John Smith Is a 64-Year-Old Patient Appointed for Extraction of #14

John Smith is a 64-year-old patient appointed for extraction of #14. He is very anxious but does not want to take any oral sedatives because he has to drive home after the procedure. He mentions that his son had N_{2,/sub>O-O2 sedation when his wisdom teeth were removed and he thinks he would like to try it. His health history is significant for heavy smoking over the last 40 years, advanced COPD, hypertension, and diabetes. He walks to the operatory slowly, breathing with great difficulty.
-What medical condition(s) would contraindicate the use of N2O-O2 sedation?}