Comparison of air tonometry with gastric tonometry using saline and other equilibrating fluids: an in vivo and in vitro study.
OBJECTIVE
1) To compare saline gastric tonometry monitoring with air tonometry (Tonocap) in a group of general ICU patients. 2) An in vitro investigation of the performance of other fluids used in gastric tonometry and to assess the effects of variation of temperature and carbon dioxide concentration within the range encountered in clinical use.


METHODS
a) A prospective, observational study in ICU patients b) A comparative laboratory study.


METHODS
The general Intensive Care Unit (ICU) and the laboratory at Leeds General Infirmary.


METHODS
Nine patients in the general ICU with severe sepsis or septic shock.


RESULTS
In vivo comparison of saline and air tonometry demonstrated a difference between the two techniques. Bland & Altman analysis showed a mean bias in the measurement of gastric PCO2 of 1.88 kPa with a precision of 1.22 kPa, with saline giving the lower result. In vitro, saline, air (Tonocap), gelatin and heparinised blood were used, at temperatures of 33-42 degrees C and at carbon dioxide concentrations of 4-8 kPa. While gelatin and blood gave unpredictable results, dependent on temperature and carbon dioxide concentration, air tonometry gave highly reproducible results. A consistent bias between the results with saline and air tonometry was seen over the range of temperatures and carbon dioxide (CO2) concentrations studied. The mean bias was 0.85 kPa with a precision of 0.40 kPa, saline consistently giving lower results.


CONCLUSIONS
There are clinically significant differences in values for gastric mucosal PCO2 measured by air tonometry and saline tonometry both in vivo and in vitro.
Academic Unit of Anaesthesia, The General Infirmary at Leeds, UK.
B
B
Barry
A
A
Mallick
G
G
Hartley
A
A
Bodenham
M
M
Vucevic
D000138:Acidosis / Q000097:blood / Q000175:diagnosis*; D000328:Adult; D000368:Aged; D002245:Carbon Dioxide / Q000097:blood; D003422:Critical Care / Q000379:methods*; D005260:Female; D005745:Gastric Acidity Determination / Q000295:instrumentation; D005753:Gastric Mucosa / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D000860:Hypoxia / Q000175:diagnosis*; D008297:Male; D008365:Manometry / Q000295:instrumentation / Q000592:standards; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000295:instrumentation / Q000592:standards; D010313:Partial Pressure; D011446:Prospective Studies; D015203:Reproducibility of Results; D012965:Sodium Chloride / Q000737:chemistry; D013696:Temperature; D013997:Time Factors
D002245:Carbon Dioxide; D012965:Sodium Chloride