Predictive Power of Peripheral Perfusion Index During Induction of Aneasthesia

Haemodynamic monitoring during general anaesthesia (GA) traditionally relies on simple and readily available parameters such as blood pressure and heart rate. Most patients will only have intermittent non-invasive monitoring of blood pressure. During the induction phase an abrupt reduction in blood pressure is often seen, with possible deleterious consequences for organ perfusion [1,2]. The availability of continuous monitoring of systemic haemodynamics is limited by cost and scarcity of equipment and personnel.

The peripheral perfusion index (PPI) is obtained non-invasively by photoplethysmography - ubiquitously present in the perioperative setting [3,4]. The PPI is a simple ratio describing the proportion of pulsatile to non-pulsatile signal attenuation. No specialized equipment is needed as the PPI is inherent to photoplethysmography already ubiquitous during GA, although not all pulse-oxymeters are set up to display PPI. The PPI in awake patients is dominated by sympathetic tone [4] creating a highly positively skewed distribution [3]. Conversely, during GA cardiac stroke volume (SV) becomes the major determinant of PPI [5,6]. Very little evidence exists regarding the efficacy of PPI as a monitor during the induction of GA. Presumably, the net effect will be a composite of two opposing mechanisms: Sympatholysis increasing PPI, with decreased SV/CO causing the opposite effect.

The present study was designed to explore the clinical utility of the non-invasively obtained peripheral perfusion index to detect cardiovascular compromise during induction of general anaesthesia. We hypothesized that during induction of GA changes in systemic haemodynamics in the form of mean arterial pressure (MAP) and cardiac stroke volume (SV) and -output (CO) during GA would be reflected in the PPI, albeit in a complex manner. Thus, a predominant vasodilatory response might be differentiated from a response dominated by decreased CO.

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