A pilot assessment of alpha-stat vs pH-stat arterial blood gas analysis after cardiac arrest

Abstract Purpose 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 Pa o 2 and Pa co 2 in such patients. Materials and 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 Pa o 2 and Pa co 2 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 Pa o 2 changed from 122 (95-156) to 107 (82-143) mm Hg with pH-stat and median Pa co 2 from 39 (34-46) to 35 (30-41) mm Hg (both P o 2 reclassified approximately 20% of patients. Using the categories of hypercapnia, normocapnia, and hypocapnia, pH stat estimation of Pa co 2 reclassified approximately 40% of patients. The mortality of patients in different Pa o 2 and Pa co 2 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 Pa o 2 , Pa co 2 , and patient classification but not on associated outcomes.