Fluid, Electrolyte, and Acid-Base Balance Flashcards
(120 cards)
Review slide 6 and 7 for a good overview video and flowchart of fluid balance
Does water rely on active transport for movement between body compartments?
No, water moves freely from one body water compartment to another according to osmolar gradient
Do electrolytes (Na+, K+, Cl-, PO4-) rely on active transport for movement between body water components?
Yes, their movement between intracellular and extracellular compartments requires active transport
What ions maintain osmolality in extracellular fluid (ECF)?
Primarily by Na+, but also by chloride and bicarbonate anions
What ions maintain osmolality in intracellular fluid (ICF)?
Primarily by K+ (cations), but also by anion proteins and phosphate
Do proteins like albumin contribute to osmolality?
Yes, but are only found in intracellular fluid and within blood vessels
Proteins are not found in interstititial ECF
This lack of proteins in the interstitial ECF helps maintain osmotic gradient between the interstitial fluid and blood vessels (if pt has low serum albumin, it can cause edema due to loss of osmotic gradient towards vessels)
What causes low albumin states to result in edema?
If pt has low serum albumin, it can cause edema due to loss of osmotic gradient towards vessels. More fluid remains in the interstitial space
Review oncotic pressure
What is the severe consequence of plasma hyperosomolality?
Brain cell shrinkage (water moves into plasma from cell)
This results in somnolence, confusion -> if
severe enough -> cerebral
bleeding, death
What is plasma osmolality?
concentration of effective solutes in plasma (relative to water)
What is the severe consequence of plasma hyo-osmolality?
Brain cell swelling ->
headache, N+V, gait
instability -> seizures,
coma, death
What are osmoreceptors?
Specialized cells that recognize changes in plasma osmolality and initiate corrective actions by the release of hormones, etc.
When is vasopressin/ADH released by osmoreceptors?
Released in response to increased plasma osmolality (as sensed by osmoreceptors
ex. increased Na+ after salty meal
Also released in response to non-osmotic stimuli when osmoreceptors in the brain detect ↓ circulating
blood volume or ↓ blood pressure
ex. diarrhea, poor kidney perfusion, extreme blood loss
What are the corrective actions associated with vasopressin/ADH when increased osmolality is detected by osmoreceptors?
Stimulates water reabsorption in the distal tubule/collecting duct of the kidney (↓ diuresis) -> excretion of a
more concentrated urine (hold on to more fluid)
Also stimulates thirst (increase fluid intake)
What corrective actions are associated with vasopressin/ADH in response to lower blood volume?
Water conservation restores circulating blood volume at the expense of decreased serum osmolality
-> dilutional hyponatremia
What stimulates release of aldosterone?
- ↓ blood volume or ↓ blood pressure activates Renin-Angiotensin-Aldosterone System (RAAS) ->stimulates
release of aldosterone - ↑ serum K+ or ↓ serum Na+ can also stimulate aldosterone release
What is the role of aldosterone on fluid balance?
Stimulates reabsorption of sodium from the distal convoluted tubule of the kidney -> ↑ serum Na+ (and
therefore water because water follows sodium) and ↓ serum K+ (risk of hypokalemia)
What stimulates the release of natriuretic peptides?
Released by the atria/ventricles of the heart in response to ↑ blood pressure and/or ↑ blood volume
What is the role of natriuretic peptides on fluid balance?
Inhibit the activity of aldosterone by reducing sympathetic nervous system activity (↓ RAAS activation) and also increases vasodilation
Oppose the effects of ADH and aldosterone
What is the role of the kidney in maintaining fluid balance?
Kidney regulates water excretion to keep serum osmolality relatively constant (275-290 mOsm/kg) despite variability in water intake
What determines serum osmolality?
Primarily determined by sodium concentration
- ~90% of the body’s sodium is extracellular
- Sodium is the predominant solute in the ECF
Also affected by glucose and urea concentrations
Serum osmolality = (2 x serum Na+) + serum glucose + serum urea
What is included in supplemental fluid therapy?
Water
Electrolytes (usually 75-175 mEq Na+ and 20-60 mEq K+ per day)
Dextrose (100-150g/day to prevent catabolism and starvation ketoacidosis)
Review slide 19
What are some mechanisms by which the body looses water?
Fluid loss in urine + fluid loss in stool + insensible fluid loss from skin, respiratory tract
Minimum amount of fluids needed per day ~ 1400 mL (or 60mL/hr) to recover losses
What are the primary causes of hypovolemia?
Volume depletion generally results from decreased total body sodium due to renal or extrarenal sodium loss from the ECF