Spinal anaesthesia is one of the commonly used anaesthetic technique in elderly patients. It tends to be safe and simple procedure and also avoid the various complications associated with general anaesthesia. Despite many recent advances, haemodynamic instabilities associated with it is a daily challenge for the anaesthesiologists. Post spinal anaesthesia hypotension occurs due to sympatholysis, leading to loss of tone of venous capacitance vessels and drop in central venous pressure . Hypotension caused by the spinal anaesthesia is proportional to the spinal anaesthesia block height .Elderly age group having a compromised cardiopulmonary system and reduced physiological reserve makes these hemodynamic instabilities more intolerable as they cannot effectively increase the cardiac output .Intra operative hypotension management by infusion of fluids and crystalloids is effective but can lead to fluid overload in this group of patients. Moreover, vasopressors used to combat hypotension can cause tachycardia, hypertension and coronary ischaemia .

The perfusion index (PI) is relatively a new parameter estimating the plusatility of blood in the extremities, calculated using infrared spectrum. It can be easily derived from a pulse oximeter noninvasively. It assesses peripheral perfusion dynamics occurring due to changes in peripheral vascular tone. PI is calculated as the ratio of pulsatile blood flow to non-pulsatile blood in peripheral tissue. The formula for its calculation is as follows 

Perfusion index   = AC÷DC × 100

Where AC is the infrared signal’s pulsating component and is the light absorbed by the pulsatile blood flow in the artery. The normal range of PI is 0.02% (very feeble strength) to 20% (very strong strength ). PI estimates the status of microcirculation which is densely innervated by sympathetic nerves.  Therefore, multiple factors altering the systemic vascular resistance (SVR) can be assessed by this indicator.  The resting SVR can influence incidence and severity of post-spinal hypotension. Value of PI can be used to assess (SVR). Therefore, assuming that vasodilatation reflecting higher baseline PI can been associated with reduction in blood pressure (BP) following spinal anaesthesia. Previous studies regarding the baseline PI and hypotension following spinal anaesthesia have shown positive correlation in parturients undergoing caesarean surgery.. Not much study has done assessing the correlation between the incidence of post spinal hypotension and PI in elderly age group. Therefore, the aim of this study is to find the correlation between baseline perfusion index and incidence of hypotension in elderly patients undergoing hernioplasty under spinal anaesthesia.