- maintain constant physiologic fluid volume intracellularly and extracellularly
- maintain a stable composition of solute in the above fluid compartments
- intake = output ; equilibrium
Fluid intake and output are balanced during steady-state conditions. Fluid intake must be carefully matched with water output to prevent body fluid volumes from dramatically increasing or decreasing.
2100 ml per day is ingested
200 ml per day synthesized as result of oxidation of CHO (krebs cycle)
average total fluid volume intake: 2300 ml per day
variable on climate, habits, physical activity
- not consciously aware of it
- respiratory tract - 350 ml per day of insensible loss
- inspired air becomes saturated with moisture at 47 mmHg at 37*C
- because atmospheric water vapor pressure is less, lungs continually lose moisture via respiration ([ ] gradient)
- in cold weather atmospheric vapor pressure decreases --> even more water loss from lungs as temperature decreases
- Extracellular (1/3)
- 75% interstitial
- 25% plasma
- Intracellular (2/3)
Intake:
- Fluids ingested: 2100 ml
- fluids metabolized: 200 ml
- total: 2300 ml
- insensible loss skin: 350 ml
- insensible loss lungs: 350 ml
- sweat: 100 ml
- bowel: 100 ml
- bowel/urine: 1400 ml
- total: 2300 ml
Intake:
- additional fluid from metabolism: 200 ml
- insensible loss skin: 350 ml
- insensible loss lungs: 650 ml
- sweat: 5000 ml
- UOP: 500 ml
- Total: 6600 ml
- total body water is 60% of body weight --> 42 L
- for women: 50%
- elderly: percentage of total body water decreases as fat increases
- less muscle, less water
- newborn: water is 75% of body weight
- higher concentration of proteins in plasma
- capillaries have low permeability to plasma protein (so proteins stay in capillaries)
- interstitial spaces contain small amounts of plasma proteins
by a highly permeable capillary membrane
- there are more cations in plasma (than in interstitial fluid)
- plasma proteins are negatively charged --> attract cations Na+ and K+
- The donnan effect is extra osmotic pressure attributed to cations attached to dissolved plasma proteins
- accounts for 1/3 of intravascular osmotic pull
- more anions in interstitial fluid - negatively charged proteins repel anions.
major intracellular ion: K+
extracellular ions: Na+, Cl-
- contains both extracellular fluid (plasma) and some intracellular fluid in RBC
- average blood volume of adults approximates 5 L
- 60% is plasma, 40% is red cell mass
In healthy states, intracellular and extracellular compartments are in equilibrium. Water moves across the cell membrane rapidly any intracellular fluid remains isotonic with the extracellular fluid
The net diffusion of water across a selectively permeable membrane from an area of high water concentration to one with lower water concentration.
If NaCl is removed from the extracellular fluid, water will diffuse from the extracellular fluid through the cell membrane into the cell because there is less solute and more water on the extracellular side.
The total number of particles in solution is measured in Osmoles
1 Osmole (osm) = 1 mole of solute particles = 6.02 x 10^23 (avogadros number)
The term osmole refers to the number of osmotic reactive particles in solution. The Osmole is too large for expressing osmotic activity in body fluids. The term Milliosmole (mOsm) is used instead = 1/1000 of an osmole
0.9% NS = 0.9 gm NaCl per 100 ml solution = 900 mg per 100 ml = 9 mg/ml
or
9gm per 1000 ml solution
Molecular weight of NaCl is 58.5 gm per mole
- Find the molarity of the solution: 9 gm/L / 58.8 gm/mol = 0.154 mol per liter
- each molecule of NaCl = 2 osmoles (NaCl dissociates into 2 osmotically active particles)
- 0.154 mol/L x 2 osmoles = 0.308 Osm/L = 308 mOsm/L --> potential osmotic pressure of the solution
- Apply Hoff's osmotic coefficient: 0.93
- 0.93 x 308 = 286 mOsm/L
OSMOLARITY OF BODY FLUID
- 80% of total osmolarity of interstitial fluid and plasma is d/t Na and Cl ions
- intracellular fluid relies on K+ ions to create 50% of its osmolarity
- Impermeate solutes = particles that will not permeate the cell membrane (NaCl, protein)
- the effects of the presence of various concentration of the solutes in solution effects the behavior of both cells and solution
*D5W is isotonic in the bag. After it enters the body, it becomes hypotonic because dextrose is quickly metabolized to glucose (left with water)
has a lower concentration of solutes. water will rush into cell causing it to swell diluting intracellular fluid and concentrating extracellular fluid seeking equilibrium. cells swell --> lysis
water will rush out of cell into extracellular fluid concentrating the intracellular fluid. The cell will shrink until the two concentrations are at equilibrium; crenation
Difference Between OSMOSIS & DIFFUSION:
Diffusion: one-way movement from areas of high concentration to low concentration: perfume, skunk --> can occur with any material
Osmosis: one way movement of water through a semi-permeable membrane from areas of high water concentration to low water concentration; skin wrinkling in bath water - more solutes in skin than water in tube
Cause: loss of NaCl from extracellular fluid --> dehydration, diarrhea, vomiting, diuretics, Addison's disease (adrenal insufficiency --> low cortisol and aldosterone), hypoaldosteronism
or, addition of excess water to extracellular fluid diluting the sodium load --> TURP syndrome, excessive secretion of ADH
serious symptoms occur when Na+ is < 120 mEq/L
symptoms are nonspecific: anorexia, nausea, weakness, progressive cerebral edema results in lethargy, confusion, seizures, death
- rapid reduction in plasma Na+ concentration can cauase brain cell edema and neurologic symptoms
- h/a, N/v, lethargy, disorientation
- seizures, permanent brain damage and death
- brain cannot increase volume by more than 10% without herniation
- CHF, cirrhosis, renal failure, nephrotic syndrome
- progressive impairement of renal water excretion parallels underlying disease severity, you may see an increase in total body sodium
- Na+ is in the peripheral tissues not the central compartment
- ADH release and decreased delivery of fluid to the diluting segment of the nephrons
- the effective circulating volume is reduced
- may be en with normal total body sodium in the absence of edema or hypovolemia
- glucocorticoid insufficiency
- hypothyroidism
- SIADH (too much ADH = antipee)
- normal urine osmolality is usually greater than 100 mOsm per kg
- normal urine Na+ concentration is normally greater than 40 mEq per L
- when this evolves more slowly, other tissue respond by: CSF recruits water from the ECF compartment to help protect the brain
- the transport of (effective osmoles) Na, K, organic solutes such as glutamate and urea from cells into the extracellular compartment
- this blunts the osmotic flow of water into the cells and subsequent swelling of the brain tissues
- rapid correction of chronic hyponatremia may result in osmotic demyelination injury to the neurons (pontine)
- brain has pumped out its intracellular solute load for protection
- pontine demyelination = quadraplegia, further CNS damage, death
- demyelination can be avoided by limiting the correction of hyponatreimato 10-12 mmol per liter in 24 hours
- slow correction permits the brain to recover the lost osmoles
- water restriction is the treatment for hyponatremia ; patients with normal or increased total body sodium
- loop diuretics encourage free water reduction
- don't over diurese
- water restriction allows the balance between plasma and sodium to achieve homeostasis
- treat hormonal (adrenal, thyroid) dysfunction
- antagonize ADH activity and water restrict patients with SIHADH (hypersecretion)
- address the underlying sodium disorder
- PSS is generally the treatment of choice in patients with decreased total body sodium content
- **hyponatremia is the most common elyte disorder in clinical practice
- >130 mEq/L is safe for general anesthesia
- lesser values may result in intraoperative cerebral edema manifesting itself as confusion and combativeness, or lethargy upon awakening
- result of loss of water from the extracellular fluid such as dehydration
- or an increase in sodium content in the extracellular fluid: salt water drowning
- increasing osmolarity
- may be caused by the inability to secrete ADH as in Central Diabetes Insipidus
- Centralized hypernatremia may be caused by a lesion of the hypothalamus and pituitary stalk
- transient DI is seen following neurosurgical procedures and head trauma
- neurologic manifestations predominate and are caused by cellular dehydration
- restlessness, lethargy, hyperreflexia, seizures, coma, death
- Kidneys inability to respond to ADH such as Nephrogenic Diabetes Insipidus
- excessive secretion of sodium retaining hormone aldosterone
- may result in hypernatremia and over hydration
- aldosterone also encourages water retention in addition to sodium, so the scenario is not usually serious
- >160 mEq/L
- causes cell shrinkage
- promotes intense thirst helping thwart huge increases in plasma Na+ levels
- not all thirst mechanisms are intact
- hypothalamic lesions may impair the thirst sense
- elderly patients with altered mental status
- chronic hypernatremia is better tolerated than the acute form
- after 48 hours of rising Na+, intracellular osmolarity begins to rise d/t increases in intracellular inositetol and amino acid concentrations
- this increases intracellular solute concentrations slowly increasing neuronal water content
- need time to equilibrate
- may have decreased total body sodium require isotonic fluids to restore plasma volume
- only then should hypotonic solutions be given to restore intracellular volume status
- patients will increased total body sodium require loop diuretic therapy and hypotonic solutions
- rapid correction of hypernatremia may result in seizures, brain edema, permanent neurologic damage and death
- plasma Na concentrations should not be decreased faster than 0.5 mEq/L/hr
Impairement of function of lymphatic vessels
caused by blockade or surgical excision
Results in plasma protein leaking into interstitium - raising colloidal osmotic pressure of the interstitium - attracting fluid to diffuse across the capillary membrane
Causes:
- parasitic infection can block lymph flow
- filaria nematodes live in human lymph system
- a mosquito disseminated infection
- may develop elephantiasis in females
- men may develop scrotal swelling (hydroseal)
- lymphatic filariasis affects 120 million people
(read notes)
abnormalities that cause edema must be severe in order to overcome intrinsic physiologic safety factors
- negative interstitial pressure enhances low compliance of the interstitial space
- lymph flow has the ability to increase up to 50 fold if called upon
- "wash down" of interstitial fluid proteins concentration reducing osmotic load
change in volume per millimeter HG pressure change
*in interstitial space, compliance is low; increases in volume result in significant changes in pressure
as long as the interstitium remains in the negative pressure range (-1 to -3)
read in notes
Fluid in interstitium is in gel form; fluid is bound in proteoglycan network
Brush pile of proteoglycan filaments - add structure to the cell body and prevent occurence of free fluid in this space. if the pressure here becomes positive, the filaments are pushed apart and free fluid occurs.
proteoglycan filaments prevents fluid from flowing easily through the tissue spaces. Without these an individual simply standing up would cause huge amounts of fluid to shift from the upper to the lower body. When edema of the lower extrem occur, rivulets of free fluid form and fluid can move quickly bypassing the filaments. The best way to relieve lower extremity edema is to put your feet up.
Lymph flow as a safety mechanism:
The lymphatics return proteins leaking from capillaries into interstitium
without continuous circulation of proteins, plasma volume would rapidly be depleted and interstitial edema would develop. Lymphatic flow can increase from 10 to 50 x normal when fluid begins to accumulate in the tissues.
lymphatics carry away large amounts of fluid and proteins in response to increase capillary filtration; this prevents interstitial pressure from becoming +
The safety factor of increased lymph flow has ben calculated to be about 7 mmHg
washout
The capillaries are relatively impermeable to proteins but not so with lymph vessels
lymph flow increases - proteins are washed out of the interstitial fluid and enter the lymph vessels as lymph flow increases
net filtration pressure through capillary is then decreased; by decreasing interstitial fluid protein colloidal concotic pull
- pleural cavity
- pericardial cavity
- peritoneal cavity
- joint cavity and bursa
- surfaces almost touch each other; only a thin layer of fluid separates them
- to facilitate sliding, a viscous proteinaceous fluid lubricates the surface
- capillaires adjacent to the space allows fluid to diffuse into interstitial space and into adjacent potential space; each potential space is connected with lymph vessels to facilitate the removal of protein from the space.
- The pleural cavity and peritoneal cavity possess large vessels within the cavity itself to facilitate this removal
lymph obstruction cause excessive capillary filtration results in effusion similar to interstitial edema
effusion in abdominal cavity = ascites
20 L of ascites fluid may accumulate
fluid pressure is negative; pressure is subatmospheric in interstitial tissue
fluid hydrostatic pressure is normally about:
- pleural cavity -7 to -8 mmHg
- joint space -3 to -5 mmHg
- pericardial -5 to -6 mmHg
- pleural
- synovial
- peritoneal
- pericardial
- cerebrospinal fluid
- intraocular spaces
- totals < 2 L
- does not contribute greatly to total body water
notes
transport of nutrients to tissue
removal of cell excretion --> shit
thin; constructed of single layer of permeable endothelial cells
water, cell nutrients, cellular end products (excreta) move quickly and easily btwn tissues and circulating blood
10 billion capillaries
total surface area 700 m2
1/8 of football field
no body cell is > 25 nm away from a capillary
*the most important means by which substances are transferred between plasma and interstitial fluid; water and dissolved molecules continuously diffuse back and forth through capillary wall; random motion occurs with molecules bounding in every direction.
blood flows intermittently turning on and off every few seconds or minutes; caused by intermittent contraction of meta-arterioles - precapillary sphincters and small arterioles
Lympho-Kinetic Motion
*Vasomotion is slower when tissue O2 demand is higher
diffuse directly through cell membrane; no not need to go through pores
O2 and CO2 readily and quickly diffuse through membranes
Na and glucose must traverse capillary endothelium through pores - slower
varies according to size and size of substance trying to pass through
H2O - 0.35 nm
protein 7-8 nm
Na, Cl, urea, glucose somewhere inbtwn
H2O will diffuse 1000 x faster than protein molecules; various tissue present extreme difference in their permeability characteristics
In brain, capillary junctions are tight; H2O, O2 and CO2 pass freely in and out of brain tissue
In liver, clefts here are wide open; almost all dissolved substances of plasma can pass from blood into liver tissue; easily leaks out when channels are blocked (sweat)
[CO2] tissues > blood > alveolus
moves down concentration gradient
1/6 of total volume of body water exists between cells - interstitial fluid; possess same constituents as plasma except for plasma proteins
- capillary pressure: +7
- interstitial fluid pressure:-8
- capillary plasma colloidal osmotic pressure: -28
- interstitial fluid colloid osmotic pressure:-14
- removes excess fluid
- removes excess protein molecules
- removes debris and other matter from tissue spaces
- this overall process (of pumping fluid into central circulation) creates a slight negative pressure for fluid in the interstitial spaces
28 mmHg average colloid osmotic pressure
19 mmHg d/t molecular effects of dissolved protein
9 mmHg d/t Donnan effect - extra osmotic pressure from cations held in plasma by proteins
80% of total colloid osmotic pressure results from albumin
20% from globulin
fibrinogen noncontributory
- return of proteins to blood from intersitial spaces
- with this we would die in 24 hours
- lymphatics carry proteins and large particles which cannot be removed by absorption directly into blood capillaries
- valves exist in all lymph channels
- segmental valves allow lymph vessels to pump from valve to valve
- each segment is capable of functioning as an independently pumping segment emptying into next segment
- lymphatic system compressed by skeletal muscle, movement of body parts, arterial pulsations adjacent to lymphatics, compression of tissues by forces outside body, pneumatic stockings, blood pressure cuffs, padded armrests, OR tables
- from lower part of body empty into thoracic duct --> empties into venous system at the juncture of the left IJ and L SC vein
- L IJ lines may cause kylothorax (lymph in lungs)
- lymph from L side of head, arms, and chest enters the thoracic duct for emptying into veins
- lymph from R side of neck, head enters very small right lymph duct which empties into R SC and IJ
- derived from interstitial fluid that flows into lymphatics
- protein concentration in interstitial fluid is 2 g/dL
- intestines 4 g/dL
- liver 6 g/dL
- 2/3 of lymph is derived from liver and intestine
- thoracic duct 10 g/dl
- major route for absorption of nutrients, especially fats
- after fatty meal, thoracic duct lymph can contain as much as 2% fat
line lymph nodes
bacteria cannot be absorbed through capillary membrane into blood; bacteria enter lymph into lymph nodes located intermittently through lymphatic chain
100 ml/her through thoracic duct
20 ml flows into circulation /hr through other channels
total estimated lymph flow: 120 ml/hr x 24 hr = 2880 ml/day
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