Continuous positive pressure ventilation during epidural blockade--effects on cardiac output distribution

Ropivacaine may have advantages compared to bupivacaine in porcine endotoxemic shock

Patients that undergo major abdominal surgery often receive epidural postoperative analgesia. Septic complications are frequently seen in this cohort. In a porcine model of endotoxemic shock, resembling human gram-negative septic shock, we evaluated the effects of two widely used local anaesthetics, bupivacaine and ropivacaine given intravenously. In the endotoxin-ropivacaine group mixed venous saturation and platelet count were higher as compared to endotoxemic controls. Mean arterial blood pressure and platelet count were higher in ropivacaine-endotoxin pigs than in bupivacaine-endotoxin ones. Bupivacaine augmented endotoxin-mediated decrease in left ventricular stroke work index. Ropivacaine displays pathophysiological advantages compared to bupivacaine in septic shock, which may be explained by improved tissue perfusion by ropivacaine.

Effects of thoracic epidural anaesthesia on microvascular gastric mucosal oxygenation in physiological and compromised circulatory conditions in dogs

BACKGROUND

The effects of thoracic epidural anaesthesia (TEA) on gastric mucosal microvascular haemoglobin oxygenation (microHbO(2)) are unclear. At the splanchnic level, reduction of sympathetic tone may promote vasodilation and increase microHbO(2). However, these splanchnic effects are counteracted by systemic effects of TEA (e.g., decreased cardiac output (CO) and mean arterial pressure (MAP)), thus making the net effect on microHbO(2) difficult to predict. In this respect, effects of TEA on microHbO(2) may differ between physiological and compromised circulatory conditions, and additionally may depend on adequate fluid resuscitation. Furthermore, TEA may alter the relationship between regional microHbO(2) and systemic oxygen-transport (DO(2)).

METHODS

Chronically instrumented dogs (flow probes for CO measurement) were anaesthetized, their lungs ventilated and randomly received TEA with lidocaine (n=6) or epidural saline (controls, n=6). Animals were studied under physiological and compromised circulatory conditions (PEEP 10 cm H(2)O), both with and without fluid resuscitation. We measured gastric mucosal microHbO(2) by reflectance spectrophotometry, systemic DO(2), and systemic haemodynamics (CO, MAP).

RESULTS

Under physiological conditions, TEA preserved microHbO(2) (47 (3)% and 49 (5)%, mean (sem)) despite significantly decreasing DO(2) (11.3 (0.8) to 10.0 (0.7) ml kg(-1) min(-1)) and MAP (66 (2) to 59 (3) mm Hg). However, during compromised circulatory conditions, TEA aggravated the reduction in microHbO(2) (to 32 (1)%), DO(2) (to 6.7 (0.8) ml kg(-1) min(-1)) and MAP (to 52 (4) mm Hg), compared with controls. During TEA, fluid resuscitation completely restored these variables. TEA preserved the correlation between microHbO(2) and DO(2), compared with controls.

CONCLUSIONS

TEA maintains microHbO(2) under physiological conditions, but aggravates the reduction of microHbO(2) induced by cardiocirculatory depression, thereby preserving the relationship between gastric mucosal and systemic oxygenation.