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Urinary System > Acid Base Balance - Pt 2 > Flashcards

Acid Base Balance - Pt 2 Flashcards

1
Q

What do respiratory and renal disorders affect?

A

Resp. = PCO2
Renal = conc. of HCO3-

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2
Q

Describe respiratory acidosis

A

pH has fallen and is due to resp. change
PCO2 is increased
Results from reduced ventilation and retention of CO2

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3
Q

What are the acute causes for respiratory acidosis?

A

Drugs which depress medullary respiratory centres - barbiturates and opiates
Obstructions to major airways

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4
Q

What are the chronic causes for respiratory acidosis?

A

Lung disease - bronchitis, emphysema and asthma
PCO2 increased so increase secretion of H+ and HCO3-
Need to protect pH so increase HCO3-
Generation of new HCO3- but also increased reabsorption

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5
Q

What do acid conditions stimulate?

A

Renal glutaminase - more NH3 produced but it takes time

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6
Q

In chronic causes of respiratory acidosis - why does original disturbance not corrected?

A

Renal compensation for increase HCO3- protects pH but only restoration of ventilation can remove primary disturbance
So BG values are never normalised - kidney maintains high HCO3-

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7
Q

Describe respiratory alkalosis

A

Alkalosis of resp. origin so must be due to fall in PCO2 and can occur through hyperventilation and CO2 blow off

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8
Q

What are the acute causes of respiratory alkalosis?

A

Voluntary hyperventilation, aspirin and first ascent to altitude

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9
Q

What are the causes of chronic alkalosis?

A

Long term residence at altitude so PCO2 below 60mmHg stimulates peripheral chemoreceptors to increase ventilation
Ventilation must be normal to correct disturbance

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10
Q

What are alkaline condition dealt with?

A

HCO3- reabsorption mechanism
If PCO2 drops then less H+ available for excretion so less filtered HCO3- reabsorbed so HCO3- lost in urine

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11
Q

Describe metabolic acidosis

A

Metabolic origin - loss of HCO3-
Decreased HCO3- either from increased buffering or direct loss of HCO3-
PCO2 must be decreased

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12
Q

What are the causes of metabolic acidosis?

A

Increased H+ production - ketoacidosis or lactic acidosis
Failure to excrete dietary load of H+ in renal failure
Loss of HCO3- as in diarrhoea - failure to reabsorb intestinal HCO3-

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13
Q

Describe Kussmaul breathing

A

Degree of hyperventilation - increase depth of breathing so max 30l/min when pH falls to 7
Sign of renal failure or diabetic ketoacidosis

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14
Q

What is the problem in metabolic acidosis?

A

Normally kidneys correct disturbance by restoring HCO3- and getting rid of H+ ions
Source of H+ ions is the carbonic acids from CO2 but resp. compensation lowers PCO2 to protect pH

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15
Q

What would complete compensation lead to?

A

Would remove the drive to correct the original disturbance
Then there is no pressure to correct disturbance - further perturbation may push system too far so compensation may longer not be effective

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16
Q

What does decreased PCO2 lead to?

A

Total amount of H+ secretion by renal tubule will be less than normal but because of plasma HCO3- conc. and filtered HCO3- conc. is reduced

17
Q

What does a reduced plasma HCO3- and filtered HCO3- load mean?

A

Less total H+ is needed for HCO3- reabsorption and therefore greater proportion is available for excretion to form titratable acid and NH4+
Less H+ secretion = Decreased HCO3- reabsorption and increase new HCO3-

18
Q

What does increase metabolic H+ in body lead to?

A

Immediate buffering in ECF and then ICF
Resp. compensation within minutes
Renal correction takes longer - to develop response to increase H+ excretion and generates new HCO3-

19
Q

What does respiratory compensation do in metabolic acidosis?

A

Delays the renal correction but protects the pH

20
Q

Describe metabolic alkalosis

A

HCO3- must have increased and PCO2 will increase to protect the pH

21
Q

What are the causes of metabolic alkalosis?

A

Increase H+ ion loss in vomiting
Increase H+ loss in aldosterone excess and liquorice ingestion
Excess administration of HCO3- - renal impairment
Massive blood transfusions

22
Q

How can massive blood transfusions lead to metabolic alkalosis?

A

Bank blood contains citrate to prevent coagulation which is converted to HCO3- but need 8 units for this

23
Q

What does increased filtered load of HCO3- lead to?

A

Exceeds the level of H+ secretion to reabsorb it, even in presence of increased PCO2
So excess lost in urine
Resp. delays renal correction but protects the pH

24
Q

What is the summary of respiratory acidosis?

A

Increase H+ so decreases pH
Primary disturbance is increase PCO2
Compensation is increase HCO3- conc.

25
Q

What is the summary of respiratory alkalosis?

A

Decrease H+ so increase pH
Primary disturbance is decrease PCO2
Compensation is decrease HCO3- conc.

26
Q

What is the summary of metabolic acidosis?

A

Increase H+ so decrease pH
Primary disturbance is decrease HCO3- conc.
Compensation is decrease PCO2

27
Q

What is the summary of metabolic alkalosis?

A

Decrease H+ so increase pH
Primary disturbance is increase HCO3- conc.
Compensation is increase PCO2

28
Q

What is a decrease in pH caused by?

A

Decreased HCO3-
Increased PCO2

29
Q

What is an increase in pH caused by?

A

Increased HCO3-
Decreased PCO2

30
Q

Does chronic or acute resp. acidosis cause bigger decrease in pH

A

Acute
Because NH3 production takes 4-5 days to turn on and off

31
Q

What can a haemorrhage lead to?

A

Lactic acidosis

32
Q

What is happening in a patient with metabolic acidosis, respiratory acidosis, and lactic acidosis?

A

Diabetic ketoacidosis decreases pH
Chronic bronchitis decompensates
Haemorrhage loss means additional metabolic acidosis
Brings pH to brink of survival
High acidity causes hyperkalaemia as H+ ions are buffered intracellularly in exchange for K+

33
Q

What would you do for a patient with metabolic and respiratory acidosis?

A

Insulin (and glucose if non-diabetic) which stimulates cellular uptake of K+
Hyperkalaemia - calcium resonium
Ca gluconate IV which increases excitability of heart

34
Q

What does calcium resonium do?

A

Exchanges Ca2+ ions for K+ ions

35
Q

What happens in a bad case of vomiting - hypovolaemia and metabolc alkalosis?

A

Loss of NaCl + H2O and HCl
Hypovolaemia - stimulates aldosterone to increase distal tubule Na reabsorption
In avid Na reabsorption Na is exchanged for H+
PCO2 helps drive H+ secretion and exacerbates metabolic alkalosis

36
Q

What takes precedence between volume and metabolic correction?

A

Volume

37
Q

What is given in bad case of vomiting - hypovolaemia and metabolic alkalosis?

A

Give NaCl to restore volume then alkalosis will be corrected

38
Q

What does liquorice contain?

A

Glycyrrhizic acid which similar to aldosterone - so excess ingestion causes metabolic alkalosis

Urinary System (26 decks)

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