Timing of hypothermic temperature control does not affect neurological outcomes after cardiac arrest: a systematic...

Out-of-hospital cardiac arrest is associated with a low rate of favourable neurological recovery, estimated at 8%. Lowering the cerebral metabolic rate with hypothermic temperature control is hypothesized to improve this outcome. Given the importance of temperature control after cardiac arrest, we investigated whether initiating early hypothermic temperature control in the prehospital setting could further enhance neurological recovery. A pre-registered systematic search (PROSPERO: CRD42024601051) was run in PubMed, Embase and Cochrane Central on November 3, 2024 (updated on March 30, 2026) to identify randomised controlled trials that compare prehospital vs. in-hospital initiation of hypothermic temperature control of out-of-hospital cardiac arrest patients. The Cochrane Handbook was followed for data extraction and synthesis. The RoB 2 tool was used for risk of bias assessment. The meta-analyses were conducted using a random-effects model. A total of 7117 articles were screened, and 7 studies including 3288 patients were included in the analysis. The intervention group achieved target temperature of 33 °C significantly earlier (MD: -97.27 min; 95% CI: -139.46 to -55.08; p = 0.010). In the intervention group, no significant difference was observed in the odds for favourable neurological outcome (OR: 0.98; 95% CI: 0.80-1.22, p = 0.855). The rate of recurrent cardiac arrest in the intervention group was significantly higher than in the control group (OR: 1.33; 95% CI: 1.20-1.47; p = 0.009) and the odds for pulmonary oedema were also significantly higher (OR: 1.66; 95% CI: 1.24-2.23; p = 0.001). The results show that despite reaching the target temperature significantly earlier, prehospital initiation of hypothermic temperature control did not improve favourable neurological recovery compared to in-hospital initiation. Furthermore, early initiation also significantly increased the odds for recurrent cardiac arrest and pulmonary oedema. Therefore, these findings do not support the implementation of prehospital hypothermic temperature control in out-of-hospital cardiac arrest, although evidence regarding fluid-sparing approaches such as transnasal evaporative cooling remains limited.