The application of the exclusion criteria to the initial case study has led to the selection of seven types of procedures that represent 61% of the total DRGs provided by the pediatric surgery and urology facilities of the Lazio Region in 2010. In these DRGs, 80% are outpatients. The best DRG-specific performance determines a theoretical 10% increase. There are no sufficient clinical and organizational data to determine the causes of the high recourse to the one-day surgery, which accounts for nearly 1/3 of all regular admissions. It is quite likely that even a part of these admissions with overnight stay could be transferred to day surgery.
The age group included in the study is represented by patients who are over six months of age. This helps to assess the regional volume of procedures that could be supposedly carried out in a freestanding surgery center using the same minimum age cut-off for treatment of the Ambulatory Surgery Centers . As for patients under six months of age, the literature concurs that newborn babies and premature babies with a gestational age below the 60th week of post-conceptional life  should be excluded from day surgery. It is advisable that, depending on the protocols adopted by the individual healthcare facilities, babies whose age is included between two and six months be admitted to a hospital-based day surgery unit or dedicated nursing beds . With reference to the age group referred to above, a total of 588 patients have been treated in 2010 by the healthcare facilities taken into consideration. Most of them have been treated having recourse to a regular admission procedure and, in fact, the FI is very low (14.6%).
The organizational models and the FI of the healthcare facilities are independent. Paradoxically, the model of partial de-hospitalization, represented by day surgery units, features a lower FI than the model of the dedicated nursing beds in departments for acute patients. The difference is statistically significant. The analysis of the causes is complex and the phenomenon highlights the inadequacy of the FI as the only indicator of the quality and appropriateness of the day surgery services. It is quite likely that an improved understanding of these causes could be gained by monitoring the indicators laid down in the regulations of the Lazio Region . As for the latter, the one relative to the measures connected with the dedicated nursing beds model could be an aspect to be kept under observation. Other elements that should be considered include the analysis of costs in the two models and the time analysis of the activity data. In any case, it may be assumed that, given the want of resources, in a forthcoming future the model of dedicated nursing beds in mixed (adult and pediatric) continuous-cycle hospitals could be negatively affected by the progressive greater care complexity of adult patients with respect to pediatric patients. This phenomenon could be heightened when the surgical activity takes place in operating units that are not reserved to day surgery. On the other hand, the obstacles to the development of day surgeries could be less significant in exclusively pediatric hospitals owing to the lower ASA Physical Status grading values and the relative time stability of such conditions with respect to grown-ups. Furthermore, with a view to ensuring ongoing quality, effectiveness and efficiency, the only pediatric hospital - the Bambin Gesù Pediatric Hospital (OPBG) - got prevailingly organized with day surgery units for the patients' stay and specific operating units.
The place of origin of the patients, often considered a factor limiting the recourse to a day surgery if located far away from the healthcare facility, has not conditioned the choice of the type of hospital admission within the Region. This may be inferred from the comparison of the FI with the Chi Square test, which has not proved significant based on the place of origin. Indeed, the data relative to Latina and its Province point to the inferiority of Rome. The case is altogether different when dealing with places of origin from outside the Region, the significance of which gives evidence of an inappropriate use of the hospital as the place of an overnight stay.
The study presents additional limitations.
The FI has been constructed by modifying the indicators used for the assessment of the appropriateness of hospital admissions of the APPRO (Appropriateness of hospital admissions) method , the transferability of the volumes of day surgery of the MAAP (Model of Analysis of the Procedure Appropriateness) method  and the assessment of the balanced scorecard system performance [12, 13].
Until now, such methodologies have been prevailingly used for adult patients.
The APPRO, built by the Public Health Agency of the Lazio Region, is based on hospital discharge cards (SDO) and has partly recourse to an isogravity classification system called All Patient Refined Diagnosis Related Groups (APR-DRGs) . The method has been conceived with a view to assessing the behavior of hospital facilities in the provision of care services characterized by a low complexity to patients who are not affected by a clinically severe illness, reasonably assuming that, in these cases, the regular admission to a hospital is as a rule an inappropriate organizational procedure . The APPRO method is used in particular to calculate the admissibility thresholds (to regular admission) for DRGs with a high risk of inappropriateness . In this method, the DRG-specific hospital or regional threshold of "tolerated inappropriateness" is a proportion where the numerator is the number of regular admissions of patients affected by illnesses with a minimum level of severity > 1 day and the denominator is the total number of regular admissions of patients affected by illnesses with a minimum level of severity to the hospital or the day surgery unit. The APPRO method is used in order to enforce systems of rewards or sanctions.
The MAAP method has been adopted by the Puglia Region to build indicators of the care setting transferability, DRGs with a high volume of cases, from regular hospitals admissions to day hospitals and ambulatory surgery centers. The transferability volume indicator is used when the DRG volume exceeds 0.5% of the admissions for the entire case study.
The assessment of the performance of the healthcare systems has been made on behalf of the Ministry of Health by the Management and Health Laboratory of the Sant'Anna School of Advanced Studies in Pisa through a set of 34 indicators calculated on the SDOs in 2007 and 2008 . The regional health systems were benchmarked having recourse to target and quintiles methods that allow moving from measurement to assessment. These indicators include those that analyze the appropriateness of the surgical services, namely the share of surgical DRGs falling within the essential levels of care (LEAs), provided in day surgery and one-day surgery facilities. The volume of transferability into freestanding centers of the regular admissions of the least performing facilities with respect to the best performance that has been adopted in this study presents a few analogies with the assessment systems referred to above, with the difference that the method of quintiles has been turned into quartiles.
The available data are incomplete and this has not allowed determining the extent of the change of the system of admission from outpatient to inpatient and vice versa. This aspect should be monitored as it could invalidate the day surgery activity. Hence, the assessment of the healthcare results with administrative data has both advantages and disadvantages. The immediate access to data on relatively uniform computer files and the possibility of estimating shares of inappropriateness within the context of selected case records are definite advantages. On the other hand, the disadvantages are due to the uncertainty of the nature of the administrative datum (potentially incomplete, inaccurate, and distorted) and the absence of references to the context where the admission takes place (e.g., social conditions of the patient). It ensues that the inner validity of the appropriateness assessment methods depends on the comprehensiveness and accuracy of the SDO compilation and coding.
Notwithstanding the aforementioned limitations, there are also additional systems that back up the recourse to administrative data. In fact, the FI is similar to the ASC proportion of the pay for performance (P4P) system . Within this context, it is used in a few states of the USA in both adult and pediatric age starting from patients over the sixth month of life. The P4P system produces a rewarding payment mechanism for the best performing facilities [19, 20].
The avoidable hospitalization is a subject that is well known to pediatricians. By analogy with the studies of the ambulatory care-sensitive conditions that have led to a radical reduction of the medical admissions to hospitals, a few studies that are likely to promote a partial surgical de-hospitalization should be implemented . In fact, in the surgical field, the comparison between ASC and hospital-based facility is still an open question, besides being quite a controversial point [22–24].
Furthermore, there is also considerable confusion about the meaning of de-hospitalization . For administrative personnel, de-hospitalization merely means the passage of a few types of services from the regular hospital setup to a day surgery unit, regardless of the care setting where the process takes place. On the other hand, one needs considering the type of hospital wards and surgery units and, in particular, their inclusion in continuous cycle or day-only facilities. In our opinion, the real de-hospitalization of day surgery is represented by the provision of that activity in daytime facilities and, therefore, with specific hospital wards and surgery units.
The day surgery cases reported in this pilot study only concern pediatric surgery and urology. They should be considered minimum case studies susceptible of increase, since other specialties are also having recourse to day surgery (e.g., ORL, orthopedics, ophthalmology, digestive endoscopy, etc.). Therefore, a considerable part of the services currently provided in a number of continuous-cycle hospital facilities could be concentrated in a hypothetical inter-hospital health facility. We believe that the positive trend of the outpatient/inpatient ratio with respect to previous years, the significant volumes of real and potential activities highlighted in this pilot study, the abolition of the one-day surgery and the extension of the analysis to other disciplines could further the setting up of a freestanding inter-hospital facility of pediatric day surgery in the Lazio Region.