Gastric air tonometry during laparoscopic cholecystectomy: a comparison of two PaCO2 levels

PURPOSE

Pneumoperitoneum can cause disturbances in acid-base balance and splanchnic perfusion. We studied the effect of ventilation on acid-base balance and gastric mucosal tonometric values in patients undergoing laparoscopic cholecystectomy.

METHODS

Twenty-four patients (ASA I-II) were randomly allocated into two groups. In the fixed ventilation group, ventilation was constant allowing free increase in PCO2, while in the constant CO2 group end-tidal PCO2 was fixed with ventilatory adjustment. Intraabdominal pressure was limited to 12 mmHg. Arterial acid-base balance, automated air tonometric variables and gastric mucosal to arterial PCO2 gap were determined frequently from anesthesia induction until three hours postoperatively.

RESULTS

During pneumoperitoneum, in the fixed ventilation group arterial PCO2 changed from 5.0 +/- 0.2 to 6.6 +/- 0.4 kPa and pH from 7.43 +/- 0.03 to 7.33 +/- 0.04, tonometric PCO2 from 5.1 +/- 0.5 to 6.9 +/- 0.4 and pH from 7.44 +/- 0.04 to 7.33 +/- 0.04. In the constant CO2 group these variables remained at control levels (P < 0.01 between groups). The PCO2 gap remained unchanged without any differences between the groups. In the recovery room all measured variables were within normal range in both groups.

CONCLUSION

Despite inter-group differences in arterial and tonometric PCO2 and pH values during CO2 pneumoperitoneum, the patients did not develop splanchnic hypoperfusion detectable by air tonometric method, as indicated by normal PCO2 gap in both groups throughout the study.

Validation of air tonometric measurement of gastric regional concentrations of CO2 in critically ill septic patients

OBJECTIVE

To evaluate the accuracy of continuous air tonometry (Tonocap, Tonometric Division, Instrumentarium, Helsinki, Finland).

DESIGN

The accuracy of air tonometry was tested by comparing it with conventional saline tonometry in mechanically ventilated, critically ill septic patients and in vitro determining the partial pressure of carbon dioxide (PCO2) of humidified gases with known concentrations of CO2.

SETTING

A mixed intensive care unit in a university hospital.

PATIENTS

16 mechanically ventilated patients with sepsis.

MEASUREMENTS AND RESULTS

Two gastric tonometer catheters (TRIP NGS catheter, Tonometric Division, Instrumentarium, Helsinki, Finland) were introduced into the patients' stomachs. The control catheter was used as a conventional saline tonometer and the other catheter was used with the Tonocap monitoring device. A total of 153 paired measurements was made and analysed according to Bland and Altman. The mean difference between air PCO2 and saline PCO2 values (bias), the standard deviation of the differences (precision), and the Pearson correlation coefficient between air PCO2 and saline PCO2 were calculated. The data on patients were pooled and calculated for different cycle times. The mean bias (kPa) was-0.02 with a 10-min cycle time, 0.31 with 15 min, 0.56 with 30 min and 0.21 with 60-min. The precisions were 0.39, 0.54, 0.44 and 0.76, respectively. Pearson correlation coefficients were 0.93, 0.97, 0.95 and 0.82, respectively (p < 0.0001). In vitro tonometry with the Tonocap was performed in a gas chamber fully saturated with known CO2 concentrations. The clinically important 10-min cycle time was tested with 5 Tonocap monitors. Except for the first 10-min cycle time, PCO2 values determined by the Tonocap monitoring systems were comparable to known CO2 concentrations.

CONCLUSIONS

The accuracy of Tonocap continuous air tonometry is close to that of conventional saline tonometry. Moreover, the clinically important 10-min cycle time with air tonometry correlated very well with saline tonometry and the time response with air tonometry was short.