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It was not true under therapeutic hypothermia

      To the Editor,
      A recently published article in Switzerland by Kustermann et al.
      • Kustermann T.
      • Nguepnjo Nguissi N.A.
      • Pfeiffer C.
      • et al.
      Electroencephalography-based power spectra allow coma outcome prediction within 24 h of cardiac arrest.
      has reported a high level of the predictive performance of electroencephalography-based power spectra within 24 h from coma onset in patients following cardiac arrest (CA). The authors evaluated the ability of electroencephalography (EEG) to predict long-term outcomes and claimed that on the first day of coma following CA, low power spectra values around 10 Hz, typically linked to impaired cortico-thalamic structural connections, are highly specific of unfavourable outcome. However, despite this exemplary work, we have some concerns in regards to their study conclusion.
      Mild therapeutic hypothermia (TH) is an effective treatment approach for organ protection following CA.
      • Callaway C.W.
      • Donnino M.W.
      • Fink E.L.
      • et al.
      Part 8: post-cardiac arrest care: 2015 American Heart Association Guidelines update for cardiopulmonary resuscitation and emergency cardiovascular care.
      Studies have confirmed that cooling can cause peripheral vasoconstriction and shivering, reduce vascular volume and lead to skin breakdown, infection and increased oxygen consumption, and the patient seems relatively hypovolemic reductions.
      • Callaway C.W.
      • Donnino M.W.
      • Fink E.L.
      • et al.
      Part 8: post-cardiac arrest care: 2015 American Heart Association Guidelines update for cardiopulmonary resuscitation and emergency cardiovascular care.
      To prevent the above complications (pain, vasoconstriction and shivering), anesthetics, neuromuscular blocker and sedatives were usually administered during TH in patients following CA.
      • Callaway C.W.
      • Donnino M.W.
      • Fink E.L.
      • et al.
      Part 8: post-cardiac arrest care: 2015 American Heart Association Guidelines update for cardiopulmonary resuscitation and emergency cardiovascular care.
      Under such the setting, a key question is raised: the true and accurate neurological function status was not reflected by the EEG during the phase of cooling while patients were administered sedative, neuromuscular blocker agents and anesthetics after CA.
      First, new indexes using part of the cortical frontal electroencephalographic (EEG) signal (e.g., Bispectral Index, Entropy, Patient State Index) have failed to demonstrate their reliability and superiority.
      • Rimbert S.
      • Schmartz D.
      • Bougrain L.
      • et al.
      MOTANA: study protocol to investigate motor cerebral activity during a propofol sedation.
      Indeed, current brain monitors available for intraoperative analysis of the cortical frontal EEG may not adequately reflect an attempt of movement from the patient under anesthesia, especially if paralytics (neuromuscular blocker agents) are used.
      • Rimbert S.
      • Schmartz D.
      • Bougrain L.
      • et al.
      MOTANA: study protocol to investigate motor cerebral activity during a propofol sedation.
      Second, the value and amplitude of EEG could be affected by sedatives and anesthetics, and change with the changes in the depth of anesthesia. In addition, how to accurately control the depth of sedation is still a difficult problem during cooling in patients following CA. Furthermore, hypothermia may alter the pharmacokinetics of anesthetics and result in prolonged systemic clearances of anesthetic agents.
      • Empey P.E.
      • Miller T.M.
      • Philbrick A.H.
      • et al.
      Mild hypothermia decreases fentanyl and midazolam steady-state clearance in a rat model of cardiac arrest.
      During reduced core temperature, a doubling of vecuronium-induced neuromuscular block duration has been demonstrated in humans.
      • Fritz H.G.
      • Holzmayr M.
      • Walter B.
      • et al.
      The effect of mild hypothermia on plasma fentanyl concentration and biotransformation in juvenile pigs.
      The anesthetic/analgesic regimen after traumatic brain injury (TBI) may dramatically influence the response to hypothermia.
      • Fritz H.G.
      • Holzmayr M.
      • Walter B.
      • et al.
      The effect of mild hypothermia on plasma fentanyl concentration and biotransformation in juvenile pigs.
      Mild TH plus the accumulative effect of sedatives could have a significant impact on the activity of neurological function.
      Therefore,EEG would not be the native representation of neurological function during the interventional phase of cooling in patients following CA and its predictive value becomes questionable.

      Conflict of interest

      No conflict of interest exits in the submission of this manuscript, and manuscript is approved by all authors for publication.

      References

        • Kustermann T.
        • Nguepnjo Nguissi N.A.
        • Pfeiffer C.
        • et al.
        Electroencephalography-based power spectra allow coma outcome prediction within 24 h of cardiac arrest.
        Resuscitation. 2019; 142: 162-167
        • Callaway C.W.
        • Donnino M.W.
        • Fink E.L.
        • et al.
        Part 8: post-cardiac arrest care: 2015 American Heart Association Guidelines update for cardiopulmonary resuscitation and emergency cardiovascular care.
        Circulation. 2015; 132: S465-S482
        • Rimbert S.
        • Schmartz D.
        • Bougrain L.
        • et al.
        MOTANA: study protocol to investigate motor cerebral activity during a propofol sedation.
        Trials. 2019; 20: 534
        • Empey P.E.
        • Miller T.M.
        • Philbrick A.H.
        • et al.
        Mild hypothermia decreases fentanyl and midazolam steady-state clearance in a rat model of cardiac arrest.
        Crit Care Med. 2012; 40: 1221-1228
        • Fritz H.G.
        • Holzmayr M.
        • Walter B.
        • et al.
        The effect of mild hypothermia on plasma fentanyl concentration and biotransformation in juvenile pigs.
        Anesth Analg. 2005; 100: 996-1002