Transcript *Thermo Combined-20 - Outcomes Research Consortium

Department of OUTCOMES RESEARCH
Thermoregulation & Heat Balance
Thermoregulation during anesthesia
Temperature monitoring
Consequences of hypothermia
Maintaining normothermia
The Department of Outcomes Research receives funding from
various companies who produce warming and/or temperature
monitoring systems. Dr. Sessler has no personal financial interest
related to this presentation. And he drives a 12-year-old car.
Providing the evidence for evidence-based medicine©
Normal Thermoregulation
Sweating
Active vasodilation
37
Vasoconstriction
36
Shivering
Anesthesia Impairs Regulation
38
Sweating
Constriction
36
34
Shivering
32
30
Threshold
(°C)
0.0
2.0
4.0
6.0
0.0
[Desflurane] (%)
0.1
0.2
0.3
[Alfentanil] (µg/ml)
38
36
34
32
30
0.3
0.6
0.9
[Dexmedetomidine] (ng/ ml)
0.0
2.0
4.0
6.0
8.0
[Propofol] (µg/ml)
Hypothermia During Anesthesia
0
-1
∆Core
Temp
(°C)
-2
-3
0
2
4
Elapsed Time (h)
6
Redistribution Hypothermia
Intraoperative Heat Transfer
Hypothermia During Anesthesia
0
-1
∆Core
Temp
(°C)
-2
-3
0
2
4
Elapsed Time (h)
6
Summary: General Anesthesia
Central thermoregulatory inhibition
• Little effect on warm defenses
• Dose-dependent increase in interthreshold range
Intraoperative hypothermia
• Redistribution of heat (initial decrease)
• loss exceeding heat production (slow linear decrease)
• Core-temperature plateau with sufficient hypothermia
Central Inhibition During Neuraxial Anesthesia
38
Sweating
37
Threshold
(°C)
Vasoconstriction
Shivering
36
35
Control
Spinal
Reduced Shivering Gain & Maximum
600
Control
400
VO2
(ml/min)
Epidural
200
0
35
36
37
Core Temperature (°C)
Behavioral Inhibition
0.0
∆ TM - 0.5
Te mp - 1.0
(°C)
60
50
VAS
40 Score
( mm)
0
30
Injection
60
90
120
Ti me (min)
Summary: Neuraxial Anesthesia
Central regulatory inhibition
• Increased inter-threshold range
Peripheral sympathetic and motor block
• Reduced shivering gain and max intensity
Behavioral inhibition
• Hypothermia fails to trigger cold sensation
Hypothermia
• Comparable to general anesthesia
• Worst when general and regional combined
Temperature Monitoring
Core Sites
• Pulmonary artery
• Distal esophagus
• Nasopharynx
• Tympanic membrane thermocouple
Other generally-reliable sites
• Mouth
• Axilla
• Bladder
Sub-optimal
• Forehead skin
• Infrared “tympanic”
• Infrared “temporal artery”
• Rectal
Anesth Analg 2008
Complications of Mild Hypothermia
Many!
Well documented
• Prospective randomized trials
• 1-2°C hypothermia
Effects on many different systems
• Most patients at risk for at least one complication
Myocardial Outcomes: Frank, et al.
Blood Loss
20% less blood loss per
Transfusion Requirement
22% less blood
Transfusion per °C
Wound Infections
Wound Infections: Melling, et al.
Wound Infection (%)
16
P = 0.001
12
8
4
0
Hypothermic
Normothermic
Normothermia
is more
effective than
antibiotics!
Duration of Vecuronium
80
Duration
of Action
(min)
60
40
20
Normothermic
(36.6 ± 0.1°C)
Hypothermic
(34.6 ± 0.3°C)
Recovery Duration
Time (min)
Thermal Discomfort
Normothermic
60
40
Thermal
20
Comfort
0
(mm)
Hypothermic
0
1
2 3 4 5
Time (h)
6
Summary: Consequences of Hypothermia
Benefits
• Improves neurologic outcomes after cardiac arrest
• Improves neurologic outcomes after neonatal asphyxia
Major complications
• Increases morbid myocardial outcomes
• Promotes bleeding and increases transfusion requirement
• Increases risk of wound infections and prolonges hospitalization
Other complications
• Decreased drug metabolism
• Prolonged recovery duration
• Thermal discomfort
Insulating Covers
120
100
Heat
Loss
(W)
Plastic
Cotton
Cloth
80
Paper
60
-20
-0
20
40
Time (min)
60
ThermalDrape
More Layers Do Not Help Much
100
80
1 Unwarmed
60
1 Warm
3 Unwarmed
Heat
Loss 40
(W)
3 Warm
20
0
-20
0
20
Time (min)
40
60
Forced-Air vs. Circulating-Water
38
Forced-Air
36
3.5°C
Temp
(°C) 34
Circulating-Water
0
4
8
Time (h)
12
Over-body Resistive Warming
Negishi, A&A 2003
Röder, BJA 2011
Fluid Warming
Cooling by intravenous fluids
• 0.25°C per liter crystalloid at ambient temperature
• 0.25°C per unit of blood from refrigerator
Fluid warming does not prevent hypothermia!
• Most core cooling from redistribution
• 80% of heat loss is from anterior skin surface
Cooling prevented by warming solutions
• Type of warmer usually unimportant
Surgical Care Improvement Project (SCIP)
Patients included (denominator)
• Surgical procedure
• General or neuraxial anesthesia ≥60 minutes
• Not having documented intentional hypothermia
Criteria (numerator), any one of:
• Active intraoperative over-body warming
• Core temp ≥36°C within 30 min before anesth end time
• Core temp ≥36°C within 15 min after anesth end time
Comments
• “Core temperature” sites and devices undefined
• A similar “pay-for-reporting” measure effective Jan 2010
The Rule: Monitor and Warm
Monitor core temperature
• General anesthesia >30 minutes
• Large procedures under neuraxial anesthesia
Maintain normothermia: core temp ≥36°C
Forced-air heating
• Best combination of efficacy, cost, and safety
• But any method(s) okay
Department of OUTCOMES RESEARCH
Potential Benefits of Mild Hypothermia
Improves neurologic outcome after cardiac arrest
•
•
•
•
•
Bernard, et al.
Hypothermia after cardiac arrest study group
Now recommended by European and American Heart Associations
Number needed to treat: ≈6
Hypothermia recommended by International Liaison Committee
Improves neurologic outcome in asphyxiated neonates
•
•
•
•
Shankaren, et al.
Gluckman, et al.
Eicher, et al.
Number needed to treat: ≈6
No benefit in major human trials
• Brain trauma in adults (Clifton, et al.) or children (Hutchison, et al.)
• Anurysm surgery: Todd, et al.
• Acute myocardial infarction: Dixon, et al
Prewarming Prevents Hypothermia
38
37
TM
36
(°C)
35
No Warming
Pre-Warming
34
-60
0
Time (min)
60