Quality review of included studies
| Study identification | Confounding* | Participant selection† | Classification of interventions‡ | Deviation from intended interventions§ | Missing data¶ | Outcomes** | Selective reporting†† | Overall bias |
| Alanezi45 2004 | Serious | Moderate | Low | Moderate | Low | Serious | Moderate | Serious |
| Barnard4 2017 | Serious | Moderate | Low | Moderate | Moderate | Moderate | Moderate | Serious |
| Beck46 2016 | Moderate | Moderate | Low | Low | Moderate | Moderate | Moderate | Moderate |
| Calkins34 2002 | Serious | Low | Low | Low | Low | Serious | Moderate | Serious |
| Capizzani35 2010 | Moderate | Low | Low | Low | Low | Serious | Moderate | Serious |
| Chia47 2017 | Moderate | Low | Low | Moderate | Low | Moderate | Moderate | Moderate |
| Chiang48 2015 | Moderate | Low | Low | Moderate | Low | Moderate | Low | Moderate |
| Chien49 2016 | Serious | Low | Low | Low | Moderate | Moderate | Moderate | Serious |
| David50 2007 | Moderate | Low | Low | Moderate | Low | Moderate | Moderate | Moderate |
| Deasy51 2012 | Moderate | Low | Low | Low | Serious | Moderate | Moderate | Serious |
| Di Bartolomeo19 2005 | Serious | Low | Low | Low | Low | Moderate | Moderate | Serious |
| Djarv52 2018 | Moderate | Low | Low | Low | Serious | Moderate | Moderate | Serious |
| Duchateau53 2017 | Moderate | Low | Low | Low | Low | Moderate | Moderate | Moderate |
| Evans44 2016 | Moderate | Low | Low | Low | Moderate | Moderate | Moderate | Moderate |
| Falcone54 1995 | Serious | Low | Low | Moderate | Low | Serious | Moderate | Serious |
| Fisher55 1999 | Serious | Low | Low | Moderate | Low | Serious | Moderate | Serious |
| Graesner56 2011 | Moderate | Low | Low | Moderate | Moderate | Moderate | Moderate | Moderate |
| Hillman57 2016 | Serious | Moderate | Low | Moderate | Serious | Serious | Moderate | Serious |
| Huber-Wagner58 2007 | Moderate | Moderate | Low | Moderate | Serious | Moderate | Moderate | Serious |
| Keller37 2013 | Serious | Serious | Low | Low | Serious | Moderate | Moderate | Serious |
| Kleber23 2014 | Serious | Low | Low | Moderate | Low | Moderate | Moderate | Serious |
| Lawhon20 1995 | Serious | Low | Low | Low | Low | Serious | Moderate | Serious |
| Lin59 2016 | Moderate | Moderate | Low | Low | Low | Moderate | Moderate | Moderate |
| Love60 2016 | Moderate | Low | Low | Moderate | Low | Serious | Moderate | Serious |
| Lundy61 2011 | Moderate | Moderate | Low | Moderate | Low | Moderate | Moderate | Moderate |
| Molina62 2008 | Serious | Low | Low | Low | Low | Serious | Moderate | Serious |
| Mollberg63 2011 | Serious | Low | Low | Moderate | Low | Serious | Moderate | Serious |
| Moore64 2011 | Moderate | Low | Low | Low | Low | Moderate | Moderate | Serious |
| Moore44 2016 | Moderate | Low | Low | Low | Low | Moderate | Moderate | Moderate |
| Murphy65 2010 | Serious | Low | Low | Low | Low | Serious | Moderate | Serious |
| Perron66 2001 | Moderate | Low | Low | Low | Serious | Moderate | Serious | Serious |
| Pickens67 2005 | Moderate | Moderate | Low | Low | Low | Moderate | Moderate | Moderate |
| Powell68 2004 | Serious | Serious | Low | Low | Low | Moderate | Moderate | Serious |
| Rabinovici69 2014 | Moderate | Low | Low | Low | Low | Serious | Moderate | Serious |
| Shimazu70 1983 | Serious | Moderate | Moderate | Low | Low | Serious | Moderate | Serious |
| Stratton71 1998 | Moderate | Low | Low | Low | Low | Moderate | Moderate | Moderate |
| Tarmey43 2011 | Serious | Low | Low | Moderate | Low | Moderate | Moderate | Serious |
| Vassallo72 2019 | Serious | Moderate | Low | Low | Moderate | Moderate | Moderate | Serious |
| Zwingmann73 2015 | Moderate | Serious | Low | Low | Low | Moderate | Moderate | Serious |
| Zwingmann21 2016 | Moderate | Serious | Moderate | Moderate | Low | Moderate | Moderate | Serious |
*Were confounding variables controlled for with statistical analysis (eg, multivariate analysis)? Did they determine these factors appropriately (eg, univariate analysis, references, subject matter expert, etc)?
†Were only survivors/non-vegetative participants assessed? Was any group excluded (eg, specific year of arrests, no rhythm on presentation, type of trauma, witnessed cardiac arrest only, etc)?
‡Was the exposure (traumatic cardiac arrest) well defined before the study? Was there a method used to identify these cases?
§Were special methods used for resuscitation (eg, therapeutic hypothermia, thoracotomy)? If so, was it reported and appropriately accounted for?
¶Were any patients lost to follow-up? Was any method used to account for this/any attempt made to recover from this? Was there a particular group of patients that were lost to follow-up?
**Was the exposure known to the person assessing neurological outcome? How were neurological outcomes assessed? Was it subjective/unclear (eg, physician-reported, self-reported, etc)? Was a standardized scale used and data reported for all categories (eg, Glasgow Outcome Scale)?
††Was there a preregistered protocol with preplanned outcomes to report? Were only specific outcomes reported in full? Were the neurological outcomes dichotomized into “good” and “poor” instead of reporting for each category?