Endocrine Flashcards
What is osmolality?
The concentration of osmoles in a mass of solvent, denoted by mOsm/kg
What is osmolarity?
The concentration of osmoses in a volume of solvent, denoted by mOsm/L
What are effective osmoles?
Osmoles that do not cross the cell membrane
What are the three broad types of hypernatraemia?
Hypovolaemic, Normovolaemic, and Hypervolaemic
What causes Hypovolaemic Hypernatraemia?
Loss of free water/low sodium fluid - GI losses, renal losses, burns
What causes Normovolaemic Hypernatraemia?
Reduced access to water, hypodipsic hypernatraemia, diabetes insipidus
What causes Hypervolaemic Hypernatraemia?
Salt gain - Salt intoxication, HTS administration, sodium bicarbonate administration, hyperaldosteronism, hyperadrenocorticism
Treatment of acute hypernatraemia
If clinical signs are present, correct at 2-3mEq/L/h until clinical signs resolve, then reduce rate
If no clinical signs are present, correct at 1-2mEq/L/h
Treatment of chronic hypernatraemia
Correct at 0.5mEq/L/h
How do you determine the rate of D5W or similar hypotonic solution to administer to a hypervolaemic patient?
- Calculate the ‘Change in serum Na’ for the infusate
- Calculate the rate of infusion
OR - Calculate the patient’s free water deficit in mL
- Calculate the time needed to correct sodium appropriately
- Calculate the rate using the water deficit and time required.
What is the formula for calculating a change in serum sodium caused by an infusate?
Change in serum Na+ = [(Infusate Na) - Serum Na]/[(0.6xweight)+1]
What is the formula for calculating the rate of infusion for correcting hypernatraemia?
Rate of infusion = [(correction target)/(infusate change in Na+)] x 1000
What is the formula for calculating a patient’s free water deficit?
Free water deficit = 0.6 x BWT x {[(Na+ patient)/(Na+ normal)]-1}
What is the sodium content of 23.4% NaCl
4mEq/mL
What is the sodium content of Hartmann’s
130mEq/L
What is the sodium content of Plasmalyte 148
140mEq/L
What is the sodium content of 0.9% NaCl
154mEq/L
Treatment for overzealous correction of hypernatraemia
Stop fluid administration, disallow drinking, administer mannitol @ 0.5-1g/kg over 20-30 min
What are the three broad causes of hyponatraemia?
Iso-osmolar, Hypoosmolar, and Hyperosmolar
What causes iso-osmolar hyponatraemia?
Artifact - seen within hyperlipidaemia and hyperproteinaemia
What causes hyperosmolar hyponatraemia?
Hyperglycaemia, azotaemia, mannitol administration.
What causes hypo-osmolar hyponatraemia?
Divided into dehydrated, over hydrated, and euhydrated.
Dehydrated - Hypoadrenocorticism, salt-losing nephropathy, diuretic administration, renal insufficiency
Euhydrated - SIADH, hypotonic fluid administration, hypothyroidism, atypical Addison’s, psychogenic polydipsia
Overhydrated - Acute or chronic renal failure, CHF, hepatic cirrhosis, water intoxication
How to correct hyponatraemia
- Calculate sodium deficit and amount of time to correct (0.5mEq/L/h). Na requirement = (0.6 x BWT) x (desired Na - serum Na)
- Calculate rate of replacement infusion:
Rate of infusion = (Na requirement x 1000)/(Infusate mEq x time)
