Measurements In addition to arterial blood sampling, complete sets of hemodynamic measurements will be performed as shown in figure 1: (a) preoperatively, before and 30 min after initiation of TEA, (b) 2 and 8 hours after surgery (postoperative day 0, [POD0]), before and 30 min after administration of salbutamol or ipratropium (6 hours apart in random order), (c) on the morning of the first postoperative day (POD1) on two consecutive sessions (6 hours apart in random order), before and 30 min after administration of salbutamol or ipratropium bromide.