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Fluid and electrolytes

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Martin Nguyen

on 20 July 2010

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Transcript of Fluid and electrolytes

By martin nguyen fluids and electrolytes Fluid status assessment Case Studies Fluids History


tests Revision normal physiology Body composition the average 70kg man but Not everyone is the same??? men 60%
women 55% (more adipose:muscle) variations by gender age tissue neonates 80% (high interstial fluid)
infant 60% (12months)
elderly 50% (more adipose:muscle)
plasma 93%
fat 10-15%
bone 20% 3 compartments compartment model water is contained within the numerous organs and tissues
these fluids can be lumped together into larger collections referred to as compartments
making it easier to discuss in a physiological logical manner 1. Intracellular Fluids (ICF)

2. Extracellular Fluids (ECF)

3. Intersitial Fluids (ISF)
water located inside cell membranes
virtual compartment
the sum of many discrete collections
33% by weight
or 330ml/kg
average person 23L (0.33 x 70kg) intracellular fluid water located outside cell membranes
27% by weight
or 270ml/kg
average person 23L (0.33 x 70kg)
low in potassium & magnesium and high in sodium and chloride

plasma 50 ml/kg
interstitial 150 ml/kg
transcellular 50 ml/kg (functional fluid) extracellular fluid electrolyte distribution Na+

Osmolarity 10

290 plasma 50 ml/kg
only major fluid compartment that exists
high protein content
functions as transport (via bulk flow)

also contains intracellular fluid
in RBC (part of ICF)
interstitial fluid (ISF) 'virtual' fluid
fluid lying in the interstices of all body tissues
bathes all cells and in the link between ICF and intravascular compartment (plasma)
allowing O2, nutrients, wastes and chemical messengers all pass through the ISF
similar to ECF but is low in protein
lymph is considered as a part of the ISF but is high in protein functional fluid aka transcellular fluid
formed from the transport activity of cells
for example CSF, GIT fluid, bladder urine
specialised functions
electrolyte compositions are dissimilar

NB GIT fluid flux can be large

typical compostion
Gastric Juice

Pancreatic Juice


Ilial Fluid


CSF [Na+]






147 [K+]






3 [Cl-]






113 [HCO3-]






25 diffusion

osmotic pressure

oncotic pressuRe importance Fluid therapy is fundamental in every hospitalized patient.
Can be life-saving in certain conditions
loss of body water : mild lightheadedness to convulsions, coma, and death.
inappropriate fluid therapy : overload, APO, convulsions, coma and death Diffusion Random movement of molecules from a region of higher concentration to one of lower concentration

The result is a gradual mixing leading to an equilibrium Diffusion across a cell membrane simple diffusion
substance passes through a membrane without the aid of an intermediary membrane protein
usually lipid soluable eg. O2,CO2 facilitated diffusion
substance passes through membrane facilitated by transport proteins
usually polar molecules eg. Na+, K+ Osmotic pressure is the pressure applied by a solution to prevent the inward flow of water across a semipermeable membrane Osmosis passive process like diffusion
movement across a semi-permeable membrane
movement of water from high water concentration to low, or low solute concentration to high
until equilibrium is reached

think of the presence of ions diluting the water molecules a form of osmotic pressure exerted by proteins in blood plasma that usually tends to pull water into the circulatory system
mainly albumin

more important than you think Oncotic pressure Role of Albumin Reabsorption prevents fluid from leaving the capillaries
Albumin is a large molecule and will not pass through the capillary membrane
When fluid filters through the capillary, the protein albumin remains behind
When the concentration of albumin increases, fluid begins to move back into the capillary wall by osmosis
The pulling force of albumin in the intravascular space is called plasma colloid oncotic pressure
What happens when we give fluid here osmolarity Osmolarity is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per liter (L)
the number of particles in solution
for example 0.5 mole of NaCl in a 1L water will produce a 1 molar solution

Tonicity is a measure of the osmotic pressure
Generally to contrast fluid across membranes in relation to normal physiological osmolarity
Osmolarity of plasma is 275-295 mOsm/L
tonicity Basically 3 types of fluid



blood products Crystalloids aqueous solutions of mineral salts or other water-soluble molecules
Normal Saline
4%Dextrose 1/5 NS
5% dextrose

easy to store with long shelf life
readily available
very low incidence of adverse reactions
a variety of formulations are available
effective for use as replacement fluids or maintenance fluids
no special compatibility testing is required.
no religious objections to their use

advantages of crystalloids 9g sodium chloride in 1L water
154 mmols of Na+ and Cl-
304mosmol/L (hypertonic solution)

used to rehydrate and as maintence
head injury

caution too much too fast can could hyperchloremic metabolic acidosis

Normal Saline Hartmanns the 'physiological' IV fluid or is it????

sodium = 131 mmol/L (140mmol)
chloride = 111 mmol/L (103mmol/L)
lactate = 29 mmol/L (0.5 mmol/L)
potassium ion = 5 mmol/L (3.5mmol/L)
calcium ion = 2 mmol/L (2 mmol/L)
osmolarity 284mosml/L (hypotonic)

used during surgery or to rehydrate during stress response

contraindicated in diabetes mellitus :lactate may worsen hyperglycaemia

can produce elevated high lactate in liver failure, but no acidosis.

Hartmanns Dextrose containing 5% dextrose
4% dextrose 1/5 NS

given as maintenance in healthy fasting patients

basically just free water

water immediately distributes
dextrose is metabolised leaving only free water
other electrolytes diffuse across membrane taking water with it via osmosis

approx one third will remain intravascular in 30 minutes

Distribution of crystalloids colloids large molecular weight (MW > 30,000)
the plasma proteins are the major colloids present.
exert oncotic osmotic force across wall of capillaries

gelatin is produced by the action of alkali and then boiling water on collagen from cattle bones
MW ranges from 5,000 to 50,000 with a weight-average MW of 35,000
colloids - gelatins advantages Lower infusion volume required as compared to crystalloids
Cheaper and more readily available then plasma protein solutions
No infection risk from the product if stored and administered correctly
Only limit to the volume infused is the need to maintain a certain minimum [Hb] (In comparison, dextrans have a 20ml/kg limit).
Readily excreted by renal mechanisms
Favourable storage characteristics: long shelf life, no refrigeration
No interference with blood cross-matching
Compatible with other IV fluids except Ca++ can cause problems with citrated blood products.

• Higher cost then crystalloids
• Anaphylactoid reactions can occur
• No coagulation factors and its use contributes to dilutional coagulopathy
disadvantages distribution same as cystalloids but slower
colloid components diffuse very very slowly due to size
colloids lose their effect by being metabolised/excreted
renally excreted

therefore 1/3 will remain in intravascular circulation at 8 hours
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