Fluid And Electrolytes Flashcards
How is osmolality taken
Measured with osmometer using principle of freezing point depression
How is osmolarity taken
Calculated: 2Na + urea + glucose
Osmolal gap formula?
Osmolality - osmolarity
(Increases when other osmoles increase)
Normal osmolal gap?
<10
Name 3 physiological methods in which ECF osmolality is restored when water is lost
• Stimulation of vasopressin (adh) release → renal water retention
• stimulation hypothalamic thirst centre → increased intake
• redistribution of water from ICF
Define laboratory and clinical hyponatraemia
Lab <135 mmol/l
Clinical ≤ 125
Name 2 causes pseudo hypo Na
• Excess lipids
• excess protein
(Will have normal osmolality)
Normal sodium value?
135-145 mmol/l
Clinical consequence of acute hypona?
Cerebral oedema
Symptoms range from nausea and vomiting, confusion, coma death
Treatment hypervolaemic hyponatraemia?
Lasix and fluid restriction
Treatment euvolaemic hyponatraemia?
Fluid restriction
Treatment hypovolaemic hyponatraemia?
Saline rehydration
(True hypo Na )
Cause of hyper osmolar hypo na?
High glucose
Name 2 causes of hyponatraemia with urine sodium ≤ 30 mmol / L and decreased ECF volume
Sodium depletion:
• Gastrointestinal
• cutaneous
Name 3 causes of hyponatraemia with urine sodium ≤ 30 mmol / L and increased ECF volume
Sodium and water excess (oedema)
• heart failure
. Liver cirrhosis
• nephrotic syndrome
Name 2 causes of hyponatraemia with urine sodium > 30 mmol / L and decreased ECF volume
Sodium depletion
• adrenal failure
• renal salt wasting
• cerebral salt wasting
• diuretics
Name 3 causes of hyponatraemia with urine sodium > 30 mmol / L and normal ECF volume
Water excess (no oedema)
• syndrome of inappropriate adh (diagnosis of exclusion)
• ckd
• excess iv fluid infusion
Name 5 diagnostic criteria for syndrome of inappropriate adh
SIADH:
(Diagnosis of exclusion)
• serum euvolaemic: normal ECF volume
• > 100 urine osmolality: urine must not be maximally diluted (osmolality >100 mosm/kg)
• adrenal,thyroid function, kidney, normal
• drug not cause hypo Na
• hypo Na <135 and low serum osmolality <275
Continued natriunesis despite low plasma sodium, aldosterone secretion doesn’t increase
Name 5 causes and diagnosis hypovolaemic hypernatraemia
Assess clinically: dehydrated
Water very low and sodium low, but high concentration
Do urine sodium
Urine Na >40: renal losses
• osmotic diuresis or diuretic use
• ATN polyuric disease
- AKI/CKD
Urine Na < 25: extra-renal losses
• GI LOSS: osmotic diarrhoea, git fistula
• DERM LOSS: sweating/burns
MOLE: Meds (diuretics), Osmotic diuresis, Excessive water loss, Low water intake
Name 2 causes euvolaemic hypernatraemia
Clinically dehydrated.
Low water, normal sodium lab value but high concentration
Do urine:plasma osmolality
Urine osmolality <1:renal losses
• diabetes insipidus - central or nephrogenic (differentiate with desmopressin)
Urine osmolality >1: extra renal losses
• insensible losses
LED: Low water intake (extrarenal), Diabetes insipidus, Excess water loss
Name 5 causes hypervolaemic hypernatraemia
Clinically oedema, overhydrated.
“Classic” because Na will be >145. And water high
• Hypertonic saline infusion
• iv naHco3 as emergency for severe metabolic acidosis
• overconcentrated formula milk
• hypertonic dialysis
• sea water ingestion
- hyperaldosteronism
Name 4 trans cellular movement causes of hypo K
• alkalosis
• insulin administration
• refeeding syndrome
• increased k excretion
Name 5 renal causes of hypo K
• Diuretics
• AKI: early diuretic phase
• renal tubular acidosis 1 and 2
• mineralocorticoid excess: primary and secondary aldosteronism, Cushing
• tubular (distal) disorders: batter syndrome, Liddle syndrome, Gitelman’s syndrome
Name  2 extrarenal causes of hypo K
• diarrhea
• vomiting
Treatment hypervolemic hyper na?
Furosemide (loop diuretic) and 5% dextrose (hypotonic fluid) iv
Possibly dialysis if severe
(Dextrose causes hyper osmolality so water moves intracellular to extra cellular, creating dilutional effect)
Treatment euvolemic hyper na?
5% dextrose iv or water orally
Treatment hypovolemic hyper na?
Isotonic saline slowly and 5% dextrose iv
Name 6 factors that influence urinary potassium excretion
• Circulating aldosterone (cause hypo k in favour of sodium)
• amount of sodium arriving at distal tubules
• relative availability hydrogen and potassium of cells at distal tubules and collecting ducts
• capacity of cells to secrete hydrogen ions (h and K go together)
. Dietary K intake
• intravascular volume (reduction stimulate aldosterone)
Name 4 causes spurious (“false”) hyperkalaemia
•Hamolysis
. EDTA contamination
• old sample
• abnormal blood cells: leukemia, thrombocytosis
Name 7 causes transcellular movement hyperkalaemia
• Acidosis
• tissue damage (tumour lysis syndrome)
• vigorous exercise
. Decrease K excretion
• AKI and CKD
• K sparing diuretics
. Mineralocorticoid deficiency: Addison’s, aurenolectomy, hyporeninaemic hypoaldosteronism
What is ADH, where produced and function
- ADH = vasopressin
- posterior pituitary
- main function = water reabsorption by increase aquaporin 2 channels on DCT and CD
- stimulated by increased plasma osmolarity (high na) and to lesser extent low blood volume
- also vasoconstriction by increase vascular resistance
What is aldosterone, where produced and function
- Activated by RAAS (which is activated by low blood volume and pressure) and low Na or high K
- adrenal cortex
- activate eNAC channels and na/k ATP ase on DCT
- reabsorb Na and water, excrete K
What are natriuretic peptides, where produced and function
- BNP, ANP
- heart
- stimulated by high blood pressure and volume
- inhibit renin and therefore RAAS by
A) decrease sympathetic response
B) afferent arteriole vasodilation → increase GFR → naturesis
Ultimately inhibit aldosterone → decrease Na and H2O - also vasodilation
