The effect of prewarming on hypothermia during orthopaedic surgery and related postoperative complications.

Perioperative hypothermia, defined as a core body temperature below 36°C is a
common problem in patients undergoing surgery. It is estimated that 50 to 90%
of surgical patients experience hypothermia during surgery. Hypothermia results
in higher morbidity and mortality, in longer hospital stay and in decreased
patient satisfaction. It has been indicated that 80% of the observed reduction
in core body temperature during the first hour of general anesthesia is caused
by blood redistribution; mixing the *low temperature* peripheral blood with the
*high temperature* core blood. The impact of this *redistribution hypothermia*
may be attenuated by *pre-warming* of the low temperature peripheral blood,
thereby decreasing the temperature gradient between core and periphery.
A promising and non invasive tool to monitor core body temperature during
surgery is a portable telemetric system using a temperature pill swallowed by
the patient. This advanced technologically to measure body temperature
continuously and the use of a novel pre-warming clinical intervention in
surgical patients will enable us to provide essential physiological and
clinical information in the prevention of perioperative hypothermia.

In this present study we will assess the effect of a pre-warming intervention
before surgery, in order to decrease the temperature gradient from core to
periphery and thereby minimize redistribution hypothermia under anesthesia, on
(I) the occurrence of perioperative hypothermia (II) the incidence of
postoperative complications and the length of stay in the hospital after
surgery.

This study is a randomized intervention study in which the subjects will be
randomly assigned to one of the 2 groups, i.e. a standard care + pre-warming
intervention or standard care alone.
All participants will ingest the temperature pill at least 12 hours before
surgery (4 hours to ensure passage through the stomach and 8 hours to measure
temperature before surgery) which records the temperature for up to 48 hours.
Skin temperature will be measured for a total of 24 hours, starting 8 hours
before surgery at distinct locations (calf, upper leg, upper arm, lower arm,
chest, fore head). 2 hours prior to the start of the surgery, the pre-warming
intervention will be applied with the Bair Paws® system, allowing patients to
adjust the temperature of the air flowing through the gown to a level that
feels right for them

2 hours prior to start of the surgery, a novel pre warming intervention will be
applied using the Bair Paws® system, which offers active, adjustable warming
capabilities in a patient gown allowing participants to adjust the temperature
of the air flowing through the gown to a level that feels right for them.

The intake of the telemetry pill is non-invasive and not dangerous as it can be
swallowed similarly as any medication pill. An ingestion of this pill will
also cause no harm to the body and its function due to the sophisticated
elaboration of protection to its surrounding. The pill has been proved to be
reliable and valid for measuring core body temperature at rest and during
exercise and is now being used and registered at the *Food and Drug
Administration (FDA)* for 19 years. Important advantages of this system are its
non-invasive character, validity, ability to monitor temperature continuously
and it can be used without noticing by the subject. From the >35,000 pills that
have been distributed, no negative incidents have been reported.
The other techniques and measurements used in this study (skin temperature
measurement and registration of amount of blood loss, wound infections, thermal
comfort, use of interventions related to shivering, length of hospital stay)
are completely non- invasive, painless and not dangerous and as such no
additional burden for the patient.
Before and after surgery, a blood sample will be collected for the assessment
of hemoglobin (Hb) and hematocrit (Ht), providing information about blood loss.
In case of wound infections, blood values such as CRP will be measured every 24
hours. These are minimally invasive techniques with a small risk for
complications. The only possible complication is a haematoma, which is induced
in ~5% of all cases. To prevent complications, the blood withdrawal will be
performed by an experienced professional and sufficient pressure will be
provided after withdrawal of the needle.
The 2 hour pre-warming intervention allows the patients to adjust the
temperature of the air flowing through the gown to a level that feels right for
them. This warming system has been proven safe and effective and is approved by
the FDA.
Research-based evidence identifies that the normalization of body temperature
during the perioperative period significantly improves patient outcomes and
patient satisfaction, and dramatically reduces the cost of complications
related to perioperative hypothermia. Findings from the present study will
enable us to provide essential physiological and clinical information for
future advices to medical specialists in the prevention of perioperative
hypothermia and its related clinical problems.