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Comparison of patient spirometry and ventilator spirometry
This study compared different spirometry measurement sites with a focus on ventilator spirometry, where gas samples are processed in the ventilator, and patient spirometry, in which gas samples are processed at the end of the endotracheal tube, just outside the patient.
The author studied the differences in pressure parameters obtained using both kinds of spirometry and patient spirometry. An artificial lung was connected to a ventilator and a GE CARESCAPETM B650 patient monitor equipped with a CARESCAPE E-sCAiOV respiratory module. D-lite and Pedi-lite sensors were used.
A neonatal, pediatric, and an adult patient were simulated using both pressure- and volume-controlled modes. Values obtained from the ventilators and from the respiratory module were compared against reference values obtained from the artificial lung. The results support the view that patient spirometry provides, in general, more accurate values than ventilator spirometry.
From a theoretical point of view, patient spirometry is less prone to measurement errors caused by physical effects in the patient circuit. The closer to the lungs the measurement is made, the more accurately the obtained parameters reflect the situation in the lungs. There is also published data suggesting that patient spirometry is more accurate.
In the tests, patient spirometry proved more accurate than ventilator spirometry in PEEP and peak pressure measurements. However, the test data was recorded in laboratory conditions and covered a wide range of simulated patients, making it hard to draw decisive conclusions.
By: Antti Tanner, M.Sc. Test results are based on the masters thesis, “Comparison between patient spirometry and ventilator spirometry” by Saana Jenu, 2011.
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