The perfusion index (PI) is a numerical value for the ratio between pulsatile and non-pulsatile blood flow measured by a special pulse oximeter. PI represents the baseline sympathetic tone which is assumed one of the factors contributing for hypotension. Patients with low PI were reported by Mahendale and Rajasekhar to show greater hypotension after induction of anesthesia. This was explained by the high sympathetic tone in these patients which is suddenly masked by propofol administration leading to profound hypotension. Moreover, The PI has been described as a reliable tool for vascular tone assessment and monitoring.~Dicrotic Plethysmography (Dicpleth): is easily derived from the photoplethysmographic signal. It represents the relative height of the dicrotic wave compared with the maximum peak of the waveform, has been described as the amount of reflected wave, dependent on the vascular tone. M.Coutrot et al quantified Dicpleth variations to detect arterial hypotension and mentioned that Dicpleth and PI are both related to vascular tone and are easily derived from the photoplethysmographic signal. Moreover, Chowienczyk PJ et. al. demonstrated that the reduction in Dicpleth is related to the reduction of vascular tone caused by vasodilator drugs, such as salbutamol or glyceryl trinitrate
The perfusion index (PI) is a numerical value for the ratio between pulsatile and non-pulsatile blood flow measured by a special pulse oximeter. PI represents the baseline sympathetic tone which is assumed one of the factors contributing for hypotension. Patients with low PI were reported by Mahendale and Rajasekhar to show greater hypotension after induction of anesthesia. This was explained by the high sympathetic tone in these patients which is suddenly masked by propofol administration leading to profound hypotension.~This study aims to evaluate the ability of preoperative plethysmographic variability index, perfusion index and the Dicrotic Plethysmography to predict post-induction hypotension.