Volume 8, No. 1 • Spring 1993

Keep Both the Oxygen Analyzer and Pulse Oximeter

Clayton Petty, MD

To the Editor

Dr. Jurgen Link asks the value of the in-line oxygen analyzer compared to pulse oximetry in the APSF Newsletter, Summer 1992. Legal consequences are not to be considered per Dr. Link.

The analysis of oxygen in the patient circuit, either the inhalation or expiration side, is essential to safe patient care in 1992. The pulse oximeter is an end-stage analyzer for many of the conditions the oxygen analyzer will pick up faster and easier. Pulse oximetry has been a great advance to patient care but it cannot and should not substitute for the presence of an oxygen analyzer.

Deaths during anesthesia are still being reported from crossed nitrous oxide and oxygen lines, (1) and incorrectly filled medical gas cylinders. (2,3) Near misses have occurred when a medical gas cylinder was filled with carbon dioxide and nitrous oxide instead of just nitrous oxide (4) and when a machinist modified the pin index of the anesthesia machine and nitrous oxide was put an the machine instead of Entonox. (5) These are only recent examples of a continuing problem in anesthesia of hypoxic gas mixtures being administered to the patient.

The oxygen analyzer can detect the wrong gas in the hospital pipeline from crossed pipelines or from wrong gas in the delivery tank. Bypasses of the pin index safety system by human intention or from filling the gas cylinder with the wrong gas can be detected early with the oxygen analyzer. The pulse oximeter must await the development of low oxygen saturation before the anesthesiologist begins to evaluate the rapidly progressing critical situation. Not many anesthesiologists would suspect the wrong gas in the oxygen tank or crossed fines as the cause of the oxygen desaturation! The patient would continue to desaturate while the anesthesiologist is frantically trying to find out the cause. Perhaps a wise anesthesiologist would switch the patient to a self-inflating reservoir bag and deliver room air until the problem is resolved. Most likely, the patient would suffer morbidity or maybe even mortality before the problem is detected.

An oxygen analyzer measures the output of the fresh gas hose in relation to the amount of oxygen delivered. The pulse oximeter measures the percent saturation of hemoglobin. It is unwise to ask either monitor to do the job of the other since they are designed for specific analysis (just like the gas gauge and oil pressure gauge on a car).

Keep both the oxygen analyzer and pulse oximeter in place and the safety of the patient will be greatly enhanced.

Clayton Petty, MD HCA St. Mark’s Hospital

Salt Lake City, LIT


  1. Crossed N20 & 02 lines blamed for outpatient surgery death. Biomedical Safety & Standards 22:14,1992.
  2. Jawan B, Lee JH: Cardiac arrest caused by in correctly filled oxygen cylinder: A case report. Brit j Anaes 64:749,1990.
  3. Menon MRB, Lett Z: Incorrectly filled cylinders (Letter). Anaesthesia 46:155,1991.
  4. Nitrous oxide cylinders found to contain carbon dioxide. Biomedical Safety & Standards 20:84,1990.
  5. Nonstandard user modification of gas cylinder pin indexing. Biomedical Safety & Standards, circa 1989.