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British Journal of Anaesthesia, 2000, Vol. 84, No. 5 687-688
© 2000 The Board of Management and Trustees of the British Journal of Anaesthesia

Abstract

In vitro validation of the Tonocap® and a modified Paratrend 7® sensor

R. Hurley1, M. Grocott1 and M. G. Mythen1

1 Centre for Anaesthesia, The Middlesex Hospital, Mortimer Street, London W1N 8AA, UK

Abstract

Introduction: The assessment of splanchnic perfusion by measuring gastric luminal P2 is a clinically useful technique. The Tonocap® (Datex-Ohmeda) has been validated for such use but only provides a reading every 10 min. The Paratrend 7® Sensor (Diametrics Medical Ltd) is a device used for continuous blood gas monitoring capable of responding to changes in P2 within 15 s. Recently, sublingual measurement of P2 has been described as a new method of assessing splanchnic perfusion.1 We modified the Paratrend 7® sensor by encasing it in a plastic sleeve in order to protect it as would be necessary for sublingual use. It was then compared with the Tonocap® by placing them both in a water bath.

Methods: A vigorously stirred water bath of saline at a constant temperature of 37°C was bubbled with standard calibration gas mixtures of 5% and 10% CO2 with predicted CO2 tensions being calculated from atmospheric pressure and corrected for water saturation of the bath. A Trip® catheter (Tonometrics) connected to a Tonocap® was placed in the water bath alongside two Paratrend 7® sensors, one covered by a plastic sheath, the other unsheathed. The sheath consisted of the plastic tubing from a Butterfly®-19 (Venisystems-) which had a 2 cm eye cut at the end to allow more contact with the sensor but provided protection. The Tonocap® was left to equilibrate in the water bath for 30 min. A total of 52 paired readings were taken at 10-min intervals.

Results: Table 35 shows the bias and precision of each measurement technique as a percentage of predicted values.

Conclusions: The results for the Tonocap® and Paratrend 7® (unsheathed) are similar to previously reported studies.2 The sheathed Paratrend 7® was also shown to give a very accurate reading of P2 with a very small negative bias and excellent precision.


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