An updated systematic review and meta-analysis on impedance threshold devices in patients undergoing cardiopulmonary resuscitation

Introduction: Uncertainty persists on the clinical impact of impedance threshold devices in out-of-hospital cardiac arrest. We conducted an updated systematic review on impedance threshold devices. Methods: Several databases were searched for studies testing the effectiveness of impedance threshold devices in patients with cardiac arrest. The primary endpoint was long-term survival. Results: Seven trials (11,254 patients) were included. In 4 studies (2,284 patients) impedance threshold devices were used with active compression-decompression-cardiopulmonary resuscitation, and in the others alone. Overall, impedance threshold devices did not impact on the rate of return of spontaneous circulation (odds ratio= 1.17 [0.96-1.43], p= 0.114), favorable neurologic outcome (odds ratio= 1.56 [0.97-2.50], p= 0.065), or long-term survival (odds ratio= 1.22 [0.94-1.58], p= 0.127). These analyses were fraught with heterogeneity (respectively, p= 0.055, p= 0.236, and p= 0.011) and inconsistency (respectively, I-squared= 51%, I-squared= 27%, and I-squared= 67%). Exploratory analysis showed that combined use of impedance threshold devices with active compression-decompression significantly increased the likelihood of return of spontaneous circulation (odds ratio= 1.19 [1.00-1.40], p= 0.045), favorable neurologic outcome (odds ratio= 1.60 [1.142.25], p= 0.006), and long-term survival (odds ratio= 1.52 [1.11-2.08], p= 0.009). The favorable impact of the interaction between impedance threshold devices and active compression-decompression was also confirmed at meta-regression analysis (respectively, b= 0.195 [0.004-0.387], p= 0.045, b= 0.500 [0.079-0.841], p= 0.018, b= 0.413 [0.063-0.764], p= 0.021). Conclusions: The evidence base on impedance threshold devices is apparently inconclusive, with a neutral impact on clinically relevant outcomes. However, exploratory analysis focusing on the combined use of impedance threshold devices with active compression-decompression suggests that this combo treatment may be useful to improve patient prognosis.