Comparison of gastric air tonometry with standard saline tonometry
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Published on: April 7, 2026
G Tzelepis1, V Kadas, A Michalopoulos
1Surgical Intensive Care Unit, Onassis Cardiac Surgical Center, Athens, Greece.
Objective:
To compare partial pressure of carbon dioxide (PCO2) measurements obtained by sampling gastric intraluminal air with those obtained by standard saline tonometry.
Design:
Prospective, unblinded study.
Setting:
Intensive care unit in a tertiary cardiac surgical center.
Patients:
20 patients undergoing cardiac surgery.
Interventions:
Gastric tonometric catheters were inserted, gastric fluid was aspirated, and 100 cc of air was injected into the stomach.
Measurements:
After an equilibration period of 30 min, samples of gastric air and saline were anaerobically aspirated and analyzed on a standard blood gas machine. The reproducibility of PCO2 measurements in a given patient was assessed by analyzing consecutive samples of gastric air and calculating the coefficient of variation (CV).
Results:
PCO2 values measured in samples of gastric air (PCO2 air) were highly correlated with those derived by saline tonometry (PCO2ss)(r2 = 0.95, p = 0.0001); PCO2 air was significantly greater than PCO2ss (50 +/- 17 vs 48 +/- 17 mmHg, p = 0.0001). Intramucosal pH (pHi) calculated from PCO2 air was significantly lower than that calculated from PCO2ss (7.26 +/- 0.23 vs 7.28 +/- 0.24, p = 0.0001). Analysis of intermethod differences showed significant bias for both PCO2 (2.4 +/- 7.6 mmHg, mean +/- 2SD, bias +/- precision) and pHi ( -0.023 +/- 0.074, mean +/- 2SD, bias +/- precision). The within-subject variability of replicate PCO2 measurements in gastric air was low (CV = 2.6 +/- 0.8).
Conclusion:
We conclude that intraluminal PCO2 can be accurately determined in postoperative cardiac surgery patients by instilling air into the stomach and analyzing samples of gastric air on a standard blood gas machine, In comparison with saline tonometry, air tonometry consistently yields lower pHi values.
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