reference from harrison , miller, pediatric anaesthetic book by dr.rabeca.....

1. D R R I Y A S A
hypothermia

2. Introduction
 The balance b/w heat production and heat loss
determines
 Normally tightly regulated
 Speed of chemichal reaction varies
 Body enzyme sysytem has very narrow range of
temperature

3. • Basic metabolic process
• Food intake
• Muscular activity
Heat
production
• Radiation and conduction
• Vaporization of sweat
• Respiration
• Urination and defication
Heat lost

4. hypothermia
 Unintentional drop of body core temperature below
35°c or 95 °f
1° direct exposure of a previously healthy individual to
cold
2°complication of severe disease

5. Risk factors
Extremes of
age
• elderly
• neonates
enviornmental
• Occupational,sports related
• Inadequqate clothing
• immersion
Insufficient
food
• Malnutrition
• Marasmus
• kwashiorkor

6. Risk factors
Endocrine related
• DM
• Hypoglycemia
• Hypothyroidism
• Adrenal insufficiency
• hypopitutarism
neurological
• CVA
• Hypothalamic d/s
• Parkinsons d/s
• Spinal sord injury
Multi system
• trauma
• Sepsis
• Shock
• Hepatic or renal
failure
• Burns & exfoliative
dermatological
lesions
• immobility

7. Pharmacological
Ethanol
BZDS
barbiturates
Phenothiazines
carcinamatosis
Anaesthetics
antidepressants

8. thermoregulation
 Heat loss occurs through five mechanisms

 radiation
 conduction
 convection
 respiration
 evaporation

9. thermoregulation
 It’s regulated through preoptic anterior
hypothalamus

10. immediate
ANS+release
of NE
↑ses muscle
tone and
shivering
↑ ses
thermogenesis
↑ses BMR

11. thermoregulation
 Delayed  endocrine
 Cutaneous cold thermoception direct redlex
vasoconstriction
 Prolonge dexposure thyroid axis increases MR

12. Thermoregulatory mechanism
 Afferent
 Center
 efferent

13. thermoregulatory mechanism
• Increase heat production
• Shivering
• Hunger
• Increase voluntary activity
• Increase scretion of NE,E
Activated
by cold
• Decrease heat loss
• Cutaneous vasoconstrictionActivated
by cold

14. • Incease heat loss
• Cutanoeus vasodilatation
• Sweating
Activate
d by heat
• Increased respiration
• Decrease heat production

15. Terms to remember
Threshold
temperature
• Central temperature that elicit a regulating effect
Interthreshold
range
• Temperature range over which no regulatory responses
gain
• Intensity of regulatory response

16. Terms to remember
Mean body
temperature
• Physiologically weighted average temperature from
various tissues
NST
• Heat production not associated with muscle
ST • Through muscle activity

17. Terms to remember
Dietary
thermogenesis
•Heat production by
metabolism of nutrients

18. Over view
Effernt responses
Preoptic nuclei of anterior hypothalamus
heat cold
Thermal receptors
Cold warm

19. afferent
 Cold - A deta
 Warm unmyelinated C fiber

20.  Now seems like TRP
 Vanilloid
 menthol

21.  TRPV 1-4--heat activated
 TRPM8 and TRPA1cold

22. Threshold
 Mechanism is unknown
 0.5-1 degree celcius

23. Factors affecting threshold
 Exercise
 Nutrtion
 Infection
 Hypo & hyperthyroidism
 Drugs (alcohol,sedatives,nicttine)

24. Interthreshold range
 Bounded by sweating threshold at its upper end
 And vasoconstriction thgreshold at its lower end
 0.2-0.4

25. efferent
 Body responds to thermal perturbation via effector
mechanism that increases mb heat production or
alter enviornmental heat loss

26. Most
commonly
used one
behavioural

27. Cutaneous vaso
constriction
• First one to develop 36.5-37°
• Metabolic heat is lost by convection & radiation

28. Digital skin blood flow
capillary
nutrition
A – v shunt
Adrenergic nerve
sympathetic
nerve mediate
constriction in A-
V shunts
thermoregulatory

29.  Further decrease in temperature shivering
commence
 36.0-36.2°

30. Vasoconstriction & shivering characterised by
 Threshold onset  tempe at which effector activates
 Gainrate of response to given decrease in core
temperature
 Max response intensity
 GA reduces the threshold by 2-3°c
 Gain & max response intensity are unaffected

31. NST
 Increase in mb production not associated with
muscular activity
 Skeletal muscle and brown fat
 Intrascapular & perineal areas
 In infants it’s the primary response

32. Clinical features
 Mild 35° c – 32.2° c or 95 ° f – 90 °f
 Moderate ˂32.2 ° c- 28° c or 90° F-82.4 ° f
 Severe˂ 28 ° c or 82.4 ° F

33. mild
CNS
CVS
RS
• Linear depression of cerebral mb
• Amnesia , apathy
• Maladaptive behaviour
• Dysarthria
• Impaired judgement
• Tachycardia then brady
• Cardiac cycle prolongation
• Vasoconstriction
• Increased CO & BP
• Tachyponea -- ↓se in MV
•↑sed O² cpnsumpation
• Bronchorrhoea and spasm

34. mild
Renal and
endocrine
Neuro
muscular
• Diuresis
• ↑sed hormonal
levels
• ↑se in mb and
shivering
• ↑sed muscle
shivering and tone
• fatigue

35. modearate
CNS
• EEG abno
• Progressive
depression of level
of consiousness
• Pupillary dilatation
• Paradoxical dressing
• hallucination
CVS
• ↓se in PR & BP
• ↑sed atrial and
ventriculaer
arrhythmias
• J wave ECG changes
Respiratory
• Hypoventialtion
• 50 % ↓se in co₂
production
• Absence of
protective airway
reflex

36. moderate
Renal and
endocrine
• 50% ↓se in RBF
• Renal autoregulation
• Impaired insulin
activity
Neuro mucular
• hyporeflexia
• Diminished
shivering induced
thermogenensis
• rigidity

37. Severe
CNS
Loss of
cerebrovascular
autoregulation
↓se in CBF
COMA
Loss of occular reflex
Progressive ↓se in
EEG
CVS
↓se BP
HR
CO
Pre entrant cardia
arrhythmias
Max risk of
ventricular
fibrillation
asystole

38. severe
Renal and endo
• ↓sed RBF,↓se in CO
• Extrene oliguria
• 80% in Mb
neuromuscular
• No motion
• ↓se nerve conduction
velocity
• Pheripheral areflexia
• No corneal or occulo
cephalic reflex

39. Diagnosis & Stabilization
 If ventricular fibrillation  defibrillation with 2 J
/kg not reverted rewarm 30° c (80 ° F) bfore next
defibrillation
 Supplemental O₂ is always waranted
 If airway reflex are lost gentle intubation
 Atrial arrythmias should be waited

40. Diagnosis & stabilization
 Pulmonary artery catheterization should be avoided
 CVP in to the rt atrium should be avoided
 Indwelling bladder catheter
 Dehydration correction
 Acid base inbalance should be correct slowly

41. Rewarming
 Active
 passive

42. Passive
 ROR0.5-2° c
 Good for previously healthy pt,who develop aut mild
primary hypothermia
 Pt should have sufficient glycogen to support endogenous
thermogenesis

43. active
 Necessary in temp˂ 32°c or 90° f
 Extremes of age
 CNS dysfunction
 Cardio vascular instability
 Hormone insufficiency
 Suspicious secondary hypothermia

44. Active external rewarming
 Forced air heating blankets
 External heat exchange pads
 Radiant heat sources
 Hot packs
 Electric blankets should be avoided

45. Active core rewarming
 With heated humidified o₂ (40-45°c) via mask or ETT
 Crystallods should be heated 40-42° c(can use in line heat
exchanger)
 i/v medications are with held below 30
 MAP 60,if not maintaining dopamine 2-5mcg/kg/min

46. Options for rewarming
CPB
• Full circulatory support with pump and
oxygenator
• Temp gardient –5 -10 ° c
• Flow rate->2-7l/min…ROR up to 9.5° c/hr
hemodialysis
• Single or dual vessel catheter
• Exchange cycle volume—200-500ml/min
• RORup to 2-3° c

47. Options for rewarming
CAVR
• Percuta femoral cather 8.5 fr
• Requires systolic BP >60
• Flow rate225-375ml/min
• ROR3-4°c
CVV
• Central venous dual lumen or pheripheral
• Flow rate 150-400ml/min
• ROR2-3°c

48. Measuring core temperature
 Pulmonary circulation
 Tympanic memebrane
 Nasopharynx
 Oesophagus
 Rectal and bladder are not accurate as they are not
well perfused

49. Thermal regulation during anaesthesia
 GA1-3°c
 Vasoconstriction and NST are the mechanisms

50. Development of hypothermia during GA
 Results from combination of cold operating room
enviornment as well as anaesthesia impaired
regulation

51. Events that contribute
 Interfere with hypothalamic thermostat
 Ambient temperature <21°c
 Unwarmed i/v fluids
 Drug induced vasodilatation
 Decreased BMR
 Body cavities exposed to ambient temperature
 Heat is recquired to humidify inhaled gases

52. Pattern of hypothermia
Phase 1:redistribution
Phase 2:linear phase
Phase 3:plateu phase

53. Redistribution
 Laregest drop in core temp
 1-5°c with in 30-45min
 Due to vasodilatation and other effect of GA
 Vasodilatation causes redistribution of heat from core to
pheriphery

54. Linear phase
 1°c over 2-4 hrs
 Gradual reduction
 This is due to heat loss by

55. Radiation
40%
Convection
30%
Evaporation
15%
Conduction
15%
Respiratory
loss
10%

56. Plateu phase
 After 3-5 hrs
 Long cases
 Core temperature often stop decreasing
 In this phase heat loss is matched by metabolic heat
production

57. Neuroaxial anaesthesia
 Redistribution of body heat is the main stay
 Initial core hypothermia is not as pronounced as in
GA
 Other wise the first two phase are similar
 All thermoregulatory responses are neurally
mediated and affects both pheripheral and central
thermo regualtion

58. Consequences
 Cardiac arrythmia & ischemia
 Increased PVR
 Hb-0₂ dissociatio curve left shift
 Reversible coiagulopathy
 Altered mental status

59. consequences
 Impaired renal function
 Decresed drug mb
 Poor wound healing
 Increased incidence of infection
 Post operative protein catabolism and stress
response

60. Prevention and treatment of mild hypothermia
 Minimal redistribution of heat
 Cutaneous warming during anaesthesia
 Internal warming

61. Minimal redistribution of heat
 Pre operative warming of pheripheral tissue
 Preoperative pharmacological vasodilatation
(oral nifedepine)

62. Cutaneous warming
 Passive insulation
 Active warming
 Internal warming
 Airway humidification
 Invasive internal warming technique
 Amini acid infusion

63. In newborn
 Has large skin surface area compared with their body
mass and an increased thermal conductance
 Evaporation of heat loss is due to ↓sed keratin content
 Critical temperature ->this is the temperature below which an
unclothed ,unanaesthetised individual cann’t maintain a
normal core body temp
 in adults 0° c
in infants 22° c
in pre term 28° c

64. In newborn
 Neutral temperture:ambient temperture at which
the o₂ demand is minimal & temperature regulation is
achieved through non evaporative physical status
for adults 28°c
neonates  32° c
preterm  34° c

65. In newborn
 Maintanance f core temperaturebin a cool
enviornment result in an ↑sed O₂ consumption and
mb acidosis
 Particular concern is in view of thermoregulation in the
newborn in head
 Thin skull bone
 Sparse scalp hairin combination with close proximity of
well perfused brain further prefers heat loss from head

66.  Thermoregulatory vasoconstriction and
vasodilatation most likely establish during the first
day of life and can occur in both premature and the
full term infants

67. Deliberate intraoperative hypothermia
 For protection against tissue ischemia(during
cardiac and neuro surgery)
 Drugs produces less protection than hypothermia
does
 Deep hypothermia remains routine for intentional
circulatory arrest cases