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Does enteral feeding potentially alter the PCO2 gap and pHi?


Measurement of pHi or the mucosal-arterial PCO2 gap is advocated to detect splanchnic ischaemia and covert shock. Nasogastric feeding may significantly affect these measurements. We used a previously described animal model [1] to evaluate the effect of enteral feeds on the luminal PCO2 response to intermittent splanchnic ischaemia.


Adult male Wistar rats (285-425 g) were anaesthetised with sodium pentobarbitone 60 mg/kg i.p. and ventilated with 100% oxygen and isoflurane via tracheostomy to a PaCO2 of 30-40 torr. Distal aortic pressure was monitored continuously. A sensor (Paratrend 7, Diametrix Medical Inc., Bucks, UK) was inserted into the ileal lumen to record PCO2 measurements every 2 s, Four rats received no feeds (controls) whilst in another four rats an ileal cannula was inserted and feed (Nutrison, Nutricia, Zoetermeer, Holland) infused at 3 ml/h. In each rat, five two-minute episodes of aortic hypotension were induced to a mean pressure of 30 mmHg by intermittent elevation of a silk sling placed around the proximal aorta.


See Table. Feeds significantly elevated the mean baseline luminal PCO2 and delayed and blunted the PCO2 increases (∆PCO2) in response to transient ischaemia.


Assuming no differences in PaCO2 in both groups, the data suggest that enteral feeding increases the baseline mucosal-arterial PCO2 gap and reduces baseline pHi. It may also impair the detection of splanchnic ischaemia by delaying and blunting the responses of these indices to reduced mucosal perfusion.

Table Table


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

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Bawa, G., Morgan, T. & Venkatesh, B. Does enteral feeding potentially alter the PCO2 gap and pHi?. Crit Care 3 (Suppl 1), P173 (2000).

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