Mitral valve replacement via a right mini-thoracotomy in the dog: Use of carbon dioxide to reduce intracardiac air

Objective: To develop a clinically applicable method of minimally invasive mitral valve replacement (MVR) with cardioplegia, and examine the ability of carbon dioxide (CO₂) to improve de-airing. Methods: MVR was performed via a 5 x 3-cm right lateral minithoracotomy in eight greyhounds. Peripheral cardiopulmonary bypass and an ascending aortic balloon catheter (endoaortic clamp) were used for cardioplegia and aortic root venting. The endoaortic clamp was inflated in the ascending aorta under fluoroscopy and cardioplegic solution was infused. In four dogs, CO₂ at 2 l/min was used to displace air in the chest. A left atriotomy was made, the valve exposed and a mechanical valve implanted. After left atrial closure, retained intracardiac gas was aspirated from the aortic root and collected in a bubble-trap. The endoclamp was deflated and the animal weaned from bypass. Results: A satisfactory MVR was performed in all cases. The clamp time was 64 ± 13 min and all dogs were stable post-bypass. In the CO₂ group, intrathoracic CO₂ was maintained above 86% and 0.1 ± 0.1 ml of gas was collected, compared to 1.3 ± 0.8 ml in the non-CO₂ group (P <0.05). Conclusions: Femoro-femoral bypass and use of the endoaortic clamp allow a safe and efficacious MVR via a right minithoracotomy in the dog. A high intrathoracic CO₂ concentration reduces the amount of retained intracardiac gas.