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120 Cards in this Set
- Front
- Back
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What is the minimum obligate water requirement to maintain homeostasis?
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- 800mL (yield 500mL urine)
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Normal healthy individuals have obligatory water loss of ___. Where does this loss come from?
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2.5-2L/24h
- urine: 1-1.5L - GI: 100-200mL - skin/lungs: 700-1000mL |
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How do you calculate baseline IV fluid requirements for:
Kids Adults Geriatrics |
- Kids:
1-10kg: 100mL/kg 11-20kg:1000mL+50/kg>10 >20kg: 1500mL + 20/kg>20 - Adults: - 35mL/kg (2-2.5L/day) - Geriatrics: - 30mL/kg (1.5-2L/day) |
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Calculate the IV fluid needs for a a) 5 kg infant.
b) 19 kg child c) 70 kg adult |
a) 100mL x 5kg = 500mL/d
b) 1000 + (50x9) = 1450mL/d c) 35x70 = 2,450mL/d |
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What ages of patients have higher fluid requirements? Lower?
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- neonates have higher
- geriatrics have lower |
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What environmental factors affect fluid requirements?
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- ambient temp
- neonates: radiant warmers, UV phototherapy |
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What conditions increase fluid needs? lower?
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- Increase: burns, diarrhea, fever, dehydration
- Lower: CHF, renal failure, iatrogenic fluid overload, mechanical ventilation |
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Identify sources and quantity of fluid intake in adults.
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-1500mL beverages
- 750mL moist foods - 250mL metabolism Total: 2500mL |
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ID sources and quantity of fluid output in adults.
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- 1500mL urine
- 700mL insensible loss - 200mL sweat - 100mL feces TOTAL: 2500mL |
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Total body water is what percent of total body weight?
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60% (ex 42L in 70kg pt...
0.6 x 70=42) |
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Intracellular fluid is what % TBW? %body wt?
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- 67% TBW
- 40% total body wt |
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extracellular fluid is what % TBW? %body wt?
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- 33% TBW
- 20 % total body wt |
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Interstitial fluid is what percent TBW? What % of extracellular fluid?
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- 22% TBW
- 66% ECF |
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Plasma fluid is what percent of TBW? What % of ECF? What two components make up plasma fluid?
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- 11% TBW
- 33% ECF - consists of venous fluid (9%) and arterial fluid (2%) |
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What determines the distribution of water between ECF and ICF compartments? How is it determined?
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- tonicity (osmolality) of ECF
- determined by concentrations of osmoles in the ECF (solutes that cannot move across membranes) |
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What is the main "effective osmole" in ECF?
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Sodium
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Plasma osmolality reflects osmolality of body water unless what?
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- unless abnormality of sodium and fluid results in redistribution between ICF and ECF.
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Rank the fluid compartments from most to least percentage of body water
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-most: intracellular
- interstitial -least: plasma/serum |
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Describe the low pressure system volume sensors.
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- atria and pulmonary vasculature.
- decreased wall stress (volume) signals hypothalamus to secrete ADH or vasopressin. - increased stress results in secretion of natriuretic peptide |
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Describe the high pressure system volume sensors.
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- Baroreceptors in aortic arch, carotid sinus, and juxtaglomerular apparatus
- involves RAA system |
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Describe the Renin-Angiotensin-Aldosterone system.
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1. Renin is released due to:
- JGA senses decreased arteriolar wall tension. - B-1 innervation of JGA - tuboglomerular feedback senses distal nephron sodium release - Renin cleaves angiotensin to create angiotensin I - Ang. I is then cleaved by ACE (angiotensin converting enzyme) into angiotensin II - stimulates adrenal gland to secrete aldosterone - increases reabsorption of NaCl from proximal tubule - central stimulation of thirst (secretion of ADH more) - arteriolar vasoconstriction |
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D5W is a ___tonic solution that consists of _____/dL dextrose. Describe it's fluid distribution.
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- hypotonic
- 5mg/dL dextrose - 40%ECF/60%ICF |
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1/2 NS is a ____ tonic solution that consists of ____/L sodium. Describe its fluid distribution.
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- hypotonic
- 77mEq/L sodium - 63% ECF/ 37%ICF |
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NS is a ___ tonic solution that consists of ___/L sodium. Describe its fluid distribution.
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- isotonic
- 154mEq/L sodium - 100% ECF |
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3% saline is a ___tonic solution that consists of ____/L sodium. Describe fluid distribution
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- hypertonic
- 513mEq/L - 100% ECF |
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LR solution is ___tonic, contains what components, and describe its distribution/
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- isotonic
- Na+, Cl-, K+, Ca++, lactate - 100% ECF |
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What is the best use for dextrose solutions?
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Calorie replacement or hypoglycemia
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D5W = ____ tonic
D10W= ____ tonic D50W= ____tonic |
- D5= hypotonic
- D10 = isotonic - D50 = hypertonic |
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Why is dextrose able to distribute to intracellular fluid?
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uncharged molecules can cross capillaries and cell membrane
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Why is D5 a poor choice for fluid replacement?
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- distributes into ICF 60%... not as much getting into circulation
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True or false: distribution of dextrose at any concentration is dependent on osmolality.
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FALSE: all dextrose solutions are able to distribute to all compartments
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Dextrose is metabolized to what?
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CO2 and H20 soon after administration
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Hypotonic solutions of saline (1/4NS and 1/2NS) distribute to what compartments?
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- intracellular
- plasma (extracellular) - interstitial (extracellular) (1L = 335mL ICF, 165mL plasma, and 500mL interstitial) |
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Why is 0.9% NS better at fluid resuscitation than hypotonic solutions?
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- distributes only to ECF (250mL plasma + 750mL interstitial, no ICF distribution)
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NS is useful in what state? What should you consider about NS in large volumes?
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- useful in dehydration or hypovolemia
- can cause acidosis in large volumes |
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What would happen with fluid levels if you administer 3% saline?
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- hypertonic
- high solute in ECF with administration would draw water in from intracellular compartments (RARELY used) |
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If a patient requires a very large volume of fluid replacement, you should consider ___
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LR
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Which is better for replacing fluid? NS vs LR?
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- NS is better at replacement but LR doesn't cause acidosis)
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When monitoring fluid therapy, name sources of intake and output.
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- intake: PO from food/drinks, IV from meds and maintenance fluids
- output: urine, stool, GI (vomiting, GI suctioning), other losses (i.e. Chest tubes) |
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What makes a positive or negative fluid balance?
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- positive fluid balance = ins>outs
- negaitve = outs>ins |
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When would it be desirable to have fluid imbalance?
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- dehydration: input > output
- fluid overload: output> input |
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___ produces the osmotic gradient that maintains water distribution between ICF and ECF.
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Sodium distribution
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What is the major determinant of ECF osmolality? what else contributes?
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Sodium is major determinant, help form Cl and HCO3
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How is sodium removed from ICF to ECF?
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Actively pumped
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What is the reference range for serum sodium?
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135-145 mEq/L
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True or false: serum sodium levels reflect total body sodium concetrations.
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FALSE
- serum concentrations may be high with high, normal, or low total body sodium - same is true for low serum sodium concentrations |
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Elevated sodium levels, called ____, can be what three types?
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- hypernatremia
- hypervolemic, hypovolemic, isovolemic |
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When does volume get considered when classifying sodium/water disorders?
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- hypernatremias and
- hyponatremic hypotonic |
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How are hyponatremic disorders classified?
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- by tonicity: hypotonic, isotonic, hypertonic... (hypotonic is further classified by volume)
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Which drug causes SiADH?
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Carbamazepine
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Which antiepileptic causes Diabetes Insipidus?
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Phenytoin
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What is SiADH?
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Syndrome of Inappropriate (think insufficient) ADH (water retention)
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A pt with sodium/water problems from carbamazepine would have ___ osmolality, ___serum sodium, ___ urine SG, and ___urine output
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(SiADH)
- decreased osmolality - decreased serum sodium - increased urine SG (concentrated) - decreased urine output |
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Pt with Na/H20 problems from phenytoin would have ____osmolality, ____serum sodium, ____ urine SG, and ____urine output.
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(Diabetes insipidus)
- increased osmolality - increased serum Na - decreased urine SG - increased urine output. |
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What is osmolality?
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THe count of number of particles in a fluid sample
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Describe how ADH regulates plasma osmolality.
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- in response to small increases in plasma osmolality, ADH is released from pituitary causing reabsorption of water in the distal tubules and collecting ducts to correct inc. osmolality
- opposite with low osmolality- decreased ADH and increased water loss via kidneys |
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What is important to note about ADH in hypovolemia vs osmolality>
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ADH is secreted in response to hypovolemia. This stimulus will override any response to osmolality (so if you are hypovolemic but have low osmolality, you won't lose water)
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What is the reference range for urine osmolality?
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- there isn't one... it depends on the clinical condition to determine appropriate response. (may vary between 50 and 1200 in healthy people based on hydration status)
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What is the best measure of urine concentration?
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Urine osmolality... high values = maximal concentration, low values = very dilute urine
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What is the main factor for determining urine concentration?
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The amount of water reabsorbed in distal tubules and collecting ducts in response to ADH
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How do you calculate osmolality?
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2 x Na + glucose + urea
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What two circumstances warrant evaluation of serum osmolality?
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1. investigation of hyponatremia and ID of an osmolar gap
2. testing renal concentrating ability, ID disorders of ADH mechanism, and ID causes of hyper- or hypo-natremia |
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When is hypernatremia associated with tonicity?
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Hypernatremia = ALWAYS hypertonic
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What is considered hypertonic?
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Serum Os: >295 mOsm
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What are common causes of hypervolemic hypernatremia?
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- Sodium overload from sodium bicarb or albumin
- mineralcorticoid excess |
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What are common causes of isovolemic hypernatremia?
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- Diabetes insipidus
- osmotic diuretics - hyperglycemia - no access to water |
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Identify substances gained/lost in the following forms of hypernatremia:
- hypervolemic - isovolemic - hypovolemic |
- hypervolemic: gain H20 AND Na+ with Na gain>h20 gain
- isovolemic: loss of H20 (but not to dehydration) - hypovolemic: Loss of H20 and Na+ with H20 loss>Na loss) |
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What are common causes of hypovolemic hypernatremia?
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Renal disorders
Diuretics Diarrhea Laxatives Excess sweating |
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Diabetes Insipidus is a disorder of ___
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ADH (aka vasopressin) release
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How does ADH cause water reabsorption?
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- binds to V2 (vasopressin) receptors in collecting ducts to increase renal water reabsorption
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What are the two types of Diabetes Insipidus?
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1. Central: no release of ADH when needed
2. Nephrogenic: appropriate release but inadequate response of collecting duct to ADH |
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Describe the clinical presentation of DI
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- dehydration
- volume depletion relative to Na - increase in urine output |
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What are causes of DI
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1. CNS tumors, cerebral clots/bleeds, head trauma
2. Renal disease 3. Infection (meningitis, syphilis, TB) 4. Drug-induced (lithium, phenytoin, foscarnet, demeclocycline. |
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What drugs can cause DI?
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- lithium
- phenytoin - foscarnet - demeclocycline |
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What is the general clincal presentation of hypernatremia?
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- rise in plasma sodium concentration and osmolality causes acute water movement from ICF to ECF
- Decrease in neuronal cell volume - Decrease in brain volume may cause rupture of cerebral vein, hemorrhage, and irreversible neurological damage - initially: lethargy, weakness, confusion, restlessness, irritability - progress to: twitching, seizures, coma (Na>160) - may lead to death (Na>180) |
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Describe signs of hypernatremia based on volume status:
- hypervolemic - hypovolemic - isovolemic |
- hypervolemic: edematous, pulmonary congestion
- isovolemic: asymptomatic - hypovolemic: postural hypotension, tachycardia, delayed cap refill, poor perfusion |
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How quickly should you correct serum sodium concentration in hypernatremia?
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- as quickly as possible without altering cell volume.
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What are goals of hypernatremia therapy?
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- resolve symptoms
- correct serum Na - Normalize ECF volume (if volume changed) - Avoid adverse rxn from too rapidly correcting - avoid overcorrection - prevent recurrence |
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How should you treat hypervolemci hypernatremia?
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(excess Na> excess water)
- dilute sodium and remove excess Na and H20 - dilute with D5W @ 1.5 to 2mL/kg/hr - loop diuretic - decerase Na serum concentration slowly to avoid cerebral edema, sz, neuro damage - decrease by 0.5 to1 mEq/L/hr - measure q 2-4h to guide |
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How should you treat isovolemic hypernatremia?
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(free water loss, Na+ nml)
- replace water deficit - D5W at 1.5-2mL/kg/hr - treat DI if it exists |
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How do you treat central DI?
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- Treat with an ADH analogue
- DDAVP Intranasal (preferred over PO) - Vasopressin for injection - titrate to achieve appropriate urine volume (1.5-2L) and serum Na (137-142) - Drugs with ADH properties can also be useful adjuncts or instead of ADH analogue (HCTZ, Carbamazepine, Chlorpropamide) |
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How do you treat nephrogenic DI?
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- Thiazide diuretic and dietary sodium restriction
(inhibit Na+ reabsorption and therefore cause increased exretion of Na and H20) - combo can decrease urine volume by 50%! - increase proximal water absoprtion and thereby decreases volume of filtrate - also can use NSAIDS but may increase serum Cr. (potentiate effects of ADH) |
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How do you treat central DI?
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- Treat with an ADH analogue
- DDAVP Intranasal (preferred over PO) - Vasopressin for injection - titrate to achieve appropriate urine volume (1.5-2L) and serum Na (137-142) - Drugs with ADH properties can also be useful adjuncts or instead of ADH analogue (HCTZ, Carbamazepine, Chlorpropamide) |
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How do you treat hypovolemic hypernatremia?
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(ECF loss>Na loss)
- restore volume with NS (200-300mL/hr to stablize fluid status) - once volume restored, switch to D5W or 1/2 NS to restore water - Replace free water deficit |
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How do you treat nephrogenic DI?
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- Thiazide diuretic and dietary sodium restriction
(inhibit Na+ reabsorption and therefore cause increased exretion of Na and H20) - combo can decrease urine volume by 50%! - increase proximal water absoprtion and thereby decreases volume of filtrate - also can use NSAIDS but may increase serum Cr. (potentiate effects of ADH) |
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How can you calculate free water deficit?
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Water deficit = normal TBW-current TBW
Normal = 0.6L/kg * wt Current = normal TBW*(140/serum Na+) |
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How do you treat hypovolemic hypernatremia?
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(ECF loss>Na loss)
- restore volume with NS (200-300mL/hr to stablize fluid status) - once volume restored, switch to D5W or 1/2 NS to restore water - Replace free water deficit |
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What factors are important when treating hypovolemic hypernatremia?
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- decrease serum concentrations slowly to avoid cerebral edema, sz, neuro damage
- rate of free water deficit correction depends on rate of hypernatremia development (acute vs chronic, hours vs days) |
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How can you calculate free water deficit?
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Water deficit = normal TBW-current TBW
Normal = 0.6L/kg * wt Current = normal TBW*(140/serum Na+) |
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What are the guidelines for correcting serum sodium for hypovolemic hypernatremia?
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- rate of 1mEq/L if developed over several hours
- rate of 0.5mEq/L if over 24+ hrs - monitor q 2-3h for first 24 hrs - as symptoms resolve, and NA< 149, assess q 6-12 hours |
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What factors are important when treating hypovolemic hypernatremia?
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- decrease serum concentrations slowly to avoid cerebral edema, sz, neuro damage
- rate of free water deficit correction depends on rate of hypernatremia development (acute vs chronic, hours vs days) |
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What are the guidelines for correcting serum sodium for hypovolemic hypernatremia?
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- rate of 1mEq/L if developed over several hours
- rate of 0.5mEq/L if over 24+ hrs - monitor q 2-3h for first 24 hrs - as symptoms resolve, and NA< 149, assess q 6-12 hours |
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What is the most common electrolyte abnormality in a hospitalized pt?
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Hyponatremia
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A hyponatremic pt presents with Serum osm of 220, BP 70/40, and HR 124. You classify them as having ___
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hypotonic hypovolemic hyponatremia
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How can you determine if a hyponatremic pt also has hypervolemia?
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Edema, pulmonary congestion
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Hypotonic hyponatremia may present how, clinically?
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asymptomatically
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Describe pathophys of hypertonic hyponatremia.
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- normal body Na+
- Excess osmols in ECF (like glucose) - Excess osmols cause redistribution of water from ICF to ECF, results in relatively low Na |
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In hypertonic hyponatremia, serum sodium falls by ____ for each 100mg/dL increase in glucose.
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1.6 mEq/L
(glucose pulls water froM ICF to ECF, results in rise of serum Osm of 2mOsm/kgH20 due to glucose) |
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Describe the pathophys of isotonic hyponatremia (pseudohyponatremia)
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- Normal Na and water
- likely a lab error due to overestimating volume of serum in a sample - OR displacement of Na-rich fluid with non-osmolar, non-aqueous material (like excess lipids or proteins) |
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How do you treat non-hypotonic hyponatremia?
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- treat underlying problem
- administer insulin for uncontrolled diabetes - correct water, Na and K deficits |
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Describe the general pathophys of hypotonic hyponatremia.
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- represents excess waer in relation to existing sodium stores
- must determine volume status |
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Describe the pathophys of hypervolemic, hypotonic hyponatremia.
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- Excess of Na and ECF, but ECF excess>Na excess
- caused by CHF, cirrhosis, hypoalbuminemia, or decrease in effective circulating plasma vol. |
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What is the clinical presentation of a pt with hypervolemic, hypotonic, hyponatremia?
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Edema, acute weight gain, pulm congestion
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Describe the pathophys of isovolemic, hypotonic, hyponatremia.
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- Normal Na, Small inc in ECF
- usually asymptomatic - Causes: imbalance of I/O, excess ADH (SSRI, Ecstasy), defective renal diluting mechanism, altered thirst, psych |
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SiADH is a type of ___ natremia
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Isovolemic, hypotonic, hyponatremia.
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SiADH is the release of ___ when ___. This results in ___.
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- release of ADH when not needed, or increased response to ADH
- results in inappropriate water reabsorption by collecting ducts |
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How does SiADH present?
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- some fluid overload, but largely euvolemic
- hyponatremic from excess fluid - minimal water excretion results in dec. urine output and very concentrated urine. |
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What are non-drug causes of SiADH?
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- cns tumors, cerebral thrombosis or bleed, head trauma, infectious disease
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What drugs can induce SiADH?
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- NSAIDS
- carbamazepine - vincristine - opioids - phenobarbitol - thiazides - TCAs - Ecstasy |
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Describe the pathophys of hypovolemic, hypotonic hyponatremia.
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- Decreased total body Na and ECF
- Na deficit is > than ECF deficit - Caused by: GI loss (N/V/D), renal loss (diuretics, adrenal insuff, salt wasting neuropathy), extrarenal losses (sweat), iatrogenic (replacement of NA-rich with Na-Free fluids) |
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How can you diagnose the etiology of sodium loss in hypovolemic, hypotonic hyponatremia?
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- urine Na <20mEq/L = loss from extrarenal cause
- urine Na >20 = loss from renal cause |
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Describe clinical symptoms of hypovolemic, hypotonic, hyponatremia.
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- relate to hypovolemia (poor perfusion, low BP, weak pulses)
- relate to hyponatremia/tonicity (cerebral swelling, vomiting, confusion, agitation)... if Na<120 may have sz, coma, death - rapid decline = more severe than gradual |
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What are the goals of treatment for hyponatremia?
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- Prevent life-threatening signs and symptoms
- Raise serum Na to normal (or close) - Avoid tx-related adverse events (demyelination syndrome) - treat underlying cause |
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What is osmotic demyelination?
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- rare but serious condition may develop after aggressive tx of hyponatremia by ANY method
- shrinkage of the brain triggers demyelination of pontine and extrapontine neurons - may result in neuro dysfunction incl quadriplegia, pseudobulbar palsy, sz, coma, death - Increased risk in pts with hepatic failure, K+ depletion, and malnutrition |
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Hyponatremia tx depends on what?
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-cause/classification
- severity - concurrent disease state - ECF volume - rate of decline of Na concentration - degree of hyponatremia |
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Describe treatment of hypervolemic hypotonic hyponatremia
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- restrict salt and water
- fluid restrict to 1 to 1.2L/day - restrict Na to 1-2g/day - may need loop diuretics to removewater |
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Describe treatment of hypOvolemic hypotonic hyponatremia.
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- restore vital organ perfusion
- replace Na and volume loss with NS (200-400mL/hr based on symptoms, 100-155mL/h once hemodynam. stable) - avoid too rapid correction (demyelination) - Pts with rapid onset <48h should consider HYPERTONIC saline |
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Describe tx of isovolemic (euvolemic) hypotonic hyponatremia tx
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- correct the cause (hypothyroid, glucocorticoid deficiency)
- induce negative water balance (outs>>ins by several hund. mL/day) - fluid restrict to about 1 to 1.2L/day |
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Describe tx of isovolemic hypotonic hyponatremia specific to SiADH
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- treat underlying cause
- restrict fluid intake - may need to tx hyponatremia with hypertonic saline - pharmacotherapy: -dameclocycline (abx, derivative of tetracycline, potent inhibitor of ADH) - lithium (antidepressant, antimanic agent, inhibits ADH action at collecting tubules) - phenytoin (anticonvulsant, inhibits release of ADH) |
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Describe tx for severe euvolemic hypotonic hyponatremia. What indicates this condition?
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- serum Na < 125mEq/L, plus symptomatic
- hypertonic saline (CAREFULLY) - fluid restriction - loop diuretic |
