Monitoring initial volume therapy after coronary bypass surgery by gastric tonometry
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KeywordsPulmonary Artery Catheter Extracorporal Circulation Coronary Bypass Surgery Volume Replacement Critical Care Patient
Gastric tonometry is a very sensitive, non-invasive method to detect hypovolemia in critical care patients. Several studies document the predictive value of tonometry for patients' outcome. Especially a widened arterial to gastric-intramucosal PCO2 difference (aiDCO2) warns of complications. This study demonstrates the use of tonometry as a monitoring device for actual aspects of volume status and tissue oxygenation in patients after cardiac surgery.
After IRB approval we studied 24 patients admitted to the ICU after aorto-coronary bypass surgery. In addition to standard monitoring each patient received a nasogastric tube (TRIP, NGS catheter: Tonometrics, Helsinki, Finland), a fiberoptic pulmonary artery catheter (CCO catheter for Vigilance monitor; Baxter Healthcare Corp., Irvine, USA) and a polarographic intramyocardial oxygen catheter (Licox; Kiel, Germany). Documentation of standard parameters followed every 15 resp. 60 min. intra- and postoperative until extubation. Retrospectively patients were divided into two groups (2 × 12) by the amount of postoperative colloid volume replacement: Group 1: <750 ml colloids during the first 3 postoperative hours; Group 2: >1000 ml colloids during the first 3 postoperative hours. Statistics were done by using Mann-Whitney-U and Friedman-test.
There were no significant differences between group 1 and 2 with regard to age, ejection fraction, duration of extracorporal circulation, number of bypasses, arterial or mixed venous blood gas analyses, arterial or pulmonary arterial hemodynamics, lactate, heart rate and central venous pressure. Regional oxygenation differed significantly between the groups. Group 1 (<750 ml/3 h) showed a small aiDCO2 during the first 5 postoperative hours. Afterwards splanchnicus perfusion impaired (aiDCO2 >20 mmHg). In group 2 (>1000 ml/3 h) an initially higher aiDCO2was lowered by volume therapy. Group 2 developed a significantly lower postoperative increase in intramyocardial oxygen then group 1. More than 5 h after extracorporal circulation there was a significantly increasing need of epinephrine in group 2 and cardiac index was lower in group 2 without reaching significance.
Volume replacement after coronary bypass surgery should be monitored by gastric tonometry since hemodynamic parameters are less sensitive. High volume replacement without need (aiDCO2 <20 mmHg) can improve splanchnicus perfusion but might impair myocardial oxygenation and myocardial function.