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
