"De-airing" in open heart surgery: report from the CVSAP nation-wide survey and literature review

Retained intracardiac air in cardiovascular surgery: a re-visited problem

Intracardiac air remains an unsolved problem in the realm of cardiac surgery, leading to embolic events encompassing conduction disturbance, heart failure, and stroke. Transesophageal echocardiography allows the visualization of three distinct types of retained intracardiac air: pooled air, coarse bubbles, and microbubbles. The former two predominantly manifest in the right upper pulmonary vein, left atrium, and left ventricle, exhibiting passive movement along the vessel walls by buoyancy. De-airing, involving "eradication" of air from circulation and "expulsion" of air from the heart into the systemic circulation assumes paramount importance in averting embolic events. Optimal de-airing strategies necessitate the thorough elimination of air during the static phase before the resumption of cardiac activity, achieved through aspiration or guided exit leveraging buoyancy. While the dynamic phase, characterized by active cardiac beating, presents challenges for air eradication, the majority of air expulsion occurs towards the aorta during this period. In this latter phase, collaborative efforts among the surgeon, anesthesiologist, and clinical engineer are pivotal to mitigate the risk of bolus air embolism. The efficacy of carbon dioxide insufflation is limited, as it is rapidly aspirated by wall suction or absorbed into the bloodstream. Consequently, the "air" identified by TEE is acknowledged as conventional air. Understanding the distinctive properties of air as well as timely and judicious collaboration for detection and removal, with the ultimate goal of eradication, emerges as an essential prerequisite for successful de-airing in the evolving era of cardiac surgery.

The Case of the "Disappearing Ventricle": A Report

Embolization of entrapped intracardiac air represents a significant risk to the patient undergoing open-heart surgery. Entrapment of as little as 0.5 mL of gas in the heart can cause temporary myocardial dysfunction, cardiac arrhythmias, and systemic emboli. In contrast, larger emboli can disrupt the evaluation of heart function by limiting visualization during echocardiography. We present the case of a 67-year-old male who presented with dizziness, nausea, and chest pain. A left heart catheterization revealed multi-vessel disease. Undergoing general anesthesia, the patient received three-vessel coronary artery bypass grafting, mitral valve repair, ring annuloplasty, and left atrial appendage closure. Upon aortic unclamping, transgastric echocardiography showed significant gas almost wholly obscuring the left heart chambers despite de-airing maneuvers. Successful resolution relied upon higher mean blood pressure and time, demonstrating the importance of intraoperative imaging and interdisciplinary collaboration.

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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13019-022-01916-5.

Development of a Gastight Thoracotomy Model for Investigation of Carbon Dioxide Field-Flooding Efficacy

Carbon dioxide (CO₂) field-flooding during cardiac surgery is a prevention technique to avoid blood-air contact and subsequent embolization. Although it was first used more than 60 years ago, there is still some perplexity around its efficacy, mainly because the gas is invisible and air embolization is difficult to quantify.

An accurate assessment of field-flooding can, therefore, best be performed in models where various methods can be tried in a controlled environment and evaluated with industrial-grade sensors. Multiple options are available for anatomically correct models that reproduce a sternotomy situation, but models for minimally invasive cardiac surgery are expensive and normally meant for training of surgical techniques where only the top side of the model is important.

We created a low-cost and “home-made” gastight mini-thoracotomy model with internal organs and left atrial incision to investigate CO₂ insufflation in a simulated minimally invasive mitral valve surgery. The model was validated with CO₂ field-flooding tests with a commercial diffuser, while three sensors continuously registered the local concentration of CO₂ gas.

Polymeric Microfiltration Membranes Modification by Supercritical Solvent Impregnation-Potential Application in Open Surgical Wound Ventilation

This study investigated supercritical solvent impregnation of polyamide microfiltration membranes with carvacrol and the potential application of the modified membranes in ventilation of open surgical wounds. The impregnation process was conducted in batch mode at a temperature of 40 °C under pressures of 10, 15, and 20 MPa for contact times from 1 to 6 h. FTIR was applied to confirm the presence of carvacrol on the membrane surface. In the next step, the impact of the modification on the membrane structure was studied using scanning electron and ion beam microscopy and cross-filtration tests. Further, the release of carvacrol in carbon dioxide was determined, and finally, an open thoracic cavity model was applied to evaluate the efficiency of carvacrol-loaded membranes in contamination prevention. Carvacrol loadings of up to 43 wt.% were obtained under the selected operating conditions. The swelling effect was detectable. However, its impact on membrane functionality was minor. An average of 18.3 µg of carvacrol was released from membranes per liter of carbon dioxide for the flow of interest. Membranes with 30–34 wt.% carvacrol were efficient in the open thoracic cavity model applied, reducing the contamination levels by 27% compared to insufflation with standard membranes.

Investigation of air bubble properties: Relevance to prevention of coronary air embolism during cardiac surgery

Although de-airing procedures are commonly performed during cardiac surgery, use of these procedures is not necessarily based on evidence. Uncertainly remains around the size of bubbles that can be detected by echocardiography, whether embolized air or carbon dioxide can be absorbed, and the reasons for embolic events occurring despite extensive de-airing. Since air bubbles are invisible in the blood, we used simple experimental models employing water and 10% dextran solution to determine the correlation between actual bubble size and the depicted size on echocardiography, bubble size, and floatation velocity and the absorption of carbon dioxide under embolization and irrigation conditions. Bubbles depicted as larger than 1 mm were overestimated by echocardiography: the actual size was larger than 0.4 mm in diameter. While bubbles of 0.5 mm had a floatation velocity of 2 to 3 cm/s, the buoyancy of bubbles smaller than 0.3 mm was negligible. Thus, bubbles that are depicted as larger than 1 mm on echocardiography or that present with apparent buoyancy should be visible and need to be meticulously removed. However, echocardiography cannot distinguish bubbles of around 0.1 mm in diameter from those of capillary size (<10 μm). Thus, we advise continuous venting of dense bubbles until they become sparse. While carbon dioxide was rapidly absorbed when circulating, the absorption of embolized carbon dioxide was negligible. These results suggest that detected intracardiac air represents residual "air," with carbon dioxide already absorbed. Therefore, the use of conventional de-airing procedures needs reconsideration: air and buoyant bubbles should be removed from the heart before they are expelled into the aorta; this requires timely and precise assessment with transesophageal echocardiography and effective collaboration between surgeons, anesthesiologists, and perfusionists.

Continuous-flow total artificial heart port-to-port connection technique using dedicated de-airing sleeve

Preventing the introduction of air while a mechanical circulatory support device is being implanted is critical for successful outcomes. A substantial amount of air may be introduced into the circulation during the pump-to-outflow and/or pump-to-inflow port connection, which can be detrimental to optimal pump function and long-term survival. We have developed a novel connecting sleeve that enables an airless connection of the continuous-flow total artificial heart to the conduits. Herein, we describe the device design and surgical techniques evaluated in vivo.