Reported practice of temperature adjustment (α-stat v pH-stat) for arterial blood gases measurement among investigators from two major cardiac arrest trials

Background: Two major cardiac arrest trials are evaluating different strategies that may potentially mitigate neurological injury after cardiac arrest and are allowing co-enrolment. However, one trial will target hypothermia and the other will target mild hypercapnia, in which the carbon dioxide (CO ₂ ) measurement may be influenced by the choice of temperature adjustment during arterial blood gases (ABGs) measurement. The trials have agreed to standardise assessment by the α-stat method. Objectives: To describe the Targeted Therapeutic Mild Hypercapnia after Resuscitated Cardiac Arrest (TAME) and Targeted Hypothermia versus Targeted Normothermia after Out-of-hospital Cardiac Arrest (TTM2) site investigators’ self-reported practice of ABG analysis and, in particular, their view of whether α-stat or pH-stat assessment of ABGs is considered optimal. Methods: We performed an online anonymous multichoice survey. Of the 136 site investigators emailed, 70 (51%) responded. Of these, 19 (27%) were participating in the TAME trial only, 22 (31%) were in TTM2 only, and 29 (41%) were participating in both. Results: The majority of respondents identified α-stat (41/68, 60%) compared with pH-stat (27/68, 40%) as their usual approach to ABG analysis when targeting 33°C. In addition, the proportion and pattern of concern over hyperventilation was similarly reported as either “not concerned” or “neutral” when using an α-stat (46/69, 66%) or pH-stat (50/68, 73%) ABG analysis approach. Finally, for the purpose of a randomised controlled trial, most respondents either “strongly agreed”, “agreed” or “neither agreed nor disagreed” to use the α-stat (59/69, 85%) or the pH-stat (61/70, 87%) approach. Conclusion: Our survey findings support the acceptability of the decision to apply the α-stat approach across participating sites for both trials.