1. THERMOREGULATION Dr Mohua Jain Peri-operative Teaching June 2008
Specialist Anaesthetist

2. Definitions CORE TEMPERATURE PERIPHERAL TEMPERATURE NORMOTHERMIA
HYPOTHERMIA

3. CORE TEMPERATURE
Thermal compartment of body, highly perfused tissues, uniform and higher temperature.
Trunk, brain – 2/3 body heat
PERIPHERAL TEMPERATURE
Skin, subcutaneous – all body, inc limbs
Usually 2 to 3 °C below core but can be much more

4. Core and peripheral temperatures both influence comfort about equally.
Only core influences metabolic processes
As peripheral temp drops, heat flows from core to periphery (gradient)

5. NORMOTHERMIA
Core temp range of 36°C to 38°C
HYPOTHERMIA
Core temp less than 36°C
MILD HYPOTHERMIA
Core temp range 34°C to 36°C

7. Definitions (NICE) Preoperative - 1 hour before induction
Intraoperative - the total anaesthesia time
Postoperative - 24 hours after entry into the
recovery area in the theatre suite
Hypothermia - a patient core temperature of
below 36.0°C.
Comfortably warm - the expected normal
temperature range of adult patients
Temperature - used to denote core temperature
NOTES FOR PRESENTERS:
Key points to raise:
It is important that the audience understand the terms used in this presentation in order to obtain a good understanding of the intentions of this clinical guideline:
Hypothermia is when a patient has a core temperature of below 36.0°C
Comfortably warm - the expected normal temperature range of adult patients (between 36.5°C and 37.5°C) This term is used in the recommendations relating to both the preoperative and postoperative phases.
Temperature - used to denote core temperature.
The perioperative pathway is divided into three phases:
Preoperative - when the patient is prepared for surgery on the ward or in the emergency department.
Intraoperative – the total anaesthesia time
Postoperative – this includes the transfer to and time spent on the ward.

8. Maintenance of Heat Balance of heat production and loss Nervous system
Hormones
Vessels
Behaviour
Variations during day and month

9. Heat Production Metabolism Exercise Shivering
Non-shivering thermogenesis (fat and muscle)
Basal metabolic rate (BMR) is energy needed to maintain constant temperature

10. Heat Loss Radiation (40 to 60%) Convection (25 to 30%)
Evaporation (10 to 20%)
Respiration (10% by heating of air and evaporation)
Energy loss can be up to 15 x BMR
Sweating can be up to 1 litre per hour for short time, taking heat with it!

11. Don’t forget
Hypothermia can be present regardless of temperature if patient complains of feeling cold or has the obvious signs
Body needs to maintain set temperature as all processes involving enzymes are sensitive to temp and pH

12. Signs
Usually below 36.5°C
Peripheral vasoconstriction (esp stressed patients)
Hairs standing on end (pilo-erection)
Shivering
Cold peripheries
High diastolic blood pressure
Importance of ‘behavioural’ actions

13. Measurement of Core Temperature
accurate (patient, operator, instrument - variable readings)
consistent,
repeatable,
keeping up with rapid changes,
accessible,
safe

14. Core Temperature Measurement Sites
RELIABLE
ESTIMATE
Pulmonary artery
Tympanic membrane (direct and indirect)
Nasopharynx
Distal oesophagus
Rectal
Bladder
Oral
Skin
Axillary

15. Adverse Effects of Hypothermia
CNS (Nervous system)
RS (Respiratory system)
CVS (Cardiovascular system)
Renal and electrolytes
Immune
Blood
Drug effects
Others

16. CNS Reduced neuronal function Confusion Disorientation Stupor
Raised intracranial pressure from shivering
Seizures
Coma

17. RS Hyperventilation then hypoventilation Lower respiratory rate
Lower volumes (effect on CNS)
Increased oxygen consumption from shivering
Organ ischaemia

18. CVS More adrenaline (and other catecholamines) Vasoconstriction
Raised blood pressure
Bradycardia
Myocardial ischaemia and infarction
ECG changes
Arrhythmias

19. Renal & Electrolytes ‘Cold diuresis’ Renal tubule damage
Constriction of skin and gut vessels
Potassium, Magnesium, Calcium and Phosphate all decrease

20. Immune Infections Wound breakdown and infections
Collagen linking less as oxygen drops
Less subcutaneous oxygen
White blood cells function less

21. Blood Less coagulation Less platelet function More viscosity
More blood loss
More blood transfusions

22. Drug effects
Usually prolongs actions of all drugs, (esp those needing enzymes for their metabolism)
Muscle relaxants and opiates last longer
Less IV and volatile agents needed for same degree of unconsciousness

23. Other More patient discomfort with shivering
More time in PACU / Recovery
Thresholds for pain and nausea
Difficulty with cannulation
More time in hospital
More time to establish diet
More costs from all above

24. Shivering
Usually temperature related – uncomfortable involuntary rhythmic muscle contractions to maintain core temperature
Complex , patterns of tremors
Can occur post GA or during labour even with normal temperature. Mechanism unknown ?pain and stress
Post-op 20 to 40%?
Problem for monitoring
Elderly rarely shiver

25. Drugs to treat Post-op Shivering (clinical and experimental)
Tramadol
Pethidine
Alfentanil
MgSo4
Clonidine
Ketamine
Propofol
Ondansetron
Doxapram
Nefopam
Meperidine
Ketanserin
Physostigmine

26. Effects of General and Regional Anaesthesia
Impaired thresholds for responses so they happen later
3 stage drop in temperature 1 to 3°C
Rapid in 1st hour (Redistribution of heat from core to periphery - vasodilation)
Gradual (Heat loss causes then exceed heat production causes)
Plateau (Production catches up)

27. So far... Definitions Heat balance – how and why needed
Measurement of core temperature
Bad effects of Hypothermia
Shivering (normally and post-op)
Anaesthesia
So, how can we prevent hypothermia?

28. Evidence - Research and Clinical
Recommendations and guidelines (esp 2000 onwards)
WHO - ambient temperature
American Society of Anesthesiologists (ASA)
American Society of PeriAnesthesia Nurses (ASPAN)
National Institute of Clinical Excellence (NICE)

29. Common Sense Guidelines
Minimising heat loss from the body
Giving heat to the body

30. Common Sense Guidelines
Pre-operative
Intra-operative
Post-operative
ASSESSMENT (identify, measure, observe & ask)
INTERVENTION (preventative, passive and active)

31. Identification of Risks
Very young
Very old
Female
GA / RA
Large surface area / gut exposed
Ambient temp (circulating air)
Poor nutritional status
Length of surgery
Fluid shifts
Irrigation fluids
Trauma/burns
Cold transfers

32. Patients at higher risk of perioperative hypothermia (NICE)
Some patients are at higher risk of inadvertent perioperative hypothermia; they should be managed accordingly if any two of the following apply:
ASA grade II to V
preoperative temperature below 36.0°C
undergoing combined general and regional
anaesthesia
undergoing major or intermediate surgery
at risk of cardiovascular complications.
NOTES FOR PRESENTERS:
Key points to raise:
The higher the ASA grade, the greater the risk
Patients who have a temperature of below 36.0°C should normally be warmed preoperatively; however, this is not always possible because of clinical urgency.
Additional information:
ASA (American Society of Anesthesiologists) Physical Status Classification System
Class I A normal healthy patient
Class II A patient with mild systemic disease
Class III A patient with severe systemic disease
Class IV A patient with severe systemic disease that is a constant threat to life
Class V A moribund patient who is not expected to survive without the operation
Class VI A declared brain-dead patient whose organs are being removed for donor purposes

33. Expectations Core temperature never to drop below 36°C at any stage
To avoid symptoms and signs
If GA will last 30 mins or more, must measure temp through operation
More strict if high risk group
Start actions BEFORE theatre

34. Preoperative warming
If the patient’s temperature is below 36.0°C in the hour before they leave the ward or emergency department:
forced air warming should be started preoperatively on the ward or in the emergency department (unless there is a need to expedite surgery because of clinical urgency)
forced air warming should be maintained throughout the intraoperative phase.
NOTES FOR PRESENTERS:
Key points to raise:
Examples of clinical urgency are bleeding and critical limb ischaemia.
Other related recommendations are:
The patient’s temperature should be measured and documented in the hour before they leave the ward or emergency department [1.2.4, NICE guideline].
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) [1.2.6, NICE guideline]
Additional information:
On transfer to the theatre suite:
the patient should be kept comfortably warm
the patient should be encouraged to walk to theatre where appropriate [1.2.7, NICE guideline]
Recommendation in full:
If the patient’s temperature is below 36.0°C:
forced air warming should be started 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)
forced air warming should be maintained throughout the intraoperative phase. [1.2.5, NICE guideline]

35. Intraoperative phase
The patient’s temperature should be measured and documented before induction of anaesthesia and then every 30 minutes until the end of surgery. Induction of anaesthesia should not begin unless the patient’s temperature is 36.0°C or above.
NOTES FOR PRESENTERS:
Key points to raise:
Surgery should not begin if the patient’s temperature is below 36.0°C unless there is a need to expedite surgery because of clinical urgency, for example bleeding or critical limb ischaemia.
A further recommendation is:
Standard critical incident reporting should be considered for any patient arriving at the theatre suite with a temperature below 36.0°C [1.3.2, NICE guideline]
Additional information:
Other related recommendations for the intraoperative phase are:
In the theatre suite:
the ambient temperature should be at least 21°C while the patient is exposed
once forced air 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 [1.3.4, NICE guideline]
The patient should be adequately covered throughout the intraoperative phase to conserve heat, and exposed only during surgical preparation [1.3.5, NICE guideline]
Key recommendations in full: as shown on slide [1.3.1, NICE guideline]
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). [1.3.3]

36. Passive – to minimise heat loss
For hypothermic AND normothermic patients
Ambient temp at least 20°C (upto 30° if burns or neonates!)
Passive insulation (layer of air)
Warmed cotton aircell blankets
Space blanket?
Circulating water mattress?
Hats (esp Paeds) Socks etc
(Special cases – pre veins, post flaps)
(Before – preop vasodilation)

37. Active – add to heat gain
For hypothermic patients
Skin – Forced air warming / convective
(Bair Hugger) – upto 50 W heat given (no infection evidence)
Internal – IV, irrigation (1 litre fluid at room temp will lower core temp by 0.25°C)
Airway - humidification (HMEF)

38. Cardiopulmonary bypass
Dialysis
(Protein infusion to increase metabolism)
Watch out for over-heating of skin and fluids (keep below 45°C)

39. Warming intravenous fluids
Intravenous fluids (500 ml or more) and blood products should be warmed to 37°C using a fluid warming device.
NOTES FOR PRESENTERS:
Key point to raise:
Related recommendation:
All irrigation fluids used intraoperatively should be warmed in a thermostatically controlled cabinet to a temperature of 38–40°C [1.3.10, NICE guideline]
Key recommendation in full:
As shown on slide [1.3.6, NICE guideline]

40. Postoperative phase
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
NOTES FOR PRESENTERS:
Key points to raise:
Once patients are back on the ward, they should be kept comfortably warm (see additional information).
Additional information:
Related recommendations:
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 one cotton sheet plus two blankets, or a duvet [1.4.2, NICE guideline]
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 [1.4.3, NICE guideline]
Key recommendation in full:
As shown on slide [1.4.1, NICE guideline]

41. Any questions???

42. Costs and savings per 100,000 population
Recommendations with significant costs
Costs
(£ per year)
Increased use of forced air warming blankets
43,000
Increased warming of IV fluids and blood products
23,000
Estimated cost of implementation
66,000
Recommendations with significant savings
Savings
Expected reduction in surgical site infections
–43,000
Estimated annual net cost of implementation
ADAPTING THIS SLIDE FOR LOCAL USE:
We are aware that local factors such as incidence and baseline can vary considerably when compared with the national average. NICE has provided a costing template for you to calculate the financial impact this guideline will have locally. We encourage you to calculate the local impact of this guideline by amending the local variations in the template such as incidence, baseline and uptake. You can then remove the national figures from the table and replace them with your local figures to present to your colleagues.
NOTES FOR PRESENTERS:
The information on this slide has been extracted from the NICE costing report, which has been provided by NICE to support implementation of this guidance. It was developed after careful consideration of the available data and by working closely with the guideline developers and other people in the NHS. It is not NICE guidance. Assumptions used in this report are based on assessment of the national average and it is recognised that local practice or circumstances may differ from this. The costs published in this report are estimates only and are not to be taken as the Institute's view of desirable, or maximum or minimum figures.
NICE has also provided a costing template to help calculate the local costs associated with implementing this guideline. The costs per 100,000 population are summarised in the table. It is recognised that implementation of the recommendations may take place over a number of years.
Implementation of the guidance may also result in savings through a reduction in morbid cardiac events and blood transfusions. These savings have not been quantified in the costing report, but may be identified at a local level.
In addition, compliance with NICE guidance is one of the criteria indicating good risk reduction strategies, and in combination with meeting other criteria could lead to a discount on contributions to the NHS Litigation Authority schemes, including the clinical negligence scheme for trusts (CNST).
For further information please refer to the costing template and costing report for this guidance on the NICE website.

43. Discussion
Which key areas of local practice differ from the guideline?
To ensure effective implementation:
what equipment is needed?
what are staff training needs?
What will the impact be on the average length of patient stay if the guideline is implemented fully?
How should Risk and Safety Managers be involved in the implementation of the guideline?
NOTES FOR PRESENTERS:
These questions are suggestions that have been developed to help provide a prompt for a discussion at the end of your presentation – please edit and adapt these to suit your local situation.

44. SUMMARY Understanding of heat balance
Understanding why this is important
Why to prevent temp below 36°C
How to measure temperature
Recommendations of how to assess
Passive and active ways of helping the patient from pre- to post-op