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Clinical Chemistry > Blood Gases > Flashcards

Blood Gases Flashcards

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1
Q

List body buffer systems (and which one is the most important)

A
  • Bicarb (most important)
  • Proteins
  • Phosphates
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1
Q

When is body acid-base at equilibrium?

A

pH = pKa
Equal conc of protonated and unprotonated spp. for given buffer system

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2
Q

CO2 transport

A

CO2 + H2O -> H2CO3 -> HCO3 + O2 + H cation -> HHb venous

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3
Q

Two main kidney functions

A
  1. Reabsorb bicarb from glomerular filtrate in proximal tubule
  2. Kidneys also excrete H+ for buffering capacity
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4
Q

How does increased plasma pH correlate with Na-H exchange and HCO3 reabsorption?

A

Both decreased Na-H exchange and HCO3 reabsorption

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5
Q

How does decreased plasma pH correlate with Na-H exchange and HCO3 absorption?

A

Both increased Na-H exchange and HCO3 reabsorption

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6
Q

Normal HCO3 to H2CO3 ratio and pH?

A

20:1 and pH = 7.0

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7
Q

Respiratory component of acid-base homeostasis

A

dissolved CO2 (dCO2) expelled by lungs

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8
Q

Metabolic component of acid-base homeostasis

A

How kidneys control bicarb conc by reabsorption or depletion

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9
Q

Reference range for pH

A

7.35-7.45

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10
Q

How does body compensate for metabolic acidosis?

A

Hyperventilation because the body compensates by altering the factor not associated with the primary process

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11
Q

Primary respiratory acidosis/alkalosis

A

Respiratory dysfunction caused by change in pCO2

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12
Q

Metabolic acidosis/alkalosis

A

Renal/metabolic dysfunction caused by change in bicarb level

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13
Q

Compensation

A
  • Response to maintain acid-base homeostasis
  • Accomplished by organ not associated with primary process
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14
Q

Fully compensated

A

pH returned to normal range and bicarb: carbonic acid is approaching 20:1

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15
Q

Partially compensated

A

pH approaching normal

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16
Q

Uncompensated

A

pH abnormal and body has not started compensating for acid-base imbalance

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17
Q

Causes of metabolic acidosis

A
  • Overdose of acid-producers (aspirin, ethanol, methanol, ethylene glycol)
  • Reduced excretion of H+ (renal tubular acidosis)
  • Excessive loss of bicarb from diarrhea (hyperchloremic acidosis)
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18
Q

Causes of respiratory acidosis

A
  • Hypoventilation -> reduced CO2 expelled from lungs -> increased pCO2 (hypercarbia/hypercapnia)
  • Airway obstruction (COPD)
  • Drug overdose that leads to hypoventilation and increases pCO2 in blood
  • Decreased cardiac output (congestive heart failure) -> less blood presented to lungs and therefore higher pCO2
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19
Q

Causes of metabolic alkalosis

A
  • Excessive loss of stomach acid through vomiting or nasogastric suctioning
  • Prolonged use of diuretics -> increased H+ renal excretion
  • Excess admin of sodium bicarb or excess ingestion of antacids
  • Hypokalemia causes H+ to shift intracellularly -> increased bicarb reabsorption in the kidneys
20
Q

Causes of respiratory alkalosis

A
  • High altitudes decrease pCO2 -> hyperventilation
  • Anxiety -> hyperventilation
  • Aspirin overdose stimulates hyperpnea
  • Pulmonary embolism or pulmonary fibrosis impair oxygen exchange
21
Q

List primary and compensatory responses to metabolic acidosis

A

Primary
- Increased H+
- Decreased pH
- Decreased bicarb

Compensatory
Decreased PCO2 due to hyperventilation

22
Q

List primary and compensatory responses to metabolic alkalosis

A

Primary
- Decreased H+
- Increased pH
- Increased bicarb

Compensatory
Increased PCO2 due to hypoventilation

23
Q

Disturbances in which 7 conditions can result in hypoxia and poor tissue oxygenation?

A
  1. Binding of Hgb
  2. Available atmospheric oxygen
  3. Adequate ventilation
  4. Gas exchange btwn lungs and arterial blood
  5. Enough Hgb amt
  6. Adequate blood flow to tissues
  7. Ability of oxygen to release to tissues
24
Q

How is a patient’s oxygen status evaluated?

A

Measure pO2, pH, and pCO2 in routine blood gas analysis

25
Q

Percentages of oxygen, CO2, and N2 in air

A
  • O2 = 21%
  • CO2 = 0.3%
  • N2 = 78%
26
Q

How do the gas percentages and vapor pressures vary with altitude?

A

Percentages stay the same but vapor pressures vary

27
Q

Tracheal/bronchial air pO2 and pCO2

A

pO2: 149 mm Hg
pCO2 0.2 mm Hg

28
Q

Alveolar air pO2 and pCO2

A

pO2: 100 mm Hg
pCO2: 36 mm Hg

29
Q

Venous circulation pO2 and pCO2 (pH 7.35)

A

pO2: 40 mm Hg
pCO2 46 mm Hg

30
Q

Tissue surface pO2 and pCO2

A

pO2 20 mm Hg
pCO2: 60 mm Hg

31
Q

Arterial circulation pO2 and pCO2 (pH 7.40)

A

pO2: 90 mm Hg
pCO2: 40 mm Hg

32
Q

List factors that influence amount of oxygen that moves to the alveoli

A
  • Destruction of the alveoli
  • Pulmonary edema
  • Airway blockage
33
Q

List factors that influence the amount of O2 delivered to the tissue

A
  • Inadequate blood supply
  • Diffusion of CO2 and O2
    -Intrapulmonary shunting
  • Anemia
34
Q

Oxyhemoglobin (O2Hgb)

A

O2 hemoglobin containing ferrous (Fe2+) iron in the heme group that is reversibly bound to oxygen

35
Q

Deoxyhemoglobin (HHb)

A

Reduced hemoglobin without oxygen

36
Q

Carboxyhemoglobin COHb)

A

Hgb bound to carbon monoxide

37
Q

Methemoglobin

A

Hemoglobin unable to bind oxygen because iron is in an oxidized (Fe3+) state instead of reduced

38
Q

Hgb-O2 binding capacity

A

97-99% normal

39
Q

Four parameters commonly used to assess pt’s oxygen status

A
  1. Oxygen saturation (SO2)
  2. Fractional % oxyhemoglobin (FO2Hb)
  3. Trends in oxygen sat assessed by transcutaneous and pulse oximetry (SpO2)
  4. Amount of oxygen dissolved in plasma (pO2)
40
Q

Hgb affinity for O2 depends on which factors?

A
  • pH
  • pCO2
  • pCO
  • Body temp
  • 2,3-DPG conc
41
Q

Left shift

A
  • Increased pH
  • Decreased pCO2, 2,3-DPG, and temp
42
Q

Right shift

A
  • Decreased pH
  • Increased pCO2, 2,3-DPG, and temp
43
Q

T/F: Unique structure of Hgb allows it to act as both acid-base buffer and O2 buffer

A

True dat

44
Q

Oxygen and gas exchange in tissue

A

Elevated CO2 and H+ results in enhanced O2 release (oxygen buffering) -> accelerates uptake of CO2 and H+ by hemoglobin (acid-base buffering)

45
Q

Oxygen and gas exchange in lungs

A

Microenvironment promotes uptake of oxygen and release of CO2

46
Q

Potentiometry

A

Measures electric potential between two electrodes -> change in voltage indicates concentration of each analyte (pCO2, pH)

47
Q

List calculated parameters

A
  • HCO3
  • H2CO3
  • Total CO2
  • Base excess

Clinical Chemistry (21 decks)

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