Fluids and Electrolytes

Question 1

Total Body Water

Answer 1

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

Question 2

What determines osmotic pressures

Answer 2

Proteins –> determine plasma / interstitial compartment osmotic pressures
Na –> determines intracellular / extracellular osmotic pressure

Question 3

Volume overload

Answer 3

most common cause is iatrogenic; first sign is weight gain

Question 4

Cellular catabolism

Answer 4

can release a significant amount of H20

Question 5

0.9% normal saline

Answer 5

Na 154, Cl 154

Question 6

LR

Answer 6

Na 130, K 4, Ca 2.7, Cl 109, bicarb 28

Question 7

Plasma osmolarity

Answer 7

(2 x Na) + (glucose / 18) + (BUN / 2.8)

normal 280-295

Question 8

Best indicator of adequate volume replacement

Answer 8

urine output

Question 9

Fluid loss during open abdominal operations

Answer 9

0.5 - 1.0 L / h unless there are measurable blood losses; usually do not have to replace blood lost unless it is > 500cc

Question 10

Insensible fluid losses

Answer 10

10cc/kg/day; 75% skin, 25% respiratory, pure water

Question 11

D5 1/2NS + 20K

Answer 11

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)

Question 12

GI fluid secretion (stomach, biliary system, panc, duo)

Answer 12

stomach 1-2 L / day

biliary, pancreas and duodenum 500 - 1000 mL / day each

Question 13

Normal K requirement

Answer 13

0.5 - 1.0 mEq/kg/day

Question 14

Normal Na requirement

Answer 14

1 - 2 mEq/kg/day

Question 15

GI electrolyte losses

sweat, saliva, stomach, panc, bile, SB, colon

Answer 15

sweat - hypotonic
saliva - K+ (highest concentration of K in body)
stomach - H+ and Cl-
pancreas - HCO3-
SB - HCO3-, K+
Colon - K+

Question 16

Hyperkalemia

Answer 16

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

Question 17

Hypernatremia

Answer 17

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)

Question 18

Hyponatremia

Answer 18

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)

Question 19

Pseudohyponatremia

Answer 19

caused by hyperglycemia; for each 100 increment of glucose over normal, add 2 points to Na value

Question 20

Hypercalcemia

Answer 20

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

Question 21

Hypocalcemia

Answer 21

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

Question 22

HyperMagnesemia

Answer 22

causes lethargic state; burn, trauma, renal dialysis patients; tx: calcium

Question 23

hypomag

Answer 23

similar to hypocalcemia; hyperreflexia

Question 24

Anion gap

Answer 24

Na - (HCO3 + Cl); normal 10-15

Question 25

Anion gap acidosis

Answer 25

methanol, uremia, diabetic ketoacidosis, paraldehydes, isoniazid, lactic acidosis, ethylene glycol, salicylates

Question 26

normal gap acidosis

Answer 26

usually due to loss of Na/HCO3 (ileostomies, SB fistulas)

Question 27

Metabolic alkalosis

Answer 27

• 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)

Question 28

Henderson Hesselbach equation

Answer 28

pH = pK + log [HCO3] / [CO2]

Question 29

FeNA

Answer 29

(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

Question 30

Contrast dyes

Answer 30

volume expansion best prevents renal damage (HCO3 and n-acetylcysteine gtt)

Question 31

Myoglobin

Answer 31

converted to ferrihemate in acidic environment, which is toxic to renal cells; tx: alkalinize urine

Question 32

Tumor lysis syndrome

Answer 32

• 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

Question 33

Vitamin D (cholecalciferol)

Answer 33

• 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

Question 34

Chronic renal failure

Answer 34

decrease active vit D (decrease 1-OH hydroxylation) –> decrease Ca reabsorption from gut (decrease Ca-binding protein); anemia from low erythropoietin

Question 35

transferrin

Answer 35

transporter of iron

Question 36

ferritin

Answer 36

storage form of iron