|Very hot dry environments|
|Very hot dry environments||Mike Golden||01.07.98|
|Re: very hot dry environments||Ted Greiner||03.07.98|
|water needs in malnutrition - very hot dry environments||Mike Golden||03.07.98|
Date: Wed, 01 Jul 1998 16:51:30 +0100
From: Michael Golden <m.goldenatabdn.ac.uk>
Subject: very hot dry environments
I have recently been in Northern Mali and Tchad where the temperature was
between 44 and 47C and a very low relative humidity.
(this is the hottest time of year). All the severely malnourished children
had good skin - I think that bad skin in that environment would be lethal
because of the rate of water loss. I was worried because I saw a number of
children with clinical hypernatraemic dehydration. [skin with the
consistency of dough, loss of consciousness, convulsions]. Clearly, at
sustained temperatures above body heat the only way heat can be dissipated
is by evaporation (I drank 8-10 litres a day and urinated 3 times in 5 days
in Mali); they will gain heat by radiation and conduction. Children with
a low weight/body surface area ratio must be very susceptible to pure water
deficiency, which if treated with electrolyte solutions will lead to
hypernatraemia - perhaps if sufficient is given to maintain a good urine
flow rate and their renal concentrating ability is not as compromised as it
is elsewhere (like the skin) this problem could be avoided - but this may
take very large volumes which is not recommended.
I do not know of literature of water balance/requirements in young children
exposed to sustained temperatures over body heat and a relative humidity
<15%. The literature on premature infants does not include these
conditions. However, rough calculations from Ultman JS (Computational Model
for insensible water loss from the newborn - Pediatrics 79:760-765,1987)
indicate that the water loss can be very high. Have conventional ORS
solutions been tested in these extreme temperatures?
It is not easy to measure a child's temperature under these conditions as
the thermometers are above body temperature. Are cheap robust user-friendly
thermocouple thermometers available from any supplier?
All metal items potentially burn the children such as metal tapes on
measuring boards etc because of the high specific heat of metal.
The signs of shock change so that "cool peripheries" become "warm
peripheries" and if blood flow to the skin is reduced then hyperthermia can
result. Indeed, failure to have dilated skin vessels (scalp) was a very
poor prognostic sign in these conditions.
The children should be cooled with wet cloths.
It is likely that the management of severe malnutrition under these
environmental circumstances should not be the same as in "normal" tropical
temperatures and the diets and other provisions of most manuals varied to
take into account the problems of water and heat exchange. All the ACF
centres now have maximum-minimum thermometers in the phases to monitor the
Have those who have worked in the Sahel and other hot desert areas seen
similar problems. Parenthetically, in the winter in the desert the
temperature can fall at night to very low levels and we have seen
hypothermia under these conditions.
I wonder what the sweat sodium is in the young children and newborn infants
in these areas and whether they have a greater renal concentrating ability
than in other areas - perhaps loss of renal concentrating ability would be
a lethal change similar to my observations with the skin.
Prof. Michael H.N.Golden
Date: Fri, 03 Jul 1998 13:13:40 +0100
From: Ted Greiner <Ted.Greineratich.uu.se>
Subject: Re: Ngonut: very hot dry environments
Dear Dr. Golden,
You may find the following two references of interest. In the first one,
Almroth1 reviews the relevant literature on renal concentrating capacity in
infants (some of which would be unethical to do today) and compares this
with the osmolarity of the urine of exclusively breast-fed infants under
Jamaica's warm but somewhat humid conditions. In the second one,2 she and
Bidinger examine the outcome under conditions nearly as extreme as those
you mention. (Not much urine was produced, but it was dilute. Recall that,
unlike everyone else, exclusively breast-fed babies have no excess protein
or minerals to excrete--the main reason we need to drink water or risk
electrolyte disequilibrium and death--despite our bodies still being made
up large of water at death. Your question of the sodium content of sweat is
interesting, but urinary osmolality is the "bottom line" and therefore
presumably sufficient. Nonetheless, there may be times during illness when
these infants do need additional water.) A study in Pakistan arrived at
similar findings under almost equally intense environmental conditions.
They also tested the infants' renal concentrating capacity and found it to
be adequate3. (This may be another example in which the fact that some few
individuals are lacking in this capacity has been generalized so that
physicians often assume that virtually all young infants have low renal
concentrating capacity. Again, prematures are of course another issue.)
Almroth and Bidinger also document that temperature and humidity vary
enormously in 24-hour cycles in such a setting, with evening and early
morning values being much easier to tolerate. Thus one strategy is to
remain indoors during the worst period, particularly if homes have thick
walls of mud or stone, as the cooling of the night passes through to the
inside during the day and vice versa. Did you notice many infants being
exposed to outdoor conditions when they were worst at mid-day?
On the issue of ORS, I think it is particularly relevant to keep in mind,
as Almroth and Latham pointed out4, that all relevant studies have found
that many mothers make ORS or SSS too strong. Thus it is irrational to
promote these solutions for PREVENTING dehydration in normal circumstances.
Better are any foods or fluids already available in the household, since
these are unlikely to be excessively high in sodium or cause osmotic
diarrhea through being too high in sugar. Indeed they maintain hydration
through the actions of amino acids, peptides and carbohydrates which
simulate intestinal fluid absorption just like ORS does. Indeed, in some
places it would appear that promotion of ORS as the "water of life" leads
to a version of it called "water with sugar and salt" being used regularly
even when the infant does not have diarrhea. Anything that threatens
exclusive breastfeeding may have a triple negative effect, replacing breast
milk, increasing the renal solute load, and introducing bacterial and other
contaminants to the infant. Moreover, well-meaning medical intervention may
have harmed traditional practices supportive of giving extra food to
infants with diarrhea5.
In case you want to correspond directly with Dr. Almroth on any of this
research, her email address is included as a cc above. She now works with
Population Council's regional office in Delhi.
1. Almroth SG. Water requirements of breast-fed infants in a hot climate.
American Journal of Clinical Nutrition 1978;31:1154-1157.
2. Almroth A, Bidinger PD. No need for water supplementation for
exclusively breast-fed infants under hot and arid conditions. Transactions
of the Royal Society of Tropical Medicine and Hygiene 1990;84:602-4.
3. Ashraf RN, Jalil F, Aperia A, Lindblad BS. Additional water is not
needed for healthy breast-fed babies in a hot climate. Acta Paediatrica
4. Almroth S, Latham MC. Rational home management of diarrhoea. Lancet
5. Almroth S, Mohale M, Latham MC. Grandma ahead of her time: traditional
ways of diarrhoea management in Lesotho. Journal of Diarrhoeal Disease
Ted Greiner, PhD, Nutritionist
Section for International Child Health, Department of Women's and Children's Health, Entrance 11
Uppsala University, 75185 Uppsala, Sweden
Date: Fri, 03 Jul 1998 13:17:39 +0100
From: Michael Golden <refugeesatabdn.ac.uk>
Subject: Ngonut: water needs in malnutrition - very hot dry environments
Thank you very much for your thoughtful message. Indeed, I was in Jamaica
when one of the studies was done in Port Antonio, and remember it well. I
fully agree totally that in the all tropical countries where studies have
been done NOTHING is required, apart from breast milk, for normal infants.
The environmental conditions in the Sahara are very extreme. Indeed, the
difference between 40 and 45 degrees is very substantial as water loss
rises exponentially this temperature. And the very low relative humidity
The conditions in the studies that you site are not as extreme as these:
(Almroth,'78 = 24-28C, humidity 62-90%: Almroth '90 = 35-40C, humidity
10-35%: Ashraf '93 = 27-40, humidity 24-77).
However, I was not addressing the normal breast fed infant - but rather
severely malnourished children, most of whom are over 6 months of age but
less than 70% weight for height and severely stunted (so that their surface
area/weight is very large). Here the formulae that are used elsewhere may
indeed be inappropriate because of the high renal solute load and attempts
to make the diets "energy-dense". Even in the Jamaican climate we had to
stop giving any child with fever or a rapid respiratory rate and all small
children the standard diet that was advocated at that time (135 kcal/100ml)
because of the high renal solute load/low water intake. More dilute
formulae are now used - but in conditions such as the Sahel they may still
be to concentrated.
There have been studies of renal concentrating ability in severe
malnutrition, and the maximum is about 600 mOsm/l in most children in
Jamaica and sometimes much less - but as I said in my message the children
adapted to the Sahalian environment may have retained renal function in a
way that was not seen in Jamaica. Alternatively, those who become
malnourished that do not retain this ability may not be available for study
as they will have passed on - and we could make incorrect assumptions when
we only look at a survivor cohort.
With the current formulae I have calculated the maximum insensible water
loss tolerable for various volumes of intake and maximum renal
For example the tables give the insensible water loss in ml/kg/d:
Intake 100 kcal/kg/d:
Urine osmolality = 600 800 1000
F100 45 57 66
F100-diluted* 77 91 98
F75 104 112 117
F135** 30 41 48
Intake 150 kcal/kg/d:
Urine osmolality = 600 800 1000
F100 66 86 98
F100-diluted* 116 136 >140
F75*** >140 >140 >140
F135** 45 61 71
*diluted to give 75 kcal/100 ml
** no longer recommended
*** F75 is only given at 100 kcal/kg/d included here for comparison only.
In health full term infants not exposed to extreme environments the
insensible water loss is between 30 and 70 ml/kg/d.
>From the above calculations it is clear that F100 has sufficient water for
most children with a surface area/weight similar or less disadvantageous
than a healthy full-term (say 3.5kg) - water may become the limiting
nutrient with this diet in smaller children who have fever, tachopnoea,
mild diarrhoea or under extreme environmental conditions.
For small children (say less than 4 kg) the dilution of F100 to 75kcal/100
ml should ensure sufficient water when the child gets a fever, tachopnoea
or mild increases of stool water when there is excessive evaporative loss.
With F75 there should not be any difficulty except under the most extreme
of conditions in small infants.
These figures show that F135 is dangerous and its use should only be
contemplated for large children who do not have a fever, respiratory
infection or diarrhoea, take more than 100 kcal/kg/d, are not in a very hot
or dry environment and can be closely monitored so that the diet can be
changed if they develop intercurrent infection.
Clearly though the conditions that prevail in the Sahara are quite unusual
- we need to know at what weight children should be given the more dilute
feed as a routine when the temperature is sustained above 40C with very low
Prof. Michael H.N.Golden