Fluid Balance Flashcards
Adequate blood volume is required for…
Tissue perfusion
Serum osmolality is an important determinant of…
Intracellular fluid volume - important in the brain
Total body water makes up of ____ body weight
50-60%
1L is approximately 1 kg
_____ of total body water is intracellular. ____ of total body water is extracellular.
2/3. 1/3.
Extracellular fluid consists of both ____
Interstitial fluid (3/4) and plasma (1/4)
Water is able to move freely from one compartment to another, however electrolytes…
Require active transport
Extracellular fluid osmolality is maintained primarily by…
Sodium
And anion counterparts chloride + bicarbonate, as well as glucose + urea concentrations
About 90% of body’s sodium is extracellular
Intracellular fluid osmolality is determined by…
Potassium concentration
and accompanying anion proteins + phosphate
Water moves freely across cell + vascular membranes, but it often follows ____ in order to…
Sodium - keep intra/extracellular osmolality equal
Proteins are present within intracellular fluid and within blood vessels (albumin), but NOT in the interstitial extracellular fluid. This helps to…
Maintain an osmotic gradient between interstitial fluid and intravascular space of the extracellular fluid.
Holds fluid in the blood vessels - AKA oncotic pressure
Recall that low albumin states lead to decreased oncotic pressure in blood vessels, leading to increased fluid in interstitial spaces
Cells are able to regulate their internal volume in response to osmotic stress, via…
Activation of membrane carrier proteins and channels
Despite cell mechanisms, rapid +/- extreme changes in osmolality can cause…
Cell swelling or shrinkage
Plasma hyper-osmolality causes…
Brain cell shrinkage - somnolence, confusion, which could progress to cerebral bleeding + death
Plasma hypo-osmolality causes…
Brain cell swelling - headache, N/V, gait instability, which could progress to seizures, coma, death
Plasma osmolality refers to…
The concentration of effective solutes in plasma (relative to water)
The body’s ability to sense + respond to changes in plasma osmolality is mediated by ____ - their roles is to…
Osmoreceptors - initiate corrective actions by release of hormones
Key to regulating water homeostasis
Antidiuretic hormone is AKA…
Vasopressin
ADH is released in response to…
Increased plasma osmolality
Too much sodium, other solutes as sensed by osmoreceptors
ADH actions involve…
Stimulating water reabsorption in the distal tubule/collecting duct of the kidney, reducing diuresis. Results in excretion of a more concentrated urine
Stimulates thirst
Corrective measures of ADH result in…
Increasing amount of water in circulation, restoring plasma osmolality to normal
ADH is also released in response to non-osmotic stimuli, when the osmoreceptors detect…
Decreased circulating blood volume or decreased blood pressure
Ex: vomiting, diarrhea, poor kidney perfusion, extreme blood loss
Water conservation via ADH in response to non-osmotic stimuli is able to restore circulating blood volume, but at the expense of…
Decreased serum osmolality = dilutional hyponatremia
Aldosterone is released in response to…
Low blood volume or BP stimulating RAAS, as well as increased serum potassium/decreased serum sodium
Aldosterone actions involve…
Stimulating reabsorption of sodium from distal convoluted tubule of kidney.
Resulting in increased serum sodium (and water since water follows sodium) and decreased serum potassium
Natriuretic peptides are relased in response to…
Increased BP +/- blood volume - released by atria/ventricles
Natriuretic peptide actions involve…
Inhibiting activity of aldosterone by decreasing SNS activity (decreasing RAAS activation) and increasing vasodilation
Opposite effects of ADH and aldosterone
The role of the kidney in fluid balance is to…
Regulate water excretion to keep serum osmolality relatively constant, despite variability in water intake
In a euvolemic patient, the goal of fluid/electrolyte administration is to…
Maintain homeostasis
Ideally best way to do this would be to continue eating/drinking normally
If it is not possible for a euvolemic patient to eat/drink normally…
These fluid losses will need to be replenished
Minimum amount of fluid needed per day is around 1400 mL (60 mL/hr)
Maintenance fluid therapy includes…
Water
Electrolytes
Dextrose (prevent protein catabolism, starvation ketoacidosis)
Volume depletion generally results from…
Decreased total body sodium - due to renal or extrarenal sodium loss from extracellular fluid
Renal volume depletion losses may be due to…
Increased diuresis, salt-wasting nephropathies, mineralocorticoid deficiencies
Extrarenal volume depletion losses may be due to…
Fluid loss from GI tract
Skin loss
Hemorrhage
Increased capillary permeability
A LOT of free water would have to be lost to cause volume depletion, because…
Most of the water is in intracellular fluid
This is mostly a sodium deficiency issue
Signs of hypovolemia may involve…
Decreased JVP
Postural hypotension, postural tachycardia
Decreased sweat
Symptoms of hypovolemia may involve…
Mild - may be asymptomatic
Thirst, fatigue, muscle cramps, orthostatic dizziness
Severe - mental status changes, renal failure, hypovolemic shock
Lab values in hypovolemia may involve…
Decreased urine sodium, decreased fractional excretion of sodium
Decreased urine chloride
Increased urine osmolality
May be helpful but needs to be correlated with the clinical picture
Mild hypovolemia can be corrected…
Orally
Fluid replacement - sodium + water (pedialyte)
Factors that necessitate IV therapy for hypovolemia include…
Symptomatic fluid loss
Hemodynamic instability
Intolerance to oral administration
Frequent reassessment of fluid status is required in order to…
Prevent over-correction
The goal of hypovolemia treatment is to…
Replenish intravascular volume by expanding ECF compartment
Sodium-based solutions are used because…
Sodium will remain in extracellular fluid compartmet
Isotonic fluids are used, since they contain sodium concentration….
Similar to that of the plasma fluid in the extracellular compartment. Therefore, fluids will remain in this spce
Normal saline generally preferred
Fluids can be administered as a ____ or at a ____.
Bolus, or at a steady infusion rate.
Symptomatic volume depletion = usually administer with bolus to expand intravascular space
Hypovolemia treatment needs to be cautioned in…
Poor cardiac function
Peripheral edema
Volume overload
Water IV cannot be administered to correct hypovolemia because…
It will go straight into cells (intracellular fluid)
Sodium helps keep fluid in blood vessels which helps replenish volume
Hypervolemia is primarily from two criteria…
Surplus of todal body sodium (disorder of renal sodium retention)
Decreased effective circulating volume (HF, cirrhosis…)
Expansion of the interstitial fluid compartment of the extracellular fluid may result in…
Peripheral edema
Ascites
Pleural effusions
Expansion of the intravascular compartment of the extracellular fluid may result in…
Increased JVP
Pulmonary rales
DIfferent heart sounds
Elevated BP
Hypervolemia is primarily a ____ diagnosis
Clinical - lab values are generally unremarkable
Chest X-ray can help detect pleural effusion, pulmonary edema
Symptoms of hypervolemia may involve ____. Signs and symptoms do not usually appear until…
Dyspnea
Orthopnea
Leg swelling
Abdominal distention
3-4L of fluid retention has occurred
In any case of hypervolemia, it is important to address…
The underlying cause
HF, liver, kidney disease
Sodium excess can be managed with…
Dietary sodium restriction
Diuretics
Thiazides work by…
Blocking NaCl transporters in the distal convoluted tubule
However, often results in compensatory water reabsorption in the proximal tubule
More sodium than water lost
Loop diuretics work by…
Blocking sodium/potassium/chloride transporter in thick ascending loop of henle.
Preferred for brisk + immediate diuresis
Potassium-sparing diuretics work by…
Decreasing sodium reabsorption in the collecting duct
Relatively small diuretic effect
Thiazide diuretics effect on electrolytes include…
Decreasing sodium, potassium, magnesium
Increasing calcium
Loop diuretics effect on electrolytes include…
Neutral sodium
Decreasing potassium, magnesium, calcium.
Potassium-sparing diuretics effect on electrolytes include…
Increasing potassium
Neutral effect on sodium, magnesium, calcium
