VIEWS: 80 PAGES: 23 POSTED ON: 7/16/2011
Neeraj Badjatia, MD MSc Columbia University, College of Physicians and Surgeons firstname.lastname@example.org Historical hypothermia Baltimore, 1955 Philadelphia, July 1936 Radiation Evaporation Transfer of heat between the separated Heat loss derived from the evaporation of surfaces of two objects via electromagnetic water from skin & lungs (infrared) radiation. Accounts for ±15% of heat loss (5% from Accounts for 50–70% of heat loss in awake the skin, 10% from the lungs) patients Convection Conduction Direct transfer of between surfaces Transfer of heat from a surface to the Amount of heat loss is closely related to surrounding air. contact surface Accounts for 20–30% of heat loss Increases in the sitting or lying position Thermal compartments and cooling Peripheral compartment Core compartment skin and extremities trunk and head (excluding the Peripheral cooling skin) Core cooling Convection Conduction ○ Fans, air cooling blankets ○ Intravascular catheters Conduction ○ Cooling blanket (Arctic Sun) ○ Ice pack, water cooling blankets, immersion ○ Ice-cold crystalloid/colloid infusions Evaporation ○ Extracorporeal circulation ○ Alcohol baths Radiation ○ Exposure (Operating Room) Neuromuscular blockade Traditionally most efficient method by which to induce and maintain hypothermia Eliminates thermoregulatory defense mechanisms that try to prevent hypothermia Promotes cooling by convection (primary) Eliminates ability to follow neurological exam Tolerable for 24 hours in this disease model Neuromuscular blockade Concerns/Precautions Difficult to regulate temperature if used in isolation (overshoot) Monitoring (ie TOF) problematic in hypothermia ○ Rely on continued clinical exam, changes in ETCO2/ventilatory patterns Association with Critical Illness Polyneuropathy (CIP)? ○ Prolonged use and multi-organ disease ○ Risk outweighed by potential for considerable benefit Induction of hypothermia Peripheral techniques with paralysis utilized in two NEJM studies Time to target HACA: 8 hours (4 – 16) Bernard: 0.9 C/hr TIME IS BRAIN More rapid induction needed Target core cooling Advances in Temperature Management Technological advancements Several new, FDA approved devices Target core temperature via conductive heat loss in a controlled feedback mechanism Feedback loops allow for tighter control of the rate and depth of hypothermia ○ Less time to goal temperature ○ Easier maintenance of temperature Range of temperature reduction 1.5 – 6.0 ºC / hr Markedly diminished nursing time Overshoot (Temp below 32°C) 90 “Overshoot” more 80 common with the 70 Blanketrol II device 60 P=0.016 50 Blanketrol II 40 (overall 77%) 30 Arctic Sun 20 (overall 14%) 10 0 none mild moderate severe (31-32C) (30-31C) (<30C) Proceed Amer Thor Soc 2007; A392 Innercool: Celsius Control System Intravascular Cooling Catheters (9F,10.5F) & Surface Vest system Medivance: Arctic Sun Pads connected to a bedside cooling unit that circulates cold, sterile water 40% body surface covered Pads may be left in place for three days (72 hours) Cincinnati Sub – Zero Update of previous blanketrol II device Covers more surface area Bedside unit allows for more programmable options for depth/rate of cooling Actual rates of cooling? ALSIUS: CoolGard System •Triple lumen subclavian catheter (9.3 F) •Standard central catheter length (22 cm) •Three lumens for infusion •Two lumens connect to bedside unit for circulation of sterile saline through micro-balloons (closed-loop) Life Recovery Systems: Thermosuit Extremely rapid cooling by ice water immersion Esophageal temperature probe Await more extensive clinical experience Induction with cold fluids Baumgardner et al. (Anesth Analg 89:163–169) Infusion of 5 mL/kg of refrigerated albumin 5% Neurosurgical patients who had already been cooled to 34°C Average temperature reductions of 0.6 ± 0.1°C Rajek et al (Anesthesiology 93(3):629 – 637) Infusion of 40 mL/kg of 4 C saline Induction of nine healthy volunteers Average temperature reductions of 2.5 ± 0.4°C Bernard et al. (Resuscitation 56(1):9-13) Infusion of 30 mL/kg of ice-cold Ringer’s lactate & ice packs Induction in 22 patients following cardiac arrest Average temperature decrease was 1.7°C Virkkunen et al. (Resuscitation 62(3):299-302) Infusion of 30 mL/kg Ringer’s lactate 13 cardiac arrest patients Average temperature reduction of 1.8°C Cold crystalloid and colloid solutions Overall average cooling rates of 0.8°C - 1.2°C per liter infused None reported serious adverse effects None on use with established maintenance techniques Combined approach better? Induction with cold crystalloid and colloid solutions Polderman et al (Crit Care Med 2005; 33:2744–2751) Infusion of cold saline and albumin with cooling blankets (Arctic Sun and Blanketrol) 134 patients with various types of neurologic injury (postanoxic encephalopathy, subarachnoid hemorrhage, traumatic brain injury) Core temperatures decreased: 36.9 ±1.9°C to 34.6 ± 1.5°C at 30 mins and to 32.9 ± 0.9°C at 60 mins (target temperature: 32°C–33°C No patient developed pulmonary edema Combined approach faster than either in isolation 50 patients Indications for mild hypothermia or strict euthermia Randomized to 5 groups ○ “Conventional” = 30cc/kg cold IVF + ice/cold packs ○ Water circulating blankets (Blanketrol II, Cincinnati Subzero) ○ Air circulating blankets ○ Arctic Sun ○ Intravascular balloon device Endpoints: speed of cooling, % time above or below temperature range Crit Care 2007;11:R91 Cooling efficacy Induction of hypo- and normothermia. Maintenance of target temperature. Pace of cooling expressed as°C/h Depicted as the percentage of time the patient's temperature was 0.2°C below or above the target temperature. Crit Care 2007;11:R91 Cooling efficacy Water-circulating blankets, gel-coated water circulating pads and intravascular cooling were equally efficient in inducing hypothermia and normothermia Intravascular cooling with heat-exchange balloons Mean temperature deviation from target temperature. was the most effective way to maintain goal temperature Crit Care 2007;11:R91 Devices: Cooling safety Endovascular: Surface: Benefits: Benefits: excellent temperature safe and easy to use modulation good temperature cooling speed modulation feedback loop feedback loop Risks: Risks: Infection, thrombosis, slower cooling bleeding mild temperature flux positioning issues / shivering comfort shivering What does the future hold? Peritoneal cooling (Velomedix) Summary Adequate therapeutic hypothermia can be performed by a combination of methods. Cold fluids, surface and endovascular alternatives Commercial cooling devices with feedback mechanisms improve the rate of cooling increase the percentage of time at goal temperature decrease overshoot Therapeutic hypothermia is nursing-intensive, and requires time, close attention, and training. Appropriate cooling device depends on your needs, specific safety concerns, and finances.
Pages to are hidden for
"Neurological"Please download to view full document