AA is one of the most common general surgical emergencies worldwide. The reported life-time risk of appendicitis in the USA is 8.6% in men and 6.7% in women, with an annual incidence of 9.38 per 100.000 persons. In Spain, according to the registry of the Ministry of Health, 44.168 patients were treated for acute AA in 2017 [24].

The severity of clinical classification of AA is based on preoperative assessment. During the WSES in 2015 [1], a group of AA experts discussed many current aspects ending with a new comprehensive disease grading system. Gomes et al. [25] proposed a new comprehensive grading system of AA. Operative findings and intraoperative grading seem to correlate better than histopathology in terms of morbidity, overall outcomes, and costs. This intraoperative grading can determine the optimal postoperative management according to the grade of the disease and the improvement of the utilization of resources [1].

Different options have been described for the treatment of AA. Some authors have proposed a non-surgical treatment [1, 26]. However, major complications have been reported in the antibiotic-alone treatment group, and a high recurrence rate (22.6%) during the first year of the appendicitis episode [1, 26]. For this reason, the COMA trial concludes that surgery should continue to be the mainstay of treatment for AA [27].

Several systematic reviews of RCTs compared LA with open appendectomy. They reported that LA is often associated with longer operative times and higher operative costs, but leads to less postoperative pain, shorter stay, lower incidence of surgical site infection, earlier return to work and physical activity, and better outcomes. Quality of life scores [1, 28]. Thus, in most hospitals in Western countries, LA has become the preferred approach.

The first experience of ambulatory care in the management of AA was published in 2015 by Lefrancois [17] as a prospective descriptive study. Multivariate analysis was performed to create a predictive score of same-day discharge. It allowed to select patients eligible for ambulatorization with a success rate of 97%. However, this study did not assess the severity of appendicitis based on the intraoperative findings. This type of care needs to be validated on a largest cohort.

Trejo-Avila demonstrated in 2019 that implementation of ERAS for appendectomy is associated with a significantly shorter LOS, allowing for outpatient management. The authors concluded that outpatient LA is safe and feasible with similar morbidity and readmission rates compared to conventional care [29].

Recently, Di Saverio in a 2020 update to the WSES Jerusalem [1] guidelines, and Wijkerslooth in a systematic review, established that outpatient LA for uncomplicated AA is feasible and safe with no difference in morbidity and readmission rates. These results are associated with the potential benefits of earlier recovery after surgery and lower hospital and social costs. However, the quality of the evidence was moderate and the strength of recommendation weak (2B).

To date, only four comparative studies have been published in adult patients, using a prospective protocol of a historical control cohort [9, 12, 17, 30]. In addition, two other non-RCT multicenter studies [9, 31] and only one systematic review [11] with significant heterogeneity were published. As a result of this lack of evidence, we decided to design this randomized clinical trial.

Regarding the definition of outpatient criteria, the definitions used so far for early discharge vary widely. For this reason, in the design of our study we used the discharge criteria described by Viñoles [20], Cosse [10], and the Spanish Ministry of Health [19], in which a hospital stay of less than 23 h was defined as the standard for ambulatory surgery. Although these standards do not include emergency procedures, we consider that an appendectomy in selected patients could be comparable with a laparoscopic cholecystectomy, included in group II of the Davis classification [32].

LOS was our primary endpoint. LOS was significantly lower in the OG, 8.82 h (SD 0.83), while in the HG it was 45.43 h (SD 0.96). Coinciding with the literature, where the mean LOS ranged between 3.1 h and 9.6 h [11, 16, 33].

One readmission was observed in the OG for adynamic intestinal ileus. No readmissions were observed in the HG (p = 0.320). Based on similar studies, we have shown that following an ERAS protocol and outpatient management of uncomplicated AA in adult patients is a safe procedure, with low complications and readmission rates ranging from 0 to 4.6% [9, 12, 17, 30].

We observe a lower percentage of complications especially Clavien-Dindo 1 (all related to the presence of postoperative abdominal pain) in the OG than in the HG. For these remarkable and significant findings, there is no clear clinical or pathophysiological explanation despite having evaluated inflammatory parameters, such as C reactive protein and leukocyte levels, and surgical findings. It would be interesting to carry out other studies to try to explain these findings.

In terms of costs, AA is associated with a considerable financial burden due to its high incidence and the cost of hospitalization. The effective use of resources by minimizing costs and maintaining quality is the goal of health care. In 2009, the estimated cost of hospitalization for patients with AA was estimated to be $1,900 in the USA [7]. In our study, health savings were €493.43($516.52) per patient. In the literature, various prospective studies with same-day surgery reported a median reduction in hospital costs ranging from $323 to $4111 per patient [11, 16, 30].

Assessing the possible limitations of this study, the fact that the study design is not blind can be considered a limitation, but the nature of the interventions performed (OG vs HG) made it clear to patients and physicians which group was assigned treatment. Furthermore, the main variables are objective measures, so they are unlikely to be affected by this fact.

Another possible limitation of the study is that the COVID-19 pandemic occurred during the patient recruitment period, which spanned 2020–2021. During the first stage of the COVID-19 pandemic, there was a significant increase in the rate of complicated appendicitis [34]. In addition, a PCR test was added to the protocol, which could increase the hours of stay. However, outpatient management during the pandemic allowed a greater availability of hospital beds to care for patients with medical conditions. Thus, outpatient appendectomy allows better optimization of resources.

In our study design, we decided to calculate a sample size with a high number of follow-up losses. The reason for increasing the sample was to avoid bias due to the low power of the study at the end of data entry. In the sample calculation, a minimum number of 92 patients was obtained to reach the power of the study. To these 92 patients, it was decided to add 30% more patients (28 patients) to avoid bias due to loss of patients. A total of 120 patients were calculated, including estimated losses. At the end of the study, there were 97 patients and 23 actual losses (compared to the previous estimated 28 lost patients). A total of 97 patients exceed the minimum requirements for study potential (which was a minimum of 92 patients).

Our results agree with those reported in most studies [9, 11, 12, 15,16,17, 35, 36]. We can conclude that in our experience it is possible to start an ERAS protocol and an outpatient appendectomy program with an experienced team. Although several studies [9, 11, 15] had shown, before ours, a reduction in LOS in patients selected for outpatient treatment, it had not been possible to draw solid recommendations due to the significant clinical and methodological heterogeneity between the different studies. Along the same lines, the international guidelines [1] could not give strong recommendations due to the lack of scientific evidence from randomized clinical trials. This is the first RCT on the subject. We have shown that ambulatory appendectomy with the ERAS protocol is safe in selected patients, due to the improvement in terms of quality of care, clinical and economic benefits.