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South Afr J Anaesth Analg 2021; 27(6) http://www.sajaa.co.za
Southern African Journal of Anaesthesia and Analgesia. 2021;27(6):292-298
https://doi.org/10.36303/SAJAA.2021.27.6.2600
Open Access article distributed under the terms of the
Creative Commons License [CC BY-NC 3.0]
http://creativecommons.org/licenses/by-nc/3.0
South Afr J Anaesth Analg
ISSN 2220-1181 EISSN 2220 -1173
© 2021 The Author(s)
ORIGINAL RESEARCH
Introduction
Inadvertent perioperative hypothermia is dened as an
unplanned core temperature of less than 36 °C occurring dur-
ing the perioperative period.1,2 It is associated with numerous
adverse patient outcomes3-5 including increased surgical site
infection rates,4-6 blood loss,5,7 length of hospital stay6 and
cost of care.1,8-10 Despite the ubiquity of guidelines to prevent
perioperative hypothermia, the reported incidence ranges
between 20% and 90%.3,11
In the non-anaesthetised person, peripheral thermoregulatory
vasoconstriction maintains the core temperature by limiting
blood ow to the skin which interfaces with the cold environ-
ment. This creates a heat exchange system with a core-to-
peripheral temperature gradient, allowing the core temperature
to be maintained despite mean body temperature changes.12,13
Mean body temperature is the average temperature of the
body. Under normal thermoregulation, peripheral temperature
changes to allow either heat conservation or heat loss for the
purpose of maintaining a constant core temperature. With
heat conservation, the gradient between the core and the skin
is high and the mean body temperature is lower compared
to a heat loss state, where the gradient between the core
and the skin is low and the mean body temperature is higher.
Anaesthesia obliterates this mechanism by causing peripheral
vasodilatation and lowering the hypothalamic thresholds
at which thermoregulatory vasoconstriction and shivering
responses are initiated.14 Redistribution hypothermia will occur
even in the presence of intraoperative warming.15 The heat
gain from intraoperative warming is not enough to prevent
the core temperature from decreasing to hypothermic levels
due to the pre-existing temperature gradient between the core
and the peripheries.16 During the rst thirty minutes of general
anaesthesia, close to 90% of the decrease in core temperature
is due to redistribution of heat from the core to the periphery.
From thirty to sixty minutes, 66% of the ongoing decrease in
core temperature is attributable to heat redistribution.17 In the
absence of prewarming, re-establishing normothermia after
redistribution can take longer than an hour.18 Prewarming sup-
plies heat to the peripheries, reducing the core-to-peripheral
gradient prior to anaesthesia-induced heat redistribution.17
Background: Despite numerous guidelines on perioperative temperature management, perioperative hypothermia remains
common. Prewarming to prevent redistribution hypothermia is supported by evidence, but not widely practised. We investigate
the measurement of preoperative mean body temperature as a potential tool for individualising the practice of prewarming.
Methods: We hypothesised that patients who experience intraoperative hypothermia have a lower preoperative mean body
temperature. A longitudinal study was conducted in adult patients presenting for ophthalmological surgery under general
anaesthesia, to describe the relationship between the incidence of hypothermia within the rst hour of anaesthesia and
preoperative mean body temperature.
Results: Sixty-ve patients were enrolled. Twelve participants (18%) presented to the operating theatre hypothermic (core
temperature < 36.0 °C). A further 28 (43%) became hypothermic during the procedure. All hypothermia events occurred
within 60 minutes after induction of anaesthesia, and half of the events occurred within 19 minutes. The dierence in
preoperative mean body temperature between those with and without intraoperative hypothermia was only -0.2 °C (95%
CI -0.4, 0.1). This is neither clinically relevant nor statistically noteworthy. In Cox proportional hazards analysis, BMI and ASA status
compounded the observed association between preoperative mean body temperature and the incidence of intraoperative
hypothermia. A higher BMI and ASA are associated with a lower incidence of hypothermia.
Conclusion: We conclude that intraoperative hypothermia is common and occurs early after induction of anaesthesia. We
observed no useful dierence in preoperative mean body temperature to help distinguish between patients who become
hypothermic and those who do not. Without a useful risk prediction tool, a generic approach to prewarming remains appropriate.
Preoperative screening for pre-existing hypothermia should be practised, even in cases considered as low risk.
Keywords: inadvertent perioperative hypothermia, redistribution hypothermia, mean body temperature, mean skin temperature
A descriptive study of the relationship between preoperative body temperature
and intraoperative core temperature change in adults under general
anaesthesia
F Steyn, L du Toit, T Naidoo, R Hofmeyr
1 Department of Anaesthesia and Perioperative Medicine, Faculty of Health Sciences, University of Cape Town, and Groote Schuur Hospital,
Cape Town, South Africa
2 Statistical Consulting Services, University of Cape Town, South Africa
Corresponding author, email: fcoissteyn@gmail.com
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A descriptive study of the relationship between preoperative body temperature and intraoperative core temperature change
Mechanistically, adverse outcomes are not only related to a
single temperature measurement at the end of surgery or on
arrival in the postoperative recovery area, but to the duration
of hypothermia exposure.18 Inadvertent hypothermia should
be prevented at all times, making prewarming the logical gold
standard.
Numerous guidelines are available on perioperative temperature
management.1,2,19,20 Prewarming is commonly recommended.
Despite evidence supporting the ecacy of prewarming
periods as short as 10 minutes,21 the practice has not been
widely adopted. Poor adoption has been attributed to a lack
of buy-in from practitioners,11 increase in expenses, and lack
of knowledge.11 Some day-case surgery centres claim a low
incidence of hypothermia with short procedures and do not
want to accrue the extra expense of an active warming device.22
In an age of precision medicine, guidelines should strive to be
patient specic. Although some guidelines include preopera-
tive hypothermia risk assessment, this does not translate to any
specic prewarming recommendations,1 with the exception
that those found to be hypothermic preoperatively be warmed
prior to induction of anaesthesia. We seek a more individualised
approach to prewarming of surgical patients.
The primary objective of this study was to describe the dierence
in preoperative mean body temperature between patients
who develop intraoperative hypothermia, and those who do
not. Secondary aims included testing the eect of measured
confounders on the association between preoperative body
temperature and intraoperative hypothermia. Risk factors as-
sociated with inadvertent hypothermia include low ambient
temperature, large surface area exposure, open body cavities,
cold intravenous uids, extremes of age, and low body mass
index (BMI).1 We hypothesised that estimated preoperative mean
body temperature predicts the extent of initial core temperature
decrease post induction of general anaesthesia, with patients
who develop intraoperative hypothermia before sixty minutes
having a lower preoperative mean body temperature than those
who do not develop intraoperative hypothermia.
Methods
Study design, setting and participants
With approval of the Human Research Ethics Committee of
the University of Cape Town (HREC772/2018) and the written
informed consent of participants, this study was conducted at a
tertiary level hospital in Cape Town, South Africa. We employed
a longitudinal study design with repeated measurement of
temperature over time. We used consecutive sampling of adult
patients presenting for elective ophthalmic surgery requiring
general anaesthesia, where the surgery had an expected
duration of at least an hour. Ophthalmic surgery was selected
due to minimal environmental exposure of the patients, and the
lack of blood loss and uid shifts. This was done as a method of
restricting these known confounding factors from biasing the
observed eect of heat redistribution after induction of general
anaesthesia.
Patients were deemed eligible if they were 18 years or older.
Patients with a recent fever or known sepsis were excluded.
Recruitment and informed consent took place in the ward,
typically on the day prior to surgery.
Variables and methods of measurement
The primary outcome was preoperative mean body tempera-
ture. Secondary outcomes were preoperative mean skin
temperature and zero heat ux (ZHF) temperature. Mean skin
temperature is the average temperature of the skin. Dierent
skin regions have dierent temperatures which are related to
blood ow and adipose distribution. In this study the mean
skin temperature was calculated using the Ramanathan
method.23 ZHF temperature is a non-invasive core temperature
measurement. It consists of a sensor placed on the forehead
Figure 1: Measured variables. Zero heat flux (ZHF), intravenous (IV)
Theatre temperature
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A descriptive study of the relationship between preoperative body temperature and intraoperative core temperature change
which creates a zone of insulation that eliminates heat loss to
the environment. An isothermic pathway is formed which allows
core temperature to be measured at the skin surface.24
Baseline variables were collected in the ward during the
recruitment visit, and in the induction room of the operating
theatre prior to anaesthesia. Skin temperature was measured
in the induction room, using a handheld thermocouple
thermometer with a surface probe (ThermapenTM, Electronic
Temperature Instruments Ltd., West Sussex, United Kingdom).
Operating room temperature and core temperature according
to a ZHF monitor (3MTM SpotOnTM, St. Paul, Minnesota, USA)
were recorded immediately prior to induction. Thereafter, from
the time the participant was connected to monitoring in the
operating theatre until the time of tracheal extubation, body
core temperature was measured continuously using both the
ZHF monitor and a thermistor placed in the mid-oesophagus
or nasopharynx. After induction of general anaesthesia, the
patient’s core temperature was documented every 15 minutes.
The time-to-hypothermia interval was recorded in one-minute
increments. Data collection procedures during the study as well
as the body sites and calculation used are described in Figure 1.
Other recorded baseline variables were patient demographics:
ASA status, Edmonton frailty scale,25 sex, age, BMI, and case-
related variables: airway management (endotracheal tube or
supraglottic airway), volume of intravenous uid administered
during the procedure, and duration of the procedure from
induction of anaesthesia to emergence. All uids were warmed
preoperatively in a uid warmer set at 40 °C.
Four pre-identied body sites based on the Ramanathan
method,23 were used to calculate mean skin temperature.26
Mean body temperature was calculated using a weighted
formula involving both the mean skin temperature and the
core temperature (Figure 1).23 The thermometer used for
skin temperature measurements has an accuracy of 0.4 °C,
within the range of -49.9 °C to 299.9 °C. During and after these
measurements, the patient was covered as much as possible with
a cotton blanket to prevent heat loss. The temperature sensor
was applied to the skin for two minutes to allow equilibration
of each reading. The ZHF sensor was attached to the forehead
above the non-operative eye. The ZHF sensor has an accuracy
of 0.23 °C.
The choice of anaesthetic technique and agents was left to
the discretion of the attending anaesthesiologist. After endo-
tracheal intubation, an oesophageal thermistor was placed
orally at 20 cm from the teeth. The thermistor has a range of
25–45 °C and an accuracy of 0.1 °C. In cases where a supraglottic
airway was used, the thermistor was placed in the nasopharynx.
Intravenous uids were limited to as little as necessary, and the
volumes were recorded at the end of the case.
A forced-air warming blanket was placed over each patient but
not switched on. Active warming of the patient was initiated
if the core temperature dropped below 36 °C. At this point,
the time to hypothermia was documented, and temperatures
recorded subsequently were excluded from analysis.
Classication of hypothermia was based on oesophageal tem-
perature, except when a supraglottic airway was used, in which
case the ZHF temperature was considered a more accurate
method of determination. During pilot data collection it was
observed that the thermistor placed in the nasopharyngeal
position in the presence of a supraglottic airway device
frequently produced spurious readings. Oesophageal readings
were favoured over the ZHF readings as it is a more widely used
modality and its accuracy is well established. When oesopha-
geal temperature readings were recorded below 36.0 degrees
from the start of the case (baseline), the case was classied as
preoperative hypothermia (left censored) and excluded from
the primary analysis.
Study size
The incidence of hypothermia was unknown in this population,
and no previous studies pertaining to the correlation between
preoperative mean body temperature and perioperative
hypothermia could be found. Therefore, a pilot study was
conducted to inform our sample size calculation. The pilot study
was conducted over 10 consecutive theatre days (11 February to
2 March 2019). Seventeen patients were investigated, of whom
eight (57%) became hypothermic.
We used the pilot study data to estimate the required sample size
for a two-sample t-test. Given an eect size of 0.3 °C dierence
in mean body temperature between groups (SD 0.37), to obtain
power of 0.8 at a two-sided level of signicance of 0.05, required
a sample size of 50 patients with a ratio of 1:1. Based on this
estimate it was determined a priori that recruitment would be
continued until the smallest comparison group (with or without
an incident of hypothermia) included 25 participants.
Statistical method
Baseline and outcome variables were described using
summary statistics; mean (SD) for continuous variables, median
(interquartile range) for ordinal variables and count (percentage)
for categorical variables.
The primary objective (dierence in preoperative mean body
temperature between those who develop hypothermia in the
rst 60 minutes of anaesthesia compared to those who do not)
and secondary objectives (dierence in preoperative mean skin
temperature and ZHF temperature between those who develop
hypothermia in the rst 60 minutes of anaesthesia compared to
those who do not) were assessed using a two sample t-test.
A survival analysis using Kaplan-Meier estimation and Cox
proportional hazards analysis was conducted to explore eects
of all measured variables on the experience of hypothermia and
the association between preoperative mean body temperature
and hypothermia. Model building used the likelihood ratio test
and Bayesian information criterion (BIC) in sequential models
with increasing number of variables and rst order interactions
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A descriptive study of the relationship between preoperative body temperature and intraoperative core temperature change
to identify the model that best ts the data. Proportional hazards,
overall t, outliers, inuential observations and functional form
of variables were assessed in model diagnostics.
Statistical analysis was conducted with R (R Core Team, 2020.
R Foundation for Statistical Computing, Vienna, Austria). The
survival analysis made use of the ‘survival’27 and ‘survminer’28
packages. This manuscript was prepared in accordance with the
STROBE statement.29
Results
Participants
Of the patients approached during recruitment, three did not
consent and were not enrolled. A total of 65 participants were
enrolled in the study during the period from 24 June until
1 August 2019.
Mean participant age and BMI were 49 years and 26.1 kg.m-2
respectively. Fifty-four per cent (35/65) of the participants were
female. Median ASA grade was 2. Table I reports additional
details of participant and case characteristics.
Missing data: One participant’s oesophageal temperature sen-
sor produced (“non-physiological”) readings; for this case data
from the ZHF sensor was substituted for analysis. Data for
calculating BMI was not recorded in four participants, IV uid
administered was not recorded for eight participants and the
room temperature was not recorded for four participants.
Outcome data
Of the 65 enrolled participants, 12 (18.5%) were hypothermic
at baseline, 28 (43%) became hypothermic after induction
of anaesthesia, and only 25 (38.5%) did not experience
hypothermia. (Table II). The dierence (95% condence interval)
in preoperative mean body temperature between those who
developed hypothermia after induction of anaesthesia and those
who did not was -0.2 °C (-0.4, 0.1) (Figure 2). The dierences in
ZHF temperature and mean skin temperature were -0.1 °C (-0.4,
0.1) and -0.2 (-0.7, 0.3).
Further analysis of the change in core temperature over time
using a Kaplan-Meier estimate demonstrated median time (95%
CI) to hypothermia as 19 (13, 23) minutes after induction of
anaesthesia (Figure 3). Hypothermia events occurred early after
induction of anaesthesia: 86% (24 of 28 events) occurred within
30 minutes and no events occurred after the rst hour.
Table I: Participant and case characteristics reported as mean (SD) for continuous variable, median (IQR) for ordinal variables, and frequency
(proportion) for dichotomous variables
Hypothermia at baseline
(n = 12)
Hypothermia during anaesthesia
(n = 28)
No hypothermia observed
(n = 25)
Age (years) 49.8 (14.8) 46.0 (17.1) 52.5 (15.9)
Body mass index (BMI)θ26.0 (3.6) 24.0 (4.2) 28.4 (4.7)
Sex: Female 6/12 (0.50) 15/28 (0.54) 14/25 (0.56)
ASA status* 2 (2.3) 2 (1.2) 3 (2.3)
Edmonton frailty score‡ 2 (1.4) 3 (2.5) 3 (2.4)
Duration of anaesthesia (min) 97 (24) 110 (45) 107 (38)
IV fluid volume (l)Δ0.883 (0.252) 0.743 (0.306) 0.684 (0.279)
Room temperature (°C)φ21.2 (1.1) 20.5 (1.1) 20.8 (1.3)
SGA (cp. Endotracheal tube) 1/12 (0.08) 4/28 (0.14) 2/25 (0.08)
* Maximum observed ASA status = 3. ‡ Maximum observed frailty score = 8. ASA – American Society of Anesthesiologists Physical Status Classification, IV – intravenous, SGA – supraglotic
airway device. θ BMI data was missing for 1 and 3 participants in the ‘hypothermic before anaesthesia’ and ‘hypothermia during anaesthesia’ groups. Δ IV fluid volume was not recorded for 1, 4
and 3 participants in the groups ‘hypothermic before anaesthesia’, ‘hypothermia during anaesthesia’ and ‘no hypothermia’. φ Room temperature was not recorded for 3 and 1 participants in the
‘hypothermia during anaesthesia’ and ‘no hypothermia’ groups.
Table II: Preoperative body thermometry, mean (SD), grouped by participant experience of hypothermia during the first 60 minutes of anaesthesia
Hypothermia at baseline
(n = 12)
Hypothermia during anaesthesia
(n = 28)
No hypothermia observed
(n = 25)
Preoperative ZHF temperature (°C) 36.2 (0.8) 36.8 (0.5) 36.9 (0.4)
Preoperative mean skin temperature (°C) 32.8 (0.8) 32.6 (0.9) 32.8 (0.9)
Preoperative mean body temperature (°C) 34.7 (0.6) 35.3 (0.5) 35.4 (0.4)
ZHF – zero heat flux forehead reading
Preop mean body temperature
36.0
35.5
35.0
34.5
34.0
Hypothermic Normothermic Left censored
Figure 2: Box and dot plot of preoperative mean body temperature
distribution by core temperature outcome during the first 60 minutes
of anaesthesia. Left censored data are those participants who were
hypothermic at baseline and therefore excluded from the primary
outcome
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A descriptive study of the relationship between preoperative body temperature and intraoperative core temperature change
The results of the Cox proportional hazards analysis are sum-
marised in Table III. Of the variables considered for inclusion in
the model – preoperative mean body temperature, age, ASA,
BMI, Edmonton frailty score, room temperature and volume of
IV uid infused – only preoperative mean body temperature, BMI
and ASA were included in the nal model as the other variables
were not independently associated with the development of
hypothermia or did not improve the model when comparing
sequential models. Inclusion of rst-order interactions did not
improve the model and were not included in the nal model
reported here.
Table III: Final multivariable Cox proportional hazard model
HR 95% CI p-value
Preoperative mean body
temperature (°C)
0.23 0.07–0.77 0.017
Body mass index (BMI) 0.83 0.74–0.94 0.002
ASA (reference: 1)
ASA: 2 0.71 0.29–1.77 0.467
ASA: 3 0.19 0.06–0.62 0.006
The relationship between BMI and hypothermia is demonstrated
in the Supplemental Figure – the hazard of hypothermia was
lower in those with a higher BMI and higher in those with a lower
BMI (p = 0.002; log-rank test).
Discussion
Key results
There was no statistically notable nor clinically relevant dif-
ference in the preoperative mean body temperature between
the group who became hypothermic and the group who
remained normothermic (mean [SD] 35.3 [0.5] °C and 35.4 [0.4]
°C respectively). The same held true for preoperative mean skin
temperature and preoperative core body temperature. Even in
our relatively healthy study population of patients with nearly no
body surface exposure, inadvertent perioperative hypothermia
was very common (a prevalence of 62%), with an incidence of
hypothermia after induction of anaesthesia of 43%.
Study limitations
The study was conducted at only one institution. By design,
the observed decrease in core temperature is believed to be
mainly representative of redistribution hypothermia. However,
the amount of heat loss to the environment was not measured.
Our outcome of primary interest was preoperative mean body
temperature, but there was no practical way to measure this
directly in our study. Our calculation of this variable, although
previously validated, could be a source of measurement error.
Our data cannot be used to estimate the drop in core tempera-
ture in other types of surgery, as the amount of heat loss will
be signicantly higher in surgeries with more surface exposure.
Although the number of enrolled participants was sucient
to address our primary objective, it remains too small to ade-
quately explore other predictors of redistribution hypothermia.
Our time-to-event analysis suggests the importance of BMI and
possibly ASA status as predictors, but other measured variables
cannot be excluded as determinants due to the limited sample
size and restricted observed ranges of participant characteristics.
Interpretation
The high incidence of inadvertent perioperative hypothermia
in our study is in keeping with ndings of other researchers,
such as Moola and Lockwood, Inal et al. and Sun et al.3,11,18 We
demonstrate this to be true even in surgery that is considered low
risk, where exposure is limited, and there is minimal blood loss.
The importance of preoperative screening for hypothermia has
been highlighted in this study, with 19% of patients arriving at
theatre hypothermic. This supports the guidance of the National
Institute of Health and Care (NICE) in the UK, which states that
patients should be screened preoperatively in the ward and
should not be allowed to go to the operating theatre if they are
hypothermic, but should instead be actively warmed until they
are normothermic (except in the case of an emergency).1
Our study demonstrates a limitation in the understanding of
redistribution hypothermia. Prewarming increases peripheral
heat content and therefore decreases the core to peripheral
gradient. This mechanism has repeatedly been shown to prevent
redistribution hypothermia.3,4,9,11,16,20 Our failure to demonstrate a
relationship between the mean preoperative body temperature,
the mean skin temperature and the core temperature to the
incidence of redistribution hypothermia suggests that other
important determinants exist and are commonly at play, or that
these measures are not a true reection of the core to peripheral
gradient
Survival probability
Minutes
1.00
0.75
0.05
0.25
0.00
0 30 60 90 120 150 180 210 240
Figure 3: Kaplan-Meier plot of time to hypothermia in patients
with starting core temperature greater than 36.0 °C. Median time to
hypothermia is 19 minutes. Number at risk indicated at bottom of
plot area along with corresponding time in minutes. Censoring events
indicated with a ‘x’. Survival probability on the y-axis is the cumulative
probability of NOT developing intraoperative hypothermia
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A descriptive study of the relationship between preoperative body temperature and intraoperative core temperature change
The observed short time to development of hypothermia is
noteworthy. Redistribution of heat occurs rapidly, with most of
the observed events in our study occurring within 30 minutes
following induction of anaesthesia. Literature typically report
the incidence of hypothermia in the rst hour of anaesthesia18,30
or the absolute core temperature decrease in the rst hour,13,31
rather than time to hypothermia.
Short procedures should not be seen as low-risk for hypo-
thermia. No hypothermic events occurred after an hour of
anaesthesia, which suggests that redistribution takes less
than an hour. It also suggests that the study was successful in
observing only redistribution as a reason for decrease in core
temperature. Other literature reports hypothermic events after
an hour.13,18,30 These studies, however, include surgeries where
ongoing heat losses played a role. In these studies, the rate of
temperature decrease changes at about one hour, which is
further evidence that redistribution is complete at this time and
that continued decrease in temperature is due to ongoing heat
loss to the environment.13,18
Further exploration of our data using time-to-event analysis
generated hypotheses about other determinants of
redistribution hypothermia. Although preoperative mean body
temperature was not predictive of hypothermia when assessed
across the whole study sample, a lower BMI was a notable risk
factor for development of hypothermia, while a higher BMI
appears to have been protective. The observed data ts the
hypothesis that preoperative mean body temperature becomes
an important determinant of the intraoperative development
of hypothermia in those with a lower BMI. This observation is in
keeping with the research of Ozer et al. and Fernandes et al.32,33
An association with unexpected direction was observed
between ASA status and the development of hypothermia,
whereby those with an ASA status of 3 experienced a lower
hazard of hypothermia compared to those with an ASA status
of either 1 or 2. This unexpected association may be spurious,
due to the relatively small dataset and restricted spectrum
of participants, and interrater variability in ASA classication.
The association did not appear to be solely explained by any
association between BMI and ASA status. Numerous studies
have looked at the relationship between ASA status and the
development of perioperative hypothermia. The results are
incongruent, with some studies demonstrating that ASA has
an impact on the development of hypothermia,34-36 while other
studies found no such correlation.37,38 We are not aware of any
studies that show a protective element with higher ASA scores.
One reason for a true discrepancy may be that our design
eectively studied heat redistribution, while in other studies,
heat loss to the environment is the dominant determinant of
body temperature.
Conclusion
Inadvertent perioperative hypothermia is common, even in low-
risk patients and low-risk procedures. Our ndings underpin
the importance of screening for preoperative hypothermia
as described in the current NICE guidelines.1 Hypothermia
resulting from heat redistribution occurs early after induction
of anaesthesia (within the rst hour), so that prewarming (even
for short procedures) should strongly be considered. Future
work should explore BMI and ASA status along with other
determinants of hypothermia, striving towards a patient-specic
approach to perioperative warming that is informed by a better
understanding of perioperative thermal physiology.
Acknowledgements
Statistical analysis: Anneli Hardy for review of pilot data and
input into study design.
Data collection: Modjadji Maake, Tshepo Nokwane, Zenande
Sikhakhane and Chun Ting Li
3M contact: Gregg Nowell
Conflict of interest
The authors declare no conict of interest.
Funding source
The study was supported by departmental funding. The SpotOn
monitor and sensors were sponsored by 3M South Africa. 3M
South Africa had no inuence over the study design, conduct,
analysis or reporting.
Ethical approval
With approval of the Human Research Ethics Committee of
the University of Cape Town (HREC772/2018) and the written
informed consent of participants, this study was conducted at a
tertiary level hospital in Cape Town, South Africa.
ORCID
F Steyn https://orcid.org/0000-0002-8952-5254
L du Toit https://orcid.org/0000-0003-0146-4002
T Naidoo https://orcid.org/0000-0001-9970-2421
R Hofmeyr https://orcid.org/0000-0002-9990-7459
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Supplemental figure
Kaplan-Meier plot of the probability of not experiencing hypothermia stratified by tertiles of body mass index (BMI) with p-value for the log-rank test.
Upper yellow tertile (27; 39), middle teal tertile (23; 27), lower purple tertile (18; 23). Survival probability on the y-axis is the cumulative probability of
NOT developing intraoperative hypothermia.
Survival probability
Minutes
0 30 60 90 120 150 180 210 240
1.00
0.75
0.50
0.25
0.00
