This observational study was conducted in the Hospital Dr. Hernán Henríquez Aravena, Temuco, Chile, between July 2017 and January 2018.

PAED scale

The Pediatric Anesthesia Emergence Delirium (PAED) scale is a reliable tool to measure ED and involves five items: eye contact, purposeful actions, awareness of surroundings, restlessness, and inconsolability (Additional file 1). These five items are scored from 0 to 4. Patients with a total PAED score of ≥ 10 are defined as having an ED event [8].

Translation and cross-cultural adaptation

Translation and cross-cultural adaptation processes were carried out in six stages, as recommended by the literature. In Stage 1 (translation), the PAED scale was first translated into Spanish by three independent native Spanish anaesthesiologists who were fluent in English. In Stage 2 (synthesis), the three translated versions were combined into one version; any disagreements were resolved by consensus under the supervision of three methodologists. In Stage 3 (back-translation into English), three native English speakers who were fluent in Spanish and blinded to the purpose of the study independently performed back-translation. Stage 4 (expert committee review) involved a consensus meeting to resolve any remaining problems, ambiguities, and discrepancies and to establish a prefinal Spanish version of the scale (all authors). In Stage 5 (Pretesting), 54 paediatric anaesthesiologists and 47 anaesthesia recovery nurses in 22 health institutions in Chile were interviewed; they were asked about the importance and acceptability of the scale in clinical settings and to evaluate the scale’s wording accuracy and ease of understanding. In Stage 6 (Integration), the answers of the pretesting stage were summarized, evaluated by all the authors, and integrated into a final version of the scale. Minor discrepancies were addressed based on consensus [12,13,14].

Reliability of the Spanish version of the PAED scale

The reliability of the Spanish version of the PAED scale was evaluated in paediatric patients in the postanaesthetic period after major outpatient surgery. The scale was applied by previously trained observers (anaesthesiologists and/or PACU nurses), with each observer using a couple of measures at 0 min (the moment of recovery of consciousness) and 10 min after the recovery of consciousness in the postanaesthesia care unit (PACU). The scale was applied by two or three observers at the same time. The anaesthesiologist and/or nurse were blinded to each other’s score. Data were recorded in real time in a web-based ad hoc database (DPAP app) with synchronized clocks and were then encrypted once registered. We based all PACU management on the clinical conditions of the children and not on their PAED scores.

Observer training

Both anaesthesiologists and nurses received one month of training. The training consisted of education sessions about ongoing research, paediatric anaesthesia emergence delirium, the use of the instrument (translated PAED scale), and the use of the electronic application (DPAP app). All observers independently assessed at least 50 patients who were not included in the study. In addition, nurses had to have at least three years of experience in postanaesthetic care, and anaesthesiologists had to have at least 3 years of experience.

Study population

This study was conducted in compliance with the principles of the Declaration of Helsinki. The protocol of this study was reviewed and approved by the Institutional Review Board (Res Ext N0. 27,685/2016) and the Ethics Committee of the Universidad de La Frontera (File No. 018/2017). Written informed consent was obtained from parents/guardians by a research assistant. The inclusion criteria were as follows: children with an ASA physical status class of I, II or III, children who were cognitively intact, and children aged from 2–16 years who were undergoing elective outpatient surgery and general anaesthesia over a period of 7 months. The exclusion criteria were as follows: children with psychological, psychiatric or emotional disorders, children with developmental delays, children with neurological injuries, and children who needed sedative medication before induction.

Anaesthesia

Children underwent general anaesthesia with total intravenous anaesthesia (TIVA) or sevoflurane anaesthesia (SEVO), as per the staff anaesthesiologist. Patients fasted for at least 6 h before the surgery but were allowed to drink clear fluids until 3 h before the surgery. No standardization was made for the methods of induction and maintenance of anaesthesia. A parent was present in the operating room (OR) for each induction if desired.

TIVA induction and maintenance

After the placement of an IV cannula, anaesthesia was induced with a bolus of lidocaine (0.5–1 mg/kg) followed by target controlled infusion (TCI) anaesthesia using the Paedfusor model for propofol [15]. The desired effect site concentration was programmed by the staff anaesthesiologist. Remifentanil was maintained using an infusion of a fixed concentration solution of 20 μg/ml and was titrated as per the staff anaesthesiologist (0.2–0.5 μg/kg/min). For children in whom an IV cannula could not be placed, the use of inhalation induction with sevoflurane was not a contraindication to TIVA use. Conversion to TIVA after inhalation induction includes a slower loading dose administration or starting TCI at a lower target and slowly increasing it.

SEVO induction and maintenance

Anaesthesia was induced with a mixture of 50% O2 in air by mask for 30 s followed by incremental increases in inspired sevoflurane (1–7%) until unconsciousness was achieved. IV access was obtained, and a bolus of lidocaine (0.5–1 mg/kg) and fentanyl (2 μg/kg) was administered. Anaesthesia was maintained by the titration of sevoflurane with 50% O2 in air as per the staff anaesthesiologist.

Intraoperative anaesthetic management

Following the induction of anaesthesia, all subjects received a standard intraoperative IV analgesic medication of acetaminophen 15 mg/kg and ketoprofen 2 mg/kg and antiemetic prophylaxis of dexamethasone 0.15 mg/kg. In the SEVO group, supplementary doses of fentanyl (2 μg/kg) were administered after the induction dose until the end of surgery at the discretion of the attending anaesthesiologist.

Statistical analysis

Demographic data are expressed as the mean ± standard deviation or percentages. Interobserver reliability was assessed using the Kappa [16] statistic. Internal consistency was estimated using Cronbach’s alpha test. A Cronbach’s alpha value ranging from 0.70 to 0.95 was considered adequate. The Bland‒Altman method was applied to calculate the difference and mean of measures. Data were analysed using Stata 14.0 software (version 14.0, Stata Corporation, College Station, TX). P < 0.05 was considered statistically significant. The sample size was estimated using the method of Tinsley [17], with the use of 5–10 subjects per item up to a total of approximately 300 patients.