Basic Concepts of Fluid and Electrolyte Therapy

Once resuscitation has been achieved as judged by normalisation
of vital signs and urine output or of parameters from more invasive
measurements, the prescriber should switch to a maintenance regimen
with accurate replacement of any on-going losses. Exceeding
such requirements, on the unwarranted assumption that the
patient will excrete any excess, is deleterious to outcome and
delays recovery.
b. Replacement: any fluid prescription should incorporate not only
daily maintenance requirements, but replacement of any ongoing
abnormal losses. In the case of a patient with losses from the gastrointestinal
tract, e.g. from a fistula or from nasogastric aspiration,
the fluid prescription should include the daily maintenance
requirements plus like-for-like water and electrolyte replacement
of any losses. In order to achieve this, the prescriber should be
aware of the approximate electrolyte content of fluid from various
parts of the gastrointestinal tract (Chapter 1, Table 3).
c. Maintenance: Maintenance prescriptions should aim to restore
insensible loss (500-1000 ml), provide sufficient water and electrolytes
to maintain normal status of body fluid compartments,
and sufficient water to enable the kidney to excrete waste products
500-1500 ml (Chapter 1, Tables 2 and 3). The average person
requires 25-35 ml/kg water, 1 mmol/kg Na and 1 mmol/kg K + per
day. Examples of how to provide this maintenance requirement are
summarised in Table 10.
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