Effects of epidural anesthesia on intrathoracic blood volume and extravascular lung water during on-pump cardiac surgery

Background: The most important side effect of epidural anesthesia is hypotension with functional hypovolemia. Aggressive infusion therapy can reduce the hypotension effect. However, in conjunction with cardiopulmonary bypass, it can increase acute lung injury. We hypothesized that epidural anesthesia, by reducing cardiac sympathetic tonus, with subsequent better pulmonary flow, does not increase lung interstitial fluids.

Methods: Sixty patients undergoing coronary artery bypass graft (CABG) surgery with cardiopulmonary bypass (CPB) were randomized to combined general anesthesia with epidural anesthesia / analgesia, (EA) group, and to general anesthesia with i/v opiate analgesia, (GA) group. Patients in the EA group received a high thoracic epidural, preoperatively. Intraoperatively, 0.25% bupivacaine 8 mL/h was infused and general anesthesia with sevoflurane was followed by bupivacaine infusion for 48 hours postoperatively. General anesthesia in the GA group was with sevoflurane and fentanyl 10 - 12 µg/kg and analgesia with pethidinum 0.1 - 0.4 mg/kg i.v. postoperatively. Global end-diastolic volume index (GEDI), intrathoracic blood volume index (ITBI) and extravascular lung water index (ELWI) were measured before anesthesia, before CPB and 15, 60, 180, 600 min. and 24 hr after CPB. Duration of mechanical lung ventilation was registered in both groups.

Results: ITBI and GEDI were significantly higher in the EA group at all time points of measurement (ITBI 945.6±146.4 ml/m² and 870.6±146.5 ml/m ² vs. 1118±153.2 ml/m² and 1020±174.9 ml/m ²; GEDI 720±96.19 ml/m² and 775.0±159.5 ml/m ² vs. 805.4±97.59 ml/m² and 888±117.3 ml/m ²). GEDI was significantly lower in the GA group compared with baseline (801.9±132.4 ml/m² vs. 695±169.2 mL/m²). ELWI was significantly higher in the GA group (7.233±1.35 ml/kg and 7.333±1.32 ml/kg vs. 8.533±1.45 ml/kg and 8.633±1.71 ml/kg), but without significant changes in the EA group. Duration of mechanical lung ventilation was shorter in the EA group (663.7±98.39 min. vs. 362.2±33.72 min.).

Conclusions: Epidural anesthesia / analgesia does not increase interstitial lung fluids by increasing intrathoracic blood volume or the amount of infusion fluids in patients undergoing cardiac surgery under cardiopulmonary bypass. There is, also, a decreased duration of mechanical lung ventilation.