ABGs

Question 1

What is Arterial Blood Gases (ABGs)

Answer 1

A diagnostic test performed on blood taken from an artery

It gives information on the acid-base balance and the oxygenation of arterial blood

Changes in respiratory mechanics (disorders of ventilation) and changes in the respiratory system that impedes diffusion (disorders of oxygenation) results in a change in the levels oxygen and carbon dioxide in the blood

Changes to the renal system will also alter bicarbonate levels

Question 2

ABG procedure:

Answer 2

• Sample is obtained either through a catheter placed in an artery or by using a needle and syringe to puncture an artery
• Arterial stab: Radial (1st choice), Brachial, Femoral

Question 3

Complications of procedure:

Answer 3

1. Arteriospasm
2. Haematoma
3. Nerve damage
4. Fainting or vasovagal response
5. Others - ↓ BP, sweating

Question 4

Normal values for acid-base balance:

Answer 4

pH (Hydrogen ion) = 7.35 – 7.45
PaCO2 (partial pressure of carbon dioxide) = 4.7 – 6 kPa
HCO3 (amount of Bicarbonate ions) = 22 – 26 mmol-1

Question 5

Normal values for oxygenation

Answer 5

PaO2 (partial pressure of oxygen) = 10 – 14 kPa

Question 6

Acidosis is:

Answer 6

When the pH is below 7.35, the blood is said to be acidic:

• Respiratory acidosis = PaCO2 > 6Kpa in blood
• Metabolic acidosis = HCO3 < 22 mmol-1 in blood

Question 7

Alkalosis is:

Answer 7

When the pH is above 7.45, the blood is said to be alkalotic:

• Respiratory alkalosis = PaCO2 < 4.7Kpa in the blood
• Metabolic alkalosis = HCO3 > 26 mmol-1 in the blood

Question 8

Causes of respiratory acidosis:

Answer 8

Diseases causing Hypoventilation. Problems with:

• Respiratory centre: Depression of Hypercapnic and hypoxic ventilatory drives by drugs/GA/normal occurrence in sleep/CVA/TBI
• Medulla/spinal cord: Trauma(CVA/TBI)/neoplasm
• Innervation of respiratory muscles: Phrenic nerve paralysis
• Respiratory muscles weakness or fatigue: MND/GBS/SCI/COPD/Chest wall disorders
• Upper airway obstruction: Foreign body/OSA
• Excessive WOB: Added load on the mechanics of breathing (rib#, abdominal distension, chest wall disorders), Acute severe asthma/acute exacerbation of COPD
• Pulmonary disorders such as atelectasis, pneumonia, pneumothorax, pulmonary oedema, or COPD

Question 9

Respiratory acidosis occurs by:

Answer 9

the increase of CO2 which combines with water to produce carbonic acid. Carbonic acid dissociates into hydrogen ions and bicarbonate. The bicarbonate stored very quickly by the kidneys leaving the concentration of hydrogen ions thus lowering pH.

Question 10

Respiratory alkalosis is caused by:

Answer 10

Hyperventilation - removes carbon dioxide at a faster rate than normal, subsequently resulting in a decrease in hydrogen ions
Conditions include: Panic, anxiety, stress, hyperventilation syndrome, CNS dysfunction (CVA, TBI), caffeine, increased altitude, fever (increased RR)

Question 11

Metabolic acidosis occurs when:

Answer 11

either a deficit of bicarbonate in the bloodstream or an excess of acid (excluding increase of Carbonic acid as a result of increased CO2).

Question 12

Metabolic acidosis causes are:

Answer 12

Acid gain

• lactic acidosis
• ketoacidosis
• chronic renal failure

Bicarbonate loss

• chronic diarrhoea
• bike drainage

Question 13

Metabolic alkalosis occurs when:

Answer 13

excess of bicarbonate or a loss of acid within the body

Question 14

Metabolic alkalosis causes are:

Answer 14

Acid loss

• protracted vomiting
• potassium loss (diuretics)
• use of lactate in dialysis

Bicarbonate gain

• ingestion of antacids (GORD)
• excess production and use of bicarbonate

Question 15

A patient suffering respiratory acidosis will present with:

Answer 15

Bradycardia
Hypotension
Confusion
Somnolence (drowsiness)

Question 16

Treatments for respiratory acidosis include:

Answer 16

Increase RR
Reposition patient
Maintain a patent airway
Mechanical ventilation

Question 17

A patient with respiratory alkalosis will present with:

Answer 17

Tachycardia
Palpitations (heart is pounding or racing)
Anxiety
Seizures
Perspirations
Diaphoresis (excessive sweating)

Question 18

Treatments for respiratory alkalosis:

Answer 18

Decrease RR
Administer sedatives
Rebreather mask
Mechanical ventilation

Question 19

Hypoxaemia occurs when:

Answer 19

PaO2 < 10kPa; PaO2 < 8kPa = respiratory failure

Question 20

Normal oxygenation values on supported ventilation are:

Answer 20

% inspired concentration - 10, i.e. room air is 21% O2 so normal PaO2 is 21-10=11kPa

Question 21

Compensation is:

Answer 21

The process that returns pH to normal

Question 22

Compensation occurs depending on:

Answer 22

the body is in a acidotic or alkalotic state the body can address the changes in pH by increasing or decreasing ventilation or increasing or decreasing buffing compounds

Question 23

In a compensated condition values are:

Answer 23

• pH is normal but PaCO2 and HCO3 is abnormal

- pH normal range changes to normal value of 7.4. If pH > 7.4 condition is alkalosis if pH < 7.4 condition is acidosis.

Question 24

In a compensating condition values are:

Answer 24

• pH, PaCO2, HCO3 are abnormal.

- pH normal range changes to normal value of 7.4. If pH > 7.4 condition is alkalosis if pH < 7.4 condition is acidosis.