Nanette Wells, DNSc., CRNA, APN Regional Director of CRNA Services, MidWest, NorthStar Anesthesia

Transcription

1 Nanette Wells, DNSc., CRNA, APN Regional Director of CRNA Services, MidWest, NorthStar Anesthesia 1

2 Definition of hypothermia: Body temperature below 95 F / 35 C (ranges 34 36) Normal temperature is 98.6 F / 37 C Core temp 35 C to 37 C Peripheral tissue temp 31 C to 35 C Skin temp 28 C to 32 C Elderly normal is 0.5 C / 97.7 F or 36.5 C 2

3 Which statements are correct concerning perioperative hypothermia: Hypothermia develops with a characteristic pattern. Core temperature decreases o C during the first hour of surgery. The second phase of temperature loss is characterized by 2 or 3 h of a slower, linear, decrease in core temperature. The third phase of temperature loss is characterized by a rapid temperature decrease of 2-3 o C. 3

4 Which statements are correct regarding perioperative hypothermia: Hypothermia develops with a characteristic pattern. Core temperature decreases o C during the first hour of surgery. The second phase of temperature loss is characterized by 2 or 3 h of a slower, linear, decrease in core temperature. The third phase of temperature loss is characterized by a rapid temperature decrease of 2-3 o C. 4

5 How does perioperative hypothermia occur Develops with a characteristic pattern. Core temperature decreases o C during the first hour of surgery. Redistribution of blood from the core to the peripheral circulation contributes 81% to this initial decrease in temperature 5

6 The second phase of temperature loss is characterized by 2 or 3 h of a slower, linear, decrease in core temperature. Core temperature decreases an additional 0.4 o C/hr +/- 0.3 C, with redistribution contributing 43%. 6

7 Lastly, patient enters a plateau phase during which core temperature remains constant Redistribution contributes 65% to the entire heat loss during the first 3 h of anesthesia 7

8 8

9 Body heat content is not normally distributed evenly. Instead, tonic thermoregulatory vasoconstriction maintains a core-to-peripheral temperature gradient. Induction of general anesthesia inhibits vasoconstriction, allowing a core-toperipheral redistribution of body heat. 9

10 Induction of GA produces vasodilation GA reduces the vasoconstriction threshold temperature (core temperature that triggers a thermoregulatory response) to well below core temperature Inhibiting centrally mediated thermoregulatory constriction Anesthetics directly cause vasodilation 10

11 After one hour of anesthesia core temperature decreases ~ 1.6 o C During the subsequent 2 h core temperature decreases ~ 1.1 o C - 2 o C 11

12 12

13 Redistribution hypothermia in the obese patient: Is increased Is decreased Does not occur Is consistent with a very thin patients 13

14 Redistribution hypothermia in the obese patient: Is increased Is decreased Does not occur Is consistent with a very thin patients 14

15 Obese patients redistribute core temperature less than those of normal weight Normally have thermoregulatory problems dissipating metabolic heat due to excess adipose. Consequently, they spend much of their time in vasodilation. The result is that their peripheral tissue temperature is higher than normal, which reduces core-to-peripheral flow of heat after induction of anesthesia. 15

16 The Linear Phase of heat loss is defined as: The second portion of the hypothermia curve Results from heat loss exceeding metabolic heat production of approximately 0.5 o C/hr Heat loss mediated by radiation, conduction, convection and evaporation Heat loss from radiation contributes most to heat loss during this phase. 16

17 The Linear Phase of heat loss is defined as: The second portion of the hypothermia curve Results from heat loss exceeding metabolic heat production of approximately 0.5 o C/hr Heat loss mediated by radiation, conduction, convection and evaporation Heat loss from radiation contributes most to heat loss during this phase. 17

18 70% of the body s heat loss to the environment Occurs via infrared radiation Loss of body heat to cooler objects in the room No physical contact with objects required for radiant heat loss to occur Prevented by simple covering 18

19 Loss of heat to air currents flowing over the body Wind-chill effect Cool, drafty operating rooms (Laminar flow rooms) Second major source of heat loss during anesthesia and surgery Simple covering helps prevent convective loss 19

20 Loss of heat to cooler objects the body is touching, Accounts for 5% of heat loss in OR Operating tables Small losses unless patient is wet which can increase conduction loss 25-fold Mechanism by which cold IV fluids and blood products decrease body temperature 20

21 1L crystalloid infused at room temperature (20 C) causes patient to expend 17 kcal to warm the fluid to 37 C Approximately 25% of a patient s hourly caloric production which can t be increased in the anesthetized patient Body temperature will fall ~ 0.2 C/L of crystalloid infused at room temperature 21

22 Blood products Infusion of 2-4 units of cold blood can decrease core temp by almost 1 C 22

23 Loss from sweating, insensible fluid losses, airway humidification of dry gases, evaporation from large wound surfaces Normally, a small factor Respiratory evaporative losses are less than 10% Losses from extensive wounds can become significant 23

24 Core temperature that triggers a thermoregulatory response Response modified by Thermosensivity (gain) :proportional response Magnitude of change relative to goal temperature Maximal response Further change in core temp elicits no increase in response 24

25 No autonomic response within this range 0.2 o C range for normal adults Core temperatures beyond this range will elicit response Vasoconstriction / shivering for cold Vasodilation / sweating for heat 25

26 Cooling of core body temperature by IV fluids is the result of which type of heat: 1. Conduction 2. Convection 3. Radiation 4. Evaporation 26

27 Cooling of core body temperature by IV fluids is the result of which type of heat: 1. Conduction 2. Convection 3. Radiation 4. Evaporation 27

28 Loss of body temperature from the OR table reflection which type of heat loss: 1. Conduction 2. Convection 3. Radiation 4. Evaporation 28

29 Loss of body temperature from the OR table is a result of which type of heat loss: 1. Conduction 2. Convection 3. Radiation 4. Evaporation 29

30 Loss of body temperature from the surgical incision is a result of which type of heat loss: 1. Conduction 2. Convection 3. Radiation 4. Evaporation 30

31 Loss of body temperature from the surgical incision is a result of which type of heat loss: 1. Conduction 2. Convection 3. Radiation 4. Evaporation 31

32 The major cause of heat loss during anesthesia is via what mechanism: 1. Conduction 2. Convection 3. Radiation 4. Evaporation 32

33 The major cause of heat loss during anesthesia is via what mechanism: 1. Conduction 2. Convection 3. Radiation 4. Evaporation 33

34 Perioperative heat loss that results from the application of skin prep solutions is an example of what type of heat transfer? 1. Conduction 2. Convection 3. Radiation 4. Evaporation 34

35 Perioperative heat loss that results the application of skin prep solutions is an example of what type of heat transfer? 1. Conduction 2. Convection 3. Radiation 4. Evaporation 35

36 Heat loss varies according to which skin preparation is used. Which skin preparation will cause the greatest heat loss? 1. Water 2. Chlorhexidine 3. Hibiclens 4. Alcohol 5. Betadine 36

37 Heat loss varies according to which skin preparation is used. Which skin preparation will cause the greatest heat loss? 1. Water 2. Chlorhexidine 3. Hibiclens 4. Alcohol 5. Betadine 37

38 The decrease in mean body temperature in a 70 kg patient ranges from to o C/m 2 The greater surface area covered the greater the heat loss. 38

39 The final phase of the hypothermia curve is characterized by which of the following: 1. Reversal of redistribution hyperthermia 2. Constant core temperature 3. Slowly decreasing core temperature C/h 4. Characterized by a passive or active plateau 39

40 The final phase of the hypothermia curve is characterized by which of the following: 1. Reversal of redistribution hyperthermia 2. Constant core temperature 3. Slowly decreasing core temperature C/h 4. Characterized by a passive or active plateau 40

41 Passive Plateau A passive plateau results when metabolic heat production equals heat loss, without activating thermoregulatory defenses. 41

42 Active Plateau Patients who become sufficiently hypothermic trigger thermoregulatory vasoconstriction and develop an actively maintained plateau. The difference between a passive plateau and active plateau is that an active plateau depends on thermoregulatory vasoconstriction to decrease heat loss and to alter distribution of heat within the body. In this regard, core temperature is maintained much as it is normally. A core temperature between 34 and 35 C is necessary to trigger thermoregulatory vasoconstriction during anesthesia 42

43 Steady State temperature regulation is interrupted during anesthesia 1. Anesthesia significantly decreases metabolic heat production. 2. Heat loss may be abnormally high because of: 2. Cool operating room environment 3. administration of cool intravenous and irrigating fluids 4. evaporative and radiative losses from within surgical incisions. 3. Behavioral compensations are not available to unconscious patients 4. Autonomic responses are impaired, at least until patients become quite hypothermic. 43

44 Neuraxial anesthesia inhibits thermoregulatory control by: 1. Blocking the PNS 2. Preventing Shivering 3. Acting on central mechanisms 4. Decreasing behavioral control 5. All the above 6. None of the above 44

45 Neuraxial anesthesia inhibits thermoregulatory control by: 1. Blocking the PNS 2. Preventing Shivering 3. Acting on central mechanisms 4. Decreasing behavioral control 5. All of the above 6. None of the above 45

46 Redistribution decreases core temperature about twice as much during regional as during general anesthesia. True or False 46

47 Redistribution decreases core temperature about twice as much during regional as during general anesthesia. True or False 47

48 Redistribution decreases core temperature about half as much during major conduction anesthesia as during general anesthesia. Patients don t feel cold and do not complain 48

49 Metabolic heat production remains near normal Start linear hypothermia phase at a higher temperature due to a decreased loss to redistribution in initial phase 49

50 During relatively short procedures, hypothermia is likely to be greater in patients administered general anesthesia. Patients administered regional anesthesia will generally start the linear hypothermia phase at a relatively high temperature because they initially lost less to redistribution. Furthermore, hypothermia may develop at a reduced rate during neuraxial anesthesia because metabolic heat production remains near normal. 50

51 After long and large operations, the opposite pattern is likely to prevail because in patients administered general anesthesia a core temperature plateau will develop, whereas those undergoing neuraxial anesthesia often continue to become hypothermic. Whether core hypothermia is worse with general or regional anesthesia is thus likely to depend largely on the duration and magnitude of surgery. 51

52 52

53 After neuraxial block, an initial core temperature drop is caused by vasodilation in the lower body and heat redistribution from the core to the periphery, similar to that observed during general anesthesia. Afterward, temperature continues to decrease linearly as a result of enhanced heat loss through vasodilated skin. Unlike during general anesthesia, core temperature might never reach a plateau phase during central neuraxial block and could continue to decrease unless active warming is started. This is because neuraxial block inhibits vasoconstriction and shivering in the lower part of the body. Lack of thermal sensation from the blocked areas overrides the hypothalamus, and therefore, the patient fails to feel cold and to report it to the anesthesiologist. When general and epidural anesthesia are combined, the decrease in vasoconstriction as a result of the latter does not allow a core temperature plateau to be reached and results in lower body temperatures than with general anesthesia alone. 53

54 During neuraxial anesthesia, body temperature is negatively correlated with block level and with patient s age. Elderly patients are at increased risk of developing hypothermia while undergoing regional anesthesia as a result of a decreased temperature threshold for shivering. Surprisingly, duration and magnitude of the surgery do not seem to predict the extent of hypothermia nor does room temperature. Identifying patients who are at risk for developing hypothermia during neuraxial block can be difficult, and anesthesiologists could fail to estimate its presence based only on clinical grounds. As a result of the potential for significant temperature loss, temperature should be monitored during most neuraxial anesthetics. However, most anesthesiologists do not measure this variable during regional anesthesia. In a recent survey, only 33% of the participating clinicians reported they monitored body temperature while conducting regional anesthesia. 54

55 Combined Neuraxial and General Anesthesia. The patients at greatest risk for inadvertent perioperative hypothermia are those in whom regional and general anesthesia are combined. The reason is that these patients will initially become rapidly hypothermic because of redistribution to all four extremities. During the linear phase, they will continue to cool, but at the relatively higher rate associated with general anesthesia. Three additional factors contribute to hypothermia during combined regional general anesthesia. 55

56 The first is that neuraxial anesthesia per se reduces the vasoconstriction threshold. General anesthesia does also, but the epidural effect is superimposed on the general anesthetic effect. As a result, vasoconstriction occurs later and at a lower core temperature in patients administered both epidural and general anesthesia. The second factor is that general anesthesia inhibits the shivering that might otherwise increase heat production during neuraxial anesthesia. The third and most important factor is that peripheral nerve block prevents vasoconstriction in the legs. As a result, vasoconstriction once initiated centrally is relatively ineffective, and core temperature continues to decrease. 56

57 The principle defenses against hypothermia include all the following except: 1. Skin vasomotor activity 2. Non-shivering thermogenesis 3. Shivering 4. Modulation of pre-optic area of the posterior hypothalamus 57

58 The principle defenses against hypothermia include all the following except: 1. Skin vasomotor activity 2. Non-shivering thermogenesis 3. Shivering 4. Modulation of pre-optic area of the posterior hypothalamus 58

59 Preoptic area anterior hypothalamic nuclei (POAHN) Receives input from afferent peripheral and central receptors (includes the hypothalamus itself) 10/21/

60 Anterior hypothalamus Promotes heat loss Vasodilation sweating Posterior hypothalamus Promotes heat conservation Decrease blood flow Piloerection Shivering Promotes heat production Increase secretion thyroid hormone Epinephrine and norepinephrine secretion increase the BMR 10/21/

61 Vigorous shivering increases metabolic heat production up to % above basal level

62 Vigorous shivering increases metabolic heat production up to % above basal level

63 Vigorous shivering increases Oxygen consumption up to % above basal level

64 Vigorous shivering increases Oxygen consumption up to % above basal level

65 May increase O2 requirments by % 65

66 Shivering is an involuntary, oscillatory muscular activity that augments metabolic heat production. Vigorous shivering increases metabolic heat production up to 600% above basal level. 66

67 Which statement about shivering is false: 1. Shivering is elicited when the preoptic region of the hypothalamus is cooled. 2. Shivering is uncomfortable and worsens post-op pain. 3. Shivering is associated with a marked decrease in catecholamine levels. 4. Shivering is rare in the elderly. 67

68 Which statement about shivering is false: 1. Shivering is elicited when the preoptic region of the hypothalamus is cooled. 2. Shivering is uncomfortable and worsens post-op pain. 3. Shivering is associated with a marked decrease in catecholamine levels. 4. Shivering is rare in the elderly. 68

69 Which are the most effective measure to decrease intraoperative hypothermia is: 1. Warming pre-operatively 2. Warming intra- operatively pre-induction 3. Warming intra- operatively post-induction 4. Warming postoperatively 69

70 Which are the most effective measure to decrease intraoperative hypothermia is: 1. Warming pre-operatively 2. Warming intra- operatively pre-induction 3. Warming intra- operatively post-induction 4. Warming postoperatively 70

71 Post induction warming -The overall heat loss during this relatively short time is relatively small, and therefore, warming the patient after induction does not control the initial temperature drop. On the contrary, warming started before induction limits the redistribution of heat by reducing the temperature gradient between the core and peripheral compartments. This strategy is simple and is probably worthwhile in the patients who are most likely to experience the complications of intraoperative hypothermia. 71

72 Pulmonary artery catheter, is considered a gold standard for core temperature measurement and is often used as a reference for other monitoring devices. 72

73 Esophageal temperature readings can artifactually decrease during thoracotomy and rapid infusion of cold fluids and can be effected by the temperature of the inspired gases. The optimal position for the thermistor is in the lower esophagus, approximately 45 cm from the nose and 12 to 16 cm distally to the point where heart and breath sounds are best heard. complications such as esophageal perforations and burns are possible 73

74 Nasopharyngeal temperature can be measured with an esophageal probe positioned above the palate and is reasonably close to brain and core temperature. Its use has been suggested during use of a laryngeal mask. Bladder urinary catheter probe Not effective measure during low UOP and lower abdominal surgeries Rectal temp Affected by stool and bacteria that produce heat Does not reflect acute changes in core temperature 74

75 Temperatures at different skin locations can differ considerably, and at least 4 distinct monitoring sites are necessary to obtain an estimate of the average skin temperature. Axillary temperature is thought to be relatively close to the core value and can probably be a reasonable choice if other core temperature measurements are impractical. Careful probe location is essential at this site, and even then, significant inaccuracy is still possible. 75

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78 The hypothalamic set point temperature normally average about 98.6 F. All of the following factors can alter the set point except? 1. Skin temperature 2. Pyrogens 3. Antipyretics 4. Thyroxin 78

79 The hypothalamic set point temperature normally average about 98.6 F. All of the following factors can alter the set point except? 1. Skin temperature 2. Pyrogens 3. Antipyretics 4. Thyroxin 79

80 Pyrogens released from toxic bacteria or degenerating tissues of the body can increase the set-point temperature. Fever-reducing medication such as ASA, ibuprofen and tylenol are called antipyretics Thyroxine can increase metabolic rate and therefore increase the rate of heat production, but does not change the set-point temp of the hypothalamus. A decrease in skin temperature causes the setpoint temperature to increase, and the set-point temperature decreases when the skin is hot. 80

81 Most of the heat loss from an unclothed person at room temperature occurs by which of the following mechanisms? 1. Conduction to air 2. Conduction to objects 3. Convection 4. Evaporation 5. Radiation 81

82 Most of the heat loss from an unclothed person at room temperature occurs by which of the following mechanisms? 1. Conduction to air 2. Conduction to objects 3. Convection 4. Evaporation 5. Radiation 82

83 About 60% of the body heat is lost by radiation. Loss of heat by radiation means loss in the form of infrared heat waves, which is a type of electromagnetic wave. All objects radiate heat waves; thus, heat waves are radiated from the walls of rooms and other objects toward the body is greater than the temperature of surrounding objects, more heat radiates from the body than is radiated to the body 83

84 Which of the following mechanisms cause heat loss from a normal person when the environmental temperature is 106 F and the relative humidity is less than 10%. 1. Conduction 2. Convection 3. Evaporation 4. Radiation 84

85 Which of the following mechanisms cause heat loss from a normal person when the environmental temperature is 106 F and the relative humidity is less than 10%. 1. Conduction 2. Convection 3. Evaporation 4. Radiation 85

86 Evaporation is the only means of heat loss when the air temperature is greater than the body temperature Each gram of water that evaporates from the surface of the body causes 0.58 kilocalories of heat to be lost from the body Even when the body is not sweating, water evaporates insensiblhy from the skin and lungs at a rate of 450 to 600ml/day, which is about 12 to 16 kilocalories of heat loss per hour. 86

87 A scuba diver explores an underwater lava flow where temperature is 102 F. Which of the following profiles best describes the mechanisms of heat loss that are effective in this man? 1. Evaporation 2. Radiation 3. Convection 4. Conduction 5. None of the above 6. All of the above 87

88 A scuba diver explores an underwater lava flow where temperature is 102 F. Which of the following profiles best describes the mechanisms of heat loss that are effective in this man? 1. Evaporation 2. Radiation 3. Convection 4. Conduction 5. None of the above are correct 6. All of the above are correct 88

89 None of the mechanisms of heat loss are effective when a person is placed in water that has a temperature greater than body temperature. Instead, the body temperature becomes equal to the water temperature. 89

90 Which of the following sets of changes occurs at point W, compared with point V? 1. Shivering 2. Sweating 3. Vasoconstriction 4. Vasodilation 105F 103F W 101F Y 99F V 98F Hours Diagram shows the effect of changing the set-point of the hypothalamic temperature controller. The red line indicates the body temperature, and the blue line represents the hypothalamic set-point temperature. 90 X

91 Which of the following sets of changes occurs at point W, compared with point V? 1. Shivering 2. Sweating 3. Vasoconstriction 4. Vasodilation 105F 103F 101F 99F 98F V W X Y Hours 91

92 When the hypothalamic set-point temperature is greater than the body temperature, the person feels cold, and exhibits responses that lead to an elevation of body temperature. These responses include shivering and vasoconstriction as well as piloerection and epinephrine secretion. Shivering increases heat production. The increase in epinephrine secretion causes an immediate increase in the rate of cellular metabolism, which is an effect called chemical thermogenesis. Vasoconstriction of the skin blood vessels decreases heat loss through the skin. 92

93 Which of the following sets of changes occurs at point Y, compared with point V? 1. Shivering 2. Sweating 3. Vasoconstriction 4. Vasodilation Diagram shows the effect of changing the set-point of the hypothalamic temperature controller. The red line indicates the body temperature, and the blue line represents the hypothalamic set-point temperature. 105F 103F 101F 99F 98F V W X Y Hours 93

94 Which of the following sets of changes occurs at point Y, compared with point V? 1. Shivering 2. Sweating 3. Vasoconstriction 4. Vasodilation 105F 103F 101F 99F 98F V W X Y Hours 94

95 When the hypothalamic set point temperature is lower than the body temperature, the person feels hot, and exhibits responses that cause body temperature to decrease These responses include sweating and vasodilation Sweating increases heat loss from the body by evaporation Vasodialtion of skin blood vessels facilitates heat loss from the body by increasing the skin blood flow. 95

96 Which of the following sets of changes occurs at point X, compared with point Y? 1. Shivering 2. Sweating 3. Vasoconstriction 4. Vasodilation Diagram shows the effect of changing the set-point of the hypothalamic temperature controller. The red line indicates the body temperature, and the blue line represents the hypothalamic set-point temperature. 105F X 103F 101F 99F 98F V W Y Hours 96

97 Which of the following sets of changes occurs at point X, compared with point Y? 1. Shivering 2. Sweating 3. Vasoconstriction 4. Vasodilation 105F 103F 101F 99F 98F V W X Y Hours 97

98 When the hypothalamic set-point temperature is equal to the body temperature, the body exhibits neither heat loss nor heat conservation mechanisms, even when the body temperature is far above normal Therefore, the person does not feel not even when the body temperature does not feel hot even when body temperature is 104 F 98

99 A 54 year old man is admitted to the emergency department after being found lying in his yard near a running lawnmower on a hot summer day. His body temperature is 106 F, blood pressure is normal, and heart rate is 160 beats/min. Which of the following sets of changes is most likely to be present in this man? 1. Sweating 2. Hyperventilation 3. Vasodilation of skin 99

100 A 54 year old man is admitted to the emergency department after being found lying in his yard near a running lawnmower on a hot summer day. His body temperature is 106 F, blood pressure is normal, and heart rate is 160 beats/min. Which of the following sets of changes is most likely to be present in this man? 1. Sweating 2. Hyperventilation 3. Vasodilation of skin 100

101 This patient is suffering from heat stroke. Patients with heat stroke exhibit tachypnea and hyperventilation caused by direct CNS stimulation, acidosis, or hypoxia. The blood vessels in the skin are vasodilated, and the skin is warm. Sweating ceases in patients with true heatstroke, most likely because the high temperature itself causes damage to the anterior hypothalamic-preoptic area. The nerve impulses from this area are transmitted in the autonomic pathways to the spinal cord and then through sympathetic outflow to the skin to cause sweating. 101

102 What is the definition of kcal? 1. Amount of heat needed to raise the temperature of 1 kg of water by 1 o C 2. Amount of heat needed to raise the temperature of 10 kg of water by 1 o C 3. Amount of heat needed to raise the temperature of 1 kg of water by 10 o C 4. Amount of heat needed to raise the temperature of 10 kg of water by 100 o C 102

103 What is the definition of kcal? 1. Amount of heat needed to raise the temperature of 1 kg of water by 1 o C 2. Amount of heat needed to raise the temperature of 10 kg of water by 1 o C 3. Amount of heat needed to raise the temperature of 1 kg of water by 10 o C 4. Amount of heat needed to raise the temperature of 10 kg of water by 100 o C 103

104 The average 70kg adult produces 70kcal of heat/hr (average 1680 kcal/day) During anesthesia 70 kg adult produces 42kcal of heat/hr For every 58 kcal heat loss, there is a 1 o C decrease in body temperature Approximately q 2 hrs you will loose 1 o C 104

105 Which is not a complication of hypothermia? 1. Increased surgical blood loss 2. Decreased UOP 3. Shivering 4. Appearance of J wave at QRS-ST junction 5. PE 105

106 Which is not a complication of hypothermia? 1. Increased surgical blood loss 2. Decreased UOP 3. Shivering 4. Appearance of J wave at QRS-ST junction 5. PE 106

107 ANS Initial sympathetic stimulation and compensatory mechanisms < 32ºC to 33ºC (90-92) Compensatory mechanisms fail 22ºC to 24ºC (72 76) poikilothermic 107

108 Skin Peripheral vasoconstriction Piloerection Shivering 108

109 Metabolism s 6 to 8% for every 1º C in temperature Early Hyponatremia (cold diuresis) Hyperkalemia Hyperglycemia (inhibition of insulin release and block of its cellular uptake) Late Metabolic acidosis 109

110 CV system Initial stimulation HR, BP, CO, vasoconstriction (catecholamine release) Increase in circulating levels of norepinephrine of 100 to 700 % Leads to cardiac work load Temperature < 33º C (91.4) Depression of CV system, HR, BP, CO decrease < 31º C (88) Atrial and ventricular irritability < 30º C (86) Bradycardia and V-fib 19º C to 20º C (66 68F) Asystole 110

111 EKG changes 32C (90F) PR interval increases Broadening QRS complex Lengthening QT interval Appearance of J wave at QRS-ST junction Usually in lateral precordial leads 111

112 EKG of severely hypothermic patient--29ºc; asteriks show hump where QRS joins ST segment. This is J wave, also called Osborne wave. 112

113 Increased postoperative release of norepinephrine has been observed in patients who were hypothermic during surgery as compared with patients whose temperature was maintained at a normal value. This catecholamine release was associated with increased blood pressure and heart rate and with peripheral vasoconstriction. Although the observed hemodynamic changes were moderate, ischemia resulting from increased myocardial oxygen consumption is possible in high-risk patients. Besides, cold-induced catecholamine release could result in coronary constriction, offering an additional explanation to the observed incidence of myocardial ischemia. The available evidence suggests that avoidance of intraoperative hypothermia could be part of a strategy aimed at minimizing stress-related sympathetic activation with its cardiac complications. 113

114 Respiratory System Initial increase in respiratory effort Followed by respiratory depression with decreasing temperature Hypothermia-induced bronchodilation occurs, increasing anatomic and physiologic deadspace Diminished hypoxic pulmonary vasoconstriction and responsiveness to hypoxemia and hypercarbia < 30ºC (86F) bronchial secretions increase Pulmonary edema develops at 24ºC (76F) Increased O2 requirement with shivering of 400% to 700% 114

115 Left shift of oxyhemoglobin dissociation curve Reduced release of oxygen at a given po 2 O 2 consumption d 4% for each 0.5ºC drop in temperature Alkalosis Acidosis 115

116 Normal Hypothermia 116

117 CNS mentation, amnesia, obtundation, loss of pupillary and deep tendon reflexes, loss of brain activity CBF and CMRO 2 If shivering present CMRO 2 will >100% without in blood flow Peripheral nerve conduction slowed impairing nerve conduction Autonomic system depressed 117

118 Renal function Early: cold diuresis (diuresis continues due to impaired renal tubular sodium reabsorption) Late: oliguria and azotemia Muscles GI Shivering between 33ºC to 35ºC (34F 93F) Diminishes below 33ºC Stops below 30ºC Decreased gastric motility (full stomach) Decreased hepatic clearance 118

119 Coagulation disturbances Hemo-concentration Increased blood viscosity When energy is added to a liquid, the movement of the molecules increases. The increasing speed allows the molecules to slide past each other with greater ease. Week hydrogen bonds are formed between Hydrogen and Oxygen molecules in the blood which increase viscosity. Decreased O2 availability (left shift of oxyhemoglobin dissociation curve) Platelet dysfunction Platelet numbers remain normal Function impaired Reduced release of thromboxane A 2 Disruption of fibrinolytic system Clot formation impaired Disseminated intravascular coagulation 119

120 Other complications Decreased immune system response Increased infection Delayed healing / prolonged time until suture removal Delayed recovery from anesthesia Increased hospital stay cost up to $

121 Pharmacologic effects of drugs Decreased hepatic metabolism Prolonged drug metabolism probably contributes to delayed postanesthetic recovery of hypothermic patients. Decreased renal excretion Prolonged action Although few drugs have been investigated so far, it has been shown that low body temperature decreases the clearance of vecuronium, atracurium, and propofol. Inhalation agents MAC decreases 7% for each 1ºC decrease in body temperature 121

122 Normothermia Shorter hospital stay Hypothermia Decreased wound healing (vasocontriction, tissue hypoxia, inhibitory effect on immune system macrophage aggregation to site Only last a few hours, this is most critical for the establishment of bacterial growth Decreased time to suture removal Decreased collegen deposition and increased protein breakdown Decreased time of solid food ingestion 122

123 ADULT Exhibit 80% vasoconstriction response to hypothermia Exhibit 40% response to shivering ELDERLY Exhibit 55% vasoconstriction response to hypothermia Exhibit 10% response to shivering 123

124 Preoperative skin warming Adjusted ambient temperature in the OR Intraoperative temperature monitoring Heated and humidified anesthesia circuits Forced-air warming blankets Warmed intravenous fluids and blood products Postoperative mechanical ventilation Prevention and treatment of postoperative shivering Anticipation and treatment of rewarming vasodilation 124

125 All are appropriate management of perioperative hypothermia in a patient undergoing a AAA except? 1. Lower body bair hugger 2. Upper body bair hugger 3. Fluid warmer 4. Pre-operative α-2 agonist 125

126 All are appropriate management of perioperative hypothermia in a patient undergoing a AAA except? 1. Lower body Bair Hugger 2. Upper body Bair Hugger 3. Fluid warmer 4. Pre-operative α-2 agonist 126

127 Lower body bair hugger placed during cross clamping will exacerbate the tissue oxygen demand-supply imbalance Increased risk of thermal injury with warming blankets 127

128 Patient arrives to PACU with a temp 35 o C. The patient is tachypneic, hypertensive and shivering. Which of the following are appropriate treatments for this patient: 1. Forced air rewarming device cc LR fluid bolus 3. 4L Oxygen via OFM 4. Demerol 50 mg IV 5. 1,3,4 6. All of the above 128

129 Patient arrives to PACU with a temp 35 o C. The patient is tachypneic, hypertensive and shivering. Which of the following are appropriate treatments for this patient: 1. Forced air rewarming device cc LR fluid bolus 3. 4L Oxygen via OFM 4. Demerol 50 mg IV 5. 1,3,4 6. All of the above 129

130 Rewarming vasodilation Can produce acute hypotension, reflex tachycardia and myocardial ischemia Must vigorous fluid replacement essential to prevent this Vasodilator therapy as necessary 130

131 Intrathecal Fentanyl decreased shivering Bair Hugger decreased temperature during spinal anesthesia Lower vs upper vs both Use of ketamine to reduce shivering Kappa recepters 131