title: Cerebral oxygenation in mechanically ventilated early cardiac arrest survivors: The impact of hypercapnia.
abstract: BACKGROUND
  Optimal cerebral oxygenation is considered fundamental to cerebral protection in cardiac arrest (CA) patients. Hypercapnia increases cerebral blood flow and may also improve cerebral oxygenation. It is uncertain, however, whether this effect occurs in mechanically ventilated early survivors of CA.
  
  
  METHODS
  We enrolled mechanically ventilated resuscitated patients within 36h of their cardiac arrest. We performed a prospective double cross-over physiological study comparing the impact of normocapnia (PaCO2 35-45mmHg) vs. mild hypercapnia (PaCO2 45-55mmHg) on regional cerebral tissue oxygen saturation (SctO2) assessed by near infrared spectroscopy (NIRS).
  
  
  RESULTS
  We studied seven adult CA patients with a median time to return of spontaneous circulation of 28min at a median of 26h and 30min after CA. During normocapnia (median EtCO2 of 32mmHg [30-41mmHg] and PaCO2 of 37mmHg [32-45mmHg]) the median NIRS-derived left frontal SctO2 was 61% [52-65%] and the right frontal SctO2 was 61% [54-68%]. However, during mild hypercapnia (median EtCO2 of 49mmHg [40-57mmHg] and PaCO2 of 52mmHg [43-55mmHg) the median left frontal SctO2 increased to 69% [59-78%] and the right frontal SctO2 increased to 73% [61-76%])(p=0.001, for all comparisons).
  
  
  CONCLUSIONS
  During the early post-resuscitation period, in mechanically ventilated CA patients, mild hypercapnia increases cerebral oxygenation as assessed by NIRS. Further investigations of the effect of prolonged mild hypercapnia on cerebral oxygenation and patient outcomes appear justified.
authors.affiliation: Department of Intensive Care, Austin Hospital, Melbourne, VIC, Australia; Australian and New Zealand Intensive Care Research Centre, Melbourne, VIC, Australia; School of Nursing and Midwifery, Faculty of Health, Deakin University, Melbourne, Australia. Electronic address: glenn.eastwood@austin.org.au.
authors.forename: Glenn M
authors.initials: GM
authors.lastname: Eastwood
authors.affiliation: Department of Intensive Care, Austin Hospital, Melbourne, VIC, Australia; Department of Anesthesiology and Intensive Care, Osaka University Graduate School of Medicine, Suita, Osaka, Japan. Electronic address: aiko.tanaka@austin.org.au.
authors.forename: Aiko
authors.initials: A
authors.lastname: Tanaka
authors.affiliation: Department of Intensive Care, Austin Hospital, Melbourne, VIC, Australia; Australian and New Zealand Intensive Care Research Centre, Melbourne, VIC, Australia. Electronic address: rinaldo.bellomo@austin.org.au.
authors.forename: Rinaldo
authors.initials: R
authors.lastname: Bellomo
mesh_terms: D000328:Adult; D000368:Aged; D002560:Cerebrovascular Circulation / Q000502:physiology*; D018592:Cross-Over Studies; D004311:Double-Blind Method; D005260:Female; D005500:Follow-Up Studies; D006323:Heart Arrest / Q000401:mortality / Q000503:physiopathology / Q000628:therapy*; D006801:Humans; D006935:Hypercapnia / Q000209:etiology / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D010101:Oxygen Consumption / Q000502:physiology*; D011446:Prospective Studies; D012121:Respiration, Artificial; D019265:Spectroscopy, Near-Infrared; D015996:Survival Rate / Q000639:trends; D014739:Victoria / Q000453:epidemiology
keywords: Cardiac arrest; Cerebral oxygenation; Hypercapnia; Mechanical ventilation; Normocapnia