Cerebral tissue oxygen saturation during therapeutic hypothermia in post-cardiac arrest patients

Aim of the study: This observational study was performed to assess the cerebral tissue oxygen saturation during and after therapeutic hypothermia in comatose patients after out-of-hospital cardiac arrest.

Methods: We performed a prospective observational study on the cerebral tissue oxygen saturation (SctO(2)) in post-cardiac arrest patients treated with therapeutic hypothermia (TH) between March 2011 and April 2012. SctO(2) (measured by near-infrared spectroscopy) was non-invasively and continuously measured in 28 post-cardiac arrest patients during hypothermia and active rewarming.

Results: At the start of mechanically induced TH, SctO(2) was 68% (65-72) and PaCO(2) was 47.2 mmHg (36.9-51.4). SctO(2) and PaCO(2) significantly decreased to 59% (57-64; p=0.006) and 36.6 mmHg (33.9-44.7; p=0.002), respectively, within the first 3h of mechanically induced TH. Cerebral tissue oxygen saturation was significantly lower in non-survivors (n=10) compared with survivors (n=18) at 3h after induction of hypothermia (p=0.02) while the decrease in PaCO(2) was similar in both groups. During TH maintenance, SctO(2) gradually returned to baseline values (69% (63-72)) at 24h, with no differences between survivors and non-survivors (p=0.65). Carbon dioxide remained within the range of mild hypocapnia (32-38 mmHg) throughout the hypothermic period. During rewarming, SctO(2) further increased to 71% (67-78).

Conclusions: Induction of TH in comatose post-CA patients changes the balance between oxygen delivery and supply. The decrease in SctO(2) was less pronounced in patients surviving to hospital discharge.