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FFICM > Acid Base > Flashcards

Acid Base Flashcards

1
Q

Acid definition

A

Proton Donor

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2
Q

Base def

A

Proton Acceptor

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3
Q

Strong acid

A

Fully dissociates in solution

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4
Q

Weak acid

A

Partially disociates in solution

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5
Q

Buffer

A

Chemical substance that prevent large changes in H conc when acid or base is added to a solution

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6
Q

Acidaemia

A

Decrease in pH

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7
Q

Acidosis

A

Increase in H concentration

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8
Q

Acid-base buffer

A

Solution of two or more compounds that prevent marked changes in H with acid or base is added.

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9
Q

pK of a buffer

A

the pH at which the ionised and unionised forms of a chemical are at equilibiurm

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10
Q

Henderson Hasselbach eqn

A

pH = pKA + Log10 (base/acid)

= 6.1 + log 1o (24/ 2.3X5.3)
= 7.4

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11
Q

If CO2 production is constant, what determines CO2 concentration

A

alveolar vent

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12
Q

What affects alveolar vent

A

Resp centre in medulla oblangata is sensitive to change in H+ and alter the ventilation

Acts within minutes

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13
Q

Kidney role in acid base balance

A

controls secretion of H relative to amount of filtered bicarb

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14
Q

Methods of H secretion

A

1) secondary active transport of H in PCT, thick segment of asc loop and DCT

CO2 + H20 __(Carbonic) —> Carbonic acid —> H plus bicarb and H sereted into tubule

2) Primary active transport in latter DCT to renal pelvis

Acounts for 5% of H secreted
But can concentrate H 900 fold compared to 4 fold for secondary

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15
Q

Why does saline cause acidosis

A

Relative excess of chloride given

This reduces the Strong Ion Difference

Reducing SID increases water dissociation

Therefore, more H+

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16
Q

Strong Ion Difference

A

(Na+K+Ca+Mg) - (Cl - Lact)

17
Q

What happens when the SID increases

A

Less water dissociation, therefore reduced H, therefore pH rises

18
Q

When the SID decrease

A

More water dissociation making more H, so pH falls

19
Q

Is PaO2 directly or indirectly measured

A

Direct

20
Q

PaCO2 direct or indirect

A

Direct

21
Q

pH direct or indirect

A

Direct (as negative of {H}

22
Q

Standard bicarb, direct or indirect

A

Indirect from pH and CO2 using Henerson Hasselback

23
Q

What is standard bicarb

A

Conc of bicarb in an equilibriated sample to 37C and PaCO2 5.3

Range 22-26

24
Q

Base excess/defecity

A

Amount of acid or base that needs to be added to a sample under standard conditions (37C, PaCO2 5.3) to return the pH to 7.4

Rnage -2 to 2

25
Q

Anion Gap

A

(Na+K) - (Cl+HCO3)

10-18

Indicates the presence of non volatile acids
Lactic, Ketoacids, exogenous

26
Q

What happens to blood gas if it cools

A

CO becomes more solube
PaCO2 falls

pH increases by 0.015 for every degree drop in temp

27
Q

Causes of met acidosis with normal AG

A

GI bicarb loss: diarrhoea, ileostomy. uretosigmoidostomy

Renal bicarb losses - acetazaolamide, proximal RTA, hyperparathyroid

Drugs, heavy metals, paraproteins

TPN

Dilutional

28
Q

Causes of met acidosis with raised AG

A 
Organic acids (KUSMEL)
Ketones
Uraemia
Salicylate
Methanol
Ethylene Glycol
Lactate
AKI/CKD

Ketoacidosis (alcohol excess, starvation, DKA)

29
Q

Types and causes of lactic acidosis

A

Type A - Anaerobic metab

Hypotension, arrest, low CO
Sepsis
Poisoning - ethylene glycol, methanol
Extreme muscular activity

Type B - 
Metformin
Haem malig leukamia, lymphoma
AIDS
Enzyme defects - pytuvate dehydrogenous
Decrease liver lactate metab
30
Q

Causes of metabolic alkalosis

A

Loss of acid

Vomiting, NG

Hydrogen loss from kidney

Diuretics, hypokalaemia, excess steroid
Low chloride states

Addition of alkali - bicarb

Substances converted to bicarb
Lactae, acetate, citrate

31
Q

Causes of resp acidosis

A

Resp depression, drugs, cerebral injury

Weakness, GBS, myasthenia, polio

Trauma

ARDS
COPD

Artifical vent - poor MV< high PEEP

32
Q

Causes or resp alk

A 
High MV
Hypoxia
PE
Early asthma
Salicylate over dose - early

early sepsis

33
Q

Difference between type A and type B lactic acidosis and how can you tell

A

A - impaired oxygen delivery
B - normal oxygen delivery but increased cellular production, reduced clearence

Lactate increases with increased glycolysis

Lactate to pyruvate ratio distinguises between tissue hypoxia (ratio > 10:1) and normal conditions (<10:1).

34
Q

Anion Gap corrected for Albumin

A

(Serum AG) + (2.5 x (45-Albumin)

35
Q

Steward approach ideas

A

Acids increase H+ and bases decrease H+

HCO3 is not independent of pH/H but is dependent on it

Acids are strong if they fully dissociate and weak if they dont

Three things contribute to acid base

SID
Conc of non volatile weak acids
PaCO2

36
Q

What three things determine acid base balance

A

The Strong Ion Differnce
Concentration of non volatile weak acids (Atot)
PaCO2

37
Q

Is PaCO2 an indepedent determinant of acid bases

A

yes (compaed to HCO3 which isnt)

38
Q

What is the strong ion difference gap

A

Difference between the Apparent SID (normal eqn) and the effective SID which involves albumin

> 2 is elevated gap, indicating unmeasured strong cations, ketones, salicylates etc

39
Q

How does albumin alter acid base

A

It is a weak acid

Increasing albumin (or phosphate) reduces the Effective SID, and therefore the equilibrium shifts to acidosis.

Low albumin shifts to alkalosis

FFICM (57 decks)

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