Cardiac arrest remains one of the major causes of mortality and serious neurological complications in different groups of patients. The return of spontaneous circulation after cardiac arrest cannot usually guarantee successful cerebral resuscitation; that is why professionals had to develop effective emergency strategies that would be fast, reliable, and obviously neuro-protective. Induced hypothermia has come to signify a new stage of medical and scientific development. The last 10 years of medical and scientific research have confirmed the benefits of induced hypothermia following cardiac arrest.
In the light of the existing scientific information, mild induced hypothermia (MIH) is undoubtedly beneficial to post-cardiac arrest patient outcomes, including decreased overall incidence of in-hospital mortality and improved neurological function; moreover, MIH is a more cost-effective treatment modality relative to other currently utilized life-saving interventions. Significant benefits In the developed world, out-of-hospital cardiac arrest remains the leading cause of unexpected deaths.
In the United States alone, about 1500 individuals annually suffer the consequences of cardiac arrest, which results in long-term neurological complications and even death (HACA, 2002). Whether a post-cardiac arrest patient is given a chance to survive depends on how the “chain of survival” is utilized; in other words, calling emergency, external cardiac massage delivery, expired-air breathing, defibrillation, and advanced life support altogether are expected to reduce mortality risks in post-cardiac arrest patients (Collins & Samworth, 2008).
Unfortunately, when it comes to out-of-hospital cardiac arrests, the rates of survival combined with relatively positive neurological outcomes remain dangerously low; statistically, less than 5% of patients have a chance to live to hospital discharge (Collins & Samworth, 2008). The use of mild induced hypothermia (MIH) has proved to be an effective means of increasing the rates of survival in post-cardiac arrest patients and reducing the scope of neurological complications that usually follow cardiac arrest.
Early in 1997, a small-scale study of 28 patients from Japan showed a positive survival tendency among cardiac arrest patients subjected to MIH (Collins & Samworth, 2008). The hypothermic group cooled for 48 hours following cardiac arrest showed 54% survival rates compared to 33% in the normothermic group (Collins & Samworth, 2008). Later in 2001, Hypothermia After Cardiac Arrest Study Group (2002) undertook another study to investigate possible impacts of MIH on survival rates on post-cardiac arrest patients.
Their results confirmed the benefits of MIH following cardiac arrest in terms of mortality rates: 55% of deaths in normothermic group compared to 41% of deaths in hypothermic group were a good sign for using MIH following cardiac arrest (HACA, 2002). Those results were later supported by Bernard et al (2002), who monitored medical progress of 77 patients following cardiac arrest: 49 percent of patients treated with MIH were later discharged from the hospital, and only 26 percent from normothermic group were lucky to survive the cardiac arrest and to leave the hospital (Collins & Samworth, 2008).
Researches that confirm the positive potential of MIH following cardiac arrest are numerous and many: Busch et al (2006) shows 59% hospital survival rates against 32% of those without hypothermia; Laisch-Farkash et al (2007) suggest that the positive impact of MIH on cardiac arrest patients’ survival is relevant within 6 hours of arrival to the emergency room. That patients are discharged from the hospital, however, does not necessarily imply that they can avoid serious neurological complications, but MIH has proved to significantly reduce the scope of neurological effects and to improve neurological recovery in post-cardiac arrest patients.
Since 1950, hypothermia has been used to protect “the brain against global ischemia that occurred as a consequence of some open-heart surgeries” (Chakravarthy, 2009). Unfortunately, it was not before the end of the 20th century that professionals in medicine have come to realize the neurological benefits of MIH in treating post-cardiac arrest patients. HACA (2002) reports 55% of hypothermic group patients having favorable neurological outcomes, compared to 39% in normothermic group (favorable neurological outcomes imply good recovery or moderate disability).
Although the exact mechanism of MIH remains unclear, it is obvious that timely application of MIH combined with blood flow promotion strategies leads to the normalization of brain function. Hypothermia can also provide significant protection from serious deleterious biochemical mechanisms that are responsible for neurological damage following cardiac arrest (Safar & Kochanek, 2002).
The use of MIH reduces the cerebral oxygen requirement by 6% for every degree of brain temperature reduction, and thus encourages more effective and more positive recovery of brain function: the growing body of evidence shows that MIH suppresses numerous chemical reactions associated with reperfusion injury (Chakravarthy, 2009). MIH reduces the damage to DNA levels and the scope of pro-death signaling events, with both being effective mechanisms of brain protection (Chakravarthy, 2009). Unfortunately, the use of MIH following cardiac arrest is not without a problem.
Researchers report a whole set of complications that may result of using MIH in post-cardiac arrest patients. These include sepsis, hemorrhage, increased coagulopathy, long lasting arrhythmias, hemodynamic instability, hyperglycemia and depressed cardiac function. Risks Although the benefits of hypothermia seem to overweigh its possible complications, the risks of adverse effects in MIH remain extremely relevant. “A detailed analysis of the complications and an analysis of the total number of complications revealed a trend toward a higher rate of infectious problems in the hypothermia group” (HACA, 2002).
Busch et al (2006) discuss the incidence of seizures as a possible negative outcome of cooling therapy in patients after cardiac arrest. In the same study, Busch et al (2006) discuss the real and potential impact of MIH on hypokalemia and the level of insulin in post-cardiac arrest patients. It appears that hypokalemia is one of the most expected and most widely spread side-effects of MIH. As a result, it is highly recommended that patients are prescribed potassium and magnesium infusions during active phases of cooling (Busch et al, 2006).
Also, cooling is likely to lead to hyperglycemia, which even without any other adverse effects can result in bad health and survival outcomes; and currently, insulin infusion is considered a standard part of cooling therapy in intensive care units (Busch et al, 2006). Unfortunately, the list of complications is not limited to hypokalemia and seizures. Collins and Samworth (2008) report 85% of hypothermic group patients developing pneumonia, compared to 40% of pneumonic patients on normothermic group.
These data confirm the direct link between the process of cooling and pneumonia symptoms in post-cardiac arrest patients. According to Laish-Farkash (2007), the use of MIH is closely associated with the development of various hemorrhagic complications and higher rates of sepsis. Post-cardiac arrest patients can also experience higher rates of cardiogenic shocks and unfavorable infectious outcomes (Laish-Farkash, 2007). Nevertheless, the discussed complications can hardly offset the positive impact and benefits of MIH following cardiac arrest.
Taking into account that the benefits of MIH substantially overweigh possible complications, why are hospitals reluctant to actively use cooling procedures for the sake of saving patients after cardiac arrest? Why not? This professional reluctance is usually justified by the two reasons. First, hospitals and intensive care units deem MIH as costly and financially non-justified; second, hospitals and ED must meet a whole range of requirements before MIH turns into a well-developed and compulsory standard of care: in many instances, MIH is still too new to become a widely-accepted practice.
For example, only 50 percent of Canadian emergency physicians report having at least once used MIH for post-cardiac arrest patients; many of them refer to the lack or complete absence of MIH protocols; others discuss sedation, ice packs, and paralysis as the essential components of cooling (Kennedy, Green & Stenstrom, 2008). Despite the growing body of research regarding the effectiveness and positive impact of MIH on mortality and neurological outcomes in post-cardiac arrest patients, hospital units cannot overcome their concerns about cost-effectiveness of MIH and the quality of long-term medical outcomes.
Although the use of MIH is not associated with any additional costs, it does not require investing in new equipment and does not increase the length of the hospital stay for patients (Busch et al, 2006), medical facilities do not seek to broaden the range of cooling procedures in their intensive care units. In reality, not the cost, but the establishment of MIH as a standard of treatment remains the major obstacle on the way to making MIH a widely-used practice.
Apart from the fact that medical professionals are increasingly concerned about possible MIH complications, the use hypothermia for unconscious patients in ED requires establishing a specific MIH protocol. This is impossible without a concerted action between intensive care physicians, emergency physicians, and cardiologists (Bernard, 2004). Although Busch et al (2006) suggest that the use of MIH does not require investing in new technologies and equipment, Bernard (2004) states that there are numerous technical issues associated with the use of ice packs and refrigerated air blankets.
These are too difficult and too slow to guarantee that post-cardiac arrest patients are provided with timely emergency care. The effectiveness of ice-cold crystalloid fluid is still under investigation. Nevertheless, recent findings show that the use of MIH following cardiac arrest can be a relevant and a highly effective solution. MIH can substantially decrease the rates of mortality and neurological complications. In the current state of research, hospitals and intensive care units should develop effective protocols, which will gradually turn MIH into a widely-accepted standard of care.
Conclusion When compared to other less effective life-saving interventions, induced hypothermia proves to be more effective relative to its cost. The use of MIH in post-cardiac arrest patients has already proved to be an effective instrument of reducing mortality and the scope of neurological complications. Unfortunately, MIH is still associated with a whole range of adverse effects. Sepsis, hemorrhage, coagulopathy, hyperglycemia, hypokalemia, infections, seizures, and pneumonia – all these are included into the list of possible side effects of MIH following cardiac arrest.
Many hospitals are still reluctant to implement MIH. The most common misconceptions refer to the costs of MIH as well as the existing uncertainty with regard to effectiveness of MIH in different groups of patients. Nevertheless, and taking into account these difficulties and complications, the benefits of MIH overweigh its adverse effects and costs. As such, MIH can be used as a reliable instrument of emergency therapy in post-cardiac arrest patients.