constant
A
0.03 mmol/L per mmHg
5
Q
concentration of CO2
A
[CO2] = (pCO2)(0.03)
6
Q
Lung disease can ——- the pressure and hyperventilation can ——- the pressure
A
increase
decrease
7
Q
CO2 + H2O →
A
H2CO3
carbonic acid
8
Q
H2CO3 →
A
H + HCO3
9
Q
enzyme catalyzing change from CO2 to bicarb
A
carbonic anhydrase
10
Q
—% of CO2 is present as bicarbonate.
—% is bound to hemoglobin as a carbamino compound.
—% is present as dissolved gas.
A
75
20
5
11
Q
buffer
A
a solution containing a weak acid and its conjugate base that resists changes in pH when a strong acid or base is added
12
Q
4 blood buffers
A
Bicarbonate
Hemoglobin
Phosphorus
Proteins
13
Q
Henderson-Hasselbalch Equation
A
pH = pKa + log[cHCO3/(𝛼)(pCO2)]
pKa = 6.1
𝛼 = 0.03
14
Q
bicarb RR
A
22-26 mmol/L
15
Q
pCO2 RR
A
35-45 mmHg
16
Q
normal bicarbonate:carbonic acid ratio
A
20:1
17
Q
Hemoglobin accounts for about —-% of buffering capacity, but is the 2nd most important buffering system.
A
80
18
Q
hemoglobin functions
A
Transports H+, O2 and CO2
Allows for large amounts of CO2 to be carried in the blood with little or no change in pH.
Participates in the chloride shift to maintain neutral charge within the RBC
19
Q
Accounts for only about 1% of blood buffering capacity
A
phosphate buffer system
20
Q
Account for about 14% of blood buffering capacity.
A
proteins
21
Q
Proteins are primarily —— buffers.
A
cellular
22
Q
diffusion
A
movement of an uncharged, hydrophobic solute through a lipid bilayer.
23
Q
external convection system
A
lungs, the airway, and respiration muscles
24
Q
internal convection system
A
circulatory system
25
Refers to a set of anatomical features involved with respiration and includes the larynx, trachea, bronchi, lungs, and pleura.
respiratory apparatus
26
6 functions of the respiratory apparatus
1. Provide a means of **moving outside air to the alveolar air spaces.**
2. Provide a means to **carry O2 and CO2** in the blood.
3. Provide a surface for **gas exchange**.
4. Contain an internal convection system and a **circulatory system that consists of a four-chamber heart.**
5. Provide a mechanism for **locally regulating ventilation and perfusion.**
6. Provide a mechanism for **centrally regulating ventilation.**
27
Hemoglobin can bind O2 only when the iron is in the...
ferrous (Fe2+) state
28
Most important amino acid in heme is -------, which binds Fe2+.
histidine
29
Shows the relationship between percent hemoglobin saturation with oxygen
The Hemoglobin-Oxygen Dissociation Curve
30
reasons for S-shaped Hb-O2 curve
involve the four oxygen binding sites on the hemoglobin molecule.
31
factors that can cause Hb-O2 curve to shift left (higher affinity)
| lung environment
- ↑ pH
- ↓ pCO2
- ↓ 2,3-DPG
- ↓ temp
32
factors that can cause Hb-O2 curve to shift right (lower affinity)
| muscle environment
- ↓ pH
- ↑ pCO2
- ↑ 2,3-DPG
- ↑ temp
33
hemoglobin is intrinsically sensitive to...
High temperatures
High pCO2
Low p H
34
5 different forms CO2 is transported in
Bicarbonate (primarily)
Carbonate
Carbonic acid
Dissolved carbon dioxide
Carbamino compounds
35
Cl-HCO3 exchanges
chloride/hamburger shift
36
difference between serum and urine pH represents...
kidneys’ attempt to excrete nonvolatile acids that are produced by metabolic processes.
37
3 mechanisms that facilitate renal excretion of acid, and retention of bicarb
- Na-H exchange
- production of ammonia, excretion of ammonium
- reclamation of bicarb
38
chloride shift in venous blood
HCO3 out of rbcs
Cl into rbcs
39
chloride shift in arterial blood
HCO3 into rbcs
Cl out of rbcs
40
An acid-base disorder is primary if...
the imbalance results from a change in pCO2 or HCO3- (one disturbance only)
41
Result of more than one pathologic process occurring in an individual
mixed acid-base disorders
42
pO2 RR
85-108 mmHg
43
tCO2 RR
22-28 mEq/L
44
Siggaard-Andersen Acid-Base Chart
45
metabolic acidosis general causes
- Impaired renal excretion of fixed acids
- Overproduction or administration of fixed acids
- Primary bicarbonate loss via kidneys or gastrointestinal tract (base out the bottom)
- Secondary bicarbonate loss attributable to elevated serum chloride levels
46
metabolic acidosis + normal AG
- Renal tubular acidosis
- Increased serum chloride, which results in suppressed bicarbonate ion resorption
- Diarrhea
- DKA recovery
- TPN
- Carbonic anhydrase inhibitors
- Ureterosigmoidostomy
47
metabolic acidosis + high AG
- Renal failure
- Diabetic ketoacidosis
- Lactic acidosis
- Acetylsalicylic acid, methanol, formic acid, isopropyl alcohol, and ethylene glycol (MUDPILES)
48
metabolic alkalosis general causes
Addition of base to the body
Decrease in the amount of base leaving the body
Loss of acid-rich fluids
49
-------- causes are categorized by Cl responsiveness or resistance
metabolic alkalosis
50
causes of metabolic alkalosis
Via gastrointestinal tract
Vomiting and nasogastric suction
Chloride-losing diarrhea states
Renal failure
Hypercalcemia (milk-alkali syndrome)
Hormonal (hypoaldosteronism, adrenal hyperplasia, Cushing’s, pituitary adenomas)
Hypokalemia
Retention of bicarbonate ion
Administration of alkali (antacids)
Overuse of diuretics
51
respiratory acidosis causes
**Diffusion**
Alveolar destruction (emphysema)
Cancer (thickened alveolar membrane)
Congestive heart failure (fluid buildup)
**CNS**
Impaired respiratory drive
Trauma
Tumor
Vascular disorders
Epilepsy
Hypoxia
Drug ingestion (barbiturates, narcotics)
Degenerative disorders
Sleep apnea
**Impaired respiratory mechanics**
Polio
Respiratory muscle (dystrophy)
Trauma to the ribs
**Airway obstruction**
Tumors
Food/vomitus
COPD and asthma
52
causes of weakened respiratory muscle function
**Myasthenia gravis**
Periodic paralysis
Intraperitoneal aminoglycosides
**Guillain–Barré syndrome**
**Botulism**
Poliomyelitis
Amyotrophic lateral sclerosis (A L S)
Myxedema
53
chloride-responsive metabolic alkalosis
- diuretics
- vomiting
- NG tube suction
- villous adenoma
- carbenicillin
- contraction alkalosis
54
chloride-resistance metabolic alkalosis
- hyperaldosteronism
- cushings
- exogenous steroids
- licorice (glycyrrhizin)
- bartter syndrome
- milk-alkali syndrome
55
respiratory alkalosis causes
**Hypoxemia**
Pneumonia, emboli
Congestive heart failure
High-altitude exposure
Severe anemia
**Stimulation of the Medullary Respiratory Center**
Hyperventilation syndrome (anxiety)
Hepatic encephalopathy
Salicylate intoxication
Pregnancy (increased progesterone)
Neurologic disorders (CVA)
GN sepsis
Excessive mechanical ventilation
Recovery from metabolic acidosis
56
3 general methods of compensation
buffers
renal
respiratory
57
One acid/base component is abnormal, while one is normal
uncompensated
58
The second component is now starting to offset the other by going in the same direction to help pH
partial compensation
59
The pH is now normal, because the acid/base components have responded
fully compensated
60
compensation for met. alk.
Lungs hypoventilate to hold CO2. Kidneys reclaim less HCO3.
61
compensation for met. acid.
Lungs hyperventilate to lose CO2. Kidneys reclaim more HCO3.
62
compensation for resp. alk
Kidneys reclaim less HCO3.
Lungs hypoventilate to hold CO2.
63
compensation for resp. acid.
Kidneys reclaim more HCO3.
Lungs hyperventilate to lose CO2.
64
venous tCO2 RR
22-29 mmol/L
65
recommended site for ABG draw
radial artery
66
pH and blood gas sample
whole blood
67
anticoag for pH & blood gas
balanced heparin
68
sources of ABG error
Metabolism (glycolysis continues)
Diffusion of gases through the plastic container
Elevated potassium values (hemolysis)
69
preanalytical handling of ABG samples
Every effort must be made to remove air bubbles immediately and without agitation.
Sample should be mixed immediately to dissolve the heparin and prevent clotting.
Samples should be mixed thoroughly before injection into the blood-gas analyzer.
70
sample requirements for ABG
- Arterial or venous specimen tightly stoppered
- Heparinized syringe
- On ice (slow metabolism) — good for 2 hours, or 30 mins not on ice
- No air bubbles
- Perform ASAP
71
indirect pH/ABG measures
HCO3-
H-H equation
72
------- of RBCs used in order to spill and measure hemoglobin
Ultrasonic lysis
73
Measurement of potential (voltage) between two electrodes in a solution.
potentiometry
74
explain reference and indicator electrode
Reference electrode: Electrode with a constant voltage
Indicator electrode (Na, K, Cl): The measuring electrode
75
Measured cell potential is related to the molar concentration by the ------ equation
nernst
76
4 important attributes of a reference electrode
1. Potential is reversible and obeys the **Nernst** equation
2. Electrode exhibits a potential that is **constant with time**
3. Electrode **returns to its original** potential after being subjected to small currents
4. Electrode exhibits **little hysteresis** or lag with temperature cycling
77
ion selective electrode
membrane-based electrochemical transducer capable of responding to a specific ion
78
ISE advantages over other methods
Fast, sensitive, direct measurement, no reagents needed, selective, easy to maintain, precise, and cost-effective (can be reused)
79
pH electrode membrane
layers of hydrated and unhydrated glass
80
usually silver/silver chloride serves as a reference electrode
pH
81
pCO2 electrode membrane
gas-permeable membrane (Teflon or silicone)
82
measuring the quantity of electricity needed to convert the analyte quantitatively to a different oxidation states
coulometry
83
the quantity of electricity or charge that is transported in one second by a constant current of one ampere
coulomb
84
Measurement of the current flow produced by an oxidation-reduction reaction
amperometry
85
sweat chloride methodologies
Coulometry
Amperometry
86
gas-permeable membrane, usually polypropylene, that allows dissolved oxygen to pass through, but nothing else
Clark pO2 gas-sensing electrode
87
information about the analyte is derived from the measurement of current as a function of an applied potential obtained under conditions that promote polarization of an indicator, or working, electrode
voltammetry
88
Measurement of lead in whole blood samples methodology
Anodic stripping voltammetry
89
a measure of the ability of a solution to carry an electric current.
conductometry
90
The electrical resistance in ohms measured between opposite faces of a 1.00-centimeter cube of an aqueous solution at a specific temperature.
resistivity
91
pH values of calibration materials
6.8
7.4
92
frequency of gas calibration
One-point calibrations done every 30 min and 4 hrs
93
why is calibration important?
the calibration curve, or data, is used to generate all other results for quality control and patient samples
94
frequency of pH/ABG QC
all three levels of controls assayed within a 24h period (one each 8hr interval)
95
most ABG errors occur in the ----- stage
preanalytical
96
temperature correction is useful for...
patients who have been exposed to low temps for a prolonged period
97
room air contamination effects on results
↑ pH
↓ pCO2
↑ pO2
98
old sample effects on results
↓ pH
↑ pCO2
↓ pO2
99
the mEq/L base needed to change whole blood pH by 0.01 unit
Hemoglobin-dependent base excess
100
Siggaard-Andersen Alignment Nomogram
