Optimizing CO2 field flooding during sternotomy: In vitro confirmation of the Karolinska studies.

Although CO2 field-flooding was first used during cardiac surgery more than 60 years ago, its efficacy is still disputed. The invisible nature of the gas and the difficulty in determining the "safe" quantity to protect the patient are two of the main obstacles to overcome for its validation. Moreover, CO2 concentration in the chest cavity is highly sensitive to procedural aspects, such suction and hand movements. Based on our review of the existing literature, we identified four major factors that influence the intra-cavity CO2 concentration during open-heart surgery: type of delivery device (diffuser), delivery CO2 flow rate, diffuser position around the wound cavity, and its orientation inside the cavity. In this initial study, only steady state conditions were considered to establish a basic understanding on the effect of the four above-mentioned factors. Transient factors, such as suction or hand movements, will be reported separately.

Patient tilt improves efficacy of CO2 field-flooding in minimally invasive cardiac surgery.

OBJECTIVE: Space limitations during minimally invasive cardiac surgery impede consistent use of CO2 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 CO2 concentration sensor in the left ventricle. Maximum achievable CO2 concentration was compared for gas delivery via three commercial CO2 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 CO2 concentrations inside the left ventricle. At 1 l/min, approximately 2.5 min were needed to fill the supine model to its maximum CO2 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% CO2 in the ventricle. Imaging revealed constant gas exchange via the main incision, with CO2 outflow via bottom and air inflow via the top of the incision. CONCLUSIONS: CO2 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.