EndoFLIP-guided foregut surgery: toward a new era of intraoperative physiology

Traditional limitations in foregut surgery

Decision-making in surgery for foregut disorders has traditionally depended on a mix of preoperative evaluations and intraoperative anatomical observations. Nevertheless, several surgical techniques - including endoscopic and surgical myotomy as well as fundoplication - address structural concerns and functional problems, particularly regarding the EGJ. Standard methods such as HRM, upper endoscopy, and radiologic imaging offer valuable insights into luminal function^[1,2].

However, these metrics are challenging to apply both intraoperatively and postoperatively, making it difficult to integrate findings and identify the causes of persistent symptoms - raising concerns about the adequacy of surgical intervention^[2,9]. This has exposed a clinical grey area, revealing that anatomical corrections do not always ensure functional improvement, highlighting the inadequacies of strictly focusing on structural measures.

EndoFLIP as a physiological feedback tool

EndoFLIP addresses this gap by allowing real-time intraoperative assessment of EGJ compliance, distensibility, and diameter. The catheter is inserted trans orally and inflated with conductive saline within a compliant balloon that gauges both CSA and intrabag pressure across various segments, subsequently calculating the DI in mm²/mmHg^[3]. This information is especially pertinent in procedures focused on adjusting EGJ tone.

For instance, during laparoscopic Heller myotomy, intraoperative EndoFLIP can detect insufficient or excessive disruption of the lower esophageal sphincter (LES) that might lead to postoperative reflux. Pandolfino et al. revealed that a final DI > 3 mm²/mmHg correlated with favorable outcomes and reduced symptom recurrence in achalasia patients undergoing peroral endoscopic myotomy (POEM) and myotomy^[3].

How EndoFLIP differs from manometry

In fundoplication, where the “tightness” of the wrap can be somewhat subjective and depend on the operator, EndoFLIP provides a physiologic measure of how the wrap affects EGJ compliance^[4]. However, the optimal post-fundoplication DI threshold remains controversial. Some studies have suggested that very low DI values (< 0.9 mm²/mmHg) are associated with an increased risk of postoperative dysphagia, while others have reported higher thresholds for concern. Prior single-center series, such as those from Alkhatib et al., have found that post-fundoplication DI values below 1.8 mm²/mmHg correlate with higher rates of dysphagia, whereas values in the 2-3 mm²/mmHg range are associated with improved symptoms without compromising reflux control^[5]. Nonetheless, these data are derived largely from a single institution that has progressively transitioned from complete to partial fundoplication over time, and even within these reports, the benefits appear to be most pronounced at intermediate follow-up (e.g., two years) but less consistent at later intervals. Thus, while intraoperative EndoFLIP can inform calibration during fundoplication, further multi-center validation and long-term follow-up are needed before firm conclusions can be drawn.

Guiding real-time decision-making across diverse pathologies

Beyond achalasia and GERD, EndoFLIP provides actionable intraoperative insight across multiple foregut disorders. In GERD, it enables assessment of EGJ distensibility during fundoplication, helping tailor wrap tightness to balance reflux control and dysphagia risk, while identifying hypotensive or transient LES dysfunction not captured by manometry^[6]. In EGJOO, EndoFLIP helps differentiate true mechanical obstruction from transient spasm when manometry is equivocal^[1]. During POEM for jackhammer esophagus and other spastic motility disorders, endoscopic functional lumen imaging probe (FLIP) panometry guides the extent of myotomy by visualizing real-time contractile patterns^[8]. In reoperative foregut surgery, EndoFLIP provides reliable anatomical and functional assessment despite altered anatomy, without extensive dissection^[7].

The role of balloon volume in physiologic assessment

A significant benefit of EndoFLIP is its capability to deliver real-time, graded evaluations of EGJ distensibility with various balloon volumes. The balloon, typically inflated with 30, 40, or 50 mL of saline, is equipped with multiple impedance sensors that create pressure-diameter profiles of the EGJ. This enables the calculation of the DI (mm²/mmHg), which is essential for assessing luminal compliance^[9].

Using larger balloon volumes further distends the lumen, providing insights into the tissue’s elastic properties and the functional outcomes of therapeutic procedures such as myotomy or fundoplication. The application of graded balloon volumes allows healthcare professionals to evaluate baseline compliance, reserve capacity, and the dynamic responses of the EGJ under varying strain^[10].

Application of EndoFLIP in GERD surgery

EndoFLIP has also demonstrated significant value in the management of GERD, particularly during fundoplication and hiatal hernia repair. Lee et al. have reported on how EndoFLIP can calibrate the EGJ intraoperatively, offering objective measurements of distensibility to guide the degree of fundoplication tightness^[11]. These studies show that excessively low DI values (< 0.9-1.8 mm²/mmHg) predict a higher risk of postoperative dysphagia, while excessively high values (> 3.0-4.0 mm²/mmHg) may predispose patients to reflux recurrence^[12]. By providing real-time functional data, EndoFLIP allows surgeons to tailor anti-reflux surgery to the individual patient, moving beyond a one-size-fits-all approach. Integrating EndoFLIP into GERD procedures thus enhances precision, reduces variability in outcomes, and provides a physiologic framework for optimizing symptom control^[11,12].

Case-based interpretation: functional outcomes at varying balloon volumes

To facilitate interpretation of the patient-derived EndoFLIP recordings presented in subsequent figures, we include a schematic diagram of the device in situ. The EndoFLIP catheter is a balloon-based impedance planimetry system that incorporates excitation electrodes, multiple impedance sensors to measure CSA, and a pressure transducer. These elements together allow the calculation of the DI (DI = CSA/Pressure), a physiologic parameter central to understanding esophageal function. This schematic in Figure 1 provides context for how intraoperative EndoFLIP measurements are acquired and interpreted^[13].

Figure 1. EndoFLIP system and intraoperative assessment of EGJ distensibility. The EndoFLIP console and catheter (A), EGJ catheter placement schematic (B), and representative achalasia tracing demonstrating an increase in DI from 1.1 to 5.0 mm²/mmHg after myotomy (C); Intraoperative topography at 30, 40, and 50 mL (D-F) shows volume-dependent changes in EGJ geometry and pressure, with postoperative findings consistent with symptom relief thresholds and safe distension profiles^[14-18], supporting multi-volume functional assessment^[19]. (A and B) adapted from Ref.^[13]. (C-F) original. Figure assembled in BioRender. Turaga, A. (2026) https://BioRender.com/zihmyto. EndoFLIP: Endoluminal functional lumen imaging probe; EGJ: esophagogastric junction; DI: distensibility index.

Clinical utility of multi-volume assessment

Using various balloon volumes in sequence enables surgeons to assess both baseline and reserve function of the EGJ. For instance, a patient might show a slight increase in DI at 30 mL but a much greater improvement at 50 mL, indicating a structurally sound yet stiff EGJ that reacts positively to targeted disruption. On the other hand, no improvement over the different volumes could imply the necessity for a longer or more distal myotomy, or possibly a different diagnosis altogether^[20].

Additionally, research indicates that post-myotomy DI thresholds are linked to outcomes. Jung suggested that a post-procedure DI exceeding 2.8 mm²/mmHg at 40 mL is associated with decreased dysphagia, while figures below 2.0 mm²/mmHg could indicate ongoing obstruction^[21]. Likewise, Carducci et al. showed that utilizing intraoperative EndoFLIP with multiple balloon volumes facilitates the adjustment of the intervention, reducing the likelihood of under-treatment and over-treatment^[22].

Moving beyond intraoperative utility

EndoFLIP’s intraoperative use offers immediate insights into the effectiveness of interventions, but its predictive capabilities also reach into the preoperative and postoperative phases. By categorizing patients based on initial EGJ compliance and post-treatment distensibility, clinicians can anticipate symptom relief, recognize non-responders, and shape long-term management strategies.

Various studies indicate that certain DI thresholds are linked to postoperative results. A DI threshold greater than 2.8 mm²/mmHg, derived from prospective achalasia cohorts^[14,15], is generally associated with symptom relief after myotomy. This presents a chance to transition from reactive, symptom-focused choices to proactive, physiology-based surgical planning.

EndoFLIP-guided risk stratification and procedure selection in achalasia

In the preoperative context, EndoFLIP offers distinct benefits compared to relying solely on manometry and impedance studies. For instance, in cases of EGJOO - where manometric results may resemble those of early achalasia or functional dysphagia - FLIP panometry effectively differentiates between actual mechanical obstruction (characterized by a low DI and high pressure) and dynamic or spastic variants^[16,20]. In patients with Jackhammer esophagus or diffuse esophageal spasm - conditions that often result in varied symptom severity and treatment approaches - FLIP can illustrate repetitive and exaggerated contractile patterns, assisting in deciding the necessary length for myotomy or whether any intervention is warranted^[16].

Guiding postoperative expectations and interventions

Postoperative EndoFLIP measurements are crucial in customizing follow-up strategies and guiding further interventions. A low DI following myotomy may indicate inadequate disruption of the EGJ, prompting the need for early re-intervention or pharmacologic support. In contrast, a high DI could indicate excessive opening, which may result in reflux and affect the decision regarding fundoplication augmentation^[19]. Hirano et al. have suggested incorporating EndoFLIP metrics into postoperative surveillance protocols, especially in complex or reoperative foregut cases where symptoms continue despite previous treatments^[23]. However, these measurements must ultimately be interpreted in conjunction with clinical symptoms, endoscopic findings, imaging studies, and preoperative pH testing to ensure accurate assessment and management.

The emerging role of machine learning and predictive models

Recent research has examined the integration of EndoFLIP-derived metrics into machine learning models for predicting outcomes. One study reported that artificial intelligence algorithms trained on FLIP panometry achieved classification accuracies exceeding 90% compared with expert interpretation, highlighting its potential for automated diagnosis^[19]. Another large-scale analysis of more than 700 patients demonstrated that FLIP-based clustering could generate reproducible motility phenotypes with predictive value for postoperative outcomes^[24].

Limitations of EndoFLIP

Despite its advantages, EndoFLIP has several limitations. Adoption is limited by cost and availability, as specialized equipment is not universally accessible^[7]. Interpretation requires experience, and the lack of standardized training may introduce inter-operator variability. Although large panometry datasets have begun to define normative values^[25], consensus guidelines remain limited, with thresholds varying by balloon volume, technique, and patient population.

Most outcome data linking EndoFLIP metrics to clinical benefit derive from single-center or retrospective studies, limiting generalizability^[6,20]. Prospective, multicenter studies are needed to validate DI thresholds across diverse foregut disorders. Additionally, EndoFLIP measures luminal distensibility but does not assess peristaltic coordination, necessitating integration with manometry and other complementary modalities.