Hypothermic Anesthesia
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Hypothermic Anesthesia






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Hypothermic Anesthesia Hypothermic Anesthesia Presentation Transcript

    • Fall in temperature
    • Decrease in body metabolism
    • Decreased oxygen requirement of body tissues & organs
    • E.g.
    • In dog O2 requirement decreased to 50% at 30◦c & 65% at 25◦c.
    • Metabolic rate of isolated slices of heart was reduced by 90% at 10◦c.
    • Potassium arrested heart at 37◦c utilizes
    • 4 times glycogen and produces 3 times lactic acid as by heart at 17◦c.
    • However O2 consumption varies for different organs at a particular temperature.
    • Conclusion ;- vital organs (liver, brain, heart) can survive at low temperature for considerable period when deprived of all or a portion of blood supply.
  • Level of hypothermia;
    • In Small lab. animals recovery rate was 80%-100% just above freezing point with cardiac & respiratory arrest for 1 hr.
    • Dog survived cooling to 1.5◦c on pump oxygenator
    • For induction of quick hypothermia shivering is to be controlled by deep anesthesia or light anesthesia with tranquilization.
    • Moderate hypothermia in dog produced rectilinear decrease in anesthetic dose (MAC) for cyclopropane , diethyl ether, fluroxene, halothane, & methoxyflourane.
    • Reduces concentration of anesthetic required to produce apnea.
  • Methods of producing whole body hypothermia
    • 1) Surface cooling.
    • 2) Body cavity cooling.
    • 3)Extracarporeal method.
    • Surface cooling :- animal directly imersed in ice cold water or kept in cold matress. It needs hyperventilation to keep blood pH (7.2-7.4) on alkaline side to prevent cardiac arrhythmias & fibrillation.
    • Below 28◦c no anesthetic only ventilation required.
    • Cooling stopped when approx. ⅔ of desired temp. fall is accomplished
    • Body cavity cooling :- pouring cold saline water into open thoracic cavity.
    • Extracorporeal method :- running blood from a cannulated artery via a heat exchanger with tap water as a cooling medium with the help of a pump.
    • Used to lower brain temp. below that of general body temp. by cannulating carotid artery to 14◦c while body temp. remains at 31-32◦c.
    • Adv: -
    • Best control over body temp. & quick rewarming.
    • Disadv:-
    • Hemolysis.
    • Interference with blood coagulation.
    • Thrombosis.
  • Uses :-
    • Surgery of heart, great vessels, brain & spinal cord.
    • Treatment of shock, stroke, cerebral & spinal contusion preventing brain damage from severe hypoxic episode.
    • Removal of heartworms & repair of cardiac anomalies in dog.
  • Limitations of hypothermic anesthesia
    • 1) cardiac crisis ;-
    • Fall of B.P may be drastic due to decreased cardiac output & H.R and increased peripheral resistance.
    • In dog cardiac crisis occur b/w 23 & 15◦c characterised by intense bradycardia , ventricular extra- systoles & ventricular fibrillation .
    • Hypercapnia , Acidemia,& myocardial hypoxia also lead to ventricular fibrillation , Prevented by adequate ventilation or by some cardioplegic solutions.
    • Prolonged PR interval , ↑ST interval ,spreading of QRS complex (ECG)
    • 2) Prolongation of clotting time.
    • 3) Reduced platelet count.
    • 4) Decreased Hb conc.
    • 5)Decreased WBC count.
    • 6) Decreased MCHC.
    • 7) Prolonged hypothermia can lead to CV colapse, depletion of cerebral energy stores.
    • 8) Damage to liver , kidney & adrenal glands in dog at 25◦c for hours.
    • Induction of hypothermia in dog
    • Phenothiazine tranquilizer given I/V as preanaesthetic
    • Thiobarbiturate (G.A); Endotracheal catheter is inserted
    • Inhalant anesthetic for maintenance
    • 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 esophagus @ heart level & rectum
    • Electrodes of ECG machine attached to feet – constant monitoring required
    • Ice water used for rapid cooling
    • 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
    • Rewarmin g:-
    • 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
    • Principle :- electric stimulation of brain activate opiate or non-opiate pain controlling pathway or both thus producing analgesia.
    • Clinical trials in vety practice first performed by
    • Sir Frederic Hobday in England in 1932.
    • Used in situations requiring prolonged anesthesia.
    • Electrodes operating at A.C (35-50 mAmp & 40V) or D.C or in combination are applied to head.
    • Individual variations are adjusted.
    • Characterized by convulsions on induction , profuse salivation & hyperthermia.
    • Clotting time , ESR , Hb conc. , PCV , total WBC count or DLC do not differ much.
    • B.P rises sharply & then gradually falls to near normal level.
    • No effect on oxygen content of blood.
    • Glucose level rises.
    • Difficult to assess depth of anesthesia. Muscle relaxation may vary from adequate to poor and surgical pain may cause body movements in apparently unconscious animal.
    • Photo motor reflexes are probably best means to determine depth.
    • Quick recovery following removal of current by slight stimulus & animal resumes all normal activities.
    • Merits:-
    • Economy and immediate recovery
    • Demerits:-
    • Brain lesions demonstrated.
    • Skin burns.
    • Severe stress.
    • Non-availability of suitable equipments and standardized technique in clinical application.
  • Acupuncture analgesia
    • Acus – needle; Punctura – to prick
    • Current meaning – any type of stimulation (Acupressure, moxibustion, heat, cold, ultrasound, aquapuncture, electro stimulation, implantation and laser) at acupuncture points to produce analgesia or to cure certain diseases.
    • Used increasingly in man & animals for producing analgesia.
    • Used in conjunction with Western treatments- surgery or pharmacological therapy
    • History :-
    • Existed in India 7000 years ago
    • Huang Ti Nei Ching (Yellow emperors classic of internal medicine) – oldest document
    • Integral part of Traditional Chinese Medicine- used more than 2500 years to treat diseases and relieve pain
    • 1921 – Ban in China
    • 1960s – Maoists regime – reintroduction
    • Acupuncture points
    • Points are called ‘ Xue’ – means ‘cave’ or ‘hole’.
    • Eastern countries- specify points different names describing their location or function e.g. ‘wei shu’ means point associated with stomach & is used for gastric diseases but are confusing.
    • Western acupuncture practitioners – identify points by number and capital letter abbr. of the meridian to which they belong e.g. BL/UB, LI, ST, SP, GB, etc.
    • Acupoints differ in their physiological behavior, electrical response,& therapeutic role.
    • Reflect various organs on surface of body.
    • Small as a pin head.
    • Referred as areas of hypersensitivity & lowered electric resistance.
    • Located on imaginary horizontal lines k/as MERIDIANS which have internal connections with the organs from which they get their name.
    • 12 organ meridians like LU, LI, ST, SP, H, SI, UB/BL, K, P, TW, GB, LIV & 2 non-organ meridians GOV(governor vessel) and COV(conception vessel) in large animals.
    • 365 classic points located along the meridians.
    • Acc. to Chinese vital energy “chi” flow through these pathways.
    • Exact location of points is important – small deviations nullify the response (classic theory)
    • Acupuncture points are cutaneous areas with high conc. Of nerves ,mast cells, capillaries ,and venules & lower electrical resistance than surrounding areas
  • Point location:-
    • Located in small hollow or depression on skin surface
    • Are tender compared with surrounding area & response (discomfort) elicited with deep palpation
    • Subjective roughness or stickiness appreciated when brushed slightly with finger
    • Clinically used points in most species are believed to be 3 – 15 mm below skin surface
    • Each point has sp. functions and indications for use
    • Stimulation of site specific acupoints induces spatially restricted analgesia.
    • Each point has sp. functions and indications for use.
    • Stimulation of site specific acupoints induces spatially restricted analgesia
    • Yang organs (hollow organs of the body)
    • ST = Stomach
    • SI = Small intestine
    • LIV = Large intestine
    • GB = Gall bladder; bile ducts
    • BL= Urinary bladder; ureter & urethra
    • TH = Triple heater
    • Yin organs (solid organs of the body)
    • LIV = Liver
    • SP = Spleen / Pancreas
    • KI = Kidney
    • HT= Heart
    • LU= Lungs
    • PC = Pericardium
    • Mechanism of action
    • Comprehensive mechanism theory (Pomeranx & Stux) :-
    • 3 mechanisms to A/analgesia
    • 1. A/ needles stimulate type 1 & 11 afferent nerves or A-∂ fibres
    • send impulses to AL-tract of spinal cord
    • Pain blocked presynaptically by release of enkephalin & dynorphin
    • Prevent pain messages from ascending in the spinothalamic tract
    • 2 A/ stimulate mid-brain structures by activating cells in periaqueductal gray matter & raphae nucleus
    • send descending signals through DL-tract release of monoamines NE & serotonin in spinal cord
    • Nts. inhibit pain presynaptically & postsynaptically by reducing transmission of signals through spinothalamic tract
    • 3. Stimulation of pituitary-hypothalamic complex
    • systemic release of β -endorphin into blood stream from pituitary gland accompanied by release of ACTH
    • Types of acupuncture
    • 1. Dry needle acupuncture (invasive methods - a/needle, electro-acupuncture chronic intradermal needle insertion),
    • 2. Wet needle acupuncture (aquapuncture / non invasive – Aquapressure, Transcutaneous electrical stimulation (TENS), Moxibustion & various stimulating patch and pellets)
    • Electrical stimulation or electro-acupuncture
    • Developed as alternative to manual stimulation of acupuncture points
    • Advantages
      • Less painful than manual stimulation
      • Requires less practitioner time spent with patient
      • Provides better analgesia
    • Facilitates standardization
    • Can be used in balanced anaesthesia to reduce the dose of sedatives/ analgesic & anaesthetics
    • Good analgesia in high risk patients without producing CNS & resp. depression ,bradycardia, hypotension
    • Excellent postoperative pain relief.
    • Fast postoperative recovery of appetite & gut and bladder function.
    • Fast postoperative wound healing with minimal infection.
    • In c-section no depressive effects on the fetus.
    • Suitable for prolonged surgery (up to 10 hrs).
    • Simple & inexpensive, less hemorrhage.
    • Electroacupuncture with high-frequency stimulation (100-200 Hz)
      • Rapid onset analgesia; cannot be blocked by naloxone
      • Mediated by NE, serotonin & dynorphins
    • Low-frequency (2-4 Hz) & medium-frequency stimulation (15-30 Hz)
      • Analgesic effect reversed by naloxone
      • Mediated by enkephalin & endorphins
      • Tendency to accumulate; last at least 1 hr after treatment ceases
    • Disadvantages :-
    • Needs very good restraint
    • Long induction period (10-40 min )
    • Variable degree of analgesia
    • Maintenance of sensation to touch ,pressure & traction
    • Poor relaxation of abdominal muscles (cause ballooning of viscera )
    • Nausea ,vomiting & shock
    • Maintenance of reflexes to sight , sound & fear in conscious animals
    • Intrathoracic surgery can’t be performed
    • Types of operations performed under EAA in dogs
    • caesarian section
    • OH
    • Abdominal laprotomy
    • Gastric & intestinal surgery
    • Nephrectomy
    • Splenectomy
    • Umbilical hernioplasty
    • Removal of mammary & skin tumors
    • Ear cropping
    • Craniotomy
    • Open reduction & repair of long bone fractures
    • Types of operations performed under EAA in horse/cattle/sheep/pig
    • Castration
    • Orchidopexy
    • Reposition of prolapsed uterus
    • Surgery of anal & vaginal region
    • Relief of dystokia
    • Surgery of esophagus & rumen
    • Repair of naval & umbilical hernia
    • Surgery on bladder & urethra
    • Orthopedic surgery
    • Equipment needed:-
    • 1. Acupuncture needles -22-26 gauze for LA
    • 26-30 gauze for SA
    • Inserted at acupoints to correct depth, taped & sutured firmly at position & connected in pairs to the output socket of an acupuncture electro-stimulator.
    • Each pair of electrode should be on same side of the spinal cord
    • 2 . Acupuncture stimulators:- shd have the following characteristics;
    • strength ,portability ,battery operated ,output for atleast 6-8 electrodes
    • 3. A handheld unit – to locate & stimulate acupuncture & trigger points using 10 Hz ,1-25 v , &1-50 mA.
    • 4 . A multiple electronic acupunctoscope
    • Detects acupuncture& auricular points
    • Points to be considered while selecting acupoints for surgery;
    • Points shd be near to operative site & shd lie on meridian traversing the area.
    • Certain points not needled in pregnant animals bcoz of possible risk of abortion.
    • All asceptic precautions shd be taken.
    • Penetration of needle to small blood vessels not of significance.