Acid Base Control Flashcards Preview

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Flashcards in Acid Base Control Deck (18)
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1
Q

1kPa = how many mmHg

A

7.5

2
Q

When do acid-base disturbances occur?

A
  • If there is a problem with ventilation,
  • Problem with renal function,
  • Overwhelming acid or base load
3
Q

What is standard bicarbonate?

A

It reflects the metabolic component of acid base balance. It is calculated from the actual bicarbonate but assuming 37 degrees and paCO2 of 5.3kPa

4
Q

What is base excess?

A

Amount of acid required to restore a litre of blood to its normal pH at PCO2 of 5.3. It becomes more negative in metabolic acidosis

5
Q

Describe the stepwise approach to the assessment of ABGs

A

1) Assess PO2 and oxygenation (P/F ratio)
2) Assess pH, acidaemia or alkalaemia?
3) Determine primary problem,
4) Is compensation occurring?

6
Q

What is a good clue to assess if compensation is occuring?

A

It is likely to be occurring if pCO2 and bicarb are moving in the same direction.

7
Q

What is the anion gap?

A

It is the sum of routinely measured cations in venous blood minus routinely measured anions. It can be early indicator of acidaemia.

8
Q

What is the normal anion gap?

A
  1. If it is increased then is signals presence of metabolic acidaemia
9
Q

Explain how endogenous acidaemia can occur from lactate

A

Results from any condition causing hypoperfusion eg, Shock or emboli. This will result in increased anaerobic metabolism with subsequent increased production of lactic acid. Lactic acidaemia can also result from severe acute hypoxia, severe convulsions or strenuous exercise.

10
Q

explain how endogenous acidaemia can occur from an increase in insulin and glucagon

A
  • In uncontrolled diabetes (can lead to ketoacidosis), alcoholic or starvation ketoacidosis
11
Q

Why would you you use venous blood instead of arterial in DKA?

A

Unless respiratory problems indicate then there is no interest in PO2. Since venous samples are less painful, faster and lower risk of harm then it is preferred.

12
Q

Name some examples of exogenous acid overload

A

Accidental/deliberate ingestion of methanol or ethylene glycol.

13
Q

What are some causes of metabolic acidosis?

A
  • Renal failure (increase anion gap)
  • Renal tubular acidosis (normal anion gap)
  • Diarrhoea - cells below pylorus secrete bicarbonate into lumen and for every bicarb ion into gut, an H+ ion enters ECF. (normal anion gap)
14
Q

Describe the compensation for metabolic acidosis

A

Respiratory. pCO2 must fall so minute volume must increase. Therefore Kussmaul respiration occurs which is a laboured deep, rapid breathing patter.

15
Q

What 2 processes happen for metabolic alkalosis to occur?

A

An initiating process and a maintaining process

16
Q

What is the most common initiating processes in metabolic alkalosis

A
  • Loss of H+ ions from the gut (above pylorus)
  • Less common is loss of H+ from the kidney due to loop and thiazide diuretics.
  • Gain of exogenous alkali is much less common
17
Q

Explain the maintenance of alkalosis

A
  • Occurs via a process which impairs the kidneys ability to excrete bicarbonate (HAV);
  • Hypokalaemia,
  • Aldosterone excess,
  • Volume and chloride depletion
18
Q

Describe the compensation for metabolic alkalosis

A

pCO2 must increase and so minute volume must fall.