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