Acid/base interpretation and disturbances

Question 1

What is an acid?

Answer 1

A molecule that donates a H+

Question 2

What is a base?

Answer 2

A molecule that accepts a H+

Question 3

What is a buffer?

Answer 3

A weak acid or base that helps protect against large changes in pH

Question 4

What is the primary extracellular buffer?

Answer 4

Bicarbonate

Question 5

What are the primary intracellular buffers?

Answer 5

• Phosphate
• Proteins
• Haemoglobin

Question 6

What role does bone play in acid-base balance?

Answer 6

Bone acts as a buffer

Question 7

What is the normal blood pH range?

Answer 7

7.35-7.45

Question 8

At what pH levels may life become incompatible?

Answer 8

< 6.9 or > 7.65

Question 9

What are the significant concerns for pH levels?

Answer 9

< 7.2 or > 7.5

Question 10

What can severe acidosis cause?

Answer 10

• Cardiac arrhythmias
• Vasodilation leading to hypotension
• Decreased cardiac contractility

Question 11

List the four basic types of acid-base disturbances.

Answer 11

• Metabolic acidosis
• Metabolic alkalosis
• Respiratory acidosis
• Respiratory alkalosis

Question 12

What is metabolic acidosis?

Answer 12

A primary gain in acid or loss of base

Question 13

What is metabolic alkalosis?

Answer 13

A primary gain in base or loss of acid

Question 14

What causes respiratory acidosis?

Answer 14

Retention of CO2 due to inadequate alveolar ventilation

Question 15

What causes respiratory alkalosis?

Answer 15

Removal of more CO2 by ventilation than is produced

Question 16

What is the normal range for arterial PO2 (mm Hg)?

Answer 16

90-100

Question 17

What is the normal range for arterial PCO2 (mm Hg)?

Answer 17

35-45

Question 18

What is the normal base excess (BE) value?

Answer 18

-4 to +4 mmol/L

Question 19

What is base excess (BE)?

Answer 19

A calculated value reflecting the metabolic contribution to acid-base balance
More reliable reflection of metabolic component than HCO3- as it can also be effected by CO2

Question 20

What is a simple approach to acid-base analysis?

Answer 20

• Evaluate the pH
• Evaluate the respiratory component
• Evaluate the metabolic component
• Define the primary process
• Assess compensation
• Check oxygenation

Question 21

What is compensation in acid-base disorders?

Answer 21

Homeostatic mechanisms attempting to return pH closer to normal

Question 22

How quickly can the lungs compensate for acid-base disturbances?

Answer 22

Within minutes

Question 23

How long does it take for the kidneys to compensate?

Answer 23

Starts after a few hours, maximum compensation in 4-5 days

Question 24

What does the absence of expected compensation indicate?

Answer 24

An additional acid-base disturbance may be present

Question 25

What characterizes respiratory acidosis?

Answer 25

Decreased blood pH and increased PCO2 due to hypoventilation

Question 26

What are common causes of respiratory acidosis?

Answer 26

* Upper airway obstruction * Diseases of the brainstem and brain * Cervical spinal cord disease * Chest wall disease * Depression of the respiratory centre * Neuromuscular disease * Restrictive disease

Question 27

What is the treatment approach for respiratory acidosis?

Answer 27

Correct the underlying problem, consider supplemental oxygen, and potentially emergency intubation

Question 28

What characterizes respiratory alkalosis?

Answer 28

Increased blood pH and decreased PCO2 due to hyperventilation

Question 29

What are common causes of respiratory alkalosis?

Answer 29

* Fear, pain, anxiety * Drugs * Decrease in arterial blood oxygen content * Neurological disease

Question 30

What are common causes of metabolic acidosis?

Answer 30

* Addition of acid to the body * Loss of base from the body

Question 31

What is the anion gap (AG)?

Answer 31

The difference in the sum of commonly measured cations and anions

Question 32

What is the formula for calculating the anion gap?

Answer 32

AG = (Na+ + K+) - (Cl- + HCO3-)

Question 33

What does a normal anion gap indicate?

Answer 33

Electroneutrality is maintained by unmeasured anions and cations

Question 34

What conditions are associated with an increased anion gap?

Answer 34

* Metabolic acidosis * Ethylene glycol poisoning * Ketoacidosis * Uraemia * Lactic acidosis | DUEL

Question 35

When is sodium bicarbonate therapy considered?

Answer 35

In cases of refractory severe metabolic acidosis or cardiovascular compromise (hypotension with vasodilattion and arrthymias)

Question 36

What are potential side effects of sodium bicarbonate therapy?

Answer 36

* Respiratory acidosis * Alkalaemia * Hypernatremia * Hyperosmolarity * Paradoxical CNS acidosis * Hypokalaemia * Ionised hypocalcaemia

Question 37

What are the potential effects of sodium bicarbonate therapy?

Answer 37

Effects include: * Hypernatremia ± volume overload * Hyperosmolarity * Paradoxical CNS acidosis * Hypokalaemia * Ionised hypocalcaemia ## Footnote not to be used in patients with hypercapnia or hypernatraemia

Question 38

How is the bicarbonate deficit calculated?

Answer 38

Bicarbonate deficit (mls) = BE x body weight (kg) x 0.3 ## Footnote BE stands for Base Excess.

Question 39

What is the typical dose range for sodium bicarbonate administration?

Answer 39

Typically, ¼ to 1/3 of the calculated bicarbonate deficit is given. ## Footnote This is often diluted in 5% dextrose or water for injection.

Question 40

What monitoring should occur when administering sodium bicarbonate?

Answer 40

Careful monitoring of: * pH * HCO3- * BE * CO2 ## Footnote Monitoring helps to avoid complications.

Question 41

What causes metabolic alkalosis?

Answer 41

Causes include: * Decrease in acid load from the body * Addition of base to the body * Compensatory response to chronic respiratory acidosis ## Footnote esecially gi loss from vomit or renal loss from loop dieuretics

Question 42

What gastrointestinal losses can lead to metabolic alkalosis?

Answer 42

Gastrointestinal losses can include: * H+ * K+ * Cl- losses in vomit ## Footnote Typically associated with gastrointestinal obstruction.

Question 43

What is the treatment approach for metabolic alkalosis?

Answer 43

Treatment should aim at correcting the underlying cause. ## Footnote This may include addressing gastrointestinal obstructions or adjusting diuretic therapy.

Question 44

What fluid therapy is preferred for patients with GI losses of Cl-?

Answer 44

0.9% NaCl because of its high Cl- concentration, often with KCl supplementation. ## Footnote This helps correct alkalosis more rapidly.