HAN scale for mask ventilation Grade 1: Ventilated by mask Grade 2 :Ventilated by mask with oral airway/adjuvant with or without muscle relaxant Grade 3 :Difficult ventilation (inadequate, unstable, or requiring two providers) with or without muscle relaxant Grade 4: Unable to mask ventilate with or without muscle relaxant. Han et al. Anesthesiology 2004 101: 267.