Br.J. Anaesth. (1977), 49, 1123
A STUDY OF BODY TEMPERATURES OF ANAESTHETIZED MAN
IN THE TROPICS
F. R. ELLIS AND S. L. V. ZWANA
SUMMARY
Body core and skin temperatures were measured in 20 African patients undergoing herniorrhaphy
in hot and humid conditions; one half of the patients received halothane and the other half received
diethyl ether. No difference was found between these two groups. Body core temperatures decreased
even with an ambient temperature of 28.7 °C and a relative humidity of 72% and all sites reached a
new thermal equilibrium at 30 min. It is suggested that the level of the re-established thermal
equilibrium is a function of the skin to ambient thermal gradient, which depends on the failure of
the countercurrent heat exchange mechanism as a result of redistribution of peripheral blood flow.
In a thermally neutral environment, general anaes- Mild hypothermia is usual during general anaes-
thesia induces a modest reduction of body core thesia, although a few patients develop an increasing
temperature. If thermosensitive probes are attached body core temperature even in cool ambient conditions
to an anaesthetized patient at various sites it can be (Stephen, 1961; Goldberg and Roe, 1966). Several
shown that, concurrent with the decrease of body core possible causes of this pyrexia have been identified
temperature, the skin temperature increases and the and these include hot carbon dioxide absorbers, in-
magnitude of the changes depends on ambient ability to sweat after an antisialogogue has been given,
temperature (Foregger, 1943). The increase in skin mismatched blood transfusion, metabolic stimulation
temperature is a result of the peripheral vasodilatation in poorly controlled thyrotoxicosis and in epilepsy,
and causes a net loss of heat from the body by physical endogenous pyrogens in acute septicaemia and other
transfer to the environment. If this heat loss is simply infections such as malaria, and i.v. administration of
a result of radiation, conduction and convection, the .exogenous pyrogens. Hot environmental conditions
total loss of heat from the body would correlate with have been blamed for pyrexia during operation and
the temperature gradient between the skin and the hyperpyrexia after operation. If environment alone
surroundings; thus in a cool environment there should could be responsible for pyrexia during anaesthesia,
be a greater heat loss than in a hot environment and if it should be encountered in thermally uncontrolled
ambient temperature is similar to skin temperature, no operating rooms in Accra, Ghana.
heat loss could occur. A study of body temperatures was made in the hot
Evaporation of sweat from the body surface results and humid conditions prevailing in Accra to determine
in loss of heat because of the consumption of latent the influence of the environment on the temperature
heat of evaporation. In a cool environment, anaes- of anaesthetized patients. In order to facilitate com-
thetized patients are unlikely to lose much heat from parisons between patients, a standardized surgical
sweating, especially if their body core temperature procedure was chosen, namely herniorrhaphy. This
has decreased (Benzinger, 1969). In hot ambient provided an opportunity to compare the influence of
conditions, sweating produces a more significant heat two different anaesthetic agents, diethyl ether and
loss than the other physical methods (Fox, 1974). The halothane, on body heat balance. The reason for this
thermal efficiency of sweating depending on the choice was that diethyl ether is known to cause a
ambient relative humidity is ineffective if the air in release of catecholamines and "ether convulsions" are
direct contact with the skin is fully saturated with associated with pyrexia. Halothane differs from ether
water. in both these regards.
METHODS
F. RICHARD ELLIS, PH.D., M.B., CH.B., F.F.A.R.C.S., University Twenty healthy male African patients between 19 and
Department of Anaesthesia, University of Leeds, Leeds,
Yorks. S. L. V. ZWANA, M.B., CH.B., F.F.A.R.C.S., Department 44 years of age undergoing herniorrhaphy were
of Anaesthetics, University of Ghana Medical School, studied. Ten unselected patients were anaesthetized
Korle Bu Hospital, Accra, Ghana. using halothane, and 10 with diethyl ether. Pethidine
1124 BRITISH JOURNAL OF ANAESTHESIA
and atropine were given routinely for premedication 37.5 halothane
and anaesthesia was induced with Althesin. The . ether
halothane group then received only nitrous oxide,
oxygen and halothane from a Fluotec vaporizer via a
temp.
Magill circuit and face mask. The ether group were rectal
given nitrous oxide, oxygen and diethyl ether from a 37.0
Boyle bottle via a Magill circuit and face mask, but in *'--., tympanic
order to avoid excitation 1.0% halothane was added to
the inspired gas for about 2 min after induction.
Before induction of anaesthesia, thermistor probes
36.5
(Yellow Springs) were placed as follows: rectum, 10 20 30 iO
tympanic membrane, brow, dorsum of thumb, dorsum t ime {m in)
of great toe, outer calf and outer thigh. The tempera- FIG. 1. Changes in body core temperatures during 40 min of
tures at these sites were read at intervals using a anaesthesia; each point represents the grouped mean values
galvanometer to measure the unbalance of a Wheat- for patients anaesthetized with either halothane or diethyl
stone bridge circuit to which each thermistor in turn ether; there is no significant difference between the halo-
was connected by means of a multipole switch. Before thane and ether groups although both sites show a significantdecrease.
starting the study, all probes were calibrated using a
mercury-in-glass solution thermometer. It was
impossible to calibrate the Wheatstone bridge circuit
because the probes had different resistances. Calibra-
tion curves were constructed for each probe and every
temperature reading was corrected later against its thigh
respective calibration curve.
temp.
All patients received anaesthesia for at least 40 min
and, to facilitate comparisons between groups, the halothane
temperatures at the various recording sites were 32 ether
plotted at 5-min intervals from the time of induction
of anaesthesia.
Ambient temperature and relative humidity were
measured using wet and dry mercury-in-glass 30
thermometers (whirling type). 0 10 20 30 to
time (min)
RESULTS FIG. 2. Changes in distal skin temperatures; there is no
No significant difference was found between the significant difference between the halothane and ethergroups.
halothane and the diethyl edier groups. The changes
in the temperatures at the seven sites are illustrated in
figures 1, 2 and 3, in which the results from the 10 halothane
patients in each anaesthetic group are averaged. tympanic ether
37
From figure 1 it can be seen that the body core
temperatures decreased initially but stabilized towards
the end of the 40-min period. The earlier change was thumbt emp.
detected in the tympanic membrane temperature
35
which preceded the decrease in rectal temperature by brow
about 15 min. The temperatures at both sites de-
creased by a similar amount, although out of phase.
The rectal temperature at the beginning and the end 33 .
was 0.15 °C greater than the tympanic temperature. 10 20 30 1.0
Some skin temperatures showed a much greater time (min)
change than the core temperature. In figure 2, it can be
FIG. 3. Changes in temperature of body core (tympanic),
seen that the skin temperature on the dorsum of the proximal skin (brow) and distal skin (thumb); there is no
great toe, which was less than 30 °C initially, showed significant difference between halothane and ether groups.
BODY TEMPERATURES AND ANAESTHESIA IN THE TROPICS 1125
the most marked increase shortly after induction of pyrexia. It may be that, even under anaesthesia, the
anaesthesia. All the skin sites on the lower limb brow skin is capable of thermal adaptation and this
showed similar qualitative changes, but the more would be brought about largely by skin blood flow
proximal sites showed least change. regulation.
The temperature of the dorsum of the thumb in- After 20 min of anaesthesia, the changes in tempera-
creased rapidly in a manner similar to that of the toe ture at most sites showed a tendency to diminish and
(fig. 3) and both these sites approached close to body at 30 min little further change was seen; a new thermal
core temperature, the difference being approximately equilibrium had been established. The operative site
1 °C. The brow temperature showed the least change was too small to make a real contribution to con-
of all the skin sites and remained fairly stable through- tinuing heat loss, and anaesthesia was stable. It is
out. tempting to suggest that the hypothermic effect of
The mean ambient conditions throughout the anaesthesia is brought about initially by disturbing
study were a mean temperature of 28.7+ 1.5 °C and the thermal equilibrium by increased loss with
relative humidity of 72.2 ± 2.5%. cutaneous vasodilatation, and after a short period the
body temperature control is re-established, but at a
new level which depends on the thermal gradient
DISCUSSION
Throughout the study it was clear that there was no between the skin and the environment.
tendency for body core temperature to increase during
ACKNOWLEDGEMENTS
anaesthesia in tropical conditions. In fact there was a We wish to thank our colleagues in Korle Bu Hospital for
small but definite decrease in body core temperature. their co-operation, and the Department of Physiology for
This finding contrasts with that of Morris (1971), who the loan of the thermometer. F. R. E. wishes to acknowledge
suggested that for anaesthetized men the neutral the financial help provided by the Inter-Universities Council
thermal range is 24-26 °C and that body temperature for the duration of this study.
will remain normal with ambient temperatures in REFERENCES
excess of 21 °C (Morris and Wilkey, 1970). However, Benzinger, T. H. (1969). Heat regulation: Homeostasis of
it is possible that the African is better adapted to central temperature in man. Physiol. Rev., 49, 671.
these ambient conditions than is the European, and Foregger, R. (1943). Surface temperature during anesthesia.
that he can still lose heat when thermal gradients are Anesthesiology, 4, 392.Fox, R. H. (1974). Temperature regulation with special
small. From these results there is no suggestion that reference to man; in Recent Advances in Physiology,
adverse thermal environmental conditions can induce (ed. R. J. Linden), p. 340. London: Churchill Livingstone.
pyrexia during anaesthesia. Goldberg, M. J., and Roe, C. F. (1966). Temperature
One interesting finding was the marked change in changes during anesthesia and operations. Arch. Surg.,93, 365.
the peripheral temperatures following induction of Hardy, R. N. (1972). Heat production and heat loss; in
anaesthesia. Using a different thermometer, it was Temperature and Animal Life, p. 25. London: Edward
possible to check that the dorsal toe temperature Arnold.
before anaesthesia was close to the ambient tempera- Morris, R. H. (1971). Operating room temperatures and
ture. The rapid increase in toe temperature must anesthetized paralysed patients. Arch. Surg., 102, 95.Wilkey, B. R. (1970). The effects of ambient tempera-
reflect a great increase in blood flow. The change in ture during surgery not involving body cavities. Anes-
the most peripheral site was greatest and a higher thesiology, 32, 102.
temperature was reached on the skin of the toe than Stephen, C. R. (1961). Postoperative temperature changes.
more proximally on the calf and thigh. It is likely that Anesthesiology, 22, 795.
the countercurrent mechanism for heat retention ETUDE SUR LES TEMPERATURES DU
(Hardy, 1972) of the conscious person is abolished or CORPS D'UN HOMME ANESTHESIE SOUS
severely attenuated. This mechanism alone could LES TROPIQUES
account for much of the heat loss from the body core
RESUME
in the anaesthetized subject.
On a mesurS les temperatures du corps et de la peau de 20
The stability of the brow temperature was sur- malades africains subissant une herniorraphie dans un
prising. Perhaps the time-honoured habit of "feeling climat chaud et humide; la moitid des malades a ete
the brow" may have some rationale, as it seems to be anesthetize par l'halothane et l'autre moiti6 par lather
comparatively unaffected by anaesthesia. The brow is diethyl. On n'a constate aucune difference entre ces deuxgroupes. Les temperatures du corps ont baisse meme par
perhaps the best thermally adapted part of the skin and une temperature ambiante de 28,7 °C et une humidite
sweating often commences on the brow during relative de 72%; tous les points ont atteint un nouvel
1126 BRITISH JOURNAL OF ANAESTHESIA
6quilibre thermique apres 30 min. II ressort de cela que le Funktion des Verhaltnisses zwischen Hauttemperatur und
niveau de l'equilibre thermique retabli est une fonction du Umgebungstemperatur ist, das von dem Versagen des
rapport entre la temperature de la peau et la temperature Gegenstromungs-Warmeaustauschmechanismus' aufgrund
ambiante qui depend de l'insumsance du mecanisme der Veranderungen des peripheren Blutkreislaufes
d'6change de chaleur a contre-courant par suite de la abhangig ist.
redistribution du debit sanguin pSripherique.
UN ESTUDIO DE TEMPERATURAS CORPORALES
EN EL HOMBRE BAJO ANESTESIA EN LOS
STUDIE DER KORPERTEMPERATUREN TROPICOS
NARKOTISIERTER PATIENTEN IN DEN
TROPEN SUMARIO
Se midieron las temperaturas cutanea e interior en 20
ZUSAMMENFASSUNG pacientes africanos sometidos a herniorafia en condiciones
Innen- und Hauttemperaturen wurden bei 20 afrikanischen aclurosas y humedas; una mitad de los pacientes recibi6
Patienten gemessen, die unter heiss-feuchten Klimabeding- halotano y la otra mitad recibio eter dietilo. No fu£ hallada
ungen einer Bruchoperation unterzogen wurden, wobei die diferencia alguna entre estos dos grupos. Las temperaturas
Halfte von ihnen mit Halothan, die andere Halfte mit interiores del cuerpo decayeron aun con una temperatura
Diathylather narkotisiert wurden. Zwischen den beiden ambiental de 28,7 °C y una humedad relativa de 72%;
Gruppen ergaben sich keine Unterschiede. Die Korperinn- todos los sectores alcanzaron un equilibrio termico a los
entemperaturen sanken bei einer Umgebungstemperatur 30 min. Se sugiere que el nivel ttanico equilibrado re-
von 28,7 °C und bei einer relativen Feuchtigkeit von 72% establecido es en funcion de la gradiente termica entre la
sogar ab, und uberall wurde nach 30 Minuten ein neues piel y el ambiente, que depende de la falla del mecanismo
thermales Gleichgewicht erreicht. Es scheint, dass die HOhe termopermutador contracorriente debida a la redistribuci6n
des wiederhergestellten thermalen Gleichgewichtes eine de la circulation sanguinea d^rmica.