Clinical acid base

Question 1

What is the state of the blood in terms of respiratory alkalosis? (think pH and CO2)

Answer 1

• alkalaemia (high pH ~7.6)

- low pCO2

Question 2

What are the potential causes of respiratory alkalosis?

Answer 2

• hyperventilation
• any cause of impaired oxygenation
• central cerebral stimulation: fever, pain, drugs, sepsis
• panic/anxiety

Question 3

What is the state of the blood in terms of respiratory acidosis? (think pH and CO2)

Answer 3

• acidaemia (low pH ~7.2)

- high pCO2

Question 4

What are the potential causes of respiratory acidosis?

Answer 4

• Reduced ventilation:
  1. airway disease
  2. neuromuscular or chest wall disease
  3. reduced respiratory drive: opiates or reduced consciousness

Question 5

How might a person with respiratory acidosis present?

Answer 5

• Breathless - high resp rate
• Drowsy
• Wheeze throughout chest
• Low O2 sats

Question 6

A patient with COPD presents to A&E after a fall, they are hypercapnic, normal (borderline) pO2, low O2 sats but are NOT acidotic. How should this respiratory status be managed?

Answer 6

They have type 2 respiratory failure and compensated respiratory acidosis
No need to rush treating this patient - continue to monitor ABGs but as they have no clinical symptoms they should be fine
–> norma for someone with COPD

*high HCO3- will show that it is being compensated for

Question 7

Patient presents with extreme breathlessness. Their respiratory status is as follows:
pH = 7.11		(7.35-7.45)
pCO2 = 2.8    (4.5-6 kPa)
pO2	 = 15	(10-13 kPa)
HCO3- = 12	(22-28mmol/L)

Why is this patient breathless?

Answer 7

• patient has metabolic acidosis
• trying to compensate b y lowering CO2
• breathing more to breathe out more CO2 = breathless

*typical in diabetic patients –> at this point you would need to test blood glucose levels

Question 8

What substances in the body can cause high anion gap metabolic acidosis?

Answer 8

1. Kentones:
   - DKA
   - Starvation or alcoholic ketoacidosis
2. Lactate:
   - tissue hypoxia/poor perfusion
   - altered cellular respiration
   - D-lactate (rare)
3. Titrable acid:
   - renal failure
4. Ingested acid:
   - ethylene glycol, methanol, salicylate

Question 9

State whether pH, HCO3- and CO2 are high or low in lactic acidosis/ketoacidosis?

Answer 9

all are usually low

same for renal failure acidosis and ingested acidosis

Question 10

What is normal anion gap metabolic acidosis also called? How does it usually arise?

Answer 10

• = hyperchloraemic metabolic acidosis
• usually due to bicarbonate loss
• -> kidney: renal tubular acidosis
• -> gut: diarrhoea
• compensatory rise in chloride to maintain electrical neutrality
• also seen in iatrogenic chloride administration

Question 11

What are the potential causes of renal tubular acidosis?

Answer 11

• diarrhoea
• external drainage of pancreas/biliary tree
• urinary diversion

Question 12

What are the acute/severe and chronic complications of acidosis?

Answer 12

Acute/severe:

• negative inotropic effects
• confusion
• Kussmaul’s breathing
• hyperkalaemia

Chronic:

• bone reabsorption, calciuria stones
• insulin resistance
• progressive renal impairment

Question 13

Why does HCO3- rise with chloride and potassium depletion?

Answer 13

Chloride depletion:

1. As H+ is lost:
   - diarrhoea
   - diuretics
   - mineralocorticoid excess
   - vomiting/NG drainage

Postassium depletion:

1. A H+ is lost:
   - vomiting/NG drainage
   - rare hypokalaemia disorders
2. As H+ moves into cells:
   - hypokalaemia