“…Although the sensation of dispnea may 5, 21 or not 26,27 be a consequence of mild hypercapnia, respiratory distress referred by few patients may be a consequence of the excitation of "J" receptors of alveolar walls, as result of blood accumulation or vasodilation by thoracic sympathetic block, especially in dependent regions 28 , or by partial blockade of respiratory muscles motor fibers with decreased respiratory dynamics, phenomenon especially observed in anxious patients. Most of the times, hemoglobin desaturation depends on respiratory depression promoted by preanesthetic opioids or associated to epidural or spinal anesthetic solutions, changes in chest compliance 29 , tachypnea with low tidal air volume resulting in low effective alveolar ventilation and inhaled O 2 concentration. Since patients in our study have received oxygen via nasal catheter during the procedures, values obtained were stable or slightly higher that baseline values ( Figure 4).…”