Continuous assessment of gastric intramucosal Pco(2) and pH in hemorrhagic shock using capnometric recirculating gas tonometry

Objectives: To test a novel device for continuous monitoring of gut intramucosal Pco(2) and pH and to compare its use with conventional intermittent saline balloon tonometry in a model of hemorrhagic shock. Design: A prospective animal study. Settings: A university research laboratory. Subjects: Eight anesthetized, mechanically ventilated mongrel dogs. Interventions: Two balloon tip tonometry catheters, one conventional and one modified for continuous recirculating gas tonometry, were inserted into each animal's stomach by the oral route. Gastric intramucosal Pco(2) was recorded continuously by capnometric recirculating gas tonometry throughout the experiment. After a baseline period of 90 mins, vital signs, arterial and mixed venous blood gases, and intramucosal Pco(2) values were obtained by recirculating gas tonometry and by the conventional method. Using a modified Wiggers' model, the animals were then subjected to hemorrhage of up to 45 mL/kg, or the volume required to effect a decrease in mean arterial pressure to <30 mm Hg. After 30 mins, the shed blood was reinfused and the experiment continued for an additional 30 mins. Vital signs, arterial and mixed venous blood samples, saline tonometry samples, and recirculating gas tonometry readings were obtained immediately before and 30 mins after reinfusion of blood. Measurements and Main Results: Mean +/- SD baseline intramucosal Pco(2) was 47.6 +/- 9.5 torr (6.3 +/- 1.3 kPa) by capnometric recirculating gas tonometry and 45.8 +/- 3.4 torr (6.1 +/- 0.5 kPa) by conventional saline tonometry (p = NS). By 5 mins after inducing hemorrhage, intramucosal Pco(2) by recirculating gas tonometry had increased significantly (49.3 +/- 9.7 torr [6.6 +/- 1.3 kPa]; p<.05), and by 30 mine, it had increased to 59.7 +/- 11.3 torr (8.0 +/- 1.5 kPa; p<.001 compared with baseline). After 30 mins of hemorrhage, the conventional method showed an increase in intramucosal Pco(2) to 63.0 +/- 20.9 torr (8.4 kPa +/- 2.8 kPa; p = NS vs. baseline by conventional method; p = NS vs. corresponding recirculating gas tonometry values). Gastric intramucosal pH, as determined by recirculating gas tonometry, decreased significantly at 5 mins after starting hemorrhage (7.13 +/- 0.10 to 7.10 +/- 0.10, p<.02). After 30 mins of hemorrhage, intramucosal pH decreased to 6.88 +/- 0.14 (from 7.10 +/- 0.10) by the conventional saline tonometry technique (p<.01) and to 6.89 +/- 0.10 by recirculating gas tonometry (p<.001 vs. baseline). Intramucosal Pco(2) by both techniques remained significantly increased above baseline values 30 mins after reinfusion of the shed blood. Conclusions: Capnometric recirculating gas tonometry allows continuous and automated assessment of gastrointestinal tract perfusion by providing on-line measurements of intramucosal Pco(2), which can also be used to derive intramucosal pH. The technique is able to detect changes in intramucosal Pco(2) in response to an induced insult over intervals as short as 5 mins.