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Assessing dehydration and shock

associated with dehydration, measured using the accepted ‘gold standard’ of the difference
between pre-hydration and post-hydration weight. However, 10 of the 13 included studies
were not blinded and had ill-defined selection criteria. Moreover, all these studies were
conducted in secondary care where children with more severe dehydration are managed.
Most children with gastroenteritis can and should be managed in the community* but there
is a lack of evidence to help primary care healthcare professionals correctly identify children
with more severe dehydration. Symptoms and signs that researchers may wish to investigate
include overall appearance, irritability/lethargy, urine output, sunken eyes, absence of tears,
changes in skin colour or warmth of extremities, dry mucous membranes, depressed fontanelle,
heart rate, respiratory rate and effort, character of peripheral pulses, capillary refill time, skin
turgor and blood pressure.

Clinical question
What symptoms and/or signs suggest the presence of hypernatraemic dehydration?

Hypernatraemic dehydration may be defined as dehydration associated with a plasma sodium
concentration greater than 150 mmol/l. Some textbooks suggest that the presenting symptoms
and signs associated with this condition differ from those in dehydration without hypernatraemia.
It is said that these patients may have ‘doughy’ skin, and tachypnoea, and that many of the signs
normally associated with dehydration (reduced skin turgor, dryness of the mucous membranes,
skin mottling, sunken eyes, altered vital signs) may not occur. The evidence for these reported
differences was sought.

Evidence overview
Only one study was found that reported signs and symptoms associated with hypernatraemic
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dehydration. A prospective comparative study was conducted in South Africa to determine
the incidence of hypernatraemia in children with diarrhoea and to define its distinguishing
symptoms and signs. Serum sodium levels were determined in all children admitted with
diarrhoea at the hospital over the course of 1 year (n = 3889). In total, 147 (3.8%) were found to
be hypernatraemic (serum sodium > 150 mmol/l). A group of 50 consecutive children with an
initial serum sodium < 150 mmol/l formed the control group. No inclusion and exclusion criteria
were reported. The study participants underwent a full clinical examination and the degree of
dehydration was categorised as ‘not dehydrated’, ‘5% dehydrated’ or ‘10% dehydrated’. The
percentage dehydration was calculated from the difference between the weight on admission
and after rehydration.
A significantly greater proportion of those with hypernatraemia were younger than 6 months
(P < 0.01) compared with the control group. There were no differences regarding gender or
nutritional status. Symptoms of central nervous system dysfunction were more common in
the hypernatraemic group compared with the non-hypernatraemic children (38% versus 4%;
P < 0.001). The authors also reported the numbers of children presenting with various central
nervous system symptoms for the two groups: 32 versus 2 were drowsy but rousable; 15 versus
0 were jittery, hypertonic or hyperreflexic; 9 versus 0 children were in coma or had convulsions.
When clinical estimation of dehydration was compared with the actual degree of dehydration
(based on weight change), dehydration was underestimated in 72.5% of the hypernatraemic
group compared with 36% of the non-hypernatraemic group (P < 0.001). The authors reported
that in the hypernatraemic group dehydration was often grossly underestimated. [EL = 2]

Evidence summary
Evidence from a single prospective study indicated that hypernatraemia was more common in
young infants (<6 months) with diarrhoea. Children with hypernatraemic dehydration had an
increased frequency of symptoms of central nervous system dysfunction. Using clinical assessment,
the severity of dehydration was more often underestimated in hypernatraemic dehydration than
in children with dehydration associated with a normal plasma sodium concentration.

* Hay AD, Heron J, Ness A; the ALSPAC study team. The prevalence of symptoms and consultations in pre-school children in the Avon
Longitudinal Study of Parents and Children (ALSPAC): a prospective cohort study. Family Practice 2005;22(4):367–74.

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