An Observational Study of the Association Between the Perioperatively Measured Peripheral Perfusion Index, Postoperative Complications and Mortality in Acute Surgical Patients

Background Perioperative haemodynamic instability is associated with postoperative morbidity and mortality. Patients undergoing acute major abdominal or hip fracture surgery have high complication rates and account for a major part of overall postoperative mortality in developed countries. These patients are often frail, with multiple comorbidities making them vulnerable to anaesthesia and surgery. Despite the benefit of a multidisciplinary effort to improve perioperative care, such patients demonstrate a high risk of complications and death. Conventional perioperative haemodynamic monitoring is often based only on heart rate (HR) and mean blood pressure (MAP). Although perioperative hypotension is associated with complications in major surgery, blood pressure is often an inadequate marker of perioperative organ perfusion, consequently leading to little precision in administration of fluid and vasoactive medication. Minimally-invasive haemodynamic monitoring of cardiac output (CO), and goal directed therapy based on stroke volume optimization, has been associated with improved outcome in major elective surgery, but high quality evidence for the advantage of such monitoring in emergency surgery is sparse.

Macrocirculatory parameters such as MAP and CO may be uncoupled from the microcirculation during sepsis and severe blood loss due to sympathetic or medically induced vasoconstriction, and as such, these parameters are not necessarily optimal for resuscitation.

Assuming that blood flow is directed from peripheral tissue to vital organs during progressive stages of circulatory impairment and shock, a non-invasive method to detect impaired peripheral perfusion could be a relevant endpoint.

The peripheral perfusion index (PPI) has the advantage that is derived from the photoelectric plethysmographic pulse oximetry signal most likely obtained in all patients for evaluation of arterial oxygen saturation (SAT) already in the emergency room and continued during and after surgery as in wards and in the ICU. The PPI reflects the ratio between the pulsatile and non-pulsatile component of the arterial waveform as assessed by light traversing the tissue addressed, most often the finger, and it decreases in response to hypoperfusion.Thus, PPI reflects changes in peripheral perfusion and blood volume and reduced peripheral perfusion is associated with morbidity following acute surgery, in critically ill patients, and patients presenting septic shock. However, it remains uncertain which threshold for PPI should trigger intervention in patients undergoing acute surgery reflecting that evaluation is made only in relatively small populations of mixed medical and surgical patients.

Hypothesis We hypothesize that PPI reflects impaired peripheral circulation and that patients with low intraoperative PPI, independent of MAP, have higher risk of postoperative complications and mortality than patients with normal or high PPI.