some additional stuff on this that you might find useful:
What is edema?
Soft tissue swelling due to expansion of interstitial volume=ECF only!!! (not cells)
True or False, edema can be localized or generalized?
True or False, generalized edema is due to retention of water only?
False, if only water were retained, it would disperse among the other 60% (both ECF and ICF). When Na is retained, water stays in the ECF better (tries to reduce osmolality)
True or False, generalized edema can occur with low, normal, or high serum Na?
True, it really depends on the osmolality of the serum, not just Na [ ]
How is the volume of interstitial fluid maintained?
Net fluid movement out of capillary. (described by Starling's law)=10mmHg
How does Starling's law describe the state of the volume of interstitial fluid?
Net fluid movement=(net hydrostatic pressure)-(net oncotic pressure)
What are 5 causes of generalized edema?
1)increased hydrostatic pressure, 2)reduced oncotic pressure (1-less proteins made, 2-increased vascular permeability), 3)lymph flow obstructed, 4)inappropriate retention of Na and water
What 2 things can cause hydrostatic pressure to increase?
1)CHF (congestion back thru venous system), 2)cirrhosis
What 3 things can cause reduced oncotic pressure?
1)nephrotic syndrome, 2)cirrhosis, 3)malnutrition
What can cause lymph flow obstruction?
What can cause in increase in permeability to protein?
Inflammation, angioneurotic edema
What 2 things can cause inappropriate retention of Na and water?
1)renal failure (not as much is filtered), 2)nephrotic syndrome
True or False, almost all clinical cases of edema are due to body holding on to too much water and Na?
What is effective arterial blood volume (effective circulating volume)?
Adequate perfusion pressure. Normal EABV=cardiac output and venous return are normal
How is EABV reduced?
1)blood loss (bleeding, dehydration), 2)vasodilation (cirrhosis, sepsis), 3)reduced cardiac output (heart failure)
True or False, reduced EABV can be in the setting of low, normal, or high actual blood volume?
True, EABV is not merely a measure of volume, but volume needed to meet tissue demands
How does the kidney respond to a drop in EABV?
It tries to increase perfusion pressure by retaining Na and water
How does the kidney retain Na and water when perfusion pressure drops?
Renin is released. Ang II causes efferent arteriole vasoconstriction which causes more fluid to be filtered and its oncotic pressure to rise. Fluid in the proximal tubule is massively reabsorbed to reduce the peritubular capillary osmotic presssure. Aldosterone and ADH also help in the distal tubule
What happens to blood flow in CHF?
Heart doesn't pump well so vessels vasoconstrict to try to increase pressure. Most of blood is diverted to brain, heart and lungs. The kidneys see a drop in perfusion pressure and do what I just described
What is a real danger of severe CHF regarding water/ion balance?
Hyponatremia. If CHF is severe, body tries so hard to conserve water that urine is concentrated and Na can be lost
How can liver cirrhosis lead to decreased EABV?
1)portal hypertension-fibrosis blocks blood flow (increased hydrostatic pressure), 2)hypoalbuminemia (decreased osmotic pressure), 3)SPLANCHNIC VASODILATION=MAJOR FACTOR (perceived drop in perfusion pressure)
How does cirrhosis lead to splanchnic (mesenteric) vasodilation?
It either doesn't degrade or overproduce vasodilating factors=vasodilation=decreased perfusion pressure
How does the body respond to the effects of cirrhosis?
The same way as in CHF. It does whatever possible to hold on to H20 and Na (1)efferent vasoconstriction, 2)renin release, 3)aldosterone release, 3)ADH)
What is one serious side effect (besides edema) of portal hypertension?
It can cause ascites (really just a really severe edema of the peritoneum
What is the nephrotic syndrome?
Losing protein in the urine (>/= 3.5g/day) resulting in hypoproteinemia. Edema and hyperlipidemia are also present
What are 2 mechanisms for edema in nephrotic syndrome?
1)Na and H2O retention=MAJOR CAUSE (unknown why), 2)hypoproteinemia results in reduced oncotic pressure (H2O goes to interstitium)
What is one plausible explanation as to why Na and H2O are retained in nephrotic syndrome?
Hypoproteinemia-->reduced oncotic pressure-->edema (H2O leaves vessels). If enough water leaves ECV will drop (perfusion pressure) and the kidney tries to hold onto Na and water
What are reasons for treating edema?
1)painful, 2)impairs circulation/venous return, 3)impairs wound healing, 4)increases infection, 5)unattractive, 6)pul edema reduces gas exchange, 7)MEANS SOMETHING ELSE IS WRONG
What is the FRACTIONAL EXCRETION OF NA (FENa) test?
A test to see if the body is holding onto water (CHF, renal failure, cirrhosis, nephrotic syndrome, etc.)
What is the formula for determining FENa?
(Urine [Na]/Plasma [Na])/(Urine [creatinine]/Plasma [creatinine])
What do values of FENa tell you?
<1 means the body is retaining Na, >1 signifies a volume expanded state (too much Na/water intake)
What are the 4 steps to treating edema?
1)treat underlying cause, 2)reduce Na/water intake, 3)increase Na/water excretion (diuretics), 4)don't make it worse (diuretics may cause volume depletion=many other problems)
True or False, reducing Na intake will reduce edema?
False, it really just holds it in check so it doesn't get worse
True or False, IV's can cause edema in hospital patients with problems excreting Na?
True. the least osmotic solution will still give ~19mEq/day. A person with problems clearing Na may only clear 15mEq=EDEMA
How do diuretics work?
They block Na and water reabsorption