CO2 Versus Lund De-airing Technique in Heart Surgery

Aortic Valve Disorder

Cardiac de-airing, CO2 insufflation, Air emboli, Trans cranial doppler, Intraoperative echocardiography

To evaluate which of the two de-airing methods (CO2 insufflation vs. Lund de-airing technique) can shorten the left heart de-airing time and prevent or minimize cerebral air emboli during open surgery involving exposure of the left heart to the ambient air. To evaluate the cost effectiveness and possible side effects of CO2 de-airing technique compared to Lund de-airing technique.

Study design: Prospective, randomized and controlled study involving 20 patients, 10 in each group. The de-airing time and the efficiency of the techniques will be assessed by trans-esophageal echocardiography (TEE) and trans-cranial echo-doppler monitoring (TCD). The cardiologists analyzing the TEE recordings will be blinded to the de-airing technique used (the recorded videos will be analyzed at the end of the study). The TCD monitoring will be done by on-line automatic recording of the micro embolic signals (MES) from the right and or left middle cerebral arteries and performed by single surgeon. The CO2 insufflation of the operating field will be performed according to manufacturer's guide lines. During entire study course one type of extracorporeal perfusion system will be used.The study will be registered in the international database. A prior approval will be sought from the hospital ethical committee for the study. Patient selection: Patients planned for aortic valve/root replacement or repair will be selected for the study Exclusion criteria: Patients with known: a) chronic obstructive pulmonary disease, b) emphysema, c) previous thoracic or cardiac surgery, d) history of CVA or stroke and e) evidence of intraoperative pleural adhesions will be excluded from the study. Patients requiring internal mammary artery coronary bypass will also be excluded. Patient consent: A written consent previously approved by the hospital ethical committee will be obtained from all patients before they are enrolled in the study (enclosure 3). De-airing procedure: Enrolled patients will be assigned randomly to one of the two following groups: Control group ( newly developed de-airing technique in Lund ) : In these patients (n=10) the pleura will be opened on both sides and the ventilator will be disconnected before aorta is cross-clamped and cardioplegia administered. At the end of the cardioplegic arrest, the aortic root and the LV will be actively vented and aortic cross clamp released. The time will be noted down (T1). The heart will be defibrillated to sinus or pacemaker induced rhythm. The heart will be kept empty by the LV vent and ejection avoided as monitored by continual intraoperative TEE and systemic arterial pressure tracing. At 35 Celsius body temperature, as measured from the thermistor in the urinary bladder, and with apparently good cardiac contraction the de-airing will begin. Inotropic drugs or systemic arterial vasodilators will be used as and when necessary to achieve good cardiac contraction. The time will be noted down (T2) (T2 - T1 = Pre ejection de-airing time). The LV preload will first now be successively increased by reducing the venous return from the heart-lung machine to raise CVP between 5-10 cm water. LV vent will be continuously regulated depending upon the amount of residual air showing in the left heart. When no air is seen on TEE monitoring in the left heart (LA, LV & Aorta), half the calculated minute ventilation with 100% oxygen and a PEEP of 5 cm H2O will be started. De-airing will be continued and when the TEE shows no or minimal air in left heart, full ventilation with unchanged PEEP will be restored. The patient will be weaned successively from the CPB thereby ensuring that entire cardiac output is diverted through the native fully ventilated lungs. When TEE will show no air in the left heart, the de-airing will be considered complete and the time noted again (T3) (T3 - T2 = Post ejection de-airing time). All cardiac cannulae including the LV vent will be left in situ but clamped, patient weaned completely from the cardiopulmonary bypass and monitored for residual air by TEE & TCD for 10 minutes continually. The LV vent will be re-opened whenever the residual air in the left heart exceeds grade II. The frequency of theses measures will be noted in the protocol. If the patient has by now achieved 36 Celsius core temperature, the heart will be decannulated and CPB removed. Otherwise CPB will be restarted and patient warmed to 36 Celsius before final weaning and decannulation. Study group ( CO2 insufflation ): In these patients (n=10) the pleurae will not be opened. During aortic cross-clamp period the ventilator will be adjusted to provide dead space ventilation only i.e. 5cm PEEP, ventilator frequency 5/min and the minute ventilation = 1,5 liter. Fio2 = 50%. The operating field will be insufflated with CO2 at a flow rate of 10 L / minute starting 2 minutes before cardiac cannulation and continued until 10 minutes after termination of the CPB. At the end of the cardioplegic arrest, the aortic root and the LV will be actively vented and the time noted down (T1). The LV preload will be successively increased by reducing the venous return from the heart-lung machine to raise CVP between 5-10 cm water. LV venting will be continued and when no air bubbles are seen in the left heart (LA, LV & Aorta) under TEE monitoring, the calculated minute ventilation with 100% oxygen and PEEP of 5 cm H2O will be restored. De-airing will be continued and when no or minimal air is seen in the left heart the time will be noted down (T2) (T2 - T1 = Pre ejection de-airing time). Aortic cross-clamp will be released now and heart defibrillated to sinus or pacemaker induced rhythm and de-airing continued. At 35 Celsius body temperature, as measured from the thermistor in the urinary bladder, and with apparently good cardiac contraction the patient will be weaned successively from the CPB ensuring thereby that the entire cardiac output is diverted through the native fully ventilated lungs. Inotropic drugs or systemic arterial vasodilators will be used as and when necessary to achieve good cardiac contraction. When TEE will show no air in the left heart, the de-airing will be considered complete and the time noted again (T3) (T3 - T2 = Post ejection de-airing time). The patient will be weaned completely from the cardiopulmonary bypass and all cardiac cannulae including the LV vent will be left in situ but clamped. The patient will be monitored now for residual air by TEE & TCD for 10 minutes continually. The LV vent will be re-opened whenever the residual air showing on TEE in the left heart exceeds grade II. The frequency of theses measures will be noted in the protocol. The C02 insufflations will continue until the 10- minute post CPB monitoring interval is completed. If patient by now has achieved 36 Celsius core temperature, the heart will be decannulated and CPB removed. Otherwise CPB will be restarted and patient warmed to 36 Celsius before final weaning and decannulation. Trans-esophageal echocardiographic study (TEE): After completion of the cardioplegic arrest and for 10 minutes after termination of the CPB, all the patients will be monitored by TEE for air in the left heart. The residual air showing on TEE after the termination of CPB will be quantified in 4 grades depending upon presence of air in LA, LV and aortic root during one cardiac cycle (grade 0 = no or occasional air in LA, grade 1 = air showing in LA only, grade 2 = air showing simultaneously in LA and LV, grade 3 = air showing simultaneously in LA, LV and the aortic root). The 10-minute post CPB TEE recording will be saved on a video-tape. Trans-cranial echo-doppler study (TCD): After release of the aortic cross clamp and for 10 minutes after the patient has been weaned off from the CPB, the patient will be continuously monitored for micro embolic signals by on-line automatic TCD placed on middle cerebral arteries. Blood gases will be monitored in all patients as following: Blood gas analysis from arterial & venous blood of the patient every 15 minutes in the operating room in both groups until 15 minutes post CPB) - following attached tables (Anesthesia, Perfusion and TCD & Invous monitoring) Measurement of end-tidal PCO2 and volume of expired CO2 every 15 minutes after the patient is intubated and till the time patient leaves the operating room in both groups. (No measurements possible in the control group during cardioplegic arrest) Blood gas analysis from arterial & venous blood lines of the oxygenator and from the LV vent line every 15 minutes while the patient is on CPB in both groups. Continuous on-line monitoring of CO2 content and PCO2 in the blood at the inflow and outflow ports of the oxygenator in both groups using CDI & new machine. Variations in gas flow and the FiO2 needed to adjust PaCO2 to within a fixed desirable range will be recorded and extra blood gas sample will be taken whenever any such adjustment is made. Alfa stat will be employed for blood gas analysis. A core temperature at 30 C will be used for all patients unless positively indicted.

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