Determinants of heat generation in patients treated with therapeutic hypothermia following cardiac arrest

Target temperature management versus normothermia without temperature feedback systems for out-of-hospital cardiac arrest survivors

Objective

The clinical benefit of automatic temperature control devices remains unclear. We investigated the outcomes of out-of-hospital cardiac arrest (OHCA) survivors who had undergone either target temperature management (TTM) with a temperature feedback system (TFS) or maintenance of normothermia without a TFS during post-resuscitation care.

Methods

This study was a retrospective analysis of a multicenter prospective cohort of OHCA survivors who had received postcardiac arrest care from August 2014 to December 2018. The overlap propensity score weighting method was applied for adjustment between groups.

Results

A total of 405 OHCA survivors were included. TTM with a TFS and normothermia without a TFS were applied to 318 and 87 patients, respectively. Fever events were more common in patients with normothermia without a TFS. After propensity score matching, no statistically significant differences were observed in the 1-month good neurologic outcome (odds ratio 0.99, 95% confidence interval [CI] 0.56–1.25) or survival rate (odds ratio 1.25, 95% CI 0.88–1.78).

Conclusion

No significant differences in the 1-month neurologic outcome were observed between patients receiving TTM with a TFS and those undergoing normothermia without a TFS.

Water Temperature Variability Is Associated with Neurologic Outcomes in Out-of-Hospital Cardiac Arrest Survivors Who Underwent Targeted Temperature Management at 33°C

We examined the association between variability in body temperature (BT) and water temperature (WT) during the maintenance period of targeted temperature management (TTM) and neurologic outcomes in out-of-hospital cardiac arrest (OHCA) survivors. Adult (≥18 years), comatose OHCA survivors who underwent TTM at 33°C between October 2015 and December 2019 were included. We collected data on BT and WT recorded every minute during the TTM maintenance period. Temperature variability was measured as the standard deviation of BT and WT during the 33°C maintenance period. The primary outcome was a poor neurologic outcome, defined as a cerebral performance category scale 3-5 at 6 months. Of the 154 included patients, 96 (62.3%) had poor outcomes. The BT variability in the poor outcome group was lower than that in the good outcome group (0.16°C [0.13-0.27°C] vs. 0.13°C [0.11-0.18°C]). In addition, the WT variability during the maintenance period in the poor outcome group was lower than that in the good outcome group (2.24°C [1.80-3.96°C] vs. 1.77°C [1.26-2.32°C]). In the multivariate analysis, WT variability (odds ratio 0.508; 95% confidence interval, 0.295-0.874; p = 0.014) was independently associated with poor neurologic outcome. BT variability and cooling beyond 33.0°C ± 1.0°C were not associated with poor neurologic outcomes. WT variability during the maintenance period was independently associated with neurologic outcomes in OHCA survivors who underwent TTM at 33°C. In addition, overcooling or undercooling during the maintenance period was not associated with neurologic outcomes.

Quality of targeted temperature management and outcome of out-of-hospital cardiac arrest patients: A post hoc analysis of the TTH48 study

BACKGROUND

No data are available on the quality of targeted temperature management (TTM) provided to out-of-hospital cardiac arrest (OHCA) patients and its association with outcome.

METHODS

Post hoc analysis of the TTH48 study (NCT01689077), which compared the effects of prolonged TTM at 33 °C for 48 h to standard 24-h TTM on neurologic outcome. Admission temperature, speed of cooling, rewarming rates, precision (i.e. temperature variability), overcooling and overshooting as post-cooling fever (i.e. >38.0 °C) were collected. A specific score, ranging from 1 to 9, was computed to define the "quality of TTM".

RESULTS

On a total of 352 patients, most had a moderate quality of TTM (n = 217; 62% - score 4-6), while 80 (23%) patients had a low quality of TTM (score 1-3) and only 52 (16%) a high quality of TTM (score 7-9). The proportion of patients with unfavorable neurological outcome (UO; Cerebral Performance Category of 3-5 at 6 months) was similar between the different quality of TTM groups (p = 0.90). Although a shorter time from arrest to target temperature and a lower proportion of time outside the target ranges in the TTM 48-h than in the TTM 24-h group, quality of TTM was similar between groups. Also, the proportion of patients with UO was similar between the different quality of TTM groups when TTM 48-h and TTM 24-h were compared.

CONCLUSIONS

In this study, high quality of TTM was provided to a small proportion of patients. However, quality of TTM was not associated with patients' outcome.

Thermal Index for early non-invasive assessment of brain injury in newborns treated with therapeutic hypothermia: preliminary report

Perinatal asphyxia (PA) is the 3rd most common cause of neonatal death and one of the most common causes of severe neurological impairments in children. Current tools and measurements mainly based on the analysis of clinical evaluation and laboratory and electrophysiological tests do not give consistent data allowing to predict the severity of hypoxic-ischemic encephalopathy (HIE) until a magnetic resonance imaging (MRI) score is performed. The aim of this work is to evaluate the usefulness of the new index, called Thermal Index (TI) in the assessment of the degree of brain damage in newborns in the course of therapeutic hypothermia (TH) due to PA. This was a prospective, observational, pilot study which did not require any changes in the applicable procedures. Analysis has been applied to six newborn babies treated with TH in Neonatal/Paediatric ICU in University Hospital in Opole in 2018 due to PA. They all met criteria for TH according to the current recommendations. Brain MRI was performed after the end of TH when the children were brought back to normal temperature, with the use of a 1.5 T scanner, using T1-, T2-weighted images, fluid-attenuated inversion recovery (FLAIR), inversion recovery (IR), susceptibility-weighted imaging (SWI), and diffusion-weighted imaging (DWI). The images were assessed using MRI score according to the scoring system proposed by Weeke et al. The Thermal Index assessing endogenous heat production was calculated according to the formula proposed in this paper. A high, statistically significant positive correlation was found between MRI scores and TI values (0.98; p = 0.0003) in the 1st hour of therapy. High correlation with MRI assessment, the non-invasiveness of measurements and the availability of results within the first few hours of treatment, allow authors to propose the Thermal Index as a tool for early evaluating of the brain injury in newborns treated with TH. Further research is required to confirm the usefulness of the proposed method.

Thermoregulation in post-cardiac arrest patients treated with targeted temperature management

OBJECTIVE

Evaluate the relationship between heat generation during rewarming in post-cardiac arrest patients receiving targeted temperature management (TTM) as a surrogate of thermoregulatory ability and clinical outcomes.

METHODS

This is a prospective observational single-centre study conducted at an urban tertiary-care hospital. We included post-cardiac arrest adults who received TTM via surface cooling device between April 2018 and June 2019.

RESULTS

Patient heat generation was calculated by multiplying the inverse of the average machine water temperature with time to rewarm to 37 °C and standardized in two ways to account for target temperature variation: (1) divided by number of degrees between target temperature and 37 °C, and (2) limited to when patient was rewarmed from 36 °C to 37 °C. The primary outcome was poor neurologic status, defined as Cerebral Performance Category (CPC) score 3-5, and the secondary outcome was 30-day survival. Sixty-six patients were included: 45 (68%) had a CPC-score of 3-5 and 23 (35%) were alive at 30 days. Besides initial rhythm and arrest downtime, baseline characteristics were similar between outcomes. Heat generation was not associated with poor neurological outcome (CPC 3-5: 6.6 [IQR: 6.1, 7.4] versus CPC 1-2: 6.6 [IQR: 5.7, 7.6], p = 0.89) or survival at 30 days (non-survivors: 6.6 [IQR: 6.6, 7.4] vs. survivors: 6.6 [IQR: 5.7, 8.0, p = 0.78]).

CONCLUSION

Heat generation during rewarming was not associated with neurologic outcomes. However, there was a relationship between poor neurological outcome and higher median water temperatures. Time to rewarm was prolonged in patients with poor neurological outcome.

Impact of controlled normothermia following hypothermic targeted temperature management for post-rewarming fever and outcomes in post-cardiac arrest patients: A propensity score-matched analysis from a multicentre registry

AIM OF THE STUDY

We investigated whether controlled normothermia (CN) after the rewarming phase of targeted temperature management (TTM) is associated with preventing post-rewarming fever and outcomes 6 months after out-of-hospital cardiac arrest (OHCA).

METHODS

This was an analysis of a prospective registry comprising OHCA patients treated with TTM at 22 academic hospitals between October 2015 and December 2018. We calculated the incremental area under the curve (iAUC) for body temperature greater than or equal to 37.5 °C for each patient during the first 24 h after the end of rewarming. The relationships among CN and iAUC, 6-month survival and good neurological outcome were analysed. To minimize differences in the baseline characteristics of the patients, we used propensity score-matched analysis.

RESULTS

In total, 1144 patients were enrolled. After propensity score matching, 646 patients (comprising 323 pairs) were obtained. In the unmatched cohort, post-rewarming CN was significantly associated with a lower iAUC (0.34 [1.38] vs. 1.19 [2.27]; p < 0.001) but not 6-month survival (adjusted odds ratio (OR): 1.121; 95% confidence interval (CI): 0.836-1.504; p = 0.446) and good neurological outcome (adjusted OR: 1.030; 95% CI: 0.734-1.446; p = 0.863). The results were similar in the propensity score-matched cohort (0.38 [1.56] vs. 1.03 [2.21], p < 0.001, OR: 1.347, 95% CI: 0.989-1.835, p = 0.059 and OR: 1.280, 95% CI 0.925-1.772, p = 0.137, respectively).

CONCLUSION

Post-rewarming CN prevents high fever in the normothermia phase of TTM. However, our data suggest the lack of association between CN and the patient's 6-month survival and good neurological outcome.

Theoretical basis for the use of non-invasive thermal measurements to assess the brain injury in newborns undergoing therapeutic hypothermia

The aim of this paper is to propose a new non-invasive methodology to estimate thermogenesis in newborns with perinatal asphyxia (PA) undergoing therapeutic hypothermia (TH). Metabolic heat production (with respect to either a neonate’s body mass or its body surface) is calculated from the newborn’s heat balance, estimating all remaining terms of this heat balance utilising results of only non-invasive thermal measurements. The measurement devices work with standard equipment used for therapeutic hypothermia and are equipped with the Global System for Mobile Communications (GSM), which allows one to record and monitor the course of the therapy remotely (using an internet browser) without disturbing the medical personnel. This methodology allows one to estimate thermogenesis in newborns with perinatal asphyxia undergoing therapeutic hypothermia. It also offers information about instantaneous values of the rate of cooling together with values of remaining rates of heat transfer. It also shows the trend of any changes, which are recorded during treatment. Having information about all components of the heat balance one is able to facilitate comparison of results obtained for different patients, in whom these components may differ. The proposed method can be a new tool for measuring heat balance with the possibility of offering better predictions regarding short-term neurologic outcomes and tailored management in newborns treated by TH.

Early Post-Rewarming Fever Is Associated with Favorable 6-Month Neurologic Outcomes in Patients with Out-Of-Hospital Cardiac Arrest: A Multicenter Registry Study

We investigated the association between post-rewarming fever (PRF) and 6-month neurologic outcomes in cardiac arrest survivors. This was a multicenter study based on a registry of comatose adult (≥18 years) out-of-hospital cardiac arrest (OHCA) survivors who underwent targeted temperature management between October 2015 to December 2018. PRF was defined as peak temperature ≥ 38.0 °C within 72 h after completion of rewarming, and PRF timing was categorized as within 24, 24–48, and 48–72 h epochs. The primary outcome was neurologic outcomes at six months after cardiac arrest. Unfavorable neurologic outcome was defined as cerebral performance categories three to five. A total of 1031 patients were included, and 642 (62.3%) had unfavorable neurologic outcomes. PRF developed in 389 (37.7%) patients in 72 h after rewarming: within 24 h in 150 (38.6%), in 24–48 h in 155 (39.8%), and in 48–72 h in 84 (21.6%). PRF was associated with improved neurologic outcomes (odds ratio (OR), 0.633; 95% confidence interval (CI), 0.416–0.963). PRF within 24 h (OR, 0.355; 95% CI, 0.191–0.659), but not in 24–48 h or 48–72 h, was associated with unfavorable neurologic outcomes. Early PRF within 24 h after rewarming was associated with favorable neurologic outcomes.

Increased Heat Generation in Postcardiac Arrest Patients During Targeted Temperature Management Is Associated With Better Outcomes

OBJECTIVES

Assess if amount of heat generated by postcardiac arrest patients to reach target temperature (Ttarget) during targeted temperature management is associated with outcomes by serving as a proxy for thermoregulatory ability, and whether it modifies the relationship between time to Ttarget and outcomes.

DESIGN

Retrospective cohort study.

SETTING

Urban tertiary-care hospital.

PATIENTS

Successfully resuscitated targeted temperature management-treated adult postarrest patients between 2008 and 2015 with serial temperature data and Ttarget less than or equal to 34°C.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Time to Ttarget was defined as time from targeted temperature management initiation to first recorded patient temperature less than or equal to 34°C. Patient heat generation ("heat units") was calculated as inverse of average water temperature × hours between initiation and Ttarget × 100. Primary outcome was neurologic status measured by Cerebral Performance Category score; secondary outcome was survival, both at hospital discharge. Univariate analyses were performed using Wilcoxon rank-sum tests; multivariate analyses used logistic regression. Of 203 patients included, those with Cerebral Performance Category score 3-5 generated less heat before reaching Ttarget (median, 8.1 heat units [interquartile range, 3.6-21.6 heat units] vs median, 20.0 heat units [interquartile range, 9.0-33.5 heat units]; p = 0.001) and reached Ttarget quicker (median, 2.3 hr [interquartile range, 1.5-4.0 hr] vs median, 3.6 hr [interquartile range, 2.0-5.0 hr]; p = 0.01) than patients with Cerebral Performance Category score 1-2. Nonsurvivors generated less heat than survivors (median, 8.1 heat units [interquartile range, 3.6-20.8 heat units] vs median, 19.0 heat units [interquartile range, 6.5-33.5 heat units]; p = 0.001) and reached Ttarget quicker (median, 2.2 hr [interquartile range, 1.5-3.8 hr] vs median, 3.6 hr [interquartile range, 2.0-5.0 hr]; p = 0.01). Controlling for average water temperature between initiation and Ttarget, the relationship between outcomes and time to Ttarget was no longer significant. Controlling for location, witnessed arrest, age, initial rhythm, and neuromuscular blockade use, increased heat generation was associated with better neurologic (adjusted odds ratio, 1.01 [95% CI, 1.00-1.03]; p = 0.039) and survival (adjusted odds ratio, 1.01 [95% CI, 1.00-1.03]; p = 0.045) outcomes.

CONCLUSIONS

Increased heat generation during targeted temperature management initiation is associated with better outcomes at hospital discharge and may affect the relationship between time to Ttarget and outcomes.

Mild therapeutic hypothermia after out-of-hospital cardiac arrest: What does really matter?

BACKGROUND

Mild therapeutic hypothermia (MTH) is a recommended treatment of comatose patients after out-of-hospital cardiac arrest (OHCA). The aim of the study was to examine determinants of clinical outcome in OHCA survivors treated with MTH and variables associated with MTH induction time.

METHODS

Presented herein is an analysis of combined results from a retrospective and a prospective observational study which included 90 OHCA survivors treated with MTH from January 2010 to March 2018. Multivariate regression analysis was performed to determine variables associated with poor neurologic outcome (Cerebral Performance Category 3-5), mortality, and prolonged induction time.

RESULTS

At hospital discharge, 59 (65.6%) patients were alive, of whom 36 (61%) had a good neurologic outcome. Older patients (odds ratio [OR] 1.07, 95% confidence interval [CI] 1.03-1.12) with lower Glasgow Coma Scale (GCS) (OR 0.49, 95% CI 0.30-0.80) were at higher risk of poor neurological outcome. The predictors of in-hospital death included: older age (OR 1.08, 95% CI 1.02-1.13), lower GCS score (OR 0.47, 95% CI 0.25-0.85), presence of cardiogenic shock (OR 3.43, 95% CI 1.11-10.53), and higher doses of adrenaline (OR 1.27, 95% CI 1.04-1.56). Longer induction was associated with shorter cardio-pulmonary resuscitation (CPR) (unstandardized coefficient -3.95, 95% CI -7.09 to -0.81) and lower lactate level (unstandardized coefficient -18.55, 95% CI -36.10 to -1.01).

CONCLUSIONS

Unfavorable neurologic outcome in OHCA patients treated with MTH is associated with age and lower GCS score. Risk factors for in-hospital mortality include age, high-dose adrenaline administration, lower GCS score and presence of cardiogenic shock. CPR duration and lactate level were predictive of prolonged MTH induction time.

Relationship between timing of cooling and outcomes in adult comatose cardiac arrest patients treated with targeted temperature management

AIM OF THE STUDY

Studies examining associations between time to target temperature and outcomes in cardiac arrest patients who underwent targeted temperature management (TTM) have shown inconsistent results. We examined these associations separately for time from restoration of spontaneous circulation to TTM initiation (pre-induction time) and time from TTM initiation to target temperature (induction time). Furthermore, we examined whether critical time thresholds exist if there is an association.

METHODS

This was a single-centre retrospective observational study including adult cardiac arrest patients treated with TTM from 2008 to 2015. We tested the associations of pre-induction time and induction time with outcomes at hospital discharge using multivariate logistic regression analysis. We then performed additional multivariate analyses, each with the significant timing variable at different binary cutoffs.

RESULTS

A total of 515 patients were analysed. At hospital discharge, 357 patients (69.3%) were alive, of whom 161 (31.3%) had a favourable neurologic outcome. In multivariate analysis, a shorter pre-induction time was independently associated with a favourable neurologic outcome (odds ratio [OR], 1.110; 95% confidence interval [CI], 1.025-1.202), whereas the induction time was not (OR, 0.954; 95% CI, 0.852-1.067). We found two pre-induction time thresholds (120 and 360min) that were associated with neurologic outcome.

CONCLUSION

We found that a shorter pre-induction time was independently associated with a favorable neurologic outcome at hospital discharge, whereas induction time was not. We also found two time thresholds at 120 and 360min, after which initiation of cooling was associated with a worse neurologic outcome.

Billing diagnoses do not accurately identify out-of-hospital cardiac arrest patients: An analysis of a regional healthcare system

BACKGROUND

International Classification of Diseases 9th Edition's Clinical Modification (ICD-9CM) codes are frequently used in health services research. We tested the operating characteristics of ICD-9CM codes for identifying out-of-hospital cardiac arrest (OHCA) subjects.

METHODS

We used ICD-9CM codes to generate an "administrative cohort" of subjects treated after possible OHCA at one of six emergency departments (EDs) between January 2010 and April 2014. We performed a structured chart review to determine proportion of this administrative cohort with actual OHCA (true positive rate for the ICD-9CM-based search method). The largest study site maintains a prospective registry of consecutive OHCA subjects, which we used to construct a "registry cohort". We used this cohort to calculate the sensitivity of the ICD-9CM-based search strategy at this site, and compared in-hospital mortality and discharge dispositions between the two cohorts using Chi-square tests.

RESULTS

ICD-9CM codes identified 2461 subjects that comprised the administrative cohort. Of these, the true positive rate for actual OHCA on chart review was 40%. ICD9-CM code sensitivity was 100% for subjects coded as dead on arrival and 19% for subjects coded as surviving to ED disposition. There were 609 OHCA subjects in the registry cohort and 268 subjects in the administrative cohort who presented to registry site. Only 26 subjects appeared in both cohorts. In-hospital mortality was significantly higher in the administrative cohort than the registry cohort (91% vs. 61%, p<0.001), and hospital discharge disposition of survivors was less favorable (p<0.001). Neither difference persisted after excluding subjects surviving <6h.

CONCLUSION

Compared to a prospective registry, ICD-9CM codes are an insensitive method to identify OHCA subjects. Moreover, ICD-9CM codes identify a biased sample of the OHCA population with higher mortality.

Association of left ventricular systolic function and vasopressor support with survival following pediatric out-of-hospital cardiac arrest

OBJECTIVES

To characterize the association of hospital discharge survival with left ventricular systolic function evaluated by transthoracic echocardiography and vasoactive infusion support following return of spontaneous circulation after pediatric out-of-hospital cardiac arrest.

DESIGN

Retrospective case series.

SETTING

Single-center tertiary care pediatric cardiac arrest and critical care referral center.

PATIENTS

Consecutive out-of-hospital cardiac arrest patients less than 18 years surviving to PICU admission who had a transthoracic echocardiography obtained by the clinical team within 24 hours of admission from January 2006 to May 2012.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Fifty-eight patients had a post-return of spontaneous circulation transthoracic echocardiography performed within 24 hours of admission. The median time from return of spontaneous circulation to echo was 6.5 hours (interquartile range, 4.7, 15.0 hr). Left ventricular systolic function was decreased in 24 of 58 patients (41%). The mortality rate was 67% (39 of 58). Thirty-six patients (62%) received vasoactive infusions at the time of transthoracic echocardiography, and increased vasopressor inotropic score was associated with increased mortality on univariate analysis (p < 0.001). After controlling for defibrillation, vasopressor inotropic score, and interaction between vasopressor inotropic score and left ventricular systolic function, decreased left ventricular systolic function was associated with increased mortality (odds ratio, 13.7; 95% CI, 1.54-122).

CONCLUSIONS

In patients receiving transthoracic echocardiography within the first 24 hours following return of spontaneous circulation after pediatric out-of-hospital cardiac arrest, decreased left ventricular systolic function and vasopressor use were common. Decreased left ventricular systolic function was associated with increased mortality.