ABG (Arterial Blood Gas)

Question 1

What are the normal ranges for pH, pCO2, HCO3- and pO2 in ABGs?

Answer 1

• pH 7.35-7.45 (indicates acidosis/alkalosis)
• pCO2 4.5-6.0 kPa (indicates whether acidosis/alkalosis is respiratory)
• HCO3- 22-26 mmol/litre (indicates whether is metabolic)
• pO2 is 11.3-12.6 kPa

Question 2

When can respiratory acidosis occur?

Answer 2

• Choking
• Pneumonia
• Asthma/COPD
• Respiratory Distress Syndrome
• RESPIRATORY DEPRESSION - Anasthesia and Overdose

Question 3

When can respiratory alkalosis occur?

Answer 3

• Hyperventilation
• Mechanical overventilation
• Raised intracranial pressure

Question 4

What are the symptoms of respiratory acidosis?

Answer 4

• Hypoventilation leading to hypoxia
• Reduced blood pressure
• Skin paling to cyanosis
• Headaches
• Hyperkalaemia
• Disorientation
• Muscle Weakness
• Rapid Shallow Breathing

Question 5

What are the symptoms of respiratory alkalosis?

Answer 5

• Hyperventilation
• Tachycardia
• Reduced to normal blood pressure
• Hypokalemia
• Seizures
• Heightened anxiety

Question 6

What can cause metabolic acidosis?

Answer 6

• Increased H+ production or ingestion (drugs, alcohol)
• Impaired H+ excretion/base conservation
• Loss of HCO3-
• Diabetic ketoacidosis
• Renal failure
• Diarrhoea

Question 7

What can cause metabolic alkalosis?

Answer 7

• Loss of H+ in vomit
• Alkali ingestion
• Potassium deficiency
• Diuretics
• Excessive NaHCO3/aldosterone

Question 8

What are the symptoms of metabolic acidosis?

Answer 8

• Headache
• Reduced BP
• Hyperkalemia
• Vasodilation causing warm,flushed skin
• Nausea
• Drowsiness
• Kussmaul Respirations

Question 9

What are the symptoms of metabolic alkalosis?

Answer 9

• Restlessness followed by lethargy
• Tachycardia
• Compensatory hypoventilation
• Hypokalemia
• Tremors
• Nausea

Question 10

Describe acid-base compensation.

Answer 10

• Response to acid-base imbalance
• With respiratory disorders, RENAL COMPENSATION. NO RESP. COMPENSATION
• With metabolic disorders, RESPIRATORY COMPENSATION.

Question 11

What are the differences in renal compensation in both respiratory acidosis and alkalosis?

Answer 11

• RESPIRATORY ACIDOSIS - Conserves HCO3- and excretes H+
• Reverse for respiratory alkalosis

Question 12

Describe the differences between metabolic acidosis and alkalosis.

Answer 12

• ACIDOSIS - Gain of H+. Loss of HCO3-. Reverse for alkalosis
• ALKALOSIS - Respiratory compensation by hypoventilation. Reverse for acidosis
• ACIDOSIS - Conserve HCO3-. Excrete H+. Reverse for alkalosis

Question 13

Describe renal compensation in respiratory acidosis.

Answer 13

• Increased pCO2 - so increased H+ (lower pH)
• Due to impaired ventilation
• Renal compensation can be partial or full
• Kidney excretes H+ and reabsorbs HCO3-
• Renal compensation occurs slowly

Question 14

Describe respiratory compensation in metabolic acidosis and alkalosis.

Answer 14

• ACIDOSIS - Decrease HCO3-. Increase H+. Hyperventilation occurs so reduced pCO2
• Opposite for alkalosis
• Compensation occurs quickly within hours

Question 15

What are the three types of compensation?

Answer 15

• FULL COMPENSATION - pH back to normal
• PARTIAL - pH out of range, pCO2/HCO3- out of range
• UNCOMPENSATED - pH out of range, pCO2/HCO3- normal

Question 16

Interpret the following ABG results.
- pH 7.36 (7.35-7.45)
- pCO2 7.7 (4.7-6.0 kPa)
- HCO3- 32 (21-29 mmol/litre)

Answer 16

• pH within range
• pCO2 out of range so suggests acidosis
• HCO3- out of range and basic so suggests renal compensation (increases pH by raising HCO3-).
• Fully compensated as pH back within range
• FULLY COMPENSATED RESPIRATORY ACIDOSIS

Question 17

Interpret the following ABG results:
* pH 7.33 (7.35 – 7.45)
* pCO2 7.7 (4.7 – 6.0 kPa)
* HCO3- 30 (21 – 29 mmol/L)

Answer 17

• pH out of range - suggests acidosis
• pCO2 is also out of range so suggests respiratory
• HCO3- out of range and raised suggesting renal compensation
• NOT FULL COMPENSATION - pH still out of range
• PARTIALLY COMPENSATED RESPIRATORY ACIDOSIS