Multi-site and multi-depth near-infrared spectroscopy in a model of simulated (central) hypovolemia: lower body negative pressure

Purpose: To test the hypothesis that the sensitivity of near-infrared spectroscopy (NIRS) in reflecting the degree of (compensated) hypovolemia would be affected by the application site and probing depth. We simultaneously applied multi-site (thenar and forearm) and multi-depth (15-2.5 and 25-2.5 mm probe distance) NIRS in a model of simulated hypovolemia: lower body negative pressure (LBNP). Methods: The study group comprised 24 healthy male volunteers who were subjected to an LBNP protocol in which a baseline period of 30 min was followed by a step-wise manipulation of negative pressure in the following steps: 0, -20, -40, -60, -80 and -100 mmHg. Stroke volume and heart rate were measured using volume-clamp finger plethysmography. Two multi-depth NIRS devices were used to measure tissue oxygen saturation (StO2) and tissue hemoglobin index (THI) continuously in the thenar and the forearm. To monitor the shift of blood volume towards the lower extremities, calf THI was measured by single-depth NIRS. Results: The main findings were that the application of LBNP resulted in a significant reduction in stroke volume which was accompanied by a reduction in forearm StO2 and THI. Conclusions: NIRS can be used to detect changes in StO2 and THI consequent upon central hypovolemia. Forearm NIRS measurements reflect hypovolemia more sensitively than thenar NIRS measurements. The sensitivity of these NIRS measurements does not depend on NIRS probing depth. The LBNP-induced shift in blood volume is reflected by a decreased THI in the forearm and an increased THI in the calf

Effect of extracorporeal CO2 removal on right ventricular and hemodynamic parameters in a patient with acute respiratory distress syndrome

We present a female patient with severe acute respiratory distress syndrome (ARDS) necessitating intubation and mechanical ventilation on the intensive care unit (ICU). High ventilatory pressures were needed because of hypoxia and severe hypercapnia with respiratory acidosis, resulting in right ventricular dysfunction with impaired haemodynamic stability. A veno-venous extracorporeal CO2 removal (ECCO2R) circuit was initiated, effectively eliminating carbon dioxide while improving oxygenation and enabling a reduction in applied ventilatory pressures. We noted a marked improvement of right ventricular function with restoration of haemodynamic stability. Within one week, the patient was weaned from both ECCO2R and mechanical ventilation. Besides providing adequate gas exchange, extracorporeal assist devices may be helpful in ameliorating right ventricular dysfunction during ARDS

Defining fluid responsiveness: a guide to patient-tailored volume titration

Anesthesiolog

Low tidal volume ventilation ameliorates left ventricular dysfunction in mechanically ventilated rats following LPS-induced lung injury

High tidal volume ventilation has shown to cause ventilator-induced lung injury (VILI), possibly contributing to concomitant extrapulmonary organ dysfunction. The present study examined whether left ventricular (LV) function is dependent on tidal volume size and whether this effect is augmented during lipopolysaccharide(LPS)-induced lung injury. Twenty male Wistar rats were sedated, paralyzed and then randomized in four groups receiving mechanical ventilation with tidal volumes of 6 ml/kg or 19 ml/kg with or without intrapulmonary administration of LPS. A conductance catheter was placed in the left ventricle to generate pressure-volume loops, which were also obtained within a few seconds of vena cava occlusion to obtain relatively load-independent LV systolic and diastolic function parameters. The end-systolic elastance / effective arterial elastance (Ees/Ea) ratio was used as the primary parameter of LV systolic function with the end-diastolic elastance (Eed) as primary LV diastolic function. Ees/Ea decreased over time in rats receiving LPS (p = 0.045) and high tidal volume ventilation (p = 0.007), with a lower Ees/Ea in the rats with high tidal volume ventilation plus LPS compared to the other groups (p < 0.001). Eed increased over time in all groups except for the rats receiving low tidal volume ventilation without LPS (p = 0.223). A significant interaction (p < 0.001) was found between tidal ventilation and LPS for Ees/Ea and Eed, and all rats receiving high tidal volume ventilation plus LPS died before the end of the experiment. Low tidal volume ventilation ameliorated LV systolic and diastolic dysfunction while preventing death following LPS-induced lung injury in mechanically ventilated rats. Our data advocates the use of low tidal volumes, not only to avoid VILI, but to avert ventilator-induced myocardial dysfunction as wel

Predicting Fluid Responsiveness by Passive Leg Raising: A Systematic Review and Meta-Analysis of 23 Clinical Trials

Passive leg raising creates a reversible increase in venous return allowing for the prediction of fluid responsiveness. However, the amount of venous return may vary in various clinical settings potentially affecting the diagnostic performance of passive leg raising. Therefore we performed a systematic meta-analysis determining the diagnostic performance of passive leg raising in different clinical settings with exploration of patient characteristics, measurement techniques, and outcome variables. PubMed, EMBASE, the Cochrane Database of Systematic Reviews, and citation tracking of relevant articles. Clinical trials were selected when passive leg raising was performed in combination with a fluid challenge as gold standard to define fluid responders and non-responders. Trials were included if data were reported allowing the extraction of sensitivity, specificity, and area under the receiver operating characteristic curve. Twenty-three studies with a total of 1,013 patients and 1,034 fluid challenges were included. The analysis demonstrated a pooled sensitivity of 86% (95% CI, 79-92), pooled specificity of 92% (95% CI, 88-96), and a summary area under the receiver operating characteristic curve of 0.95 (95% CI, 0.92-0.98). Mode of ventilation, type of fluid used, passive leg raising starting position, and measurement technique did not affect the diagnostic performance of passive leg raising. The use of changes in pulse pressure on passive leg raising showed a lower diagnostic performance when compared with passive leg raising-induced changes in flow variables, such as cardiac output or its direct derivatives (sensitivity of 58% [95% CI, 44-70] and specificity of 83% [95% CI, 68-92] vs sensitivity of 85% [95% CI, 78-90] and specificity of 92% [95% CI, 87-94], respectively; p < 0.001). Passive leg raising retains a high diagnostic performance in various clinical settings and patient groups. The predictive value of a change in pulse pressure on passive leg raising is inferior to a passive leg raising-induced change in a flow variabl

Abnormal Right Ventricular Myocardial Performance Index Is Not Associated With Outcomes in Invasively Ventilated Intensive Care Unit Patients Without Acute Respiratory Distress Syndrome—Post hoc Analysis of Two RCTs

Background: The objective of the study was to determine the association between right ventricular (RV) myocardial performance index (MPI) and successful liberation from the ventilator and death within 28 days. Methods: Post hoc analysis of 2 ventilation studies in invasively ventilated patients not having ARDS. RV-MPI was collected through transthoracic echocardiography within 24–48 h from the start of invasive ventilation according to the study protocols. RV-MPI ≤ 0.54 was considered normal. The primary endpoint was successful liberation from the ventilator < 28 days; the secondary endpoint was 28-day mortality. Results: A total of 81 patients underwent transthoracic echocardiography at median 30 (24–42) h after the start of ventilation—in 73 (90%) patients, the RV-MPI could be collected. A total of 56 (77%) patients were successfully liberated from the ventilator < 28 days; A total of 22 (30%) patients had died before or at day 28. A total of 18 (25%) patients had an abnormal RV-MPI. RV-MPI was neither associated with successful liberation from the ventilator within 28 days [HR, 2.2 (95% CI 0.47–10.6); p = 0.31] nor with 28-day mortality [HR, 1.56 (95% CI 0.07–34.27); p = 0.7]. Conclusion: In invasively ventilated critically ill patients without ARDS, an abnormal RV-MPI indicative of RV dysfunction was not associated with time to liberation from invasive ventilation

Assessing Extravascular Lung Water in Critically Ill Patients Using Lung Ultrasound: A Systematic Review on Methodological Aspects in Diagnostic Accuracy Studies

Lung ultrasound (LUS) is a non-invasive bedside method used to quantify extravascular lung water (EVLW). To evaluate the methodology and diagnostic accuracy of LUS in studies assessing EVLW in intensive care unit patients, PubMed and Embase were searched for studies comparing LUS with imaging modalities. In 14 relevant studies a wide variety of equipment used and training of examiners were noted. Four scoring systems were reported: (i) a binary score (the presence of three or more B-lines); (ii) a categorical score; (iii) a numerical score; (iv) a quantitative LUS score using software. The diagnostic accuracy of LUS varied: sensitivity ranged from 50%–98%, specificity from 76%–100% and r² from 0.20–0.91. Methodology and diagnostic accuracy varies substantially in published reports. Further research is needed to correlate methodological factors with diagnostic accuracy. Hospitals should standardize LUS methodology. Consensus is needed to harmonize LUS methodology for lung water assessment

The microcirculatory response to compensated hypovolemia in a lower body negative pressure model

The objective of the present study was to test the hypothesis that controlled, adequately compensated, central hypovolemia in subjects with intact autoregulation would be associated with decreased peripheral microcirculatory diffusion and convection properties and, consequently, decreased tissue oxygen carrying capacity and tissue oxygenation. Furthermore, we evaluated the impact of hypovolemia-induced microcirculatory alterations on resting tissue oxygen consumption. To this end, 24 subjects were subjected to a progressive lower body negative pressure (LBNP) protocol of which 14 reached the end of the protocol. At baseline and at LBNP=-60 mm Hg, sidestream dark field (SDF) images of the sublingual microcirculation were acquired to measure microvascular density and perfusion; thenar and forearm tissue hemoglobin content (THI) and tissue oxygenation (StO2) were recorded using near-infrared spectroscopy (NIRS); and a vascular occlusion test (VOT) was performed to assess resting tissue oxygen consumption rate. SDF images were analyzed for total vessel density (TVD), perfused vessel density (PVD), the microvascular flow index (MFI), and flow heterogeneity (MFIhetero). We found that application of LBNP resulted in: 1) a significantly decreased microvascular density (PVD) and perfusion (MFI and MFIhetero); 2) a significantly decreased THI and StO2; and 3) an unaltered resting tissue oxygen consumption rate. In conclusion, using SDF imaging in combination with NIRS we showed that controlled, adequately compensated, central hypovolemia in subjects with intact autoregulation is associated with decreased microcirculatory diffusion (PVD) and convection (MFI and MFIhetero) properties and, consequently, decreased tissue oxygen carrying capacity (THI) and tissue oxygenation (StO2). Furthermore, using a VOT we found that resting tissue oxygen consumption was maintained under conditions of adequately compensated central hypovolemi

A mini-fluid challenge of 150mL predicts fluid responsiveness using ModelflowR pulse contour cardiac output directly after cardiac surgery

The mini-fluid challenge may predict fluid responsiveness with minimum risk of fluid overloading. However, the amount of fluid as well as the best manner to evaluate the effect is unclear. In this prospective observational pilot study, the value of changes in pulse contour cardiac output (CO) measurements during mini-fluid challenges is investigated. Prospective observational study. Intensive Care Unit of a university hospital. Twenty-one patients directly after elective cardiac surgery on mechanical ventilation. The patients were subsequently given 10 intravenous boluses of 50mL of hydroxyethyl starch with a total of 500mL per patient while measuring pulse contour CO. We measured CO by minimal invasive ModelflowR (COm) and PulseCOR (COli), before and one minute after each fluid bolus. We analyzed the smallest volume that was predictive of fluid responsiveness. A positive fluid response was defined as an increase in CO of >10% after 500mL fluid infusion. Fifteen patients (71%) were COm responders and 13 patients (62%) COli responders. An increase in COm after 150mL of fluid >5.0% yielded a positive and negative predictive value (+PV and -PV) of 100% with an area under the curve (AUC) of 1.00 (P 6.3% after 200mL was able to predict a fluid response in COli after 500mL with a +PV of 100% and -PV of 73%, with an AUC of 0.88 (P <0.001). The use of minimal invasive ModelflowR pulse contour CO measurements following a mini-fluid challenge of 150mL can predict fluid responsiveness and may help to improve fluid managemen

Assessing Extravascular Lung Water in Critically Ill Patients Using Lung Ultrasound: A Systematic Review on Methodological Aspects in Diagnostic Accuracy Studies

Lung ultrasound (LUS) is a non-invasive bedside method used to quantify extravascular lung water (EVLW). To evaluate the methodology and diagnostic accuracy of LUS in studies assessing EVLW in intensive care unit patients, PubMed and Embase were searched for studies comparing LUS with imaging modalities. In 14 relevant studies a wide variety of equipment used and training of examiners were noted. Four scoring systems were reported: (i) a binary score (the presence of three or more B-lines); (ii) a categorical score; (iii) a numerical score; (iv) a quantitative LUS score using software. The diagnostic accuracy of LUS varied: sensitivity ranged from 50%–98%, specificity from 76%–100% and r² from 0.20–0.91. Methodology and diagnostic accuracy varies substantially in published reports. Further research is needed to correlate methodological factors with diagnostic accuracy. Hospitals should standardize LUS methodology. Consensus is needed to harmonize LUS methodology for lung water assessment