Arterial blood gases

Question 1

When are ABGs done

Answer 1

diagnosis treatment and monitoring of respiratory and cardiac illnesses

Also used for intra-operative monitoring and in intensive care

Question 2

Steps to interpret ABG

Answer 2

ph- academia or alkalaemia>
PCo2 and HCo3-= respiratory or metabolic?
Compensation-is there any

Question 3

Respiratory compensatory mechanisms

Answer 3

Acidic Co2 excreted through hypervantilation or retained through hypoventilation

Question 4

Metabolic compensatory mechanisms

Answer 4

• Renal excretion of H+ in urine in respiratory acidosis

- Increase in HCo3- concentration in hypoventilation or respiratory acidosis

Question 5

pH for acidaemia

Answer 5

pH <7.35

Question 6

pH for alkalaemia

Answer 6

pH >7.45

Question 7

High pCO2?

Answer 7

Respiratory acidosis

Question 8

Low pCO2

Answer 8

Respiratory alkalosis

Question 9

What is base excess

Answer 9

The theoretical amount of acid needed to bring a pt fully oxygenated blood to a normal pH at room temp

Question 10

What does a high base excess mean

Answer 10

metabolic alkalosis

Question 11

What does a low base excess mean

Answer 11

Metabolic acidosis

Question 12

What is respiratory acidosis

-What is bicarbonate like

Answer 12

• Decrease in gaseous exchange leading to retention of CO₂
• High PCO₂ leads to renal retention of bicarbonate to buffer excess H⁺
• Compensation by the kidneys results in an increase in secretion of H⁺ over 3-5 days leading to increase in plasma bicarbonate level

Question 13

Central causes of respiratory acidosis

Answer 13

Drugs e.g morphine and sedatives
Stroke
Infection

Question 14

Airway causes of respiratory acidosis

Answer 14

Asthma

COPD

Question 15

Parenchymal emphysema causes of respiratory acidosis

Answer 15

Pneumoconiosis
Bronchitis
Acute respiratory distress syndrome

Question 16

Neuromuscular causes of respiratory acidosis

Answer 16

Poliomyelitis
Kyphoscoliosis
Myasthenia gravis
Muscular dystrophies

Question 17

Miscellaneous causes of respiratory acidosis

Answer 17

Obesity

hypoventilation

Question 18

What is respiratory alkalosis

• hat is co2 like and ammonium like
• What is bicarbonate like

Answer 18

• Alveolar hyperventilation leads to excess exhalation of CO₂, resulting in low PCO₂
• Compensation by the kidneys results from decreased ammonium (NH₄⁻) excretion, leading to a fall in bicarbonate

Question 19

CNS causes of respiratory alkalosis

Answer 19

Pain, anxiety, psychosis
Fever
Cerebrovascular accident/stroke
Meningitis/encephalitis
Trauma

Question 20

Hyperaemia or tissue hypoxia causes of respiratory alkalosis

Answer 20

High altitude
Pneumonia
Pulmonary oedema
Aspiration
Severe anaemia

Question 21

Drugs or hormonal causes of respiratory alkalosis

Answer 21

pregnancy, progesterone, salicylates

Question 22

Stimulation of thoracic neural receptors causes of respiratory alkalosis

Answer 22

haemothorax, flail chest
Cardiac failure
Pulmonary embolism

Question 23

Miscellaneous causes of respiratory alkalosis

Answer 23

septicaemia
Mechanical hyperventilation
Hepatic failure
Heat exposure

Question 24

What is metabolic acidosis

• What is Bicarbonate like
• What do the lungs do

Answer 24

-Results from the body producing too much acid or the kidneys failing to excrete enough (H⁺)
-Initially this creates a decrease in bicarbonate as carbonic acid is produced to buffer the H⁺
The lungs compensate by hyperventilation and blowing off the CO₂

Question 25

What can be used to differentiate the causes of metabolic acidosis

Answer 25

Anion gap. If the gap is normal, bicarbonate is being lost either by GI loss e.g. diarrhoea or renal disease allowing loss High anion gap results from increased production of acids e.g. lactic acid, rate or diabetic ketoacidodis or large amounts of acid e.g. aspirin overdose

Question 26

High anion gap causes of metabolic acidosis

Answer 26

Lactic acidosis Ketoacidosis: e.g. diabetic, alcohol abuse, starvation Renal failure: acute and chronic Toxins e.g. methanol, salicylates

Question 27

Bicarbonate loss from GI tract (Normal anion gap) causes of metabolic acidosis

Answer 27

Diarrhoea Extra-renal pancreatic or small bowel drainage Drugs e.g. CaCl2, magnesium sulphate

Question 28

Renal acidosis (normal anion gap) causes of metabolic acidosis

Answer 28

Proximal renal tubular acidosis | Distal renal tubular acidosis

Question 29

Drug induced causes of metabolic acidosis (normal anion gap)

Answer 29

K+ sparing diuretics, spironolactone, trimethoprim, ACEi, NSAIDs

Question 30

Other causes of metabolic acidosis

Answer 30

Rapid saline infusion

Question 31

What is metabolic alkalosis What is bicarbonate like What is compensatory mechanism

Answer 31

- Results from increased bicarbonate due to either decreased H⁺ concentration (e.g. due to vomiting) or a direct increase in bicarbonate - Bicarbonate shift can occur from retention, an intracellular shift in H⁺ or by ingestion of large amounts of alkali (e.g. antacids). - The lungs compensate by slower breathing to retain more CO₂

Question 32

GI causes of metabolic alkalosis

Answer 32

Vomiting NG suction Villous adenoma

Question 33

Renal diuretic causes of metabolic alkalosis

Answer 33

Hypercalcaemia | Recovery from lactic acidosis or ketoacidosis

Question 34

Effective extracellular volume expansion of metabolic alkalosis

Answer 34

``` High renin: renal artery stenosis Accelerated hypertension Aldosteronism Cushing's Steroids ```

Question 35

How to assess respiratory failure

Answer 35

IS PaO2 <8? no: pt is not in resp failure yes: pt is in rest failure Is PaCO2 <6? Yes: pt is in T1RF (type 1 respiratory failure) NO: pt is in T2RF