Acid-base balance

Question 1

Findings in vomitting

• Cl-
• K+
• eGFR
• Urine osmalality
• urea, cr
• water status and its consequences

Answer 1

Low chloride, potassium
- High bicarb= alkalosis

Volume depletion= dehydration

• low eGFR
• Increase cr and urea and proteins: HCT, albumin

High urine osmolality, low urine sodium due to electrolyte loss.

Question 2

Cause of metabolic alkalosis

Answer 2

H+ loss in GI

• Vomiting (low serum and urine Cl-)
• Gastric aspiration

H+ loss in kidneys

• Diuretics= HypoK+, increase urine Cl-
• Hyperaldosteronism, Cushing’s=

HCO3- excess
- Oral/ IV

GI loss of

Question 3

Causes of metabolic acidosis

• High anion gap (5)
• Normal anion gap (3)
• Others (1)

Answer 3

High gap

• DKA, lactic acidosis
• Salicylate overdose (aspirin)
• Kidney failure
• Methanol/ ethanol
• Paracetamol overdose

Normal gap

• GI loss: diarrhoea, fistula
• RTA
• Ureterostomy

IV NaCl

Question 4

Buffering systems for H+ in the body

• Extracellular
• Intracellular

Answer 4

Negatively charged proteins

Extracellular

• Albumin (Na)
• Bicarbonate (Na)

Intracellular

• Haemoglobin (K)
• Muscle protein (K)

Question 5

Respiratory acidosis causes

Answer 5

Decreased CNS depression

• Head trauma, opiates
• High CO2, low O2

Neuromuscular disease

Question 6

Respiratory alkalosis causes

Answer 6

Hyperventilation

• Psychological: panic attack, anxiety
• Asthma attack
• Hypoxia: anaemia, high altitude
• Low CO2

Question 7

Causes of hyperkalaemia

• Artefactual
• Intake
• Decreased loss
• Redistribution

Answer 7

Artefactual

• Haemolysis sample
• Delayed separation
• High plt, WBC

XS intake
- Oral, IV

Decreased loss

• Kidney: CKD, AKI
• Drugs: ACEi, ARB, spironolactone
• Adrenal failure, aldosterone insufficiency

Redistribution

• Severe tissue damage
• Metabolic acidosis

Question 8

Hypokalaemia causes

• intake
• Loss
• Redistribution

Answer 8

Intake
- Low oral intake

Loss

• Metabolic alkalosis/ RTA
• Cushing’s, hyperaldosteronism (Conn’s)
• GI loss
• Drugs: diuretics,

Redistribution
- Glucose and insulin
-

Question 9

Hypernatraemia causes

• Intake
• Loss
• Retention

Answer 9

Intake
- Fluids NaCl

Water Loss

• Low water intake
• dehydration causes: burns, diarrhoea, sweating, hyperventilation
• Diabetes insipidus: central/kidney

Na sodium

• Hyperaldosteronism
• Cushing’s
• IV Na

Question 10

Hyponatremia causes

• Loss
• Water retention
• artefactual

Answer 10

Loss

• Vomiting
• Kidneys
• diuretics
• Skin
• Addison’s

Water retention

• SIADH
• Cardiac/ kidney (nephrotic) / liver failure (ascites)
• AKI

XS water intake

• Pscyhogenic polydipsia
• IV fluids
• High beer intake

Artefactual

• High TG
• Glucose
• Drip arm

Question 11

Metabolic consequences of AKI

- H+, PO4, H+, Ca2+

Answer 11

Raised: kidneys cannot excrete

• K+
• H+

Low: Kidneys cannot absorb

• Phosphate
• Ca2+