Should Air Bubble Detectors Be Used to Quantify Microbubble Activity during Cardiopulmonary Bypass?

Air bubble detectors (ABDs) are utilized during cardiopulmonary bypass (CPB) to protect against massive air embolism. Stockert (Munich, Germany) ABD quantify microbubbles >300 μm; however, their reliability has not been reported. The aim of this study was to assess the reliability of the microbubble data from the ABD with the SIII and S5 heart-lung machines. Microbubble counts from the ABD with the SIII (SIII ABD) and S5 (S5 ABD) were measured simultaneously with the emboli detection and classification (EDAC) quantifier in 12 CPB procedures using two EDAC detectors and two ABDs in series in the arterial line. Reliability was assessed by the Spearman correlation co-efficient (r) between measurements for each detector type, and between each ABD and EDAC detector for counts >300 μm. No correlation was found between the SIII ABD (r = .008, p = .793). A weak negative correlation was found with the S5 ABD (r = -.16, p < .001). A strong correlation was found between the EDAC detectors (SIII; r = .958, p < .001), (S5; r = .908, p < .001). With counts >300 μm, the SIII ABDs showed a correlation of small-medium effect size between EDAC detectors and ABD1 (r = .286, p < .001 [EDAC1], r = .347, p < .001 [EDAC2]). There was no correlation found between ABD2 and either EDAC detector (r = .003, p = .925 (EDAC1), r = .003, p = .929 [EDAC2]). A correlation between EDAC and the S5 ABD, was not able to be determined due to the low bubble count detected by the EDAC >300 μm. Both SIII ABD and S5 ABD were found to be unreliable for quantification of microbubble activity during CPB in comparison with the EDAC. These results highlight the importance of ensuring that data included in the CPB report is accurate and clinically relevant, and suggests that microbubble counts from devices such as the SIII ABD and S5 ABD should not be reported.