SIADH

Question 1

SIADH stands for

Answer 1

syndrome of inappropriate anti-diuretic hormone secretion

Question 2

definition

Answer 2

hyponatraemia and hypo-osmolality caused by the inappropriate secretion of anti-diuretic hormone (despite normal or increased plasma volume)

Question 3

anti-diuretic hormone acts on the

Answer 3

collecting ducts which resorb water back into the blood

Question 4

the cells of the collecting ducts contains

Answer 4

proteins called aqaupaorins which allows water to pass through

Question 5

the more ADH being secreted

Answer 5

the more aquaporins become available to facilitate water resorption

Question 6

if ADH is continuously released even when plasma osmolality is normal

Answer 6

it causes increased water resorption which dilutes the sodium present in the blood

Question 7

the extra fluid also

Answer 7

increases the blood volume which inhibits the RAAS system resulting in no production of aldosterone

Question 8

less aldosterone means

Answer 8

sodium in the blood gets excreted in the urine, water follow sodium which normalises the plasma volume but causes reduced sodium plasma osmolality causes hyponatraemia

Question 9

causes of SIADH

Answer 9

• brain damage
• ectopic ADH production
• infection
• drugs

Question 10

brain damage causing SIADH

Answer 10

strokes, meningitis, subarachnoid haemorrhage

Question 11

drugs causing SIADH

Answer 11

carbamepazine (anti-epileptic), SSRI’s (citalopram), chemotherapeutic agents (vincristine, vinblastine, cyclophosphamide)

Question 12

Ectopic ADH production most common caused by

Answer 12

small cell lung cancer

Question 13

infection causing SIADH

Answer 13

pneumonia, lung abscess, brain abscess

Question 14

initial symptoms of SIADH

Answer 14

• nausea
• vomiting
• muscle cramps
• headaches
• tremors

Question 15

later symptoms of SIADH as sodium plasma concentrations continue to fall

Answer 15

neurons in the brain swell causing cerebral oedema, hallucination, confusion, seizures, coma and death

Question 16

biochemistry which should shout out at you this is SIDADH

Answer 16

hyponatraemia in a person who has symptoms

Question 17

other biochemistry

Answer 17

• reduced serum osmolality
• elevated urine osmolality
• high sodium urine concentration

Question 18

after you diagnose SIADH what should you do

Answer 18

find the cause

Question 19

how do you find the cause

Answer 19

• thorough medication history for drugs that may cause SIADH
• chest CT is small cell lung cancer or lung infection suspected to be the cause
• head CT if brain damage/ brain abscess suspected to be the cause

Question 20

ectopic ADH production from small cell lung cancer is a type of what

Answer 20

paraneoplastic syndrome

Question 21

management if acute presentation of SIADH

Answer 21

• IV hypertonic saline (3% NaCl)

Question 22

what should you be very careful about when replacing someones sodium

Answer 22

you must check there sodium levels every 2 hours, sodium levels must not be increased by more than 1-2mEq/l/hour as if you replace sodium to quickly you can cause central pontine myelinolysis

Question 23

what else is required other than sodium replacement

Answer 23

treat the underlying cause

Question 24

central pontine myelinolysis

Answer 24

severe devastating damage to the myelin sheath of the pons causing:

• acute paralysis
• dysphagia
• dysarthria (difficulty speaking)