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Monitoring outcomes after cardiac arrest: All resuscitated patients matter

  • Emily S. Bartlett
    Correspondence
    Corresponding author.
    Affiliations
    Department of Emergency Medicine, University of Washington, Seattle, Washington, United States

    University of Washington-Harborview Center for Prehospital Emergency Care, Seattle, Washington, United States
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  • Graham Nichol
    Affiliations
    Department of Emergency Medicine, University of Washington, Seattle, Washington, United States

    University of Washington-Harborview Center for Prehospital Emergency Care, Seattle, Washington, United States
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      We read with interest the recent paper by Dr. Abazi and colleagues,
      • Abazi L.
      • Awad A.
      • Nordberg P.
      • et al.
      Long-term survival in out-of-hospital cardiac arrest patients treated with targeted temperature control at 33 °C or 36 °C: a national registry study.
      which did not detect a difference in 6 month survival for patients resuscitated from out-of-hospital cardiac arrest (OHCA) before vs. after adoption of a target temperature of 36 °C versus 33 °C among 2899 patients in 69 ICUs in Scandinavia. The authors themselves note that the results of the Targeted Temperature Management (TTM) randomized trial
      • Nielsen N.
      • Wetterslev J.
      • Cronberg T.
      • et al.
      Targeted temperature management at 33 °C versus 36 °C after cardiac arrest.
      may have been misinterpreted by some as signifying that fever control alone can supplant therapeutic hypothermia. We are concerned that some may also misinterpret the results of study by Abazi et al.
      In contrast with the results cited above, there is recent evidence supporting the hypothesis that a target temperature below 34 °C improves outcomes in patients resuscitated from cardiac arrest when compared to 36 °C. Specifically, an observational study in multiple intensive care units in Australia and New Zealand (16,252 patients in 140 hospitals) examining clinical practice and patient outcomes before and after publication of the TTM trial found that a lower minimum temperature was independently associated with significantly increased survival.
      • Salter R.
      • Bailey M.
      • Bellomo R.
      • et al.
      Changes in temperature management of cardiac arrest patients following publication of the target temperature management trial.
      As well, a recent randomized trial demonstrated significantly improved neurologic outcome with cooling to 33 °C vs 37 °C in patients with an initial nonshockable rhythm.
      • Lascarrou J.
      • Merdji A.
      • Le Gouge G.
      • et al.
      Targeted temperature management for cardiac arrest with nonshockable rhythm.

      How can we account for the results of Abazi et al?

      First, the authors did not report or adjust for time to target temperature or for method of induced hypothermia. Their assessment of the relationship between different target temperatures and outcome may have been confounded by differences in these factors. Second, Abazi et al. excluded patients who did not receive any form of TTM from their outcome assessment. Since a significantly greater percentage of patients resuscitated from OHCA did not receive any form of therapeutic hypothermia after vs. before publication of the TTM trial, it seems plausible that the presence of selection bias or confounding by indication may have impacted their estimate of the effect of hypothermia.
      We believe that the cumulative evidence accrued from animal models and prior observational and randomized trials in humans suggests that IH should be applied as quickly as possible to achieve a temperature of less than 34 °C in patients resuscitated from cardiac arrest. Moreover, we believe that efforts to temper or abandon use of IH in patients resuscitated from cardiac arrest are premature. We encourage the authors to evaluate the overall outcomes of all patients resuscitated from OHCA in the Swedish Intensive Care Registry before and after the publication of TTM data. Prior to the publication of the TTM trial, several group had reported overall trends towards improved survival from OHCA.
      • Salter R.
      • Bailey M.
      • Bellomo R.
      • et al.
      Changes in temperature management of cardiac arrest patients following publication of the target temperature management trial.
      • Daya M.R.
      • Schmicker R.H.
      • Zive D.M.
      • et al.
      Out-of-hospital cardiac arrest survival improving over time: results from the Resuscitation Outcomes Consortium (ROC).
      All patients with this devastating condition matter, and detecting a trend towards worsened overall outcomes in the Scandinavian registry, including among those who did not receive dedicated TTM, would be an important call to action to re-consider the apparent less stringent adherence to current guidelines seen after the TTM trial.

      Conflict of interest statement

      The authors report the following disclosures:
      Bartlett — Principal investigator (PI) of a feasibility trial of remote ischemic conditioning for patients resuscitated from cardiac arrest funded by ZOLL Foundation, Chelmsford, MA
      Nichol — Consultant and PI, STEMI COOL trial of intravascular cooling in patients with ST-elevation myocardial infarction, funded by ZOLL Circulation Inc; Consultant, QOOL Therapeutics Inc, Mountain View, CA.

      References

        • Abazi L.
        • Awad A.
        • Nordberg P.
        • et al.
        Long-term survival in out-of-hospital cardiac arrest patients treated with targeted temperature control at 33 °C or 36 °C: a national registry study.
        Resuscitation. 2019; 42: 142-147
        • Nielsen N.
        • Wetterslev J.
        • Cronberg T.
        • et al.
        Targeted temperature management at 33 °C versus 36 °C after cardiac arrest.
        New Engl J Med. 2013; 369: 2197-2206
        • Salter R.
        • Bailey M.
        • Bellomo R.
        • et al.
        Changes in temperature management of cardiac arrest patients following publication of the target temperature management trial.
        Crit Care Med. 2018; 46: 1722-1730
        • Lascarrou J.
        • Merdji A.
        • Le Gouge G.
        • et al.
        Targeted temperature management for cardiac arrest with nonshockable rhythm.
        New Engl J Med. 2019; (Online Oct 2)https://doi.org/10.1056/NEJMoa1906661
        • Daya M.R.
        • Schmicker R.H.
        • Zive D.M.
        • et al.
        Out-of-hospital cardiac arrest survival improving over time: results from the Resuscitation Outcomes Consortium (ROC).
        Resuscitation. 2015; 91: 108-115