Dead space is reduced in tracheotomy:

Airflow resistance of the normal upper airway is substantial, constituting up to 80% of total airway resistance during nose breathing and 50% during mouth breathing. Theoretically, tracheostomy tubes should decrease airflow resistance, but in fact this does not occur because of the smaller radius (inner diameter 7–8 mm) of the tubes. Tracheostomy tubes may reduce dead space by up to 100 mL -150 mL 30 or 50% , when compared to spontaneous breathing.This occurs because the tubes are small and bypass the glottic and supraglottic spaces