Nitrous oxide hazards and pharmacologic effects Hazards for the Patient 1.      If enclosed space-contraindicated such as pneumothorax. 2.      Upper Respiratory tract infection. 3.      Respective depression where respiration is on CO2 drive, as O2 increase will diminish this drive e.g. bleomycin therapy-pulmonary fibrosis. 4.      Pregnancy as spontaneous abortions may occur. ( in general ...