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Comparison of gastric air tonometry with standard saline tonometry

Abstract

Objectives

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 (PCO2air) were highly correlated with those derived by saline tonometry (PCO2ss)(r 2=0.95,p=0.0001); PCO2air 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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Correspondence to G. Tzelepis.

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Tzelepis, G., Kadas, V., Michalopoulos, A. et al. Comparison of gastric air tonometry with standard saline tonometry. Intensive Care Med 22, 1239–1243 (1996). https://doi.org/10.1007/BF01709342

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Key words

  • Tonometry
  • Intramucosal pH
  • Gastric air
  • Carbondioxide