Southern Medical Journal:
Community-Based Application of Mild Therapeutic Hypothermia for Survivors of Cardiac Arrest
Prior, John DO; Lawhon-Triano, Mary CRNP-C; Fedor, David DO; Vanston, Vincent J. MD; Getts, Roger DO; Smego, Raymond A. Jr MD, MPH
From the Sections of Nephrology and Palliative Medicine, Department of Medicine, Mercy Hospital; and The Commonwealth Medical College, Scranton, PA.
Reprint requests to John Prior, DO, Northeast Pennsylvania Nephrology, 802 Jefferson Avenue, Scranton, PA 18510. Email: JPrior@tcmedc.org
Presented in part at the 2008 Scientific Session of the American Heart Association, New Orleans, November 12–16.
Accepted October 8, 2009.
Objective: To demonstrate that the application of therapeutic hypothermia is technically feasible in a community-based setting.
Background: Implementation of therapeutic hypothermia for survivors of cardiac arrest in the United States has been slow, at least partially because of the perception that this therapy is technically difficult, especially at the community level.
Study Design: Retrospective cohort study with historical controls.
Methods: At our three community hospitals and after return of spontaneous circulation (ROSC), survivors of cardiac arrest were treated with therapeutic hypothermia using ice and cooling blankets or suits in order to cool patients to 32°C–34°C within 4 hours to achieve goal temperature within 8 hours and to maintain goal temperature for 24 hours.
Results: Beginning in 2004, 44 survivors of cardiac arrest were managed with therapeutic hypothermia. The mean time from ROSC to initiation of therapeutic hypothermia was 2.8 hours (range, 0.2–7.8 hours), the mean time from ROSC to goal temperature was 7.2 hours (range, 0.8–15.1 hours), and the mean time maintained at goal temperature was 24.5 hours (range, 9–28 hours). Once patients achieved goal temperature, 4.4% of the temperature readings were above 34°C, reflecting undercooling, while 16.4% of the readings were below 32°C, indicative of overcooling. Overall survival until hospital discharge with good neurologic outcome was 43%, compared to only 13% (P < 0.001) among selected controls. There were no major complications directly attributable to the induction of hypothermia or rewarming.
Conclusion: A simple protocol of mild therapeutic hypothermia using locally available resources is technically feasible and safe in a community-based setting.
* Using a standardized therapeutic hypothermia protocol and locally available resources, community hospitals can successfully implement American Heart Association (AHA) recommendations for survivors of in-hospital and out-of-hospital cardiac arrest.
* Survival of patients with ventricular fibrillation or ventricular tachycardia as the initial cardiac rhythm appeared to be better than for those with other arrhythmias.
* Many institutions are including patients with asystole and other first post-arrest rhythms in their evidence-based therapeutic hypothermia protocols.
Numerous animal studies and human clinical trials have clearly demonstrated the neuroprotective effect of induced hypothermia in reducing the degree of anoxic brain injury and improving neurologic recovery in clinical situations involving cardiopulmonary and cerebral resuscitation.1–12 Evidence-based, post-resuscitative recommendations of the American Heart Association (AHA) and the International Liaison Committee on Resuscitation (ILCOR) include the technique of therapeutic hypothermia for survivors of out-of-hospital cardiac arrest, as a proven way of improving neurologic outcomes.
Despite these endorsements there is a concern that therapeutic hypothermia is being underutilized in clinical practice.13,14 Data from a number of surveys in Europe and North America suggest that rates of use of therapeutic hypothermia among physicians may be as low as 30% to 40%, even in academic centers.4,14–16 Herein, we report our preliminary experience with 44 patients managed with therapeutic hypothermia at three community hospitals in Pennsylvania, focusing on the technical feasibility of the procedure in a community-based setting.
Patients and Methods
Scranton, Pennsylvania is a community of 75,000 people and is served by three hospitals with a total inpatient bed capacity of 700. In 2003 after reviewing ILCOR recommendations and the literature on therapeutic hypothermia for cardiac arrest in our evidence-based intensive care unit (ICU) journal club, a decision was made to implement the recommendation in each of our hospitals. Our common study protocol called for mild therapeutic hypothermia (TH) to be initiated within four hours, achievement of a goal temperature of 32°C to 34°C (89.6°F to 93.2°F) within 8 hours, and maintenance of the goal temperature for 24 hours. Therapeutic hypothermia was performed using surface cooling techniques and resources available locally, ie cooling blankets, cooling suits, and ice packs. A multidisciplinary group of healthcare workers (nurses, physicians, and pharmacists) developed the orders for the use of therapeutic hypothermia. These orders were drafted according to standards used in the studies by Holzer et al17 and Bernard et al.18 The order set was approved intact by the executive committees of each of the hospitals and patients were placed on the protocol at the medical staff's discretion. Eligibility was similar to the above mentioned studies (ie out-of-hospital ventricular fibrillation/ventricular tachycardia arrest) but also included unwitnessed cardiac arrest, in-hospital arrest, and nonventricular fibrillation arrest. Prior to and during initiation of the protocol, a comprehensive education program was started and targeted health care workers most likely to care for survivors of cardiac arrest. All patients were mechanically ventilated, sedated with propofol, and paralyzed with vecuronium. Therapeutic hypothermia was induced by the use of cooling blankets, cooling suits (RaprRoundTM and Medi-Therm® III hypothermia machine; Gaymar Industries, Orchard Park, NY), and ice bags as necessary to achieve and maintain a goal temperature of 32°C–34°C for 24 hours. Body temperatures were monitored via bladder temperature recordings. Cooling blankets or cooling suits were used in all patients. Ice bags applied to the groin, axillae, and neck were required in 75% of cases in order to achieve the goal temperature. Routine intensive care unit (ICU) care included deep venous thrombosis prophylaxis, stress gastritis prophylaxis, glycemic control, and skin care. At the end of 24 hours of hypothermic management, patients were passively warmed (ie cooling techniques were withdrawn and temperatures allowed to rise on their own), and paralysis followed by sedation were discontinued when the patient's temperature was 36.5°C. Hyperthermia that occurred after warming was treated with the use of cooling blankets and antipyretics.
This was a retrospective cohort study with historical controls. The medical charts of the first 44 cardiac arrest patients consecutively managed with the therapeutic hypothermia protocol since 2004 were retrospectively reviewed and the cardiac arrest and post-cardiac arrest data were compiled using the Utstein style.19 In addition, cooling data (time to initiation of TH, times to goal temperature, and temperatures outside of range) and clinical outcomes were extracted in a uniform fashion using a standardized data collection tool by reviewers trained in its use. Patients were followed to the time of discharge or death, and a good neurologic outcome was defined as a Pittsburgh Cerebral Performance Scale (CPS) of 1: discharge to home neurologically intact or 2: discharge to a rehabilitation center with mild cognitive impairment.20,21 Mortality and neurologic outcome data were compared to those of institutional cardiac arrest control patients admitted to the study hospitals during the years 2002–2003. Statistical analysis of data was performed using a statistical software package, SPSS® 16.0 (SPSS, Inc., Chicago, IL) to calculate descriptives, frequencies, Chi-squared and Pearson two tailed t test.
Control subjects included 368 patients with a discharge diagnosis of cardiac arrest (221 patients) or ventricular fibrillation (147 patients), including both in-hospital and out-of-hospital arrest and were seen at two of the study hospitals (Mercy and Moses Taylor Hospitals) during the years 2003–2004.
Baseline patient demographics and cardiac arrest data are shown in Table 1. Patients in the study cohort were mostly Caucasian (91%) and elderly (mean age, 65 years), reflecting the demographics of our local community and the population at risk for cardiac arrest. Most subjects had an out-of-hospital cardiac arrest that was witnessed, and two-thirds received bystander cardiopulmonary resuscitation (CPR). About half of the patients had nonventricular fibrillation arrests.
Cooling data are shown in Tables 2 and 3. In addition, the mean time from initiation of TH to goal temperature was 4.4 hours (range, 0–9.8 hours), and the mean warming time (ie from discontinuation of TH to 36.5°C) was 10.1 hours (range, 1–22 hours). The initiation of TH within 4 hours of ROSC occurred in 71% of all treated patients, and the goal temperature (34°C) was achieved within <8 hours in 59% of subjects. The mean time patients were maintained at the goal temperature was just over 24 hours, and the goal duration of ≥24 hours was achieved in 68% of the study cohort. Patients with a good CPS score: 1) were less likely to achieve goal temperature within 8 hours (42% vs. 72%) (P < 0.05); 2) had a higher baseline temperature than those with a poor CPS score (36.8°C vs. 35.6°C) (P = 0.001); and 3) were cooled longer (27.3 hours vs. 22.4 hours) (P < 0.02). Among all subjects cooled for longer than 24 hours, however, there was no significant difference between those with a good neurologic recovery and those with a poor outcome (79% vs. 60%, respectively) (P = 0.2). Once patients achieved goal temperature, 4.4% of the temperature readings were above 34°C, thereby reflecting undercooling, while 16.4% of the readings were below 32°C and indicated overcooling.
Nineteen (43%) hypothermia-managed patients survived with a good neurologic outcome. Of those who survived until hospital discharge, good neurologic outcomes (CPS1, 58% or CPS2, 42%) occurred in all patients. Survival for patients with ventricular fibrillation or ventricular tachycardia as the initial cardiac rhythm was 61% compared to 24% of subjects with other arrhythmias (eg asystole, bradycardia, etc.) (P < 0.05). Arrhythmia requiring drug treatment (52%) was the most common complication encountered in patients managed with therapeutic hypothermia. Sepsis (41%) was also common, with aspiration pneumonia being the most frequent primary infection. Other clinical complications included acute kidney injury (50%), bleeding (9%), and skin breakdown (7%). There were no major complications directly attributable to the induction of hypothermia or rewarming.
For the historical control subgroup with ventricular fibrillation, a good clinical outcome, defined as discharge to home or to a rehabilitation center, occurred in 50 patients (34%). In contrast, for 221 patients hospitalized with a diagnosis of “cardiac arrest,” only 28 (13%) had a good clinical outcome.
Changes in clinical practice do not always parallel advances in medical knowledge, and widespread application of clinical management guidelines often fall short of expectations. Examples of this disparity are adherence to post-myocardial infarction care and the treatment of congestive heart failure.22,23 Furthermore, the use of clinical practice guidelines in the community often lags behind their use in academic centers.
Despite convincing scientific evidence of its benefit and lack of therapeutic alternatives, three recent surveys from the United States, United Kingdom, and Germany have documented that the use of therapeutic induced hypothermia after cardiac arrest is still surprisingly low.24–27 Reasons given for the lack of widespread implementation include logistical or resource issues,25 perceived lack of scientific evidence,25,26 belief that cooling is technically too difficult,26,27 and that therapeutic hypothermia is not yet considered part of advanced life support.26 Factors also linked to suboptimal utilization include hospital and ICU size (with more frequent use in university and affiliated hospitals and bigger ICUs), composition of the ICU team (more frequent among internal medicine physicians than anesthesiologists), and concern over use in patients other than those with witnessed out-of-hospital cardiac arrest with initial ventricular fibrillation.28
Several other studies have explored the issue of underutilization of the guidelines for therapeutic hypothermia. In a 2008 survey of the use of induced hypothermia after cardiac arrest among Canadian emergency physicians, only about half of respondents reported that they had used therapeutic hypothermia in practice, and a majority of these physicians were located in academic centers.13 Cited barriers against induced hypothermia included a lack of institutional policies and protocols (39%) and a lack of resources (29%). Lack of support from consultants was relatively uncommon (9%) in Canadian practice. In a US survey of the National Association of Emergency Medical Services Physicians, common perceived barriers to the prehospital initiation of therapeutic hypothermia after out-of-hospital cardiac arrest included the following: being overburdened with other tasks (62%), short transport times (61%), lack of refrigeration equipment (60%), and receiving hospitals' failure to continue therapeutic hypothermia (57%).15 A small but significant percentage (22%) believed that the lack of guidelines specifically addressing prehospital cooling was a barrier to initiating a protocol, and only 62% correctly identified 32°C–34°C as the recommended target temperature range. Among those who reported prehospital use of TH, only one of eight (12.5%) recalled having cooled greater than 10% of eligible patients in the field. Studies indicate that emergency room physicians may be less likely to initiate therapeutic hypothermia than critical care specialists.13,15,16 Using a linear model to assess the potential public health impact, Majersik et al29 projected that an additional 2,298 patients per year could be expected to have a good neurological outcome, if US physicians were to implement hypothermia fully in all eligible comatose survivors of out-of-hospital cardiac arrest.
In following the 2003 and 2005 AHA/ ILCOR recommendations, using a standardized therapeutic hypothermia protocol and locally available resources, we have successfully applied this treatment modality to 44 patients at our three community hospitals. Of note, in our study cohort we included patients with both ventricular fibrillation/ventricular tachycardia-related cardiac arrest and nonventricular fibrillation/ventricular tachycardia arrest in light of successes recently reported among this latter group in several national registries.30 Survival and neurologic outcomes, as well as rates of adverse events, in our treated patients compared favorably to our community cardiac arrest outcomes and to previously published results of therapeutic hypothermia trials.2,8,31–34 We met our goals of initiation of cooling within 4 hours, achieving goal temperature within 8 hours, and maintaining goal temperature for 24 hours in 71%, 59% and 68% of all patients, respectively. Our mean time from ROSC to target temperature achievement was comparable to previous reports (7.2 vs. 5.0–9.2 hours, respectively).8,33,35 Interestingly, although our success rate in achieving the target temperature was lower (59% vs. 62.5%–96%) compared to prior TH implementation studies, our clinical outcomes were as good or better.8,32,34,36
Patients with good neurologic outcomes tended to be warmer at the outset of hypothermic management and were less likely to achieve goal temperature within 8 hours, ie were harder to cool, than those with poorer outcomes. We are uncertain of the reason(s) behind this interesting observation, although this finding could be a reflection of the severity of the anoxic injury in the latter group leading to greater disruption in the thermoregulatory function of the brain.37 Although the small sample size of our study was not designed to address this point, it seems extremely unlikely that these results indicate that early TH is harmful. Furthermore, we found that a longer mean duration of TH and more frequent overcooling, but not undercooling, was associated with improved neurologic outcomes.
The external cooling methods we employed were simple and economically reasonable, and have been used effectively by other observational studies.8,17,18,34,36 These resources should be available in most hospitals throughout the United States regardless of type or geographic location. For a majority of our patients, surface cooling with ice bags and cooling blankets or suits was sufficient to achieve and maintain mild hypothermia for 24 hours, although such simple and inexpensive surface cooling with this method led to overcooling in 16.4% of the hours cooled.
Various methods are available to induce and maintain therapeutic hypothermia after cardiac arrest and include external cooling with water-circulating blankets, suits, or gel-coated pads; air-circulating blankets; intravascular cooling using infusion of large-volume, ice-cold intravenous fluids32; extracorporeal circulation; and extracorporeal membrane oxygenation.35,38 At an academically affiliated urban hospital, Flint et al39 compared the performance characteristics and safety of simple surface cooling with or without an endovascular cooling catheter system among 42 comatose survivors of cardiac arrest. Hypothermia was induced and maintained by simple ice packs and cooling blankets with or without placement of an endovascular cooling catheter system with automated temperature feedback regulation. Overall, the rate of active cooling was not different between patients treated with endovascular catheter-assisted hypothermia and those treated with surface cooling alone, although the use of a larger (14F) catheter was associated with faster cooling rates. Maintenance of goal temperature (34°C) was better controlled with the use of a cooling catheter. Use of surface cooling alone was associated with significant temperature overshoot. Patients treated with surface cooling alone spent more time in a bradycardic state. In another prospective comparison of cooling methods among 52 ICU patients, cooling with water-circulating blankets and gel-pads and intravascular cooling was more efficient compared to conventional cooling and air-circulating blankets.40 The intravascular cooling system was most reliable in maintaining a stable temperature. Two other recent publications have raised concerns about overcooling when applying simple external measures.41,42 Extracorporeal circulation is considered the gold standard in the treatment of hypothermic cardiocirculatory arrest.37 However, both this technique and standard extracorporeal circulation are generally available only at larger tertiary care centers.
As Soreide and Sunde24 have suggested, each institution should choose a method, or combination of methods, that suits its infrastructure and logistics. When evaluating different cooling methods, ICU nurses have noted how each method has its own strengths and weaknesses.43 Additional comparative studies of the various available cooling techniques (external and internal; invasive and noninvasive) are needed.
Future improvements in our protocol will focus on several areas to better achieve cooling goals. Enhanced education should result in more timely initiation of TH allowing achievement of goal temperature in <8 hours in a greater percentage of patients. Use of iced intravenous saline and cooling suits will also help reduce the time from ROSC to target goal safely and inexpensively. Although the numbers are small and the results not statistically significant, patients cooled with cooling suits took less time (5.3 hours vs. 7.6 hours; P = 0.1) and were more likely to achieve goal temperature within 8 hours (75% vs. 56%; P = 0.3). These suits will have the added benefit of decreasing the workload for bedside nurses and should help prevent overcooling.
We observed no major complications directly attributable to the induction of hypothermia or to rewarming. One survivor's passive rewarming occurred very quickly after only one hour, yet he experienced no systemic or neurologic adverse effects that have been described in animal and human studies of rapid rewarming after therapeutic hypothermia.44–46
In conclusion, therapeutic hypothermia is currently recommended for all survivors of ventricular fibrillation/ventricular tachycardia out-of-hospital cardiac arrest. The ideal goal is to perform therapeutic hypothermia on all eligible survivors of out-of-hospital cardiac arrest regardless of their presentation to a university hospital, urban hospital, or community hospital. Our data show that this treatment modality is technically possible even in smaller centers and can be successfully performed with locally available resources.
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cardiac arrest; community hospital; feasibility; outcome; therapeutic hypothermia
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