The perfusion index (PI) is an indirect non-invasive measurement of peripheral perfusion, calculated as a ratio of the pulsatile signals to the non-pulsatile signals obtained from pulse oximetry, derived from the amount of infrared (940nm) light absorbed. A decreased PI suggests vasoconstriction while a high value of PI would imply peripheral vasodilation. The sympathetic system being inherently related to pain, when it is activated by pain, an increased vasomotor tone and contraction of peripheral blood vessels would decrease PI. Similarly, when pain is relieved with adequate analgesia, PI would increase. Studies in adults have shown it as a promising tool in pain assessment. The objectivity of this tool as a potential pain assessor may be harnessed in the paediatric population as well. Literature search revealed that it has been used in paediatric postoperative pain assessment only in adenotonsillectomy patients.

The current study is being designed to assess the reliability of this objective marker in postoperative pain assessment in paediatric patients undergoing open abdominal, thoracic and orthopaedic procedures. The primary objective being to find a correlation between the severities of postoperative pain assessed by FLACC score and the corresponding postoperative perfusion index.