Automated gas tonometric measurement of gastric tube carbon dioxide gap following oesophageal resection predicts post-operative complications

Background

Gastric mucosal perfusion can be assessed tonometrically by measuring the gastric intra-mucosal pH (pHi) and its ability to predict outcome in the critically ill and following major surgery has been demonstrated by several previous studies. It has been suggested that the CO₂ gap (tonometer pCO₂) may provide a more sensitive measurement of mucosal hypoxia than pHi. Post-operative anastomotic leak and stricture following oesophageal resection and restoration of gastrointestinal continuity with a pro-peristaltic gastric tube has a multi-factorial aetiology. However, gastroplasty involves division of short gastric, left gastric and left gastroepiploic vessels and the consequent hypoperfusion and tissue hypoxia at the gastric end of the oesophago-gastric anastomosis is thought to be the most important causative factor. This study employed the new technique of automated gas tonometry to measure both gastric CO₂ gap and pHi following oesophagectomy to test the predictive ability of the technique for anastomotic complications.

Method

Gastric tonometers (Tonometric Division, Instrumentarium Division Helsinki, Finland) were placed in the gastric tube of 30 consecutive patients undergoing oesophageal resection and pro-peristaltic tubular gastroplasty based upon the right gastroepiploic and right gastric arteries. These were connected to a 'Tonocap' analyzer (Datex-Engstrom Division, Instrumentarium Corporation, Helsinki, Finland) which automatically samples gas from the tonometer balloon and measures the CO₂ concentration within it. In conjunction with simultaneously taken arterial blood samples the gastric CO₂ gap and pHi were calculated at 12 hourly intervals up to 48 h post-operatively. Those patients who survived were followed for 3 months and all post-operative complications recorded. Statistical comparison was made using the Mann-Whitney test for non-parametric data.

Results

Eleven patients suffered an anastomotic leak or benign stricture post-operatively, whilst five others suffered a life threatening complication not related to the anastomosis, of whom two survived. Because of balloon failure or re-operation within 48 h of initial surgery data was not available for one patient from each of the complication and no complication groups. Mean (SD) CO₂ gap and pHi over the first 48 post-operative hours were 1.7 kPa (0.8) and 7.26 (0.06) in the no complication group and 3.5 kPa (1.4) and 7.18 (0.09) in the complication group, respectively. The difference in CO₂ gap between the two groups was more significant than in pHi (P < 0.005 and P < 0.05). A mean CO₂ gap of 2.5 kPa or above had a sensitivity of 82% and a specificity of 70% for predicting anastomotic complications. The CO₂ gap was a better predictor of outcome than the pHi (<7.22 for predicting complications), with areas under their respective ROC curves of 0.847 and 0.684.

Conclusion

Gastric tube CO₂ gap and pHi are easily measured post-operatively using recirculating gas tonometry. Mean CO₂ gap was higher and pHi lower over the first 48 h following surgery in those patients in whom an anastomotic complication subsequently developed than in those in whom it did not. The CO₂ gap proved to be a better predictor of complications than the pHi. These findings confirm the suggestion that the CO₂ gap may be a more useful clinical tool than the pHi and that measures to improve gastric cube CO₂ gap post-operatively might reduce the incidence of anastomotic failure.