37 °Celsius
Although just about every detail is taken into
account in operating rooms – from antiseptic materials
and tiled rooms to infusion bottles – heat is too
rarely considered. Efforts to restore patients’ health
and well-being should also include maintaining
the right BODY TEMPERATURE in the operating room.
A show of hands: Do the
patient's extremities have an adequate blood supply?
Thermograms deliver quick
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results – and
provide safety
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H y p ot hermi a H os pi tal
37°C
36°C
32°C
28°C
34°C
Photography: Get t y Images; Graphic: picture-alliance / Wissen Media Verlag
L
ife is dependent on warmth, and
too much cold can bring it to a
halt. Some animals, such as the
arctic painted turtle, turn into ice themselves in winter. And although emperor
penguins love the cold, they don’t want
their body parts to freeze. They are protected by a clever mixture of fat and feathers that largely prevents cold air from getting through. Thanks to this protection,
penguins even enjoy diving into frigid
water. The birds’ behavior also helps to
keep them warm, since they adhere to
the principle of “all for one and one for
all.” By huddling close together, moving
continuously, and rotating from inside
the group to the outside and back, penguins can survive even the coldest nights.
Cold conditions are a real challenge
for human beings, most of whom would
probably consider mass cuddles to be
pretty awful. As isothermal animals, people – like penguins – have to maintain an
optimal operating temperature. Our bodies do this with all the means at their disposal. If the inside of the body gets too
warm (i.e. if the temperature rises above
37 °C), human beings begin to sweat.
The resulting moisture evaporates, causing the body to cool off. If the temperature drops below a certain level, the body
initiates heat-inducing processes that
cause the person to shiver.
For human beings, the difference between freezing and overheating is just 15
degrees Celsius. A healthy human being’s
body temperature varies between 36 and
37.8 °C (the normothermic range). If it
rises above 42 °C, the person’s circulation
is in danger of collapsing and the body’s
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31°C
In a warm environment
In a cold environment
Human beings’ highly sophisticated
heat regulation system is a result of evolution. Its main goal is to keep the brain at operating temperature
proteins may undergo denaturation. By
contrast, if it drops below 27 °C, the person begins to freeze to death. When naked, people have no problems keeping
their body temperature stable if the external temperatures are between 26 and
28 °C. The colder it is outside, the more
protection is needed. However, in human
beings, feathers and fat are replaced by
warm clothing.
Even a mild chill has serious consequences
Human beings can move, shiver, and actively protect themselves as long as they remain conscious. If a person becomes unconscious, he or she will cool off without
being able to do anything to prevent it. The
system is then in danger, and catching a
cold – the threat parents use to get their
children to wear their hats – is the least
of the potential risks. In the early 1990s,
researchers discovered the first links between low body temperature (hypothermia) and complications during or after
surgery. They found out that if a patient’s
temperature remains stable during surgery and does not drop below the normothermic range, there is a much lower risk
of complications after the operation.
One of the pioneers in this area of medicine is Anselm Bräuer, a physician specializing in anesthesia. Bräuer works at the
Center for Anesthesiology, Emergency and
Intensive Care Medicine in Göttingen, Germany, where he heads the Hypothermia
working group. “Hypothermia has a variety of effects during surgery,” he explains.
He also points out that the basic problem
is that there is often no discernible link
between hypothermia and complications.
“Among the direct effects is that the wound
caused by the operation does not heal properly or may even get infected. However, this
generally occurs very late, and that makes
it very difficult to establish a connection.
All you can then say is that the patient
somehow became ill.” In these cases, the
wound doesn’t heal properly or becomes
infected due to hypothermia-induced peripheral vasoconstrictions, i.e. narrowing
of the blood vessels in a patient’s extremities. This reduction of the blood supply
means that less oxygen is supplied to the
extremities, even though oxygen is needed
for the wound to heal properly. Clotting disorders can also lead to increased fluid loss
and the need for blood transfusions.
Hypothermia can have particularly
dramatic consequences for patients suffering from cardiovascular diseases. “These
patients are more likely to suffer from irregular heartbeat or unstable angina pectoris, and there are even indications that
hypothermia increases the mortality rate
of at-risk patients,” says Bräuer. Despite
the insights that Bräuer, his team, and
other medical professionals have gained,
recent studies have shown that only 20
percent of the operating rooms in Eu- >
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Hospi tal H yp ot herm i a
28°C–32°C
32.2°C–35°C
Moderate hypothermia, impaired consciousness
27
28
27°C
Fatal below this limit
29
30
31
28°C
Light hypothermia (shivering)
32
33
34
33°C
Severe hypothermia,
unconsciousness
Hypothermia
The narrow range of life
> rope monitor patients’ body temperature.
“Although body temperature is one of the
basic vital signs, it is often neither monitored nor do staff members actively take
measures to warm the patient,” explains
Bräuer. “Even though scientists have been
investigating this crucial topic for the past
15 years, the insights haven’t been fully
taken into account yet, nor have all the
consequences been drawn.”
Hypothermia is also recognized as a
problem by Andrea Kurz, an Austrian anesthesiologist who now lives in Cleveland,
Ohio. For Kurz, paying close attention to
patients’ core body temperature is part of
her daily work. In the U.S., the medical
profession has recognized that body temperature is a key vital sign. “I would never
let anyone cool down below 36 °C because of post-surgery complications such
as wound infections, cardiac problems,
and the increased risk of bleeding,” she
explains. “The U.S. has very clear guidelines, according to which we have to demonstrate that patients were either actively
kept warm or that their body temperature
was above 36 °C right after surgery.”
Body temperature changes when
an anesthetic is administered
The body begins to cool off while the anesthetic is still being administered. “Prior to
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Photography: Caro / Oberhaeuser
Infrared images show the temperature of various body parts. This temperature normally ranges from 28 ° C
(extremities) to 37 ° C (core part of the body). Measurements are normally made of the core body temperature,
which ranges between 36.2 °C and 37.2 °C in a healthy individual. Unless specified otherwise, the numbers
next to the color scale above indicate the core body temperature. The temperatures are average values taken
from medical publications and are only approximations (which slightly vary in the literature).
“Sleeping Beauty” in the operating room: A blanket filled with warm air prevents
the patient from cooling off and reduces the risks accompanying surgery
surgery, the patient has a normal body temperature which is constantly kept within
a range of 0.2 to 0.3 °C, using sophisticated control mechanisms. However, this
changes as soon as an anesthetic is administered and varies according to the way it
is employed,” says Kurz. She adds that all
types of anesthetics and narcotics influence the body’s central thermoregulation
center, thus expanding the neutral zone
to as much as 5 °C. This expansion of the
neutral zone necessarily results in dose-de-
pendent hypothermia. This effect intensifies with age. In the early 1990s, Kurz conducted a study in which she found that all
of the patients being prepared for surgery
experienced vasoconstriction (narrowing
of the blood vessels) in their extremities
so they had cold hands and feet. However,
anesthetics are vasodilators, which means
that they widen the blood vessels. “Heat
therefore flows from the body’s core to
the periphery, leading to a relatively large
drop in body temperature as soon as an an-
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36.7°C
Normal human core body
temperature, sublingual
35
36
36.5°C
Normal human core body temperature, armpit
37°C
37
38
36.2°C–37.2°C
Normal temperature range during the course of a day
esthetic is administered,” she concluded.
The solution to hypothermia is actually
pretty simple. “It therefore makes sense
to warm the patient prior to surgery, especially the extremities,” says Kurz. According to the second law of thermodynamics, heat equalizes within a system over
time, meaning that it flows from hotter
to cooler areas until the temperatures are
the same. If peripheral areas are warmed
so that their temperatures are almost as
high as that of the body’s core, heat will no
longer be distributed. Prior to surgery, patients are primarily warmed with the help
of blankets through which warm air flows
or by lying on heatable mats.
Bräuer believes this is one of the
first challenges that must be met before
the procedure can become widespread.
“Sensible prophylactic care requires not
only purchasing the equipment, but also
changing organizational processes.” And
that’s where things begin to get difficult.
“Patients need to be with us at least 30 to
45 minutes prior to surgery, so more time
has to be planned in.”
This is an important step toward preventing patients from cooling off while an
anesthetic is administered. Heated blankets, mats, or infusions can keep body
temperature stable even during surgery.
That’s because “the larger the operating
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Circulatory
collapse
High fever
39
37.8°C–38.5°C
Mild fever
42°C
39°C
Normal human core body
temperature (rectal)
40
41
40°C–42°C
Very high (hyperpyretic) fever
39.1°C
Up to
Core body temperature following a fire drill
field is, the greater the risk the patient will
cool off,” says Kurz. If the body is not kept
warm during long operations with large
operating fields, patients’ body temperatures can drop down to as low as 33 °C,
which can lead to complications during
and after surgery. However, the body’s
core temperature can also undergo clinically relevant changes during operations
as short as a half an hour.
The body’s heat generation system is switched off
Body temperature drops when heat loss
is greater than heat gain, and due to anesthesia the body’s automatic protective
measures don’t become effective until
later. The body produces less heat during
anesthesia, and this output cannot be increased. At the same time, the room temperature is far below the level that is required to maintain thermal balance: 26
to 28 °C. Medical professionals can only
stand such a room temperature because
they move around – and that’s one of the
most important means of maintaining
body heat. Patients can’t do this until
much later – they generally begin to shiver
when they are in the recovery room.
The patient’s temperature therefore
has to be monitored at all times. Unfortunately, the best method for doing this is
42
43
41.4°C
“Almost never
exceeded”
42.6°C–42.8°C
Death resulting from the denaturation of proteins and enzymes
not always feasible. The bladder mainly
delivers reliable data, but many patients
do not have a catheter. Temperature can
also be measured in the esophagus or the
nasal area or by means of a catheter in a
vein. “Unsuitable methods include measuring the temperature inside the ear or
the rectum, as the data obtained in this
way is too imprecise,” says Bräuer. Choosing the right measuring method can be especially difficult after surgery, when high
body temperatures have to be detected
early on in order to prevent sepsis or infections of wounds.
Kurz is satisfied when her patients are
generally normothermic following an operation. “I can then clearly estimate how
long the medication will be working and
how soon the patient will wake up,” she
says. “This too depends on the body temperature. However, my plans fail if hypothermia accidentally sets in.”
An exception to this is surgery in
which the body temperature is deliberately reduced: some types of heart operation or neurosurgery involve deliberate
influencing of the patient’s metabolism.
The patient’s body then briefly goes into
hibernation, like that of the arctic painted
turtle – except that nobody will give the
turtle an electric blanket when it wakes
up in the spring.
Isabell Spilker
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