Acid Base

Question 1

Acid definition

Answer 1

Proton Donor

Question 2

Base def

Answer 2

Proton Acceptor

Question 3

Strong acid

Answer 3

Fully dissociates in solution

Question 4

Weak acid

Answer 4

Partially disociates in solution

Question 5

Buffer

Answer 5

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

Question 6

Acidaemia

Answer 6

Decrease in pH

Question 7

Acidosis

Answer 7

Increase in H concentration

Question 8

Acid-base buffer

Answer 8

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

Question 9

pK of a buffer

Answer 9

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

Question 10

Henderson Hasselbach eqn

Answer 10

pH = pKA + Log10 (base/acid)

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

Question 11

If CO2 production is constant, what determines CO2 concentration

Answer 11

alveolar vent

Question 12

What affects alveolar vent

Answer 12

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

Acts within minutes

Question 13

Kidney role in acid base balance

Answer 13

controls secretion of H relative to amount of filtered bicarb

Question 14

Methods of H secretion

Answer 14

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

Question 15

Why does saline cause acidosis

Answer 15

Relative excess of chloride given

This reduces the Strong Ion Difference

Reducing SID increases water dissociation

Therefore, more H+

Question 16

Strong Ion Difference

Answer 16

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

Question 17

What happens when the SID increases

Answer 17

Less water dissociation, therefore reduced H, therefore pH rises

Question 18

When the SID decrease

Answer 18

More water dissociation making more H, so pH falls

Question 19

Is PaO2 directly or indirectly measured

Answer 19

Direct

Question 20

PaCO2 direct or indirect

Answer 20

Direct

Question 21

pH direct or indirect

Answer 21

Direct (as negative of {H}

Question 22

Standard bicarb, direct or indirect

Answer 22

Indirect from pH and CO2 using Henerson Hasselback

Question 23

What is standard bicarb

Answer 23

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

Range 22-26

Question 24

Base excess/defecity

Answer 24

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

Question 25

Anion Gap

Answer 25

(Na+K) - (Cl+HCO3) 10-18 Indicates the presence of non volatile acids Lactic, Ketoacids, exogenous

Question 26

What happens to blood gas if it cools

Answer 26

CO becomes more solube PaCO2 falls pH increases by 0.015 for every degree drop in temp

Question 27

Causes of met acidosis with normal AG

Answer 27

GI bicarb loss: diarrhoea, ileostomy. uretosigmoidostomy Renal bicarb losses - acetazaolamide, proximal RTA, hyperparathyroid Drugs, heavy metals, paraproteins TPN Dilutional

Question 28

Causes of met acidosis with raised AG

Answer 28

``` Organic acids (KUSMEL) Ketones Uraemia Salicylate Methanol Ethylene Glycol Lactate AKI/CKD ``` Ketoacidosis (alcohol excess, starvation, DKA)

Question 29

Types and causes of lactic acidosis

Answer 29

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 ```

Question 30

Causes of metabolic alkalosis

Answer 30

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

Question 31

Causes of resp acidosis

Answer 31

Resp depression, drugs, cerebral injury Weakness, GBS, myasthenia, polio Trauma ARDS COPD Artifical vent - poor MV< high PEEP

Question 32

Causes or resp alk

Answer 32

``` High MV Hypoxia PE Early asthma Salicylate over dose - early ``` early sepsis

Question 33

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

Answer 33

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).

Question 34

Anion Gap corrected for Albumin

Answer 34

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

Question 35

Steward approach ideas

Answer 35

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

Question 36

What three things determine acid base balance

Answer 36

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

Question 37

Is PaCO2 an indepedent determinant of acid bases

Answer 37

yes (compaed to HCO3 which isnt)

Question 38

What is the strong ion difference gap

Answer 38

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

Question 39

How does albumin alter acid base

Answer 39

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