Introduction
Many patients have been in and out of hospital after suffering from cardiac arrest. A number of these patients die during their stay in hospital or develop severe permanent neurological impairment. The only therapy that has been developed to improve patients’ condition after successful recovery from sudden cardiac arrest is the induction of mild therapeutic hypothermia for 12–24 hours. This medical process, also known as protective hypothermia, lowers the patient’s body temperature in order to help reduce the risk of the ischemic injury to tissue resulting from a period of insufficient blood flow. Insufficient blood flow often results from a cardiac arrest or the occlusion of an artery by an embolism, as in the case of stroke. Therapeutic hypothermia may be induced either through invasive or non-invasive techniques. In the former, a catheter is placed in the inferior venacava via the femoral vein while the latter involves wrapping or covering the patient’s torso or legs using a blanket dipped in cooled water. Most studies have proven that patients who develop ischemic brain injuries have better outcomes if a hypothermia procedure is incorporated in their treatment regimen. Therapeutic hypothermia also decreases energy use and oxygen consumption in the brain and heart and glucose consumption during the early stages of cardiac arrest.
Discussion
The main role of a therapeutic hypothermic treatment is to protect the brain after a cardiac arrest. Indeed, cardiac arrest patients who have been given up for dead have been resuscitated and discharged to return back to their families and jobs with all or nearly all of their intellectual abilities intact after undergoing a hypothermic treatment. The most commonly used and cheapest method of this form of treatment is the use of cooling blankets and mattresses in combination with ice packs. In some cases, cooled intravenous (IV) fluids are used. Other methods include ice lavage, surface cooling helmets, and endovascular heat-exchange catheters. As soon as a patient’s heartbeat is restored, doctors and cardiologists quickly apply ice and other coolants to moderately lower the patient’s body temperature by about six degrees. The temperature reduction should be achieved within the shortest time possible, normally within 3 to 4 hours, until a temperature of approximately 33o C is attained. The patient is then put in a drug-induced coma in intensive care for 24 hours before progressively being warmed back up to normal temperature. Passive rewarming techniques are undertaken to allow the patient’s body to return to normal temperature. Active rewarming techniques use warming blankets or warmed IV fluids. At normal temperatures, the resumption of normal blood flow can have fatal effects on the brain. Therefore, a process known as icing is undertaken. Icing the body slows metabolism and protects the brain from at least some of the damage caused by the restored blood flow. However, doctors caution that not all cardiac-arrest patients are candidates for therapeutic hypothermia, and even some patients who receive it still do not benefit, but cooling still remains just one part of the process and quick use of CPR or defibrillators to restore heart rhythm remains critical, as does monitoring of cooled patients by nurses in the ICU. Studies have revealed an increasing effectiveness of therapeutic hypothermia in medical practice and have resulted in higher neurologic recovery rates. The rationale behind the new treatment is that the brain is more resilient than previously believed during the early period after the cardiac arrest.
Medical uses
Hypothermic therapies may effectively treat neurogenic fever following brain trauma, cardiac arrest, ischemic stroke, traumatic brain or spinal cord injury and neonatal encephalopathy.
Cardiac arrest
Therapeutic hypothermia has been shown to improve neurological outcome in cardiac arrest. Active cooling a patient to 32°C to 34°C is a technique that has been used to protect the brain from ischemia during cardiac surgery. Research on patients with cardiac arrest show that 49% of the patients treated with hypothermia following cardiac arrest experienced good outcomes, compared to only 26% of those who received standard care (Park, Bell, & Baker, 2008).
Hypothermia therapy for neonatal encephalopathy
Therapeutic hypothermia has been proven to improve the outcomes for newborn infants affected by perinatal hypoxia-ischemia, hypoxic ischemic encephalopathy or birth asphyxia. Selective cooling of the head or the whole body to a temperature of 32°C to 34°C initiated within 6 hours of birth and sustained for 72 hours significantly reduces mortality and reduces cerebral palsy and neurological defects in children. Hypothermia therapy for neonatal encephalopathy reduces brain damage and enhances a newborn’s chance of developing into a normal child.
Stroke/ Heat stroke
Heat stroke is the most severe form of heat related injury that occurs when the internal body temperature rises above 40°C with acute mental status changes, including impaired attention and memory, drowsiness, incapacitating personality changes and delirium. Research on the effectiveness of hypothermia in treating stroke is limited to animals, more studies are yet to be done to determine its efficacy in humans. The traditional treatment of heat stroke has been to reduce internal body temperatures by the quickest means possible and with the production of sophisticated hypothermic devices, internal body temperatures can be lowered at faster rates (Koran, 2008)). Although not proven in clinical studies, it is thought that extended reduction of a patient’s body temperature will improve the patient’s medical outcome.
Traumatic brain and Spinal code injury
Traumatic Brain Injury (TBI) is an attack on the brain that disrupts normal neurological activity. While patients may remain stable after the primary attack, progressing secondary mechanisms can lead to neurological deterioration (Park, 2008). Hypothermic medicine may be used in the future to improve neurological outcomes after TBI by reducing the subsequent secondary effects. Up to date, clinical trials have reached mixed conclusions because trials done used varying methodologies. These variations included temperatures goals and the duration taken to reach these goals.
Spinal Cord Injury (SCI) affects over 11,000 people per year in the U.S. resulting in severe neurological disabilities. Therapeutic Hypothermia has been shown enhance neurological outcomes when fever was present post-injury. However, the use of hypothermic treatment in SCI has not provided significant evidence to cause its adoption in mainstream medical practice.
Adverse Effects of Therapeutic Hypothermia
Therapeutic Hypothermia has shown some adverse effects such as discomfort, arrhythmia, decreasing clotting threshold, increased risk of infections, excessive shivering and increased risk of electrolyte imbalance. Research recommends that these adverse events can be alleviated only if proper procedures are followed and medical professionals must avoid exceeding the target temperature. Even though these issues can be managed with medications, the addition of further medication carries with it a new set of risks and possible complications to the patient.
The future of therapeutic hypothermia
Currently, medical literature recommends that therapeutic hypothermia should be initiated on patients who have experienced a cardiac arrest and had a return of spontaneous circulation. For therapeutic hypothermia to be effective, it should be started within 6 hours of the cardiac arrest. As cited by Dietrich (2008), studies are also being done to determine if this treatment provides better outcomes in patients who have experienced traumatic cardiac arrest. Although therapeutic hypothermia is still disputed in the pediatric population, it still remains an accepted practice in newborns with hypoxic ischemic encephalopathy and it has been shown to reduce mortality and neurologic deficits. While there are short-term adverse effects, such as thrombocytopenia, they are significantly outweighed by the positive outcomes of the regimen. Therapeutic hypothermia after cardiac arrest with return of spontaneous circulation has been studied comprehensively and the research findings have proven that patients experience better outcomes when it is administered as soon as possible after arrest. Emergency departments to have an obligation to their patients to not only initiate this procedure but also collaborate with ICU departments to continue therapeutic hypothermia protocol.
Conclusion
Therapeutic hypothermia is a medical treatment that lowers a patient’s body temperature in order to help reduce the risk of the ischemic injury to tissue resulting from a period of insufficient blood flow. It effectively treats neonatal encephalopathy, cardiac arrest, ischemic stroke, traumatic brain or spinal cord, and neurogenic fever. However, similar to most treatment regimens, this treatment has adverse effects such as arrhythmia, decreasing clotting threshold, increased risk of infections, excessive shivering and increased risk of electrolyte imbalance. For it to be effective it should be initiated within 6 hours of the arrest. However, future studies should be conducted to determine its efficacy.
Reference List
Park, E., Bell, J, and Baker, A. (2008) Traumatic Brain Injury: Can the Consequences be stopped? Canadian Medical Association Journal, 178 (9), 567-78.
Dietrich, W., D. (2008). Therapeutic Hypothermia for Spinal Cord Injury. Critical Care Medicine, 37(7), 238-242.
Koran, Z., E. (2008). Therapeutic Hypothermia in the post resuscitation Patient: The Development and Implementation of an Evidence-Based Protocol in the Emergency Department. Advanced Emergency Nursing Journal, 30(4), 319-333.