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Enteral feed delays response times of a tissue PCO2 sensor


Real time assessment of gut luminal PCO2 is possible with rapidly responsive tissue CO2 sensors [1]. The impact of the presence of feeds in the gut on the rapidity of response of the sensor to a change in mucosal CO2 tension has not been evaluated.


The speed of onset of response and the 90% response time of a commonly used tissue gas sensor the Paratrend 7 (Diametrics Medical, UK) to a change in ambient CO2 tension were compared in normal saline (control) and an enteral feed solution (Nutrison, Nutricia, Zoetermeer, Holland). Probe onset and 90% response times were determined for a step up and step down change in CO2 tensions in saline and feed solutions by bubbling the following three pairs of gases A) 2% CO2 and 10% CO2 B) 10% CO2 and 5% CO2 and C) 5% CO2 and 2% CO2 through these solutions maintained at 37°C in a bubble tonometer. After calibration, the sensor was equilibrated in saline bubbled with the first gas of each pair. After equilibration the second gas of each pair was bubbled through the solution. This was repeated for a total of six equilibrations between each pair of gases. The experiment was then repeated with the feed solution.


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The presence of enteric feed significantly slows down the onset time and response time of the sensor to a change in ambient CO2 tension. Altered viscosity and CO2 binding by the feed are possible mechanisms for the altered response of the sensor. The reduction in response time may impact on the ability of tissue CO2 sensors to provide accurate real time data in clinical practice.

Table The presence of enteric feed


  1. Morgan TJ, Venkatesh B, Endre ZH: . Crit Care Med 1997, 25: 1575-1578. 10.1097/00003246-199709000-00027

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Bawa, G., Venkatesh, B. & Morgan, T. Enteral feed delays response times of a tissue PCO2 sensor. Crit Care 3 (Suppl 1), P174 (2000).

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