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29 Cards in this Set
- Front
- Back
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What is normal serum osmolality?
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280-290 mosm/kg H20
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What is the main contributor to serum osmolality?
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Na
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Is measured plasma osmolality typically higher than calculated osmoalility? Why?
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Yes
There are other unmeasured osmoles inside the plasma |
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What is the normal value for the osmolar gap? If this is elevated, what could it miean?
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<10 mosm/L
There are effective osmoles present causing changes in concentrations |
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What kind of pathology presents with these labs:
BP 90/60 Na: 162 mEq/L Plasm osm 332 mosm/kg Urine osm 745 mosm/kg Who do you see this in? |
Dehydration
Low volume status (low BP, very concentrated serum sodium) impairment in the thirst mechanism |
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What are causes of hypernatremia?
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Sodium gains in excess of water done by physicans to treat something (cerebral edema)
Water loss in excess of sodium (diarrhea, renal loss, dehydration) |
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What types of people are at especially enlarged risks for hypernatremia?
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People with an impaired thirst sensation: elderly, hypothalamus lesions, psychosis
Impaired access to H20 |
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What conditions present with these labs:
High urine output Normal physical exam Sodium: 152 mEq/L Urine osm 105 mosm/kg |
Diabetes insipidus
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What are the different types of diabetes insipidus?
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Central: inpaired synthesis, transport, release of ADH from brain
Nephrogenic: reduced response to ADH in the collecting tubule |
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What test can you do to distinguish between the types of diabetes insipidus?
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Deprive people of water
If heightened urine osm, they've got primary polydipsia If ADH improves the urine osmolarity, it's central If not, it's nephrogenic |
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What do you have to be careful about when correcting for hypernatremia? Why?
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DON'T DO IT TOO FAST
YOU'RE GOING TO BLOW UP SOMEONE'S BRAIN! (the brain adjusts to chronically altered serum electrolyte levels...changing things up fast causes a rapid increase in intraneuronal volume, causing rupture) --> cerebral edema |
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What is the formula for water deficit?
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.6*weight* (1-140/[Na])
Be sure to continuously monitor, though. |
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What is the effect of administering .9% NS on normally osmolar serum volume ? .45%? DSW?
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Nothing!
500 mL free water 1 L free water |
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What is the most common electrolyte disturbance?
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Hyponatremia
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What are the symptoms of hyponatremia?
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Neurologic!
Acute: confusion, disorienttion, seizures, coma, death Chronic: asymptomatic until <125mEq/L |
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If you suspect that someone has hyponatremia, what are the three questions that you ask in your diagnostic algorhythm?
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1. Is the patient hypo-osmolar (Serum osm corrected for urea abnormal)
2. Are the patient's kidneys responding appropriately to clear free water (how does the urine osmolarity correspond with the serum) 3. Does the patient have an effective intravascular volume (Urine Na>20, physical exam) |
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Why don't we want to consider urea in diseases of osmoregulation?
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It's an ineffective osmole
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If a diabetic who has taken half of her normal insulin doese presents with the following labs, what should you think:
Glucose: 800 mg/dL Plasma osm 320 mosm/kg Sodium: 128 mEq/L |
Whe's got non-hypoosmosmolar hyponatremia
The glucose concentration in the blood is so high that she is having increased intravascular volume due to the glucose, diluting the amount of glucose she's got |
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What should you think in a person with the following labs:
Plasma osm: 265 mosm/kg Urine osm: 80 mosm/kg Sodium: 125 mEq/L |
1. There isn't a problem with his kidneys, here. He has low plasma osm and the kidney is responding appropriately by excreting low osm urine.
2. A problem like this is due to primary polydypsia |
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What is the treatment for primary polydypsia?
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Stop the person from drinking water!
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What are causes for a reset osmostat? Treatment?
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Causes:
Malnutrition Psychosis Pregnancy Malignancy Treat the underlying cause, not the hyponatremia |
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What should you think if someone presents with the following labs and a history of recent diuretics starting:
Sodium: 110 mEq/L Plasma osm: 238 mosm/kg Urine sodium: 30 mEq/L Urine osm: 300 mosm/kg |
The patient is hypo-osmolar and isn't clearing free water correctly: the urine has far too much sodium in it for how hyponatremic he is.
It could be that the person is being aggressive with his taking of the diuretic |
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What are some causes of hyponatremia with impaired water excretion?
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ADH effect
Advanced renal failure Endocrine disturbances (hypothyroidism, adrenal insufficiency) |
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What should you think if a patient with a history of CHD and edema presents with the following labs:
Sodium: 125 mEq/L Plasma osm: 265 mosm/kg Urine sodium < 10 mEq/L Urine osm: 350 mosm/kg |
You should think that this man is in decompensated heart failure:
Lots of volume in the interstituim due to heart failure. Kidneys see low volume--> ADH secretion to hold onto sodium. |
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What should you think in a man with an extensive smoking history, L lobe mass presents with these labs;
Sodium: 118 mEq/L Plasma osm: 250 mosm/kg Urine osm: 600 mosm/kg Urine sodium: 32 mEq/L |
He's got lung cancer that's secreting ADH abnormally
He's excreting far too many solutes for how low his blood levels are. Also, he doesn't have a problem with volume: sodium levels are fine |
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What are some causesof inappropriate ADH secretion?
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Increased hypothalamic production of ADH
Ectopic production (SC lung cancer) ADH potentiation (drugs, psychosis) |
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What is the management of SIADH?
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Treat the underlying cause
Free water restrict Hypertonic saline (513mEq/L) + diuretic Demeclocycline (ADH antagonist) V2 receptor antagonist |
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What is the effect on giving .9% NS to a person with SIADH? Why? How can you get around this?
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You're giving them free water; they'll excrete the solute with ease and keep the remaining water.
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What is the general principle for the management of hyponatremia?
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Manage it slowly!!!
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