title: Comparison of gastric air tonometry with standard saline tonometry.
abstract: OBJECTIVE
  To compare partial pressure of carbon dioxide (PCO2) measurements obtained by sampling gastric intraluminal air with those obtained by standard saline tonometry.
  
  
  METHODS
  Prospective, unblinded study.
  
  
  METHODS
  Intensive care unit in a tertiary cardiac surgical center.
  
  
  METHODS
  20 patients undergoing cardiac surgery.
  
  
  METHODS
  Gastric tonometric catheters were inserted, gastric fluid was aspirated, and 100 cc of air was injected into the stomach.
  
  
  METHODS
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Surgical Intensive Care Unit, Onassis Cardiac Surgical Center, Athens, Greece.
authors.forename: G
authors.initials: G
authors.lastname: Tzelepis
authors.forename: V
authors.initials: V
authors.lastname: Kadas
authors.forename: A
authors.initials: A
authors.lastname: Michalopoulos
authors.forename: S
authors.initials: S
authors.lastname: Geroulanos
mesh_terms: D000368:Aged; D001784:Blood Gas Analysis / Q000379:methods; D002245:Carbon Dioxide / Q000378:metabolism*; D006348:Cardiac Surgical Procedures; D003422:Critical Care; D005753:Gastric Mucosa / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008365:Manometry / Q000379:methods*; D008875:Middle Aged; D010313:Partial Pressure; D011182:Postoperative Care / Q000379:methods; D011446:Prospective Studies; D015203:Reproducibility of Results
chemical_list: D002245:Carbon Dioxide