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The key ED intervention for postresuscitation syndrome is the prompt delivery of systemic cooling therapy, also called therapeutic hypothermia or targeted temperature management. Cooling of resuscitated adult cardiac arrest patients to a core body temperature of 32 to 36°C (89.6 to 96.8°F) for 24 hours following arrest and ROSC can dramatically improve survival and neurologic outcomes.32,33,34 The ideal temperature is not clear. Neurologic outcome after ROSC can be assessed by the Cerebral Performance Score (Table 26-1),35 where a score of 4 or 5 predicts poor quality of life with a sensitivity of 55.6% (95% confidence interval 42-67%) and specificity of 96.8% (95% confidence interval 94-98%). A European study33 demonstrated that therapeutic hypothermia instituted for 24 hours following cardiac arrest and ROSC resulted in a Cerebral Performance Score of 1 or 2 in 55% of hypothermia-treated patients, whereas only 39% of patients in the control group achieved a score of 1 or 2. Six-month mortality was 41% in the hypothermia group and 55% in controls. The trial only enrolled out-of-hospital cardiac arrest patients with ventricular fibrillation/ventricular tachycardia (VF/VT) as an initial rhythm; no definitive trial has been performed for patients with either pulseless electrical activity (PEA) or asystole as the initial arrest rhythm. However, a body of clinical evidence suggests that therapeutic hypothermia also improves outcomes for patients with PEA or asystole.36,37,38,39
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INCLUSION AND EXCLUSION CRITERIA FOR THERAPEUTIC HYPOTHERMIA
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Patients who are awake and appropriately alert following ROSC are excluded from consideration (Table 26-2). Patients with very poor neurologic status before arrest and resuscitation are often not considered for therapeutic hypothermia, as treatment can at best only restore patients to their prearrest clinical state. Other inclusion and exclusion criteria are less well defined. For example, many hospital protocols for postarrest care exclude pregnant patients; however, several case reports have demonstrated good outcomes for postarrest pregnant patients.41,42 Because coagulopathy and bleeding can result from lowering of core body temperature, patients with clinically significant bleeding at the time of arrest or who have arrested from penetrating trauma are generally excluded from therapeutic hypothermia. Anticoagulation is not considered a contraindication. Therapeutic hypothermia may benefit patients resuscitated from hanging-related asphyxial arrest.43
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PRACTICAL CONSIDERATIONS
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The technique requires the coordination of care between the ED, critical care units, and cardiology intensive care units. A standing hospital protocol is a crucial step for hospital systems. Sample protocols are available on the Internet.44 Protocols should delineate processes for hypothermia induction, maintenance, and rewarming, as well as adjunctive pharmacologic interventions (sedation, paralysis) and monitoring. Incorporation of these protocols into electronic order sets for postarrest care encourages uniformity of treatment. An overview of the time course of treatment is shown in Figure 26-2.
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Cooling and Supportive Care
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Table 26-3 outlines elements of cooling and supportive care. To lower core body temperature to 32 to 36°C (89.6 to 96.8°F), apply commercially available clinical cooling systems (both surface-wrap or catheter-based cooling solutions exist), or apply chilled saline or ice packs to the axillae and groin. The aim is to reach goal temperature within several hours of resuscitation, so a combination of these approaches is often employed.
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Maintain hypothermia for 12 to 24 hours following lowering of core temperature. It is difficult to maintain a steady temperature with chilled saline or ice packs alone.45,52,53 Commercial cooling devices take input from temperature probes to modify cooling power and carefully hold core temperature steady. During hypothermia maintenance, check serum electrolytes frequently (every 4 h) as hypokalemia can result from cold-mediated diuresis.53,54 Monitor hemodynamic parameters carefully to maintain a mean arterial pressure sufficient to enable cerebral perfusion (often a mean arterial pressure >60 mm Hg [>8kPa] is considered minimum).55 After the maintenance phase, rewarm over 12 to 24 hours. More rapid rewarming can induce hypotension from vasodilation as well as electrolyte shifts.
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A number of possible adverse effects have been associated with temperature-targeted hypothermia (Table 26-4). Bradycardia is very common and often pronounced (heart rate <50 beats/min is common) with induction, but usually is of little clinical consequence and requires no treatment.32 Tachydysrhythmias, atrial fibrillation, and nonsustained ventricular tachycardia are uncommon unless core body temperature is <32°C (89.6°F). QTc prolongation has been observed, so continuous cardiac monitoring and interval electrocardiograms are necessary.56
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Shivering can impede the lowering of body temperature. A variety of treatment approaches to shivering exist, the most definitive being neuromuscular blockade. Bleeding can be exacerbated by lowered core temperature but occurs in <5% of cases.32,57 Hypokalemia and hypomagnesemia can result from intracellular shifts and diuresis mediated by lowered core temperature.
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SPECIAL CONSIDERATIONS FOR TARGETED TEMPERATURE MANAGEMENT (THERAPEUTIC HYPOTHERMIA)
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The indications for therapeutic hypothermia after cardiac arrest in children are not well established. Although hypothermia improves outcomes after neonatal hypoxic ischemic encephalopathy, no supporting randomized trial evidence exists for its use after pediatric sudden cardiac arrest.58 Regardless, some hospitals use hypothermia protocols for resuscitated children.
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Prehospital Application
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Therapeutic hypothermia could have maximal benefit when begun immediately after ROSC.59,60 Although effective hospital-based interventions exist, they may be used infrequently due to multiple barriers such as lack of knowledge, experience, resources, and infrastructure.61 These barriers and the safety and relative ease of inducing hypothermia in the prehospital setting have led some EMS systems to implement protocols directed at induction of cooling prior to hospital arrival.62,63,64 Although this strategy has logical validity, the impact of prehospital hypothermia induction on outcomes is not well established.65,66,67