Fluid and Electrolytes 59
1
Other Regulatory Factors
Other factors influence fluid and electrolyte
transport indirectly, including acid-base homeo-
stasis, gut motility, luminal flow rates, intestinal
permeability, blood oncotic pressure and plasma
volume, venous and arterial pressure, and physi-
cal and psychological stress.
Effects of Environment and Physical Activity
Thermoregulation is essential to the body’s prop-
er functioning. The body’s core temperature is
carefully regulated and maintained. Accordingly,
there are multiple mechanisms to dissipate ex-
cess heat, which include sweat evaporation, ra-
diation, convection, and conduction, with evap-
oration being the most effective. These same
mechanisms essential for thermoregulation may
also lead to fluid loss and electrolyte abnormali-
ties. In hot climates, a considerable volume of
water may be lost through perspiration for evap-
orative cooling and is further increased with in-
creased humidity and during periods of physical
exertion ( fig. 3 ) [8].
Compared to adults, children have a greater
surface area/body mass ratio and rely more on
dry heat dissipation than evaporative heat loss.
However, older children and adolescents do not
have inferior thermoregulatory ability or physi-
cal exertion tolerance with higher heat injury
rates than adults, even during extreme heat. Poor
hydration status and excess physical exertion, es-
pecially in a hot environment, are the main deter-
minants of exertional heat illness; modifiable
risk factors include extreme exertion, inadequate
recovery from repeated periods of exercise, and
excessive clothing or sports equipment, among
others [9].
Breastfed infants, including low-birth-weight
infants, in hot climates can be adequately main-
tained on breast milk exclusively and do not re-
quire supplemental water. In developing coun-
tries, supplementation is associated with greater
infant morbidity and mortality from diarrhea
and respiratory illness, decreased milk intake,
and early cessation of breastfeeding which syner-
gistically promotes the development of malnutri-
tion [10].Principles of Rehydration and Fluid
MaintenanceThe degree of dehydration as graded by clinical
characteristics determines the fluid and electro-
lyte regimen to be used, regardless of the specific
etiology. Except for severe dehydration or if the
child cannot tolerate enteral fluids, oral ORS
(Na + ) should be used for rehydration and accom-
plished rapidly over 3–4 h ( table 1 ) [11]. The
WHO and UNICEF recommend a 245-mmol/l
ORS of NaCl 2.6 g (75 mmol/l), glucose 13.5 g (75
mmol/l), KCl 1.5 g (20 mmol/l), and citrate 2.9 g
(10 mmol/l). Breastfeeding should continue dur-
ing and immediately following rehydration; in
nonbreastfed infants, an unrestricted age-appro-
priate diet should be provided immediately fol-
lowing initial rehydration. If formula food is be-
ing used, it should not be diluted and does not
need to be specialized, since lactose-containing
formulas are usually well tolerated. Ongoing stool
losses should be replaced with ORS.
Severely dehydrated children usually require
initial rehydration with intravenous f luids, after
which hydration can usually be maintained oral-
ly with ORS ( table 1 ). Ringer’s lactate (Na + 130
mmol/l, K + 4 mmol/l, Cl – 109 mmol/l, and lactate
28 mmol/l) with or without 5% dextrose is the
preferred intravenous solution, while normal sa-
line (0.9% NaCl; Na + 154 mmol/l) is an acceptable
alternative. In extreme situations or if the child is
unable to keep up with ongoing stool losses, in-
travenous f luids are needed beyond the initial re-
hydration period ( table 2 ) [2].
In developing countries where diarrheal dis-
ease is most prevalent and associated with theKoletzko B, et al. (eds): Pediatric Nutrition in Practice. World Rev Nutr Diet. Basel, Karger, 2015, vol 113, pp 56–61
DOI: 10.1159/000367869