Hypothermia, Electro-anesthesia & Acupuncture

MUDASIR BASHIR MVSC SCHOLAR

Hypothermia, Electro-anesthesia & Acupuncture

Shongsir Warson Monsang

Ph. D, Scholar

Hypothermia

• Artificially produced in entire body or portion of body such as heart and head

• Greatest usefulness in surgery of heart and CNS (Swan et al. 1953)

“ heat loss exceeds heat production”

Principle

Body temp. falls ↓

Decreased metabolism ↓

Decreased need of O 2

Oxygen uptake reduced by 50% @ 30ºC & 65% @ 25ºC

Bigelow et al.(1950)

Heart ,brain ,liver (vital organs) can survive at low temp. for a long period when deprived of blood supply

Small lab animals can be cooled to below 0ºC

Neonates, very lean animals & geriatric animals are @ greater risks

Control of shivering is necessary to induce hypothermic state quickly

Shivering

Imp. mechanism in protection against cold Induced by ↑ temp. gradient b/w cold

receptors in the skin & centers in the hypothalamus

Hypertonicity of skeletal muscles – cause ↑ Metabolism /Heart rate / Resp. rate

Prevented by deep anaesthesia or light anaesthesia with curarization or tranquilization (phenothiazine )

Methods of whole body cooling

1. Surface cooling By immersing the unprotected body in ice

water or placing in mattress via which water is circulated

Hyperventilation maintained throughout procedure to keep blood pH on alkaline side

No anaesthesia needed below 28ºc Cooling stopped when approx. ⅔ of desired

temp. fall is accomplished

2. Body cavity cooling

By pouring cold saline soln. into the open thoracic cavity (Blades and Pierpont, 1954)

Disadvantage

•Slow process

•Requires large volume of saline soln.

3. Extracorporeal cooling

By running blood from a cannulated artery via a heat exchanger

Cold tap water is used as a cooling medium

Heparin used to prevent thrombosis

Used to lower brain temp. below normal body temp

Disadvantage

Hemolysis Interference with blood coagulation

mechanism Thrombosis

Advantage Best control over body temp. Rewarming carried out quickly & efficiently by

running water through heat exchanger

Factors/reasons for hypothermia Anesthetic drugs - relaxing muscles

Evaporation from skin surface has cooling effects on body

Adm. of room temperature fluids

Cold gases inspired

Body cavity opened & internal organs exposed to ambient temperature

Hazards of hypothermic anesthesia

The circulatory system The skin & internal organs The metabolism

1. The circulatory system ↓ BP , ↓ C.O , ↓ heart rate( depn.

of SA node & bundle of His) ↑ Peripheral vascular resistance

Prolonged PR interval , ↑ST interval ,spreading of QRS complex (ECG)

Contd.

Blood changes ↑clotting time,↓platelets no. hemoconcentration with sludging ↓ Eosinophil , leucocyte count & Mean

corpuscular Hb. concentration (MCHC)

Knocker (1955) – damage to liver, kidneys & adrenal glands in dog @ 25ºC for hours

Benefits/Uses of hypothermia

Surgery of heart & great vessels ,brain & spinal cord

Treatment of shock ,stroke ,cerebral & spinal contusion

Prevention of brain damage following severe hypoxic episode

Repair of cardiac anomalies & removal of heartworms in dogs (use not widespread)

Induction of hypothermia in dog Phenothiazine tranquilizer given I/V as

preanaesthetic

Thiobarbiturate (G.A); Endotracheal catheter is inserted

Inhalant anaesthetic for maintainance Slow I/V drip of RL / Dextrose 5% & muscle

relaxant given

Controlled respiration is started

Placement/ positioning

Animal positioned in sink /bathtub/container with head above water

Electronic thermometer is placed in eosophagus @ heart level & rectum

Electrodes of ECG machine attached to feet – constant monitoring required

Ice water used for rapid cooling

Contd

Dog is removed from bath before reaching of desired temp.

After removed, place in inactive heating pad during operative period

Rewarming started at start of surgical wound closure

Prevention/Treatment of hypothermia First – placing pads/blankets

with circulating warm water or air

Supplement – warm water bottles and bags

Warm s/c or i/v fluids approx. 98-99ºF

Water filled balloons or latex gloves used instead of bottles

Towels or blankets warmed in dryer and wrapped around patient to trap heat

Rewarm water bottle frequently

Cautions Electric heating pad should not be used

• Severe thermal skin burn may occur

• Skin sloughing can be serious complications