Volume depletion & dehydration Flashcards
Cell Membrane
Also known as the plasma membrane
Composed of lipids and proteins (phospholipid bilayer)
Functions:
Separate the interior of the cell from the outside environment
Provides protection to the cell
Allows for selective transport of molecules
Remember LIKE dissolves LIKE
Lipid soluble molecules pass thru the membrane (passive transport)
Water soluble molecules require a channel (proteins) to pass thru the membrane (active transport)
Cell Membrane transport
Diffusion- passive/facilitated
Requires no ATP
Movement of molecules from high to low concentration along an electrochemical gradient
Simple diffusion
Movement of small or lipophilic molecules (O2, CO2)
Through the membrane for lipid soluble molecules
Osmosis: movement of water molecules (depends on solute concentration)
Facilitated diffusion
Movement of large or charged molecules via a protein channel or a carrier protein that is structurally specific (ions, sucrose)
Cell Membrane Transport
active transport
Active
Required ATP
Movement from low concentration to high concentration (against the gradient)
Carrier
Primary(direct)active transport– direct use of metabolic energy (ATP hydrolysis) to mediate transport
Secondary(indirect)active transport– coupling the molecule with another moving along an electrochemical gradient
Vesicular
Endocytosis: into the cell
What are the 2 types of endocytosis?
Exocytosis: out of the cell
Volume status
Balance between water and solutes
Solutes → majority of which is Na
Volume depletion (hypovolemia)
Refers to extracellular cellular fluid loss; loss of both water and Na
↓ circulating volume
Caused by decreased oral Na intake and/orincreased volume losses
Dehydration
Refers to a total body water loss; loss of water across all compartments
↓ circulating volume; ↓ intracellular volume
Caused by decreased oral water intake
Volume depletion and dehydration are NOT the same!
Dehydration
etiology
due to decreased oral water in take:
Acute or critical illness
Decreased access to water
Altered thirst mechanisms in childhood or old age
Dementia
Volume depletion due to decreased oral Na intake:
Acute or critical illness
Eating disorders
Dementia
Volume depletion
etiology
Volume depletion due toincreased volume losses:
Bleeding
* GI losses:
Diarrhea
Vomiting
Drains (nasogastric tube)
* Renal:
Diabeticketoacidosis
Diuretic therapy
Diabetes insipidus
* Third-space losses:
Burns
Severepancreatitis
* Insensible losses:
Skin/mucous membranes (fever, excessive sweating)
dehydration
patho
Fluid shifts with illness/disease
Occur due todiffusion across asemipermeable membrane
Regulated by a difference inplasma osmolality between ECF andICF
Dehydration:
Water is lost, but not Na
Water is lost from ECF → ECFosmolality increases → water diffuses fromICF to ECF
Net effect: ECF hypertonicity andhypernatremia
Example: ↓ water intake or inadequate water replacement in critical illness
Volume depletion
Hypotonic loss of fluid
Water > Na
Hypotonicfluid is lost from ECF → ECFosmolalityincreases → water diffuses fromICFto ECF
Example: Increased insensible losses (fever or excessive sweating)
Volume Depletion
Isotonic loss of fluid
NA = water
Isotonicfluid is lost from ECF → ECFosmolalitydoes not change → no gradient fordiffusionwithICF
Plasmaosmolalityand serum Na do not change
Example: diarrhea, loss of whole blood
Volume Depletion
Hypertonic loss of fluid
Na > water
Fluid is lost from ECF → ECF contracts and ECFosmolalitydecreases → water shifts from ECF toICFviadiffusion
Example: loop diuretics, primary adrenal insufficiency
dehydration
S/Sx
Varies greatly depending on the severity - asymptomatic to potentially fatal hypovolemicshock
Symptoms of mild and moderateare often nonspecific:
Fatigue
Dizziness
Thirst
Musclecramps and/or headache
Decreased urination
Symptoms with severehypovolemia:
Severe dizziness
Cool extremities
Confusion/altered mental status
dehydration
PE
Signs of dehydration andhypovolemia:
Dry mucous membranes
Dryskin
Decreasedskin turgor
Orthostatic hypotension
Weight loss
dehydration
Signs of shock
Hypotension (systolic blood pressure <100mm Hg)
Tachycardia (>90–100 beats/min)
Tachypnea (respiratory rate >20)
Cool extremities
Altered mental status
dehydration
Dx/blood tests
BUN/creatinine ratio:
Normal: approximately 10:1
Elevated ratio (>20:1) suggestshypovolemia
Inaccurate ifglucocorticoids or GI bleeding
Serum Na+:
Can be high or low, depending on thetonicity of fluid lost
Hypovolemia stimulatesantidiuretic hormone (ADH)secretion
Serum K+:
Can be high or low, but is usually low
Elevated: if there is decreasedsecretionfrom renal dysfunction
Low: if K+is lost in GI fluids or if there is increasedsecretion from highaldosterone state
positive orthostatic hypotension
change in 30 bpm
20mmHg systolic
10mmHg diastolic
acid base disturbances
Metabolic alkalosis
Metabolic acidosis
Metabolicalkalosis: ifhypovolemiais due todiuretics or upper GI blood losses
Metabolicacidosis: withbicarbonate loss due todiarrhea, lacticacidosis withshock, orketoacidosis with diabeticketoacidosis (DKA)
dehydration/volume depletion
Albumin and hematocrit
Concentration increases withhypovolemia
Must consider baseline values
dehydration
urine studies
Urine studies:
Urine sodium (UNa+): < 20 mEq/L suggestshypovolemia
Urine osmolality: > 450 mOsm/kg suggestshypovolemia
Inaccurate with:
AKI/CKD (unable to concentrateurine)
Diuretics
Diabetes insipidus
Urine specific gravity:
>1.021 suggestshypovolemia
Inaccurate if recent IV contrast or severeproteinuria
hypovolemia
Mild Tx
Primary management ofhypovolemiais to replace the fluids lost with similartonicity of fluids
Electrolytes should be monitored during fluid replacement
Mild hypovolemia
If serum Na+is high or low:
Address before replacing fluid specifically forhypovolemia
If serum Na+is normal:
Give gentleisotonicIV fluids (usuallynormal saline)
Increased oral intake of fluids alone may be sufficient if very mild
hypovolemia
moderat-severe Tx
Moderate-to-severe hypovolemia
Initialrehydration:
Bolus of 1–2 Lisotonic IV fluids to start (usuallynormal saline)
Treat aggressively to prevent possible progression toshock
Na management
normal serum Na
Normal serum Na+:
Continueisotonic IV fluids until signs/symptoms improve
May need continuous maintenanceIV fluids if there are ongoing losses (diarrhea)
Na management
Hypernatremia:
Hypernatremia:
Switch tohypotonic fluids (0.45% NaCl or 5%dextrose in water) oncehypovolemia symptomatically improves
Exception: may need to use 5%dextrose in water earlier if there is severehypernatremia
Monitor closely to avoid overcorrection
Na management
hyponatremia
Hyponatremia:
Acutely symptomatichyponatremia → give 3% NaCl (hypertonic saline) until symptoms improve
Moderate-to-severehyponatremia, but not acutely symptomatic → giveisotonic fluids (normal saline) at a more conservative rate than if serum Na+is normal
Mildhyponatremia → giveisotonic fluids at a similar rate as with normal serum Na+
