Article COVID-19 Critical Illness Deep Learning Humans Hypoxia Intensive Care Units Oxygen Saturation Pandemics SARS-CoV-2 SpO2 Waveform ICU Forecasting Technique blood coronavirus disease 2019 critical illness critically ill patient decision support system deep learning epidemiology human hypoxemia hypoxia intensive care unit isolation and purification oxygen saturation pandemic pathophysiology prediction resource allocation virology