Oxygen Analyzers

Abstract

Oxygen is a drug; an accurate dose is vital for therapeutic efficacy, while an under-dose or overdose can provoke therapeutic failure, complications, and death. Thus, periodic monitoring of delivered oxygen values is necessary. Four types of oxygen monitors in current use are based on the paramagnetic, wheatstone bridge, galvanic cell, and polarographic electrode principles. All types can spot-check oxygen; the galvanic cell and polarographic electrodes models can monitor continuously. The wheatstone bridge models are accurate only in the presence of oxygen and nitrogen, while the other three types are accurate in the presence of other gases. The wheatstone bridge models are dangerous in the presence of flammable gases, but the other types are safe. The paramagnetic and wheatstone bridge analyzers do not consume oxygen, while the galvanic cell and polarographic electrode models do consume it. The wheatstone bridge models respond to the concentration of oxygen in the monitored gas, while the other types respond to the partial pressure of oxygen in the sample. Analyzers that respond to partial pressure must be recalibrated for altitudes other than sea level if they are to accurately reflect oxygen concentration. Analyzers that respond to partial pressure of oxygen or have a gas-permeable membrane are affected by pressure and humidity, such as are found in a positive-pressure ventilator circuit. Compensation calculations must be made in these circumstances in order to obtain true oxygen concentration values.