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Abstract #15765 Published in IGR 2-3
Comparison of the response of saline tonometry and an automated gas tonometry device to a change in CO2
Noone RB Jr; Bolden JE; Mythen MG; Vaslef SNCritical Care Medicine 2000; 28: 3728-3733
OBJECTIVE: To examine the speed of response of saline tonometry and an automated gas tonometry system by using standard tonometry catheters. DESIGN: In vitro validation study. SETTING: Experimental research laboratory. INTERVENTIONS: Tonometry catheters were placed in a test chamber designed to simulate the lumen of a hollow viscus and were exposed to a rapid change in CO2 from 0% to 5% or 10%. Measured CO2 over time was fit to a mathematical model to determine the response time constant (the time to reach 63% of the final value) for each system. MEASUREMENTS AND MAIN RESULTS: Response time to a change in CO2 was significantly faster with the automated gas system than with traditional saline tonometry. The mathematical time constant for a 5% change in CO2 in a gas environment was 2.8 minutes (95% confidence interval, 2.6-3.0 minutes) for the gas and 6.3 minutes (95% confidence interval, 5.8-7.3 minutes) for the saline technique. These times were longer for the CO2 change in a liquid environment: The time constant was 4.6 minutes (95% confidence interval, 4.5-4.7 minutes) for the gas system and 7.8 minutes (95% confidence interval, 7.15-8.6 minutes) for the saline tonometry. There was a significantly lower final equilibration value for the CO2 measurement with saline tonometry. There was essentially no difference in time constants for each system for a 5% change compared with a 10% CO2 change, except for a slightly faster time constant for the gas tonometry system with a 5% change in the gas environment (5%: 2.8 minutes versus 10%: 3.3 minutes). CONCLUSIONS: The automated gas tonometry system has a significantly faster response to a change in CO2 than conventional saline tonometry.
Dr. R.B. Noone Jr., Department of Surgery, Duke University Medical Center, Durham, NC 27710, USA
Classification:
6.1 Intraocular pressure measurement; factors affecting IOP (Part of: 6 Clinical examination methods)
