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Respiratory System > 13. Acid Base Regulation > Flashcards

13. Acid Base Regulation Flashcards

1
Q

What is the base excess (BE)?

A
  • Concentration of bases compared with the ‘expected concentration’
  • Normal = 0
  • Excess = +ve
  • Deficit = -ve
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2
Q

What is the haematocrit?

A

Proportion of the blood volume occupied by red blood cells (around 0.45)

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3
Q

What is the FHbCO and FHbO2?

A
  • FHbCO - proportion of Hb bound to CO (usually <1%)

* FHbO2 - proportion of Hb bound to oxygen (>95%)

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4
Q

What is FMetHb?

A
  • Proportion of Hb that is in the ferric methaemoglobin state (usually <1%)
  • Important to know what kind of inspiratory gases the patient has been breathing and pressure e.g. supplemental oxygen
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5
Q

Why is it important to maintain pH in the body?

A

• Changes can alter structure of proteins
- impair their function
- impeded biological processes
• Affect drug metabolism and clotting

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6
Q

What are the normal pHs of fluids in the body?

A
  • Intracellular - 7.0
  • Extracellular - 7.4
  • Arterial - 7.4
  • Venous - 7.34
  • Stomach - 2.4
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7
Q 
What do the following describe:
• Alkalaemia
• Acidaemia
• Alkalosis
• Acidosis
A
  • Alkalaemia - higher than normal pH of blood
  • Acidaemia - lower than normal pH of blood
  • Alkalosis - describes circumstances decrease [H+] (increase pH)
  • Acidosis - describes circumstances that will increase [H+] (decrease pH)

(can have have acidaemia but be in a state of alkalosis)

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8
Q

What usually causes respiratory acidosis/alkalosis?

A
  • Problems with lungs

* e.g. emphysema or COPD

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9
Q

What usually causes metabolic acidosis/alkalosis?

A
  • Problems with another part of the body other than the lungs
  • e.g. diabetic ketoacidosis
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10
Q

What is the difference between a weak and strong acid?

A

Ha <=> (H+) + (A-)
• Strong acid - mostly dissociated (forward)
• Weak acid - more conjugated acid (backward)

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11
Q

What is a base?

A
  • Anionic (negative) compound that binds
  • Reversibly binds to free H+ ions
  • Can be referred to broadly as being a buffer e.g. HCO3-
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12
Q

What units do we use for measurements of ions?

A
  • Equivalence per litre (Eq/L)
  • NOT mmol/L
  • As they are charged e.g. proton has equivalence of 1 and calcium ion has 2
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13
Q

Why do we use pH to measure acidity rather than [H+]?

A
  • Very low concentration of H+ ions compared to other ions in the blood
  • Logarithmic scale
  • pH increase of 1 represents 10x decrease in [H+]
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14
Q

What was the Pitts and Swan experiment?

A
  • Strong acid injected into a dog
  • Expected decrease in pH and death
  • Buffering capacity of blood caused immediate reaction to imbalance
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15
Q

What are the sources of respiratory of metabolic acids?

A
  • Respiratory acid - CO2 forms carbonic acid
  • Metabolic acid - e.g. lactic acid

(respiratory acid is much greater than metabolic acid - 99:1)

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16
Q

What is the Henderson and Henderson-Hasselbalch equation used to calculate?

A
  • Henderson - dissociation constant (Ka)

* Henderson-Hasselbalch - combines the Sorensen equation (pH = -log10[H+]) and Henderson equation

17
Q

How is the respiratory and metabolic acid component assessed?

A
  • Respiratory acid - PaCO2

* Metabolic acid - Base Excess (BE)

18
Q

What causes a rise and fall in base excess?

A 
• Rise 
- increase in renal excretion of acid
- ingestion/administration of base
- vomiting (loss of stomach acid)
• Fall
- overproduction of metabolic acids
- ingestion of acid
- reduction/failure of acid excretion by kidney
- excessive loss of alkali during diarrhoea (leading to metabolic acidosis)
19
Q

What are the basic guidelines for O2 kPa

A
  • Normal: >10 kPa
  • Mild hypoxaemia: 8-10 kPa
  • Moderate hypoxaemia: 6-8 kPa
  • Severe hypoxaemia: <6 kPa
20
Q

What causes a rapid and slow compensatory response?

A
  • Rapid - changes in ventilation to change CO2 and pH
  • Slow - changes in HCO3- and H+ retention/secretion in the kidneys

(issues with lungs fixed slowly by the kidney, issues with the kidneys and metabolism in the rest of the body fixed quickly by the lungs)

21
Q

What does it mean when the pH is uncompensated, partially compensated and fully compensated?

A
  • Uncompensated - acidosis/alkalosis deranges pH
  • Partially compensated - pH returning to normal but not within normal range
  • Fully compensated - pH in normal range (CO2 and BE abnormal)
22
Q

What causes uncompensated respiratory acidosis and how is it compensated?

A
  • Hypoventilation
  • Build up of CO2 in blood (increased H+)

• Acute phase:
- CO2 in erythrocytes + H2O to form bicarbonate (moves out via AE1)
- more plasma bicarbonate - equilibrium shifts left, less H+
• Chronic phase:
- increased reabsorption of bicarbonate in the kidneys

(Partially compensated - low pH, high PCO2, high BE)

  • pH eventually returns to normal
  • BE and PCO2 will still be high
23
Q

What causes uncompensated respiratory alkalosis and how is it compensated?

A
  • Hyperventilation
  • Reduces PACO2 - reduced [H+]

• No acute phase
• Chronic phase:
- reduced reabsorption of bicarbonate in the renal nephrons
- increase bicarbonate secretion into the collecting ducts

(Partially compensated - high pH, low PCO2, low BE)

  • pH eventually returns to normal (as more carbonic acid dissociates)
  • BE and PCO2 will still be low
24
Q

What causes uncompensated metabolic acidosis and how is it compensated?

A
  • Diarrhoea
  • Bicarbonate lost
  • Low BE
  • More carbonic acid dissociates to compensate for the lost bicarbonate
  • More H+ produced too - pH decreases = uncompensated metabolic acidosis
  • Increased ventilation - reduces PACO2 and increases the diffusion gradient
  • More CO2 leaves the blood

(Partially compensated - low pH, low PCO2, low BE)

  • Decrease in PCO2 - (carbonic acid) equilibrium shifts left so lost CO2 can be replaced
  • More H+ taken up
  • Increased pH to normal - compensated
  • BE and PCO2 are low
25
Q

What causes uncompensated metabolic alkalosis and how is it compensated?

A
  • Vomiting
  • Loss of stomach acid
  • More carbonic acid dissociates to compensate for the lost H+
  • More bicarbonate produced too - high BE, pH increases = uncompensated metabolic alkalosis
  • Reduced ventilation - more CO2 stays in the blood
  • Increases PaCO2

(Partially compensated - high pH, high PCO2, high BE)

  • (Carbonic acid) equilibrium shifts right so more H+ is produced
  • Decreased pH to normal
  • BE and PCO2 are high
26
Q

Why should the rest of the blood components be looked at, even if pH is normal?

A
  • Could be acidosis/alkalosis in a state of full compensation
  • However you cannot tell what is the cause and compensatory mechanism
27
Q

What 4 things to you look at when assessing blood acid/base contents?

A
  • Type of imbalance - acidosis/alkalaemia/normal
  • Aetiology - respiratory/metabolic/both/normal
  • Compensation
  • Oxygenation - hypoxaemia/normoxaemia/hyperoxaemia

Respiratory System (18 decks)

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