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Clinical Chemistry > Blood Gases > Flashcards

Blood Gases Flashcards

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1
Q

Gas

A

Substance that can exist above it’s critical temperature

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2
Q

Acid

A

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

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3
Q

Base

A

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

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4
Q

Buffer

A

substance that helps resist a change in pH

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5
Q

Boyle’s Law

A

volume inverse to pressure

P1V1 = P2V2

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6
Q

Charles Law

A

volume proportional with temperature

V1/T1 = V2/T2

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7
Q

Gay-Lussac’s Law:

A

Temperature proportional with pressure

P1/T1 = P2/T2

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8
Q

Dalton’s Law

A

sum of partial pressures of gases equals total pressure

Total gas pressure = % gas + Barometric Pressure

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9
Q

Barometric Pressure:

A

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

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10
Q

Ideal Gas Law

A

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
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11
Q

how PCO2 can be converted to total CO2?

A

Total CO2 = HCO3- + H2CO3 + PCO2

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

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11
Q

how PCO2 can be converted to total CO2?

A

Total CO2 = HCO3- + H2CO3 + PCO2

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

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12
Q

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

A
  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.
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13
Q

role of carbonic anhydrase.

A

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.

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14
Q

normal ratio of bicarbonate to carbonic acid

A

20:1 ratio HCO3- : H2CO3

20 bicarbonates for every 1 carbonic acid

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15
Q

substance exchanged for CL- in the chloride shift.

A

HCO3

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

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16
Q

Describe CO2 elimination in the lungs.

A
  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
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17
Q

pH

A

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.

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18
Q

Henderson Hasselbach Equation

A

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

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

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19
Q

primary blood buffer

A

Bicarbonate (HCO3)

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20
Q

Bohr effect

A

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

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21
Q

effect of pH on the respiratory system.

A

↑ pH less H+ slower breathing to compensate Respiratory Alkalosis

↓ pH more H+ faster breathing to compensate Respiratory Acidosis

22
Q

Describe the respiratory component of acid-base balance.

A

PCO2 decreases
less H+
pH increases (alkalosis)

PCO2 increases
more H+
pH decrease (acidic)

23
Q

Acidosis vs. Alkalosis

A

Acidosis pH < 7.35 (Lethargy, Coma)

Alkalosis pH > 7.45 (Irritability, Convulsions)

24
Q

Causes of Respiratory Alkalosis ( ↑pH ↓PCO2)

and Compensation…

A

Sepsis
Exercise
Pain, fever,
Anxiety

Compensation:
Renal excretion (HCO3-) balances
Slow breathing	(retains H+)
25
Q

Causes of Respiratory Acidosis (↓pH ↑PCO2)

and Compensation

A

Over Sedation
Lung Disease
Respiratory Failure

Compensation:
renal Retention of (HCO3-)
rapid breathing (excretes H+)
(acidic, H+ must be balanced)

26
Q

Identify the metabolic component of acid-base balance

A

Metabolic component is the renal component HCO3-

Regulated by re-absorption and excretion of Bicarbonate

27
Q

Define Base Excess

A

The amount of bases in the blood

Increased Base Excess Alkalosis
Decreased Base Excess Acidosis

28
Q

Causes of Metabolic Alkalosis (↑pH ↑HCO3)

A

NAHCO3 administration
Vomiting
Diuretics
Potassium (K+) depletion

29
Q

Causes of Metabolic Acidosis (↓pH ↓HCO3-)

A

Normal Gap:
Elevated Cl-
Renal Failure
Diarrhea

Increased Gap
   Overdose
   Sepsis
   Ketoacidosis
   Diabetic
30
Q

Compensation vs. Correction

A

Compensation: body is adjusting to bring pH closer to normal

Correction: pH is in normal range; fully compensated

31
Q

oxygen, carbon dioxide, and pH electrodes

A

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

32
Q

tonometry in blood gas analysis

A

Reference method that produces known concentrations for pCO2 and pO2 by bubbling gasses into liquid

Used for QC: timely and cumbersome

33
Q

Calibration for Blood Gases

A

One Point: pH 7.38 CO2 5% O2 12% or 20%

Two Point: pH 6.83 CO2 10% O2 0%

34
Q

Protein Fouling of electrode:

A

build up of protein on electrode due to improper cleaning/maintenance

Sluggish or erratic results

35
Q

effect of temperature on accurate blood gas analysis

A

PO2 falsely increased

Diffuses through plastic and shifts left on curve

K+ increases

36
Q

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

A

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

37
Q

anticoagulant used for blood gas samples

A

Lyphilized lithium heparin (dry)

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

38
Q

quality control of blood gases.

A

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)

39
Q

Physiologic effects of decreased PO2.

A 
Tachycardia (increased heart rate)
Hypertension (increased blood pressure)
Vasoconstriction (increased blood pressure)
Confusion / loss of judgment
Dysrhythmia (irregular heartbeat)
Increased respiration
40
Q

Causes of Increased PO2

A

O2 administration

Hyperventilation (fast breaths)

41
Q

Causes of Decreased PO2

A

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

42
Q

Right Shift

A

↓ pH (acidosis/more H+)
↑ PCO2
↑ 2,3-DPG
↑ Temp (fever)

* Never reach PO2, low affinity for O2*

43
Q

Left Shift

A

↑ pH (alkalosis/fewer H+)
↓ PCO2
↓ 2,3-DPG
↓ Temp (hyperthermia)

* Reach PO2 max sooner, higher affinity for O2*

44
Q

Oxygen Saturation

A

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

45
Q

Define and illustrate the hemoglobin dissociation curve

A

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

46
Q

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

A 
SAT     02%  35% – 45%
PO2	  <50     (venous only pH and pO2 usable)
HCO3       24 – 25
PCO2	41 – 51
pH           7.32 – 7.42
47
Q

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

A 
SAT 02%	>95%
pH		7.35 – 7.45	
PCO2	35 – 45	
HCO3	22 – 26			
PO2		80 – 110
Base Excess	-2 to +2
48
Q

Bicarbonate (HCO3-):

A

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

49
Q

Carbonic Acid (H2CO3):

A

weak acid (carbon dioxide dissolved in water)

50
Q

PCO2

A

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

51
Q

Base Excess:

A

amount of acid or base to bring pH to 7.4

52
Q

pH:

A

Ideal is 7.4 (Acidosis 7.35)

Clinical Chemistry (5 decks)

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