Chem Path Flashcards
What is the most common electrolyte abnormality in hospital patients? How common is it?
Hyponatraemia. It is found in 1 in 4 patients.
What is the underlying pathology of hyponatraemia?
It is due to an excess of ADH, causing an excess of water in the body.
What is the normal range for plasma sodium?
135-145mmol/L
What is the first step is assessing a patient with hyponatraemia?
Assessing the hydration status
What is the best way to assess the hydration status of a patient?
Clinical picture, and the urine sodium
What are the symptoms of hyponatraemia, in order of earliest to latest?
- Nausea and vomiting
- Confusion
- Seizures
- Coma and death
What is involved in the clinical assessment of a patient’s hydration status?
- Heart rate and blood pressure
- Skin turgor
- Mucosal surfaces
- Urine output
What would you find on clinical assessment of a hypovolaemic patient?
- Dry mucosal surfaces
- Reduced skin turgor
- Reduced urine output
- Reduced blood pressure
What would you find on clinical assessment of a hypervolaemic patient?
- Raised JVP
- Peripheral and pulmonary oedema
In hypervolaemic hyponatraemia, what are the main causes? How do these cause a low sodium?
‘The Three Failures’
- Heart failure (reduced BP, increased ADH)
- Liver failure (increased NO, reduced BP, increased ADH)
- Renal failure (not excreting the water)
In hypovolaemic hyponatraemia, what are the main causes?
GI:
- Diarrhoea and vomiting
Renal:
- Diuretics
- Salt losing nephropathy
What are the two main stimuli to ADH secretion?
- Reduced blood pressure
- Increased serum osmolality
How should you treat hypervolaemic hyponatraemia?
- Fluid restriction
- Correct the cause
In euvolaemic hyponatraemia, what are the main causes? How do these cause a hyponatraemia?
- Hypothyroidism (reduced BP, increased ADH)
- Adrenal insufficiency (reduced cortisol, reduced water loss)
- SIADH (too much ADH)
How should you treat hypovolaemic hyponatraemia?
- Restore fluid with 5% dextrose
How should you treat euvolaemic hyponatraemia?
- Investigate causes with TFTs, synACTHen test and urine/plasma osmolality
In a patient with SIADH, what osmolalities would you fin din the serum/urine?
- Reduced serum osmolality
- Raised urine osmolality
In fluid restricting a patient, how much total fluid should be taken in?
750ml a day (less than 1L)
When is the use of hypertonic saline (2.7%) indicated?
When the hyponatraemia is causing either:
- A reduced GCS
- Seizures
Seek expert help before administering
When correcting hyponatraemia, what rate should the sodium be corrected at? What is at risk at higher rates?
No more than 8-10mmol/L per hour. At higher rates, you risk a central demyelination.
If it has been corrected too quickly, bring the sodium bac down again.
How can SIADH be diagnosed?
As a diagnosis of exclusion, endocrine tests must be performed, and the serum and urine osmolalities must be low and high respectively.
What are the causes of SIADH?
- Any cerebral pathology (malignancy, infection)
- Any pulmonary pathology (malignancy, infection)
- Drugs (opiates, SSRIs)
How should you treat SIADH?
- Fluid restrict
- Treat the cause
There are some medial therapies with demeclocycline and tolvaptan, but these are rarely used.
In hypovolaemic hypernatraemia, what are the most common causes?
GI:
- Diarrhoea and vomiting
Skin:
- Excessive sweating, burns
Renal:
- Loop diuretics
In hypervolaemic hypernatraemia, what are the most common causes?
- Mineralocorticoid excess (Conn’s syndrome)
- Use of hypertonic saline
In diabetes insipidus, what are the initial investigations you should perform and why?
- Blood glucose (exclude mellitus)
- Blood potassium and calcium (exclude other electrolyte imbalances
- Assess urine to plasma osmolality
Once diabetes insipidus is suspected, what investigation will determine the type and, therefore, treatment? How does this work?
The water deprivation test. After 8 hours of no fluid, assess the change in urine concentration:
- Normal: >600 change
- Primary polydipsia: less than this
- Central: will increase with desmopressin
- Nephrogenic: will not change with desmopressin
How do you treat diabetes insipidus?
- Treat the hypovolaemia and hypernatraemia with 5% dextrose
What is the normal range of potassium?
3.5 - 5.5 mmol/L
What two hormones control potassium levels?
- Angiotensin II
- Aldosterone
What are the main causes of hyperkalaemia?
- Renal failure
- Drugs (ACEi, ARB, spironolactone)
- Low aldosterone
- Increased release (rhabdomyolysis, acidosis)
How do you treat hyperkalaemia?
- 10mls of 10% calcium gluconate (to stabilise the myocardium)
- 100mls of 20% dextrose
- 10mls of insulin (K+ absorption into cells)
- Nebulised salbutamol
- Treat the underlying cause
In a patient with high sodium and low potassium, what does this suggest?
Conn’s syndrome (hyperactive adrenals)
In a patient with low sodium and high potassium, what does this suggest?
Addison’s disease (inactive adrenals)
How does acidosis cause hyperkalaemia?
The intake of H+ ions to correct the pH, will push K+ ions out of the cell.
What are the main causes of hypokalaemia?
- GI loss (diarrhoea and vomiting)
- Renal loss (hyperaldosterism, excess cortisol, diuretics, Bartter)
- Redistribution into the cells (alkalosis)
What is Bartter’s syndrome?
A disease which causes malformed Na+/K+/Cl channels, raising distal nephron Na+ levels.
Describe each type of renal tubular necrosis
Type I:
- Distal failure of H+ excretion, causing acidosis and hypokalaemia
Type II:
- Proximal failure to reabsorb bicarbonate, causing acidosis and hypokalaemia
Type III:
- Rare and rarely relevant
Type IV:
- Aldosterone deficiency or resistance, causing acidosis and hyperkalaemia
How do you manage a patient with hypokalaemia?
If potassium is >3.0:
- Oral SandoK tablets
- Monitor serum potassium levels
If potassium <3.0
- IV potassium chloride
- Maximum rate of 10mmol/L per hour (can cause arrhythmias if higher)
For any potassium imbalance, treat the underlying cause.
What is the normal range for blood pH?
Between 7.35 and 7.46
What is the normal CO2 level in the blood?
4.7 - 6 kPa
What is the normal bicarbonate level in the blood?
22 - 30 mmol/L
What is the normal O2 level in the blood?
10 - 13 kPa
In metabolic acidosis what will you expect the parameters of a blood gas to be? What can cause this?
- pH: reduced
- CO2: normal or reduced (depends on compensation)
- Bicarbonate: reduced
This can be caused by excess lactate in DKA, or renal tubular acidosis (decreased H+ excretion) or an intestinal fistula (bicarbonate loss).
In respiratory acidosis what will you expect the parameters of a blood gas to be? What can cause this?
- pH: reduced
- CO2: reduced
- Bicarbonate: normal or increased (depends on compensation)
This can be caused by lung injury (pneumonia, COPD) or decreased ventilation (morphine overdose)
In metabolic alkalosis what will you expect the parameters of a blood gas to be? What can cause this?
- pH: increased
- CO2: normal or increased (depends on compensation)
- Bicarbonate: increased
This can be caused by pyloric stenosis, hypokalaemia or an ingestion of bicarbonate.
In respiratory alkalosis what will you expect the parameters of a blood gas to be? What can cause this?
- pH: increased
- CO2: reduced
- Bicarbonate: normal or reduced (depends on compensation)
This can be caused by mechanical ventilation or an anxiety/panic attack
What is the anion gap? What is it usually contributed to by, and what is the usual range?
It is the gap between the total cation and anion charge. It is usually accounted for by albumin, with a normal range of 14 - 18 mmol/L.
What can cause an elevated anion gap?
KULP:
- Ketoacidosis (DKA, alcoholism, starvation)
- Uraemia (renal failure)
- Lactic acidosis
- Toxins (ethylene glycol, methanol, paraldehyde, salicylate)
What is the osmolar gap? What is the normal range?
The difference between the measures osmolality and the calculated osmolarity. It is normally less than 10.
What can cause an elevated osmolar gap?
This is indirect evidence of an abnormal solute in the blood. It can be used to differentiate causes of an elevated anion gap.
What is involved in the normal function of the liver?
- Intermediary metabolism
- Xenobiotic metabolism
- Protein synthesis
- Bile synthesis
- Reticulo-endothelial function (immune modulating)
What is intermediary metabolism?
It is an enzyme controlled process that extracts energy and uses it to construct cellular components.
In liver failure, why can a patient become encephalopathic?
There is increased ammonia, which is encephalotoxic
What enzyme is involved in many of the xenobiotic functions of the liver?
P450
What is the function of bile?
- Excretion
- Micelle formation
- Digestion
In a liver function test, what is measured?
Liver cell damage:
- AST and ALT
- AlkPhos
- GGT
- Bilirubin
- AFP
Liver function:
- Clotting factors
- Albumin
- Glucose
What is the function of the aminotransferases?
They are involved in amino acid metabolism
Where can they be found? What is the normal level? When can they be raised?
They are predominately found in hepatocytes, but can be found in the muscle, brain and kidneys.
The normal level is less than 40iu/L.
They can be raised in hepatocellular death.
How can the relative levels of the aminotransferases specify the cause of hepatocellular death?
If AST:ALT is >2 this is likely alcoholic.
If it above this with no alcohol history, it is likely cirrhosis.
If AST:ALT is <1.1, it is likely viral damage.
What is the function of alkaline phosphatase?
This is largely unknown.
What is the normal level of ALP? When can it be raised?
It is normally between 30 and 150 iu/L.
It can be raised in cholestasis and bone disease. It is also raised in pregnancy and malignancy.
What is gamma-glutamyl transferase involved in?
It is involved in amino acid metabolism.
What is the normal level of GGT? When can it be raised?
It is normally between 30 and 150 iu/L.
It is raised in chornic alcohol use. It can also be raised in bile duct disease and metastasis.
What is the role of albumin?
It is primarily involved in controlling the oncotic pressure of blood.
When can albumin levels be low?
- Low production (liver disease)
- Loss of albumin (renal or GI loss)
- Sepsis (capillary leakage)
Why can clotting factors be a better marker than albumin for acute disease?
The half life of clotting factors is much shorter (albumin is 20 days, clotting factors are mere hours) so any change can be detected far closer to a change in pathology.
What is the role of alfa fetoprotein?
It is primarily involved in foetal immune modulation. In adults, its purpose in unclear.
When can alfa fetoprotein be raised?
It is raised in hepatocellular carcinoma, and is a good cancer marker for testicular cancer as well. It is also raised in pregnancy.
In raised bilirubin, what is the best way to consider the pathology involved?
Consider the rest of the liver function test:
Normal hepatic enzymes:
- Haemolysis
- Gilbert’s syndrome
Raised ALP:
- Obstructive jaundice (gall stones, pregnancy)
- Non-obstructive jaundice (PBC, PSC)
Raised AST/ALT:
- Acute or chronic hepatocellular damage
What is the significance of pale stools and dark urine when considering a raised bilirubin?
This shows the jaundice is obstructive, giving this clinical picture.
What is the ‘liver panel’?
This are further tests that can be made when the liver function test is unclear. It involved:
- Hepatitis screen
- CK, TFTs
- Alpha-1-antitrypsin
- Immunoglobulins
In a patient with a raised ALT, what must be considered when discussing management?
You must look at the other markers in the LFTs.
If isolated raised ALT:
- Discuss lifestyle changes
If symptomatic/unisolated raised ALT:
- Conduct liver function tests and liver screen to determine cause
- Treat the cause
