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Objective: Exposure to hyperoxemia and hypoxemia is common in out-of-hospital cardiac arrest (OHCA) patients following return of spontaneous circulation (ROSC), but its effects on neurological outcome are uncertain, and study results are inconsistent. Methods: Exploratory post hoc substudy of the Target Temperature Management (TTM) trial, including 939 patients after OHCA with return of spontaneous circulation (ROSC). The association between serial arterial partial pressures of oxygen (PaO 2 ) during 37 h following ROSC and neurological outcome at 6 months, evaluated by Cerebral Performance Category (CPC), dichotomized to good (CPC 1-2) and poor (CPC 3-5), was investigated. In our analyses, we tested the association of hyperoxemia and hypoxemia, time-weighted mean PaO 2 , maximum PaO 2 difference, and gradually increasing PaO 2 levels (13.3-53.3 kPa) with poor neurological outcome. A subsequent analysis investigated the association between PaO 2 and a biomarker of brain injury, peak serum Tau levels. Results: Eight hundred sixty-nine patients were eligible for analysis. Three hundred patients (35%) were exposed to hyperoxemia or hypoxemia at some time point after ROSC. Our analyses did not reveal a significant association between hyperoxemia, hypoxemia, time-weighted mean PaO 2 exposure or maximum PaO 2 difference and poor neurological outcome at 6-month follow-up after correction for co-variates (all analyses p = 0.146-0.847). We were not able to define a PaO 2 level significantly associated with the onset of poor neurological outcome. Peak serum Tau levels at either 48 or 72 h after ROSC were not associated with PaO 2 . Conclusion: Hyperoxemia or hypoxemia exposure occurred in one third of the patients during the first 37 h of hospitalization and was not significantly associated with poor neurological outcome after 6 months or with the peak s-Tau levels at either

Objective: Exposure to hyperoxemia and hypoxemia is common in out-of-hospital cardiac arrest (OHCA) patients following return of spontaneous circulation (ROSC), but its effects on neurological outcome are uncertain, and study results are inconsistent. Methods: Exploratory post hoc substudy of the Target Temperature Management (TTM) trial, including 939 patients after OHCA with return of spontaneous circulation (ROSC). The association between serial arterial partial pressures of oxygen (PaO 2 ) during 37 h following ROSC and neurological outcome at 6 months, evaluated by Cerebral Performance Category (CPC), dichotomized to good (CPC 1-2) and poor (CPC 3-5), was investigated. In our analyses, we tested the association of hyperoxemia and hypoxemia, time-weighted mean PaO 2 , maximum PaO 2 difference, and gradually increasing PaO 2 levels (13.3-53.3 kPa) with poor neurological outcome. A subsequent analysis investigated the association between PaO 2 and a biomarker of brain injury, peak serum Tau levels. Results: Eight hundred sixty-nine patients were eligible for analysis. Three hundred patients (35%) were exposed to hyperoxemia or hypoxemia at some time point after ROSC. Our analyses did not reveal a significant association between hyperoxemia, hypoxemia, time-weighted mean PaO 2 exposure or maximum PaO 2 difference and poor neurological outcome at 6-month follow-up after correction for co-variates (all analyses p = 0.146-0.847). We were not able to define a PaO 2 level significantly associated with the onset of poor neurological outcome. Peak serum Tau levels at either 48 or 72 h after ROSC were not associated with PaO 2 . Conclusion: Hyperoxemia or hypoxemia exposure occurred in one third of the patients during the first 37 h of hospitalization and was not significantly associated with poor neurological outcome after 6 months or with the peak s-Tau levels at either

Background: Dyscarbia is common in out-of-hospital cardiac arrest (OHCA) patients and its association to neurological outcome is undetermined. Methods: This is an exploratory post-hoc substudy of the Target Temperature Management (TTM) trial, including resuscitated OHCA patients, investigating the association between serial measurements of arterial partial carbon dioxide pressure (PaCO2) and neurological outcome at 6months, defined by the Cerebral Performance Category (CPC) scale, dichotomized to good outcome (CPC 1 and 2) and poor outcome (CPC 3-5). The effects of hypercapnia and hypocapnia, and the time-weighted mean PaCO2 and absolute PaCO2 difference were analyzed. Additionally, the association between mild hypercapnia (6.0-7.30kPa) and neurological outcome, its interaction with target temperature (33°C and 36°C), and the association between PaCO2 and peak serum-Tau were evaluated. Results: Of the 939 patients in the TTM trial, 869 were eligible for analysis. Ninety-six percent of patients were exposed to hypocapnia or hypercapnia. None of the analyses indicated a statistical significant association between PaCO2 and neurological outcome (P=0.13-0.96). Mild hypercapnia was not associated with neurological outcome (P=0.78) and there was no statistically significant interaction with target temperature (P interaction=0.95). There was no association between PaCO2 and peak serum-Tau levels 48 or 72h after return of spontaneous circulation (ROSC). Conclusions: Dyscarbia is common after ROSC. No statistically significant association between PaCO2 in the post-cardiac arrest phase and neurological outcome at 6 months after cardiac arrest was detected. There was no significant interaction between mild hypercapnia and temperature in relation to neurological outcome.

Background: Dyscarbia is common in out-of-hospital cardiac arrest (OHCA) patients and its association to neurological outcome is undetermined. Methods: This is an exploratory post-hoc substudy of the Target Temperature Management (TTM) trial, including resuscitated OHCA patients, investigating the association between serial measurements of arterial partial carbon dioxide pressure (PaCO2) and neurological outcome at 6months, defined by the Cerebral Performance Category (CPC) scale, dichotomized to good outcome (CPC 1 and 2) and poor outcome (CPC 3-5). The effects of hypercapnia and hypocapnia, and the time-weighted mean PaCO2 and absolute PaCO2 difference were analyzed. Additionally, the association between mild hypercapnia (6.0-7.30kPa) and neurological outcome, its interaction with target temperature (33°C and 36°C), and the association between PaCO2 and peak serum-Tau were evaluated. Results: Of the 939 patients in the TTM trial, 869 were eligible for analysis. Ninety-six percent of patients were exposed to hypocapnia or hypercapnia. None of the analyses indicated a statistical significant association between PaCO2 and neurological outcome (P=0.13-0.96). Mild hypercapnia was not associated with neurological outcome (P=0.78) and there was no statistically significant interaction with target temperature (P interaction=0.95). There was no association between PaCO2 and peak serum-Tau levels 48 or 72h after return of spontaneous circulation (ROSC). Conclusions: Dyscarbia is common after ROSC. No statistically significant association between PaCO2 in the post-cardiac arrest phase and neurological outcome at 6 months after cardiac arrest was detected. There was no significant interaction between mild hypercapnia and temperature in relation to neurological outcome.

Objective: To conduct a pilot study to evaluate the prognostic potential of serum tau protein measurements to predict neurological outcome 6 months following resuscitation from cardiac arrest. Methods: In this retrospective observational study, we employed a new ultra sensitive digital immunoassay technology to examine serial serum samples from 25 cardiac arrest patients to examine tau release into serum as a result of brain hypoxia, and probe for its significance predicting six-month neurological outcome. Serial blood samples were obtained from resuscitated cardiac arrest survivors during their first five days in an intensive care unit, and serum total tau was measured. Cerebral function assessments were made using Cerebral Performance Categorization (CPC) at discharge from the ICU and six months later. Tau data were analyzed in the context of 6-month CPC scores. Results: Tau elevations ranged from modest (< 10 pg/mL) to very high (hundreds of pg/mL), and exhibited unexpected bi-modal kinetics in some patients. Early tau elevations appeared within 24 h of cardiac arrest, and delayed elevations appeared after 24-48 h. In patients with delayed elevations, areas under the curves of tau concentration vs. hours since cardiac arrest were highly predictive of 6-month outcome (P < 0.0005). Conclusion: High-sensitivity serum tau measurements combined with an understanding of tau release kinetics could have utility for hypoxic brain injury assessment and prediction of cerebral function outcome.