FLUID AND ELECTROLYTES

Question 1

DESCRIBE THE FLUID COMPARTMENTS

Answer 1

Fluid compartments
i. Plasma is the fluid component of blood surrounding the red cells
ii. Intracellular fluid (ICF) is fluid within the body’s cells
iii. Interstitial fluid (ISF) is fluid found between the cells, outside blood vessels
iv. The ISF and plasma together make up the extra cellular fluid (ECF)
 Water is present in plasma, ISF and ICF and passes freely between compartments under osmotic influence

Question 2

LIST AND EXPLAIN TH RATIONALE BEHIND FLUID REPLACEMENT

Answer 2

Fluid replacement should address: shock/resuscitation 10-20mls/kg bolus of 0.9% N/S or R/L
I. Deficit- Fluid deficit may develop as a result of a period of fasting or a pathologic process.
 Fluid Deficit = Maintenance requirements per hour x number of hours fasted).
 Or calculated based on the level of dehydration- Mild = 2.5%, moderate =5% and severe = 10%.
E.g. for severe dehydration, deficit = BWT x 10 x level of dehydration
 Common conditions associated with preoperative fluid deficits: Fractured hip, femur, pelvis, Bowel
obstruction, Preoperative bowel preparation, Trauma, Protracted vomiting and diarrhea, Bums,
Sepsis and Pancreatitis
II. Daily maintenance requirements- Maintenance infusion rates, should meet pts daily water, sodium and
potassium requirements. Exercise caution when administering crystalloids such as NS or RL in
congestive heart failure, renal failure, or advanced age:
 Pt <10kg = 100mls/kg, 11-20kg =1000mls + 50mls for every kg above 10 and those above
20kg= 1500mls + 20mls/kg for every Kg above 20, up to a max of 240mls daily
III. Losses
 Third Space Losses: A reduction in ECF vol during surgery results from evaporative losses,
exudative losses, tissue edema due to surgical manipulation & fluid sequestration in organs, i.e. bowel
and lung. Guideline for replacing 3RD space fluid losses is 4 - 6 - 8 ml/kg/hr rule. 4 for minor, 6 for
moderate and 8mlkg/hr for major surgical trauma given in addition to maintenance requirements,
fluid deficit, and ongoing blood losses-NS/RL

Question 3

HOW DOES FLUID LOSS OCCUR?

Answer 3

Fluid losses occur by four routes:
1. Lungs. About 400 mL of H2O is lost in expired air each
24 hrs.
2. Skin. In a temperate climate, skin (i.e. sweat) losses are
between 600 and 1000 mL/day.
3. Faeces. Between 60 and 150 mL of water are lost daily in pts with normal bowel function.
4. Urine. The normal urine output is approximately 1500 mL/ day

Question 4

WHAT IS OSMOLALITY?

Answer 4

Osmolality of a solution is assessed by the amount of solute dissolved in a solvent like water measured in
weight (kg).
Osmolality of plasma = 0.54 × 103 mOsm/kg
1.86
 It is based on the fact that solution of 1 mOsmol/kg freezes at-
1.86°C; whereas normal plasma freezes at – 0.54°C.
 Normal plasma Osmolality is 285 mOsm/kg (275–295).

Question 5

WHAT IS OSMOLARITY?

Answer 5

Osmolarity of a solution is assessed by the amount of solute dissolved in a solvent like water measured in
volume (litre).
 Osmolality of plasma = 2 × (Na) + (Glucose mg %) + (Blood urea mg %)
18 6
 Based on the concentrations of major solutes in plasma. So sodium concentration contributes mainly
to the osmolality

Question 6

WHAT ARE THE INDICATIONS FOR FLUID THERAPY?

Answer 6

Indications for fluid
2) For rapid restoration of fluid and electrolytes in dehydration due to vomiting, diarrhoea, shock due to
haemorrhage or sepsis or burns.
3) Total parenteral nutrition.
4) Anaphylaxis, cardiac arrest, hypoxia.
5) Post-gastrointestinal surgeries.
6) For maintenance, replacement of loss or as a special fluid

Question 7

WHAT ARE CRYSTALLOIDS? LIST THEM

Answer 7

1. Crystalloids- are aqueous solutions of mineral salts or other water soluble molecules. They are used mainly
   to improve the volume and electrolyte supplementation e.g. N/S, Ringers lactate and dextrose. Crystalloids
   are substances which contain relatively small molecules that dissociate into ions to form true solutions
   a) 0.9% sodium chloride
   b) Ringers lactate or hartmann’s solution
   c) 5% dextrose
   d) 10% dextrose
   e) 4% dextrose, 0.18% sodium chloride
   f) 5% dextrose, o.9% sodium chloride
   g) 5% dextrose, 0.45% sodium chloride
   h) Darrow’s solution
   i) Half – strength darrow with 5% glucose
   j) Half – strength ringers lactate with 5% g