Conducting feasibility studies in clinical trials are an investment to ensure a good study

      We congratulate Professor Eastwood and the Carbon Control and Cardiac Arrest (CCC) trial group on an informative and thought-provoking pilot study, which provides an insight into further potential research.
      • Eastwood G.M.
      • et al.
      Targeted therapeutic mild hypercapnia after cardiac arrest: A. Phase II multi-centre randomised controlled trial (The CCC Trial).
      Increases in PaCO2 are well known to produce an increase in cerebral blood flow (CBF), mediated by its vasodilatory actions on cerebral vascular smooth muscle.
      • Kety S.S.
      • Schmidt C.F.
      The effects of altered arterial tensions of carbon dioxide and oxygen on cerebral blood flow and cerebral oxygen consumption of normal young men.
      Outside of extremes of PaCO2 levels this relationship is linear with a 1 mmHg increase in PaCO2 causing an increase in CBF of 1–2 ml/100 g/min.
      • Brian J.E.J.
      Carbon dioxide and the cerebral circulation.
      Further to improved cerebral perfusion, carbon dioxide also has anti-convulsant
      • Tolner E.A.
      • Hochman D.W.
      • Hassinen P.
      • et al.
      Five percent CO2 is a potent, fast-acting inhalation anticonvulsant.
      and anti-inflammatory properties.
      • Shoja M.M.
      • Tubbs R.S.
      • Shokouhi G.
      • Loukas M.
      • Ghabili K.
      • Ansarin K.
      The potential role of carbon dioxide in the neuroimmunoendocrine changes following cerebral ischemia.
      It has been postulated that following cardiac arrest, the cerebral vasodilatation associated with mild hypercapnia will improve reperfusion and consequently neurological outcomes. Previous observational studies have suggested that patients admitted to intensive care units (ICU) following cardiac arrest have improved short and long-term outcomes if their arterial carbon dioxide levels had been recorded above 45 mmHg within the first 24 h of their ICU admission.
      • Vaahersalo J.
      • Bendel S.
      • Reinikainen M.
      • et al.
      Arterial blood gas tensions after resuscitation from out-of-hospital cardiac arrest: associations with long-term neurological outcome.
      • Schneider A.G.
      • Eastwood G.M.
      • Bellomo R.
      • et al.
      Arterial carbon dioxide tension and outcome in patients admitted to the intensive care unit after cardiac arrest.
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