Dyspnea may occur due to proprioceptive blockade of afferent fibers from abdominal and chest wall muscles. Need to assess adequacy of ventilation then reassure the patient.
Apnea may occur due to reduced medullary blood flow accompanying severe hypotension or from direct C3-C5 blockade, inhibiting phrenic nerve output. Immediate ventilator support required.
Similar respiratory effects could be seen by spinal and epidural anesthesia. However with use of lower doses and weaker local anesthetics in epidural anesthesia, you could expect differential blockade with less motor blockade, thus leading to less reduction in expiratory reserve volume.
Effects on Pulmonary Function Test (PFT)
- Slight decrease in VC and FEV1 without clinical significance.
- PFT is insensitive test to measure expiratory volumes.
- Marked decrease in expiratory effort and cough strength due to thoracoabdominal muscle paralysis. (Up to 50% reduction in intrathoracic pr. as well as intraabdominal pr. has been reported)