Evaluation of role of perfusion index as a predictor of post subarachnoid block hypotension in geriatric patients A prospective observational study

Hypotension is common in elderly patients for surgery under spinal anaesthesia with an incidence of over 50%. Old age is one of main risk factors for  development of hypotension during spinal anaesthesia. The main cause of hypotension is sympathetic block with associated decrease in systemic vascular resistance. The response is exaggerated in elderly due to negative influence of a relatively higher resting sympathetic tone and decreased baroreceptor activity leading to a higher incidence of hypotension. Geriatric patients may have difficulty tolerating the negative effects of hypotension and this may lead to an increased incidence of complications. Therefore, careful consideration and monitoring are essential when using spinal anaesthesia in elderly patients, especially those with pre-existing comorbidities

Non-invasive blood pressure (NIBP) measurement is the established approach for monitoring intraoperative hemodynamic. The perfusion index is a ratio calculated with pulsatile light absorption over continuous light absorption and gives information about vascular tone and volume status with data obtained from pulse oximeter which is part of a standard anaesthesia monitor. The perfusion index (PI) is defined as the ratio of pulsatile blood flow to non-pulsatile blood flow in the peripheral vascular tissue. It is assessed using a pulse oximeter that measures amount of Infrared light absorbed. The PI serves to evaluate perfusion dynamics and is being considered as a non-invasive means to predict likelihood of hypotension development.This technology was used in the fluid responsiveness in trauma and septic patients, estimating the success of regional anaesthesia, and predicting hypotension in parturient. The standard monitoring site for pulse oximetry is the fingertip, where the normal PI ranges from 0.02% to 20%.

Masimo Signal Extraction Technology (SET) pulse oximetry provides continuous and simultaneous absolute values and trends for PI, arterial oxygen saturation (SaO2), and pulse rate. These values are generated using validated signal extraction technology, which also offers associated alarms to alert medical personnel to any concerning changes in these parameters.

We have planned this study as there are scarce data available regarding efficacy of pulse oximetry-derived perfusion index as predictor of post-spinal hypotension in geriatric patients