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An Improved Sensor and a Method for Transcutaneous CO 2 Monitoring
Author(s) -
Beran Anthony V.,
Shigezawa Gordon Y.,
Yeung Hong N.,
Huxtable Robert F.
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.tb01404.x
Subject(s) - electrode , pco2 , analytical chemistry (journal) , medicine , reference electrode , thermistor , biomedical engineering , anesthesia , partial pressure , coefficient of variation , glass electrode , electrical engineering , chromatography , oxygen , chemistry , electrochemistry , organic chemistry , engineering
Since CO 2 diffuses readily through intact skin along a reasonably short diffusion path, measurement of transcutaneous CO 2 (tcP co2 ) is possible, provided the CO 2 consumption of the electrode is minimal and epidermal capillary blood flow and stratum corneum permeability are maintained well. In this paper, a sensor and a methodology for measurement of arterial P co2 (Pa co2 ) by a continuous non‐invasive transcutaneous technique is described. The sensor detects changes in pH which in turn is inversely proportional to the logarithm of partial pressure of CC 2. The pH is measured by a pH‐sensitive glass electrode whose half cell potential is sensitive to hydrogen ion concentration. The sensor consisted of a pH‐sensitive electrode, a Ag/AgCl reference electrode, a thermistor to measure true sensor temperature, a buffer amplifier to increase signal‐to‐noise ratio, a servo‐controlled heater unit, and an in situ calibration unit. Response time (90%) was 20 ± 2.7 sec. Maximum deviation in slope at 37d̀C during the four day period was from 59.16±3.38 to 60.64 ± 3.34 mV/decade. Temperature coefficient was specific for each electrode and varied between +0.37 to ‐2.12 mV/d̀C. The overall four day drift based on the first day slope and temperature coefficient was 0.87±0.47 kPa P co2. Changes in mean drift value during 24 h were within 0.27 kPa P co2. The sensor was applied on rabbits and newborn patients. For the best correlation between Pa co2 and tcP co2 , the skin surface temperature in rabbits was maintained between 40 and 42d̀C. Based on the in situ calibration, the fitted regression line of tcP co2 versus P aco2 had a slope of 0.92, an intercept of 0.3 kPa, and a standard error of 0.51 kPa. Preliminary data obtained on newborn patients suggest that for optimal tcP co2 to Pa co2 correlation a temperature of 38d̀C is required. These data indicate the usefulness of tcP co2 monitoring to indicate Pa co2 changes under normal physiologic conditions.