Fluid and Electrolytes
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Fluid and Electrolytes
Fluid Electrolytes PHPR521
Fluid and Electrolytes
What is the normal serum osmolality?
What is the equation to calculate serum osmolality?
2[Na] + (Glu/18) + (BUN/2.8)
What is the normal serum sodium concentration?
What is the norma serum level of glucose?
What is the normal serum level for BUN?
What creates oncotic pressure?
What function does aldosterone have?
secreted when plasma volume is low (perfusion pressure)
Enhances sodium reabsorption in the distal tubules (water follows)
potassium goes out as sodium comes in
What is the fx of Antidiuretic Hormone (ADH)?
secreted when osmolality is high
regulates fluid and electrolyte intake (think thirst)
regulates reabsorption of free water in distal tubules
part of RAAS!!!!
What are sensible and insensible water gains and losses?
water of oxidation (Krebs cycle)
lungs, skin, feces
What can be used to assess fluid levels?
BP (not very good, by the time BP decreases, you have problems)
heart sounds (S
- fluid overload)
electrolytes (Na, BUN, SCr - BUN/SCr ratio)
What BUN/SCr ratio means dehydration?
if BUN/SCr = >20
What is the normal serum level for creatinine?
What are the replacement solutions we use to increase fluid levels?
electrolyte solutions (NS, D
contain electrolytes and/or glucose
used for volume expansion
do NOT contain plasma proteins
plasma protein or other colloidal molecules (albumin, hetastarch)
Which crystalloids are isotonic?
Which crystalloids are hypotonic?
0.45% NS, D
Which crystalloids are hypertonic?
What should be used for standard fluid maintenance?
NS + 20mEq KCl @ 100cc/h
What should never be given to adjust or maintain fluids?
sterile water IV
What are the sodium rules?
total body salt rules volume - too much volume means too much Na
, too little volume means too little Na
water rules tonicity (serum sodium)
What effect to diruetics have on urine?
lock you into urine that =
as pt loses Na, they lose free water - need to replace free water to avoid hyponatremia
(sweat also equals
NS - all the time)
If you give diretics and replace the loss with free water, what do you get?
If you give diuretics and you replace the loss with NS, what do you get?
What are the clinical features of hyponatremia?
death (mortality is 5-50%)
What is cerebral edema?
not enough Na holding water outside the brain, so too much water gets inside
What is hypotonic, hypovolemic hyponatremia?
low total sodium
low water (relative excess of water)
if urine Na < 20, it's extrarenal loss (GI, skin, third spacing
if urine Na > 20, it's renal loss (diruetics, osmotic diuresis, salt-losing nephropathy) (90% of cases)
What is hypotonic isovolemic hyponatremia?
normal total sodium
Syndrome of Inappropriate ADH (SIADH)
too much ADH
high free water levels
What can cause SIADH?
pulmonary infections, acute resp failure, COPD
lung carcinoma, pancreas carcinoma
acute psychosis, stroke, abcess/tumor of the CNS
How do you treat SIADH?
remove offending drugs
restrict free water
use NS for IVF (not D
demeclocycline (long-term tx for SIADH)
What is hypotonic hypervolemic hyponatremia?
high total sodium
very high water
heart failure = decreased renal perfusion = decreased aldosterone
cirrhosis = lose water to intraabdominal space = decreased renal perfusion
nephrotic syndrome = lose protein = lose fluid to extravascular space = decreased renal perfusion
renal failure = decreased perfusion
What is hypertonic hyponatremia?
high glucose = high water volume
How should hyponatremia be treated?
increase Na by no more than 2 mEq/L/h
no more than 12 mEq/L/d (can cause central pontine myelinolysis - damage to myelin sheaths)
target goal 120-125 mEq/L
assess serum Na q 2-4h
correct underlying cause
What is hypovolemic hypernatremia?
low total sodium
very low water
replace with NS utnil BP fixed, then
NS to replace free water
What is isovolemic hypernatremia?
low urine osmolality (peeing more water)
avoid rapid correction b/c brain produces its own osmols to keep water there....add water too fast and it goes straight to the brain!!
decrease sodium by 0.5-1 mEq/L/h
What causes diabetes insipidous?
Central DI (ADH not being secreted)
Nephrogenic DI (kidneys not responding to ADH)
drugs (lithium, demeclocycline, thiazides)
What is the normal serum level of K?
What causes hypokalemia?
aldosterone (sodium retention)
can't correct K without treating low Mg!!!
What are the sx of hypokalemia?
How do you treat hypokalemia?
foods rich in K
K supplementation (required if < 3.0 mEq/L)
check Mg level
How should K supplementation be given?
chloride salt - otherwise won't hang on to K very well
IV - dose 10-20 mEq over at least 1h
peripheral 10 mEq/h
central 20 mEq/h (only with monitor)
NEVER give IV push - burn out the vessel
check K levels after every 30-40 mEq
What causes hyperkalemia?
elevated body stores
decreased excretion (renal failure, ACEI, ARBs, NSAIDs, K sparing diuretics)
What are the sx of hyperkalemia?
peaked T wave
How do you treat hyperkalemia?
CaCl or Ca gluconate - first line
insulin + glucose (if needed)
kayexelate (could cause fluid retention d/t increased Na)
lasix (if fluid volume will tolerate it)
stabilize the heart
remove from body
What is the normal serum level of phosphorus (phosphate)?
What is considered to be mild to moderate hypophosphatemia?
What is considered to be severe hypophosphatemia?
What are the causes of hypophosphatemia?
vitamin D deficiency
What are the sx of hypophosphatemia?
How do you treat mild-moderate hypophosphatemia?
50-60 mmol/d divided into 3-4 doses (notice dose is in mmol, not mEq)
K-Phos Neutral 1-2 tabs QID w/water
0.08 - 0.15 mmol/kg
repeat until serum phosphorus > 2mg/dL to avoid going hyperphosphatemic
How do you treat severe hypophosphatemia?
0.25 - 0.5 mmol/kg IV
repeat until serum phosphorus > 2 mg/dL to avoid going hyperphosphatemic
What are the causes of hyperphosphatemia?
What are the sx of hyperphosphatemia?
soft tissue calcification (keep Ca-Phosphate product < 55)
How do you treat hyperphosphatemia?
aluminum or magnesium antacids
calcium (first line if Ca is not too high)
sevelamer (give with meals)
What is the normal serum level of magnesium?
What is the best choice for treating mild hypomagnesemia (1-1.5 mEq/dL) without sx?
Mag Ox tabs (least chance of diarrhea)
What is the treatment for moderate hypomagnesemia (<1 mEq/dL with no life-threatening sx)?
: 1 mEq/kg/d IV cont infusion of MgSO
Days 2-5: 0.5 mEq/kg/d IV of MgSO
What is the treatment for severe hypomagnesemia (<1 mEq/L with life-threatening sx)
0.5 mEq/kg IV over 6h,
0.5 mEq/kg IV over 18h
What are the symptoms of hypomagnesemia?
torsades de pointes
Which electrolyte is considered to be a "sedative for the CV system"?
increases arterial dilation
What are the SE of IV magnesium?
What are the SE of oral magnesium?
What are the sx of hypermagnesemia?
decreased deep tendon reflexes
What is the treatment for hypermagnesemia?
avoid Mg products
saline + loop diuretics
Hemodialysis (HD) in pt with End Stage Renal Disease (ESRD)
What is the normal serum level of Ca?
8.5-10.5 mg/dL (2.1-2.7 mmol/L)
4.6-5.2 mg/dL (1.15-1.38 mmol/L)
What is the function of potassium?
maintains resting potential
lots of other fx
What is the fx of Ca?
bone and teeth
neuromuscular activity (SA node, AV node)
muscle cell contraction
What is the effect of PTH on serum calcium?
What is the effect of calcitonin on serum calcium?
How does calcitonin lower serum calcium?
increases deposition in bone
reduces absorption in the gut
decreases absorption in the kidneys
How does PTH increase serum calcium?
increases absorption in the kidneys
increases absorption in the gut
increases release from bone
What is the equation to calculate corrected calcium when a pt has low albumin?
(4-alb)0.8 + Ca
What are the causes of hypocalcemia?
vitamin D deficiency
hyperphosphatemia (secondary hypoparthyroidism)
bisphosphonates, loops, calcitonin, phenytoin
How are calcium and phosphate related in the homeostasis provided by calcitonin and PTH?
As one goes up, the other goes down
What are the sx of hypocalcemia?
prolonged QT interval
What are the treatments for acute symptomatic hypocalcemia?
1g CaCl IV
2-3 g Ca gluconate (not efficient in low liver fx)
What are the treatments for chronic asymptomatic and corrected symptomatic hypocalcemia?
1-3g/d of elemental Ca (vit D optional):
carbonate (Tums, OsCal, VIACTIV) 40% elemental Ca
Acetate (PhosLo) 25% elemental Ca used as a phos binder
What are the sx of hypercalcemia?
prolonged PR and QRS
How do you tx hypercalcemia?
200-300cc/h NS + lasix 40-80mg IV q 1-4h (first line)
4 units/kg calcitonin SQ or IM q 12h
pamidronate 30-90mg IV over 2-24h
monitor albumin, ECG, serum Ca q 6-12h if symptomatic (daily if mild-moderate)