Page 24 - ANZCP Gazette APRIL 2022
P. 24
significance, there seems to be a difference in emboli numbers between the two groups.
When looking at emboli counts, the PASC group clearly has a higher cerebral embolic count compared to the SACC group, which a larger sample size may have shown. Of interest, total bypass time median emboli count for gaseous emboli was 471.5 for SACC and 556.5 for PASC (p-value 0.547). Total bypass time median emboli count for solid emboli was 26 and 55.5 for SACC and PASC respectively (p-value 0.072)
Figure 2 shows the total emboli count for the two groups. We can see the medial total emboli count was higher in PASC compared to SACC, although there is no statistical significance to prove this. Neither data set show any potential outliers that require a closer look.
When differentiating between solid and gaseous emboli during our phase of interest, the majority of detected emboli were gaseous. Similarly with total emboli between the two groups, gaseous emboli counts were higher with partial clamp use (Figure 3). However again, there is no statistical significance to prove this and neither data set show any potential outliers that require a closer look.
When looking at solid emboli, the median of solid emboli is only slightly higher with partial clamp use, when compared to single clamp use (Figure 4). It is important to note that only small emboli numbers are dealt here, although there still seems to be a potential difference to note between the two clamp techniques. There is no statistical significance to prove this and neither data set show any potential outliers that require a closer look, although PASC group distribution is positively skewed.
To put these comparisons into perspective, Figure 5 shows the average number of emboli between the two groups, with respect to differentiation into gaseous and solid emboli. The
presented data displays that there is a difference in the average cerebral embolic load in the PASC group when compared to the SACC group. The mean was reported to capture differences in raw emboli numbers as both comparisons were not equal in number. Average total emboli count was 115 and 220 for SACC and PASC respectively; average gaseous emboli count was 103 and 190 for SACC and PASC respectively, and average solid emboli count was 12 and 29 for SACC and PASC respectively.
Discussion
Although statistically insignificant, a difference in number of gaseous and solid emboli was shown between the two aortic clamp techniques; which favored single aortic cross clamping as a method relating to less cerebral embolic count.The initial hypothesis was made on the basis that more aortic manipulation and additional clamp application with the partial clamp use, would dislodge more solid emboli; however as shown on the graphs, the total emboli count is mostly attributed to gaseous emboli. This may be from the variations in deairing techniques of the surgeons when performing the proximal anastomosis which was evident when consulting with different surgeons. Some were filling the aortic root before their last stitch, and some finished their proximal anastomosis without filling the root and solely relied on the aortic root vent which could mean more gas entrapment.
The rate and duration of aortic root venting can also be a factor contributing to the difference in emboli counts. It may also be that careful clamp application do not cause much aortic damage as expected. A longer phase of interest seemed to correspond to a higher embolic count, which was not surprising.
A recent single centre report and meta-analysis performed by Chen et al. reported a reduced CPB time with the SACC technique (17), which was also in accordance with the results of our study. The disadvantage of utilising cardiopulmonary bypass is also likely to be reduced, with a decrease in CPB time such as organ dysfunction and blood loss.
Study limitations
Our study involved a very small sample size which contributed to a probable type II statistical error. The fact that we did not achieve significance, can possibly be ascribed to the fact that we did not achieve the sample sizes estimated from a power calculation (we would require 48 patients in each group for a 80% power, and 64 patients in each group for a 90% power). Therefore, this may not represent a failure to find significance, but rather represents the reality of the available resources to measure effect; such as the number of patients. Looking into future prospective, this opens up the possibility of conducting the study to a larger sample size and therefore being able to obtain a definitive result.
Conclusion
Although clear differences were identified in embolic counts between the two groups, the results cannot statistically confirm the primary hypothesis. However, there appears to be potential trend in which a larger study may prove. Such findings provide guidance to re-evaluate and modify current surgical techniques to reduce cerebral embolic events during CABG.
21 APRIL 2022 | www.anzcp.org
