Lecture 5: Acid-base disturbances in poisoning

Question 1

What is the normal plasma pH

Answer 1

7.36 - 7.46

Question 2

What organs regulate acid-base disturbances

Answer 2

Kidneys and lungs

Question 3

How is acid-base balance maintained

Answer 3

removal of acids accumulated from normal metabolism

Question 4

What is used as a buffer in ECF to neutralise metabolically produced acids

Answer 4

Bicarbonate ions

Question 5

How is acid lost from the body

Answer 5

• exhalation of CO2
• renal tubular H+ secretion

Question 6

What causes disturbances in acid-base balance

Answer 6

Altered respiratory or metabolic processes

Question 7

Metabolic acidosis effect

Answer 7

• Decreased pH
• Decreased ECF [HCO3-]

Question 8

Metabolic alkalosis effect

Answer 8

• Increased pH
• Increased ECF [HCO3-]

Question 9

Respiratory acidosis effect

Answer 9

• Decreased pH
• Increased pCO2

Question 10

Respiratory alkalosis effect

Answer 10

• Increased pH
• Decreased pCO2

Question 11

What are the measurements seen in Metabolic acidosis

Answer 11

• pH <7.36 (below physiological pH)
• Plasma [HCO3-] <21mmol/L
• low pCO2

Question 12

Why is low pCO2 seen in metabolic acidosis

Answer 12

Patients are excessively breathing to remove XS CO2
(compensatory hyperventilation)

Question 13

Anion gap equation

Answer 13

Anion gap = Sum measured cations - Sum measured anions

Question 14

What does the anion gap show

Answer 14

Lactate and anions in plasma that are not normally measured

Question 15

Why does the anion gap increase in metabolic acidosis

Answer 15

Due to a loss of bicarbonate, not accumulation of acid

Question 16

What is renal tubular acidosis

Answer 16

urinary loss of bicarbonate when renal tubules are damaged

Question 17

How is renal tubular acidosis compensated for by the body

Answer 17

retention of chloride ions to retain tubular electroneutrality

Question 18

Two types of lactic acidosis

Answer 18

Type A - hypoxic
Type B - non-hypoxic

Question 19

How does lactic acidosis occur

Answer 19

renal failure due to retention of acid from protein metabolism as kidneys cannot clear them

Question 20

When does Type A lactic acidosis occur

Answer 20

When hypoxia causes impaired oxidative metabolism of pyruvate

In absence of O2, lactate converted to pyruvate to allow anaerobic respiration

Question 21

What are the causes of Type A lactic acidosis (3)

Answer 21

• Cardiorespiratory depression
• Repeated convulsions
• Impaired O2-carrying capacity of blood

Question 22

What causes Type B lactic acidosis (2)

Answer 22

• When normal oxidative metabolism of pyruvate cannot occur due to inhibition of mitochondrial respiratory chain
• Liver failure so lactate cannot be processed leading to accumulation

Question 23

What measurements are seen in Metabolic alkalosis

Answer 23

• pH >7.46
• plasma bicarbonate conc. >35 mmol/L

Question 24

How does metabolic alkalosis occur in poisoning

Answer 24

occurs due to severe volume depletion and arises as part of the renal compensatory mechanism

Question 25

What measurements are seen in respiratory acidosis

Answer 25

• pH <7.36
• pCO2 > 6KPa = retention of CO2
• normal plasma bicarbonate

Question 26

What is the normal plasma bicarbonate range

Answer 26

21 - 25 mmol/L

Question 27

What normally causes respiratory acidosis

Answer 27

hypoventilation due to poisoning with drug that reduces CNS drive of ventilation

Question 28

What measurements are seen in respiratory alkalosis

Answer 28

• pH >7.46
• pCO2 < 4.5 KPa = low CO2
• normal plasma bicarbonate

Question 29

What causes respiratory alkalosis

Answer 29

Poisoning with drugs that stimulate CNS respiratory centre

Question 30

What two conditions show in aspirin poisoning on an ABG and why

Answer 30

Respiratory alkalosis = stimulation of respiratory centre
Metabolic acidosis = accumulation of salicylic acid