The aim of this study was to estimate and compare the value of the preoperative fentanyl test and the short OSAS screening scale to diagnose severe obstructive sleep apnea；and to observe the required amount of hydromorphone and the adverse respiratory events after adenotonsillectomy.

The results of polysomnography were obtained before adenotonsillectomy, and the short OSAS screening scale was completed by the subjects' parents in preoperative interview. All children were induced by sevoflurane inhalation. After eyelash reflex disappeared and pharyngeal airway insertion, giving 1 mcg/kg fentanyl when the End-tidal concentrations of sevoflurane were maintained at 3.0 and the spontaneous respiratory frequency was stable, observing the changes of respiratory rate. Severe OSAS was diagnosed as respiratory rate decreased by more than 50%. Anesthesia was maintained with desflurane and 60% nitrous oxide in oxygen. The children were transferred to the PACU after extubation. The postoperative pain and agitation were assessed according to the Children's Hospital of Eastern Ontario Pain Scale (CHEOPS) and The Pediatric Anesthesia Emergency Delirium (PAED) score, and all children were given hydromorphone for pain relief according to our protocol.

Inclusion Criteria:

1. The American society of anesthesiologists (ASA) class Ⅰ ~ Ⅱ
2. Age greater than or equal to 3 years
3. Children were diagnosed by polysomnography and plan to adenotonsillectomy.

Exclusion Criteria:

1. craniofacial malformations
2. mental retardation
3. BMI > 30 kg/m2
4. Combined with other neuromuscular diseases
5. a recent history of opioid use