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 in tramucosal Pco(2) and pH and to compare its use with conventional inte rmittent saline balloon tonometry in a model of hemorrhagic shock. Des ign: A prospective animal study. Settings: A university research labor atory. Subjects: Eight anesthetized, mechanically ventilated mongrel d ogs. Interventions: Two balloon tip tonometry catheters, one conventio nal and one modified for continuous recirculating gas tonometry, were inserted into each animal's stomach by the oral route. Gastric intramu cosal Pco(2) was recorded continuously by capnometric recirculating ga s tonometry throughout the experiment. After a baseline period of 90 m ins, vital signs, arterial and mixed venous blood gases, and intramuco sal 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 req uired to effect a decrease in mean arterial pressure to <30 mm Hg. Aft er 30 mins, the shed blood was reinfused and the experiment continued for an additional 30 mins. Vital signs, arterial and mixed venous bloo d samples, saline tonometry samples, and recirculating gas tonometry r eadings were obtained immediately before and 30 mins after reinfusion of blood. Measurements and Main Results: Mean +/- SD baseline intramuc osal Pco(2) was 47.6 +/- 9.5 torr (6.3 +/- 1.3 kPa) by capnometric rec irculating gas tonometry and 45.8 +/- 3.4 torr (6.1 +/- 0.5 kPa) by co nventional saline tonometry (p = NS). By 5 mins after inducing hemorrh age, 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 tor r (8.4 kPa +/- 2.8 kPa; p = NS vs. baseline by conventional method; p = NS vs. corresponding recirculating gas tonometry values). Gastric in tramucosal 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 dec reased to 6.88 +/- 0.14 (from 7.10 +/- 0.10) by the conventional salin e tonometry technique (p<.01) and to 6.89 +/- 0.10 by recirculating ga s tonometry (p<.001 vs. baseline). Intramucosal Pco(2) by both techniq ues remained significantly increased above baseline values 30 mins aft er reinfusion of the shed blood. Conclusions: Capnometric recirculatin g gas tonometry allows continuous and automated assessment of gastroin testinal tract perfusion by providing on-line measurements of intramuc osal Pco(2), which can also be used to derive intramucosal pH. The tec hnique is able to detect changes in intramucosal Pco(2) in response to an induced insult over intervals as short as 5 mins.