title: A pilot assessment of alpha-stat vs pH-stat arterial blood gas analysis after cardiac arrest.
abstract: OBJECTIVE
  Resuscitated cardiac arrest (CA) patients typically receive therapeutic hypothermia, but arterial blood gases (ABGs) are often assessed after adjustment to 37°C (alpha-stat) instead of actual body temperature (pH-stat). We sought to compare alpha-stat and pH-stat assessment of PaO2 and PaCO2 in such patients.
  
  
  METHODS
  Using ABG data obtained during the first 24 hours of intensive care unit admission, we determined the impact of measured alpha vs calculated pH-stat on PaO2 and PaCO2 on patient classification and outcomes for CA patients.
  
  
  RESULTS
  We assessed 1013 ABGs from 120 CA patients with a median age of patients 66 years (interquartile range, 50-76). Median alpha-stat PaO2 changed from 122 (95-156) to 107 (82-143) mm Hg with pH-stat and median PaCO2 from 39 (34-46) to 35 (30-41) mm Hg (both P < .001). Using the categories of hyperoxemia, normoxemia, and hypoxemia, pH-stat estimation of PaO2 reclassified approximately 20% of patients. Using the categories of hypercapnia, normocapnia, and hypocapnia, pH stat estimation of PaCO2 reclassified approximately 40% of patients. The mortality of patients in different PaO2 and PaCO2 categories was similar for pH-stat and alpha-stat.
  
  
  CONCLUSIONS
  Using the pH-stat method, fewer resuscitated CA patients admitted to intensive care unit were classified as hyperoxemic or hypercapnic compared with alpha-stat. These findings suggest an impact of ABG assessment methodology on PaO2, PaCO2 , and patient classification but not on associated outcomes.
authors.affiliation: School of Nursing and Midwifery, Deakin University, Melbourne, Australia; Department of Intensive Care, Austin Hospital, Victoria, Melbourne, Australia. Electronic address: glenn.eastwood@austin.org.au.
authors.forename: Glenn M
authors.initials: GM
authors.lastname: Eastwood
authors.affiliation: Department of Anesthesiology and Resuscitology, Okayama University Hospital, Okayama, Japan. Electronic address: Suzuki-s@mtc.biglobe.ne.jp.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Suzuki
authors.affiliation: Department of Intensive Care, Hospital Universitari Mutua Terrassa, Barcelona, Spain. Electronic address: clluchcandal@gmail.com.
authors.forename: Cristina
authors.initials: C
authors.lastname: Lluch
authors.affiliation: Department of Intensive Care Medicine and Burn Center, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland. Electronic address: Antoine.Schneider@chuv.ch.
authors.forename: Antoine G
authors.initials: AG
authors.lastname: Schneider
authors.affiliation: Department of Intensive Care, Austin Hospital, Victoria, Melbourne, Australia; Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Victoria, Australia. Electronic address: rinaldo.bellomo@austin.org.au.
authors.forename: Rinaldo
authors.initials: R
authors.lastname: Bellomo
mesh_terms: D000328:Adult; D000368:Aged; D001158:Arteries; D001784:Blood Gas Analysis; D001831:Body Temperature; D005260:Female; D006323:Heart Arrest / Q000097:blood* / Q000401:mortality; D006801:Humans; D006935:Hypercapnia / Q000097:blood / Q000175:diagnosis*; D018496:Hyperoxia / Q000097:blood / Q000175:diagnosis*; D007036:Hypothermia, Induced; D000860:Hypoxia / Q000097:blood / Q000150:complications; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D010865:Pilot Projects; D012189:Retrospective Studies
keywords: Arterial blood gas; Cardiac arrest; Hyperoxemia; Hypocapnia; Hypoxemia; Intensive care