Fluids, Electrolytes-Nagelhout Ch 21 Flashcards
What tissues have a slight positive Interstitial Fluid Pressure-Pif (usually slightly negative)?
Rigid or encapsulated tissues such as:
Kidneys
Brain
Bone Marrow
and Skeletal Muscle
What is the primary determinant of Both capillary (πp) and interstitial oncotic pressure (πif)? Why?
Albumin. Small molecular weight and a higher concentration than other plasma proteins.
Increases in capillary hydrostatic pressure (Pc) and Interstitial Oncotic Pressure (πif) favor fluid filtration into the?
Interstitial space.
Pc pushes fluid out of intravascular space
πif pulls it out of intravascular space
Increases in the Interstitial Fluid Pressure (Pif) and Plasma Oncotic Pressure (πp) favor fluid filtration into the?
Intravascular space.
Pif pushes fluid out into intravascular space
πp pulls fluid into the intravascular space
What is “Pif”
Interstitial Fluid Pressure
What is “πif”
Interstitial Oncotic Pressure
What is “πp”
Plasma Oncotic Pressure
What is “Pc”
Plasma (capillary) hydrostatic pressure
Positive Net Filtration favors fluid exudation into the?
tissues
Negative Net Filtration favors fluid absorption into the?
vasculature
Describe the overall balance of filtration pressures within the body
Arterial end capillaries tend to be slightly positive
Venous end capillaries tend to be slightly negative.
The overall balance is slightly positive, with a small percent of intravascular volume constantly filtering into interstitial space under normal conditions
Within the interstitial space, fluid movement from the interstitial space into and out of the cell occurs via?
Osmosis
Which electrolyte is a primary determinant of serum osmolality and water transport, thus making ECV dependent on it?
Sodium
Normal daily alterations in TBW are regulated by:
RASS
ADH
and Atrial natriuretic system (SNP)
How does RASS regulate sodium hemostasis?
- Cardiac and renal baroreceptors detect hypotension.
- Juxtaglomerular cells in kidneys release Renin.
- Renin is the precursor for cleaving angiotensin I into active form
- Angiotensin I exerts local vasoconstriction but is the primary precursor for Angiotensin II
- Angiotensin-converting enzyme converts angiotensin I into Angiotensin II in the lungs
- Angiotensin II is a potent vasoconstrictor and directly stimulates renal tubules to reabsorb sodium and water.
- Agt II also causes the adrenal cortex to release aldosterone, which further stimulates sodium and water retention by the kidneys
What does RASS regulate compared to ADH
RASS regulates sodium hemostasis
ADH functions primarily to regulate water balance
How does ADH regulate water balance
- Slight increases in serum osmo are detected by osmoreceptors in the hypothalamus
- Posterior Pituitary Gland releases ADH, and the hypothalamus stimulates thirst
- This causes kidneys to open aquaporin channels within the kidney to reabsorb large water volume
How does ADH play a role in blood pressure?
Decreases in circulating volume detected by baroreceptors stimulate ADH release. Potent vasoconstrictor.
How does Atrial Natriuretic Peptide (ANP) reduce intravascular volume?
- Stretch receptors in cardiac atria release ANP when preload or hypervolemic state is detected.
- This stimulates kidneys to release sodium and water into urine to reduce blood volume.
Additionally, it increases GFR and inhibits renin and ADH release.
Due to low molecular weight, crystalloid solutions contribute to the hemodilution of plasma proteins, which leads to a decrease in which transcapillary pressure?
Plasma Oncotic Pressure
πp
Approximately what percent of administered isotonic crystalloids filter into the interstitial space?
~75-80% once the oncotic pressures are at equilibrium on both sides of the membrane
Normal Saline 0.9% is slightly hyper or hypo osmolar?
Hyper ~310osmo
Lactated Ringers-LR is slightly hyper or hypo osmolar?
Hypo ~275osmo
How does the concentration of sodium and chloride compare in Normal Saline
Equal concentrations. (Even though this is not physiologically normal)
What can occur if Normal Saline is used for acute volume resuscitation?
High chloride load in NS can contribute to dose-dependent hyperchloremic metabolic acidosis. pH may be maintained but with large alterations in base excess.
Hypercholoremia has a substantial impact in?
Renal Function
leading to a decrease in GFR and may also impair the renal handling of bicarbonate.
The increased sodium load introduced by large volumes of NS can cause:
Increased salt and water retention
Hemodilution
Interstitial edema
well into post-op period
In small volumes in neurosurgical patients, which isotonic fluid is preferred for patients at risk for cerebral edema?
0.9% NS due to its mild hyperosmolality