Systematic review of the mechanisms driving effective blood flow during adult CPR.

Background: High quality chest compressions is the most significant factor related to improved short-term and long-term outcome in cardiac arrest. However, considerable controversy exists over the mechanisms involved in driving blood flow.

Objectives: The aim of this systematic review is to elucidate major mechanisms involved in effective compression-mediated blood flow during adult cardiopulmonary resuscitation (CPR).

Design And Setting: Systematic review of studies identified from the bibliographic databases of PubMed/Medline, Cochrane, and Scopus.

Selection Criteria: All human and animal studies including information on the responsible mechanisms of compression-related blood flow.

Data Collection And Analysis: Two reviewers (MG, TX) independently screened all potentially relevant titles and abstracts for eligibility, by using a standardized data-worksheet.

Main Results: Forty seven studies met the inclusion criteria. Because of the heterogeneity in outcome measures, quantitative synthesis of evidence was not feasible. Evidence was critically synthesized in order to answer the review questions, taking into account study heterogeneity and validity. The number of included studies per category is as follows: blood flow during chest compression, nine studies; blood flow during chest decompression, six studies; effect of chest compression on cerebral blood flow, eight studies; active compression-decompression CPR, 14 studies; and effect of ventilation on compression-related blood flow, 13 studies.

Conclusion: The evidence so far is inconclusive regarding the major responsible mechanism in compression-related blood flow. Although both 'cardiac pump' and 'thoracic pump' have a key role, the effect of each mechanism is highly depended on other resuscitation parameters, such as positive pressure ventilation and compression depth.