The Peripheral Perfusion Index tracks systemic haemodynamics during general anaesthesia

Stable intraoperative haemodynamics are associated with improved outcome and even short periods of instability are associated with an increased risk of complications. During anaesthesia intermittent non-invasive blood pressure and heart rate remains the cornerstone of haemodynamic monitoring. Continuous monitoring of systemic blood pressure or even -flow requires invasive or advanced modalities creating a barrier for obtaining important real-time haemodynamic insight. The Peripheral Perfusion Index (PPI) is obtained continuously and non-invasively by standard photoplethysmography. We hypothesized that changes in indices of systemic blood flow during general anaesthesia would be reflected in the PPI. PPI, stroke volume (SV), cardiac output (CO) and mean arterial pressure (MAP) were evaluated in 20 patients. During general anaesthesia but before start of surgery relative changes of SV, CO and MAP were compared to the relative changes of PPI induced by head-up (HUT) and head-down tilt (HDT). Furthermore, the effect of phenylephrine (PE) during HUT on these parameters was investigated. ∆PPI correlated significantly (p < 0.001) with ∆SV (r = 0.9), ∆CO (r = 0.9), and ∆MAP (r = 0.9). HUT following induction of anaesthesia resulted in a decrease in PPI of 41% (25-52) [median (IQR)], SV 27% (23-31), CO 27% (25-35), and MAP 28% (22-35). HDT led to an increase in PPI of 203% (120-375), SV of 29% (21-41), CO 22% (16-34), and MAP 47% (42-60). After stabilizing a second HUT decreased PPI 59% (49-76), SV 33% (28-37), CO 31% (28-36), and MAP 34% (26-38). Restoration of preload with PE increased PPI by 607% (218-1078), SV by 96% (82-116), CO by 65% (56-99), and MAP by 114% (83-147). During general anaesthesia changes in PPI tracked changes in systemic haemodynamics.