Acid/base

Question 1

How is plasma electroneutrality maintained?

Answer 1

Number of cations = number of anions

Question 2

What are the unmeasured cations?

Answer 2

Calcium and magnesium

Question 3

What are theunmeasured anions?

Answer 3

Lactate, phosphate, albumin

Question 4

What is the anion gap?

Answer 4

([Na] +[K]) - ([Cl] +(HCO3])

Question 5

When does a normal anion gap acidosis occur?

Answer 5

When the reduction in HCO3 is matched by an increase in chloride ions

Question 6

When does an increased anion gap acidosis occur?

Answer 6

When there is an increase in unmeasured anions (endogenous e.g. lactate or exogenous e.g. methanol)

Question 7

Causes of raised anion gap acidosis?

Answer 7

Lactate: shock, hypoxia, sepsis, bowel ischaemia, heart or liver failure
Ketoacidosis:DKA, alcohol, starvation 
Uraemia: eGFR <15
Methanol
Ethylene glycol

Question 8

What are the causes of normal anion gap acidosis?

Answer 8

Loss of HCO3 from bowel:diarrhoea, biliary/pancreatic drains, ileostomy, ureterosigmoidostomy
RTA: chronic renal failure
Carbonic anhydrase inhibitors: e.g. acetazolamide

Question 9

What is a metabolic alkalosis?

Answer 9

A rise in pH due to primary rise in HCO3

Question 10

What electrolyte imbalances are most colsely linked to a metabolic alkalosis?

Answer 10

K+ and Cl-

Question 11

What are the main causes of a metabolic alkalosis?

Answer 11

Acid lost from the stomach:vomiting, NGT
Diuretics: thiazides, loop
Mineralocorticoid excess: Conn’s, Cushings

Question 12

How would you manage a metabolic acidosis?

Answer 12

Underlying cause
IVI bolus + reassess. HRdown, BP up and improvement in UOall indicate further IVI
CVVH if refractory
Sodium bicarb raises pH but is metabolised to CO2 and excreted by the lungs. Therefore COPD patients may develop hypercapnia.
CO2 can produce respiratory acidosis and worsen the already present acidaemia. Sodium +fluid may worsen overload in cardiac/renal patients
Sodium bicarb can be used in the hands of specialists to reduce acidaemia that impairs effect of vaso-active substances

Question 13

What causes ARA by increased dead space?

Answer 13

Multilobar pneumonia
Pulmonary oedema
P.E.
O2 therapy

Question 14

What causes CRA by increased dead space ventilation?

Answer 14

Emphysema
Pulmonary fibrosis
Pulmonary vascular disease

Question 15

What causes ARA by respiratory muscle dysfunction?

Answer 15

Fatigue

GB

Question 16

What causes CRA by respiratory muscle dysfunction?

Answer 16

Paralysed diaphragm
Muscular dystrophy
Neuromuscular disorder

Question 17

What causes ARA by upper airway obstruction?

Answer 17

Angioedema

Question 18

What causes CRA by upper airway obstruction?

Answer 18

Tracheal stenosis

Question 19

Cause of ARA by lower airway obstruction?

Answer 19

Status epilepticus

Question 20

Cause of CRA by lower airway obstruction?

Answer 20

COPD

Question 21

Cause of ARA by pleural/chest wall stiffness?

Answer 21

PTX
Flail chest
Abdominal distension

Question 22

Cause of CRA by pleural/chest wall stiffness?

Answer 22

Obesity

Kyphoscoliosis

Question 23

Cause of ARA by reduced central drive?

Answer 23

GA
Sedation
Cerebral oedema

Question 24

Cause of CRAby reduced central drive?

Answer 24

OSA
Opioid dependence
Hypothyroidism

Question 25

How do the kidneys compensate for a chronic rise in PaCO2?

Answer 25

By increasing HCO3 generation at the expense of Cl- resorption (takes several days)

Question 26

Hypoxic causes of a respiratory alkalosis?

Answer 26

High altitude
Pneumonia
PE
Drowning
Severe anaemia
Pulmonary oedema
Asthma
ARDS
PTX
Flail chest

Question 27

CNS causes of a respiratory alkalosis?

Answer 27

Pain
Anxiety
Fever
SAH

Question 28

Drug causes of a respiratory alkalosis?

Answer 28

Salicylates

Nicotine

Question 29

Misc causes of a respiratory alkalosis?

Answer 29

Pregnancy
Exercise
Sepsis
Liver failure

Question 30

Mx hyperkalaemia

Answer 30

10ml 10%calcium gluconate

10-15 units actrapid with 50ml 50% glucose over 20 mins