Second hit phenomenon: existing evidence of clinical implications.

The last two decades extensive research evidence has been accumulated regarding the pathophysiology of trauma and the sequelae of interventions that follow. Aim of this analysis has been to collect and categorise the existing data on the so-called "second hit" phenomenon that includes the biochemical and physiologic alterations occurring in patients having surgery after major trauma. Articles were extracted from the PubMed database and the retrieved reports were included in the study only if pre-specified eligibility criteria were fulfilled. Moreover, a constructed questionnaire was utilised for quality assessment of the outcomes. Twenty-six articles were eligible for the final analysis, referring to a total of 8262 patients that underwent surgery after major trauma. Sixteen retrospective clinical studies including 7322 patients and 10 prospective ones, including 940 patients were evaluated. Several variables able to reproduce a post-operative second hit were identified; mostly related to pulmonary dysfunction, coagulopathy, fat or pulmonary embolism, and the inflammatory immune system. Indicative conclusions were extracted, as well as the need for further prospective randomised trials. Suggestions on the content and the rationale of future studies are provided.