Hysterectomy can be performed via several surgical approaches, including vaginal, abdominal, laparoscopic, and robot-assisted routes. Among these, the International Society for Gynecologic Endoscopy recommends vaginal hysterectomy (VH) as the first-line approach [1] because it is associated with lower complication rates and superior postoperative recovery [1-4]. However, its clinical use has steadily declined [5]. This trend can be attributed to the limited availability of training in vaginal surgical techniques and the advantages of laparoscopic surgery, which allows direct visual observation and improved access to the adnexa.

Transvaginal natural orifice transluminal endoscopic surgery (vNOTES) was introduced to overcome some technical limitations associated with VH by providing enhanced visualization through laparoscopic endoscopy. In our initial series, we demonstrated that vNOTES was feasible and safe for vaginal hysterectomies [6], adnexal surgeries [7], and robotic hysterectomies [8]. Subsequent studies established vNOTES hysterectomy (vNH) as a safe and viable approach [9-11]. However, vNOTES requires a specialized transvaginal port to maintain pneumoperitoneum, which introduces challenges such as the need for complex suturing and knotting techniques within the confined vaginal cavity. Additionally, pneumoperitoneum-based vNOTES is prone to CO₂ gas leakage, and the need for suction can further complicate this procedure.

The development of the current technique was based on the hypothesis that, while single-port laparoscopic techniques traditionally rely on pneumoperitoneum, isobaric single-port hysterectomy [12] and myomectomy [13] can be performed effectively without CO₂ insufflation. Hybrid techniques that combine CO₂ insufflation with isobaric methods have also been successfully implemented [14]. In the context of NOTES hysterectomy, some procedures, such as total NOTES hysterectomy (TNH), utilize a fully pneumoperitoneum-based approach [11,15]. However, the most widely adopted method is vNOTES, which combines CO₂ insufflation with an isobaric technique [6-10]. In this context, we hypothesized that an entirely isobaric approach without pneumoperitoneum would also be feasible in the NOTES framework. To test this hypothesis, we developed an isobaric NOTES hysterectomy (iNH) technique as an alternative to vNH that eliminates the need for CO₂ pneumoperitoneum. This technique was subsequently adapted for robotic surgery, enabling a scarless, gasless approach for robotic NOTES hysterectomy [16]. In this study, we describe the iNH technique in detail and evaluate its feasibility and surgical outcomes in comparison with those of conventional single-port laparoscopy-assisted vaginal hysterectomy (SP-LAVH).

Among the 137 patients included in this study, 59 underwent iNH, and 78 underwent SP-LAVH. There were no statistically significant demographic differences between the groups (iNH vs. SP-LAVH) in terms of age, BMI, parity, nulliparity, and history of pelvic surgery (Table 1).

Surgical outcomes of the two groups are shown in Table 2. One patient in the iNH group required a hybrid NOTES procedure assisted by single-port laparoscopy. However, there was no conversion to conventional laparoscopy or laparotomy in either group. No intra-or postoperative complications were observed in the iNH group. In contrast, the SP-LAVH group had two intraoperative complication cases, specifically bowel and bladder injuries, which were promptly identified and successfully repaired laparoscopically without postoperative sequelae.

There were no significant intergroup differences in additional surgical procedures, including adhesiolysis, adnexal surgery, and cystectomy. Likewise, no differences were noted in other perioperative outcomes such as blood transfusion rates, febrile complications, or the number of analgesic drugs required. Median operative time and median uterine weight were also comparable between the iNH and SP-LAVH groups, with median operative times of 70 minutes (range, 40 to 150) for iNH and 82.5 minutes (range, 40 to 145) for SP-LAVH, and median uterine weights of 273.5 g (range, 87.3 to 897.6) vs. 266.0 g (range, 49.1 to 901.0), respectively.

General linear model analysis indicated that operative time was influenced by factors such as uterine weight, patient BMI, and requirement for adhesiolysis (P<0.05).

Notably, the iNH group demonstrated significant improvements in several intraoperative and postoperative outcomes compared with the SP-LAVH group. The iNH group had significantly lower median estimated blood loss (120 [range, 20 to 400] vs. 200 mL [range, 10 to 800]; P=0.004) and a smaller change in hemoglobin levels on postoperative day 1 (0.9 [range, 0 to 3.2] vs. 1.2 g/dL [range, −0.2 to 4.7]; P=0.003). Furthermore, the median length of postoperative hospital stay was significantly shorter in the iNH group than in the SP-LAVH group (3 [range, 2 to 4] vs. 4 days [range, 3 to 7]; P<0.001).

Gas leakage remains a major disadvantage of platforms designed to establish pneumoperitoneum [17,18]. During vNH, loosening of the CO₂ insufflation platform can further restrict the already limited operative space, particularly during suturing, and exacerbate CO₂ leakage. Additionally, maintaining a tightly sealed pelvic cavity during vNH poses a challenge because of the inherent floppiness and weakness of the transvaginal incision compared with the more robust sealing capabilities of a transumbilical puncture wound. Furthermore, frequent suction maneuvering and gas leakage from the transvaginal working ports may further reduce the narrowed space of the transvaginal operative field. The isobaric technique was developed as an alternative to laparoscopic surgery for pneumoperitoneum [12-14,19]. In isobaric studies, continuous suction combined with conventional laparoscopic instruments does not compromise the stability of the working port [19], and can reduce operative times [13]. Isobaric laparoscopic surgery has also been effectively applied for the suturing of uterine defects following leiomyoma removal, enhancing the ease and control of the suturing process [13,14]. This isobaric technique for laparoscopic surgery can also be applied vaginally, allowing for isobaric NOTES [16]. Our findings demonstrate that iNH is a feasible and safe procedure, with clinical outcomes comparable or superior to those of SP-LAVH. Specifically, iNH resulted in reduced hemoglobin changes, lower estimated blood loss, and shortened postoperative hospital stay relative to SP-LAVH, highlighting its potential benefits. Notably, the three-step gasless iNH technique proved viable even in patients with large uteri and significant pelvic adhesions, underscoring its adaptability and effectiveness in complex surgical contexts. These findings support iNH as a promising addition to the spectrum of minimally invasive procedures with potential implications for broadening surgical options in this field. To the best of our knowledge, this is the first report of iNH with a single-hole vaginal platform.

Compared to vNH, iNH offers five distinct advantages. First, iNH creates ample space for instrument manipulation, as the single-hole vaginal platform provides easy access and optimal exposure under gasless conditions. This setup facilitates manipulation even in anatomically challenging situations, such as narrow vaginal canals, nulliparous patients, or large uteri with leiomyomas of up to 895 g. Second, iNH eliminates the need for a closed cavity, allowing surgeons to use continuous suction to clear blood and smoke from the pelvic cavity without affecting the intra-abdominal pressure or destabilizing the working port. This approach aids in maintaining a stable operative field and may reduce operative time, thereby enhancing surgical efficiency. Third, the single-hole platform permits simultaneous use of multiple instruments, thereby improving both suturing efficiency and visualization. Suturing and knotting with barbed sutures at the upper pedicle were smoothly performed using laparoscopic instruments or conventional needle holders under isobaric endoscopic vision. In addition, an assistant can retract the bowel or other tissues using standard instruments to facilitate the procedure. Fourth, iNH mitigates CO₂-related risks by avoiding insufflation, thus reducing complications such as subcutaneous emphysema, cardiopulmonary dysfunction, and hypercapnia [20,21]. Finally, iNH simplifies the surgical workflow by eliminating the need for repeated port reinsertions. In traditional vNH, pneumoperitoneum maintenance often requires repeated insertion and removal of specialized transvaginal port devices for uterine removal and reestablishing access for subsequent procedures. In contrast, the iNH operates entirely within an isobaric state from the outset, streamlining the workflow and reducing procedural complexity.

Recent systematic reviews and meta-analyses have further established the efficacy and safety of vNH for benign gynecological indications. Marchand et al. [22] reported no significant differences in estimated blood loss, operative time, postoperative pain, or length of hospital stay compared with conventional VH. A prospective cohort study by Tang et al. [23] showed earlier bowel function recovery and a faster return to work among vNOTES patients. Additionally, analysis of elderly patients by Mat et al. [24] confirmed that vNOTES can be safely and effectively performed in those aged ≥65 with low complication rates. Regarding gasless techniques, a systematic review by Aruparayil et al. [25] highlighted that gasless laparoscopy is non-inferior to conventional pneumoperitoneum-based laparoscopy in terms of intraoperative complications, conversion rate, and hospital stay in both general and gynecologic surgeries. These findings underscore the clinical relevance of iNH as a gasless NOTES alternative, with comparable safety and recovery profiles. Although discharge was scheduled for the third postoperative day in both groups, patients in the SP-LAVH group remained hospitalized more frequently beyond this point. This delay was primarily attributed to increased postoperative discomfort, such as pain, general weakness, and mild nausea or dizziness. By contrast, patients in the iNH group typically experienced less discomfort, allowing timely discharge within the scheduled period.

A major technical limitation of iNH is the challenge of consistently maintaining a clear operative field. Unlike traditional vNH, which utilizes a CO₂ pneumoperitoneum to elevate the abdominal wall and optimize pelvic cavity visualization, iNH employs a gasless, isobaric approach. This approach can result in peritoneal descent even when upward traction is applied using a right-angle retractor. The difficulty in achieving adequate visualization and access is particularly pronounced in obese patients, where restricted visibility further complicates the procedure. Therefore, a well-coordinated surgical team is required to overcome these challenges. One assistant was tasked with elevating the peritoneal cavity to ensure optimal exposure, while the other managed tissue retraction using laparoscopic instruments. This collaborative effort is essential for maintaining procedural precision and enabling surgeons to achieve favorable clinical outcomes. However, to fundamentally address these procedural challenges and successfully implement isobaric techniques in transvaginal surgery, it is imperative to develop specialized instruments and platforms tailored for isobaric NOTES. Such advancements will refine procedural precision and enhance the clinical applicability of iNH, firmly positioning it as a valuable approach within the spectrum of minimally invasive surgeries. All procedures in both groups were performed by a single experienced surgeon, thereby minimizing variations in surgical technique. However, owing to its retrospective design, selection bias may still exist. In particular, patients with suspected pelvic adhesions on preoperative imaging may have been more likely to undergo SP-LAVH, potentially influencing postoperative outcomes, such as blood loss and hospital stay. Additionally, this study has certain methodological limitations, including its single-center design, relatively small patient cohort, and retrospective nature, which may have restricted the generalizability of the findings. Larger prospective randomized trials are necessary to confirm the reproducibility and clinical utility of iNH at different centers. While our study focused on iNH, it is important to distinguish it from traditional pneumoperitoneum-based NOTES hysterectomies, such as vNH and TNH. Although we did not include vNH cases in this study, our team has gained extensive experience with robot-assisted and conventional vNH, and we plan to directly compare their clinical outcomes with those of iNH. Our findings suggest that iNH is a feasible gasless alternative to vNH while maintaining the advantages of natural orifice access.

In conclusion, iNH merges the procedural simplicity of VH with the visual advantages of NOTES, while avoiding pneumoperitoneum. Therefore, it represents a distinct approach within the spectrum of transvaginal hysterectomies (Table 3). Future comparative studies should clarify its role in relation to vNH and TNH.