DISCUSSION
In complex aortic surgery especially in repairing of dissected aortas or
in complex situations where cerebral circulation could be compromised,
for example in redo aortic arch surgery, monitoring of the brain
perfusion/oxygenation is of paramount importance. New modalities like
NIRS that monitor oxygen saturation of the brain (rSO2)
as a surrogate, can give an optimal peri-operative assessment. The NIRS
device monitors in real time the cortical regional cerebral oxygenation
and gives us an instant information about cerebral perfusion/oxygenation
adequacy as well as the incidence and time course of cerebral hypoxia.
At the same time, it may help to identify the causes and find methods of
preventing and managing cerebral hypoperfusion and hypoxia during
cardiac surgery [1].
In our case, the observed NIRS dropped dramatically after the LV venting
started. That was probably due to the stealing of a significant amount
of anterograde cardiac flow by the LV venting suction in the context of
a severe AR. As a result, the brain perfusion was compromised and the
brain rSO2 dropped. By reducing the LV vent drainage (until aortic
cross-clamping), we managed to perform the rest of the operation without
difficulty.
The use of a LV venting prevents distension of the left ventricle in so
avoiding sub-endocardial ischemia to the muscle from excessive
stretching. Vents can be placed in the aortic root, left atrium or left
ventricle via the left superior pulmonary vein, left ventricular apex,
or pulmonary artery. It was originally recommended to insert the LV
venting cannula just after applying the cross clamp in the aorta to
minimise introduction of air into the left heart and subsequent systemic
air embolism [2]. Alternatively, nowadays we are using the RSPV
cannulation as a LV venting. To minimize risk of air insertion during
cannulation the heart is usually allowed to fill before vent insertion
and clamped immediately after connection to the venting cannula of the
CPB. This technique, however, can bear complications [3]. This is
most likely to occur at the time of insertion or removal of the venting
catheter from the RSVP. Finally, errors in function of the suction
(positive pressure in reservoir, misdirection of tubing into roller pump
head, reversal of roller pump) may cause air to be pumped into the
ventricle. A number of cardiac surgeons to avoid these potential
complications refrain from the use of an LV venting and use only a small
transvalvular cardiotomy suction while performing valve replacements
[4].
We suggest keeping this rare complication of LV venting via the RSVP in
mind, in the context of severe AR and dilated LV. In doubt, it is safer
to start it after aortic cross clamping. NIRS can be, in this particular
context, a useful monitoring tool to prevent potential severe
neurological damage.
Authors ‘contributions :
Concept/design: SD, TT
Data analysis/interpretation: TT, HS, PS
Drafting article: HS, PS, TT, FF
Critical revision of article: TT, SD
Approval of article: SD, TT
Data collection: FF