Continuous field flooding versus final one-shot CO2 insufflation in minimally invasive mitral valve repair

Patient and data collection

A retrospective, observational study was undertaken of prospectively collected data in one hundred consecutive patients undergoing MIMVR from January 2018 to November 2021 at our Institution Anthea Hospital, GVM Care & Research, Bari, Italy. The median (interquartile range [IQR]) age was 66 (62–76) years, one hundred patients underwent MIMVR through a right thoracotomy approach. Patient characteristics are reported in Table 1. None of the study patients reported the use of psychiatric drugs, alcohol, and carotid artery stenosis prior to the procedure.

Table 1 Characteristics of the study population

Fifty patients were insufflated with continuous CO2 1 min before opening the left atrium and ended after its closure, and fifty patients were insufflated with one shot CO2 10 min before the start of left atrium closure, at a continuous CO2 flow rate of 3 L/min via diffuser (Table 1). The main reason for performing two different methods of CO2 delivery during MIMVR was due to the different techniques used by cardiac surgeons for minimally invasive cardiac surgery. The aim and the methodology of the study was internal discussed with the ethics committee of the hospital according to the General Data Protection Regulation. Because of the retrospective nature of this study, the local ethics committees waived the need for patient consent. The transesophageal echocardiographic (TEE) protocol for the detection of micro-emboli requires to record intraoperative TEE from cross-clamping to 20 min after end of CPB.

Post-operatively, a blinded assessor determined the maximal number of gas emboli during each consecutive minute in the left atrium, left ventricle, and ascending aorta. The primary outcome of the study was the incidence of TPOCD (in particular agitation and delirium occurring 5 h following weaning from anesthesia), MV duration and ICU length of stay.

During the two procedures, correction for hypercapnia during CPB and monitoring of VCO2 changes were recoreded.

Surgical technique

Our surgical approach for minimally invasive direct view during mitral surgery was described elsewhere [11]. Arterial perfusion was always retrograde and peripheral and aortic cross-clamping was external in all patients. Venous cannulation was peripheral with vacuum support and a double site insertion of the cannulas (jugular and femoral). The valve inspection and procedure were through the left atrium with direct vision and the reconstruction technique was standardized [11].

CO2 insufflation management and CPB de-airing

A small PVC flexible drain tube was used for CO2 insufflation as per standardized procedure [12, 13] and flow measurement was performed with a flowmeter for medical CO2. The perfusionist regulates the flow according to pCO2 and pH. PaO2 during CPB was maintained between 150 and 250 mmHg, PaCO2 was maintained through the sweep gas (air flow from gas blender) between 40 and 45 mmHg with pH stat management, and mean arterial pressure was maintained between 50 and 70 mmHg [14, 15]. In both groups, the venting flow was maintained 800 ml/min after cross-clamping. Air embolism was managed under TEE guidance; the heart sections were filled, thus obstructing the venous return from CPB and increasing the cavity diameter, and the lungs were manually expanded using an Ambu® resuscitator (Ambu A/S,Ballerup, Denmark) at a rate of 4 inflations per minute. The ventricular and aortic intracavitary aspirators were managed at 750 ml/min and 800 ml/min after cross-clamp removal, and the aortic root vent was removed at the elimination of total gaseous micro-emboli.

Statistical analysis

Continuous data are expressed as median with IQR and categorical data as percentages. Cumulative survival was evaluated with the Kaplan–Meier method. All reported P-values are two-sided, and P-values of < 0.05 were considered to indicate statistical significance. All statistical analyses were performed with SPSS 22.0 (SPSS, Inc., Chicago, IL, USA).

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