Chest
Volume 99, Issue 5, May 1991, Pages 1211-1215
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Clinical Investigations
Response Characteristics of a Dual Transcutaneous Oxygen/Carbon Dioxide Monitoring System

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We tested the response characteristics of a dual transcutaneous (tc) PO2/PCO2 monitoring system in healthy subjects who breathed various gas mixtures, and we compared steady-state tc readings to simultaneous arterial blood gas analysis in 20 stable respiratory outpatients. The electrodes were simple to apply, required very little skin preparation, and had trivial signal drift. In healthy subjects, tcPCO2 lag time during CO2 rebreathing was 16.8 seconds, with a 90 percent response time of 77.9 seconds after CO2 breathing was discontinued. The 90 percent response times of the O2 electrode when subjects breathed a hypoxic mixture was 257 seconds after a lag of 31 seconds. When inhaled gas mixtures were changed from hypoxia to room air, the lag time was shorter (12.5 seconds), but 90 percent response time exceeded 5 minutes. In stable patients with respiratory disease, tcPCO2 and tcPO2 were linearly related to PaCO2 (range, 19 to 53 mm Hg) and PaO2 (range, 45 to 99 mm Hg), respectively (tcPCO2=1.4 PaCO2-9.44, with r = 0.90 and SEE = 5.35 mm Hg; tcPO2 = 0.56 PaO2 + 20.4, with r = 0.53 and SEE = 11.7 mm Hg). We conclude that the response of the dual transcutaneous monitoring system is more rapid for the CO2 than the O2 electrode and may be rapid enough to be useful in some clinical settings; however, the O2 system fails to offer the response characteristics and accuracy that would allow it to be substituted for arterial gas tensions in unstable clinical situations. (Chest 1991; 99:1211-15)

Section snippets

MATERIALS AND METHODS

The transcutaneous combined PO2PCO2 monitor (Radiometer TCM3) is 24 × 8 × 23 cm and weighs 2.7 kg. The front panel displays time or site temperature, PO2, and PCO2. The unit is powered by-battery or a standard electrical outlet. It is capable of analog or serial digital outputs. The combined electrode is 15 mm in diameter and 11 mm in height and weighs 3.8 g.

RESULTS

The application of the dual transcutaneous monitor was simple and involved only brief skin preparation (cleaning with an alcohol swab). No subject complained of discomfort associated with the monitor. There was mild transient erythema over the site following prolonged use (ie,. 2 hours).

DISCUSSION

In our previous experience with transcutaneous electrodes, we reported on the traumatizing effects on the skin, the fastidious care that was necessary in skin preparation, and the inaccuracies that arose when preparation was hastened or incomplete.3 By contrast, the system reported herein was simple to apply, took no longer than 10 minutes to obtain stable readings, and caused no skin trauma either from abrasion or heat in the period tested. As to the performance of the monitoring system, we

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Manuscript received August 09; revision accepted October 11.

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