Dr John Andrzejowski

Royal Hallamshire Hospital

Sheffield

316 hospitals GA: temp monitor in 25% (Naso-pharyng)

43% actively warmed

Regional: temp monitor in 6% (tympanic)

28% warmed

A. Torossian & TEMMP study group. EJA (2007), 24:668-675

If you don't measure temperature you will never find hypothermia!

Why IPH occurs

Risk factors

NICE guidelines

Sensible implementation

INADVERTENT PERIOPERATIVE HYPOTHERMIA (IPH): < 36OC.

1. Day Case unit PACU (94pts)

1. 40% were < 36OC

2. 8% <35.5OC. 2. Major Surgery

1. 44% of patients <36°C intraop

2. 35% of patients <36°C in PACU. 3. Main theatres PACU: ORMIS

1. 7,631 out of 26,435 were < 36OC =29%

Hoyle & Andrzejowski JODS 2008;18(3):76-8

SENSORS:

Skin

Brain

Spinal cord

Deep tissues

Hypothalamus HYPOTHALAMUS:

SET POINT 37.1

36.7

Active vasodilation

Sweating

Behaviour

TR Vasoconstriction

Shivering

Behaviour

NS Thermogenesis

Inter-threshold

range

Direct vasodilatation Central effects on thermoregulation

Vasoconstriction thresholds fall

Shivering inhibited Heat Loss > production

Radiation

Convection; air currents – v impt.

Conduction; cool bed & IV fluids

Evaporation; up to 25%

Sessler: Anesthesiology 2000;92(2):578

Sessler: Anesthesiology 2000; 92(2):578

Redistribution

Ht loss > production

Plateau

Ambient temp

Surgery; length & type

Body morphology

ASA

Type of anaesthetic

Age

Premeds

90% of heat lost by radiation & convection Radiation; ≈ (temp diff)4

Keep theatre @ 21OC until covered Especially for short

cases

Major cases are higher risk

open abdomens

lots of washout etc

xtra fluids Don’t forget short cases...

NICE says warm any lasting over 30minutes

High risk need warming from start.

Kurz et al. Anesth Analg 1995; 80: 562-7

% body fat

< Favours higher ASA ..... Favours ASA 1 >

Not just GAs Regionals:

often feel warm!

Central effect

Vasodilatation; unabated heat loss

TR Thresholds affected above block

Change in afferent input?

Cold sensation not triggered

Combined regional & GA at most risk

Vasoconstriction & shivering thresholds lower younger patients shiver @ 36.1°C

80yr old may not shiver until temp < 35.2°C

Vasocontriction less efficient

Lower metabolic rate produce heat more slowly.

Recovery from even mild hypothermia prolonged

Definitely at greater risk if allowed to get cold...

< Favours control ..... Favours Midazolam >

Ambient temp

Surgery; length & type

Body morphology

ASA

Type of anaesthetic

Age

Premeds

Wound infections

Coagulopathy

Prolonged drug action

Myocardial morbidity

Recovery times prolonged

Shivering

400 patients colon surgery Ambient or 40°C blower Prophylactic antibiotics Outcomes: Post op wound infection

Feeding,

Length of stay

Stopped after 200 patients

Kurz A et al. NEJM 1996;334(19):1209-15

NEJM 1996;334(19):1209-15

• Wound infection α s/c O2 tension for 4 hours after bacterial exposure.

• IPH → ↓tissue blood flow & ↓ s/c O2

• Direct impairment of (T cell & Neutrophil) immune function

• ↓ synthesis of collagen

Platelet function impaired

Local phenomenon

↓release of thromboxane A2

Fibrinolytic activity unaffected

Clot formation affected rather than ↑lysis

Standard coag tests unchanged @ 37°C

Prolonged when performed @ patient temp

Intrinsic & extrinsic probably affected

N=60 Normothermic

36.6 0C P

Intraoperative blood loss

1.2 +/- 0.5 L <0.001

Transfusion requirement

1 unit <0.05

Schmied H et al. Lancet 1996; 347: 289-92

Schmied H et al. Lancet 1996; 347: 289-92

N=60 Normothermic

36.6 0C Hypothermic

-1.6 0C P

Intraoperative blood loss

1.2 +/- 0.5 L 1.7 +/- 0.3 L <0.001

Transfusion requirement

1 unit 8 units in 7 patients

<0.05

618

488

0

100

200

300

400

500

600

700

Conventional

36.1C

Aggressive 36.5C

Blo

od

lo

ss (

mls

)

86

40

80

29

0

10

20

30

40

50

60

70

80

90

100

MAP mmHg Number transfused

Conventional 36.1C

Aggressive 36.5C

Winkler M. Anesth Analg. 2000;91:978-84

0

10

20

30

40

50

60

70

80

Vecuronium -2 deg C Atracurium -3 deg C

du

ratio

n (

min

s)

Normothermia

Hypothermia

Volatiles: • Hypothermia ↓MAC

• More soluble; ↑ body content –

• longer recovery

[propofol] ↑ 30% @ 3

C hypoth. • ↓ Hepatic metabolism

[fentanyl] ↑ ~ 5% per

C hypothermia

Wound infections

Coagulopathy

Prolonged drug action

Myocardial morbidity

Recovery times prolonged

Shivering

Frank SM et al Anesthesiology 1995; 82:83–93

300 pts: intra vs post-op • ECG events

• Ischaemia, arrhythmia

• Morbid cardiac events

• Unstable angina

• Cardiac arrest

• Infarction 0

5

10

15

20

25

ECG event Morbid cardiac

event

Overall

Postoperative cardiac outcomes

%

Normothermia 36.7 0 C

Hypothermia 34.5 0 C

Frank et al JAMA 1997; 277:1127-34

< Favours hypothermia.... Favours normothermia >

NEJM 1996;334(19):1209-15

50,689 patients between 2000 and 2008 first 24 h in ICU after elective non-cardiac surgery.

23,165 (46%) were hypothermic transient in 22,810 (45%)

persistent in 608 (1.2%)

Neither transient nor persistent hypothermia

was independently associated with increased hospital mortality or length of stay.

Karalapillai et al. Anaesthesia 2013, 68, 605–611

• Cold sensation ‘worse than surgical pain’.

• Aggravates postoperative pain

• Impedes monitoring

• ↑ intraocular & IC pressures

• Can occur @ normothermia

• Brain & S Cord recover at diff rates • SV > IPPV • Males > females

• Body needs help • Warming prn • Phamacological: NNT 2

• pethidine 25 mg

• clonidine 150 mcg

• doxapram 100 mg

Kranke. Anesth Analg. 2002;94(2):453-60

Preventing perioperative

hypothermia

2008 NICE clinical guideline 65

Implementing NICE guidance

on

Inadvertant Perioperative Hypothermia

Patients (& families and carers) should be informed before and on admission 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 to help them keep comfortably warm

• they should tell staff if they feel cold at any time during their hospital stay.

Each patient should be assessed for their risk of IPH and potential adverse consequences before transfer to theatre.

1 hour before

When using any device to measure patient temperature, healthcare professionals should:

be aware of, and carry out, any adjustments that need to be made in order to obtain an estimate of core temperature from that recorded at the site of measurement

be aware of any such adjustments that are made automatically by the device used.

We all use different devices...

METOPIC REGION. FEMALES COLDER THAN MALES!

SUPERFICIAL TEMPORAL & POST AURICULAR

Physiological measurement 2008; 29: 341–8

Langham & Sessler. Anesthesiology 2009;111:90-6

• Electronic oral temperatures best for postop use. • Axillary temperature is a reasonable substitute. • Temporal artery thermometry (TAT) seemed

accurate but additional validation prudent before adopting TAT for routine postop use

• May miss hypothermia & hyperthermia.

• Intraop temperatures more accurate than

postop: more reliable for performance measures.

If core temperature is < 36.0°C in the hour before they leave the ward or emergency department: FAW should be started on the

ward or in A&E (except for clinical urgency)

FAW should be maintained intraoperatively

If started early, lists should not be affected

• 421 pts having short, ‘clean’ surgery

• breast, VV, hernias: 50 mins av • Standard, local or systemic warming

• Non contact radiant heat dressing • Reviewed @ 2 & 6 weeks post op. • Wound infection • ASEPSIS scoring system • Antibiotic use

Melling AC et al. Lancet 2001; 358: 876-880

Warmed n=277 Standard n=139

Post op ABs 7% 16%

Wound inf 5% 14%

ASEPSIS > 10 7% 17%

NNT 10 local

15 systemic

Melling AC et al. Lancet 2001; 358: 876-880

BUT....no perioperative temps were recorded!

• 68 adults - spinal surgery

• 37 controls

• 31 prewarmed @ 70 mins

• @ 38

C, using Bair Paws®

• Routine FAW intraop.

35.6

35.8

36.0

36.2

36.4

36.6

36.8

37.0

Induction 20 40 60 80 100 120 140 160

Time (minutes)

Tem

pera

ture

(OC

)

Non Prewarmed

Prewarmed

Andrzejowski et al. BJA; Nov 2008

Core temp 0.3OC ↑at 40, 60 and 80 minutes

(p < 0.05). Andrzejowski et al BJA 2008: 101; 627-31

Non warmed overall = 57%

Prewarmed overall = 32%

0

5

10

15

20

25

30

35

40

45

50

Indu

ction

20 40 60 80 100

120

140

160

Time (minutes)

% p

ati

en

ts h

yp

oth

erm

ic (

<36.0

°C)

Prewarmed

Nonprewarmed

Non warmed overall = 57%

Prewarmed overall = 32%

Horn et al. Anaesthesia 2012; 67: 612-617,

Non prewarmed

10 minutes

20/30 minutes

• Induction of anaesthesia should not begin unless the patient’s temperature is

> 36.0°C

• The patient’s temperature should be measured and documented before induction of anaesthesia & every 30 mins

Diff to cook a patient in < 1hour!!

? temp probes for

> 60 mins

Most patients!

Leave the blanket on!

Active warming (FAW) from induction for

anaesthesia > 30 mins &

IPH ‘high risk’ patients having anaesthesia < 30

mins

If any two of the following apply, patients are at higher risk of IPH.

ASA grade II to V

preoperative temperature < 36.0°C

undergoing combined GA and regional

undergoing major or intermediate surgery

at risk of cardiovascular complications.

Sessler DI. Anesth Clin North Am 1994; 12:425-56

∆ in mean body

temperature 0C

Plug in & switch on

pre-induction

Sceptical and skint!

Intravenous fluids (500 ml or more) and blood products should be warmed to

37

C using a fluid warming device

Group Room

Temperature

Warming Cabinet

+

Inline warmer

Chi

squared

% of patients with temp

<36 C at any point

intra op

68%

47%

0.085

% of patients with temp

<36 C on arrival

in PACU

33%

14%

0.03 *

Andrzejowski et al. Anaesthesia. 2010: 65; 942

Warming Cabinet

Room Temperature

In-line warmer

Andrzejowski et al. Anaesthesia. 2010: 65; 942

* p=0.006 (warming cabinet vs

room temperature)

• Temperature should be measured and documented on admission to PACU and then every 15 minutes...

• Ward transfer only if temperature > 36.0°C. • If temperature is < 36.0°C: active FAW

• Until discharged from PACU or until comfortably warm

Warm blankets are placebo!

Conclusions:

• Hypothermia can have serious sequelae

• Keep patients warm preop

• Consider prewarming.

• Measure temperature

• Short cases & regionals get cold

• Warm hard & early

• Warm all fluids

Total Studied

n < 360C %

Prewarming study (BJA) 37 3 8%

Snapshot RHH (July 2008!) 164 11 7%

Fluid warming study 61 7 11%

Circadian rhythm... Elderly have less variation