Fluid and Electrolyte Prescribing Flashcards
Identify the main kinds of IV fluids.
1) Glucose 5%
2) Sodium Chloride 0.18% and glucose 4%
3) Saline 0.9%
4) Balanced crystalloids
5) Colloids
How well does colloid fluid pass through semi-permeable membrane ? 5% dextrose ? Saline ? Crystalloids ? NaCl 0.18% and glucose 4% ?
-Colloid- large proteins in it, will not pass (in intravascular space, stays there)
-Dextrose 5%- passes through (Initially distributes through ISF and plasma; glucose
metabolised so effectively adding just water. Further distributes into cells as well as ISF and plasma)
-Saline and crystalloids- Similar to extracellular fluid, passes through and disperse into other extracellular compartments
-Sodium 0.18% and dextrose 4%- passes through (disperses into other compartments including both extra and intracellular)
Identify the major fluid divisions. State the Volumes ff each.
INTRACELLULAR (28)
EXTRACELLULAR (14)
- Plasma (3)
- Interstitial (11)
Total (for an average 70 kg male)= 42 L
Why are UandE results always good indicators of K+ levels ?
Intracellular potassium acts as a reservoir (attenuates change, so low K+ may not appear in plasma).
HENCE, low K+ reflects VERY significant loss of total body K+
What is the barrier between plasma and interstitial fluid ? To what extent can ions, water, and proteins pass freely ?
Capillary wall (water and ions can pass freely, but not proteins)
What is the barrier between extracellular and intracellular fluid ? To what extent can ions, water, and proteins pass freely ?
Plasma membrane (water can pass freely, ions have to pass through channels, proteins cannot pass)
Describe exchange of fluid across the capillary membrane.
Arterial end: hydrostatic force larger, will push fluid out
Venous end: Oncotic force will force fluid back into plasma from interstitial space
State the following for the intracellular compartment:
K+ Na+ Mg2+ Cl- pH
INTRACELLULAR K+: 150 mM Na+: 10 mM Mg2+: 2.5 mM Cl-: 10 mM pH: around 7.0
EXTRACELLULAR Interstitial K+: 4.5 mM Na+: 130 mM Mg2+: 0.85 mM Cl-: 110 mM pH: 7.4
Plasma K+: 4.5 mM Na+: 130 mM Mg2+: 0.85 mM Cl-: 110 mM pH: 7.4
What is the main difference between plasma and ISF in terms of composition ?
Proteins (oncotic P higher in plasma)
Intracellularly, where does most of the negative charge come from ? Extracellularly ?
INTRA
Negatively charged proteins
Phosphate
EXTRA
Chloride
Identify the main gains, and losses of total body fluid, and the V of fluid lost through each of these on average per day.
GAINS
Food and water intake; oxidation of food
LOSSES
- Urine(variable; average 1500ml)
- Faeces (variable; average 100 ml)
- Sweat (variable; average 50mls)
- Insensible losses (variable; average 900ml)
How much fluid do we lose on average per day ?
2250 mmL
Identify examples of insensible water losses.
- Transepidermal diffusion: water that passes through the skin and is lost by evaporation
- Evaporation loss from the respiratory tract
Insensible losses are solute free
What is the difference between the role of sweat and insensible fluid loss.
SWEAT
Body temperature regulation
INSENSIBLE FLUID
Cannot be prevented
Evaporation of insensible fluid is a major source of heat loss from body but is NOT under regulatory control
Identify respiratory disease processes, and iatrogenic processes which can result in increased fluid loss.
RESPIRATORY
Disease process: anything which increases respiratory rate, will increase insensible losses via respiratory route (e.g. asthma, pneumonia)
Iatrogenic: Oxygen mask (dry air, takes up more humidity, increases sensible losses)
Identify GI disease processes, and iatrogenic processes which can result in increased fluid loss.
GASTROINTESTINAL
Disease process: Chorea, other causes of vomiting and diarrhea
Iatrogenic: Industrial strength laxative given before bowel surgery will cause marked fluid depletion
Identify urinary disease processes, and iatrogenic processes which can result in increased fluid loss.
URINARY
Disease process: Uncontrolled diabetes (glucose is osmotic diuretic, will be lost in urine and pull water with it)
Iatrogenic: Diuretic
Identify skin disease processes, and iatrogenic processes which can result in increased fluid loss.
SKIN
Disease process: Fever (insensible losses), burns
Iatrogenic: Surgery on abdomen with large SA of bowel exposed, moisture evaporates
How is total body fluid controlled ?
Sensors/ Central controller/ Effectors
Changes to gains/ losses result in a change in osmolality
and/or volume
Identify the main sensors of the body.
SENSORS
- osmoreceptors in the hypothalamus (daily housekeeping, sense osmolality in blood)
- low pressure baroreceptors in right atria and great veins (when dramatic event occurs e.g. shock)
- high pressure sensors (carotid sinus / aorta)
How do osmoreceptors respond to water shortages (i.e. effectors).
In times of water shortage, blood osmolality increases, sensed by osmoreceptors resulting in:
- Increased thirst (for increased water input)
- ADH secretion (for decreased water output)
What is the key driver of total volume ? How so ?
Total sodium
- If total sodium drops and osmolality (tightly regulated) stays the same, the total volume falls (including plasma volume)
- If total sodium rises and osmolality stays the same, the total volume will rise
Identify the compensatory mechanisms linked to low V and high V.
Compensatory mechanisms are really linked to low volume (low GFR, stimulation of JGA ) or high volume (increased GFR and release of ANP)
Identify the main gains and losses of NaCl.
- Gains: food and drink
- Losses: sweat (0.25g), faeces (0.25g), urine (10g)
How may your body compensate for too much/too little Sodium ?
- If you eat too much/ too little salt, the only controllable route of loss is via urine: hormonal control
- May increase losses via the other routes in a non- hormonally controlled way (exercise/heat etc causing increased sweating; diarrhoea causing increased loss via faeces)
