Therapeutic Hypothermia and Neurological Outcome after Cardiac Arrest - Essay Example

The use of therapeutic hypothermia to improve the neurological outcome after cardiac arrest This paper heralds a future research study into investigating whether therapeutic hypothermia initiated by infusion of cold () normal saline (2L) will be sufficient in producing better neurologic outcomes in patients of out-of-hospital cardiac arrest. The paper has proposed three hypotheses the proving correct of which shall entail success. The main significance of the study is to correctly ascertain the optimal duration of hypothermia, the optimal target temperature and the rates of cooling and rewarming. Its importance lies in the fact that many patients of cardiac arrest experience global ischemia that inflicts often irreparable damage to neurologic cellular mechanisms leading to very poor neurologic outcomes and, often, even mortality and vegetative existence. This is so because paramedics who usually have to treat such patients initially do not have sufficient therapeutic means to stymie this neurologic damage process during ischemic conditions. Introduction: Background: Mild hypothermia () have been induced in patients with cardiac arrest as a therapeutic means for protecting the brain against the global ischemia that usually accompanies open-heart surgery (Nolan et al, 2003). This therapeutic means was available since the late 1950s after which it was discontinued for some time because there was indefinite indication of benefits to patients (Nolan et al, 2003). Much later, this means has again been reintroduced in the context of cardiac arrest for a select group of patients and there are positive indications that when this therapeutic means is used after return of spontaneous circulation after cardiac arrest there is improved functionality and preemption from histological defects to the brain. This is true of a number of animal models, including the human one (Nolan et al, 2003). As late as 2000, when the 'Guidelines 2000 for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care' was brought out, there was still insufficient evidence of the therapeutic benefits of using hypothermia after resuscitation after cardiac arrest (Nolan et al, 2003). A couple of highly publicized studies with patients selected through stringent and complex inclusion criteria in Europe and Australia has established that neurological outcomes (ability to live independently and work at least part-time, etc.) are selectively available for groups of patients free from certain pathological complications (Nolan et al, 2003). Nevertheless, there are significant adverse effects that entail more research on the treatment option (Nolan et al, 2003). Mechanisms of action of induced moderate/mild hypothermia primarily include reduction of cerebral metabolic rate for oxygen @ 6% for every degree (Celsius) fall in temperature >. This reduces chances of mitochondrial damages and apoptosis from decreased production of free radicals, excitatory amino acids and calcium shifts (Nolan et al, 2003). External cooling techniques to induce mild to moderate hypothermia include use of cooling blankets, application of ice packs to groin, axillae and neck, use of wet towels and fanning and use of cooling helmets (Nolan et al, 2003). Recent internal techniques such as intravenous infusion of crystalloids and intravascular heat exchange devices are beginning to become available (Nolan et al, 2003). Since it is found that though extracorporeal techniques are efficient they are too invasive for use in prehospital treatments and most emergency departments this paper shall now discuss research on introducing a hypothermia therapeutic technique that is internal, safe, easily administrable out-of-hospital and cheap and includes infusion with selective crystalloids like common salt. This following section shall be deemed as the problem statement of the paper. Problem Statement: As has already been mentioned, the need for an internal technique that is not invasive and that can be performed safely and cheaply out of hospital and in emergency departments where time and equipment is short is urgent. Almost 1 out of 1500 adults in the developed world meet with unexpected death because of out-of-hospital cardiac arrest (Bernard, 2004). Successful recovery from such situationally sensitive cardiac arrest is dependent upon proper and timely administering of the 'chain-of-survival': immediate call to the emergency ambulance service, bystander delivery of cardiac massage and expired-air breathing, defibrillation and other provisions of advanced life support by paramedics (Bernard, 2004). Bernard, 2004, notes that hospital discharge for almost 95% of such out-of-hospital cardiac cases becomes impossible, in the Australian context and elsewhere. Those patients that are discharged have often suffered from neurologic damage that severely constrains their future cardiovascular systems (Bernard, 2004). This is so because response time for ambulances to arrive often exceeds more than 5 minutes - a period sufficient for the prolonged cardiac arrest to inflict irreparable neurologic damage. This is despite bystander-administered cardiopulmonary resuscitation (Bernard, 2004). Though paramedics are usually successful in transporting the patient alive to emergency departments with return of spontaneous circulation such patients arrive at a comatose state induced by the prolonged ischemic conditions (Bernard, 2004). Also, it is noted that, even in intensive care units, cardiologic interventions are deferred till a proper neurologic assessment is available and this, again, has usually to be deferred to up to three days after the cardiac arrest event (Bernard, 2004). Thus, it is widely advocated that, to improve neurologic outcomes, the time between cardiac arrest and defibrillation must be shortened drastically. Bringing the ambulance arrival time to below 5 minutes is not feasible (Bernard, 2004). Other measures such as installation of defibrillators in public places remain impractical. This dismal scenario prompts return of an 'old' therapeutic means to stymie neurologic damage from prolonged ischemic conditions after out-of-hospital cardiac arrest, This is induction of mild to moderate hypothermia. As per Georgiadis and colleagues (Source: Dietrich and Kuluz, 2003) an endovascular cooling technique using circulation of temperature-adjusted normal saline in a closed-loop system in patients with acute ischemic stroke was reported feasible and, importantly, allowed more control during the rewarming phase (Dietrich and Kuluz, 2003). Kim et al, 2005, report that initiating mild hypothermia immediately after return of spontaneous circulation in 17 hospitalized patients afflicted with out-of-hospital cardiac arrest proved effective. The particular technique used by Kim et al, 2005, was included in a pilot study where patients, included at 18 years and above and with other exclusion factors, resuscitated by paramedics from out-of-hospital cardiac arrest were infused with the cold crystalloid solution before consciousness returned. Consent was acquired from legal next of kin (Kim et al, 2005). A full list of inclusion and exclusion factors are to be found listed in Figure 1, Kim et al, 2005. Except for those suffering from trauma, patients with all causes of cardiac arrest such as ventricular fibrillation, asystole and pulseless electrical activity were included (Kim et al, 2005). Despite a number of research studies in recent years that have established the effectiveness of therapeutic hypothermia in the case of global ischemia events like cardiac arrest and also despite the effectiveness of a specific technique like infusion of cold normal saline the paper undertakes to propose this particular technique as the point of further study. It thus proposes that its problem statement is to ascertain whether infusion with cold () normal saline does prove effective against ischemic events like cardiac arrest. This technique is easily administrable by paramedics and it greatly reduces possibilities of neurologic damage induced by ischemic conditions prevalent after out-of-hospital cardiac arrest. Sub-Problems: Now that the main problem has been stated the paper proposes three associated sub-problems. It is noted here that there are numerous problems associated with initiation of therapeutic hypothermia by infusion with cold normal saline yet the paper, for its future research purpose, separates three of these for its own purpose. 1st Sub-Problem: The earlier parts of the paper have noted, as per research studies reviewed, that infusion with cold normal saline as therapeutic hypothermia initiation technique must be begun as soon as spontaneous circulation returns (Kim et al, 2005). This research study shall contrive to earmark how early that may be for the maximum degree of effectiveness in allowing cardiac arrest victims to return to relatively normal functioning as an indicator of neurological outcomes. Kim et al, 2005, note that, for the purpose of their study, the cooling protocol was started 6 hours within admission to the hospital. This research shall contrive to study the most effective temporal limits for infusion of cold fluid. 2nd Sub-Problem: The second sub-problem that this paper shall pinpoint for its research study is to note the degree of temperature drop with time after cold fluid infusion. The study shall contrive to ascertain the degree of such temperature drop with time associated with the effectiveness of the therapeutic measure against cardiac arrest in terms of neurologic outcomes. 3rd Sub-Problem: The third sub-problem associated with this particular study is to earmark the particular cooling measure - passive or active - that is most effective in sustaining hypothermia after the infusion with cold fluid - in this case cold () normal saline. The many such measures available include passive ones like fans and patient exposure and active ones like cooling blankets and neuromuscular blockade (Kim et al, 2005). Research Questions: The paper shall now propose three hypotheses for research. These are as hereunder. 1st Hypothesis: Infusion with cold () normal saline (2L) at an early stage - immediately upon return of spontaneous circulation - will be effective with desired neurologic outcomes against a global ischemic event like out-of-hospital cardiac arrest. 1st Null Hypothesis: Infusion with cold () normal saline (2L) at an early stage will not be effective against a global ischemic event like cardiac arrest. 2nd Hypothesis: Infusion with cold () normal saline (2L) at an early stage after a global ischemic event like cardiac arrest will prove a faster therapeutic hypothermia technique than others available. 2nd Null Hypothesis: Infusion with cold () normal saline (2L) at an early stage after a global ischemic event like cardiac arrest will not prove a faster therapeutic hypothermia technique than others available. 3rd Hypothesis: Active cooling measures undertaken after infusion of cold fluid will be more effective in sustaining the lowered temperature than passive ones. 3rd Null Hypothesis: Passive cooling measures undertaken after infusion of cold fluid will be more effective in sustaining the lowered temperature than active ones. Delimitations: Though the study shall incorporate appropriate inclusion and exclusion criteria within its means and also undertake to assess temperature and hemodynamic effects of hypothermia initiated by cold normal saline infusion it declares that there are certain associations it does not undertake to study. These are as follows. It shall not undertake to study the pathophysiology of ischemic brain injury that may be required to better understand the beneficial effects of hypothermia to such global ischemic events like cardiac arrest. It shall not undertake to study the variant effects of hypothermia on variant patient populations by varying inclusion and/or exclusion criteria. It shall not undertake to study the effects of locally-induced hypothermia against that of hypothermia induced as per previous research studies such as that of Kim et al, 2005. Assumptions: 1. The study firstly assumes that an intravenous technique like infusion of cold fluid is a more suitable one than extra corporeal ones for therapy of patients out of hospitals or in emergency departments. 2. It assumes that infusion with cold () normal saline (2L) will be sufficiently effective in lowering temperature. 3. It assumes that when the cold fluid is infused into the peripheral intravenous system of the patient this will be a sufficient technique for initiating hypothermia without any significance of localized effect. 4. It assumes that the inclusion/exclusion criteria inducted from reliable sources is sufficient to ensure patient safety. 5. It is also assumed, as per Kim et al, 2005, that no control group is required. Significance of Study (Conclusion): In particular context of this study four factors emerge as important. These are as follows: whether mild to moderate hypothermia leads to more effective neurologic outcomes in out-of-hospital cardiac arrest victims; the optimal duration of such therapeutic hypothermia; optimum target temperature; and rates of cooling and rewarming (Nolan et al, 2003). It is observed that therapeutic interventions targeting cerebral ischemia and other brain injuries are associated with problems of the start and duration of the cooling and rewarming phases (Dietrich and Kuluz, 2003). Another factor that influences neuropathy induced by mild to moderate hypothermia after ischemia, in this case cardiac arrest, is the temperature that significantly influences ischemic outcomes and pathology (Dietrich and Kuluz, 2003). There is also a necessity to focus hypothermia selectively as it is found in experiments that certain parts of the brain, when occluded from hypothermic conditions while others are placed in it, allows the therapeutic treatment to be more effective (Dietrich and Kuluz, 2003). Thus, to find solutions to these three above problem areas, investigations to alternate methods of cooling are actively being pursued all over the globe. While the main problem the study posits is that there is need for a systematic out-of-hospital approach to administering paramedic support to cardiac arrest patients so that their neurologic systemic damage is reduced to a minimum after return of spontaneous circulation and so they arrive at the hospital in a much better neurologic state the sub-problems highlight attendant difficulties to administration of this therapeutic means - mild/moderate hypothermia. In lieu of this the three hypotheses have been proposed to not only ascertain whether such hypothermia is feasible in conducive patients but also method, timing and duration of such hypothermia. References: Bernard, Stephen A., Therapeutic hypothermia after cardiac arrest, The Medical Journal of Australia, 2004, 181(9); 468-469. Dietrich, W. Dalton, and Kuluz, John W., New Research in the Field of Stroke, Therapeutic Hypothermia after Cardiac Arrest, Stroke, 2003: 34: 1051. (American Heart Association) Kim, Francis, et al, Pilot Study of Rapid Infusion of 2L of Normal Saline for Induction of Mild Hypothermia in Hospitalized, Comatose Survivors of Out-of-Hospital Cardiac Arrest, Circulation, 2005, 112; 715-719. (American Heart Association) Nolan, JP, et al, Therapeutic Hypothermia after Cardiac Arrest: An Advisory Statement by the Advanced Life Support Task Force of the International Liaison Committee on Resuscitation, Circulation, 2003; 108; 118. (American Heart Association) Read More