Fluid balance

70 kg man

Types of fluids

Crystalloids

Colloids

= plasma expander
= plasma substitute

Effective for 3–4 h.

Daily fluid balance

INOUT
Water 1500 mlUrine 1500 ml
Food 800 mlInsensible 800 ml
Metabolism 200 mlFaeces 200 ml
TOTAL 2500 mlTOTAL 2500 ml
Daily electrolyte requirements for 70 kg man:
Na+110–150 mmol
K+60–70 mmol

Fluid replacement

Fluid required = normal requirement + abnormal losses + initial deficit

Normal daily requirement

For a 70 kg man:
Dextrose + 20 mmol K+
Dextrose + 20 mmol K+
Normal saline + 20 mmol K+.

Otherwise:
first 10 kg:100 ml/kg/day
next 10 kg:50 ml/kg/day
every kg after that:25 ml/kg/day

Abnormal losses

Initial deficit

<5% dehydration cannot be assessed clinically. Thirst may be the only symptom.
Signs in increasing severity: