Sodium and Water Balance Flashcards
What are the key organs that control sodium and water balance
endocrine i.e. they secrete hormones
describe the relationship between water and sodium
Water follows sodium everywhere. they are inseparable.
What can happen to the patient when there is a decrease in extracellular volume
Increased use decrease in blood pressure decreased urine output Decreased consciousness Decreased skin turgor Dry mucous membranes Soft, sunken eyeballs
What controls sodium
Mineralocorticoid activity
What does mineralocorticoid activity refer to
sodium retention in exchange for potassium and / or hydrogen ions
What are some steroid which have mineralocorticoid activity
Aldosterone
Cortisol
What does too much mineralocorticoid activity mean
Sodium retention
What does too little mineralocorticoid activity mean
sodium loss
What does sodium loss mean
Water loss (water always follows sodium)
Where is ADH released
Posterior pituitary
What does ADH act on
Renal tubules
What does ADH cause
Water reabsorption
Antidiuretic effect
Describe the relationship between ADH and urine
Increased ADH results in concentrated urine
Decreased ADH results in dilute urine
What is the relationship between urine and ADH also known as
Urine osmolality
What does concentrated urine mean in terms of urine osmolality
It will be high
What does dilute urine mean in terms of urine osmolality
It will be low
If the sodium concentration is low, what 2 things can this mean
Too much water or too little sodium
IF the sodium concentration is high, what 2 things can this mean
Too little water or too much sodium
What 2 things can cause too much water
Decreased excretion e.g. SIAD or
Increased intake e.g. compulsive water drinking
What are some causes of having too little sodium
Increased sodium loss e.g. Kidneys (Addison’s), gut or skin
Decreased sodium intake (rare cause)
How can we have too little water
Increased water loss - diabetes insidious (problem with ADH secretion or action)
Decreased water intake (e.g. very young or elderly patients
Describe a typical presentation of a patient with Addison’s disease
malaise weight loss crave salty foods dizzy Postural hypotension tanned / hyper pigmentation in mouth and hand creased Low sodium
What happens in Addison’s disease
Adrenal insufficiency Cant make enough steroids not enoug mineralocorticoid activity can't retain enough sodium in the kidneys loses sodium from ECF Decreased ECF volume = dehydration
Why does excess pigmentation occur in Addison’s
excess ACTH from pituitary. ACTH molecule contains a sequence for MSH within it. ACTH is degraded by proteases eventually exposing MSH
What is the typical presentation of a patient with too much water
Often already in hospital with another illness
Routine biochemistry shows decreased Na
Volume status usually unremarkable
Patient usually has no symptoms specifically due to low sodium
Investigations for cause of sodium loss
Patient presumed to have too much water
innappropriate ADH secretion
What is SIAD
Syndrome of inappropriate antidiuresis
What are the 2 kinds of stimuli for ADH release
osmotic (in health)
or non osmotic (in disease)
What are some examples of non-osmotic stimuli
Hypovolaemia / hypotension
Pain
nausea/ vomiting
What causes water retention
ADH secreted in response to a non-osmotic stimulus
Describe the typical presentation of a patient with diabetes insipidus
Urine output is excessive
Fluid requirement is large
sodium levels are high and need correcting
Where is the most common place for problem resulting in diabetes insipidus
The pituitary or pituitary stalk
What happens if there is a problem with the pituitary or pituitary stalk
Patient can’t secrete ADH from posterior pituitary therefore none can work on the kidneys to cause water to be reabsorbed and therefore lots of water in los in the urine
Patient’s sodium is high
How can we treat diabetes insipidus
Give exogenous ADH to replace it
Desmopressin
How can we describe volume status
hypovolaemic
Euvolaemic
Hypervolaemic
What does hypovolaemia imply
Water deficit
Present when Na is low, then there must be an even bigger sodium deficit
What happens if there is hypovolaemia in hyponatraemia
Too little sodium
What is hypervolaemia most often seen as
oedema
What symptoms might a patient develop if they have seriously abnormal sodium
Altered consciousness
Confusion
Nausea
What should be measured if we suspect adrenal insufficiency
Cortisol and ACTH
What should be given immediately if we suspect adrenal insufficiency
Sodium replacement
What do we do for a patient with too much water
Fluid restrict
What do we do for a patient with too little sodium
give sodium
What do we do for a patient with too little water
Give water
What do we do for a patient with too much sodium
Get rid of excess sodium e.g. diuretics to induce natriuresis and then replace just the water
What do we assess if a patient has too little sodium or water or too much sodium or water
volume status
Na concentration
Routine investigations e.g. cortisol and osmolality
