Eligibility criteria

Eligibility of papers to be included in this study will be evaluated according to the criteria outlined below and available in Table 1.

Eligibility criteria for included studies

Children and adolescents < 18 y.o.

Young adult 18–24 y.o.

Severe malnutrition (BMI < 16 kg/m² (adult) or percent median BMI ≤70% or Z-score ≤ − 3 SD (adolescents))

OR

Moderate malnutrition (BMI 16–16.99 kg/m² (adult) or percent median BMI 70–79% or Z-score − 2 to − 2.9 SD (adolescents)) AND Acute medical instability at admission

Defining at least one the following element of an inpatient admission protocol intended for AYAs with AN:

-Refeeding plan

-Laboratory surveillance

-Cardio-respiratory stability monitoring

-Supplementation

Considering the paucity of randomized controlled trials (RCTs) in adolescents and young adults (AYAs) with Anorexia Nervosa, in order to obtain an adequate sample, we will include randomized controlled trials (RCTs) as well as prospective and retrospective cohorts, cross-sectional and case-control studies. We will exclude case reports and case series from this review as we consider that quality of evidence expected from a very limited sample size will not allow us to conclude if the clinical evolution is a direct consequence of any admission inpatient protocol used.

We will include studies that had a study population of children and/or adolescents (< 18 years old) and/or young adults, defined as adults between the age of 19 and 24 years old. In studies addressing both adults and adolescents, we will include them only if data for adolescents and adults younger than 25 years old are reported separately from adults older than 25 years old. If separate data for adolescents and young adults, either reported separately or as a combined group distinct from older adults, are not available in a study that fulfills all the other inclusion criteria, we will try to contact the author to obtain data on this specific age group. Gender will not be an exclusion criterion and we will include studies considering all gendered patients. The diagnosis of AN will be based on established criteria from the Diagnostic and Statistical Manual of Mental Disorders fifth edition (DSM-5) or fourth-text revised edition (DSM-IVR) or from the International Classification of Diseases (ICD-10). We will exclude studies including multiple Eating Disorders diagnosis, such as Bulimia Nervosa, Avoidant/Restrictive Food Intake Disorder and Other Specified Feeding and Eating Disorders, in their study population unless they provide separate analysis of patients diagnosed with AN. The severity of AN is defined in the DSM-5 as patients who are considered severely malnourished as reflected by a BMI < 16 kg/m² in adults or by a percent median BMI ≤70% based on the WHO growth charts or Z-score ≤ − 3 SD in adolescents [12]. However, we will consider also patients to have severe disease if they presented with moderate malnutrition (adult with a BMI of 16–16.99 kg/m² or adolescent with a percent median BMI of 70–79% or Z-score of − 2 to − 2.9 SD [12]) concomitant with acute medical instability at admission, such as hypothermia, hypoglycemia, significant bradycardia, hypotension or electrolytes abnormalities. We will consider studies reporting first hospital admission as well as repeated hospital admissions as long as each episode of care is reported distinctly and that criteria for severity of AN is met in all different admissions.

Studies describing at least one element of an inpatient admission protocol intended for AYAs with AN will be accepted. The refeeding plan should explicitly report the initial energy intake and refeeding methods preferred for the majority of patients, such as meal plan or nasogastric tube feeding, to be considered complete. Laboratory surveillance includes any mention of frequency of measurement of glycemia, phosphate, potassium, magnesium and calcium in patients or any other element considered relevant by based on extant literature and clinician experience. Bed-rest criteria, EKG frequency, admission to intensive care for surveillance or any other element considered relevant will be included in cardio-respiratory stability monitoring. Finally, we will evaluate if electrolytes and vitamin supplementation, including phosphate, potassium, thiamine and multivitamins, was mentioned as part of initial patient management. We will exclude studies that involved only outpatient or partial hospitalization management.