Flashcards in Fluids, Electrolytes, Acids/Bases - Step Up Deck (137):
total body water
60% of weight (50% in women)
- decreases with age and obesity
ICF is _ % of body weight; ECF is _ % of body weight, _% is interstitial fluid and _% is plasma
fluid loss due to insensible losses increases with .. (4)
fever, sweating, hyperventilation, tracheostomies (unhumidified air)
normal urine output in infants
> 1.0 ml/kg/hr
normal urine output in adults
> 0.5-1.0 ml/kg/hr
each degree over 37 C, body's water loss increases by..
what patients tend to third-space fluid?
any condition with hypoalbuminemia
- liver failure
- nephrotic syndrome
best fluid when pt is dehydrated or has lost blood
normal saline (0.9% NaCl)
what is the standard maintenance fluid?
D5 1/2 NS with 20 mEq KCl/L
(5% dextrose and 1/2 normal Saline)
which IVF should be avoided in heart failure and renal failure pts due to risk of volume overload?
which IVF is used to dilute powdered medications?
MC trauma resuscitation fluid
Ringer's Lactated solution
- excellent for replacement of IV fluids
in which situation should Ringer's Lactate be avoided?
when should you consider placing a Swan-Ganz catheter in hypovolemic pt?
pt is critically ill
pt w/ cardiac or renal failure
what do elevated serum Na, low urine Na and BUN/Cr > 20:1 suggest?
hypoperfusion to the kidneys (sign of hypovolemia)
how does hematocrit change with hypovolemia?
3% increase for every liter deficit
how does CBC and proteins in serum change with hypovolemia?
increase with an ECF deficit
decrease with an ECF excess
how do you correct volume deficit in hypovolemia?
give bolus of either Lactated Ringers or Normal Saline
do not give bolus fluids with what? (2)
dextrose - hyperglycemia
potassium - hyperkalemia
how do you calculate maintenance fluids?
4 ml for first 10 kg, 2 ml for next 10 kg, 1 ml/kg for every kg over 20
(always give 60 ml for first 20 kg)
signs of volume overload (6)
jugular venous distention
elevated CVP or PCWP
low hematocrit or albumin conc
Tx. of hypervolemia
changes in Na+ conc. are a reflection of...
changes in Na+ content are a reflection of...
main osmotically active cation of ECF
increase in Na+ intake results in...
increased ECF volume, increase in GFR and sodium excretion
normal plasma hypertonicity
formula for serum osmolarity
(2 Na) + BUN/2.8 + glucose/18
- if BUN and glucose normal, = (2Na) + 10
definition of hyponatremia
plasma Na+ conc < 135 mmol/L
when do symptoms of hyponatremia occur?
usually around Na+ conc of 120 mmol/L (except in cases of ICP where symptoms are made worse and earlier with low Na)
what happens to the deep tendon reflexes in hyponatremia?
hyperactive deep tendon reflexes
(also get muscle twitching and weakness)
how do you calculate free water deficit?
TBW (1 - actual Na+/desired Na+)
normal serum calcium
what does calcium balance depend on?
how does albumin affect Ca2+ levels?
most Ca2+ ions are bound to albumin; so if albumin is low, TOTAL Ca2+ is low, but ionized fraction is normal --> pt. does not show sx
how can you estimate ionized calcium?
total calcium - (serum albumin x 0.8)
how do you assess if person is truly hypocalcemic?
correct Ca2+ = measured total Ca2+ + 0.8 (4-albumin)
what effect does pH have on calcium?
increase pH (alkalosis) increases Ca2+ binding to albumin, total Ca2+ is normal but ionized Ca2+ decreases --> pt will manifest w/ signs of hypocalcemia
effect of PTH on calcium and phosphate
increases Ca2+ and decreases PO4-
effect of calcitonin on calcium and phosphate
decreases Ca2+ and decreases PO4-
effect of vit. D on calcium and phosphate
increases Ca2+ and increases PO4-
MCC of hypocalcemia
hypoparathyroidism - usually due to surgery
what could be the cause of LOW Ca2+ levels, but high PTH levels?
pseudohypoparathyroidism - end organ resistance to PTH
vitamin D deficiency
what electrolyte abnormalities cause hyperactive deep tendon reflexes?
what are signs of tetany?
hyperactive deep tendon reflexes
what are signs of increase neuromuscular irritability in hypocalcemia?
numbness/tingling - circumoral, fingers, toes
Grand Mal seizures
cardiovascular manifestations of hypocalcemia
prolonged QT syndrome
in the setting of hypocalcemia, when is Phosphate high?
Tx. of symptomatic hypocalcemia
IV calcium gluconate
how do you correct hypocalcemia due to PTH deficiency?
vitamin D and high oral Ca2+ intake
thiazide diuretics - lower urinary calcium
milk alkali syndrome
hypercalcemia, alkalosis and renal impairment due to excessive intake of calcium and absorbable antacids (calcium carbonate, milk)
drugs that cause hypercalcemia
ECG findings in hypercalcemia
shortened QT interval
symptoms of hypercalcemia
muscle pain and weakness
pancreatitis, PUD, gout
what additional lab finding is seen in primary hyperparathyroidism?
elevated urinary cAMP
first steps in management of anyone w/ hypercalcemia?
1. IV fluids - normal saline
what tx. inhibits bone resorption in pts with osteoclastic disease?
when can you use glucocorticoids in tx. of hypercalcemia?
vitamin-D related mechanisms
normal K+ levels
effect of pH on serum k+
alkalosis = hypokalemia
acidosis = hyperkalemia
if pt has HTN and hypokalemia...
excessive aldosterone activity is likely
if pt is normotensive and hypokalemic..
either GI or renal loss of K+ is likely
chronic volume depletion secondary to AR-defect in salt reabsorption in TAL leading to hyperplasia of JG apparatus and increase renin levels and aldosterone levels; cause of hypokalemia
GI losses leading to hypokalemia (5)
vomiting, NG suction - alkalosis
decreased K+ absorption
renal losses leading to hypokalemia
renal tubular or parenchymal disease
other causes of Hypokalemia
insufficiency dietary intake
antibiotics - bactrim, amphotericin B
increased entry of K+ into cells
vit. B12 replacement
ECG changes in hypokalemia
T wave flattens out or inverts if severe
U wave appears
arrhythmias - prolongs normal cardiac conduction
effect of K+ levels on deep tendon reflexes
both hypo and hyperkalemia cause DECREASED deep tendon reflexes
CF of hypokalemia
decreased deep tendon reflexes
exacerbates digitalis toxicity
what two electrolytes are difficult to correct in case of hypomagnesemia?
preferred method of K+ replacement
oral K+ - safest
- 10 mEq of KCl increases K+ levels by 0.1 mEq/L
what kind of fluid should you avoid in hypokalemia?
dextrose containing fluids - increase insulin and cause further K+ shifts into cell
when can you give IV KCl
hypokalemia severe (<2.5)
pt has arrhythmias
infusion rate of IV KCl
max 10mEq/hr in peripheral IV line; max 20 in central line
- add 1% lidocaine to decrease burning pain
in setting of hypokalemia, what does a urine K+ < 20 imply?
- renal loss has Urinary K+ > 20
causes of increased total body K+
renal failure/ type IV RTA
drugs that cause hyperkalemia
what can cause a shift of K+ OUT of cells
tissue/cell breakdown - burns, rhabdo
effect of acidosis on K+ levels
- every 0.1 decrease in pH, K+ increases by 0.7 points
what can cause pseudohyperkalemia (spurious elevation)
tight/prolonged tourniquet application
delay in processing - RBC hemolysis
effect of hyperkalemia on ammonia
inhibits ammonia synthesis and reabsorption = metabolic acidosis which shifts K+ out of cells and exacerbates it further
ECG changes in hyperkalemia
peaked T waves --> widened QRS --> prolonged PR --> loss of P waves --> sine wave pattern --> V.fib
CF of hyperkalemia
muscle weakness and flaccid paralysis
decreased deep tendon reflexes
NVD, intestinal colic
Tx of severe hyperkalemia with ECG changes, muscle paralysis or level > 6.5
IV calcium gluconate
methods to immediately/quickly lower K+ levels
1. insulin + glucose (30-60 min)
2. sodium bicarbonate - emergency measure in severe hyperkalemia
methods of removing K+ from the body
Kayexalate - sodium polystyrene sulfonate (cation exchange resin)
who is hemodialysis reserved for in hyperkalemia tx.?
pts with renal failure
normal Mg2+ levels
MCC of hypomagnesemia
causes of hypomagnesemia
GI - steatorrhea, malabsorption, prolonged fasting, TPN, fistulas
renal causes - SIADH, diuretics, Bartter's, drugs, renal transplant
drugs causing hypomagnesemia
neuromuscular and CNS sx of hypomagnesemia
muscle twitching/weakness, tremor
mental status changes
ECG changes in hypomagnesemia
T wave flattening
torsades de pointes
Tx. of hypomagnesemia
mild - oral Mg (Mg2+ oxide)
severe - IV Mg (Mg sulfate)
first sign of hypermagnesemia
progressive loss of deep tendon reflexes
CF of hypermagnesemia
loss of deep tendon reflexes
ECG changes same as in hyperkalemia
somnolence --> coma and muscular paralysis
Tx. of hypermagnesemia
IV calcium gluconate for emergent sx
saline + furosemide
dialysis in renal failure pts
normal plasma phosphate conc.
decreased intestinal absorption of phosphate due to..
alcohol abuse (MCC)
vit D deficiency
excessive use of antacids
TPN and/or starvation
increased renal excretion of phosphate due to...
excess PTH states
renal tubular acidosis
other causes of low phosphate levels?
hungry bones syndrome
Tx. of hypophosphatemia
oral supplementation - neutra-phos capsule, K-phos tablets, milk
severe - parenteral supplementation
CF of hyperphosphatemia
metastatic calcifications and soft tissue calcifications - binds calcium (hypocalcemia)
Tx. of hyperphosphatemia
phosphate binding antacids contatining AlOH or carbonate
Na - (HCO3 + Cl)
- normally between 5-15
- represents ions present in serum but unmeasured
effects of acidosis
right shift of O2-Hb dissociation curve
decreases pulmonary blood flow
impairs myocardial function
effects of alkalosis
decreases cerebral blood flow
left shift on O2-Hb curve
an (1) in lactate results in a (2) in HCO3-
1 - increase
2 - decrease
what causes an increased AG acidosis?
1. ketoacidosis - DKA, starvation, alcohol
2. lactic acidosis
3. renal failure - decreased NH4 excretion
acid-base defect in salicylate overdose
primary respiratory alkalosis AND AG metabolic acidosis
what causes a normal AG acidosis (hyperchloremic)
1. renal tubular acidosis - decreased HCO3 absorption or decreased production of HCO3
2. carbonic anhydrase inhibitors
3. GI loss - diarrhea, pancreatic fistulas, small bowel fistulas, ureterosigmoidostomy
4. adrenal failure
MCC of non-AG acidosis?
proximal tubular acidosis
causes nonAG acidosis by decreasing reabsoprtion of HCO3-
- multiple myeloma
- Wilson's disease
distal tubular acidosis
inability to make HCO3-
caused by: SLE, Sjogrens and ampho.B
CF of metabolic acidosis
hyperventilation - Kussmaul breathing
decreased tissue perfusion
expected PaCO2 = 1.5 (HCO3) + 8 (+/- 2)
in Winter's formula, if actual PaCO2 > calculated PaCO2...
metabolic acidosis with respiratory acidosis
in Winter's formula, if actual PaCO2 < PaCO2..
metabolic acidosis with respiratory alkalosis
Tx. of severe metabolic acidosis
NaHCO3 --> tx. up to a pH of 7.20 (no higher)
saline-sensitive metabolic alkalosis
Urinary Cl < 20 = ECF contraction and hypokalemia
saline-resistant metabolic alkalosis
Urinary Cl > 20 - ECF expansion and HTN
causes of saline-sensitive metabolic alkalosis
NG tube suction
villous adenoma of colon
causes of saline-resistant metabolic alkalosis
excessive black licorice consumption
Tx. of saline-sensitive metabolic alkalosis
IVF with normal saline and K+
Tx. of saline-resistant metabolic alkalosis
IVF will NOT help
- underlying cause must be addressed
- spironolactone may help
compensation in acute respiratory acidosis
HCO3- rises acutely -> 1 mmol/L for every 10 mmHg increase in PCO2
compensation in chronic respiratory acidosis
renal compensation takes about 5 days to complete --> HCO3- rises 4 mmol/L for every 10 mmHg increase in PaCO2
what is the main cause of respiratory acidosis
major causes of alveolar hypoventilation (5)
1. primary pulmonary disease - COPD, sleep apnea, CH, Obesity
2. neuromuscular dz - myasthenia, ALS
3. CNS - injury to brainstem, stroke
4. drug-induced - opiods, sedatives
5. respiratory muscle fatigue
signs of acute CO2 retention
effect of elevated PaCO2 on CNS
elevated PaCO2 = increased cerebral blood flow = increased ICP = generalized CNS depression
which situations in respiratory acidosis require intubation?
1. severe acidosis
2. PaCO2 > 60 or inability to raise PaO2 w/ O2
3. deterioration in mental status
4. respiratory fatigue
PaCO2 is primarily determined by...
1.respiratory rate - any disorder that increases RR can lead to alkalosis
9 major causes of alveolar hyperventilation:
2. PE, pneumonia, pulm edema, atelectasis, effusion
4. hypoxia - high altitudes
5. mechanical ventilation
7. liver disease
8. medications - aspirin
9. hyperventilation syndrome
CF of respiratory alkalosis
1. decreased cerebral blood flow - lightheaded/dizzy, anxiety, paresthesias, perioral numbness