Fluids and Electrolytes Flashcards
Total Body Water
roughly 2/3 of total body weight is water (men); infants have a little more body water, women have a little less
2/3 of water weight is intracellular (mostly muscle)
1/3 of water weight is extracellular
2/3 of extracellular water is interstitial
1/3 of extracellular water is in plasm
What determines osmotic pressures
Proteins –> determine plasma / interstitial compartment osmotic pressures
Na –> determines intracellular / extracellular osmotic pressure
Volume overload
most common cause is iatrogenic; first sign is weight gain
Cellular catabolism
can release a significant amount of H20
0.9% normal saline
Na 154, Cl 154
LR
Na 130, K 4, Ca 2.7, Cl 109, bicarb 28
Plasma osmolarity
(2 x Na) + (glucose / 18) + (BUN / 2.8)
normal 280-295
Best indicator of adequate volume replacement
urine output
Fluid loss during open abdominal operations
0.5 - 1.0 L / h unless there are measurable blood losses; usually do not have to replace blood lost unless it is > 500cc
Insensible fluid losses
10cc/kg/day; 75% skin, 25% respiratory, pure water
D5 1/2NS + 20K
5% dextrose will stimulate insulin release, resulting in amino acid uptake and protein synthesis; also prevents protein catabolism; d5 1/2 NS @ 125/h provides 150g glucose per day (525 kcal/day)
GI fluid secretion (stomach, biliary system, panc, duo)
stomach 1-2 L / day
biliary, pancreas and duodenum 500 - 1000 mL / day each
Normal K requirement
0.5 - 1.0 mEq/kg/day
Normal Na requirement
1 - 2 mEq/kg/day
GI electrolyte losses
sweat, saliva, stomach, panc, bile, SB, colon
sweat - hypotonic saliva - K+ (highest concentration of K in body) stomach - H+ and Cl- pancreas - HCO3- SB - HCO3-, K+ Colon - K+
Hyperkalemia
peaked T waves initial finding on EKG
calcium gluconate (membrane stabilizer for heart)
hypokalemia (t waves disappear); may need to replace mag before you can correct K
Hypernatremia
restlessness, irritability, ataxia, seizures
correct with D5 water slowly to avoid brain swelling
total free water deficit =
0.6 x patient’s weight (kg) x [(Na+/140) - 1]
water requirement = desired change in Na over 1 day x TBW / desired Na after giving water requirement
TBW = 0.6 x patients weight (kg)
change Na 0.7 mEq/h (16 mEq/day for below)
Hyponatremia
headaches, delirium, seizures, nausea, vomiting
Na deficit = 0.6 x (weight in kg) x (140-Na)
water restriction is first treatment for hyponatremia, then diuresis, then NaCl replacement
correct Na slowly to avoid central pontine myelinosis (no more than 1mEq/h)
(e.g., SIADH)
Pseudohyponatremia
caused by hyperglycemia; for each 100 increment of glucose over normal, add 2 points to Na value
Hypercalcemia
lethargic state; breast cancer most common malignant cause
no LR (contains Ca)
no thiazide diuretics (these retain Ca)
Tx: NS 200-300cc/h, lasix
for malignt diseaes: mithramycin, calcitonin, alendronic acid, dialysis
Hypocalcemia
hyperreflexia, chvostek’s sign (tapping on face gets twitching), peiroral tingling and numbness, Trousseau’s sign (carpopedal spasm), prolonged QT interval
may need to correct mag before being able to correct Ca
protein adjustment for Ca: for every 1 g decrease in protein add 0.8 to Ca
HyperMagnesemia
causes lethargic state; burn, trauma, renal dialysis patients; tx: calcium
hypomag
similar to hypocalcemia; hyperreflexia
Anion gap
Na - (HCO3 + Cl); normal 10-15
Anion gap acidosis
methanol, uremia, diabetic ketoacidosis, paraldehydes, isoniazid, lactic acidosis, ethylene glycol, salicylates
normal gap acidosis
usually due to loss of Na/HCO3 (ileostomies, SB fistulas)
Metabolic alkalosis
- usually a contraction alkalosis; nasogastric suction results in hypochloremic, hypokalemic, metabolic alkalosis and paradoxical aciduria
- loss of Cl and H ion from stomach 2/2 NG tube (hypochloremia and alkalosis)
- loss of water causes kidney to reabsorb Na in exchange for K (Na/K ATPase), thus losing K (hypokalemia)
- Na/H exchanger activated in an effort to reabsorb water along with K/H exchanger in an effort to reabsorb K (results in paradoxical aciduria)
Henderson Hesselbach equation
pH = pK + log [HCO3] / [CO2]
FeNA
(urine Na/Cr) / (plasma Na/Cr)
prerenal FeNa < 1%, urine Na < 20, BUN/Cr ratio > 20, urine osmolality > 500 mOsm
*70% of renal mass must be damaged before increase Cr and BUN
Contrast dyes
volume expansion best prevents renal damage (HCO3 and n-acetylcysteine gtt)
Myoglobin
converted to ferrihemate in acidic environment, which is toxic to renal cells; tx: alkalinize urine
Tumor lysis syndrome
- release of purines and pyrimidines leads to increase PO4 and uric acid, decrease Ca
- can result in increase BUN and Cr, EKG changes
tx: hydration, allopurinol (decrease uric acid production), diuretics, alkalinization of urine
Vitamin D (cholecalciferol)
- made in skin (UV sunlight) from 7-dehydrocholesterol
- goes to liver for (25-OH) then kidney for (1-OH); this creates active form of vitamin D
- active form vitamin D increase calcium-binding protein, leading to increase intestestinal calcium absorption
Chronic renal failure
decrease active vit D (decrease 1-OH hydroxylation) –> decrease Ca reabsorption from gut (decrease Ca-binding protein); anemia from low erythropoietin
transferrin
transporter of iron
ferritin
storage form of iron
