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Problems of Calibration and Stabilization of tcP o2 Electrodes
Author(s) -
Severinghaus John W.,
Thunstrom Avghi
Publication year - 1978
Publication title -
acta anaesthesiologica scandinavica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.738
H-Index - 107
eISSN - 1399-6576
pISSN - 0001-5172
DOI - 10.1111/j.1399-6576.1978.tb01395.x
Subject(s) - electrolyte , electrode , cellophane , membrane , polypropylene , analytical chemistry (journal) , composite material , reference electrode , chromatography , medicine , materials science , chemistry , biochemistry
The stirring effect factor Ø, used to correct tcP o2 readings for the gradient of P o2 induced in skin by electrode O 2 consumption, was measured with 20 μm cathode electrodes at 44d̀C for various membrane, spacer and electrolyte combinations. Two in vitro models closely resemble skin Ø values: (1) 50% ethylene glycol/water equilibrated with air at 44d̀C, compared to air above this liquid; (2) a mock skin consisting of 25 μm Teflon on foam rubber, in air, dry. Ø varied from 1.01 with 22 μm polypropylene over a 12 μm cellophane spacer, with either aqueous or nonaqueous, chloride‐free alkaline electrolyte, to more than 1.10 when 25 μm Teflon was tested without a spacer. Ø may be predicted: Ø = 1+ 0.44 i/(M + 10C + 20) where i is pA/mmHg electrode sensitivity, and M and C are membrane and cellophane thickness, μm. Pressure sensitivity, tested against foam rubber, was minimized by use of a spacer, and often increased with age of Teflon membrane. Drift may result from water vapour movements across membranes if calibration media have P(H20) either too high or too low. Minimum drift on skin was seen after electrode equilibration with P(H 2 0) = 58 mmHg. Drift on skin is also caused by a slow effect of P co2 on reference electrode potential, and this is minimized by buffering electrolyte with K 2 B 4 O 7.