Halothane Mimics Oxygen in Oxygen Microelectrodes

Abstract

The effects of halothane and enflurane [anesthetics] on the polarographic measurement of O2 with 5 Pt and 3 Au microelectrodes were examined. Oxygen microelectrodes were calibrated in saline solution equilibrated with either N2 or air, then either halothane, 1.0%, or enflurane, 2.0%, was added to the gas mixture. For each electrode, polarographic curves were determined during exposure to 5 equilibrating gas mixtures: N2, air, N2 plus halothane, air plus halothane, and N2 plus enflurane. Halothane variably increased the current produced (and therefore the estimated O2 tension [pO2]) at all polarizing voltages in saline solution equilibrated with either N2 or air. The effect was present in both conical Pt electrodes and recessed-tip Au electrodes and was not prevented by membrane coatings of polystyrol, Rhoplex or collodion. Enflurane did not alter the polarographic measurement of O2. Tissue pO2 measurements, made with these microelectrodes and membranes, may be unreliable in the presence of halothane. At the present time, clinical use of tissue O2 electrodes, such as for evaluating muscle ischemia, is not common in the USA, although it is more so in Europe. The implications for their use in the presence of halothane are obvious.