Electrolytes Flashcards
Na is principle determinant of ECF volume & ultimately shifting of what?
fluid b/t ECF & ICF comparments
Major cation in ECF?
Na
Major cation in ICF?
K
Major anions in ECF?
Cl & HCO3
Negatively charged molecules in ECF (Cl, HCO3) maintain electroneutrality with?
positively charged cations in ICF
small changes in osmolality or tonicity are detected by what?
osmoreceptors in the hypothalamus
Under normal circumstances, the kidney increases or decreases H2O excretion & is mediated by?
antidiuretic hormone (ADH)/vasopressin from pituitary
Increased ADH secretion happens in response to what?
Decreased secretion?
volume contraction
Volume expansion
Under normal circumstances, the kidney responds to altered Na level in ECF & increases or decreases Na reabsorption due to impulses from what mechanisms?
carotid baroreceptors
atrial stretch receptors
intrarenal mechanisms
Normal “set point” for plasma osmolality is appox?
285 mOsm/kg
Minimum urine osmolality?
Maximum urine osmolality?
appox 50 mOsm/kg
approx 1200mOsm/kg
With rise in plasma osmolality >295mOsm/kg what two responses occur?
thirst centers of the hypothalamus are stimulated & signals individual to drink
ADH levels rise until osmolality returns to normal
ADH is also released in response to what even if plasma osmolality is low?
hypotension or decreased effective arterial volume
Maintenance IVFs needed if NPO, how much volume per day?
30-35 ml/kg/d
Maintenance IVFs needed if NPO, how much UOP is necessary to excrete daily solute load consumed?
> 500 ml/d
Maintenance IVFs needed if NPO, how much dextrose is necessary to minimize protein catabolism and ketoacidosis?
100-150 gm/d
Volume losses to consider when prescribing IVFs
Stool?
typically lose 200 ml/d
Volume losses to consider when prescribing IVFs
Insensible losses from skin, respiratory tract?
400-500ml/d
Volume losses to consider when prescribing IVFs
Fever?
losses increase by 100-150 ml/d for each degree > 37C
Volume losses to consider when prescribing IVFs
minimum volume/d =?
1400 ml or 60ml/hr
Volume losses to consider when prescribing IVFs
What may cause patients to require more?
What may cause patients to require less?
burns/open wounds
CHF patients
Reduced ECF volume in r/t capacity
May/may not have decreased ___ level.
May appear hypovolemic d/t increased capacitance of ECF or intravascular compartment (relative hypovolemia).
What can cause this appearance?
Na
Vasodilation: meds (vasodilators), sepsis, pregnancy
Generalized edema: CHF, cirrhosis, nephrotic syndrome
3rd spacing: sequestered compartment-SQ tissue, RP/peritoneal space, GI tract-not in equilibrium with ECF
Absolute hypovolemia results in what effect on Na level?
deficit in Na level
Absolute Hypovolemia
Renal causes?
inhibit or disrupt Na reabsorption
diuretics
tubule dysfunction (AKI-disrupts)
Endocrine disorders (AI, hyperaldosteronism-disrupts)
Absolute Hypovolemia
Extrarenal causes?
bleeding
losses from GI, skin, respiratory systems
Clinical presentation of hypovolemia depends on?
rate of loss
Clinical presentation of hypovolemia
Lab results for…
BUN (BUN:Cr ratio)
UOP
CVP/JVP
Specific gravity & urine osmolality
Urine Na
Fractional excretion of Na (FeNa)
elevated (>20:1)
decreased
low
high
< 15mEq (or may be higher in setting of diuretics)
< 1%
Equation for Fractional Excretion of Na?
(urine Na x serum Cr) / (urine Cr x serum Na) x 100
Clinical presentation of hypovolemia
Symptoms expected?
tachycardia
hypotension
lactic acidosis
hemoconcentration if not bleeding
cold extremities (unless septic)
Clinical presentation of hypovolemia
in what setting is hypernatremia expected?
H2O deficit
Management of hypovolemia
Deficit can be difficult to estimate and requires what?
frequent assessment
Management of hypovolemia
Goal?
HD stability, replenish intravascular volume
Management of hypovolemia
Use what type of fluids for resusitation?
Isotonic IVF (NS/LR)
Management of hypovolemia
Isotonic IVF contain what?
small molecules that diffuse freely throughout ECF compartment
Management of hypovolemia
Because 2/3 of ECF is interstitial, a similar proportion is interstitial; meaning IVFs do what?
follow the same distribution with approx. 2/3 of IVF distributed to interstitial space
Management of hypovolemia
To acutely expand intravascular space what is often required?
1-2L bolus
Colloids (albumin) contain what?
large, poorly diffusible molecules that create osmotic pressure to keep H2O intravascular
Colloids are more effective than crystalloids at what?
Expanding intravascular volume
Considerations about crystalloids
cost?
availability?
side effect?
effectiveness of expanding intravascular volume?
survival compared to colloids?
mortality, ICU/hospital LOS, MV days, or days of renal-replacement tx compared to colloids?
inexpensive
readily available
edema formation
need for increased volumes to = that of colloids
have been associated with survival advantage compared to colloids
Have been associated with no difference in mortality, ICU/hospital LOS, MV days, or days of renal-replacement tx compared to colloids
Infusion of large volumes of NS can result in what?
metabolic acidosis (hyperchloremic acidosis)
NS usually has what kind of adverse consequences?
usually none
LR contains what? what can this affect?
Calcium
may bind to certain meds/reduce effectiveness
LRs effect on serum lactate levels in critically ill or those with hepatic insufficiency?
not known
Cost of colloids vs crystalloids
NS/LR
5% albumin
25% albumin
$1.46/L
$30.63/250ml
$30.63/50ml
What advantages do colloids have over crystalloids?
remain intravascular longer & provide more plasma volume expansion than crystalloids
Albumin is what?
Available in what % solutions?
heat-treated preparations of human serum albumin
5% (50g/L)
25% (250g/L)
Hypervolemia results in what kind of Na balance?
surplus of total body Na
Hypervolemia/Na retention is secondary to?
renal disease (AKI, glomerular disease)
Endocrine d/o (excess mineralocorticoid action)
Hypervolemia/Na retention d/t renal disease occurs because?
Limited ability to excrete Na & H2O
Disruption of capillary Starling forces result in shifting of fluid from intravascular space to interstitium & activation of RAAS
May be secondary to hypoalbuminemia
Hypervolemia/Na retention d/t endocrine d/o
usually presents as?
May have what electrolyte abnormality?
HTN
hypokalemia
Secondary renal response to…
Reduced effective arterial blood volume resulting in?
renal Na retention, expanded ECF
Secondary renal Na retention results in?
enhanced sympathetic activity, RAAS activation
CHF (from low CO)
Cirrhosis synthetic dysfunction & hypoalbuminemia
Hypervolemia/Na retention clinical presentation
Edema
effusions
rales
elevated JVP/CVP
hepatojugular reflux
S3
HTN
Low urine Na (<15mEq/L
Secondary renal Na retention results in?
enhanced sympathetic activity, RAAS activation
CHF (from low CO)
Cirrhosis synthetic dysfunction & hypoalbuminemia
Hypervolemia/Na retention symptoms
dypnea
abd distention
edema
Management of Hypervolemia/Na retention primary goals?
address underlying problem
limit Na intake (20-40mmol/d)
Management of Hypervolemia/Na retention
What medication should be used?
Diuretics
Diuretics enhance renal Na excretion by what mechanism?
blocking various sites along nephron
Proxmial tubule diuretic to use in management of Hypervolemia/Na retention?
Diamox
Loop Diuretic to use in management of Hypervolemia/Na retention?
lasix
Distal tubule diuretic to use in management of Hypervolemia/Na retention
HCTZ
Collecting duct diuretic to use in management of Hypervolemia/Na retention?
Spironolactone
Which is the most potent diuretic to use in management of Hypervolemia/Na retention?
lasix
How does spironolactone work?
competes with aldosterone
How does spironolactone improve survival of those with Left Ventricular Dysfunction?
competitive blockade of nonepithelial mineralocorticoid receptors in heart and other vascular structures reducing fluid/Na retention
Hyponatremia results from?
processes that limit elimination of H2O or expands volume around fixed Na content
Antidiuretic hormone secretion leads to hyponatremia how?
either appropriate secretion in response to low circulating volume or inappropriate d/t neuro d/o, pulmonary disease, malignancy
Hyperosmolar Hyponatremia occurs when plasma osmolality is what?
> 295 mOsm/kg
Hyperosmolar hyponatremia is d/t?
hyperglycemia
Hyperosmolar hyponatremia causes increased ECF resulting in?
dilution of Na content
Hyperosmolar hyponatremia
For every 100 mg/dL rise in plasma glucose Na falls by?
1.6-2.4 mEq/L
Pseudohyponatremia Osmolality is?
Cause?
280-295 mOsm/kg
Lab phenomenon in which high concentrations of plasma proteins, lipids expand non-aqueous portion of plasma sample
Diagnostic approach to hyponatremia
Isotonic Hyponatremia 280-295 mOsm/kg?
Pseudohyponatremia
Diagnostic approach to hyponatremia
Hypertonic Hyponatremia >295 mOsm/kg
Hyperglycemia
Hypertonic fluid admin
Diagnostic approach to hyponatremia
Hypotonic hyponatremia <280 mOsm/kg first step?
Second step?
Assessment of volume status
hypovolemic
euvolemic
hypervolemic
Check urine sodium
Diagnostic approach to hyponatremia
Hypotonic hyponatremia <280 mOsm/kg
Hypovolemic: urine sodium > 20 mEq/L
Renal solute loss
Diagnostic approach to hyponatremia
Hypotonic hyponatremia <280 mOsm/kg
Hypovolemic: urine sodium </= 20 mEq/L
Extrarenal solute loss
Diagnostic approach to hyponatremia
Hypotonic hyponatremia <280 mOsm/kg
Euvolemic: urine sodium always >20 mEq/L
SIADH
Endocrinopathies (Glucocorticoid deficiency)
Potassium depletion (diuretic use)
Diagnostic approach to hyponatremia
Hypotonic hyponatremia <280 mOsm/kg
Hypervolemic: urine sodium > 20 mEq/L
Renal failure
Diagnostic approach to hyponatremia
Hypotonic hyponatremia <280 mOsm/kg
Hypervolemic: urine sodium </= 20 mEq/L
Edematous d/o’s
Heart failure
Cirrhosis
Nephrotic Syndrome
Hyponatremic Clinical presentation
Neurologic abnormalities d/t cerebral edema from shifting of H2O from ECF to ICF
Hyponatremic Clinical Presentation
neurologic abnormalities severity depends on?
magnitude & rapidity of fall
Hyponatremic Clinical Presentation
Acute: timeframe?
symptoms?
<2 days
nausea
malaise
H/A
lethargy
confusion
obtundation
Hyponatremic Clinical Presentation
Na 115 mEq/L results in?
stupor
seizures
coma
Hyponatremic Clinical Presentation
Chronic: timeframe?
symptoms?
> 3 days
minimization of increased ICF/symptoms
Management of Hyponatremia is determined by?
ECV (extracellular volume): low, normal, high
Presence of neuro symptoms
Symptomatic hyponatremia requires more rapid correction, however no greater increase in plasma Na than what rate?
not to exceed what level?
or how much Na mEq/L/d?
why?
0.5mEq/L/hr
130 mEq/L
>12 mEq/L/d
possible occurrence of central pontine myelinolysis (CPM) from neuronal damage from rapid osmotic shifts
Management of Hyponatremia for low ECV?
hypertonic saline 3% if symptomatic
NS if asymptomatic
Management of Hyponatremia for normal ECV?
lasix
hypertonic saline if symptomatic
NS if asymptomatic
Management of Hyponatremia for high ECV?
lasix
hypertonic saline if symptomatic
lasix if asymptomatic
water restriction
Formula for expected change in Na?
[(Na conc in IVF + K conc in IVF) - serum Na] / (kg x 0.6 +1)
ADH is secreted by and transmitted to?
hypothalamus
posterior pituitary
ADH is released in response to?
decreased effective circulating volume as sensed by baroreceptors
ADH MOA?
H2O reabsorption
urine concentration
SIADH is what?
inappropriate levels of ADH are secreted despite absence of osmotic or volume related stimuli
SIADH is a dysregulation of what?
cells secreting ADH or in feedback mechanisms responsible for release