People have the right to be involved in discussions and make informed decisions about their care, as described in your care.
Making decisions using NICE guidelines explains how we use words to show the strength (or certainty) of our recommendations, and has information about prescribing medicines (including off-label use), professional guidelines, standards and laws (including on consent and mental capacity), and safeguarding.
1.1.1 Patients (and their families and carers) should be informed that:
staying warm before surgery will lower the risk of postoperative complications
the hospital environment may be colder than their own home
they should bring additional clothing, such as a dressing gown, a vest, warm clothing and slippers, to help them keep comfortably warm
they should tell staff if they feel cold at any time during their hospital stay. 
1.1.3 When using any temperature recording or warming device, healthcare professionals should:
be trained in their use
maintain them in accordance with manufacturers' and suppliers' instructions
comply with local infection control policies. 
1.1.4 When using any device to measure patient temperature, healthcare professionals should:
1.1.5 Measure the patient's temperature using a site that produces either:
a direct measurement of core temperature, or
a direct estimate of core temperature that has been shown in research studies to be accurate to within 0.5ºC of direct measurement.
At the time of publication these sites are:
1.1.6 Do not use indirect estimates of core temperature in adults having surgery. [new 2016]
The preoperative phase is defined as the hour before induction of anaesthesia, during which the patient is prepared for surgery on the ward or in the emergency department, including possible use of premedication.
1.2.1 Each patient should be assessed for their risk of inadvertent perioperative hypothermia and potential adverse consequences before transfer to the theatre suite. Patients should be managed as higher risk (see recommendation 1.3.7) if any 2 of the following apply:
American Society of Anesthesiologists (ASA) grade II to V (the higher the grade, the greater the risk)
preoperative temperature below 36.0°C (and preoperative warming is not possible because of clinical urgency)
undergoing combined general and regional anaesthesia
undergoing major or intermediate surgery
at risk of cardiovascular complications. 
1.2.2 The patient's temperature should be measured and documented in the hour before they leave the ward or emergency department. 
1.2.3 If the patient's temperature is below 36.0°C, start active warming preoperatively on the ward or in the emergency department (unless there is a need to expedite surgery because of clinical urgency, for example bleeding or critical limb ischaemia). [2008, amended 2016]
1.2.4 If the patient's temperature is 36.0°C or above, start active warming at least 30 minutes before induction of anaesthesia, unless this will delay emergency surgery. [new 2016]
1.2.5 Maintain active warming throughout the intraoperative phase. [2008, amended 2016]
1.2.6 The patient's temperature should be 36.0°C or above before they are transferred from the ward or emergency department (unless there is a need to expedite surgery because of clinical urgency, for example bleeding or critical limb ischaemia). 
1.2.7 On transfer to the theatre suite:
active warming should be continued (or re-started as soon as possible)
the patient should be encouraged to walk to theatre where appropriate. [2008, amended 2016]
The intraoperative phase is defined as total anaesthesia time, from the first anaesthetic intervention through to patient transfer to the recovery area of the theatre suite.
1.3.1 The patient's temperature should be measured and documented before induction of anaesthesia and then every 30 minutes until the end of surgery. 
1.3.2 Standard critical incident reporting should be considered for any patient arriving at the theatre suite with a temperature below 36.0°C. 
1.3.3 Induction of anaesthesia should not begin unless the patient's temperature is 36.0°C or above (unless there is a need to expedite surgery because of clinical urgency, for example bleeding or critical limb ischaemia). 
1.3.4 In the theatre suite:
the ambient temperature should be at least 21°C while the patient is exposed
once active warming is established, the ambient temperature may be reduced to allow better working conditions
using equipment to cool the surgical team should also be considered. [2008, amended 2016]
1.3.5 The patient should be adequately covered throughout the intraoperative phase to conserve heat, and exposed only during surgical preparation. 
1.3.6 Intravenous fluids (500 ml or more) and blood products should be warmed to 37°C using a fluid warming device. 
1.3.7 Warm patients intraoperatively from induction of anaesthesia, using a forced-air warming device, if they are:
having anaesthesia for more than 30 minutes or
having anaesthesia for less than 30 minutes and are at higher risk of inadvertent perioperative hypothermia (see recommendation 1.2.1).
Consider a resistive heating mattress or resistive heating blanket if a forced-air warming device is unsuitable. [new 2016]
1.3.8 The temperature setting on forced-air warming devices should be set at maximum and then adjusted to maintain a patient temperature of at least 36.5°C. 
1.3.9 All irrigation fluids used intraoperatively should be warmed in a thermostatically controlled cabinet to a temperature of 38°C to 40°C. 
The postoperative phase is defined as the 24 hours after the patient has entered the recovery area of the theatre suite.
1.4.1 The patient's temperature should be measured and documented on admission to the recovery room and then every 15 minutes.
Ward transfer should not be arranged unless the patient's temperature is 36.0°C or above.
If the patient's temperature is below 36.0°C, they should be actively warmed using forced-air warming until they are discharged from the recovery room or until they are comfortably warm. 
1.4.2 Patients should be kept comfortably warm when back on the ward.
Their temperature should be measured and documented on arrival at the ward.
Their temperature should then be measured and documented as part of routine 4-hourly observations.
They should be provided with at least 1 cotton sheet plus 2 blankets, or a duvet. 
1.4.3 If the patient's temperature falls below 36.0°C while on the ward:
they should be warmed using forced-air warming until they are comfortably warm
their temperature should be measured and documented at least every 30 minutes during warming. 
The expected normal temperature range of adult patients (between 36.5°C and 37.5°C).
 Core temperature is the temperature of the blood and internal organs.
 A direct estimate of core temperature is the reading produced by a thermometer with no correction factors applied.
 Be aware of possible inaccuracies in core temperature estimation when using peripheral sites, such as sublingual or axilla, in patients whose core temperature is outside the normothermic range (36.5°C to 37.5°C).
 An indirect estimate of core temperature is the reading produced by a thermometer after a correction factor has been applied. Examples include infrared tympanic, infrared temporal, infrared forehead and forehead strips.