NIGHT OWL: New prediction strategies to help test for obstructive sleep apnoea and correlate patient risk with level of care. A single centre, observational study to investigate the predictive value of procedures to test for obstructive sleep apnoea in children prior to tonsillectomy surgery.

1) Polysomnography (overnight sleep study) a single overnight study will be performed by an experienced sleep scientist or technician with each participant within 3 months prior to surgery.Measurements include electroencephalogram (EEG), electrooculograms (EOG), submental electromyogram (EMGgg), oronasal airflow, chest and abdominal wall motion, and arterial O2 saturation. Anterior tibial EMG will be monitored bilaterally. Cardiac rhythm will be monitored. A pulse oximeter will measure arterial oxygen saturation. Transcutaneous carbon dioxide (TcCO2) will be monitored continuously. Snoring will be recorded by a microphone suspended 1 meter above the patient. Motion of the chest wall (rib cage and abdomen) will be measured with respiratory inductive plethysmography. To monitor sleeping position and sleep behaviour, participants will be videoed throughout the night (2) Overnight Oximetry Blood Oxygen level (SpO2) will be measured by Nonin wrist-worn oximeter device (WristOx 3150, Nonin Medical, Plymouth, MN). The Nonin WristOx 3150 is a small, lightweight pulse oximeter designed to be worn comfortably on the patient’s wrist. On the night of the pre-operative sleep study all participants will have oximetry and polysomnography simultaneously. All children will be asked to wear the Nonin WristOx2 oximetrey watches 4 nights after the in-laboratory sleep study. The following signals will be recorded- pulse oximetry and heart rate. (3) Activity monitoring Participants will be asked to wear an Actigraph. Actigraphs are ambulatory devices that determine sleep-wake patterns using accelerometers. Actigraph GT9X (3.5 x 10 cm, weight 14 grams) are designed to measure and record acceleration in all direction and have been shown to provide reliable and valid measures of sleep, physical activity and sedentary time. The digitized values are summed over a user-specified interval (15 seconds for this study), resulting in a count value per 15 second epoch. All children will be asked to wear two Actigraph activity monitors on the wrist and hip for 5 consecutive days after the pre-operative sleep study. Monitors will be fitted and explanation and instructions on their use will be given to the parents at the time of consent or a time closer to the sleep study. The Actigraph will be worn 24 hours per day on the right hip and wrist via an elasticated belt and wrist strap. (4) 3D Facial imaging Measurement of the 3-dimensional (3D) components of the human face is a new technique which allows assessment of the skeletal and soft tissues of the face and neck. It has the ability to provide information regarding linear distances and angles. It can also provide information on facial contours and soft tissue volume. Craniofacial anatomy is recognised as an important predisposing factor in obstructive sleep apnoea (OSA) pathogenesis . Therefore, 3D facial surface measurement is an ideal tool for the assessment of the role of craniofacial structure in the development of OSA. (5) Sleep Questionnaires Parents will be asked to complete two sleep questionnaires to identify children with sleep disordered breathing symptoms. Paediatric Sleep Questionnaires (PSQ)- Sleep-Disordered Breathing Subscale: The PSQ has 22 questions in 4 domains: sleep related breathing, snoring, daytime somnolence, and behaviour.The presence/ absence of the symptom can be answered as “Yes”, “No” or “Don’t Know”. A simple 1-page PSQ symptom inventory will take around 5 minutes to complete. STBUR (Snoring, Trouble Breathing, Un-Refreshed): STBUR screening tool includes five questions: snore more than half of the time, snore loudly, trouble breathing, witnessed apnoea and wake up feeling un-refreshed in the morning. (6) Upper airway collapsibility measurement Measurement of upper airway collapsibility will be carried out at two different perioperative phases; Just after induction of anaesthesia and prior to insertion of the airway device and any opioids (i.e. prior to the procedure starting) At emergence just after the removal of the airway device (i.e. after the procedure has been completed) The measurements involve the use of an anaesthetic mask and require the patient to be breathing spontaneously while anaesthesia is maintained. Pressure is continuously measured inside a facemask (pressure transducer) while airflow and phase of respiratory cycle are monitored by a pneumotachograph attached to the nasal mask (on a computer screen visible by the anaesthetist). (7) Ambulatory Sleep study Post-operative overnight ambulatory sleep study (Type II) (Nox A1 device, Nox Medical, Iceland) will be performed on the night following surgery on the ward. This study will provide information regarding the recovery profile, sleep breathing and sleep behaviour. The measurements are painless and done with simple instruments placed on the body surface. Set up will be performed by a training research team.