Page 23 - ANZCP Gazette NOVEMBER 2022

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Perfusion 00(0)
Table 2. Comparison of the total emboli and emboli counts per minute different operational phases.
for open-chamber and closed-chamber procedures at two Emboli per minute
Operational phase
Phase 1b Phase 2c Total
Total emboli
Closed chamber median (IQRa)
353 (199–770) 394 (223–592) 898 (499–1366)
Open chamber median (IQRa)
617 (163–970) 1950 (788–2526) 2617 (1007–5847)
p-Value
0.561 <0.001 0.007
Closed chamber median (IQRa)
6.8 (3.6–15.2) 9.6 (5.1–14.9) 9.3 (4.4–12.8)
Open chamber median (IQRa)
6.4 (2.0–18.1) 43.3 (19.7–60.3) 20.2 (9.6–37.5)
p-Value
0.850 <0.001 0.027
aInterquartile range.
bPhase 1 – Initiation of CPB to aortic cross-clamp removal.
cPhase 2 – Aortic cross-clamp removal to 20 minute after venous decannulation.
Table 3. Comparison of gaseous and solid embolic loads between open-chamber and closed-chamber procedures at two different operational phases.
Operational phase
Phase 1b Phase 2c Total
Gaseous
Closed chamber median (IQRa)
324 (162–698) 341 (196–509) 794 (444–1296)
Open chamber median (IQRa)
537 (143–926) 1597 (696–2139) 2240 (891–5340)
p-Value Solid
Closed chamber median (IQRa)
0.705 13 (3–33) <0.001 37 (18–49) 0.009 52 (37–94)
Open chamber median (IQRa)
22 (13–58) 209 (92–461) 304 (132–541)
p-Value
0.151 <0.001 <0.001
aInterquartile range.
bPhase 1 – Initiation of CPB to aortic cross-clamp removal.
cPhase 2 – Aortic cross-clamp removal to 20 minute after venous decannulation.
circulation: 985 (397–2422) right versus 376 (198–769) left (p<0.001), (see Table 4). This difference was more marked for gaseous emboli than for solid emboli.
Discussion
These data confirm our primary hypothesis that a con- temporary cohort of patients undergoing open-chamber cardiac operations would be exposed to higher numbers of cerebral arterial emboli after removal of the aortic cross-clamp when compared to patients undergoing closed-chamber operations. The difference was consid- erable. Moreover, these data also confirm that the vast majority of these emboli are bubbles that almost certainly arise from residual air not removed by ‘de-airing’ manoeuvres. Our finding that emboli exposure was comparable in open- and closed-chamber groups during the CPB period (up to aortic de-clamping) especially when normalized for duration (Table 2) was unsurpris- ing as there is no particular reason to expect that CPB would be any more productive of emboli in either group.
Our findings are confluent with those reported in most earlier studies that have compared emboli expo- sure in closed- and open-chamber surgery.3,10–12 The most recent study by Chung et al.13 compared five closed and five open-chamber operations using the same Doppler technology employed in the present study. Without distinguishing between gaseous and
solid emboli (but generally referring to emboli as “bub- bles”), they reported ranges of numbers of emboli detected in closed- and open-chamber operations that also revealed greater emboli exposure in OCS opera- tions (CCS: 371–1551 [Chung et al.] versus 424–7749 [present study]; OCS: 671–6476 [Chung et al.] versus 434–12517 [present study]).
Chung et al. applied a sizing algorithm to their Doppler data to derive size estimates for emboli detected. They reported a median diameter of 28 μm for bubbles detected during CPB (consistent with their use of a 38μm arterial line filter) and a median diameter after removal of the aortic cross-clamp of 72μm (IQR 28 to 202μm). A tiny number of bubbles between 1–2mm diameter were detected. It is of relevance that even bub- bles considerably larger than those detected in the Chung study have been shown in previous in vivo experiments to redistribute quickly into the venous cir- culation without arresting or producing obvious inter- ruption of flow.14,15 Indeed, it required bubbles orders of magnitude larger than measured in Chung’s study to arrest flow in pial arterioles under direct observation in a rabbit model of cerebral arterial gas embolism.15 These findings are entirely consistent with the virtually ubiqui- tous exposure of cardiac surgery patients to small cere- bral arterial bubbles (demonstrated in the present study and many others), without apparent focal ischaemic injury in the vast majority of cases.
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