Blood Gases

Question 1

Gas

Answer 1

Substance that can exist above it’s critical temperature

Question 2

Acid

Answer 2

substance that can yield H+ when dissolved in H20 (low pH)

Question 3

Base

Answer 3

substance that can yield H+ when dissolved in H20 (low pH)

Question 4

Buffer

Answer 4

substance that helps resist a change in pH

Question 5

Boyle’s Law

Answer 5

volume inverse to pressure

P1V1 = P2V2

Question 6

Charles Law

Answer 6

volume proportional with temperature

V1/T1 = V2/T2

Question 7

Gay-Lussac’s Law:

Answer 7

Temperature proportional with pressure

P1/T1 = P2/T2

Question 8

Dalton’s Law

Answer 8

sum of partial pressures of gases equals total pressure

Total gas pressure = % gas + Barometric Pressure

Question 9

Barometric Pressure:

Answer 9

total pressures of all gases at 1atm or at 760mm Hg at sea level

Question 10

Ideal Gas Law

Answer 10

PV = nRT

P = absolute pressure of gas
V = volume of the gas
n = amount of substance of gas measured in moles
R = gas constant
T = absolute temperature of gas

Question 11

how PCO2 can be converted to total CO2?

Answer 11

Total CO2 = HCO3- + H2CO3 + PCO2

(bicarbonate) + (carbonic acid) + (partial CO2)

Question 11

how PCO2 can be converted to total CO2?

Answer 11

Total CO2 = HCO3- + H2CO3 + PCO2

(bicarbonate) + (carbonic acid) + (partial CO2)

Question 12

Describe the different means of CO2 transportation in plasma and red cells.

Answer 12

1. About 5 % of carbon dioxide is transported unchanged, simply dissolved in the plasma since it is more soluble in blood than oxygen
2. About 10 % of carbon dioxide is transported bound to hemoglobin and plasma proteins
3. The majority of carbon dioxide is transported as bicarbonate
   a. Carbon dioxide enters blood cells to be carried back to lungs (CO2)
   b. It combines with water to form carbonic acid (H2CO3) this is catalyzed by carbonic anhydrase
   c. Carbonic acid dissociates into Bicarbonate (HCO3-) and Hydrogen Ions (H+)
4. Bicarbonate ions diffuse out of the red blood cell into the plasma whilst chloride ions (Cl-) diffuse in to take their place. This is known as the chloride shift.

Question 13

role of carbonic anhydrase.

Answer 13

Within the RBC, carbonic anhydrase is an enzyme that catalyzes carbon dioxide (CO2) combining with water (H2O) to from carbonic acid (H2CO3). This is then dissociated into bicarbonate and Hydrogen Ions. Carbonic Anydrase is an important enzyme in maintaining the acid/base balance. Must buffer CO2 carried in blood to prevent toxicity.

Question 14

normal ratio of bicarbonate to carbonic acid

Answer 14

20:1 ratio HCO3- : H2CO3

20 bicarbonates for every 1 carbonic acid

Question 15

substance exchanged for CL- in the chloride shift.

Answer 15

HCO3

Bicarbonate exiting the RBC into plasma is exchanged for CL- entering the RBC from plasma to maintain acid/base balance

Question 16

Describe CO2 elimination in the lungs.

Answer 16

1. Inspiration of oxygen (O2)
2. Oxygen (O2) diffuses from alveoli into blood and bound by hemoglobin (O2Hb)
3. H+ that was carried on hemoglobin is released to recombine with Bicarbonate to form carbonic acid (H2CO3)
4. Carbonic Acid disassociates to from H2O and CO2
5. CO2 diffuses through alveoli and exits through ventilation

Question 17

pH

Answer 17

a measure of the acidity or basicity of an aqueous solution.

pH less than 7 are said to be acidic
pH greater than 7 are basic or alkaline.

Question 18

Henderson Hasselbach Equation

Answer 18

pH = 6.1 + log(HCO3- / PCO2 * 0.03)

Bicarb pK = 6.1
Dissociation Constant = 0.03
HCO3 = Concentration of base
PCO2 = concentration of acid

Question 19

primary blood buffer

Answer 19

Bicarbonate (HCO3)

Question 20

Bohr effect

Answer 20

States that hemoglobin’s oxygen binding affinity is Inversely related to both acidity and concentration of CO2

↑ pH or ↓ CO2 Hemoglobin pick up more oxygen
↓ pH or ↑ CO2 hemoglobin proteins release Oxygen

Question 21

effect of pH on the respiratory system.

Answer 21

↑ pH less H+ slower breathing to compensate Respiratory Alkalosis

↓ pH more H+ faster breathing to compensate Respiratory Acidosis

Question 22

Describe the respiratory component of acid-base balance.

Answer 22

PCO2 decreases
less H+
pH increases (alkalosis)

PCO2 increases
more H+
pH decrease (acidic)

Question 23

Acidosis vs. Alkalosis

Answer 23

Acidosis pH < 7.35 (Lethargy, Coma)

Alkalosis pH > 7.45 (Irritability, Convulsions)

Question 24

Causes of Respiratory Alkalosis ( ↑pH ↓PCO2) and Compensation...

Answer 24

Sepsis Exercise Pain, fever, Anxiety ``` Compensation: Renal excretion (HCO3-) balances Slow breathing (retains H+) ```

Question 25

Causes of Respiratory Acidosis (↓pH ↑PCO2) and Compensation

Answer 25

Over Sedation Lung Disease Respiratory Failure Compensation: renal Retention of (HCO3-) rapid breathing (excretes H+) (acidic, H+ must be balanced)

Question 26

Identify the metabolic component of acid-base balance

Answer 26

Metabolic component is the renal component HCO3- Regulated by re-absorption and excretion of Bicarbonate

Question 27

Define Base Excess

Answer 27

The amount of bases in the blood Increased Base Excess Alkalosis Decreased Base Excess Acidosis

Question 28

Causes of Metabolic Alkalosis (↑pH ↑HCO3)

Answer 28

NAHCO3 administration Vomiting Diuretics Potassium (K+) depletion

Question 29

Causes of Metabolic Acidosis (↓pH ↓HCO3-)

Answer 29

Normal Gap: Elevated Cl- Renal Failure Diarrhea ``` Increased Gap Overdose Sepsis Ketoacidosis Diabetic ```

Question 30

Compensation vs. Correction

Answer 30

Compensation: body is adjusting to bring pH closer to normal Correction: pH is in normal range; fully compensated

Question 31

oxygen, carbon dioxide, and pH electrodes

Answer 31

pO2 Clark electrode sensitive to O2 pH glass electrode sensitive to H+ pCO2 modified pH electrode (severinghaus)

Question 32

tonometry in blood gas analysis

Answer 32

Reference method that produces known concentrations for pCO2 and pO2 by bubbling gasses into liquid Used for QC: timely and cumbersome

Question 33

Calibration for Blood Gases

Answer 33

One Point: pH 7.38 CO2 5% O2 12% or 20% Two Point: pH 6.83 CO2 10% O2 0%

Question 34

Protein Fouling of electrode:

Answer 34

build up of protein on electrode due to improper cleaning/maintenance Sluggish or erratic results

Question 35

effect of temperature on accurate blood gas analysis

Answer 35

PO2 falsely increased Diffuses through plastic and shifts left on curve K+ increases

Question 36

State the reference (normal) ranges for pH, PCO2, HCO3-, Base Excess.

Answer 36

pH: 7.35 - 7.45 PCO2: 35 - 45 HCO3: 22 - 26 Base Excess: -2 to +2

Question 37

anticoagulant used for blood gas samples

Answer 37

Lyphilized lithium heparin (dry) better than liquid lithium heparin since it can dilute the sample and alter equilibration with room air.

Question 38

quality control of blood gases.

Answer 38

Tonometry: reference method produces known concentrations by bulling gases into liquid Surrogate liquid (use known values of pH, PCO2, PO2) Non-Surrogate (automated internal checks to check electronic quality)

Question 39

Physiologic effects of decreased PO2.

Answer 39

``` Tachycardia (increased heart rate) Hypertension (increased blood pressure) Vasoconstriction (increased blood pressure) Confusion / loss of judgment Dysrhythmia (irregular heartbeat) Increased respiration ```

Question 40

Causes of Increased PO2

Answer 40

O2 administration | Hyperventilation (fast breaths)

Question 41

Causes of Decreased PO2

Answer 41

Hypoventilation (slow breaths) Pneumonia or asthma Diffusion defect pulmonary edema Altitude sickness

Question 42

Right Shift

Answer 42

↓ pH (acidosis/more H+) ↑ PCO2 ↑ 2,3-DPG ↑ Temp (fever) *** Never reach PO2, low affinity for O2***

Question 43

Left Shift

Answer 43

↑ pH (alkalosis/fewer H+) ↓ PCO2 ↓ 2,3-DPG ↓ Temp (hyperthermia) *** Reach PO2 max sooner, higher affinity for O2***

Question 44

Oxygen Saturation

Answer 44

measure of how much oxygen the blood is carrying as a percentage of the maximum it could carry.

Question 45

Define and illustrate the hemoglobin dissociation curve

Answer 45

The hemoglobin dissociation curve is a graph that shows the percent saturation of hemoglobin at various partial pressures of oxygen. It displays the non-linear tendency for oxygen to bind to hemoglobin. Increasing levels of PO2 after 90 plateaus, it does not yield more saturation

Question 46

pH, PCO2, HCO3-, pH, and O2 Sat of Venous Blood

Answer 46

``` SAT 02% 35% – 45% PO2 <50 (venous only pH and pO2 usable) HCO3 24 – 25 PCO2 41 – 51 pH 7.32 – 7.42 ```

Question 47

pH, PCO2, HCO3-, pH, and O2 Sat of Arterial Blood

Answer 47

``` SAT 02% >95% pH 7.35 – 7.45 PCO2 35 – 45 HCO3 22 – 26 PO2 80 – 110 Base Excess -2 to +2 ```

Question 48

Bicarbonate (HCO3-):

Answer 48

Carries majority of CO2 as primary blood buffer (metabolic component retain/excrete)

Question 49

Carbonic Acid (H2CO3):

Answer 49

weak acid (carbon dioxide dissolved in water)

Question 50

PCO2

Answer 50

partial CO2 dissolved in plasma (respiratory component blow off H+)

Question 51

Base Excess:

Answer 51

amount of acid or base to bring pH to 7.4

Question 52

pH:

Answer 52

Ideal is 7.4 (Acidosis 7.35)