Objective
To compare short- and long-term neurological outcomes in comatose survivors of out-of-hospital cardiac arrest (OHCA) treated with mild therapeutic hypothermia (MTH) presenting with non-shockable (nSR) versus shockable (SR) initial rhythms.
Design
Retrospective cohort study.
Setting
ED and ICU of an academic hospital.
Patients
One hundred twenty-three consecutive post-OHCA adults (57 nSR, 67 SR) treated with therapeutic hypothermia between 2006 and 2012.
Measurements and Main Results
Data were collected from electronic health records. Neurological outcomes were dichotomized by Cerebral Performance Category at discharge and 6-12 month follow-up and analyzed via multivariable logistic regressions. Groups were similar, except nSR patients were more likely to have a history of diabetes mellitus (p = 0.01), be dialysis-dependent (p = 0.01), and not have bystander CPR (p = 0.05). At discharge, 3/57 (5%) patients with nSR versus 28/66 (42%) with SR had a favorable outcome (unadjusted OR 0.08, 95% CI 0.02-0.3; adjusted OR 0.1, 95% CI 0.03-0. 4). At follow-up, 4/55 (7%) versus 29/60 (48%) of patients with nSR and SR respectively had a favorable CPC (OR 0.08, 95% CI 0.03-0.3; adjusted OR 0.09, 95% CI 0.09-0.3). Among those surviving hospitalization, neurological outcome was more likely at long-term follow-up than at hospital discharge for both groups (OR 2.5, 95% CI 1.3-4.7; adjusted 2.9, 1.4-6.2). No significant interaction between changes in neurological status over time and presenting rhythm was seen (p=0.93).
Conclusions
These data indicate an association between initial nSR and significantly worse short- and long-term outcomes in patients treated with MTH. Among survivors, neurological status significantly improved over time for all patients and SR patients, and tended to improve over time for the small number of nSR patients who survived beyond hospitalization. No significant interaction between changes in neurological status over time and presenting rhythm was seen.
Mechanical ventilation in patients treated with mild therapeutic hypothermia (MTH) for the postcardiac arrest syndrome may be challenging given changes in solubility of arterial blood gases (ABGs) with cooling. Whether ABG measurements should be temperature corrected (TC) remain unknown. We sought to describe practice variability in TC at a single institution and explored the association between TC and neurological outcome. We conducted a retrospective cohort study reviewing electronic health records of all patients treated with MTH after cardiac arrest. We examined whether the percentage of TC ABGs relative to total number of ABGs drawn for each subject during hypothermia was associated with the neurological outcome at hospital discharge and 6-12-month follow-up. The cerebral performance category of 1-2 was defined as a favorable outcome in the logistic regression models. 1223 ABGs were obtained during MTH on 122 subjects over 6 years. TC was never used in 72 subjects (59%; no TC group), made available in 1-74% of ABGs in 17 subjects (14%; intermediate TC group), and made available in ≥75% of ABGs in 33 subjects (27%; mostly TC group). Groups differed in the proportion of subjects with shockable presenting rhythms (47% vs. 47% vs. 76%, p=0.02) and admitting ICU (p=0.005). Favorable 6-month outcomes were more common in the mostly TC than no TC group (48% vs. 25%; OR [95% CI]: 2.9 [1.2-7.1]), but not after adjustment (OR 1.5, 95% CI 0.33-6.9). There was substantial practice variability in the temperature correction strategy. Availability of temperature-corrected ABGs was not associated with improved neurological outcomes after adjusting for covariates.
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