Patient tilt improves efficacy of CO field-flooding in minimally invasive cardiac surgery.

Objective: Space limitations during minimally invasive cardiac surgery impede consistent use of CO field-flooding. We compared different gas delivery methods, flow rates and the effect of patient inclination.

Methods: A gastight model of MICS surgery with internal organs and right thoracotomy wound was created from a mannequin and equipped with a CO concentration sensor in the left ventricle. Maximum achievable CO concentration was compared for gas delivery via three commercial CO diffusors (CarbonMini, Temed, Andocor) and also via a trocar with side port. Gas flow rates of 1, 3, 5 and 8 L per minute were tested. The model was placed either in supine position or with 20° oblique tilt. A simplified transparent model was also created and placed in an optical test bench to evaluate the gas cloud motions via real-time visualization.

Results: The trocar consistently achieved higher CO concentrations inside the left ventricle. At 1 l/min, approximately 2.5 min were needed to fill the supine model to its maximum CO concentration, which was limited to a range of 48-82% in the left ventricle. At higher flow rates, filling time and concentration were significantly improved. In a tilted model, all devices and all flow rates generated on average 99% CO in the ventricle. Imaging revealed constant gas exchange via the main incision, with CO outflow via bottom and air inflow via the top of the incision.

Conclusions: CO field flooding in minimally invasive cardiac surgery is highly effective if the patient is tilted. Else a flow rate of 5 l/min is recommended to achieve the same protection.