Fluid Assessment and Balance Flashcards
How is total fluid requirement determined?
Total requirement = maintenance + deficit + ongoing loss
Average healthy adult daily water requirement / loss sites?
Average adults needs 2.5L/d Loss to: -200mL/d GI -800mL/d insensible (resp, perspiration) -1500mL/d urine (caution w/ renal failure)
Conditions increasing fluid requirement?
- Fever
- Sweating
- GI loss (NGT/ V / D)
- Adrenal insufficiency
- Hyperventilation
- Polyuric renal disease
Conditions decreasing fluid requirements?
- Anuria / oliguria
- SIADH
- Highly humidified atmospheres
- CHF
How are the maintenance requirements for crystalloids calculated?
4: 2:1 rule =
- 4mL/kg/h ==> 1st 10kg
- 2mL/kg/h ==> 2nd 10kg
- 1mL/kg/h ==> thereafter
What are the maintenance requirements for electrolytes for average person?
Na+: 3mEq/kg/d
K+ : 1mEq/kg/d
What are the signs and symptoms of mild dehydration?
Mild = 3% water loss
- Decreased skin turgor
- sunken eyes
- dry mucous membranes
- dry tongue
- reduced sweating
What are the signs and symptoms of moderate dehydration?
Mod = 6% water loss
- Oliguria
- Orthostatic hTN
- tachycardia
- low volume pulse
- cool extremities
- reduce filling of peripheral veins and CVP
- Haemoconcentration
- apathy
What are the signs ad symptoms of severe dehydration?
Severe = 9% water loss
- Profound oliguria / anuria
- Compromised CNS function w/ or w/o altered sensorium
Sources of ongoing fluid loss?
- Tubes: Foley catheter, NGT, surgical drain
- 3rd spacing (pleura, GIT, retro-/peritoneal); evaporation via exposed viscera, burns
- ongoing loss due to surgical exposure and evaporative losses
Do IV fluids alter O2 perfusion capacity?
NO. Improve perfusion but NOT O2 carrying capacity of blood.
What is crystalloid?
Salt-containing solutions that distribute within the ECF
Replacement with crystalloid to maintain euvolemia in pt with blood loss?
Replace 3:1
What should be used if large volume replacement required?
Balanced fluids e.g Ringer’s lactate (too much NSal may lead to hyperchloremic metabolic acidosis)
What is colloid?
-Includes protein colloids (albumin and gelatine solutions) and non-protein colloids (starches e.g. hydroxyethol starch/HES and dextrans)
Where do colloids distribute?
Within the ICF
Replacement with colloid in blood loss?
1:1 (to replace intravascular volume)
What must you monitor for with large volume colloid infusions?
Coagulopathy
Describe the extracellular volume environment
- Sodium and Chloride
- Environment supports intracellular osmolality, cell membrane transport and delivery of nutrients and removal of waste (circulation)
Describe the intracellular volume environment
- Potassium, organic anions
- Environment supporting intracellular function and cell membrane transport
What percentage of body weight is total body water?
Total body water ~60% body weight
Percentage of TBW in ECF volume?
33% TBW
Primary influence on ECF volume?
ECF primarily varies with osmolar (Na+ and Cl-) content.
Subject to intake less than excretion.
i.e. LOW Na+ Content = LOW ECV; HIGH Na+ = HIGH ECV
Percentage of TBW in ICF?
66%
Primary influence on ICF volume? WHY?
Intracellular osmolarity held fairly constant (i.e. K+, organic anions)
ICV varies when water intake
How is ECV assessed?
- Hx (abn intake/excretion)
- Oedema / CV exam
- Urine concentration / [Na+]
Water shifts following loss of sodium rich fluid (e.g. diarrhoea)
ECV deplete: -low BP -tachycardia -peripheral vasoconstriction -low urine sodium -concentrated urine ICV UNCHANGED
What is the cause of low osmolality / sodium?
Water intake greater than ability to excrete (N = 20L/d)
What are the causes of low plasma osmolality / sodium?
- Increased ADH
- Decreased distal tubule flow (decreased renal perfusion)
- Other tubular factors (limiting free water excretion)
- Drugs (with variable contributions from above factors): diuretics, carbamazepine, antidepressants (SSRis 12%)
