Use of Peripheral Perfusion Index Derived From the Pulse Oximetry Signal as a Noninvasive Indicator of Perfusion

Abstract and Introduction

Abstract

Objective: Peripheral perfusion in critically ill patients frequently is assessed by use of clinical signs. Recently, the pulse oximetry signal has been suggested to reflect changes in peripheral perfusion. A peripheral perfusion index based on analysis of the pulse oximetry signal has been implemented in monitoring systems as an index of peripheral perfusion. No data on the variation of this index in the normal population are available, and clinical application of this variable in critically ill patients has not been reported. We therefore studied the variation of the peripheral perfusion index in healthy adults and related it to the central-to-toe temperature difference and capillary refill time in critically ill patients after changes in clinical signs of peripheral perfusion.
Design: Prospective study.
Setting: University-affiliated teaching hospital.
Patients: One hundred eight healthy adult volunteers and 37 adult critically ill patients.
Interventions: None.
Measurements and Main Results: Capillary refill time, peripheral perfusion index, and arterial oxygen saturation were measured in healthy adults (group 1). Capillary refill time, peripheral perfusion index, arterial oxygen saturation, central-to-toe temperature difference, and hemodynamic variables were measured in critically ill patients (group 2) during different peripheral perfusion profiles. Poor peripheral perfusion was defined as a capillary refill time >2 secs and central-to-toe temperature difference ≥7°C. Peripheral perfusion index and arterial oxygen saturation were measured by using the Philips Medical Systems Viridia/56S monitor. In group 1, measurements were made before and after a meal. In group 2, two measurements were made, with the second measurement taken when the peripheral perfusion profile had changed. A total of 216 measurements were carried out in group 1. The distribution of the peripheral perfusion index was skewed and values ranged from 0.3 to 10.0, median 1.4 (inner quartile range, 0.7-3.0). Seventy-four measurements were carried out in group 2. A significant correlation between the peripheral perfusion index and the core-to-toe temperature difference was found (R² = .52; p < .001). A cutoff peripheral perfusion index value of 1.4 (calculated by constructing a receiver operating characteristic curve) best reflected the presence of poor peripheral perfusion in critically ill patients. Changes in peripheral perfusion index and changes in core-to-toe temperature difference correlated significantly (R² = .52, p < .001).
Conclusions: The peripheral perfusion index distribution in the normal population is highly skewed. Changes in the peripheral perfusion index reflect changes in the core-to-toe temperature difference. Therefore, peripheral perfusion index measurements can be used to monitor peripheral perfusion in critically ill patients.

Introduction

Early recognition of impaired organ perfusion is important to avoid tissue hypoxia that ultimately could lead to organ failure. During circulatory shock, skin blood flow decreases to preserve vital organ perfusion. This results in the clinical signs of poor peripheral perfusion, such as a cold, pale, clammy, and mottled skin.^[1] Indexes of peripheral perfusion thus have been used to identify inadequate perfusion in critically ill patients.^[2,3,4] Peripheral perfusion can be assessed from clinical signs,^[1] from the central-to-toe temperature difference,^[2,3,5] or with techniques such as laser Doppler and capillary microscopy.^[6] Recently, the pulse oximetry signal has been suggested to reflect changes in peripheral perfusion.^[7] In addition, the ratio between the pulsatile and nonpulsatile component of the pulse oximetry signal has been related to peripheral perfusion.^[8] Because a pulse oximeter is universally available in the operating room and intensive care unit, this ratio could be used to monitor perfusion in these circumstances.

Although the manufacturer reports the lower and upper limit of normal to be 0.3 and 10.0, respectively, the variation in normal subjects and the clinical application of this ratio as an index of peripheral perfusion in critically ill patients have not yet been studied. The objective of the current study, therefore, was to assess the variation of this perfusion index in healthy adults and study the relationship between the peripheral perfusion index (PFI) and clinical signs of poor peripheral perfusion in critically ill patients.

Crit Care Med. 2002;30(6) © 2002  Lippincott Williams & Wilkins