Transcutaneous oxygen tension measurement II. The influence of halothane and hypotension.

The influence of halothane-oxygen mixtures on three different transcutaneous oxygen electrodes was investigated. The influence of hypotension caused by halothane and halothane-nitroprusside on transcutaneous oxygen tension measurement (tcPO2) in halothane-anaesthetized patients was examined as well. The electrodes differed with respect to polarization voltages (630 mV or 500 mV) and electrolyte composition (silver chloride or silver bromide). A change dependent on halothane concentration was demonstrated in the electrode readings, both with a polarization voltage of 630 mV and with silver bromide as electrolyte. Using an electrode with 500 mV in polarization voltage and silver chloride as electrolyte, no changes were observed in the readings. During induced hypotension, the tcPO2 values fell in proportion to the mean arterial blood pressure. In patients with a mean arterial blood pressure over 11kPa a tcPO2/PaO2 ratio of 0.6 was found. It is concluded that tcPO2 monitoring during halothane anaesthesia can be influenced in at least two ways, apart from changes in PaO2: (1) by oxygen electrode error due to the halothane; and (2) by changes in skin blood flow. In comparison to the changes in tcPO2 due to the haemodynamic effects of halothane anaesthesia, the changes due to halothane error are small.