Fluids and blood Flashcards
Describe the distribution of body water
In the textbook 70 kg male, water represents 60% of the total body weight. This equals 42 L
TBW can be divided into:
* Intracellular volume = 40% of total body weight (28L)
* Extracellular volume= 20% of total body weight or (14L)
ECV can be further divided into:
* Interstitial fluid = 16% of total body weight (11L)
* Plasma fluid = 4% of total body weight or (3L)
Remember 60/40/20 (15/5) or (16/4)- either will work
Which populations tend to have a greater percentage of TBW% by weight? which have less?
Populations with higher TBW% by weight: Neonates
Populations with lower TBW% by weight: Females, obese, and elderly
what are the 2 most important determinants of fluid transfer between the capillaries and interstitial space?
The plasma is in direct contact with the interstitial fluid by way of pores in the capillaries. The movement of fluid between the intravascular space and the interstitial space is determined by:
* Starling forces
* The glycocalyx
Describe the Starling forces in the context of capillary fluid transfer
- Forces that move fluid from the capillary to the interstitium:
(c= capillary, if= interstitial fluid)
* Pc= capillary hydrostatic pressure (pushes fluid out of the capillary)
* (pie symbol) if = interstitial oncotic pressure (pulls fluid out of capillary) - Forces that move fluid from the interstitium into the capillary:
* Pif= Interstitial hydrostatic pressure (pushes fluid into capillary)
* (Pie symbol) c= capillary oncotic pressure (pulls fluid into capillary)
net filtration pressure= (Pc- Pif) - (pie c- pie if)
NFP >0= filtration (fluid exits capillary)
NFP <0= Reabsorption (fluid is pulled into capillary)
What is the glycocalyx, and what factors disrupt it?
The endothelial glycocalyx forms a protective layer on the interior wall of the blood vessel. It can be viewed as the gatekeeper that determines what can pass from the vessel into the interstitial space. It also contains anticoagulant properties.
Disruption of the glycocalyx contributes to capillary leak. Accumulation of fluid and debris in the interstitial space reduces tissue oxygenation. Conditions that impair the integrity of the glycocalyx include:
- Sepsis
- Ischemia
- Diabetes mellitus
- Major Vascular surgery
what is lymph and how does the lymphatic system work?
You can think of the lymphatic system as a fluid scavenger. It removes fluid, protein, bacteria, and debris that has entered the interstitium. It accomplishes this goal with a pumping mechanism that propels lymph through a vessel network line with one-way valves. This creates a net negative pressure in the interstitial space
Edema occurs when the lymphatic system is unable to do its job.
how is lymph returned to the systemic circulation?
Lymph is returned to the venous circulation by way of the thoracic duct at the juncture of the internal jugular and subclavian vein.
You can injure the thoracic duct during venous cannulation. Since the thoracic duct is larger on the left side, there is a greater risk of chylothorax (lymph in the chest) during left-sided IJ insertion.
What is the difference between osmosis and diffusion?
Osmosis is the net MOVEMENT of WATER across a semipermeable membrane, where the direction of water movement is driven by the difference in solute concentration on either side of the membrane (only the solvent moves)
Diffusion is the net Movement of MOLECULES from a region of high concentration to a region of low concentration (solvent AND solute move)
what is osmotic pressure, and what is its primary determinant?
Osmotic pressure is the pressure of a solution against a semipermeable membrane that prevents water from diffusing across that membrane
- osmotic pressure is a function of the number of osmotically active particles in a solution
- It is NOT a function of their molecular weights
what’s the difference between osmolarity and osmolality?
Both are measures of concentration- the amount of solvent within a defined space
* Osmolarity measures the number of osmoles per liter of solution
* osmolality measures the number of osmoles per kilogram of solvent
what is the reference value for plasma osmolarity, and what are the 3 most important contributors?
Plasma osmolarity is normally 280-290 mOsm/L
The 3 most important determinants are: sodium, glucose, and BUN
Plasma osmolarity= 2(Na) + Glucose/18 + BUN/2.8
from this equation, you can see that sodium is the most important determinant of plasma osmolarity
* you should also notice that hyperglycemia or uremia can increase plasma osmolarity
What is the difference between hypotonic and hypertonic solution?
Tonicity compares the osmolarity of a solution relative to the osmolarity of the plasma. Remember that plasma is the reference point we use to make the comparison.
Since plasma is isotonic to cells, we can think about tonicity another way. We can use it to compare the tonicity of a solution to the tonicity of the cells
Isotonic: 285 mOsm/L
Hypotonic: 255 mOsm/L - cells swell
Hypertonic: 315 mOsm/L- cells shrink
Think of all the IV fluids you can. Which are hypo-, iso-, and hypertonic to plasma? Bonus points if you can list osmolarity of each
Hypotonic solutions
NaCl 0.45% - 154 mOsm/L
D5W- 253
isotonic
NaCl 0.9%- 308
LR- 273
Plasmalyte A- 294
Albumin 5%- 300
Hespan 6%- 309
Hypertonic:
NaCl 3%- 1026
D5 NaCl 0.9%- 560
D5 NaCl 0.45%- 405
D5 LR- 525
Dextran 10%- 350
What is the relationship between the hypotonicity and hypertonicity of IV solutions and increased ICP?
Hypotonic solutions have a lower osmolarity than the plasma (or cells). These fluids are the same as giving free water, and this free water distributes throughout all of the body compartments.
This is why hypotonic solutions are poor expanders of intravascular volume and why you should never give hypotonic solution to a pt with increased ICP. It will cause these cells to swell, increase their volume, and increase ICP.
Instead, hypertonic saline is useful for treating cerebral edema (it pulls water out of cells, causing them to shrink)
how does dextrose affect the tonicity of IV fluids?
you may be thinkin that glucose in IVF (such as D5W) should be osmotically active. Well…you’re half right…
* you’re right because the glucose contributes osmotically active molecules to the plasma
* the other side of the story is that this glucose is metabolized to carbon dioxide and water. What’s left over? Water, and this water is, you guessed it… hypotonic.
how do isotonic IV fluids distribute in the patient?
Isotonic solutions have an osmolarity that is very close to the plasma (or cells). These solutions expand the plasma volume and the ECV.
Crystalloids tend to remain in the intravascular space for around 30 min, before moving the the ECF
what complication can result when hypertonic saline is administered too quickly?
Central pontine myelinolysis
Compare the advantages of colloids to the advantages of crystalloids
Crystalloids:
Replacement ration= 3:1
Expands the ECF
Restores 3rd space loss
* existence of the 3rd space is debatable
Colloids
Replacement ration= 1:1
Increases plasma volume (3-6hrs)
Smaller volume needed
less peripheral edema
Albumin has anti-inflammatory properties
Dextran 40 reduces blood viscosity
* improves microcirculatory in vascular surgery
Compare the disadvantages of colloids to the disadvantages of crystalloids.
Crystalloids:
Limited ability to expand plasma volume
* increases plasma volume (20-30 min)
* higher potential for peripheral edema
Large volume of NaCl-> hyperchloremic metabolic acidosis
* Increase Cl -> HCO3 excretion by the kidney
Dilutional effect on albumin
* reduces capillary oncotic pressure
Dilutional effect on coagulation factors
Colloids:
Natural colloids:
Albumin
* binds Ca -> hypocalcemia
synthetic colloids:
FDA black box on synthetic colloids
* risk of renal injury
coagulopathy
* Dextran > hetastarch > hextend
* Don’t exceed 20mL/kg
* not a problem with voluven
Anaphylactic potential
* Highest risk = Dextran
How does Hyperkalemia affect the EKG? (list the events in order of appearance)
Potassium= 5.5-6.5:
* Peaked T waves
Potassium= 6.5-7.5
* P wave flattening
* PR prolongation
Potassium 7-8:
* QRS prolongation
Potassium >8.5:
* QRS -> sine wave-> VF
How do you treat Hyperkalemia?
Cardiac membrane stabilization:
Calcium
Redistribution (shift K intracellularly):
* Insulin +D50
* Hyperventilation
* Bicarbonate
* Albuterol
Elimination
* Potassium wasting diuretics
* Kayexalate
* Dialysis
Discuss the presentation of hypocalcemia
Skeletal muscle cramps
Nerve irritability -> paresthesia and tetany
Chvostek sign
trousseau sign
Laryngospasm
Mental status changes -> seizures
Long QT interval and short PR
discuss the presentation of hypercalcemia
Nausea
Abdominal pain
HTN
Psychosis
Mental status changes -> seizures
Short QT interval and prolonged PR
What is the treatment of hypercalcemia
0.9% NaCl
Loop diuretic