ACID – BASE DISORDERS
[Case-based Discussion]
PREAMBLE
•
•
•
•
pH
Buffers of Body
Significance of [H+] ion conc.
pH of Body Fluids [plasma,
gastric juice, pancreatic juice]
NaHCO3 = HCO3 =
Salt
= 20
Buffer = H CO
PCO2 Weak Acid
1
2
3
= Metabolic = Dealt by Kidney = X =
Resp
Dealt by Lungs


X
Cases
A[ ? ]
PCO2 [HCO3]
[mmHg mmol/L
]
25
15
pH
H+
nmol/L
7.4
40
B
[Normal]
40
25
7.4
38
C[ ? ]
45
35
7.5
30
Parameters
A
B
PCO2
[mmHg
25
40
[HCO3]
mmol/L
15
25
pH
7.4
7.4
H+
nmol/L
40
38
METABOLIC ACIDOSIS
• Renal Failure
• Diabetic Acidosis
• NH4Cl Ingestion
• K+ injections
METABOLIC ALKALOSIS
• NaHCO3 Ingestion
• Prolonged Vomiting
• Too much intake of Antacids
• K+ Deficiency
RESPIRATORY ACIDOSIS
• Asphyxia:
– Drowning
– Strangulation
• Emphysema
RESPIRATORY ALKALOSIS
• Voluntary Hyperventilation
• Ascent to High Altitude
Unacclimatised
Patient A is a 57-year-old man who has been
depressed for some time. In a suicide attempt
early that morning he had swallowed the
entire contents of a bottle of aspirin
[salicylate]. His respiration is appreciably
increased and an arterial blood sample gives
the following results:
Q’s: 1. Which is the
type of Acid base
• pH = 7.30
upset?
• PCO2 = 4kPa
2. Is there any nature
[30mmHg]
of any compensatory
response?
• standard [HCO3- ]
3. Which is the likely
= 16mmolL-1
cause underlying the
acid base upset?
Answer Patient A
1. There is a metabolic acidosis (reduced
pH and low standard [HCO3- ])
2. There has been respiratory
compensation [increased respiration,
reduced PCO2 ].
3. The cause is gastrointestinal absorption
of salicylic acid.
Patient B is a 76-year-old woman who is
suffering from an acute exacerbation of
chronic obstructive airways disease
precipitated by a lower respiratory tract
infection. She appears centrally cyanosed
[Section 4.7]. Arterial blood analysis gives the
following results:
Q’s: 1. Which is the type
of Acid base upset?
• pH = 7.30
2. Is there any nature of
any compensatory
• PCO2 = 11kPa
response?
[83mmHg]
• standard [HCO3- ] 3. Which is the likely
cause underlying the
= 34mmolL-1
acid base upset?
Answer Patient B
1. There is a respiratory acidosis [reduced
pH and raised PCO2 ].
2. There is metabolic compensation (raised
standard [HCO3- ]).
3. The cause is reduced ventilation caused
by chronic obstructive airways disease.
Patient C is a 40-year-old man who is known
to be an insulin-dependent diabetic. He was
unconscious at admission and is found to be
extremely dehydrated. Arterial blood analysis
is as follows:
Q’s: 1. Which is the
type of Acid base
upset?
• pH = 7.10
2. Is there any nature of
• PCO2 = 3.3kPa
any compensatory
[25mmHg]
response?
• standard [HCO3- ]
3. Which is the likely
= 10mmolL-1
cause underlying the
acid base upset?
Answer Patient C
1. There is a metabolic acidosis [reduced
pH and reduced standard [HCO3- ].
2. There is respiratory compensation
[reduced PCO2 ].
3. The cause is likely to be diabetic
ketoacidosis caused by insulin
deficiency.
Patient D is a 16-year-old girl who is
complaining of breathlessness of sudden
onset. She appears agitated and is breathing
very rapidly but there is no other obvious
abnormality on examination. Arterial blood
analysis gives the following results:
• pH = 7.55
• PCO2 = 3.3kPa
[25mmHg]
• standard [HCO3- ]
= 24mmolL-1
Q’s: 1. Which is the
type of Acid base
upset?
2. Is there any nature of
any compensatory
response?
3. Which is the likely
cause underlying the
acid base upset?
Answer Patient D
1. There is a respiratory alkalosis [elevated
pH and reduced PCO2 ].
2. There is no metabolic compensation
(normal standard [HCO3- ]).
3. The cause is likely to be hysterical
overbreathing.