Fluid and Electrolyte Therapy Flashcards
What fraction is water of the body’s ideal body weight?
2/3; slightly less in women
What fraction of the TBW is intracellular fluid?
2/3
What fraction of the TBW is extracellular fluid?
1/3
What fraction of the ECF is the interstitial body fluid?
2/3
What fraction of the ECF is the plasma body fluid?
1/3
What are the blood volumes in males and females?
M: 66ml/kg
F: 60ml/kg
Thus for a 70 kg pt what is the TBV?
4.2-4.6L
What separates the intravascular and interstitial fluid?
capillary endothelium
Describe the type of barrier the capillary endothelium creates.
impermeable to protiens (primarily albumin) which determine the plasma/interstitial compartment osmotic pressures
What is the primary osmotic particle in the capillary endothelium?
albumin
What separates the intracellular and extracellular membranes?
a cell membrane
Describe the types of barrier the cell membrane creates.
impermeable to ions (sodium) which determine the ICF/ECF osmotic pressures.
What determines the ICF/ECF osmotic pressures?
Na
What happens to capillaries following surgery?
they become leaky, why they are so edematous
What are various IVF choices?
blood
LR
NS
plasma-lyte
What is the main cation of blood?
Na
What is LR?
lactate ringer, more physiologically like blood; bicarb in form of lactate
When can you not use LR?
pt with liver failure
What is NS?
normal saline, pH=5, basically just NaCl
What happens if you leave the pt on NS too long?
pt will get hypercalcemic acidosis
what is plasma-lyte?
new, expensive IVF. pH is more physiologic
acetate is converted to bicarb
gluconate=sugar
Why is serum K not a good indicator of total K?
K is intracellular
Why do you give your standard surgical pt IVF?
maintenance IVF to prevent dehydration
What is the rule for IVF?
4:2:1
4cc/kg/hr for 1st 10 kg
2cc/kg/hr for 2nd 10 kg
1 for each additional kg
What the IVF for a 70kg pt?
110cc/hr
Typically for a major GI surgery what fluids do you use?
isotonic (LR or NS0 for 1st 24 hrs then switch to D5 1/2 NS + 20mEq KCl
pt is NPO so the sugar prevents muscle breakdown
in kids they deteriorate faster give D5 or D10
What does 50kg of glucose per liter cause?
stimulates insulin release resulting in AA uptake and protein synthesis (prevents protein catabolism)
What is the best indicator of adequate volume replacement?
urine output
What is the ideal UO?
> 0.5 cc/kg/hr
What MIVF do you use in a gastric loses patient?
D5 1/2 NS + 20 mEq KCl; sucking up the gastric juices thuse removing H and Cl, replacing it with normal fluids
What MIVF do you use in a pancreas/bile/small intestine surgery patient? (ie fistula, biliary drain, ileostomy)
LR, high output ileostomy, losing alot of bicarb so LR is better
What MIVF do you use in a large intestine surgery patient?
LR +/- K
give extra K as needed or can add to MIVF
-diarrhea: large intestine loses lots of extra HCO3 and K
What do you do for vary large loses? What do you have to remember?
you can write standing orders to replace 1:1, have to remember you did this so you can make sure they stay on it and you can take them off it later
When do you not give K?
renal patients, you will have to dialyse them
Hypovolemia
def?
Signs and symptoms of an underresuscitated pt:
dry mucous membranes decreased turgor extreme thirst low UO (20 pre-renal) low BP low CVP tachycardia FENA <1% (fractional excretion of Na) altered mental status
What is the gold standard for determining if a patient is hypovolemic?
UO
What is it important to note if you see a climbing BUN/Cr?
its probably been going on for awhile
How do you assess a hypovolemic patient?
ABCs
give 2 large bore IVs
foley to monitor UO
All patients are presumed _______________, must rule out otherwise.
bleeding
What do you do with a hypovolemic patient after you have checked the ABCs and hooked them up?
resuscitate with 1-2L bolus of isotonic saline (LR/NS/plasma-lyte) and assess response: BP, UO, HR and mental
if no response make sure they arent bleeding; may be massively underresuscitated and just need more fluid
FeNa
Fractional Excretion of Na
urine Na/urine Cr)/(plasma Na/plasma Cr
What is FENA a good indicator for?
pre renal azotemia
FENa<20
indicates that the kidney is trying to hold onto as much Na as possible
Hypernatremia
Serum Na > 145
What is the most common cause of hypernatremia in a surgical patient?
loss of hypotonic body fluids
Signs and symptoms of hypernatremia:
restlessness, ataxia, seizures, lethargy, altered mental status
most patients are asymptomatic, try to correct before theres a problem
What is the normal range of Na?
135-145
T/F: Any fluid that you lose has more water to salt ratio than blood
T
T/F: Burn patients have too much salt in their body
F, they have too little water
What do you give burn patients first?
LR
What is the calculation for free water deficit?
TBW x (serum Na-140)/140
What are the normal TBWs in males and females?
M- 0.6
F- 0.5
What is the restriction for correction free water deficit?
cannot give faster than 0.5 mEq/L/hr, other wise risk of cerebral edema and seizures
What else would you do in regards to the meds of a burn patient?
request the pharmacy to put their antibiotic into D5W, have to minimize Na containing fluids and meds.
Hypernatremia in association with diabetes insipidus
typically euvolemic
excess loss of free water in urine (ADH promotes water absorption in the distal tubule)
What is the hallmark diagnosis of Hypernatremia with DI?
dilute urine in the face of hypertonic plasma
Central DI:
failure of ADH release from posterior pituitary
Nephrogenic DI:
kidneys unresponsive to ADH
What is the treatment for hypernatremia in a pt with DI?
correct free water deficit as previously described, consider vasopressin/desmopressin w/central DI
With neprogenic it can be adults having a rxn, in kids they lack the receptors: give luke diuretics
Hyponatremia
Serum Na <135
What is the most common cause of hyponatremia?
SIADH, syndrome of inappropriate ADH secretion
What causes hyponatremia?
pain or stress of surgery causes elevated ADH levels post-op, kidneys retain too much free water and the urine is inappropriatley concentrated
How do you tx hyponatremia?
LR or NS, water restriction
What are the signs and symptoms of nyponatremia?
most are asymptomatic, but if severe can present with neurological problems
–delerium/mental status changes, seizures, N/V, wet lungs w/crackles
What is the level of Na where we start seeing mental status changes?
Na <120
What is the goal of resuscitation therapy?
Goal is to correct existing deficits in volume and/or electrolytes
What is the goal of maintenance therapy?
Goal is to maintain water and electrolyte balance in a patient who cannot eat/drink
Accounting for insensible losses
When does resuscitation occur in our ABCs?
Resuscitation occurs in the “C” of the ABC’s
What do we use to resuscitate?
Use Isotonic crystalloids (LR, NS, plasma-lyte)
Best choice to expand plasma volume fastest
In an immediate post op patient what do we give them?
In an immediate postoperative patient, generally give isotonic crystalloids x24hrs
How do the fluids change after the first day post op?
On postop day 1, if patient is clinically euvolemic, switch to maintenance fluids
Hyperkalemia
Serum K > 5.5
Slows the electrical conduction of the heart and can eventually lead to life threatening dysrrhythmias.
What causes hyperkalemia?
Causes: Iatrogenic, rhabdomyolysis, certain drugs, renal insufficiency, massive blood transfusions
What is the tx for hyperkalemia?
Immediately stop any K-containing infusions, Check an EKG for peaked T waves
If EKG changes are present—give IV calcium gluconate to stabilize the cardiac membrane
Then give 1 amp of D50 and 10 units of insulin to drive the potassium intracellularly
Dialysis if extremely high K and patient in renal failure
What is the role of Magnesium?
Major intracellular cation, serves as a cofactor for countless enzymatic reactions (ATP)
Also regulates the movement of calcium into smooth muscle cells
What causes magnesium def?
diuretics, alcoholics, chronic malnutrition, diarrhea, diabetics (urinary losses that accompany glycosuria)
What is the level of mg in the body that makes us think mg def?
<2.0 at shands
What are key things to remember about hypomagnesium?
Can accompany and make hypoK and hypoCa difficult to correct
Arrhythmias: Replace as needed, typically in increments of 2mg IV
Hypermagnesium:
rare, typically renal failure or iatrogenic (OB Wards)
Weakness, Hyporeflexia
Give Calcium, may require dialysis
*DDx postop hyponatremia also includes:
Loop diuretics, iatrogenic, osmotic diuresis from hyperglycemia, adrenal insufficiency
What are the manifestations of hyponatemia?
Mild Sx: anorexia, nausea, lethargy
Mod Sx: disoriented, agitated, neuro deficit
Sev Sx: seizures, coma, death
What happens in acute hyponatremia?
In acute hyponatremia, osmotic forces cause water movement into brain cells leading to cerebral edema
What is psychogenic polydipsia?
Pts drink too much water.. See often in psych pts (tea and toast, pts who drink too much tea or beer and don’t eat anything w/ salt)
What happens in hyponatremia with diuresis/adrenal insuff?
kidney is confused, not holding on to sodium as it should be
What happens in hyponatremia with diarrhea?
Diarrhea: kidney is doing its job, not dumping sodium in face of hyponatremia, but volume status is messed up so you have to fix that first..
What is the tx for urgent hyponatremia?
If symptomatic & urgent (mental status changes), give hypertonic saline (3% NaCl = 513mEq/L NaCl)
What is a complication in treating urgent hyponatremia?
Risk of central pontine myelinolysis (CPM) if corrected too rapidly
CPM- pulls sodium out of the brain
What is the tx of hyponatremia in asymptomatic pts?
Typically, in surgical patients, free water restriction is sufficient to correct hyponatremia
Concentrate all medications
Change MIVF accordingly
Make sure to follow sodium trend
What is the role of potassium in the body?
Potassium is the major intracellular cation, thus plasma levels can be an insensitive marker for total body potassium stores (i.e: DKA)
What are the daily needs of potassium?
Daily needs: 0.5-1mEq/day
Potassium: Needs 35-70mEq/day
What are the causes of hypokalemia?
Diuretics (lasix), diarrhea, Nasogastric drainage (very common in surgical patients), magnesium depletion (impairs K reabsorption across the renal tubules)
Arrythmias, Ileus, Muscle weakness if severe (<2.5)
What is the tx for hypokalemia?
Typically replace in increments of 20-60mEq (IV or PO)
Add KCl to MIVF
Whats something to keep in mind when treating a patient with hypokalemia?
If pt has healthy kidney you will not make them hyperkalemic (kidney will dump K as needed, kidney failure not so much)
What is hyperkalemia?
Serum K > 5.5
Slows the electrical conduction of the heart and can eventually lead to life threatening dysrrhythmias
What are the causes of hyperkalemia?
Causes: Iatrogenic, rhabdomyolysis, certain drugs, renal insufficiency, massive blood transfusions
What are the daily needs of Na?
Sodium: Needs 140-210mEq/day
Problem: Your patient is a 150 pound man who has a serum sodium of 114 mEq and he has become neurologically unstable. Calculate what volume of 3% saline should be used to correct the initial half of his sodium deficit and what length of time it would require?
Factors: 2.2 lbs = 1 kg; 3% Saline has 513 mEq of Na and TBW for a male is 0.65.
(1) 150 lb = 150/2.2= 68 kg; TBW = 0.65 x 68 = 44L x ½(140 – 114) = 572 mEq
(2) mEq rate to increase Na titer by ~ 0.5 mEq/L/hr: 44L x 0.5 mEq/L/hr = 22 mEq/hr
(3) 572/22= 26hr
So if a 70kg male (with TBW 45L) lost 1L of blood, how much to replace using Free water?
(Recall: Plasma is 1/9 of TBW = 1/3 x 1/3)
Takes 9L free water to replace 1L of plasma
So if a 70kg male (with TBW 45L) lost 1L of blood, how much to replace using NS?
(Recall 3-to-1 rule: Plasma is 1/3 ECF)
Takes 3L of NS to replace 1L of plasma
So if a 70kg male (with TBW 45L) lost 1L of blood, how much to replace using albumin/blood?
(1:1 replacement)
Takes 1L of 5% albumin or 3 Units = 1L PRBC
So if a 70kg male (with TBW 45L) lost 1L of blood, how much to replace using ½ NS?
Takes 3L of NS, so it should take ~6L of ½ NS
