Postural change in volunteers: sympathetic tone determines microvascular response to cardiac preload and output increases.

PURPOSE: Microvascular perfusion may be a non-invasive indicator of fluid responsiveness. We aimed to investigate which of the microvascular perfusion parameters truly reflects fluid responsiveness independent of sympathetic reflexes. METHODS: Fifteen healthy volunteers underwent a postural change from head up tilt (HUT) to the supine position, diminishing sympathetic tone, followed by a 30° passive leg raising (PLR) with unaltered tone. Prior to and after the postural changes, stroke volume (SV) and cardiac output (CO) were measured, as well as sublingual microcirculatory perfusion (sidestream dark field imaging), skin perfusion, and oxygenation (laser Doppler flowmetry and reflectance spectroscopy). RESULTS: In responders (subjects with >10 % increase in CO), the HUT to supine change increased CO, SV, and pulse pressure, while heart rate, systemic vascular resistance, and mean arterial pressure decreased. Additionally, microvascular flow index, laser Doppler flow, and microvascular hemoglobin oxygen saturation and concentration also increased. CONCLUSION: When preload and forward flow increase in association with a decrease in sympathetic activity, microvascular blood flow increases in the skin and in the sublingual area. When preload and forward flow increase with little to no change in sympathetic activity, only sublingual functional capillary density increases. Therefore, our results indicate that sublingual functional capillary density is the best parameter to use when evaluating fluid responsiveness independent of changes in sympathetic tone.

Tissue perfusion and oxygenation to monitor fluid responsiveness in critically ill, septic patients after initial resuscitation: a prospective observational study.

Fluid therapy after initial resuscitation in critically ill, septic patients may lead to harmful overloading and should therefore be guided by indicators of an increase in stroke volume (SV), i.e. fluid responsiveness. Our objective was to investigate whether tissue perfusion and oxygenation are able to monitor fluid responsiveness, even after initial resuscitation. Thirty-five critically ill, septic patients underwent infusion of 250 mL of colloids, after initial fluid resuscitation. Prior to and after fluid infusion, SV, cardiac output sublingual microcirculatory perfusion (SDF: sidestream dark field imaging) and skin perfusion and oxygenation (laser Doppler flowmetry and reflectance spectroscopy) were measured. Fluid responsiveness was defined by a ≥5 or 10% increase in SV upon fluids. In responders to fluids, SDF-derived microcirculatory and skin perfusion and oxygenation increased, but only the increase in cardiac output, mean arterial and pulse pressure, microvascular flow index and relative Hb concentration and oxygen saturation were able to monitor a SV increase. Our proof of principle study demonstrates that non-invasively assessed tissue perfusion and oxygenation is not inferior to invasive hemodynamic measurements in monitoring fluid responsiveness. However skin reflectance spectroscopy may be more helpful than sublingual SDF.

Use of a peripheral perfusion index derived from the pulse oximetry signal as a noninvasive indicator of perfusion.

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 > or = 7 degrees 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 (R =.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.