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

Abstract

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.

Fig 1. SurgerySim model simulating situation in the operating room.

(a) Overview of the setup. (b) Top view of the sternotomy model. (c) View from the Schlieren’s system. Gas sampling spots are marked as blue squares according to the following numbering: 1) surgeon’s nose, 2) left ventricle, 3) underneath the heart, 4) at fat level, 5) at skin level and 6) at table level (overflow).

Fig 2. Overview of investigated variables.

List of the four CO₂ insufflation factors with their corresponding levels and calculation of the total number of runs recorded.

Fig 3. Marginal means of CO₂ concentration for all types of diffusers as function of flow rate.

Trends are shown for both orientations and the three considered sampling spots. Concentrations below 90% are in the grey area.

Fig 4. Marginal means of CO₂ concentration for all types of diffusers as function of position.

Trends are shown for both orientations and the three considered sampling spots. Concentrations below 90% are in the grey area.

Fig 5. Schlieren’s pictures for flat orientation.

(a) Picture of an example case in the operating room where the diffuser (Temed) was positioned at flat angle and at position 3 o’clock. (b) Comparison between commercial diffusers at flat angle for all flow rates in the in vitro sternotomy model. Pictures taken with the Schlieren’s system (view from caudal to cranial).

Fig 6. Schlieren’s pictures for bent orientation.

(a) Picture of an example case in the operating room where the diffuser (Temed) was positioned at bent angle and at position 6 o’clock (caudal). (b) Comparison between commercial diffusers and the drainage catheter at bent angle and for all flow rates in the in vitro sternotomy model. Pictures taken with the Schlieren’s system (view from caudal to cranial).

Fig 7. Summary of the explorative phase.

Combinations reaching at least 90% of CO₂ in all three considered sampling spots (left ventricle, underneath the heart and at fat level) are shown in green, those reaching 90% only in the left ventricle are shown in yellow, while the others are colored in orange. Skipped combinations are colored in dark gray.