Conversion Rates, Causes, and Preoperative Associated Factors in 3,411 Laparoscopic Appendectomies: Insights after Nearly Three Decades of Laparoscopy and an Analysis of the Learning Curve

Acute appendicitis is one the most common causes of acute abdominal pain in the emergency setting [1]. Appendectomy, open or laparoscopic, is the standard treatment for acute appendicitis [2]. The benefits of laparoscopic appendectomy over open surgery have been well demonstrated. Compared to the open approach, laparoscopic appendectomy results in a lower incidence of wound infection, fewer postoperative complications, a shorter length of hospital stay, and a faster return to daily activities [3, 4].

However, conversion to open surgery is sometimes necessary to complete the procedure, even in experienced centers, if a safe laparoscopy cannot be performed [5]. Multiple factors influence the surgeon’s decision to convert a laparoscopic approach to open surgery, including the patient’s characteristics or the disease severity [6, 7]. We present a single-center study analyzing the incidence, causes and preoperative associated factors with conversion, in more than 3,000 consecutive laparoscopic appendectomies.

Our primary outcome was to identify the conversion rate from laparoscopic appendectomy to open appendectomy and how this rate changes over the learning curve. Second, we aim to determine the causes of conversion, their frequency changes over time and preoperative factors associated with conversion.

A retrospective comparative study with prospective case registry was conducted. Patients who underwent appendectomy from January 2000 to December 2023 in a high-volume center were analyzed. The cohort was divided into six periods, each spanning 4 years: P1 (2000–2003), P2 (2004–2007), P3 (2008–2011), P4 (2012–2015), P5 (2016–2019), and P6 (2020–2023). All patients who underwent totally laparoscopic appendectomy (TLA) or that required conversion to open appendectomy (COA) were included. Patients younger than 16 years old and those initially approached by open surgery were excluded.

The diagnosis of acute appendicitis was confirmed through clinical presentation, laboratory tests and image studies such as abdominal ultrasonography and/or computed tomography scan. All patients diagnosed with acute appendicitis underwent surgical treatment. Histopathological analysis was performed on all specimens and those with diagnosis other than acute appendicitis were excluded. Complicated appendicitis was defined as a gangrenous or perforated appendix with or without presence of perpendicular abscess. Purulent fluid in four quadrants was defined as generalized peritonitis.

All surgeries were performed by the same team of surgeons, each of whom had the same hours of surgical training prior to becoming part of the General Surgery Department. A laparoscopic three ports technique was used: 12-mm port in the umbilical region and two 5-mm ports, suprapubic and in the left iliac fossa. Pneumoperitoneum was done with an open technique at the umbilical port with 10 mm Hg pressure. After an exploratory laparoscopy, the appendix was identified, the mesoappendix was dissected and coagulated and the appendiceal base was tied with double endo-loop. Abdominal drains were not routinely used; the decision to place drains was based on the surgeon’s preference.

All patients were admitted for at least for 24 h for postoperative monitoring. If they were able to control pain, urinate, and resume proper oral intake, they were discharged on postoperative day one. Outpatient controls were scheduled for the first and fourth postoperative week if the recovery was uneventful. Patients with complicated appendicitis and/or with generalized peritonitis received a 7-day course of oral antibiotics.

Demographic variables such as age, gender, body mass index (BMI), American Society of Anesthesiologists (ASA) score, presence of previous abdominal surgeries, duration of symptoms, white blood cell count and conditions of the abdominal cavity were recorded.

This study was conducted in accordance with the ethical standards and with the Helsinki Declaration, following STROBE guidelines [8]. The Institutional Review Board approved this study and the requirement for written informed consent was waived by the Institutional Review Board owing to the study’s retrospective nature.

Sample size was determined taking into account previously published study´s conversion rate in laparoscopic appendectomies with 95% confidence interval and 80% power [9]. Sample size obtained after calculation was 30 conversions in the population. Therefore, we could include 3,411 eligible patients out of which 33 were converted to open surgery over a period of 24 year.

Statistical analysis was performed using GraphPad Prism 8.01 statistical software (La Jolla, USA). Univariate analysis was used to compare groups. Descriptive variables are set as mean and standard deviation, while qualitative variables are shown as percentages. Qualitative variables were compared using Mann-Whitney and Fisher’s exact test, when applicable, and Student’s t test was used for quantitative variables. Multivariate analysis was performed to identify preoperative factors independently associated with conversion. A p value <0.05 was considered statistically significant.

A total of 3,411 appendectomies were performed during the study period, including 3,378 TLA and 33 COA. The distribution of surgeries across each period was as follows: 366 (P1), 425 (P2), 490 (P3), 677 (P4), 701 (P5), and 752 (P6). The mean age of patients was 36 years (±15.4) with 52.2% (1,783) being male. The average BMI was 26.1 kg/m² (±4.4). Patient’s characteristics are detailed in Table 1.

The overall conversion rate was 0.96% (33/3,411). In P1 3.55% (13) of patients required conversion, in P2 1.64% (7), in P3 0.81% (4), in P4 0.44% (3), in P5 0.42% (3), and in P6 0.39% (3). Conversion rate demonstrated a statistically significant decrease over time (p 0.03). The learning curve slope between periods showed the following values: −1.91 (P1-P2), −0.83 (P2-P3), −0.37 (P3-P4), −0.02 (P4-P5), and −0.03 (P5-P6), indicating a plateau in the learning curve after the first three periods. See Figure 1.

Various causes of conversion were recorded. Overall, 27.2% (9/33) were due to perforation at the base of the appendix, 24.2% (8/33) to abdominal cavity adhesions, 18.1% (6/33) to visceral injury, 9% (3/33) to pneumoperitoneum intolerance (hypercapnia), 9.09% (3/33) to pregnancy, 9% (3/33) to peritonitis, and 3% (1) to hemorrhage.

Causes of conversion varied during the periods analyzed. In earlier periods (P1-P2), the most common cause of conversion was a perforated appendix base, which then decreased in frequency (P3-P4) and disappeared (P5-P6) in the later periods. In the following periods, conversions were more often due to adhesions (P3-P4) or pneumoperitoneum intolerance/hypercapnia (P5-P6). Although the incidence of adhesions decreased over time, they remained a persistent cause across all periods. Pneumoperitoneum intolerance emerged as the predominant cause of conversion in the final periods (P5-P6). See Figure 2.

Adherences (p 0.001) and hypercapnia (p < 0.00001) were the only operative findings/events significantly related to conversion during the plateau period. Complicated appendicitis was diagnosed in 798 patients, of whom 772 underwent TLA and 26 underwent COA, demonstrating that complicated appendicitis was significantly associated with conversion through all periods (p < 0.00001). See Table 2.

When analyzing preoperative factors, we found age over 65 (p 0.0001), ASA III/IV (p 0.001) and symptom duration exceeding 24 h (p 0.0007) were significantly associated with conversion at the plateau periods after univariate analysis. This was not the case for obesity (BMI >35 kg/m²), previous abdominal surgeries or leukocytosis (white blood cell count >10,000/mm³). See Table 1. Multivariate analysis showed that age (p 0.0001) and symptoms exceeding 24 h (p 0.01) were independently associated with conversion throughout the series. See Table 3.

As mentioned earlier, the benefits of laparoscopic appendectomy over open surgery are well-known, even in cases of complicated appendicitis [10]. Currently, laparoscopy is considered the standard procedure for managing acute abdomen in the emergency settings [11]. In addition to its therapeutic utility, laparoscopy offers diagnostic value by allowing assessment of the entire abdominal cavity, thereby facilitating the exclusion of associated pathologies and differential diagnosis. However, despite the known benefits of laparoscopy, conversion to open surgery is sometimes required to complete the appendectomy.

By dividing our series into six groups, each spanning 4 years, we observed that as the number of patients operated per period increased, the number of patients requiring conversion decreased; indicating a reduction in the conversion rate over the periods with a statistically significant decrease over time (p 0.03). When graphing the conversion rate over the periods, the slope of the learning curve showed a plateau in periods four to six. Our learning curve showed that after the first three periods (12 years), the conversion rate decreased from 3.55 to 0.81%, eventually reaching a plateau of approximately 0.4%. See Figure 1.

Regarding the reasons for conversion, the presence of a perforated base, which was one of the main causes of conversion in the early periods, decreased and eventually disappeared in the later periods, losing statistical significance for conversion during the plateau period (p 0.5). See Table 2. We attributed the reduction of conversions due to perforated base to the surgical team’s increased experience and the progression along the learning curve. Additionally, what was once considered an indication for conversion in the surgical management guidelines of appendicitis is no longer so today [12]. With the evolution of laparoscopic techniques, the surgical team can now address a perforated base laparoscopically, using methods such as intracorporeal suturing, epiploplasty or resection if necessary.

Concerning adhesions, despite a decrease in frequency, they persisted throughout the learning curve for conversion. See Figure 2. It is worth noting that, adhesions may still be significantly associated with conversion in the plateau of the learning curve due to reporting bias in the TLA group, potentially underreporting their presence. Furthermore, all patients converted due to adhesions had a history of previous abdominal surgeries. However, when evaluating whether previous surgeries was a preoperative factor associated with conversion, we found it not to be statistically significant in our series (p 0.4), as over 99% of patients with previous abdominal surgeries could be successfully managed laparoscopically. See Table 1.

In recent periods, conversions due to pneumoperitoneum intolerance/hypercapnia predominated. We considered this as a limitation of laparoscopy itself, rather than a limitation in Surgical Technique. Despite its low incidence, it was noted that all patients converted for this reason had an ASA III/IV score, were over 65 years old and had a symptom duration of over 24 h. These all factors that, as mentioned earlier, were statistically significantly associated with conversion at univariate analysis. It is worth noting that, this cause of conversion appears only in the later stages of the learning curve, probably because this elderly, high ASA score patients, with progressed appendicitis were initially approached with open surgery in earlier periods. These patients were excluded from our series, as mentioned above.

Finally, we identified only age (p 0.0001) and symptoms exceeding 24 h (p 0.01) as independent preoperative factors associated with conversion after multivariate analysis. We acknowledge that previous studies have shown other associations for conversion such as obesity and previous abdominal surgeries, but this was not the case in our series [9].

The main limitation of this study is its retrospective, single-center design. We also recognize the results can be affected by bias (mainly selection and performance bias) and the heterogeneity in the demographic characteristics of the analyzed population. Moreover, we had a low number of conversions despite being a large cohort. This is likely due to the highly trained surgeons in laparoscopy.

In experienced centers, conversion from laparoscopic appendectomy to open surgery is uncommon but remains necessary in certain cases. The causes of conversion have shifted from perforation of the appendix base, which is no longer an indication for conversion, to adhesions or hypercapnia, once the learning curve for conversion plateaus. In our series, previous abdominal surgeries were not significantly associated with conversion. Symptom exceeding 24 h, age over 65 years and ASA III/IV score are identified as preoperative factors significantly associated with conversion in univariate analysis. After multivariate analysis, symptoms exceeding 24 h and age were found to be independently associated with conversion. Despite identifying a population with a higher association with conversion, which should be advised preoperatively, due to the low incidence of conversions once the learning curve is overcome, the initial laparoscopic approach is always preferred.

The study was approved by the Institutional Review Board (IRB) at Buenos Aires British Hospital, Argentina (Approval No. 12240). The need for written informed consent was waived by the IRB.

The authors Dr. Lucía Aragone, Dr. Ramiro Arrechea, Dr. Mariana Toffolo, Dr. Walter Sebastián Nardi, and Dr. Daniel Pirchi have no conflicts of interest to declare.

No funding sources to be reported.

Dr. Lucía Aragone, Dr. Walter Sebastián Nardi, and Dr. Daniel Pirchi contributed to conceptualization and methodology; Dr. Ramiro Arrechea and Dr. Mariana Toffolo contributed to data collection and to data analysis and visualization; Dr. Lucía Aragone and Dr. Walter Sebastián Nardi contributed to writing – original draft preparation and to writing review and editing.

The data presented in this study are available on request from the corresponding author. The data are not publicly available for privacy reasons. Further inquiries can be directed to the corresponding author.