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Introduction

Robot-assisted partial nephrectomy (RAPN) is a widely adopted minimally invasive technique for treating localized renal tumors. However, like other laparoscopic procedures, it carries certain risks, including the rare but potentially life-threatening complication of CO ₂ embolism. ^,

CO ₂ is generally considered safe for laparoscopic surgery due to its high solubility in blood, which minimizes clinical complications even if it enters the bloodstream. ^, In fact, during laparoscopic total hysterectomy, transesophageal echocardiography frequently detects air bubbles in the atrium, despite the absence of symptomatic air embolism, suggesting that air entry into the bloodstream is not uncommon. Nevertheless, clinically significant CO ₂ embolism causing cerebral infarction is exceptionally rare, with no previously reported cases in RAPN.

Here, we present a rare case of cerebral embolism secondary to CO ₂ embolism during RAPN in an 83-year-old patient, highlighting key risk factors, management strategies, and lessons to improve prevention and outcomes.

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Case presentation

An 83-year-old man was incidentally diagnosed with a right renal tumor measuring 35 mm, located in the upper pole of the kidney (cT1aN0M0, RENAL score 7) ( Fig. 1 ). He underwent retroperitoneal RAPN using the Da Vinci Xi® system. Pneumoperitoneum was maintained with the AirSeal Intelligent Flow System® (CONMED Corporation, Utica, New York, USA) at an initial pressure of 10 mmHg, which was increased to 15 mmHg during tumor resection.

Left: Contrast-enhanced CT scan of the patient. A 35-mm tumor is located in the upper pole of the right kidney (cT1aN0M0). Right: Venous outflow is observed at the tumor’s base.

Eight minutes after clamping the sole renal artery, EtCO ₂ suddenly dropped from 45 to 20 mmHg, and SpO ₂ decreased from 100 % to 87 % ( Fig. 2 ). Suspecting pulmonary complications, the anesthesiologist initiated manual ventilation for 1–2 minutes, but SpO ₂ did not improve. Pulmonary air embolism was suspected, prompting a temporary pause in surgery and a reduction of pneumoperitoneum pressure to 8 mmHg. The patient’s respiratory status improved rapidly, and intraoperative transesophageal echocardiography (TEE) confirmed gas entry into the right heart, a right-to-left shunt, and subsequent gas entry into the left heart system ( Fig. 3 a). In addition, intraoperative imaging identified an open vein at the tumor base as the likely source of CO2 entry, which is shown in Fig. 3 b. Pulmonary CO2 embolism was diagnosed, raising concerns about a potential cerebral embolism; however, intraoperative evaluation of cerebral infarction was deemed challenging despite neurosurgical consultation. After the patient’s condition stabilized with reduced pneumoperitoneum, the pressure was carefully raised to 10 mmHg, and the surgery was successfully completed. The tumor was resected with a renal artery occlusion time of 23 minutes.

Vital signs during tumor resection after increasing pneumoperitoneum pressure to 15 mmHg. The figure illustrates changes in EtCO ₂ , SpO ₂ , and systolic blood pressure (sBP) during critical intraoperative events, including renal artery clamping, manual ventilation, surgery interruption, transesophageal echocardiography (TEE), and renal artery declamping.

(A) Left: TEE showing the atrial septum. Doppler flow (red arrow) indicates movement from the right atrium to the left atrium. Right: TEE showing the aortic valve. A high-intensity bubble (circled in red) is visible in the left atrium. LA: Left atrium, RA: Right atrium, RV: Right ventricle, TV: Tricuspid valve, AV: Aortic value was received. (B) Intraoperative imaging showing an open vein at the base of the tumor. (C) Postoperative brain MRI showing multiple acute infractions, mainly on the left side.

Postoperatively, the patient developed right hemiplegia, raising suspicion of cerebral infarction. CT and MRI performed within 3 h showed no abnormalities. However, based on the clinical course, the patient was diagnosed with cerebral CO ₂ embolism. No additional treatments, such as hyperbaric oxygen therapy or anticoagulation, were deemed necessary, and the patient was managed conservatively. Motor strength gradually improved with rehabilitation, and on postoperative day (POD) 7, MRI revealed acute infarctions in the left occipital, right occipital, and left parietal lobes ( Fig. 3 c). The patient was discharged independently on POD 11, with minor visual field deficits as the only residual symptom.

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Discussion

CO ₂ embolism during laparoscopic surgery is an extremely rare complication, with an incidence reported to be less than 0.15 %. It is most commonly reported in laparoscopic liver surgery and is even less frequent in urological procedures. However, when air embolism occurs and gas enters the left heart system through a right-to-left shunt, it can result in cerebral embolism with severe outcomes.

In our case, cerebral embolism occurred secondary to pulmonary CO2 embolism during robotic-assisted partial nephrectomy (RAPN). CO ₂ embolism occurs when intraperitoneal pressure exceeds venous pressure due to a vascular injury, allowing a significant amount of CO ₂ to enter the bloodstream. Here, an intraperitoneal pressure of 15 mmHg, set to minimize bleeding, may have facilitated CO ₂ entry through an open vein at the tumor base during renal tumor resection. Additionally, CO ₂ can diffuse through microvasculature even without significant vascular wall damage, emphasizing the need for careful pressure management.

CO ₂ typically enters the right heart and causes a pulmonary embolism; however, in the presence of a right-to-left shunt, it can bypass the lungs and flow directly into the left heart, potentially causing a cerebral embolism. Such shunts can occur via a patent foramen ovale (PFO), atrial septal defect (ASD), ventricular septal defect (VSD), or pulmonary arteriovenous malformations, or when gas inflow exceeds the filtering capacity of pulmonary capillaries. In our case, while preoperative and postoperative echocardiograms did not detect a PFO opening, intraoperative transesophageal echocardiography (TEE) revealed a right-to-left shunt. The pulmonary air embolism likely increased right atrial pressure, leading to the formation of a right-to-left shunt. Moreover, the increased thoracic pressure from manual ventilation, initiated in response to respiratory deterioration, may have exacerbated this situation. Although CO ₂ embolism is generally considered less harmful due to its high solubility and rapid absorption in blood, the cerebral embolism in this case may have been aggravated by non-CO ₂ air delivered by the AirSeal® system, which uses room air instead of pure CO ₂ .

A PubMed search as of January 2025 identified eight cases of CO ₂ embolism during laparoscopic radical or partial nephrectomy, four of which resulted in cerebral embolism ^, . Notably, most cases where the surgical side was specified involved right renal tumors, suggesting that air embolism should be considered a potential risk during right renal surgeries, particularly when manipulating around the vena cava in the left lateral position. In addition, CO ₂ embolism has been reported during retroperitoneoscopic adrenalectomy, where high insufflation pressure, unrecognized venotomy, the AirSeal® system, and the non-expansible retroperitoneal space contribute to gas entry into the circulation. A study on laparoscopic partial nephrectomy using the AirSeal® system demonstrated its ability to maintain stable pneumoperitoneum pressure, which may help reduce perioperative blood loss, potentially shortening surgery time and lowering complication rates. However, while the AirSeal® system effectively maintains constant pressure, it may require stronger air insufflation during suction, raising concerns in the narrower surgical space of the retroperitoneal approach compared to the intraperitoneal approach. Additionally, it has been suggested that the system may draw in room air under strong suction, potentially exacerbating the risk of air embolism. Our case of right-sided laparoscopic partial nephrectomy using the AirSeal® system with a retroperitoneal approach aligns with these reported risks, highlighting the importance of careful pressure management.

When CO ₂ embolism occurs, rapid recognition and intervention are essential, including promptly reducing pneumoperitoneum pressure, positioning the patient in the Trendelenburg position, and administering 100 % oxygen for ventilation. A sudden drop in EtCO ₂ or SpO ₂ should prompt immediate action. The risk is highest during tumor resection in RAPN, particularly at the tumor base, where the risks of both bleeding and air embolism are elevated. Therefore, it is crucial to perform the procedure at an appropriate pneumoperitoneum pressure that balances these risks. In our case, embolism occurred at 15 mmHg but resolved by reducing the pressure to 10 mmHg. When pressure cannot be lowered, renal vein clamping may help prevent CO2 embolism. In our case, TEE detected gas in the left ventricle, and the patient developed cerebral embolism postoperatively, but fortunately, supportive care, including oxygen therapy and rehabilitation, led to significant improvement. While hyperbaric oxygen therapy has been reported as effective treatment, its application should be considered based on the clinical situation.

In conclusion, when performing RAPN, particularly during tumor resection, careful attention to the risk of CO ₂ embolism is essential. Maintaining the lowest effective pneumoperitoneum pressure, prompt recognition, and appropriate interventions, including TEE and supportive care, are critical for preventing severe outcomes.

CRediT authorship contribution statement

Miho Shiga: Writing – original draft, Investigation, Data curation. Masanobu Shiga: Writing – review & editing, Writing – original draft, Methodology, Investigation. Bunpei Isoda: Data curation. Satoshi Nitta: Investigation. Kosuke Kojo: Investigation. Yoshiyuki Nagumo: Resources, Methodology. Takashi Kawahara: Resources, Methodology. Shuya Kandori: Writing – review & editing. Hiromitsu Negoro: Writing – review & editing. Akio Hoshi: Supervision. Bryan J. Mathis: Writing – review & editing. Hiroyuki Nishiyama: Conceptualization.

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Statement of ethics

Since this study is a case report, the Ethics Committee of the University of Tsukuba Hospital granted an exemption from ethical certification. Written informed consent was obtained from the subjects.

Funding sources

No funding was received.