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SUGER > Acid-base Balance > Flashcards

Acid-base Balance Flashcards

1
Q

pH

A

Negative log [H+]

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2
Q

Acidosis

A

Disorder tending to make blood more acid than normal

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3
Q

Alkalosis

A

Disorder tending to make blood more alkaline than normal

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4
Q

Acidemia

A

Low blood pH

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5
Q

Alkalemia

A

High blood pH

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6
Q

Factors affecting pH

A

Respiratory component: CO2 concentration
Metabolic component:
- intrinsic acid = products of metabolism
- extrinsic acid = diet, toxins
- buffering capacity = bicarbonate, other buffers

Central relationship between bicarbonate and CO2

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7
Q

Standard bicarbonate

A

Measures of metabolic component of any acid-base disturbance

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8
Q

What is standard bicarbonate standardised to

A

Bicarbonate concentration standardised to pCO2 5.3kPa and temp 37

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9
Q

Absolute bicarbonate is affected by

A

Respiratory and metabolic components

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10
Q

Base excess

A

Quantity of acid required to return pH to normal under standard conditions

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11
Q

What is standard base excess corrected to

A

Hb 50g/L

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12
Q

What can base excess be used to calculate

A

Bicarbonate dose to correct acidosis
0.3 x Wt xBE

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13
Q

Base deficit

A

Base excess is negative in acidosis

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14
Q

What is measured by an arterial blood gas

A

pH
pO2
pCO2
STD HCO3-
STD base excess
May include other measures eg lactate, Na+, K+

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15
Q

How is acid-base status interpreted

A

Henderson approach
Stewart’s theory (strong ion difference)

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16
Q

Henderson-Hasselbalch equation

A

pH = pKa + log([A-]/[HA])
pH = pKaH2CO3 + log([HCO3-]/[H2CO3])
pH = 6.1 + log([HCO3-]/0.03 x pCO2)

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17
Q

What can effect acid-base status

A

Lungs- CO2 excretion
Kidneys- H+ excretion and HCO3- recycling

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18
Q

2 major organs involved in acid-base balance

A

Lungs
Lidneys

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19
Q

Stewart’s strong ion difference

A

Principle: pH and HCO3- are dependent variables governed by:
pCO2
Concentration of weak acids (ATOT)
ATOT = Pi + Pr + Alb
Strong ion difference (SID)
SID = Na+ + K+ + Mg2+ + Ca2+ – Cl- – other strong anions (eg lactate, ketoacids)

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20
Q

Evaluation of Stewart’s strong ion difference

A

Identifies the factors controlling pH
Calculation can be very problematic- measurements introduce errors
Probably adds little in practice

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21
Q

Diagnosing acid-base disorders

A

Acidoses or alkaloses
Respiratory or metabolic

Can co-exist

22
Q

Causes of metabolic acidosis

A

Dilutional
Failure of H+ excretion
Excess H+ load
HCO3- loss

23
Q

Failure of H+ excretion

A

Renal failure
Hypoaldosteronism
Type 1 renal tubular acidosis

24
Q

Excess H+ load

A

Lactic acidosis
Ketoacidosis
Ingestion of acids eg salicylate, ethylene, glycol

25
Q

HCO3- loss

A

Diarrhoea
Type 2 renal tubular acidosis

26
Q

Clinical features of metabolic acidosis

A

Sighing respirations (Kussmaul’s resps)
Tachypnoea

27
Q

Compensatory mechanism for metabolic acidosis

A

Hyperventilation to increase CO2 excretion

28
Q

Anion gap

A

Difference between measured anions and cations
= [Na+] + [K+] - [Cl-] - [HCO3-]

Useful to identify cause of acid-base disorders

29
Q

Normal anion gap

A

10-16

30
Q

Wide anion gap causes

A

Lactic acidosis
Ketoacidosis
Ingestion of acid
Renal failure

31
Q

Causes of narrow anion gap (ie high chloride)

A

GI HCO3- loss
Renal tubular acidosis

32
Q

Causes of metabolic alkalosis

A

Alkali ingestion
Gastrointestinal acid loss - vomiting
Renal acid loss- hyperaldosteronism, hypokalaemia

33
Q

Compensatory mechanism for metabolic alkalosis

A

Hypoventilation (limited by hypoxic drive)
Renal bicarbonate excretion

34
Q

Respiratory acidosis

A

CO2 retention leading to increased carbonic acid dissociation

35
Q

Causes of respiratory acidosis

A

Any cause of type 2 respiratory failure

36
Q

Compensatory mechanism of respiratory acidosis

A

Increased renal H+ excretion and bicarbonate retention (only if chronic)

37
Q

Respiratory alkalosis

A

CO2 depletion due to hyperventilation

38
Q

Causes of respiratory alkalosis

A

Type 1 respiratory failure
Anxiety/panic

39
Q

Compensation of respiratory alkalosis

A

Increased renal bicarbonate loss (if chronic)

40
Q

ABG interpretation

A

What is the pH?
What is the respiratory component (ie pCO2)?
What is the metabolic component (std HCO3-, base excess)?
Which component is congruent with the pH?

41
Q

If pH and metabolic component are opposite

A

Respiratory problem- body trying to compensate

42
Q

If pH and metabolic component going same way

A

Metabolic component driving factor/problem

43
Q

If pH and pCO2 are opposite

A

Compensatory

44
Q

If pH and pCO2 are same way

A

Causing factor

45
Q

Low pCO2

A

Alkalosis

46
Q

Normal pCO2 range

A

4.6-6.0

47
Q

Normal base excess range

A

0-2

48
Q

Normal Std HCO3- range

A

22-26

49
Q

Normal pH range

A

7.36-7.44

50
Q

Normal pO2 range

A

9.5-12

51
Q

Alkalosis is a condition in which the body fluids have excess base (alkali). This is the opposite of excess acid (acidosis). Which of the following would cause a metabolic alkalosis?

A

Vomiting

SUGER (17 decks)

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