ABGs, electrolytes and LFTs Flashcards
General rule for ABGs
R espiratory => high pH, low CO2
O pposite => low pH, high CO2
M etabolic => high pH, high CO2
E qual => low pH, low CO2
high pH => low [H+] => alkalosis
low pH => high [H+] => acidosis
What would you expect to see on the ABG for the following conditions and why?
a) Opiate usage
b) Anxiety attack
c) COPD
d) Norovirus
e) Atelectasis
f) Diarrhoea
g) Renal tubular acidosis
a) CO2 retention therefore respiratory acidosis
b) Hyperventilation thus blowing off CO2 therefore respiratory alkalosis
c) CO2 retention therefore respiratory acidosis
d) Vomiting thus loss of [H+] therefore metabolic alkalosis
e) One part of the lung not working to expel CO2 therefore respiratory acidosis
f) Loss of bicarbonate therefore metabolic acidosis
g) Abnormal anion gap therefore metabolic acidosis
What does a ‘wide anion gap’ lead to and what are the possible causes?
Metabolic acidosis
- 4 < AG > 12
- [cations] - [anions] = AG
- causes below increase H+
K etones
U raemia
L actate
T oxins
- paracetamol, aspirin, anti-freeze, isoniazid (TB Abx)
How does Na+ homeostasis work?
ADH release triggered by:
1. decreased blood volume via baroreceptors in carotid sinus
2. decreased [Na+] via chemoreceptors at hypothalamus
ADH leads to reabsorption of water at the collecting duct via AQPII
Thus ADH compensation would drive hyponatraemia
What action does aldosterone and natriuetic peptides have on [Na+]?
None
= aldosterone will increase Na+ reabsorption (as well as K+ secretion) but this leads to water following across with Na+ so [Na+] stays the same
= natriuetic peptides increases GFR and stops RAAS thus there is reduced water retention and increased Na+ loss so [Na+] stays the same
Mx for hyponatraemia
Saline solution
- do not infuse too quickly as this leads to central pontine myelinolysis
- pons sensitive to Na+ changes and contains cardiorespiratory centre so potentially fatal if not infused at slow rate
What are possible causes of hyponatraemia?
Hypovolaemic pt
=> any water loss
=> D&V, diuretics
Euvolaemic pt
=> endocrine reasons
=> SIADH, adrenal insufficiency, hypothyroidism (decreased cardiac output triggers BNP + RAAS so maintains volume status but lose Na+)
Hypervolaemic pt
=> heart failure, liver failure, kidney failure
=> heart reduced CO, liver and kidney increased NO which leads to vasodilation
What causes hypernatraemia?
Much rarer
Due to uncompensated water loss, diabetes insipidus and hyperaldosternoism
- think of pts in ICU not drinking with renal failure or pt in nursing home with dementia
What do the results of these LFTs suggest?
a) isolated raised bilirubin
b) AST>2x ALT
c) ALP + GGT raised
d) ALT + AST in 1000s
e) aFP raised
f) hypoalbuminaemia
a) haemolytic anaemia, Gilbert’s
b) alcoholic liver disease
c) biliary pathology
d) hepatitis: toxic, ischamic, viral
e) hepatocellular carcinoma
f) liver failure, nephrotic syndrome
What should you suspect in these pts? (context of liver)
a) Young, healthy, no sex hx
b) Medically unwell, features of anaemia
c) Confusion, low GCS, alcohol/IVDU
d) Pronounced sex hx, IVDU
e) Known chronic alcoholic (LFTs pls)
a) Gilbert’s
b) haemolytic anaemia
c) alcoholic liver disease
d) viral hepatitis
e) increased bilirubin, prolonged PT, hypoalbuminaemia
An ABG was taken on room air.
pH = 7.54
PaO2 = 13
PaCO2 = 2.4
HCO3 = 18
BE = 6.6
What is the diagnosis?
1. Metabolic acidosis
2. Respiratory alkalosis
3. Type 2 respiratory failure
4. Metabolic alkalosis
- Respiratory alkalosis
An ABG was taken on air.
pH = 7.36
PaO2 = 11.1
PaCO2 = 2.2
HCO3 = 16
What is the abnormality?
1. Uncompensated Metabolic Acidosis
2. Respiratory alkalosis with full metabolic compensation
3. Metabolic acidosis with full respiratory compensation
4. Uncompensated Respiratory Acidosis
- Metabolic acidosis with full respiratory compensation
An elderly female is admitted unwell with vomiting and low blood pressure.
U+Es are taken which show the following:
Na: 136 (135 – 145)
K: 6.5 (3.5 – 5.0)
Urea: 22 (2.5 – 6.7)
Creatinine: 617 (80 – 120)
What is the most likely cause?
1. Addison’s disease
2. Rhabdomyolysis
3. Renal impairment
4. Lab error
- Renal impairment
A 74 year old female is admitted with pruritis, discolouration of the skin
and increasing lethargy. On examination she is cachexic. LFTs show the following:
Total bilirubin: 80
AST: 39
ALT: 40
ALP: 155
GGT: 178
Albumin: 38
What is the most likely cause?
1. Viral hepatitis
2. Alcoholic liver disease
3. Bile duct gallstones
4. Carcinoma of the head of the pancreas
- Carcinoma of the head of the pancreas
An 18 year old male presents with jaundice to A+E. He has just returned
from gap year trip to Thailand. Has had fevers, malaise and diarrhoea
for the last week. Admitted to getting a tattoo on the trip. LFTs show the following:
Total bilirubin: 170
AST: 2300
ALT: 2500
ALP: 200
GGT: 35
Albumin: 40
What is the most likely cause?
1. Paracetamol overdose
2. Viral hepatitis
3. Gilberts
4. Alcoholic liver disease
- Viral hepatitis
