Impact of Preoperative Bowel Preparation on Healing Outcomes in FiLaC

Introduction Anal fistula (AF) is a debilitating proctological condition characterized by chronic local pain, inflammation, and purulent discharge, significantly impacting patient quality of life [1]. Fistula tract laser closure (FiLaC) has emerged as a promising, minimally invasive, sphincter-preserving technique, demonstrating favorable healing rates with a low incidence of postoperative incontinence [2]. However, despite its increasing adoption, the precise role of preoperative bowel preparation (BP) in optimizing healing outcomes following FiLaC remains unclear.

The necessity and specific type of BP for FiLaC procedures have not been systematically evaluated in current literature. Clinical practices vary considerably; some surgeons routinely administer enemas or mechanical bowel preparation to minimize fecal contamination, while others forego BP entirely, citing a lack of conclusive evidence of benefit and concerns regarding patient discomfort [3,4]. Although potential soiling secondary to enema administration is a consideration, a clean rectum could offer advantages if intraoperative procedure modification (e.g., advancement flap) becomes necessary [5]. Current guidelines and expert consensus largely defer the decision to perform BP to surgeon discretion, as robust evidence supporting its effect on healing rates is lacking [6]. This significant clinical equipoise highlights the urgent need for a prospective, evidence-based evaluation of BP in the context of FiLaC.

Objectives The primary objective of this study is to compare clinical healing outcomes at three months between patients undergoing FiLaC with and without preoperative bowel preparation. Secondary objectives include the assessment of fistula recurrence, postoperative complications, pain levels, continence status, and time to return to normal daily activities up to six months postoperatively. We hypothesize that the omission of preoperative BP will not compromise primary healing rates.

Methods Study Design and Setting This study is designed as a single-center, prospective, non-randomized observational cohort study. It will be conducted at the KRC Colorectal Surgery Unit over a 12-month recruitment period, under the supervision of two specialized colorectal surgeons Participants

Inclusion criteria:

• Age ≥18 years
• Diagnosed cryptoglandular AF (simple or complex)
• Scheduled for FiLaC procedure
• Provided written informed consent

Exclusion criteria:

• Fistula associated with Crohn's disease, tuberculosis, or malignancy
• Signs of inflammation (presence of abscess)
• Anovaginal fistulas
• History of pelvic radiotherapy
• Incomplete data or loss to follow-up prior to 6 months

Patients will be stratified into two cohorts according to preoperative BP status:

• Group A: Patients receiving standardized BP (mechanical BP with enemas or without)
• Group B: Patients receiving no BP Standardized bowel preparation will be administered to Group A patients. This involves a clear liquid diet the day prior to surgery. Polyethylene glycol (3 liters) will be initiated at 16:00 PM on the evening before the operation, consumed as 250 mL every 10 minutes, aiming for completion by 21:00 PM. Clear liquid intake is permitted until midnight. If there are particles in the stool on the morning of the operation, a rectal enema will be administered.

Patient allocation to either cohort will be non-randomised, primarily based on the operating surgeon's established clinical practice, supplemented by patient preference. To mitigate potential selection bias inherent in this design, comprehensive stratification factors and baseline characteristics will be meticulously recorded and subsequently adjusted for during statistical analysis.

Intervention All participants will undergo the FiLaC procedure under general or spinal anesthesia. Preoperative antibiotic prophylaxis, consisting of 2g intravenous cefazolin, will be administered to all patients. The procedure involves, if the patient has a previous seton, first removing the seton. The patients will be categorized according to the Park classification [7] at the time of operation. Next, the procedure involves curettage of the fistula tract followed by the controlled application of a radial laser using a 1470 nm diode laser, which is inserted through the external opening with the Seldinger technique, utilising the seton as a guidewire. Once inserted at the mucosal level, the fiber will be withdrawn at a speed of 1 mm per second using 12 watts of energy. The FiLaC® procedure will be performed using the same diode laser, which delivers energy at a wavelength of 1470 nm uniformly over 360°. This radial-emitting laser fiber causes contraction of the surrounding fistula tract, destroying it to a depth of 2 mm. The internal orifice will be closed with absorbable 3.0 suture and performing a Z-stitch. The external orifice will be left open by curettage or core extraction. No dietary restrictions will be imposed postoperatively. Antibiotics will not be prescribed in addition to the antibiotic prophylaxis administered during the operation. Patients will be instructed to clean the external wound after defecation and in the shower at least twice a day, after which they will be discharged the same day. Patients will be advised to take paracetamol with a dose of 500 mg (which they can take three times a day) as a painkiller if they need it.

Outcomes

Primary Outcome:

• Complete clinical healing at three months, defined by the presence of a fully epithelialized external opening without discharge, inflammation, or other objective signs of fistula persistence. An independent colorectal surgeon, blinded to the bowel preparation allocation, will assess healing status during outpatient follow-up.
• Healing will be additionally evaluated using a perianal fistula disease severity score [8]: 0, no active disease or complete healing;

1. slight drainage with minimal symptoms;
2. persistent symptomatic drainage;
3. painful symptomatic drainage; and
4. severe perianal disease potentially requiring diversion.

• We defined superficial and intersphincteric fistulas as low/simple fistulas and transsphincteric, suprasphincteric, and extrasphincteric fistulas as high/complex fistulas [9].

Secondary Outcomes:

• Clinical healing at six months
• Fistula recurrence (clinically confirmed)
• Postoperative pain assessed using a Visual Analog Scale (VAS) on day 1, week 1, and at month 1 and 3.
• Continence status evaluated using the Wexner Continence Score [10] preoperatively and at three months postoperatively.
• Incidence of postoperative complications, including bleeding, infection, and urinary retention
• Time to return to normal daily activities
• Postoperative pain via quality of satisfaction assessed on day 1, week 1, and at month 1 and 3.