NURS601 Week 1 - Fluid shifts & Electrolytes
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Electrolyte homeostasis is the interplay of electrolyte intake and absorption, electrolyte distribution, electrolyte excretion, and electrolyte loss through abnormal routes
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If electrolyte excretion or loss through abnormal routes increases, electrolyte intake also must increase to prevent electrolyte imbalance
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There are many things that may cause an electrolyte imbalance
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Hormone
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Net effect
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ADH (Antidiuretic hormone)
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Blood pressure increases (with fluid intake); blood volume increases (with fluid intake); blood osmolarity decreases
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Renin-angiotensin system
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Blood pressure increases
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Aldosterone
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Blood plasma Na+ maintained, blood plasma K+ decreases. Blood volume and blood pressure maintained (by decreasing urine output)
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Atrial natriuretic peptide (ANP)
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Promotes natriuresis, elevated urinary excretion of Na+ (and Cl-), accompanied by water. Increases loss of water in urine
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Primary fluid in the body
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Most physiological processes require water
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Water delivers electrolytes & nutrients, and carried away waste.
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Helps regulate body temp. and helps maintain blood volume
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Water balance is affected by age, gender, muscle mass (more muscle = more water, more fat = less water)
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60% of an adults body weight is water - there is more water in a child and less in an eldery person, placing these populations at increased risk of fluid & electrolyte imbalances
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Daily intake requirements is 2000-3000mL (in ideal conditions, changes in situations such as fever, increased metabolism etc.)
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1L of water = 1kg weight so daily weighs can be a good indicator of whether a patient is maintaining good fluid & electrolyte balance
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Intake sources: Liquids (1500mL/day), Solid foods (800mL/day), Metabolism (300mL/day)
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Fluid loss sources: Kidney (1200-1500mL/day), Skin (500-600mL/day), Lungs (400mL/day), GI Tract (100-200mL/day)
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Measureable intake sources: Oral fluid, tube feedings, Parenteral fluid, Enemas, Retained irrigation fluid
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Measureable output sources: Urine, Emesis, Feces, Drainage from body cavities
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Not measureable intake sources: Solid foods, metabolism
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Not measurable output sources: Sweating, vaporisation through lungs
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Osmosis
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Movement of water through a semi-permeable membrane from an area of low concentration to an area of high concentration
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Diffusion
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important in the transport of gases; sometimes requires the assisstance of a transport system (facilitiated diffusion - used in insulin & glucose); similar to filtration but more about movement of particles that movement of fluid (also includes gas transport & electrolytes)
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Flitration
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Differences in water volume, i.e. hydrostatic pressure. Happens at tissue capillary level from capillaries to interstitial fluid, i.e. edema; hydrostatic pressure pushes fluid through the membranes (cell & vessel walls)
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Active Transport
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Molecules have to move against a conc. gradient, requiring active energy and a transport system - such as a Na-K pump requiring ATP - which moves 2 substances at the same time in opposite directions, againt conc. gradients.
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If intracellular fluid (ICF) becomes hypertonic relative to extracellular fluid (ECF), water moves from ICF to ECF via osmosis, causing cell death
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If ECF becomes hypotonic relative to ICF, water moves from ECF into cells, expanding the cell and potenially causing cell to burst
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