FLUIDS-AB balance Flashcards
What are 6 goals of perioperative fluid management
- Euvolemia
- CO (preload)
- O2-carrying capacity
- A-B balance
- Electrolyte balance
- Coagulation status
What percentage of body weight is water
60% (42 L in the 70-kg standard pt)
What percentage of total body weight are the following
Intracellular volume
Extracellular volume
IC vol = 40% TBW (28 L)
EC vol = 20% TBW (14 L)
What are the 3 major ions of the intracellular fluid
K+
Mg++
PO4–
What are the 4 major ions of the extracellular fluid
Na+
Ca++
Cl=
HCO3-
What are the divisions of ECF and their percentage of total body water
Interstitial fluid = 16% or 11 L
Plasma fluid = 4% or 3 L
How do neonates differ in total body water percentage
They have a higher TBW% by weight
How do females, the obese, and the elderly differ in total body water percentage
They have a lower TBW% by weight
What are 2 forces that move fluid from the capillary to the interstitial space
Pc = Capillary hydrostatic pressure (pushes fluid out)
pi if = interstitial oncotic pressure (pulls fluid out)
What are 2 forces that move fluid from the interstitial space into the capillary
Pif = interstitial hydrostatic pressure (pushes fluid in)
pi c = capillary oncotic pressure (pulls fluid in)
What is the equation for net filtration pressure at the capillary
NFP = (Pc - Pif) - (pic - piif)
What actions occurs with the following net filtration pressures in the capillaries
NFP > 0
NFP < 0
NFP > 0 = fluid EXITS capillary
NFP < 0 = fluid is pulled INTO capillary
What are 4 conditions that impair the integrity of glycocalyx in the capillary
- Sepsis
- Ischemia
- DM
- Major vascular surgery
What happens when the glycocalyx is disrupted in the capillary
It contributes to capillary leak and accumulation of fluid and debris in the interstitial space
This reduces tissue oxygenation
What makes up blood volume
The sum of plasma volume and blood cell volume
What is the hematocrit composed of
The fraction of the blood volume that is occupied by erythrocytes
What factors increase Hct
Increased number of RBCs (polycythemia)
Decreased plasma volume (hypovolemia)
What factors decrease Hct
Decreased number of RBCs (anemia)
Increased plasma volume (hemodilution)
What is the purpose of the lymphatic system
Scavenge and remove fluid, protein, bacteria, and debris from the interstitium via negative pressure
What causes edema in relation to the lymphatic system
When the rate of interstitial fluid accumulation exceeds the rate of removal by the lymphatics
How is lymph returned to circulatory system
Via the thoracic duct at the juncture of the internal jugular and subclavian vein
What is the significance of the left vs right thoracic ducts and venous access
The ducts can be injured during venous cannulation
The left side is at greater risk of chylothorax because it is larger
Define osmosis
The net movement of water across a semipermeable membrane
What are 2 factors that affect osmosis
- Solute concentration determine direction of water movement
- Water moves from areas of low to high solute concentration
Define diffusion
the net movement of a substance from an area of higher concentration to an area of lower concentration across a fully permeable membrane (both water and solute pass)
Define osmotic pressure
The pressure of a solution against a semipermeable membrane that prevents water from diffusing across that membrane
What is osmotic pressure a function of
The number of osmotically active particles in a solution NOT their molecular weights
What is an osmole
The number of osmotically active particles in a solution
How are osmolarity and osmolality similar
They both measure the concentration of particles (osmoles) in a solution
What is osmolarity
Osmoles per liter of solution (mOsm/L of total solution)
What is osmolality
Osmoles per kilogram of solvent (mOsm/kg of H2O)
What is the equation for plasma osmolarity
Osmolarity = 2(Na+) + (glucose/18) + (BUN/2.8)
What factors are included in the calculation of plasma osmolarity
Na+
Glucose
BUN
List solutions that are hypotonic
NaCl 0.45%
D5W
What is the effect of hypotonic solutions
Water enters and cells swell
List crystalloids that are isotonic
NaCl 0.9%
LR
Plasmalyte A
List colloids that are isotonic
Albumin 5%
Voluven 6%
Hespan 6%
List crystalloids that are hypertonic
NaCl 3%
D5 NaCl 0.9%
D5 NaCl 0.45%
D5 LR
Which colloid is a hypertonic solution
Dextran 10%
What is the effect of hypertonic solutions
Water moves out of cells and they shrink
Why is D5W a hypotonic solution
The glucose is metabolized to CO2 and H2O adding to free water
How does administration of hypotonic solutions affect ICF, ECF, and osmolarity
ICF = volume increase, osmolarity decreased ECF = volume increased, osmolarity decreased
How does administration of isotonic solutions affect ICF, ECF, and osmolarity
ICF = volume and osmolarity remain the same ECF = volume increase, osmolarity same
How does administration of hypertonic solutions affect ICF, ECF, and osmolarity
ICF = decreased volume, increased osmolarity ECF = increased volume, increased osmolarity
What are the benefits of dextran 40 on blood viscosity
It reduces viscosity and improves microcirculatory flow in vascular surgery
What effect does albumin have on inflammation
It has anti-inflammatory properties
What is the replacement ratio of crystalloid vs colloid
Crystalloid = 3:1 Colloid = 1:1
What is a disadvantage of albumin
It binds with Ca++ and can lead to hypocalcemia
What is the FDA black box warning for synthetic colloids
Risk of renal injury
How can coagulopathy related to colloids be minimized
Don’t exceed 20 mL/kg
Which colloids have the greatest risk of coagulopathy
Dextran > hetastarch > hextend
Which colloid has the greatest anaphylactic potential
Dextran
What are disadvantages of fluid replacement with crystalloids
- Limited ability to expand plasma volume
- Higher potential for peripheral edema
- Dilutional effect on coagulation factors
What imbalance can occur with large volumes of NaCl
Hyperchloremic metabolic acidosis
Increased Cl- => Increased HCO3- excretion by kidneys
What is the most abundant intracellular cation
Potassium
What is the role of potassium as an intracellular cation
- Regulates resting membrane potential of nervous tissue, skeletal muscle, and cardiac muscle
How does hypo vs hyperkalemia affect membrane potentials
Hypokalemia = hyperpolarizes membranes, making it harder to depolarize
Hyperkalemia = increases resting membrane potential, making depolarization easier
Which organ regulates potassium homeostasis
The kidneys
What 5 medications and conditions can shift K+ intracellularly causing hypokalemia
- Insulin + D50
- Hyperventilation
- HCO3
- Beta-2 agonist (albuterol)
- Hypokalemic periodic paralysis
What 4 medications or conditions can shift K+ extracellularly causing hyperkalemia
- Acidosis
- Succinylcholine
- Beta-blockers
- Hyperkalemic periodic paralysis
What are 3 drugs that can impair potassium excretion from the kidneys
- NSAIDs
- Spironolactone
- Triamterene
What are symptoms of hypokalemia
Skeletal muscle cramps and weakness that can lead to paralysis
How can hyperkalemia present
Cardiac rhythm disturbances
Describe the EKG changes with hypokalemia
PR interval = LONG
QT interval = LONG
T wave = FLAT
U wave present
Describe the EKG changes with hyperkalemia
EKG change = K+ concentration: Peaked T waves = 5.5-6.5 P wave flattening, PR prolongation = 6.5-7.5 QRS prolongation = 7.0-8.0 QRS-> sine wave -> VF = >8.5
How is hyperkalemia treated (8)
Cardiac membrane stabilization:
Calcium
Redistribution (shift intracellularly)
- Insulin + D50
- Hyperventilation
- HCO3
- Beta-2 agonist (albuterol)
Elimination:
- K+ wasting diuretics
- Kayexalate
- Dialysis
What are 5 ways potassium is lost via the GI tract
- Vomiting/diarrhea
- NGT suction
- Zollinger-Ellison syndrome
- Jejunoileal bypass
- Kayexalate
What is the most abundant extracellular cation and primary determinant of serum osmolarity
Sodium
3 ways that sodium homeostasis maintained
- Glomerular filtration rate
- Renin-angiotensin-aldosterone system
- Anti-natriuretic peptides (BNP)
To determine the cause of hypo/hypernatremia, what else must be evaluated
- Plasma osmolarity
2. ECF volume
Which ion is most important during neural tissue and muscle cell depolarization
Sodium