Nitrous oxide does not affect automated air tonometry in children.

PURPOSE: To evaluate the effects of nitrous oxide on automated air tonometry in the clinical setting.

MATERIAL AND

METHODS

With approval of the Hospital Ethical Committee and after obtaining informed parental consent, an 8-F tonometry catheter was inserted orogastrically in ten children aged one to three years scheduled for elective surgery with combined regional and general anesthesia. A standardized general anesthesia technique with tracheal intubation was used in all patients and consisted of sevoflurane in oxygen/nitrous oxide (30%/70%; n = 5 patients) or in oxygen/air (FIO(2) 0.3; n = 5 patients). After obtaining steady state gastric CO(2) values (PrCO(2)), fresh gas mixtures were rapidly changed from oxygen/nitrous oxide to oxygen/air (A) or vice versa (B). In addition, balloon pressures were recorded using a pressure transducer. Measurements were performed at intervals of ten minutes with recording of balloon pressures, end-tidal CO(2) (PETCO(2)) and PrCO(2) values. Pr-ETCO(2)-gap were calculated to eliminate influences of changes in PaCO(2).

RESULTS

Changing the fresh gas mixture from N(2)O/O(2) to O(2)/air resulted in a decrease of balloon pressure of -10.4% (113.4 +/- 14.7 mmHg to 101.6 +/- 25.0 mmHg). Changing the fresh gas mixture from O(2)/air to N(2)O/O(2) resulted in an increase of balloon pressures of 6.4% (107.6 +/- 19.3 mmHg to 114.0 +/- 20.3 mmHg). During both fresh gas exchange experiments no significant changes (> 0.2 kPa) in calculated Pr-ETCO(2)-gaps were observed.

CONCLUSIONS

Based on our in vivo data, nitrous oxide during general anesthesia can be used with automated air tonometry and does not affect air tonometric PrCO(2) reading in clinical practice.