ICM - Acid Base

Question 1

Acid definition

Answer 1

Proton Donor

Question 2

Base definition

Answer 2

Proton Acceptor

Question 3

What is a Strong acid

Answer 3

Fully dissociates in solution

Question 4

Weak acid

Answer 4

Partially disociates in solution

Question 5

What is a 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

What is 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

What is the SID?

Answer 16

Strong Ion Difference (SID) is the difference between the concentrations of strong cations and strong anions (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