tanda hipertermi

8/8/2019 tanda hipertermi

1/36

PerioperativeHypothermia

The New England Journal of MedicineJune 12, 1997

Daniel I.Sessler, M.D.

Senior clerk:


2/36

Introduction

The human thermoregulatory system usuallymaintains core body temperature within 0.2 of

37

Perioperative hypothermia is common becauseof the inhibition of thermoregulation inducedby anesthesia and the patient`s exposure tocool enviroment

Hypothermia complication:shivering,prolonged drug effect,coagulopathy,

surgical wound infection,morbid cardiacevent


3/36

Normal thermoregulation

Processing of thermoregulatory information:

afferent input

central controlefferent responses

Core temperature measurements

pulmonary artery

tympanic membrane

distal esophagus

nasopharynx


4/36


Afferent input: cold signal-A fiber

warm signal-C fiber

Each contribute 20% of the total thermal input:

hypothalamus

other parts of brain

skin surfacespinal cord

deep abdominal and thoracic tissues


5/36


Primary thermoregulatory control center

-hypothalamus

Control of autonomic responses is 80%

determined by thermal input from core

structures

In contrast, behavior response may

depend more on skin temperature


6/36


The interthreshold range(coretemperatures not triggering autonomic

thermoregulatory responses)is only0.2

Each thermoregulatory response can becharacterized by a threshold ,gain,

maximal response intensity

Behavioris the most effective response


7/36


Major autonomic defenses against heat:

1. sweating

2.cutaneous vasodilation

Major autonomic defenses against cold:

1.cutaneous vasoconstriction

2.nonshivering thermogenesis3.shivering


8/36


Vasoconstriction occurs in AV shunts located

primarily in fingers and toes, mediated by -

adrenergic symp. nerve. Nonshivering thermogenesis is important in

infants,but not in adults (brown fat)

Shivering is an involuntary muscle activity

that increase metabolic rate 2-3 times


9/36

Thermoregulation during general

anesthesia General anesthesia removes a p`t ability to

regulate body temperature through behavior, sothat autonomic defenses alone are available torespond to changes in temperature

Anesthetics inhibit thermoregulation in a dose-dependent manner and inhibit vasoconstrictionand shivering about 2-3 times as they restrict

sweating Interthreshold range is increased from 0.2 to

4(20 times), so anesthetized p`t arepoikilothermic with body temperaturesdetermined by the environment


10/36


anesthesia The gain and maximal response intensity of

sweating and vasodilation are well preservedwhen volatile anesthetics is given

However volatile anesthetics reduces the gainofAV-shunt vasoconstriction,without alteringthe maximal response intensity

Nonshivering thermogenesis dosen`t occur in

anesthetized adults General anesthesia decreases the shivering

threshold far more than the vasoconstrictionthreshold


11/36


anesthesia


12/36

Inadvertent hypothermia during

general anesthesia Inadvertent hypothermia during general

anesthesia is by far the most common

perioperative thermal disturbance(due toimpaired thermoregulation and coldenvironment)

Heat transferred from p`t to environment:radiation > convection >>conduction &evaporation


13/36

Patterns of intraoperative hypothermia

Phase I:

Initial rapid decrease

Phase II :

Slow linear reduction

Phase III:Thermal plateau

33

34

35

36

37

38

0 1 2 3 4 5 6


14/36


1. Initial rapid decrease heat redistribution

decreases 0.5-1.5 during 1st hr Tonic thermoregulatory vasoconstriction that

maintains a temperature gradient between the coreand periphery of2-4 is broken

The loss of heat from the body to environment islittle

Heat redistribution decreases core temperature, butmean body temperature and body heat contentremain unchanged


15/36


2. Slow linear reduction

decreases in a slow linear fashion for 2-

3hrs

Simply because heat loss >metabolic

heat production

90% heat loss through skin surface byradiation and convection


16/36


3. Thermal plateau

After 3-5 hrs,core temperature stops decreasing

It may simply reflect a steady state thatheat loss=heat production in well-warmed p`t

If a p`t is sufficiently hypothermic,plateau phasemeans activation of vasoconstriction to

reestablish the normal core-to-peripheraltemperature gradient

Temperature plateau due to vasoconstriction isnot a thermal steady state and body heatcontent continues to decrease even though

temperature remains constant


17/36

Regional Anesthesia

Regional anesthesia impairs both

central and peripheral thermoregulation

Hypothermia is common in patients

given spinal or epidural anesthetics


18/36

Thermoregulation

All thermoregulatory responses are neurally

mediated

Spinal and epidural anesthetics disrupt nerveconduction to more than half the body

The peripheral inhibition of thermoregulatory

defense is a major cause of hypothermia

during RA


19/36

RA also impairs the central control of

thermoregulationThe regulatory system incorrectly judges theskin temperature in blocked areas to beabnormally high

It fools the regulatory system into toleratingcore temperatures that are genuinely lowerthan normal without triggering a response

The thermoregulatory systems incorrect

evaluation of skin temperature in the blockedarea


20/36

Undetected hypothermia

The core temperature is rarely

monitored by medical personnel duringspinal and epidural anesthesia

Patients usually do not feel cold


21/36

Heat Balance and Shivering

Initial hypothermia (Phase I)

Redistribution of heat from core to periphery

Primarily caused by peripheral inhibition of

tonic thermoregulatory vasoconstriction

Although the vasodilatation ofAV shunts is

restricted to the lower body, the mass of thelegs is sufficient to produce substantial core

hypothermia


22/36

Subsequent hypothermia (Phase II)

Loss of heat exceeds production

Patients given SA or EA cannot reestablishcore-temperature equilibrium becauseperipheral vasoconstriction remains impaired

Hypothermia tends to progress

throughout surgery


23/36

Shivering

Occurs during spinal and epiduralanesthesia

Disturb patients and care givers butproduced relatively little heat because itis restricted to the small-muscle masscephaled to the block

Treated by warming surface of skin oradministration of clonidine / meperidine


24/36

Consequences of Hypothermia

Advantages

Provide substantial protection against

cerebral ischemia and hypoxia

Slows the triggering of malignant

hyperthermia and reduce its severity

Appear to facilitate recovery and reduce

mortality from septic ARDS


25/36

DisadvantagesWound infection---the most common

serious complication, due to

Impaired immune function decreased cutaneous blood flow

protein wasting

decreased synthesis of collagen


26/36

Coagulopathy

Hypothermia reduces platelet function and

decreases the activation of the coagulation

cascade From in vitro studies, it increased the loss of

blood and the need for allogenic transfusion

during elective primary hip arthroplasty

Just 1.5 of core hypothermia triples the

incidence ofVT and morbid cardiac events


27/36

Drug metabolism

Mild hypothermia decreases the metabolismof most drugs

Propofol ---during constant infusion, plasmaconc. is 30 percent greater than normal

Atracurium---a 3 reduction in core temp.increase the duration of muscle relaxation by

60 percent Significantly prolongs the postoperative

recovery period


28/36

Thermal comfort

Patients feel cold in postoperative

period, sometimes rating it worse than

surgical pain

Shivering occurs in ~40 percent of

unwarmed patients who are recovery

from GA


29/36

Treating and Preventing

Intraoperative HypothermiaPreventing redistribution hypothermia

The initial reduction in core temperature

is difficult to treat because it result fromredistribution of heat

Prevent by skin-surface warming

Peripheral heat content Temperature gradient

Redistribution of heat


30/36

Airway heating and humidification

Less than 10% of metabolic heat is lost

through respiratory

Two thirds of heat in humidifying

inspiratory gases

Passive or active airway heating and

humidification contribute little to thermal

management


31/36

Intravenous fluids

1L of IV fluids at ambient temperature or

1 unit of refrigerated blood decreases

the mean body temperature 0.25

Heating fluids to near 37 helps

prevent hypothermia and is appropriate

if large volumes are being given


32/36

Cutaneous Warming

The skin is the predominant source ofheat loss during surgery, mostly by

radiation and convection Evaporation from large surgical

incisions may be important

An ambient temp. above 25

isfrequently required, but this isuncomfortable for gowned surgeons


33/36

Heat loss can be reduced by covering theskin( with surgical draps, blankets, or plastic

bags)

Insulator

Forced-air warming

Typically, forced-air warming alone or

combined with fluid warming is required to

maintain normal intraoperative core temp.


34/36

The Relative Effects of Warming Methods on Mean Body

Temperature.


35/36

Conclusions

Temperatures throughout the body are

integrated by a thermoregulatory system

General anesthesia produces marked, dose-dependent inhibition of thermoregulation to

increase the interthreshold range by roughly

20-fold

Regional anesthesia produce both peripheral

and central inhibition


36/36

The combination of anesthetic-inducedthermoregulatory impairment and exposure to

cold operating rooms makes most surgicalpatients hypothermic

The hypothermia initially results from aredistribution of body heat and then from an

excess of heat loss Perioperative hypothermia is associated with

adverse outcomes, including cardiac events,coagulopathy, wound infections

Unless hypothermia is specially indicated, theintraoperative core temperature should be

above 36

Documents

tanda hipertermi