Hypothermia by Dr.jeyakrishnan

7/30/2019 Hypothermia by Dr.jeyakrishnan

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HYPOTHERMIA

Dept of AnaesthesiologyPSG IMS&R

DR.P.JEYAKRISHNAN


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Questions

Normal physiology ?

Core body temperature ?

Monitoring Sites ?

Complications associated withhypothermia ?

Prevention?


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HYPOTHERMIA

Normal human body temperature in adults is maintained

around 36.537.5 C (98100 F)

Hypothermia is defined as core body temperature below

35.0 C (95.0 F)

It is subdivided into four different degrees:

mild 3235 C (9095 F)moderate 2832 C (8290 F)

severe 2028 C (6882 F)

profound < 20 C (68 F)
http://en.wikipedia.org/wiki/Normal_human_body_temperaturehttp://en.wikipedia.org/wiki/Normal_human_body_temperature


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Introduction

Body heat is lost through: Radiation (40%)

Convection (30%)

Evaporation (30%) - 20% is lost through the skin

- 10% through respiration of which 8% is throughevaporation

2% through warming the inhaled air

Conduction (minimal)


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Physiology of TEMPERATURE CONTROL

Hypothalamus modulates temperature information from skin, central and neuraltissues

Two types ofthermostatic neurons are located in the hypothalamus

One is affected by increased temperature, the other by decreased

temperature of the blood.

Descending pathways connect mainly to cardiovascular and respiratory

centres in the brain stem and initiate heat loss or heat production

responses in an attempt to bring temperature back within normal levels.

A risein the temperature of the blood causes an increase in the respiratory

rate, peripheral vasodilation and increased perspiration.

Decreasedtemperature causes conservation of heat by vasoconstriction

and by stimulating shivering.

Heat production is also raised by the increase of the thyrotropic function of theanterior pituitary and a resulting increase in thyroid activity.


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Thermal compartments

core thermalcompartment

highly perfused tissues

head, neck and the trunk

evaluated in pulm.arterynasopharynx, tympanicmembrane,dist.oesophagus

rectum

Tympanic membrane ideal *

Periph thermal

compartment

axilla

Skin

oral

bladder


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PHYSIOLOGIC EFFECTS OF HYPOTHERMIA

Metabolic effects

decrease in O2consumption and C02 production

Serum glucose levels are increased due to catecholamine release and a decrease in insulinproduction.

Metabolic acidosis occurs resulting in an increase in potassium levels

Central nervous system

CBF is reduced, O2consumption is reduced

MAC of volatile agents is decreased therefore a smaller concentration is needed and recovery

may be delayed.

Blood

decrease in plasma volume with an increase in viscosity

Aggregation of platelets decreases their function

Respiratory system

Shivering increases oxygen consumption 3-5 times

pulse oximeter measurement becomes difficult & unreliable

There is respiratory depression due to decreasing ventilatory drive.

Hypoxic vasoconstriction is impaired resulting in an increase in ventilation/perfusion mismatchand hypoxaemia.

The O2dissociation curve is shifted to the left decreasing oxygen delivery to the tissues.


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PHYSIOLOGIC EFFECTS OF HYPOTHERMIA

Cardiovascular system

induce ventricular ectopic beats leading to unresponsiveventricular fibrillation or to bradycardia leading tounresponsive asystole.

Vasoconstriction increases systemic vascular resistanceincreasing after load and myocardial oxygen demand,causing tissue hypoxia and acidosis

Urinary system

Renal blood flow and GFR are decreased.

Decreased Na reabsorption causes impairment of urine

concentration leading to cold diuresis and hypovolaemia.Liver

liver perfusion is diminished slowing down liver function andthe metabolism of drugs


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Why during anaesthesia?Both general and regional anesthesia affect thermal

homeostasis by blunting central thermoregulationdefence mechanisms

reducing the sympathetic tone with inhibition of peripheral

vasoconstriction and consequent redistribution of bodyheat from core to the peripheral compartment

Loss of shivering

Exposure to a cold operating-room environment

Operations involving open body cavities


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Reasons for INTRA-OPERATIVE HEAT LOSS

Patient factors

There is loss of movement, a reduced capacity to shiver, exposure and an

increased surface area with increased evaporation. The introduction of coldfluids, either intravenously, as peritoneal lavage also

contributes to heat loss.

Infants have an increased surface area to body mass ratio and therefore

lose heat more rapidly than adults. Patients with burns, severe injuries and

those who are hypothyroid are predisposed to greater heat loss, as are the

elderly who have decreased sympathetic activity.

Anaesthetic factors

Dry anaesthetic gases cause extra heat and moisture loss.

Many anaesthetic drugs, such as thiopentone and halothane, cause

vasodilatation. Opiates decrease vasoconstriction and volatile agents

interfere with thermoregulation in the hypothalamus. Subarachnoid blocksalso cause vasodilatation, inactivate muscular movement and block sensory

input to the thermoregulatory centre.

Surgical factors

Prolonged exposure of abdominal organs, abdominal lavage and bladder

washouts all lead to a significant drop in body temperature.


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When to measure core temperatures? Core temperature usually decreases by 1.8*C in the first 40

minutes following induction of anaesthesia. Hypothermiaat this stage results mainly from internal re-distribution ofheat owing to anaesthetic-induced vasodilation in theperipheral tissues

core temperature perturbations during the first 30 minutesof anaesthesia are difficult to interpret, and measurementsare thus not required

Core temperature should be monitored in patients given

general anaesthesia for more than 30 minutes

Core temperature should be measured in patientsundergoing Major procedures under regional anaesthesia.


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Complications of hypothermia

CVS

higher prevalence of myocardial ischaemia andventricular tachycardia

tachycardia, hypertension, systemicvasoconstriction

imbalance between myocardial oxygen supplyand demand due to increased levels of circulatingcatecholamines

Shivering after regional anaesthesia increases O2demand can affect patients with borderlinemyocardical perfusion


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Complications contd..

Blood

impairing platelet function

Impairing Clotting factor enzyme functionThis was seen frequently during colo-rectal and

hip replacement surgery where blood

transfusion is needed

hypothermia + transfusion -> coagulopathy


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Complications contd

Wound Infection

Facilitates surgical wound infection by

peripheral vasoconstriction with a significantreduction of subcutaneous oxygen tension

directly impairs the immune function

inhibiting T-cell mediated antibody production

whose activity also depends on oxygen supply


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Complications contd.

OTHER complications :

Thermal discomfort for patients

Prolonged action of drugs used eg: relaxants

Delayed discharge from PACU

May be more prone to DVT due to peripheralvasoconstriction & venous stasis


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Prevention and Management of

hypothermiaPrevention is better

What can we do ?

1)Pre warming patients skin surface prior to surgery reduces tempgradient between core & peripheral compartment ie:minimizes re-distributive hypothermia

2)By increasing the heat content in the peripheral compartment byadministering vasodilators

Oral nifedipine ( 20 mg 12 hrs before surgery

followed by other 10 mg 1 hr before inducing anesthesia)has been reported to significantly reduce redistributive

hypothermia in surgical patients

Vassilieff N et al. Effect of premedication by nifedipine on intraoperative hypothermia.

AnnFrancaises de Anesth et de Reanim 1992; 11: 484-7


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hypothermia

Preventing radiation of heat by maintaininghigher temp in OT !

Passive insulation

surgical draping

cotton blankets

metallized plastic covers

-efficiency of this system is directly

proportional to the covered surface area


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hypothermia

Active cutaneous warming systemsforced-air warming devices are the most

commonly used and efficient ones

Provide heat by convection and prevent loss byradiation

they increase core temperature by almost

0.75C/hour


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hypothermia

Resistive heating blankets

Circulating water mattresses

Radiant warmers


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Aural probe


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Forced air warmer


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Radiant warmer


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Space blanket resistive blanket


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hypothermia

Internal Warming Systems

Intravenous Fluid Warmers*One litre of crystalloid solution or a unit of refrigerated blood decrease body

temperature by about 0.25C

airway heating and humidification- HME filters useful to preserve cilial function and prevent bronchospasm

OTHERS : peritoneal dialysis / A-v shunt

cardiopulmonary bypass

Effective but Cannot be routinely used


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I.V Fluid warmers


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Foley probe skin probe Oesophageal rectal


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Conclusion

Perioperative hypothermia seldom monitored is afrequent finding in surgical patient increasing theincidence of cardiovascular,hemorrhagic & infectiouscomplications

Hypothermia prevention is associated with significantreduction of surgery-related costs by reducing theincidence of complications and accelerating hospitaldischarge

Children, Elderly & Hypothyroid patients are the mostvulnerable and affect post-anesthesia outcomes


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Take home points

Core temperature should be monitored inpatients given GA for more than 30 minutes

Core temperature should be measured in allpatients undergoing Major procedures under

RA

best monitoring site should be chosen basedon the characteristics and site of the surgical

procedure Forced air is the most effective non-invasive

warming method


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References Best Practice & Research Clinical

Anaesthesiology Vol. 17, No. 4, pp. 569581,2003 doi:10.1016/S1521-6896(03)00048-X

HYPOTHERMIA AND TEMPERATUREREGULATION CONSIDERATIONS DURING

ANESTHESIA by Marcos Daz, D.D.S.

Clinical complications, monitoring and

management ofperioperative mild

hypothermia: anesthesiological featuresMarta Putzu, Andrea Casati, Marco Berti,

Giovanni Pagliarini, Guido Fanelli


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THANK YOU


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Lets keep our patients warm & cozy !

Hypothermia by Dr.jeyakrishnan

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Transcript of Hypothermia by Dr.jeyakrishnan