Step 2 - electrolyte conditions Flashcards
(24 cards)
causes of hypernatraemia with urine osmolality;
- < 300
- > 600
- between 300-600
hypernatraemia with urine osmolality;
< 300 = diabetes insipidus (next step is desmopressin test)
> 600 = insensible losses i.e. ng tube, intubated, or excess Na intake (next step is to assess fluid status and administer IV 0.9%)
if between 300-600 either osmotic diuresis or mild diabetes insipidus
describe the correction process for hypernatraemia
if chronic (onset > 48 hours) then correct over 48-72 hours
if acute (onset < 24 hrs) then correct within 24 hours
assess fluid volume status. If severe then correct with 0.9% NaCl before calculating free water deficits
assess free water deficit
- free water deficit = TBW X (serum Na/140 - 1)
note TBW is 60% of lean body mass in kg
- free water deficit can then be corrected with 0.45% NaCl, 5% dextrose water or enteral feeds
next step if patient has hyponatraemia and serum osmolality is < 280 and fluid status is isovolaemic and possible causes
measure urine osmolality
if < 100: beer drinkers, psychogenic polydipsia
if > 100: SiADH, hypothyroidism, glucoorticoid deficiency
next step if patient has hyponatraemia, serum osmolality is < 280 and fluid status is hypovolaemic and possible causes
urinary fractional excretion of sodium (FEN)
if < 1%: diarrhoea, vomiting, burns, third spacing
if > 2%: adrenal insufficiency, diuretics, urinary obstruction, renal tubular acidosis, metabolic alkalosis
next step if patient has hyponatraemia, serum osmolality < 280 and fluid status is hypervoalemic and possible causes
urinary fractional excretion sodium
if < 1%: chirrosis, CHF, nephortic syndrome
if > 1%: AKI, CKD
treatment of choice for hypernatraemia once immediate fluid resuscitation has been done
dextrose % water
how slowly should you correct chronic hypernatraemia
over > 72 hours
no more than reduction of 10mEq/L per day
treatment for SiADH
patients with hyponatraemia and are euvolaemic or hypervolaemic i.e. SiADH likely to be euvolaemic, treat with water restriction +/- diuretics
but if severe hyponatraemia < 120 then can give 3% NaCl esp if symptomatic (e.g. seizures).
in the setting of extreme leukocytosis or thrombocytosis, how do you confirm K is accurate on blood test
when these cells are highly elevated, K can be excreted which can falsely elevated the serum K level result and so plasma k should be measured to give a more accurate representation
in what electrolyte disturbance is sine waves found on ecg
severe hyperkalaemia (>8)
sine wave is merging of the ARS and T waves
in the treatment of hyperkalaemia, how can K be removed from the body in a patient with renal impairment
k is shifted into cells with B2 agonists (albuterol) and insulin/dextrose infusions
K is then excreted using IV saline (if hypovolaemic) or loop diuretics (normo or hypervolaemic) in patients with residual renal function. however if impaired renal function = Kayexalate (sodium polystyrene sulfonate) is a medication that exchanges sodium for potassium in the bowel and causes excretion of K
next step if patient has hypernatraemia and serum osmolality > 295
check glucose
next step if patient has hypernatraemia and isotonic with serum osmolality 280-295
check lipids and protein
causes include hypercholesterolaemia, mannitol or hyperproteinaemia
what inherited syndromes can cause hypokalaemia
barter’s syndrome
gitlemans syndrome
what 2 drugs can cause hypokalaemia
gentamicin
amphotericin B
what may falsley lower Ca levels on blood test
hypoalbuminaemia
therefore check for ionized calcium (or corrected calcium)
when correcting for serum albumin concentration, what can you predict in the level of Ca based on low albumin levels
for every 1g/dL decrease from an albumin of 4g/dL, you can presume a fall in calcium by 0.8 mg/dL
i.e. if albumin is 3 and Ca is 8, you should presume the true ionized Ca is 7.2
hypercalcaemia with low PTH and elevated 25-OH vitamin D
VITAMIN D toxicity
hypercalcaemia with low pTH and elevated 1,25-OH vitamin D
sarcoidosis
lymphoma
next step if hypercalcaemia and elevated PTH
check urinary Ca
if low = familial hypercalcaemic hypocalciuria
if elevated = hyperparathyroidism (primary or secondary)
treatment for hypernatraemia with levels < 12, 12-14 and >14
if Ca <12 then no treatment required
if asymptomatic and between 12-14 then no need for treatment
if Ca >14 then urgent treatment with saline +/- furosemide and calcitonin,
bisphosphonates can be considered
high Na helps excretion of Ca so isotonic fluid should be used
in what circumstance is hypomagnesaemia commonly found and how does this affect calcium levels
low Mg is commonly found in chronic alcohol consumption
low Mg is associated with low Ca and K levels
at what K level is potassium added to DKA treatment
< 5.3
when is bicarbonate added to DKA treatment
PH < 7.1
