Venous Gas Embolism During Radical Robotic Prostatectomy: A Case Report and Evidence-Based Management Algorithm

Robotic-assisted radical prostatectomy (RARP) has gained rapid popularity in the last two decades after early reports of excellent survival rates, quick learning curves, and minimal invasion or tissue damage. Given the anatomical location of surgical prostatectomies and the utilization of intra-abdominal gas during laparoscopy, there is a risk of developing venous air embolism (VAE). We present a case of a 62-year-old male with hypothyroidism and benign prostatic hyperplasia who underwent robotic suprapubic prostatectomy under general anesthesia. One hour after incision the ETCO2 suddenly dropped (40 mmHg to 25 mmHg) as did the SpO2 (98% to 90%). There were no other vital sign changes, nor was there significant blood loss. The surgical team was notified, which prompted the surgeon to inform us that he had just been dissecting around the pelvic venous plexus. At this point, with the clinical suspicion of VAE, abdominal insufflation pressure was lowered, and inspired oxygen was increased to 100%. After 10 minutes, SpO2 and ETCO2 normalized. A debrief and literature review inspired us to develop a laparoscopic-specific VAE management algorithm, with attention to robotic-case management issues. To the best of our knowledge, this is a rare case report describing a clinical VAE during RARP.


Introduction
Robotic-assisted radical prostatectomy (RARP) has gained popularity in the last two decades after early reports of excellent survival rates, quick learning curves, and minimal invasion or tissue damage [1]. Some argue that RARP is the new gold standard for the management of localized prostate cancer citing advantages over open radical retropubic prostatectomy (RRP) and laparoscopic retropubic prostatectomy (LRP) including decreased transfusions and conversions to open surgery, shorter hospital stay, improved one-year continence, and decreased complications when compared specifically to RRP outcomes [2,3].
Given the anatomical location of surgical prostatectomies and the utilization of intra-abdominal gas during laparoscopy, there is a risk of developing venous air embolism (VAE). While there have been a number of recent cases reporting clinical VAE using a variety of prostatectomy techniques including RRP [4], transurethral resection of prostate (TURP) [5], holmium laser enucleation of the prostate (HoLEP) [6], and greenlight laser photovaporizer (GLPV) [7], to the best of our knowledge, this is a rare case report describing a clinical VAE during RARP.
Appropriate and efficacious management of VAE has previously been outlined [8] and revised [9]. Although these reviews are thorough and provide a comprehensive foundation for VAE prevention and management, there is a need for procedure-specific management algorithms as a reference to provide efficient, proceduretailored, and standardized patient care. After the description of the case report, we present a literature review of VAE management during laparoscopic surgeries and an evidence-based algorithm for the management of VAE during robotic laparoscopies. The patient in our case provided consent for publication of this report.

Case Presentation
A 62-year-old male with a history significant for medication-controlled hypothyroidism and benign prostatic hyperplasia presented for robotic suprapubic prostatectomy under general anesthesia; the schematic is shown in Figure 1. After uneventful induction and intubation, an arterial line was placed for pulse-pressure-variation (PPV)-targeted fluid administration. The patient was positioned in steep Trendelenburg. One hour after incision, during transection of the pelvic venous plexus, the patient's endtidal carbon dioxide (ETCO 2 ) dropped from 40 mmHg to 25 mmHg in a single breath, and oxygen saturation (SpO 2 ) decreased from 98% to 90%. There were no changes in the electrocardiogram, blood pressure, or ventilation, nor was there any concomitant blood loss. The surgical team was notified and decreased abdominal insufflation pressures while the patient's inspired oxygen was increased to 100%. After 10 minutes, SpO 2 and ETCO 2 normalized. As this presentation was highly suspicious for CO 2 venous embolism, the emergence plan was modified to exclude the use of nitrous oxide. After tracheal extubation, the patient was transferred to the post-anesthesia care unit where he recovered successfully and was discharged home on the same day.

Discussion
We present the successful management of VAE during robotic-assisted prostatectomy characterized by timely identification, proper communication, and adequate support, resulting in no further decompensation. After debriefing and reflecting on the case, we conducted a literature review using Medline and Embase between January 2010 and July 2020. No restrictions on language or publication date were employed, and the terms used were "Prostatectomy," "Robotic prostatectomy," "Laparoscopy," combined with "Air Embolism," "Embolism," "CO 2 embolism," excluding the word "embolization." Our inclusion criteria were articles in which VAE was considered or discussed. Two authors (AL and CV) independently screened citations from the initial search using a two-step approach in which first the title and then the abstracts were screened for eligibility using the software Abstrackr (Brown University, School of Public Health, Providence, USA) [10]. For citations that were considered potentially relevant, the full text was retrieved and further screened for eligibility. In cases of disagreement, both reviewers discussed and achieved consensus, and consulted with the third author (SK) to include or exclude articles. After a full-text review and data extraction, we developed a management algorithm for VAE during robotic laparoscopies.
We extracted 37 articles largely comprised of review articles and case reports ( Figure 2). These articles originate from around the world and include 11 from the United States; five from Japan; four from Korea; three each from Australia and Italy; two each from China, India, and Turkey; and one each from Denmark, Singapore, Spain, the Netherlands, and the United Kingdom. All 37 articles consider VAE management during laparoscopic procedures and include four robotic laparoscopies.

Risk of VAE and pathophysiology
We did not find any published reports of VAE occurring during RARP. Although the risk of a clinically significant VAE is considered rare, it has been a well-established risk of laparoscopic surgeries with a high reported mortality rate of 28% [8,9,11]. Subclinical VAEs diagnosed with transesophageal echocardiogram (TEE) have been reported at an incidence of 17%-38% [12]. This risk of VAE and its effect on morbidity and mortality are dependent on the rate and volume of air accumulation, which varies by degree of vasculature exposed and the pressure gradient between the exposed venous system and the right heart [8,9,[13][14][15].
The diagnosis of VAE in anesthetized patients mostly presents as tachyarrhythmia, right heart strain, hypotension, decreased end-tidal carbon dioxide and oxygen saturation, and, in severe cases, neurologic sequelae that in most cases are masked until the postoperative period [8,9]. Furthermore, the presentation of VAE varies by size and rate, making its detection challenging, though adverse signs and symptoms have been elucidated based on the size of air entrainment [8,17].
Though TEE is a highly sensitive technique used for the diagnosis of VAE with a detection capability of 0.02 ml/kg of entrained air, it is invasive, expensive, and requires expertise [8,21]. Pulmonary artery catheterization has been used to detect air emboli of 0.25 ml/kg, although placement without other indications may cause more risk than warranted [8]. The use of a precordial Doppler ultrasound is highly sensitive in detecting emboli as small as 0.05 ml/kg, most cost-effective, easy to use, and least invasive [8,22]. Auscultation of a "mill-wheel" murmurs over the precordium rules in VAE [18]. Even with these options, these technologies used as a tool for VAE detection were referenced in 47% of case reports [9,14,[23][24][25][26][27][28][29][30][31].

Management: communication and robotic considerations
Communication with the perioperative team improves the timely anticipation of high-risk VAE portions of surgery [8]. If VAE is suspected by the anesthesiologist, it is imperative to inform the surgeon and start maneuvers such as flooding the exposed vasculature with saline and decreasing insufflation pressure. While flooding the surgical field is effective, it was not mentioned as a common practice in the laparoscopic case reports [9,19,28,32,33].
The use of Trendelenburg position for its effect on VAE risk has a controversial history [19]; though, it has been shown to increase the pressure in the right atrium and balance the inward pressures of insufflation [13]. Hong et al. hypothesized that this mechanism is a contributory factor to the low rate of VAE in RARP with a steep Trendelenburg angle of 30 degrees, opposed to the typical 15 degrees used in gynecologic surgeries [42]. As the performance of these maneuvers during robotic laparoscopies is not possible due to the patient's fixed position, it was excluded in the accompanying algorithm ( Figure 3).
Air aspiration from the right atrium via pulmonary artery catheter is also a debated intervention. While it has been reported that 50% of entrained air can be aspirated, most studies find this treatment inconsistent in efficacy [46][47][48]. Further, inserting a catheter solely for the purpose of aspiration has been suggested as controversial due to its risk and low yield [17]. Current recommendations are strongest for its use in hemodynamically unstable patients who have a catheter in situ and are refractory to other management interventions [8,9,17]. This review found that 39% of case reports attempted to aspirate the right atrium for air; successful aspirations also note the beneficial diagnostic ability of this procedure [23,25,[28][29][30]34,37,44,45]. Figure 3 compiles our results in a patient care algorithm. Article characteristics and descriptions are presented in Table 1.  The management of carbon dioxide embolism has been previously described [8], amended with a laparoscopy focus [9], and revised in 2017 [17]. In comparing the case report management practices to what was covered in these reviews, most were consistent with management guidelines; however, there were some expected variations. Consistent practices among case reports included the use of ETCO 2 and SpO 2 as primary indicators of VAE, termination of insufflation, use of 100% oxygen, and maintenance of hemodynamics with intravenous pharmacologic agents and fluids. In contrast, the application of more sensitive VAE detection technology like precordial Dopplers was under-utilized, although actual appropriateness is difficult to evaluate. The intervention of air aspiration was used in about half of the case reports. This inconsistency could be due to the perceived risk versus benefit involved in inserting the central catheter or that the embolic event resolved before the intervention was able to be applied.

Lead
Most cases and reviews do not comment on the importance of adequate communication as part of a treatment algorithm. While it is conceivable that proper communication is so commonplace that it is not considered a necessary step to mention, it is nonetheless harmless and imperative to optimal patient safety, cannot be understated, and is thus included in our management algorithm. In the same vein, the decision to continue or abort surgery also lacks commentary in the literature. It seems intuitive that these decisions are considered and risks stratified by the anesthetic and surgical teams as per patient stability. A specific approach to preventative mechanisms to avoid a second VAE during these cases is also not generally addressed in the articles reviewed.
Finally, post-procedural management is an important component to complete any patient care algorithm. While the detection of neurological sequelae is an important aspect to continued post-anesthetic care, some highlight the importance of monitoring right heart failure post-operatively [9] with others underscoring the importance of mitigating the VAE effect on right ventricular afterload as a precursor to causing heart failure [8].
Future research would benefit from validating our presented algorithm in managing VAE during RARP. Specific areas that merit further illumination include decision support to guide continuing or aborting surgery and VAE-specific post-procedure monitoring and support. Barriers to using supplemental monitoring, like precordial Doppler ultrasound, should be further evaluated to best understand their lack of widespread use.

Conclusions
In conclusion, we report successful management of VAE during robotic-assisted laparoscopic prostatectomy. Upon debriefing, we identified the lack of an adequate management algorithm, given the constraint from using the robot and accompanying patient position. VAE identification is challenging, and severe sequelae can occur suddenly and rapidly. Reviewing the literature to date, we provide an updated patient care algorithm in an effort to promote a standardize approach to VAE management during robotic-assisted laparoscopic procedures.

Additional Information Disclosures
Human subjects: Consent was obtained or waived by all participants in this study. Conflicts of interest: In compliance with the ICMJE uniform disclosure form, all authors declare the following: Payment/services info: All authors have declared that no financial support was received from any organization for the submitted work. Financial relationships: Suzanne Karan declare(s) a grant from NIH 1UG3HL140177-01A1. Site investigator on study 1/2: An Anesthesia-Centered Bundle to Reduce Postoperative Pulmonary Complications: The PRIME-AIR Study. The patient referred to in this manuscript is and was not enrolled in the PRIME-AIR study. . Other relationships: All authors have declared that there are no other relationships or activities that could appear to have influenced the submitted work.