Daily requirements
- For the ‘average’ 70 Kg man
- Total body water is 42 L (~60% of body weight)
- 28 L is in the intracellular and 14 L in the extracellular compartments
- The plasma volume is 3 L
- The extravascular volume is 11 L
- Total body Na+ is 4200 mmol (50% in ECF)
- Total body K+ is 3500 mmol (only about 50-60
mmol in ECF)
- Normal osmolality of ECF is 280 –295 mosmol/kg
Fluid replacement
When calculating fluid replacement for a patients need to consider:
Maintenance requirements
- Daily maintenance fluid requirements vary between individuals.
- 70 Kg male = 2.5 - 3.0L water, 120 – 140 mmol sodium and 70 mmol potassium
- 40 Kg woman = 2.0L water,70 – 90 mmol sodium and 40 mmol potassium
- Daily maintenance fluid requirements for children
- 0-10 kg is 100 ml/kg
- 10-20 kg is 1000 ml + 50 ml/kg for each kg > 10
- >20 kg is 1500 ml + 25 ml/kg for each kg > 20
Replacement of losses
- Pre-operative or pre-admission
- Ongoing losses
- Nasogastric aspirate
- Vomit, diarrhoea
- Stoma, drains, fistula etc
- Most ‘surgical ‘ ongoing losses are rich in sodium and should be replaced with 0.9% saline
Insensible losses
- Faeces approximately 100 ml/ day
- Lungs approximately 400 ml/ day
- Skin approximately 600 ml/ day
Composition of crystalloids
|
Hartmann’s Solution
|
Normal Saline
|
Dextrose Saline |
| Sodium (mmol/l) |
131 |
150 |
30 |
| Chloride (mmol/l) |
111 |
150 |
30 |
| Potassium (mmol/l) |
5 |
Nil |
Nil |
| Bicarbonate (mmol/l) |
29 |
Nil |
Nil |
| Calcium (mmol/l) |
2 |
Nil |
Nil |
- 3L of Dextrose saline is not equivalent to 2L 5% Dextrose and 1L Normal saline
- 3L Dextrose Saline = 3L water and 90 mmol sodium
- 2L 5% Dextrose saline + 1L Normal saline = 3L water and 154 mmol sodium
Composition of colloids
|
Volume effect (%)
|
Average MW (kDa)
|
Circulatory half life
|
| Gelatins (Haemaccel) |
80 |
35 |
2-3 hours |
| 4% Albumin |
100 |
69 |
15 days |
| Dextran 70 |
120 |
41 |
2-12 hours |
| 6% Hydroxyethyl Starch |
100 |
70 |
17 days |
- Monodispersed = All molecules of similar molecular weight
- Polydispersed = Molecules have spread of molecular weights
Albumin
- Monodispersed
- Expensive
- Long half life
- Accounts for 60-80% of normal plasma oncotic pressure
- No adverse effect on coagulation
Dextrans
- Polysaccharides
- Polydispersed with MW 10-90 kDa
- Reduces plasma viscosity
- Reduces platelet aggregation
- 1-5% develop anaphylaxis
Gelatins
- Polypeptides
- Polydispersed with MW ~35 kDa
- Rapidly lost from vascular space
- Hydroxyethyl starch
- Synthetic polysaccharide polymers derived from amylopectin
- Polydispersed with MW 50-450 kDa
- Large molecules engulfed by reticuloendothelial system
- Associated with bleeding diathesis
Assessment of adequacy of resuscitation
- Clinical history and observations – Pulse, blood pressure, skin turgor
- Urine output – oliguria < 0.5 ml/kg/hr
- CVP or pulmonary capillary wedge pressure
- Response of urine output or CVP to fluid challenge
- A fluid challenge should be regarded as a 200-250 ml bolus of colloid
- This should be administered as quickly as possible
- A response in the CVP or urine output should be seen within minutes
- The size and duration of the CVP response rather the actual values recorded is more important
Bibliography
Choi P T-L, Yip G, Quinonez
L G, Cook D J. Crystalloids
vs. colloids in fluid resuscitation: a systematic review.
Crit Care Med 1999; 27:
200-210.
Schierhout G, Roberts I, Alderson
P. Colloids versus crystalloids for fluid resuscitation in
critically ill patients (Cochrane Review). In: The Cochrane library, Issue
1, 1999. Oxford.
Traylor R J, Pearl R G. Crystalloid
versus colloid versus colloid: All colloids are nor equal. Anaesth Analg 1996; 83;
209-212. |