Therapeutic hypothermia after traumatic brain injury: Wrong hypotheses may lead to specious interpretations

Effects of therapeutic hypothermia on the safety of children with severe traumatic brain injury: a systematic review and meta-analysis

BACKGROUND

Therapeutic hypothermia (TH) is effective to treat adult traumatic brain injury (TBI), but there is still controversy about its safety to treat the children with severe TBI.

METHODS

Clinical studies on TH in children with severe TBI from January 2000 to September 2020 were screened in PubMed, Web of Science, Embase, Cochrane Library, Nature, NCKI, and Wanfang online databases. Data were meta-analyzed by Rev Man 5.3. Differences in mortality, adverse outcomes, duration of Pediatric Intensive Care Unit (PICU), incidence of infection, and incidence of arrhythmia were compared between experimental group and control group. The heterogeneity of the results was evaluated by chi-square test and I² test in Rev Man 5.3, and publication bias was evaluated by funnel plot.

RESULTS

Five articles were included, including 421 children. Cochrane evaluation was B grade or above, and Jadad scale score was over three points. The overall mortality between two groups showed great difference [odds ratio (OR) =1.72, 95% CI: 0.98-3.02, Z=1.87, P=0.04]. The incidence of adverse outcomes (OR =1.39, 95% CI: 0.86-2.25, Z=1.34, P=0.18), the duration of PICU [mean difference (MD) =0.51, 95% CI: -0.33 to 1.35, Z=1.19, P=0.24], the incidence of infection (OR =0.79, 95% CI: 0.51-1.23, Z=1.03, P=0.30), and the incidence of arrhythmia (OR =3.10, 95% CI: 0.77-12.50, Z=1.59, P=0.11) were not considerably different.

DISCUSSION

TH significantly reduced overall mortality in children with severe TBI, but did not significantly improve the incidence of adverse outcomes, PICU duration, infection rate, or arrhythmia. These results provided a reference for selecting proper clinical treatment methods for children with severe TBI.

POLAR Study Revisited: Therapeutic Hypothermia in Severe Brain Trauma Should Not Be Abandoned

The benefits of therapeutic hypothermia (TH) in severe traumatic brain injury (sTBI) have been long debated. In 2018, the POLAR study, a high-quality international trial, appeared to end the debate by showing that TH did not improve mortality in sTBI. However, the POLAR-based recommendation to abandon TH was challenged by different investigators. In our recent meta-analysis, we introduced the cooling index (COIN) to assess the extent of cooling and showed that TH is beneficial in sTBI, but only when the COIN is sufficiently high. In the present study, we calculated the COIN for the POLAR study and ran a new meta-analysis, which included the POLAR data and accounted for the cooling extent. The POLAR study targeted a high cooling extent (COIN of 276°C × h; calculated for 72 h), but the achieved cooling was much lower (COIN of 193°C × h)-because of deviations from the protocol. When the POLAR data were included in the COIN-based meta-analysis, TH had an overall effect of reducing death (odds rate of 0.686; p = 0.007). Among the subgroups with different COIN levels, the only significantly decreased odds rate (i.e., beneficial effect of TH) was observed in the subgroup with high COIN (0.470; p = 0.013). We conclude that, because of deviations from the targeted cooling protocol, the overall cooling extent was not sufficiently high in the POLAR study, thus masking the beneficial effects of TH. The current analysis shows that TH is beneficial in sTBI, but only when the COIN is high. Abandoning the use of TH in sTBI may be premature.