Correlation between Perfusion Index and Perioperative body temperature – A Prospective observational study.

Hypothermia is defined by a low core body temperature less than 35˚C with more conservative perioperative thresholds of 36˚C. It is estimated that 50 – 90% of patients experience hypothermia during surgery. Perioperative hypothermia affects various organ systems and alter several physiological functions. These include, sympathetic nervous system activation, impaired platelet function and coagulation cascade, postoperative shivering, blunted ventilatory response to carbon dioxide, systemic and pulmonary vasoconstriction and increased arterial blood pressure, variations in serum potassium levels, impaired neutrophils and macrophages and altering the pharmacokinetic of drugs. It may lead to increased intraoperative blood loss and transfusion, surgical site infections, cardiac events, reduced clearance of drugs and prolonged action of neuromuscular blockers, increased need for mechanical ventilation and longer duration of hospital stay. These adverse effects can be minimized by prevention, treatment and increased awareness of the problems due to hypothermia. Pulse oximetry is simple, continuous, noninvasive monitor which displays peripheral oxygen saturation and heart rate using plethysmography technology. Peripheral perfusion index (PPI) is another variable measured by pulse oximetry, which is the ratio of pulsatile flow to the non-pulsatile flow of blood in the peripheral circulation. Its normal value ranges from 0.02% (weak pulse) to 20% (strong pulse). Lower values indicate vasoconstriction and higher values indicate vasodilation. It is affected by two main determinants: cardiac output and balance between sympathetic and parasympathetic nervous systems(5). Redistribution hypothermia is the main cause of potential perioperative hypothermia. It is due to vasodilation, impaired function of hypothalamus and limited body’s ability to cause vasoconstriction, mediated by general anesthesia. Changes in PPI are noted due to vasodilation and body temperature redistribution in association with general anesthesia. Hence, the aim of our study is to identify the relationship between perfusion index and core body temperature and its role in predicting perioperative hypothermia.