Background
Mechanism | Rate (kcal/h) | Description |
---|---|---|
Radiation | 10–50 | Transfer of heat energy via electromagnetic waves down a concentration gradient without direct contact according to Boltzmann’s equation:a
Q = K(T1 – T2) |
Methods to reduce losses include: | ||
• warming blankets | ||
• increasing environmental temperature | ||
• radiant heaters | ||
• avoid unnecessary anesthesia | ||
Conduction | 16–30 | Transfer of energy between two solid objects in contact according to Fourier’s equation:b
Q = KA dt/dx
|
Methods to reduce losses: | ||
• removal of wet clothing | ||
• avoid prolonged contact with cold surfaces | ||
Convection | 10–20 | Transfer of heat energy during the mass movement of gas or liquid. |
Evaporation | 12–16 | Heat energy transferred during change of phase (water to gas): 58 kcal/g water evaporated from skin, respiratory tract, and viscera |
Methods to reduce losses for convection and evaporation: | ||
• avoid prolonged surgery with an open abdomen | ||
• warming blankets |
Classification | Conventional | Trauma patient |
---|---|---|
Mild hypothermia | 35–32 °C (95.0–89.6 °F) | 36–34 °C (96.8–93.2 °F) |
Moderate hypothermia | 32–28 °C (89.6–82.4 °F) | 34–32 °C (93.2–89.6 °F) |
Severe hypothermia | 28–20 °C (82.4–68.0 °F) | 32 °C (89.6 °F) |
Profound hypothermia | 20–14 °C (68.0–57.2 °F) |
Evidence for temperature monitoring sites in trauma
The physiological effects of hypothermia
Shivering and nonshivering thermogenesis
Neurological effects
Cardiovascular effects
Respiratory effects
Renal effects
Hematological effects
Hypothermia and trauma-induced coagulopathy
Risk factors for developing hypothermia and mortality
Prehospital phase |
Severity of injury |
Head injury |
Spinal cord injury |
Shock |
Extremes of age |
Wet clothing |
General anesthesia and prehospital intubation |
Suspected medical conditions |
Thyroid disease, adrenal disease, diabetes, cardiac dysfunction, hepatic disease, malnutrition, autonomic nervous system dysfunction |
Hospital phase |
Exposure |
Cold intravenous fluids and blood products |
Burns |
General anesthesia |
Epidural and spinal anesthesia |
Observation phase |
Size of surgery |
General anesthesia >3 h |
Intravenous crystalloids, blood products |
SAPS II scores |
Prehospital phase
Hospital phase
Observation phase
Methodologies and evidence for the prevention of hypothermia
Warming device | Manufacturer | Description | Heat transfer |
---|---|---|---|
Warming blanket | Bair Hugger 750, 505 (Arizant Healthcare Inc., Eden Prairie, MN, USA) | Air delivered to variety of blankets (upper, lower, full, torso, surgical access, pediatric, cardiac) at three settings: high (43 °C), medium (38 °C), low (32 °C) | Convection |
Equator (Smiths Medical ASD, Rockland, MA, USA) | Air delivered to adult and pediatric blankets. Settings: high (44 °C), medium (40 °C), low (36 °C) | Convection | |
Thermacare TC3000 series (Gaymar Industries, Inc., Orchard Park, NY, USA) | Air delivered to adult and pediatric quilts: low (32 °C), medium (38 °C), high (43 °C), maximum (46 °C) | Convection | |
WarmTouch 5200 (Nellcor, Pleasanton, CA, USA) | Air delivered to adult and pediatric blankets: high (42–46 °C), medium (36–40 °C), and low (30–34 °C) | Convection | |
Circulating water garment | Medi-Therm III (Gaymar Industries, Inc.) | Circulates water from the control unit to polymer hyper/hypothermia blankets. Manual settings: 4–42 °C; automatic: 30–39 °C | Conduction |
Blanketrol II Hyper–Hypothermia Water System (Cincinnati SubZero Products, Cincinnati, OH, USA) | Circulates water from the control unit to specialized blankets (adult and pediatric). Temperature range, 4–42 °C | Conduction | |
Heated air mattress | Polar Air (Augustine Medical, Inc., Eden Prairie, MN, USA) | Has not been shown to be effective [73] because only a limited amount of body surface area comes into contact with the mattress. Trauma patients may be vulnerable to burn injury | Conduction |
Hot packs | Hot Cycle 1 (Sign Manufacturing Corporation, Fairfield, CA, USA) | Temperature at approximately 54.5 °C. Mean increase in temperature of 1.4 °C compared with a mean decrease of 0.3–0.6 °C in controls. Further research is necessary [64] | Conduction |
Humidified gases | Heated Anesthesia Circuit (ANAPOD Westmed, Inc., Tucson, AZ, USA) | Delivery of warm, humidified gas can increase core temperature by 0.5–0.65 °C/h in injured patients [74] | Evaporation |
Fluid warmer | General | Warmed fluids were found to increase temperature to 36.8 °C compared with 35.5 °C in nonwarmed patients [75] | Conduction |
Level 1 System H-1200, H-1000, H-1025, H-525, H-500, H-275, H-250 (Smiths Medical ASD, Rockland, MA, USA) | Aluminum heat exchanger with countercurrent 42 °C circulating water bath. Air detector/clamp | Conduction | |
Hotline (Smiths Medical ASD) | Water bath heat exchange. Surrounds patient line with layer of 42 °C circulating fluid | Conduction | |
FW600 Medi Temp III (Gaymar Industries, Inc.) | Dry heat exchange. Plastic disposable with aluminum heating plates (set point, 41 °C) | Conduction | |
Thermal Angel TA-200 (Estill Medical Technologies, Dallas, TX, USA) | Battery-powered, portable in-line warmer. Outlet temperature, 38 ± 3 °C at flow rate 2–150 ml/min | Conduction | |
Warmflo FW538 (Nellcor) | Dry heat exchange. Single-use metal cassette. Maximum flow rate, 500 ml/min | Conduction | |
Other | AV-300: CAVR – continuous | Rapid core rewarming. Circulates colder blood of patient through Level 1 heat exchanger and returns it to patient at Smiths Medical ASD | Conduction |
CairCooler (Pentatherm Ltd, Wakefield, UK) | Forced-air cooling system. Connects to forced-air blanket to deliver 10 °C air | Conduction | |
Arctic Sun 2000 (Medivance, Louisville, CO, USA) | Circulating water temperature is controlled between 4 °C (39.2 °F) and 42 °C (107.6 °F) to achieve a preset target patient temperature | Conduction | |
Lavage | The specific heat and rate of heat transfer in water is 32-fold greater than air, which permits effective hypothermia management [76]. The rate of rewarming is 1–3 °C per hour if done continuously | Conduction | |
CPB | Hemodialysis (rate of rewarming is 2–3 °C/h), CPB using a heat exchanger (8–15 °C/h), and extracorporeal venovenous rewarming are other options for rewarming [77‐79]. CPB is therefore the only technique that can also correct the hemodynamic stability of the patient and provides the greatest heat transfer | Conduction |