ECF Volume and Water Metabolism Flashcards Preview

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Flashcards in ECF Volume and Water Metabolism Deck (56):

How do you calculate/estimate total body water? ICF? ECF? Plasma Water? Blood volume?

TBW= 60% BW in kg 9in women or elderly it is only 50%; 2/3 TBW; 1/3 TBW; 1/4 EC water; plasma water/(1-Hct)


What is hypovolemia?

loss of salt and water


What is hypervolemia?

gained both water and salt


What is the major determinant of ECF volume? What happens as it increases? decreases?

sodium in ECF; ECF volume increases and volume overload will result; decrease in ECF resulting in volume depletion


What are the three systems responsible for regulating body sodium? How?

RAAS (funct. of renal renin release), SNS (catecholamines: NE, Epi), ANP and renal vasodilators; all promotes renal Na retention


What is effective circulating volume (effective arterial blood volume)?

blood volume detected by volume sensors; not directly measurable; pressure perfusing the arterial baroreceptors


Where can effective circulating volume be sensed? How?

atria of heart (ANP), carotid sinus and aortic arch (SNS), afferent glomerular arterioles (Renin); arterial perfusion pressure or stretch in tissues


what are the two systems that are effectors of volume? What are there components?

systemic hemodynamics: SNS, Ang II; Renal Na excretion: GFR, Ang II, Peritubular capillary hemodynamics, aldosterone, SNS, ANP, pressure natriuresis


How and where is renin released?

JG cells sense changes in renal perfusion and respond by producing changes in release of renin; dec. ECF-> inc renin-> sodium retention


What stimuli increase aldosterone? What does aldosterone do?

inc. plasma Ang II levels, dec. Pna, inc Pk; inc Na reabsorption by CD


What stimuli increase catecholamines? What does catecholamines do?

SNS activation; inc. Na reabsorption by PCT


What stimuli causes release of ANP? What is ANPs action?

atrial stretch; dec. Na reabsorption by CD


What hormone is primarily responsible for osmoregulation? Derangement in osmoregulation results in what?

ADH; hypo or hypernatremia


What are the sensors in osmoregulation? Effectors? What's affected?

plasma osmolality by hypothalamic osmoreceptors and effective circulating volume depletion; ADH and thirst; water excretion and intake


what does serum sodium levels tell us?

tonicity not volume status, function of renal water handling


What happens when ADH is increased?

increased permeability of renal CT to water, water flow down gradient to be reabsorbed into medullary interstitium, renal water retention


What are some things that can be evaluated clinically to assess fluid balance?

intake & output, weight change, skin turgor/edema, mucous membranes, lung sounds (crackles/dullness), JVD & Hepato-Jugular Reflux, Orthostatic BP & HR, CVP (8-10), CO, Urine Na & Osm, Serum Nitrogen:Creatinine


What are signs and symptoms of hypovolemia?

orthostatic decrease in BP with increase HR, decreased pulse volume, venous pressure, skin turgor, and dry mucous membranes


what are some extra renal causes of hypovolemia?

(urinary Na low); GI (Vomit, diarrhea, NG or bowel aspiration, intestinal fistulae), skin/resp (burns, heat, skin disease, CF, drainage pleural effusion)


What are some renal causes of hypovolemia?

high urinary Na; Extrinsic (Solute or Osmotic diuresis- diabetic ketoacidosis, diuretics, adrenal or aldosterone insufficiency), Intrinsic (diuretic phase of acute RF, post obstructive diuresis, salt wasting nephropathy- barters & gitlemans


How do you treat hypovolemia?

IV normal saline, oral and enteral- salty food and broth, salt tablets, encourage fluids


What are clinical manifestations of hypervolemia?

hypertension, edema, pulmonary crackles, edema, pleural effusion, ascites, JVD


What are causes of hypervolemia?

primary or secondary Renal sodium retention


What are causes of primary renal sodium retention?

hyperaldosteronism, Cushing's Syndrome, Inherited Hypertension, Renal Failure, Nephrotic Syndrome


What are causes of secondary renal sodium retention?

Hypoproteinemia, Low cardiac output, Peripheral Vasodilation


Causes of hypoproteinemia?

nephrotic syndrome, protein losing enteropathy, cirrhosis w/ ascites


Causes of low cardiac output?

Pericardial effusion, CHF, Constrictive pericarditis, Valvular disease, Pulmonary Hypertension, Cardio-myopathy


Causes of peripheral vasodilation?

shunt flow away from kidney; pregnancy, sepsis, anaphylaxis, arteriovenous fistula, trauma, cirrhosis, idiopathic edema, vasodilating drugs


How do you treat hypervolemia?

slat and fluid retention, low Na diet, diuretics, drainage of sequestered fluid, correction of hemodynamics, Dialysis of fail medical management


What is the serum sodium level indicative of hyponatremia? Hypernatremia?

< 135 mEq/L; > 145 mEq/L


What is the most common electrolyte abnormality in hospitalized patients? Incidence rate in other populations?

hyponatremia (15-20%), 7% in ambulatory population, up to 53% in elderly


what is the difference between acute and chronic hyponatremia?

acute48 hours, brain excretes intracellular osmolytes to avoid cerebral edema


what are the stages and changes seen with brain adaptation and therapeutic correction with hyponatremia?

immediate- water gain in brain-> low osm-> rapid adaptation-loss of Na, K, and Cl-> slow adaption- loss of organic osmolytes; if improper therapy (rapid correction)-> osmotic demyelination


What are the three classes of hyponatremia?

psuedohyponatremia, hyperosmolar (translocation) hyponatremia, hypo-osmolar hyponatremia (true)


What are the causes of pseudo-hyponatremia?

hyperlipidemia (familial dyslipidemia in thousands), hyperparaproteinemia; iso-osmolar condition, mostly historical interest; false result cuz measure [Na] in whole plasma not just liquid phase


What are the causes of iso or hyperosmolar hyponatremia?

shift from intracellular to extracellular compartments, effective osmoles drag water out: glucose (100mg/dL above 100= fall of 1.6mEq/L Na, mannitol


what are the hypovolemic causes of hyponatremia?

Renal- osmotic diuresis or diuretic excess, Extra renal- Vomit, diarrhea, 3rd spacing- burns, pancreatitis, trauma, and hemorrhaging


How do you treat Hypovolemic Hyponatremia?

asymptomatic- normal saline, restore ECF (Watch), symptomatic- 3% saline Slow, hypertonic fluid helps decrease cerebral edema (intracranial pressure)


What are causes of hypervolemic hyponatremia?

CHF, Cirrhosis, Nephrotic syndrome


How do you treat hypervolemic hyponatremia?

asymptomatic- decrease dietary Na, fluid restrict, loop diuretics; symptomatic- 3% saline and loop diuretics


what are causes of Euvolemic hyponatremia?

glucocorticoid deficiency (Addison's), hypothyroidism, psychosis-> due to meds or increased thirst perception (psychogenic polydipsia)


what is psychogenic polydispsia?

hyponatremic by overwhelming kidneys ability to excrete H2O, ADH appropriately depressed, UNa < 100mOsm, > 10-12 L per day H2O


What is post-operative hyponatremia?

excessive infusion of electrolyte free water (hypotonic saline or D5W) and presence of vasopressin which prevents its excretion


what causes SIADH? diagnostic criteria?

carcinoma, pulmonary disorders, CNS disorders, Drugs; Posm100, euvolemia, elevated UNa despite normal Na and H2O intake, absence of: adrenal, thyroid, pituitary or renal insufficiency or diuretic use


How do you treat euvolemic hyponatremia?

Neuro symptoms- 3% saline, no neuro- SIADH: fluid restrict, high Na diet/high protein diet, others: treat underlying cause


What is osmotic demyelination?

most commonly affects central pons (CPM), all ages esp pre-menopausal women, common after liver transplant, risk related to severity and chronicity of hyponatremia; seen T2 MRI 2wks later


when is a patient dehydrated?

hypernatremic (>145mEq/L) and hypovolemic


what populations are at risk for developing hypernatremia and why?

impaired thirst- elderly, hypothalamic lesion, psychosis or impaired access to water- dementia, delirium, infants


What are the causes of hypovolemic hypernatremia?

renal loss (osmotic or loop diuretic, post-obstruction diuresis) or extra renal loss (burns, sweating, diarrhea, fistulas)


How do you manage hypernatremia?

calculate water deficit, desired correction no greater than 0.5mEq/L/hr or 8-10 mEq/L/day


What are iatrogenic and other causes of hypervolemic hypernatremia?

administration of sodium bicarb, NCl or blood products may increase TBNa and TBW


What is diabetes insipidus?

defect in renal H2O conservation, Central: impaired synthesis, transport, storage or release of ADH (hypothalamus/pituitary) or Nephrogenic: reduced response to ADHin CT (hereditary or acquired- RF, hypercalcemia, drugs)


How do you tell the difference between Central and Nephrogenic DI?

Pavp- C- not detectable, N >5pg/mL; water restrict loss 3-5% BW, aqueous AVP; inc. Uosm w/ AVP- C- substantial, N- little or none


How do you treat CDI? NDI?

Central- desmopressin 5-20mcg 1-2 per day, low Na and protein diet; NDI- remove offending drugs (lithium), HCTZ or Amiloride, Low Na and protein diet


How does the brain adapt to hypernatremia?

H2O moves extracellularly and electrolytes intracellularly to maintain brain volume; chronic-accumulate organic osmolytes increase brain volume; rapid correction may cause cerebral edema


How is hypernatremia managed?

calculate water defecit, desired rate of correction no greater than 0.5mEq/L/hr or 8-10mEq/day