April 7, 2016 - Hypernatremia Flashcards
Water Concentration Sensors
The paraventricula nucleus (PVN), and the supraoptic nucleus (SON).
These signal thirst AND create AVP/ADH
ADH Storage
Stored in vacuoles in the posterior pituitary gland until they are needed.
Plasma Osmolarity and Total Body Water (TBW)
Low plasma osmolarity = high TBW
High plasma osmolarity = low TBW
ADH Response to Osmolality
280 is the magic number
Above this number, and you will secrete ADH and below this number you will have ADH turned off.
When you are volume depleted, the threshhold moves to 270 and when you are volume expanded the threshhold moves to 290.
Hypernatremia
Too much sodium which indicates there is too little water.
Could be due to failure of taking water in, or of failure to hold water in.
Causes of Failure to Take Water In
Lack of thirst
Often seen in the extremes of age; babies and very elderly / demented
Failure to Hold Water
Diabetes Mellitus (osmosis trumps ADH) - high sugar will create a huge oncotic drive
Mannitol (brain injury)
Failure to make ADH
Failure to respond to ADH
Diabetes Insipidus
Disorders of AVP
Can be CENTRAL in which the hypothalmus/pituitary is not making AVP. This is usually acquired in most cases.
Can be NEPHROGENIC in hwich there is a lack of response to AVP. This is usually congenital in most cases.
Polydipsia
Patients who drink a lot of water (over 3L) and have the urge to drink.
Polyurea
Voiding more than 3L per day
Differentiating Primary Polyplasia from Central DI
You withhold water from the patient.
In primary polyplasia, the urine volume will decrease and the urine osmolality will increase.
In DI, urine volume will still be high and so will the osmolality.
Hypernatremia Treatment
Depends on three factors…
1. Volume status (shock will kill faster than imbalance)
2. Acute vs Chronic
3. Underlying etiology
IV Replacement for Hypernatremia
The goal is to decrease the serum sodium by a maxiumum of 0.5 per hour, or by 12 in a 24-hour period.
