Automated Detection of Gastric Luminal Partial Pressure of Carbon Dioxide during Cardiovascular Surgery Using the Tonocap

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Abstract
Background: A new automated system of air tonometry (Tonocap; Datex Ohmeda, Helsinki, Finland) allows for frequent (every 15 min) measurement of gastric luminal partial pressure of carbon dioxide. Its use has not been described in cardiac surgical patients. Methods: One hundred patients undergoing coronary artery bypass graft or cardiac valve surgery were enrolled in a prospective cohort study. After anesthetic induction and insertion of a TRIP NGS Catheter (Datex Ohmeda), measurements of gastric luminal partial pressure of carbon dioxide were obtained using the Tonocap, and gastric mucosal pH (pHi) was calculated. The main outcome measure was postoperative complication, defined as either in-hospital death or prolonged postoperative hospitalization (> 14 days). Results: Four patients (4%) died, all of multiple-system organ failure, one each on postoperative days 9, 26, 46, and 121. Postoperative complication occurred in 18 patients (18%), all of whom exhibited persistent dysfunction of at least one organ system. Perioperatively, an abnormal pHi (< 7.32) and gastric luminal minus arterial partial pressure of carbon dioxide gap (> 8 mmHg) occurred in 66% and 70% of patients, respectively. Predictors of postoperative complication included postoperative pHi (P = 0.001), gastric luminal partial pressure of carbon dioxide (P = 0.022), and gastric luminal minus arterial partial pressure of carbon dioxide gap (P = 0.013). In contrast, arterial base excess (P > 0.4) and routinely measured hemodynamic variables (e.g., heart rate, blood pressure) were either less predictive compared with Tonocap-derived variables or not predictive. Conclusions: Despite a low mortality rate, patients undergoing cardiac surgery exhibited high incidences of prolonged hospitalization and postoperative morbidity. The Tonocap was easy to use, particularly compared with saline tonometry. Several Tonocap-derived variables were predictive of postoperative complications consistent with previously published data using saline tonometry.

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