Influence of α-stat and pH-stat blood gas management strategies on cerebral blood flow and oxygenation in patients treated with therapeutic hypothermia after out-of-hospital cardiac arrest: a crossover study.

Objectives: In patients treated with therapeutic hypothermia after out-of-hospital cardiac arrest, two blood gas management strategies are used regarding the PaCO2 target: α-stat or pH-stat. We aimed to compare the effects of these strategies on cerebral blood flow and oxygenation.

Design: Prospective observational single-center crossover study.

Setting: ICU of University hospital.

Patients: Twenty-one therapeutic hypothermia-treated patients after out-of-hospital cardiac arrest more than 18 years old without history of cerebrovascular disease were included.

Interventions: Cerebral perfusion and oxygenation variables were compared in α-stat (PaCO2 measured at 37 °C) versus pH-stat (PaCO2 measured at 32-34 °C), both strategies maintaining physiological PaCO2 values: 4.8-5.6 kPa (36-42 torr).

Measurements And Main Results: Bilateral transcranial middle cerebral artery flow velocities using Doppler and jugular vein oxygen saturation were measured in both strategies 18 hours (14-23 hr) after the return of spontaneous circulation. Pulsatility and resistance indexes and cerebral oxygen extraction were calculated. Data are expressed as median (interquartile range 25-75) in α-stat versus pH-stat. No differences were found in temperature, arterial blood pressure, and oxygenation between α-stat and pH-stat. Significant differences were found in minute ventilation (p = 0.006), temperature-corrected PaCO2 (4.4 kPa [4.1-4.6 kPa] vs. 5.1 kPa [5.0-5.3 kPa], p = 0.0001), and temperature-uncorrected PaCO2 (p = 0.0001). No differences were found in cerebral blood velocities and pulsatility and resistance indexes in the overall population. Significant differences were found in jugular vein oxygen saturation (83.2% [79.2-87.6%] vs. 86.7% [83.2-88.2%], p = 0.009) and cerebral oxygen extraction (15% [11-20%] vs. 12% [10-16%], p = 0.01), respectively. In survivors, diastolic blood velocities were 25 cm/s (19-30 cm/s) versus 29 cm/s (23-35 cm/s) (p = 0.004), pulsatility index was 1.10 (0.97-1.18) versus 0.94 (0.89-1.05) (p = 0.027), jugular vein oxygen saturation was 79.2 (71.1-81.8) versus 83.3% (76.6-87.8) (p = 0.033), respectively. However, similar results were not found in nonsurvivors.

Conclusions: In therapeutic hypothermia-treated patients after out-of-hospital cardiac arrest at physiological PaCO2, α-stat strategy increases jugular vein blood desaturation and cerebral oxygen extraction compared with pH-stat strategy and decreases cerebral blood flow velocities in survivors.