U&Es Flashcards
On average, what is the normal concentration of Na+ found in plasma?
142mmol/L
What is the normal potassium concentration in the body?
4mmol/L
What is the average concentration of bicarbonate in the body?
26-30mmol/L
What % of a men and women respectively is made up of water?
60% men
55% women
Of the water in the body, what % is extracellular and what % is intracellular?
65% intracellular
35% extracellular
What is oedema?
An increase in interstitial fluid
What are the causes of oedema? (4)
- Increased hydrostatic pressure e.g. sodium and water retention in cardiac failure
- Reduced oncotic pressure e.g. as a result of nephrotic syndrome with hypoalbuminaemia
- Obstruction to lymphatic flow
- Increased permeability of the blood vessel wall e.g. at a site of inflammation, cytokines lead to an increase in vascular permeability
Which electrolyte is primarily involved in the maintenance of effective circulating volume?
Sodium
Where are the two types of volume receptors found? (2)
- Extrarenal : in the large vessels near the heart
- Intrarenal : in the afferent renal arteriole, which controls the renin-angiotensin system via the juxtaglomerular apparatus
What is produced by the atria in the heart that responds to a rise in blood pressure?
Atrial natriuretic peptide (ANP) –> leads to an increase in sodium excretion
How does extracellular volume increase?
Either as a result of increased sodium and water absorption, or due to impaired excretion by the kidney.
What are the pathological causes of increase extracellular volume?
- Cardiac failure (reduced cardiac output and impaired perfusion of the volume receptors)
- Nephrotic syndrome
- Cirrhosis
- Sodium retention (drug induced e.g. NSAIDs)
What are the signs of interstitial volume overload? (4)
- Ankle oedema
- Pulmonary oedema
- Pleural effusion
- Ascites
What are the signs of intravascular volume overload? (3)
- Raised JVP
- Cardiomegaly
- Raised arterial pressure
What is the main form of treatment for increased extracellular volume?
Diuretics
What is the cause of volume depletion? (3)
- Haemorrhage (external or internal)
- Plasma loss in burns
- Loss of salt and water from the kidneys, GI tract or skin
What are the symptoms/signs of volume depletion?
- Thirst
- Nausea
- Postural dizziness/hypotension
- Peripheral vasoconstriction
- Tachycardia
In severe burns or peritonitis, what needs to be replaced primarily?
Plasma
What is hyponatraemia in mmol/L?
Serum sodium <135mmol/L
What are the causes of hyponatraemia?
- Relative water excess (most common cause)
2. Salt loss in excess of water e.g. diarrhoea
How is it possible to determine if the hyponatraemia is a result of hypovolaemic hyponatraemia or just fluid loss as opposed to salt loss?
Hypovolaemic hyponatraemia would should a low urinary sodium level, as the kidneys would be trying to retain/conserve NaCl, whereas if there is true salt loss, the urinary levels of sodium would be elevated.
What is the cause of hyponatraemia resulting from water excess in the majority of patients?
An overgenerous infusion of 5% glucose into post-operative patients
In patients with which diseases is hyponatraemia a common occurrence? (hint: same as oedema patients) (3)
- Cardiac failure
- Nephrotic syndrome
- Cirrhosis
What is the cause of hyponatraemia in patients with no evidence of fluid excess/oedema? (3)
- Syndrome of inappropriate ADH secretion (SIADH)
- Addison’s disease
- Hypothyroidism
What is the treatment for hyponatraemia? (4)
- Treat the underlying cause
- Restrict water intake to 500-1000mL/day
- Correct magnesium and potassium deficiency
- If experiencing fits/coma:
- hypertonic saline 3% (513mmol/L) at a rate of 1- 2mL/kg/h
- furosemide
Why is important not to correct sodium concentration too rapidly?
It can lead to severe neurological syndrome - central pontine myelinolysis
How is hypernatraemia quantified?
Serum sodium > 145mmol/L
What is the cause of hypernatraemia?
Almost always result of reduced water intake
What are the symptoms/signs of hypernatraemia? (3)
- Confusion
- Nausea and vomiting
- Fever
Is potassium predominantly intra or extra cellular?
Intracellular (only 2% extracellular)
