Association Between the Peripheral Perfusion Index, Haemoglobin Levels and Blood Transfusions in Patients Undergoing Acute Abdominal- and Orthopaedic Surgery.

Background: Acute surgical patients with e.g. hip fracture (HF) or acute abdominal surgical conditions often have comorbidities and a fragile circulation. Haemodynamic challenges make these patients vulnerable during anaesthesia, and perioperative complications are frequent.

Anaemia is associated with increased mortality and adverse outcomes in patients undergoing surgery. One of the consequences of acute anaemia is reduced blood oxygen content, leading to reduced tissue oxygen delivery and development of tissue hypoxia. Patients with e.g. HF have a large drop in haemoglobin (hb) level that occurs after the injury, yet prior to the surgery. It is therefore important to be aware of the risk of preoperative anaemia even when the initial hb levels appear to be normal. Perioperative hb are associated with shorter lengths of hospital stay, reduced mortality and lower readmission rates, and patients with postoperative anaemia have increased mortality and length of hospital stay.

Haemodynamic monitoring is traditionally based on measurement of blood pressure (BP) and heart rate (HR) but these measurements may be insufficient in evaluating overall oxygen delivery and perfusion of vital organs. An apparently sufficient BP and, for patients with more specialised monitoring, cardiac output (CO), does not necessarily mean a sufficient peripheral microcirculatory flow due to compensatory mechanisms, but on the other hand a low CO may be sufficient in context of low metabolic demand.

The non-invasive peripheral perfusion index (PPI) is a numerical value of peripheral perfusion measured by the pulse oximeter derived from the photoelectric plethysmographic signal. PPI is represents the ratio between the pulsatile component (arterial) and the non-pulsatile component (venous blood, capillary blood and other tissues) of the light reaching the detector of the pulse oximeter, and reflects changes in peripheral blood flow as the pulsatile component increases with vasodilatation and decreases with vasoconstriction. It is an accessible way to obtain a measure for peripheral perfusion as pulse oximeters are universally available in all operating rooms and intensive care units. Previous studies have shown that PPI is a useful indicator of reduced peripheral blood flow both in clinical and experimental settings. Correlation between clinical symptoms of reduced peripheral perfusion such as low temperature, increased capillary response and reduced PPI in critically ill patients has been demonstrated, and a reduced peripheral perfusion may be a predictor of mortality and complications in patients undergoing major surgical procedures and in septic shock patients.

Hypothetically, patients with low values of hb are more susceptible to a deteriorating circulation reflected in poorer PPI regardless of blood pressure and that resuscitation with blood products improves PPI measurements. Moreover, that patients with low values of PPI have more surgical complications and higher mortality.