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41.Temp monitoring.ppt
- 2. INTRODUCTION Mammals are homeothermic Require nearly constant body temparature Deviation lead to metabolic derrangments
- 3. Anaesthetic induced inhibition of thermoregulation combines with exposure to cold O.T. make most unwarmed pt. hypothermic
- 4. In recent years studies shows that mild hypothermia (1-2 deg. Cen.) 1-triples morbid cardiac outcome 2-triples surgical wound infection 3-increase surgical blood loss
- 5. NORMAL THERMOREGULATION Processing of thermoregulatory information occurs in 3 phases 1. afferent thermal sensing 2. control regulation 3. efferent response
- 6. AFFERENT INPUT Warm receptors – increase firing when tem increases. Information travel by unmylinated c fibers. C fibers also transmit pain sensation so intense heat cant be differentiated by pain. Cold receptor – increase firing when temp. decreases. Cold signals travel by A delta nerve fibers. Afferent from skin, deep abdominal tissue & thoracic tissue go to ant. Spinothalamic trunk of spinal cord to hypothalamus.
- 7. CENTRAL CONTROL Primarily by hypothalamus A response intensity no longer increase with further deviation in core temp. identifies the maximum intensity. Body determines absolute threshold temp. by mechanism which is mostly mediated by –norepinephrine -dopamine -5ht -prostaglandine -neuropeptides
- 8. Threshold varies with – daily (circidian rhythum) monthly in women exercise food intake infection hypo/hyperthyroidism anaesthesia&other drugs Large frection of input controlling behaviour response is derived from the skin surface.
- 9. The “ interthreshold range “(Core temp. not triggering autonomic thermoregulatory response) is only 0.2 C This range is bounded at upper end by sweating threshold and at lower end by vasoconsriction Both threshold are 0.3 to 0.5 C are higher in females than males.
- 10. EFFERENT RESPONSE 1. RESPONSE TO COLD:- First cutaneous vasoconstriction – decreases heat loss done through convection and radiation. Nonshivering thermogenesis- increases heat production without producing mechanical work. skeletal muscle and brown fat tissue are the major sources of nonshivering thermogenesis. most imp in infants. Control primarily by norepinephrine release at nerve terminals.
- 11. 2. RESPONSE TO HEAT:- sweating- Mediated by post ganglionic cholinergic nerves. It is active process prevented by nerve block and anticholinergic drug. Active vasodilatation- it is mediated by yet to be identified factor release from sweat glands. it requires intact sweat gland so it is also inhibited by nerve block.
- 12. Sustained shivering :- increase metabolic heat production 50%to 100% Shivering does not occure in new born Centrally mediated shivering is “waxing and wanning” type 4 – 8 cycles/min.
- 13. 3. BEHAVIOURAL CONTROL:- assuming position that oppose skin exposure modifying environmental temp. voluntory movement covering the skin
- 14. Temp. regulation diminished by :- -new born -advance age -medication -decrease muscle mass -neuromuscular disease -anaeshesia induced
- 15. Development of hypothermia during G.A. HEAT TRANSFER in FOUR ways radiation convection conduction evaporation
- 16. Radiation Major type of heat loss in most surgical pt. all surfaces above absolute zero radiate heat. similarly all surfaces absorb radiant heat from surrounding environment. heat transfer by this mechanism is proportional to the fourteenth power of the absolute temperature differences between the surfaces.
- 17. (2) Convection: this is the second most common mechanism by which the heat is transferred from patient to environment. there is still air adjecent to the skin that serves as insulator when this disturbed by air currant isolative property diminish heat loss increases
- 18. it is proportional to square root of air speed. convectional loss is substantialy increases in OT with laminar flow.but this loss prevented by drapping that provide considrable thermal insulation.
- 19. (3) condution: Negligible during Sx. Proportional to temp difference between the adjecent surfaces and strength of insulation seperating them. In O.T Patient is in direct conatct of foam pad, covering most of O.T table so heat loss is minimum.
- 20. (4) Evaporation : Sweating increases evaporating loss but is rare during anaesthesia. In absence of sweating skin evaporation is < 10% of metabolic heat production in adults. But in Children this loss is high especially in premature who may evaporate fifth of metabolic heat. - there is minimal loss of heat from Respiratory Systerm.
- 21. Evaporation inside a surgical wound can contribute substantially to total heat loss. GA leads to increase the interthreshold range about 20 fold from its normal value 0.2 C to 2 – 4
- 22. (B) patterns of intraoperative hypothermia : three stages 1: initial rapid decrease in core temperature 2: linear slow decrease in core temperature 3: stabilization of temparature
- 23. initial rapid decrease in core temperature in first hour after anaesthesia vasodilation by direct peripheral action of volatile Anaesthetics inihibit tonic thermoregulatory vasoconstriction this both leads to core heat to flow peripherally ( heat redistribution ) core temparature decrease (to maintain limb temp.) also anaesthetic decreases metabolic rate by 20 to 30%
- 24. second linear slow decrease in temp. next 2 to 4 hrs linear decrease in core temp. occur due to heat loss exceeding metabolic heat production
- 25. Third plateau phase after 3to4 hrs of anaesthesia core temp. reaches to plateau and remains virtually constant. this is by thermoregulatory vasoconstrictio n triggered by core temp.33to35 degree C this leads to redistribution of metabolic heat to core ,that maintains the temp.
- 26. NEURAXIAL ANAESTHESIA Both spinal and epidural anaesthesia causes vasodilatation and decreases shivering thresholds. Regional anaeshesia blocks all thermal input from blocked regions. Primarily cold input. So brain interpret it as relative leg warming. As skin in an imp input for thermoregulatory control system this will decreases threshold for vasoconstriction and shivering.
- 27. This reduction is propotional to the number of segments blocked. Even if thermoregulatory defenses once triggered are less effective than usual during regional anae. Also neuraxial anae. Is frequently supplemented with sedative medications in which except midazolam all significantly hamper thermoregulatory control. Core hypothermia during regional anae. May not trigger a perception of cold bcoz thermal perception largely determined by skin rather than core tem.
- 28. During regional anae. Core hypothermia is accompained by a real increase in skin temp. that leads to Perception of continued or increase warmth accompained by autonomic thermoregulatory response including shivering. But as in GA in regional anae. The plateau after several hours of sx bcoz vasoconstriction is prevented by direct nerve blocks.
- 29. Shivering in regional anae. 4-8 cycle / min. Waxing and waning pattern Due to redistribution hypothermia This is normal thermoregulatory shivering. Treatment – inj. Tramadole 0.5 – 1 mg/kg -inj. Clonidine 1.5 – 2 µg/kg -inj. Mepiridine 0.5 – 1 mg/kg -inj. Ketanserine 10 mg -inj. Mgso4 30 mg/kg
- 31. BENEFITS 1. Protection against cerebral ischemia and hypoxia is provided by just 1˚c to 3˚c 2. benefit for acute MI also noted there is 8% reduction in tissue metabolic rate 3. Acute malignant hyperthermia is more difficult to trigger in mildly hypothermic tissue more over once its trigger the syndrome is less sever.
- 32. COMPLICATIONS 1. Blood loss increase: due to defect in platelet function and impaired enzymes of the coagulation cascade. 2. triples the incidence of wound infection: due to directly impairing immune function and triggering thermoregulatory vasoconstriction so decrease O2
- 33. 3. Post operative hypothermia some times felt by pt as worst part of hospital stay even worst than surgical incision. 4. post operative thermal discomfort leads to stress increase catecholamines increse HR and BP Morbid myocardial
- 34. 5. Drug metabolism decrease so duration of action of NDMR increase the onset of action time increase of neostigmine 20% MAC decreased of volaatile anaesthetics Plasma con. of propofol increase 6. Post anaesthetic recovery is
- 35. 7. Post anaeshetic shivering: - due to- thermoregulatory response -decrease sympathetic activity -uninhibited spinal reflexes - pain -pyrogen release - respiratory alkalosis
- 36. PERIOPERATIVE THERMAL MANIPULATION 1. Effect of vasomotor tone thermoregulatory vasodilatation causes initial core to peripheral redistribution of body heat. At core tem. Plateau vasoconstriction occur. Due to sufficient core hypothermia.
- 37. During post anaeshetic recovery Anaesthetic induced peripheral vasodilatation dissipates, So thermoregulatory vasoconstriction left unopposed, So impaires transfer of peripherally applied heat to core tem. Decrease peripheral to core transfer of heat so CORE WARMING DELAY
- 38. 2. Preventing redistribution hypothermia. Redistribution of heat in 1st hour of anaeshesia occur because core temp. > peripheral tem. So skin surface warming before induction of anaesthesia So increase body heat content So peripheral tissue temp.sufficiently increased So inhibition of tonic thermoregulatory vasoconstriction produces little redistrubutoion beacause heat can flow only down temp. gradient At least for 30 min.prewarming require.
- 39. 3. AIR WAY HEATING AND HUMIDIFICATION < 10% Of metabolic heat production is lost through the respi. Tract by heating of humidifying inspiratory gases. But humidification require 2/3 heat This are most effective in infant andchildren than adults Hydroscopic condenser humidifiers and heat and moisture exchanging filters (ARTIFICIAL NOSES)
- 40. 4. I.V FLUIDS 1 u of refrigerated blood or 1 litre of crystalloid solution administred at room tem. Decreases mean body tem. Appro. 0.25 ˚c. Fluid warmer little effective and should only when large amount of i.v fluid or B.T. is needed.
- 41. 5. CUTANEOUS WARMING Heat loss by skin surface is by radiation and convection and by evaporation from surgical wound . Easiest method of decreas cutaneous heat loss is to apply passive insulation to skin surface. INSULATORS 1. cotton blankets 2. surgical drapes 3. plastic sheeting 4. reflective composites
- 42. Single layer of each decrease heat loss appro. 30% with no difference among insulation type. so insulator choose should be cost effective. Cutaneuos heat loss is roughly propotional to surface area through out the body. Amount of skin surface is imp. Not the which area is insulated. Most common perianaesthetic warming system is forced air. The best forced air system transfer more than 30 w across the skin surface. Forced air usually maintain normothermia even during the longest operation. resistive heating (electric blanket ) is as effective as forced air but much less expensive. Carbon fire resistive heaters should be avoided because they frequently causes burns.
- 43. INDUCTION OF MILD THERAPEUTIC HYPOTHERMIA. Required in stroke / acute MI CPB TECHNIQUES: 1. Immersion in cold water – quicker but impractible in clinical set up Electrical activity transfer 2. administration of refreigerated saline.- Decreses body temp. 0.5 ˚c/ lit. Cant use in pt where fluid restriction require. 3. forced air cooling- easy but slows
- 44. 4. circulatory water mattresses – not appropiate 5. endovascuIar cooling – best way It includes heat transfer catheter usually inserted into the IVC Decreases temp. 4 ˚c/ hour Among with this combination of buspirone and mepiridine should be used which decreseas shivering threshold upto 34 ˚c without major side effects.
- 45. EFFECT OF HYPOTHERMIA ON DIFFERENT ORGAN GENERAL: BMR decreseas Body o2 demand decreases Toxic metabolites decreases Excitatory amino acids decreases Membrane stabilization occur So help in ischemic damage
- 46. BRAIN- Decreases CBF Functions well maintained untill 33 ˚c But consciousness lost at 28 ˚c Peripheral muscle tone increase, rigidity occurs at 26 ˚c Gag reflex and spinal reflexes remain intact untill appro. 25 c
- 47. 2. HEART HR increases Contractility increases C.O & B.P. decreases At temp. below 28 c ventricular irritability increases and electrical defibrillation becomes ineffective. Mild hypothermia decreases tissue damage in response to cardiac ischemia.
- 48. KIDNEY: RBF decreases Inhibition of tubular absorption Cold diuresis occur RESPIRATORY SYSTEM: At temp. 33c respi. Strength decreases but ventilatory co2 reflexes remains normal. HEPATIC: HBF and function decreases so metabolism of drug remain decreases.
- 49. HYPER THERMIA HYPER THERMIA ; due to 1. passive hyper thermia 2. malignant hyper thermia 3. fever :- infection mismatched B.T. blood in 4th ventricle allergic reaction Treatment: treatment of cause , antipyretics active cooling
- 50. THERMOMETERS Traditionally available mercury in glass thermometers are slow and cumbersome Electronic thermometers 1. thermistors 2. thermocouples They are – accurate inexpensive
- 51. SITES Core temp. is measured from tissue which are highly perfused in comparison to the rest of the body and whose temp. is uniform and high in comparison to rest of body. This are- 1.TYMPANIC MEMBRENE 2.NASOPHARYNX 3. LOWER END OF OESOPHAGUS 4. PULMONARY ARTERY
- 52. Core temp. also can be measured with reasonable accuracy from – 1. oral 2. axillary 3. rectal 4. bladder
- 53. THANK YOU