Post–operative pain, apart from the psychological trauma, affects the physiology of the respiratory system, cardiovascular system as well as the neuroendocrine system. Patients undergoing upper abdominal and thoracic surgical procedures show marked ventilatory compromise after surgery resulting in increased respiratory rate, increased post operative hypoxemia and decreased tidal volume (TV), vital capacity (VC), Forced Expiratory Volume in first second (FEV1) and Forced Vital Capacity (FVC) and peak expiratory flow rate (PEFR). This has been rationalized as pain related neural reflex producing increased tone in abdominal muscles during expiration.^[1] This marked ventilatory compromise due to post–operative pain increases the incidence of post–operative pulmonary complications, which are a major cause of morbidity and mortality in the post– operative period. Despite advances in technology and availability of various drugs, techniques for post–operative analgesia, which favorably improve post operative respiratory function, continues to evolve.