Methods
Study design and Subjects : This is a retrospective descriptive study of a single academic sleep center. I-DS (≤12 months old) who underwent PSG at Seattle Children’s hospital over a 6-year period (2015-2021) were included. If there were multiple studies, the first study was chosen. Both diagnostic and split night (split to O2) studies were included. For follow up PSGs following AT, the first follow up study was chosen. The study was approved by the Seattle Children’s Hospital., Seattle, WA, Institutional Review Board Study Number 00003376.
Sleep study and Clinical Data : PSG was performed according to the American Academy of Sleep Medicine (AASM) criteria(Berry et al. 2012) and data were recorded using the Sandman Elite Natus system (Natus Medical Incorporated, Pleasanton, CA, USA). Parameters recorded included electroencephalogram (EEG; two frontal, two central, and two occipital channels, referred to the contralateral mastoid); electro-oculogram, electromyogram (EMG) of the submentalis muscle, EMG of the right and left tibialis anterior muscles, respiratory signals, effort signals for thorax and abdomen, oximetry, a single-lead electrocardiogram, and video and audio recording. Either capnography (End-tidal CO2 [ETCO2]) or transcutaneous CO2 (TCCO2) or both were performed. Calibrations were performed per routine standard by technicians. Epochs were scored by a certified sleep technologist and board-certified sleep physician according to the AASM criteria.(Berry et al. 2012) Respiratory events were classified as obstructive apnea or hypopnea, according to the above-mentioned AASM criteria, and the duration and stage (Non rapid eye movement (NREM) or rapid eye movement (REM)) of each event were annotated by a certified sleep technologist. We collected obstructive apnea hypopnea index (oAHI)(/hr), central apnea index (cAI) (/hr), % time spent with CO2 levels > 50 mmHg, % time spent with saturations <88% (T88), and O2 saturation nadir (minO2sat). OSA was defined as oAHI>=1/hr. Severe OSA was defined by oAHI≥10/hr. CSA was defined as central apnea index (CAI) >= 5/hr. Hypoxemia was defined as T88 greater than 5 minutes. One infant had underlying hypoxemia at baseline resulting in extreme T88 value. This infant was excluded for analyses involving T88. Hypoventilation was defined as % time spent with CO2 levels > 50 mmHg as measured by ETCO2 or TCCO2 greater than 25%. Demographics and other medical history were obtained by reviewing electronic medical record.
Analysis : Distributions of patient characteristics and PSG results were expressed by mean (SD) or number (%) as appropriate. Severity of OSA between infants who underwent diagnostic studies and split night studies (diagnostic portion only) were compared using unpaired t test or Mann-Whitney in case of nonparametric distribution. Comparison of SDB metrics between pre and post AT within infants were made by paired t test or Wilcoxon Signed-Rank test in case of nonparametric distribution. Due to skewed distribution of AHI, nonparametric analysis was performed for all AHI-related analyses. Based on the borderline univariate analysis results wherein hypothyroidism was disproportionately more common in infants with hypoventilation, we performed logistic regression to assess the relationship between hypothyroidism and hypoventilation adjusting for OSA severity (severe OSA vs. no severe OSA). All analyses were performed using SAS 9.4 (SAS Institute, Cary, NC)