2. Introduction
ď The balance b/w heat production and heat loss
determines
ď Normally tightly regulated
ď Speed of chemichal reaction varies
ď 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
ď Unintentional drop of body core temperature below
35°c or 95 °f
1°ď direct exposure of a previously healthy individual to
cold
2°ď complication of severe disease
5. Risk factors
Extremes of
age
⢠elderly
⢠neonates
enviornmental
⢠Occupational,sports related
⢠Inadequqate clothing
⢠immersion
Insufficient
food
⢠Malnutrition
⢠Marasmus
⢠kwashiorkor
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
30. Vasoconstriction & shivering characterised by
ď Threshold onset ď tempe at which effector activates
ď Gainď rate of response to given decrease in core
temperature
ď Max response intensity
ď GA reduces the threshold by 2-3°c
ď Gain & max response intensity are unaffected
31. NST
ď Increase in mb production not associated with
muscular activity
ď Skeletal muscle and brown fat
ď Intrascapular & perineal areas
ď In infants itâs the primary response
32. Clinical features
ď Mild ď 35° c â 32.2° c or 95 ° f â 90 °f
ď Moderate ď Ë32.2 ° c- 28° c or 90° F-82.4 ° f
ď Severeď Ë 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 -- âse in MV
â˘âsed O² cpnsumpation
⢠Bronchorrhoea and spasm
38. severe
Renal and endo
⢠âsed RBF,âse in CO
⢠Extrene oliguria
⢠80% in Mb
neuromuscular
⢠No motion
⢠âse nerve conduction
velocity
⢠Pheripheral areflexia
⢠No corneal or occulo
cephalic reflex
39. Diagnosis & Stabilization
ď If ventricular fibrillation ď defibrillation with 2 J
/kg ď not reverted ď rewarm 30° c (80 ° F) bfore next
defibrillation
ď Supplemental Oâ is always waranted
ď If airway reflex are lost ď gentle intubation
ď Atrial arrythmias should be waited
40. Diagnosis & stabilization
ď Pulmonary artery catheterization should be avoided
ď CVP in to the rt atrium should be avoided
ď Indwelling bladder catheter
ď Dehydration correction
ď Acid base inbalance should be correct slowly
42. Passive
ď RORď 0.5-2° c
ď Good for previously healthy pt,who develop aut mild
primary hypothermia
ď Pt should have sufficient glycogen to support endogenous
thermogenesis
43. active
ď Necessary in tempË 32°c or 90° f
ď Extremes of age
ď CNS dysfunction
ď Cardio vascular instability
ď Hormone insufficiency
ď Suspicious secondary hypothermia
44. Active external rewarming
ď Forced air heating blankets
ď External heat exchange pads
ď Radiant heat sources
ď Hot packs
ď Electric blankets should be avoided
45. Active core rewarming
ď With heated humidified oâ (40-45°c) via mask or ETT
ď Crystallods should be heated 40-42° c(can use in line heat
exchanger)
ď i/v medications are with held below 30
ď MAP 60,if not maintaining dopamine 2-5mcg/kg/min
46. Options for rewarming
CPB
⢠Full circulatory support with pump and
oxygenator
⢠Temp gardient â5 -10 ° c
⢠Flow rate->2-7l/minâŚROR up to 9.5° c/hr
hemodialysis
⢠Single or dual vessel catheter
⢠Exchange cycle volumeâ200-500ml/min
⢠RORď up to 2-3° c
47. Options for rewarming
CAVR
⢠Percuta femoral cather 8.5 fr
⢠Requires systolic BP >60
⢠Flow rate225-375ml/min
⢠RORď 3-4°c
CVV
⢠Central venous dual lumen or pheripheral
⢠Flow rate 150-400ml/min
⢠RORď 2-3°c
48. Measuring core temperature
ď Pulmonary circulation
ď Tympanic memebrane
ď Nasopharynx
ď Oesophagus
ď Rectal and bladder are not accurate as they are not
well perfused
49. Thermal regulation during anaesthesia
ď GAď 1-3°c
ď Vasoconstriction and NST are the mechanisms
50. Development of hypothermia during GA
ď Results from combination of cold operating room
enviornment as well as anaesthesia impaired
regulation
51. Events that contribute
ď Interfere with hypothalamic thermostat
ď Ambient temperature <21°c
ď Unwarmed i/v fluids
ď Drug induced vasodilatation
ď Decreased BMR
ď Body cavities exposed to ambient temperature
ď Heat is recquired to humidify inhaled gases
53. Redistribution
ď Laregest drop in core temp
ď 1-5°c with in 30-45min
ď Due to vasodilatation and other effect of GA
ď Vasodilatation causes redistribution of heat from core to
pheriphery
54. Linear phase
ď 1°c over 2-4 hrs
ď Gradual reduction
ď This is due to heat loss by
56. Plateu phase
ď After 3-5 hrs
ď Long cases
ď Core temperature often stop decreasing
ď In this phase heat loss is matched by metabolic heat
production
57. Neuroaxial anaesthesia
ď Redistribution of body heat is the main stay
ď Initial core hypothermia is not as pronounced as in
GA
ď Other wise the first two phase are similar
ď All thermoregulatory responses are neurally
mediated and affects both pheripheral and central
thermo regualtion
59. consequences
ď Impaired renal function
ď Decresed drug mb
ď Poor wound healing
ď Increased incidence of infection
ď Post operative protein catabolism and stress
response
60. Prevention and treatment of mild hypothermia
ď Minimal redistribution of heat
ď Cutaneous warming during anaesthesia
ď Internal warming
61. Minimal redistribution of heat
ď Pre operative warming of pheripheral tissue
ď Preoperative pharmacological vasodilatation
(oral nifedepine)
63. In newborn
ď Has large skin surface area compared with their body
mass and an increased thermal conductance
ď Evaporation of heat loss is due to âsed keratin content
ď Critical temperature ->this is the temperature below which an
unclothed ,unanaesthetised individual cannât maintain a
normal core body temp
ď in adults 0° c
in infants 22° c
in pre term 28° c
64. In newborn
ď Neutral temperture:ď ambient temperture at which
the oâ demand is minimal & temperature regulation is
achieved through non evaporative physical status
for adults ď 28°c
neonates ď 32° c
preterm ď 34° c
65. In newborn
ď Maintanance f core temperaturebin a cool
enviornment result in an âsed Oâ consumption and
mb acidosis
ď Particular concern is in view of thermoregulation in the
newborn in head
ď Thin skull bone
ď Sparse scalp hairin combination with close proximity of
well perfused brain further prefers heat loss from head
66. ď 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
ď For protection against tissue ischemia(during
cardiac and neuro surgery)
ď Drugs produces less protection than hypothermia
does
ď Deep hypothermia remains routine for intentional
circulatory arrest cases